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Versions: (draft-mcdonald-nsis-qos-nslp) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14 15 16 17 18 RFC 5974

Next Steps in Signaling                                  J. Manner (ed.)
Internet-Draft                                    University of Helsinki
Expires: April, 2007                                      G. Karagiannis
                                           University of Twente/Ericsson
                                                             A. McDonald
                                             Siemens/Roke Manor Research
                                                            October 2006

                 NSLP for Quality-of-Service Signaling
                   <draft-ietf-nsis-qos-nslp-12.txt>


Status of this Memo

   By submitting this Internet-Draft, each author represents that any
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   This Internet-Draft will expire in April, 2007.

   Copyright Notice

   Copyright (C) The Internet Society (2006).















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   Abstract

   This specification describes the NSIS Signaling Layer Protocol (NSLP)
   for signaling QoS reservations in the Internet. It is in accordance
   with the framework and requirements developed in NSIS. Together with
   GIST, it provides functionality similar to RSVP and extends it. The
   QoS NSLP is independent of the underlying QoS specification or
   architecture and provides support for different reservation models.
   It is simplified by the elimination of support for multicast flows.
   This specification explains the overall protocol approach, design
   decisions made and provides examples. It specifies object, message
   formats and processing rules.


Table of Contents

   1.  Introduction ..................................................4
   2.  Terminology ...................................................5
   3.  Protocol Overview .............................................6
   3.1.  Overall Approach ............................................6
   3.1.1.  Protocol Messages .........................................9
   3.1.2.  QoS Models and QoS Specifications .........................10
   3.1.3.  Policy Control ............................................11
   3.2.  Design Background ...........................................13
   3.2.1.  Soft States ...............................................13
   3.2.2.  Sender and Receiver Initiation ............................13
   3.2.3.  Protection Against Message Re-ordering and Duplication ....13
   3.2.4.  Explicit Confirmations ....................................13
   3.2.5.  Reduced Refreshes .........................................14
   3.2.6.  Message Scoping ...........................................14
   3.2.7.  Session Binding ...........................................14
   3.2.8.  Layering ..................................................15
   3.2.8.1.  Local QoS Models ........................................15
   3.2.8.2.  Local Control Plane Properties ..........................16
   3.2.8.3.  Aggregate Reservations ..................................17
   3.2.9.  Support for Request Priorities ............................17
   3.2.10.  Rerouting ................................................18
   3.2.10.1.  Last Node Behavior .....................................19
   3.2.10.2.  Handling Spurious Route Change Notifications ...........21
   3.3.  GIST Interactions ...........................................22
   3.3.1.  Support for Bypassing Intermediate Nodes ..................22
   3.3.2.  Support for Peer Change Identification ....................23
   3.3.3.  Support for Stateless Operation ...........................23
   3.3.4.  Priority of Signaling Messages ............................23
   3.3.5.  Knowledge of Intermediate QoS NSLP Unaware Nodes ..........24
   4.  Examples of QoS NSLP Operation ................................24
   4.1.  Sender-initiated Reservation ................................24
   4.2.  Sending a Query .............................................26
   4.3.  Basic Receiver-initiated Reservation ........................26
   4.4.  Bidirectional Reservations ..................................28
   4.5.  Use of Local QoS Models .....................................29
   4.6.  Aggregate Reservations ......................................30
   4.7.  Reduced State or Stateless Interior Nodes ...................31
   4.7.1.  Sender-initiated Reservation ..............................32

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   4.7.2.  Receiver-initiated Reservation ............................33
   4.8.  Proxy Mode ..................................................34
   5.  QoS NSLP Functional Specification .............................35
   5.1.  QoS NSLP Message and Object Formats .........................35
   5.1.1.  Common Header .............................................35
   5.1.2.  Message Formats ...........................................36
   5.1.2.1.  RESERVE .................................................36
   5.1.2.2.  QUERY ...................................................38
   5.1.2.3.  RESPONSE ................................................39
   5.1.2.4.  NOTIFY ..................................................39
   5.1.3.  Object Formats ............................................40
   5.1.3.1.  Request Identification Information (RII) ................41
   5.1.3.2.  Reservation Sequence Number (RSN) .......................41
   5.1.3.3.  Refresh Period (REFRESH_PERIOD) .........................41
   5.1.3.4.  Bound Session ID (BOUND_SESSION_ID) .....................42
   5.1.3.5.  Packet Classifier (PACKET_CLASSIFIER) ...................43
   5.1.3.6.  Information Object (INFO_SPEC) and Error Codes ..........44
   5.1.3.7.  QoS Specification (QSPEC) ...............................48
   5.2.  General Processing Rules ....................................48
   5.2.1.  State Manipulation ........................................49
   5.2.2.  Message Forwarding ........................................50
   5.2.3.  Standard Message Processing Rules .........................50
   5.2.4.  Retransmissions ...........................................50
   5.2.5.  Rerouting .................................................51
   5.2.5.1.  Last Node Behavior ......................................51
   5.2.5.2.  Avoiding Mistaken Teardown ..............................51
   5.2.5.3.  Upstream Route Change Notification ......................52
   5.2.5.4.  Route Change Oscillation ................................52
   5.3.  Object Processing ...........................................52
   5.3.1.  Reservation Sequence Number (RSN) .........................52
   5.3.2.  Request Identification Information (RII) ..................53
   5.3.3.  BOUND_SESSION_ID ..........................................54
   5.3.4.  REFRESH_PERIOD ............................................55
   5.3.5.  INFO_SPEC .................................................56
   5.3.6.  QSPEC .....................................................58
   5.4.  Message Processing Rules ....................................58
   5.4.1.  RESERVE Messages ..........................................59
   5.4.2.  QUERY Messages ............................................62
   5.4.3.  RESPONSE Messages .........................................63
   5.4.4.  NOTIFY Messages ...........................................65
   6.  IANA Considerations ...........................................65
   6.1.  QoS NSLP Message Type .......................................65
   6.2.  NSLP Message Objects ........................................66
   6.3.  QoS NSLP Binding Codes ......................................66
   6.4.  QoS NSLP Error Classes and Error Codes ......................66
   6.5.  QoS NSLP Error Source Identifiers ...........................67
   6.6.  NSLP IDs and Router Alert Option Values .....................67
   7.  Security Considerations .......................................67
   7.1.  Trust Relationship Model ....................................69
   7.2.  Authorization Model Examples ................................70
   7.2.1.  Authorization for the Two Party Approach ..................70
   7.2.2.  Token-based Three Party Approach ..........................71
   7.2.3.  Generic Three Party Approach ..............................72
   7.3.  Computing the Authorization Decision ........................73

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   8.  Acknowledgments ...............................................73
   9.  Contributors ..................................................73
   10.  References ...................................................73
   10.1.  Normative References .......................................73
   10.2.  Informative References .....................................74


1.  Introduction

   This document defines a Quality of Service (QoS) NSIS Signaling Layer
   Protocol (NSLP), henceforth referred to as the "QoS NSLP". This
   protocol establishes and maintains state at nodes along the path of a
   data flow for the purpose of providing some forwarding resources for
   that flow. It is intended to satisfy the QoS-related requirements of
   RFC 3726 [RFC3726]. This QoS NSLP is part of a larger suite of
   signaling protocols, whose structure is outlined in the NSIS
   framework [RFC4080];  this defines a common NSIS Transport Layer
   Protocol (NTLP). The abstract NTLP has been developed into a concrete
   protocol, GIST (General Internet Signaling Transport) [I-D.ietf-nsis-
   ntlp]. The QoS NSLP relies on GIST to carry out many aspects of
   signaling message delivery.

   The design of the QoS NSLP is conceptually similar to RSVP, RFC 2205
   [RFC2205], and uses soft-state peer-to-peer refresh messages as the
   primary state management mechanism (i.e., state installation/refresh
   is performed between pairs of adjacent NSLP nodes, rather than in an
   end-to-end fashion along the complete signaling path).  The QoS NSLP
   extends the set of reservation mechanisms to meet the requirements of
   RFC 3726 [RFC3726], in particular support of sender or receiver-
   initiated reservations, as well as, a type of bi-directional
   reservation and support of reservations between arbitrary nodes,
   e.g., edge-to-edge, end-to-access, etc. On the other hand, there is
   no support for IP multicast.

   A distinction is made between the operation of the signaling protocol
   and the information required for the operation of the Resource
   Management Function (RMF). This document describes the signaling
   protocol, whilst [I-D.ietf-nsis-qspec] describes the RMF-related
   information carried in the QSPEC (QoS Specification) object in QoS
   NSLP messages. This is similar to the decoupling between RSVP and the
   IntServ architecture, RFC 1633 [RFC1633]. The QSPEC carries
   information on resources available, resources required, traffic
   descriptions and other information required by the RMF.

   This document is structured as follows. The overall protocol design
   is outlined in Section 3.1. The operation and use of the QoS NSLP is
   described in more detail in the rest of Section 3. Section 4 then
   clarifies the protocol by means of a number of examples. These
   sections should be read by people interested in the overall protocol
   capabilities. The functional specification in Section 5 contains more
   detailed object and message formats and processing rules and should
   be the basis for implementers. The subsequent sections describe IANA
   allocation issues, and security considerations.


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2.  Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119.

   The terminology defined by GIST [I-D.ietf-nsis-ntlp] applies to this
   draft.

   In addition, the following terms are used:

      QNE: an NSIS Entity (NE), which supports the QoS NSLP.

      QNI: the first node in the sequence of QNEs that issues a
      reservation request for a session.

      QNR: the last node in the sequence of QNEs that receives a
      reservation request for a session.

      P-QNE: Proxy-QNE, a node set to reply to messages with the PROXY
      scope flag set.

      Session: A session defines an association between a QNI and QNR
      related to a data flow. All QNEs on the path, including the QNI
      and QNR, use the same identifier to refer to the state stored for
      the association. The same QNI and QNR may have more than one
      session active at any one time.

      Session Identification (SESSION_ID, SID): This is a
      cryptographically random and (probabilistically) globally unique
      identifier of the application layer session that is associated
      with a certain flow. Often there will only be one data flow for a
      given session, but in mobility/multihoming scenarios there may be
      more than one and they may be differently routed [RFC4080].

      Source or message source: The one of two adjacent NSLP peers that
      is sending a signaling message (maybe the upstream or the
      downstream peer). Note that this is not necessarily the QNI.

      QoS NSLP operation state: State used/kept by the QoS NSLP
      processing to handle messaging aspects.

      QoS reservation state: State used/kept by Resource Management
      Function to describe reserved resources for a session.

      Flow ID: This is essentially the Message Routing Information (MRI)
      in GIST for path-coupled signaling.


   Figure 1 shows the components that have a role in a QoS NSLP
   signaling session. The flow sender and receiver would in most cases
   be part of the QNI and QNR nodes. Yet, these may be separate nodes,
   too.


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                         QoS NSLP nodes
   IP address            (QoS unaware NSIS nodes are          IP address
   = Flow                 not shown)                          = Flow
   Source                 |          |            |          Destination
   Address                |          |            |           Address
                          V          V            V
   +--------+  Data +------+      +------+       +------+     +--------+
   |  Flow  |-------|------|------|------|-------|------|---->|  Flow  |
   | Sender |  Flow |      |      |      |       |      |     |Receiver|
   +--------+       | QNI  |      | QNE  |       | QNR  |     +--------+
                    |      |      |      |       |      |
                    +------+      +------+       +------+
                            =====================>
                            <=====================
                                  Signaling
                                    Flow
            Figure 1: Components of the QoS NSLP architecture.

   A glossary of terms and abbreviations used in this document can be
   found in Appendix A.


3.  Protocol Overview


3.1.  Overall Approach

   This section presents a logical model for the operation of the QoS
   NSLP and associated provisioning mechanisms within a single node.
   The model is shown in Figure 2.

























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                                      +---------------+
                                      |     Local     |
                                      |Applications or|
                                      |Management (e.g|
                                      |for aggregates)|
                                      +---------------+
                                              ^
                                              V
                                              V
               +----------+             +----------+      +---------+
               | QoS NSLP |             | Resource |      | Policy  |
               |Processing|<<<<<<>>>>>>>|Management|<<<>>>| Control |
               +----------+             +----------+      +---------+
                 .  ^   |              *      ^
                 |  V   .            *        ^
               +----------+        *          ^
               |   NTLP   |       *           ^
               |Processing|       *           V
               +----------+       *           V
                 |      |         *           V
     ++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
                 .      .         *           V
                 |      |         *     .............................
                 .      .         *     .   Traffic Control         .
                 |      |         *     .                +---------+.
                 .      .         *     .                |Admission|.
                 |      |         *     .                | Control |.
       +----------+    +------------+   .                +---------+.
   <-.-|  Input   |    | Outgoing   |-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.-.->
       |  Packet  |    | Interface  |   .+----------+    +---------+.
   ===>|Processing|====| Selection  |===.|  Packet  |====| Packet  |.==>
       |          |    |(Forwarding)|   .|Classifier|     Scheduler|.
       +----------+    +------------+   .+----------+    +---------+.
                                        .............................
           <.-.-> = signaling flow
           =====> = data flow (sender --> receiver)
           <<<>>> = control and configuration operations
           ****** = routing table manipulation

                       Figure 2: QoS NSLP in a Node

   This diagram shows an example implementation scenario where QoS
   conditioning is performed on the output interface. However, this does
   not limit the possible implementations. For example, in some cases
   traffic conditioning may be performed on the incoming interface, or
   it may be split over the input and output interfaces. Also, the
   interactions with the Policy Control component may be more complex,
   involving interaction with the Resource Management Function, and the
   AAA infrastructure.

   From the perspective of a single node, the request for QoS may result
   from a local application request, or from processing an incoming QoS
   NSLP message. The request from a local application includes not only
   user applications (e.g., multimedia applications) but also network

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   management (e.g. initiating a tunnel to handle an aggregate, or
   interworking with some other reservation protocol - such as RSVP) and
   the policy control module (e.g., for explicit teardown triggered by
   AAA). In this sense, the model does not distinguish between hosts and
   routers.

   Incoming messages are captured during input packet processing and
   handled by GIST. Only messages related to QoS are passed to the QoS
   NSLP. GIST may also generate triggers to the QoS NSLP (e.g.,
   indications that a route change has occurred). The QoS request is
   handled by the RMF, which coordinates the activities required to
   grant and configure the resource. It also handles policy-specific
   aspects of QoS signaling.

   The grant processing involves two local decision modules, 'policy
   control' and 'admission control'. Policy control determines whether
   the user is authorized to make the reservation. Admission control
   determines whether the network of the node has sufficient available
   resources to supply the requested QoS. If both checks succeed,
   parameters are set in the packet classifier and in the link layer
   interface (e.g., in the packet scheduler) to obtain the desired QoS.
   Error notifications are passed back to the request originator. The
   resource management function may also manipulate the forwarding
   tables at this stage, to select (or at least pin) a route; this must
   be done before interface-dependent actions are carried out (including
   sending outgoing messages over any new route), and is in any case
   invisible to the operation of the protocol.

   Policy control is expected to make use of the authentication
   infrastructure or the authentication protocols external to the node
   itself. Some discussion can be found in a separate document on
   authorization issues [QOS-AUTH]. More generally, the processing of
   policy and resource management functions may be outsourced to an
   external node leaving only 'stubs' co-located with the NSLP node;
   this is not visible to the protocol operation. A more detailed
   discussion of authentication and authorization can be found in
   Section 3.1.4.

   Admission control, packet scheduling, and any part of policy control
   beyond simple authorization have to be implemented using specific
   definitions for types and levels of QoS. A key assumption is made
   that the QoS NSLP is independent of the QoS parameters (e.g., IntServ
   service elements). These are captured in a QoS Model and interpreted
   only by the resource management and associated functions, and are
   opaque to the QoS NSLP itself. QoS Models are discussed further in
   Section 3.1.3.

   The final stage of processing for a resource request is to indicate
   to the QoS NSLP protocol processing that the required resources have
   been configured. The QoS NSLP may generate an acknowledgment message
   in one direction, and may forward the resource request in the other.
   Message routing is carried out by the GIST module.  Note that while
   Figure 2 shows a unidirectional data flow, the signaling messages can
   pass in both directions through the node, depending on the particular

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   message and orientation of the reservation.


3.1.1.  Protocol Messages

   The QoS NSLP uses four message types:

      RESERVE: The RESERVE message is the only message that manipulates
      QoS NSLP reservation state. It is used to create, refresh, modify
      and remove such state. The result of a RESERVE message is the same
      whether a message is received once or many times.

      QUERY: A QUERY message is used to request information about the
      data path without making a reservation. This functionality can be
      used to reservations or for support of certain QoS models. The
      information obtained from a QUERY may be used in the admission
      control process of a QNE (e.g., in case of measurement-based
      admission control). Note that a QUERY does not change existing
      reservation state.

      RESPONSE:  The RESPONSE message is used to provide information
      about the result of a previous QoS NSLP message. This includes
      explicit confirmation of the state manipulation signaled in the
      RESERVE message, the response to a QUERY message or an error code
      if the QNE or QNR is unable to provide the requested information
      or if the response is negative. The RESPONSE message does not
      cause any reservation state to be installed or modified.

      NOTIFY:  NOTIFY messages are used to convey information to a QNE.
      They differ from RESPONSE messages in that they are sent
      asynchronously and need not refer to any particular state or
      previously received message. The information conveyed by a NOTIFY
      message is typically related to error conditions. Examples would
      be notification to an upstream peer about state being torn down or
      to indicate when a reservation has been preempted.

   QoS NSLP messages are sent peer-to-peer. This means that a QNE
   considers its adjacent upstream or downstream peer to be the source
   of the each message.

   Each protocol message has a common header which indicates the message
   type and contains various flag bits. Message formats are defined in
   Section 5.1.2. Message processing rules are defined in Section 5.4.

   QoS NSLP messages contain three types of objects:

      1. Control Information:  Control information objects carry general
      information for the QoS NSLP processing, such as sequence numbers
      or whether a response is required.

      2. QoS specifications (QSPECs):  QSPEC objects describe the actual
      resources that are required and depend on the QoS model being
      used. Besides any resource description they may also contain other
      control information used by the RMF's processing.

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      3. Policy objects:  Policy objects contain data used to authorize
      the reservation of resources.

   Object formats are defined in Section 5.1.3. Object processing rules
   are defined in Section 5.3.


3.1.2.  QoS Models and QoS Specifications

   The QoS NSLP provides flexibility over the exact patterns of
   signaling messages that are exchanged. The decoupling of QoS NSLP and
   QSPEC allows the QoS NSLP to be ignorant about the ways in which
   traffic, resources, etc. are described, and it can treat the QSPEC as
   an opaque object.  Various QoS models can be designed, and these do
   not affect the specification of the QoS NSLP protocol. Only the RMF
   specific to a given QoS model will need to interpret the QSPEC.  The
   Resource Management Function (RMF) reserves resources for each flow.

   An ongoing effort attempts to specify a QSPEC template [I-D.ietf-
   nsis-qspec]. The QSPEC template contains object formats for generally
   useful elements of the QoS description, which is designed to ensure
   interoperability when using the basic set of objects.

   The QSPEC fulfills a similar purpose to the TSpec, RSpec and AdSpec
   objects used with RSVP and specified in RFC 2205 [RFC2205] and RFC
   2210 [RFC2210]. At each QNE, the content of the QSPEC is interpreted
   by the Resource Management Function and the Policy Control Function
   for the purposes of traffic and policy control (including admission
   control and configuration of the packet classifier and scheduler).

   The QoS NSLP does not mandate any particular behavior for the RMF,
   instead providing interoperability at the signaling protocol level
   whilst leaving the validation of RMF behavior to contracts external
   to the protocol itself. The RMF may make use of various elements from
   the QoS NSLP message, not only the QSPEC object.

   Still, this specification assumes that resource sharing is possible
   between flows with the same SESSION_ID that originate from the same
   QNI or between flows with a different SESSION_ID that are related
   through the BOUND_SESSION_ID object. For flows with the same
   SESSION_ID, resource sharing is only applicable when the existing
   reservation is not just replaced (which is indicated by the REPLACE
   flag in the common header. We assume that the QoS model supports
   resource sharing between flows. A QoS Model may elect to implement a
   more general behavior of supporting relative operations on existing
   reservations, such as ADDING or SUBTRACTING a certain amount of
   resources from the current reservation. A QoS Model may also elect to
   allow resource sharing more generally, e.g., between all flows with
   the same DSCP.

   The QSPEC carries a collection of objects that can describe QoS
   specifications in a number of different ways. A generic template is
   defined in [I-D.ietf-nsis-qspec]. A QSPEC describing the resources
   requested will usually contain objects which need to be understood by

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   all implementations, and it can also be enhanced with additional
   objects specific to a QoS model to provide a more exact definition to
   the RMF, which may be better able to use its specific resource
   management mechanisms (which may, e.g., be link specific) as a
   result.

   A QoS Model defines the behavior of the RMF, including inputs and
   outputs, and how QSPEC information is used to describe resources
   available, resources required, traffic descriptions, and control
   information required by the RMF. A QoS Model also describes the
   minimum set of parameters QNEs should use in the QSPEC when signaling
   about this QoS Model.

   QoS Models may be local (private to one network), implementation/
   vendor specific, or global (implementable by different networks and
   vendors).  All QSPECs must follow the QSPEC template [I-D.ietf-nsis-
   qspec].

   The definition of a QoS model may also have implications on how local
   behavior should be implemented in the areas where the QoS NSLP gives
   freedom to implementers. For example, it may be useful to identify
   recommended behavior for how a RESERVE message that is forwarded
   relates to that received, or when additional signaling sessions
   should be started based on existing sessions, such as required for
   aggregate reservations. In some cases, suggestions may be made on
   whether state that may optionally be retained should be held in
   particular scenarios.  A QoS model may specify reservation
   preemption, e.g., an incoming resource request may cause removal of
   an earlier reservation.


3.1.3.  Policy Control

   Getting access to network resources, e.g., network access in general
   or access to QoS, typically involves some kind of policy control. One
   example of this is authorization of the resource requester. Policy
   control for QoS NSLP resource reservation signaling is conceptually
   organized as illustrated below in Figure 3.

















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                                      +-------------+
                                      | Policy      |
                                      | Decision    |
                                      | Point (PDP) |
                                      +------+------+
                                             |
                                     /-\-----+-----/\
                                 ////                \\\\
                               ||                        ||
                              |      Policy transport      |
                               ||                        ||
                                 \\\\                ////
                                     \-------+------/
                                             |
       +-------------+ QoS signaling  +------+------+
       |  Entity     |<==============>| QNE = Policy|<=========>
       |  requesting | Data Flow      | Enforcement |
       |  resource   |----------------|-Point (PEP)-|---------->
       +-------------+                +-------------+

           Figure 3: Policy control with the QoS NSLP signaling.

   From the QoS NSLP point of view, the policy control model is
   essentially a two-party model between neighboring QNEs. The actual
   policy decision may depend on the involvement of a third entity (the
   policy decision point, PDP), but this happens outside of the QoS NSLP
   protocol by means of existing policy infrastructure (COPS, Diameter,
   etc). The policy control model for the entire end-to-end chain of
   QNEs is therefore one of transitivity, where each of the QNEs
   exchanges policy information with its QoS NSLP policy peer.

   The authorization of a resource request often depends on the identity
   of the entity making the request. Authentication may be required The
   GIST channel security mechanisms provide one way of authenticating
   the QoS NSLP peer which sent the request, and so may be used in
   making the authorization decision.

   Additional information might also be provided in order to assist in
   making the authorization decision. This might include alternative
   methods of authenticating the request.

   The QoS NSLP does not contain objects to carry authorization
   information. [NSLP-AUTH] provides this functionality for the QoS NSLP
   and the NATFW NSLP.

   It is generally assumed that policy enforcement is likely to
   concentrate on border nodes between administrative domains. This may
   mean that nodes within the domain are "Policy Ignorant Nodes" that
   perform no per-request authentication or authorization, relying on
   the border nodes to perform the enforcement. In such cases, the
   policy management between ingress and egress edge of a domain relies
   on the internal chain of trust between the nodes in the domain. If
   this is not acceptable, a separate signaling session can be set up
   between the ingress and egress edge nodes in order to exchange policy

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   information.


3.2.  Design Background

   This section presents some of the key functionality behind the
   specification of the QoS NSLP.


3.2.1.  Soft States

   The NSIS protocol suite takes a soft-state approach to state
   management. This means that reservation state in QNEs must be
   periodically refreshed. The frequency with which state installation
   is refreshed is expressed in the REFRESH_PERIOD object. This object
   contains a value in milliseconds indicating how long the state that
   is signaled for remains valid. Maintaining the reservation beyond
   this lifetime can be done by sending a RESERVE message periodically.


3.2.2.  Sender and Receiver Initiation

   The QoS NSLP supports both sender-initiated and receiver-initiated
   reservations. For a sender-initiated reservation, RESERVE messages
   travel in the same direction as the data flow that is being signaled
   for (the QNI is at the side of the source of the data flow).  For a
   receiver-initiated reservation, RESERVE messages travel in the
   opposite direction (the QNI is at the side of the receiver of the
   data flow).

   Note: these definitions follow the definitions in Section 3.3.1. of
   RFC 4080 [RFC4080]. The main issue is, which node is in charge of
   requesting and maintaining the resource reservation. In a receiver-
   initiated reservation, even though the sender sends the initial
   QUERY, the receiver is still in charge of making the actual resource
   request, and maintaining the reservation.


3.2.3.  Protection Against Message Re-ordering and Duplication

   RESERVE messages affect the installed reservation state. Unlike
   NOTIFY, QUERY and RESPONSE messages, the order in which RESERVE
   messages are received influences the eventual reservation state that
   will be stored at a QNE, that is, the most recent RESERVE message
   replaces the current reservation. Therefore, in order to protect
   against RESERVE message re-ordering or duplication, the QoS NSLP uses
   a Reservation Sequence Number (RSN). The RSN has local significance
   only, i.e., between a QNE and its downstream peers.


3.2.4.  Explicit Confirmations

   A QNE may require a confirmation that the end-to-end reservation is
   in place, or a reply to a query along the path. For such requests, it

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   must be able to keep track of which request each response refers to.
   This is supported by including a Request Identification Information
   (RII) object in a QoS NSLP message.


3.2.5.  Reduced Refreshes

   For scalability, the QoS NSLP supports an abbreviated form of refresh
   RESERVE message. In this case, the refresh RESERVE references the
   reservation using the RSN and the SESSION_ID, and does not include
   the full reservation specification (including QSPEC). These reduced
   refreshes require an explicit acknowledgment to ensure that the RSN
   reference will be understood. It is up to a QNE that receives a
   message containing an special flag bit to decide whether it wants to
   accept reduced refreshes and provide this explicit acknowledgment. It
   sends a NOTIFY message as answer to the received RESERVE.


3.2.6.  Message Scoping

   A QNE may use local policy when deciding whether to propagate a
   message or not. The QoS NSLP also includes an explicit mechanism to
   restrict message propagation by means of a scoping mechanism.

   For a RESERVE or a QUERY message, two scoping flags limit the part of
   the path on which state is installed on the downstream nodes that can
   respond. When the SCOPING flag is set to zero, it indicates that the
   scope is "whole path" (default). When set to one, the scope is
   "single hop". When the PROXY scope flag is set, the path is
   terminated at a pre-defined Proxy QNE (P-QNE). This is similar to the
   Localized RSVP [LRSVP].

   The propagation of a RESPONSE message is limited by the RII object,
   which ensures that it is not forwarded back along the path further
   than the node that requested the RESPONSE.


3.2.7.  Session Binding

   Session binding is defined as the enforcement of a relation between
   different QoS NSLP sessions (i.e., signaling flows with different
   SESSION_ID (SID) as defined in GIST [I-D.ietf-nsis-ntlp]).

   Session binding indicates a unidirectional dependency relation
   between two or more sessions by including a BOUND_SESSION_ID object.
   A session with SID_A (the binding session) can express its
   unidirectional dependency relation to another session with SID_B (the
   bound session) by including a BOUND_SESSION_ID object containing
   SID_B in its messages.

   The concept of session binding is used to indicate the unidirectional
   dependency relation between the end-to-end session and the aggregate
   session in case of aggregate reservations. In case of bidirectional
   reservations, it is used to express the unidirectional dependency

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   relation between the sessions used for forward and reverse
   reservation.  Typically, the dependency relation indicated by session
   binding is purely informative in nature and does not automatically
   trigger any implicit action in a QNE. A QNE may use the dependency
   relation information for local resource optimization or to explicitly
   tear down reservations that are no longer useful. However, by using
   an explicit binding code, see Section 5.1.3.4, it is possible to
   formalise this dependency relation, meaning that if the bound session
   (e.g., session with SID_B) is terminated also the binding session
   (e.g., the session with SID_A) must be terminated.

   A message may include more than one BOUND_SESSION_ID object. This may
   happen, e.g., in certain aggregation and bi-directional reservation
   scenarios, where an end-to-end session has an unidirectional
   dependency relation with an aggregate session and at the same time it
   has an unidirectional dependency relation with another session used
   for the reverse path.


3.2.8.  Layering

   The QoS NSLP supports layered reservations. Layered reservations may
   occur when certain parts of the network (domains) implement one or
   more local QoS models, or when they locally apply specific transport
    characteristics (e.g., GIST unreliable transfer mode instead of
   reliable transfer mode). They may also occur when several per-flow
   reservations are locally combined into an aggregate reservation.


3.2.8.1.  Local QoS Models

   A domain may have local policies regarding QoS model implementation,
   i.e., it may map incoming traffic to its own locally defined QoS
   models. The QoS NSLP supports this by allowing QSPEC objects to be
   stacked.

   By using QSpec staking, an increase in flexibility, modularity and
   signaling performance an be achieved. The flexibility and modularity
   increase can be achieved by providing the possibility to any existing
   or future QoS model applied in a local QoS NSLP aware domain to use
   and stack any required local QoS model information on QoS NSLP
   signaling messages passing through the local domain (see requirement
   5.4.2 in RFC3762).

   The signaling performance increase can be achieved by reducing the
   number of required local QoS NSLP signaling messages, when local QoS
   model information is stacked on the QoS NSLP signaling messages that
   are passing through the local domain.

   When a domain wants to apply a certain QoS model to an incoming per-
   flow reservation request, each edge of the domain is configured to
   map the incoming QSPEC object to a local QSPEC object and push that
   object onto the stack of QSPEC objects. QNEs inside the domain look
   at the top of the QSPEC object stack to determine which QoS model to

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   apply for the reservation.

   The position of the local QSPEC object in the stack implies a trade-
   off between the speed with which incoming messages can be processed
   and the time it takes to construct the outgoing message (if any). By
   mandating the locally valid object to be on top of the stack we value
   ease of processing over ease of message construction.

   Consider a scenario where a domain D implements its own QoS model Q.
   An end host outside the domain D wants to make a resource reservation
   using some QoS model different from Q, and sends a RESERVE message.
   When the message reaches the ingress edge of the domain D, there are
   two options on how to set up a reservation inside domain D with QoS
   model Q:

   a) The ingress router initiates and maintains a separate signaling
   session with the egress router of the domain, and uses the QoS
   request from the received RESERVE to format a resource using Q. The
   egress router forwards a RESERVE towards the recipient with the
   original QSPEC. The ingress router must provide the egress router the
   necessary information about the received RESERVE.

   b) The ingress router generates a QSPEC of the QoS model Q, and adds
   this object into a subsequent RESERVE it will send toward the egress
   router; the end-to-end signaling session remains, no separate local
   signaling session is needed. The egress router removes the added
   QSPEC and sends the RESERVE forward towards the recipient.

   This latter option is similar to RSVP and the "IntServ over DiffServ"
   framework, where an RSVP message can carry a DCLASS object to
   indicate the DiffServ class of an intermediate DiffServ domain the
   RSVP reservation request should be marked to.


3.2.8.2.  Local Control Plane Properties

   The way signaling messages are handled is mainly determined by the
   parameters that are sent over GIST-NSLP API and by the domain
   internal configuration. A domain may have a policy to implement local
   transport behavior. It may, for instance, elect to use an unreliable
   transport locally in the domain while still keeping end-to-end
   reliability intact.

   The QoS NSLP supports this situation by allowing two sessions to be
   set up for the same reservation. The local session has the desired
   local transport properties and is interpreted in internal QNEs. This
   solution poses two requirements: the end-to-end session must be able
   to bypass intermediate nodes and the egress QNE needs to bind both
   sessions together. Bypassing intermediate nodes is achieved with
   GIST. The local session and the end-to-end session are bound at the
   egress QNE by means of the BOUND_SESSION_ID object.




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3.2.8.3.  Aggregate Reservations

   In some cases it is desirable to create reservations for an
   aggregate, rather than on a per-flow basis, in order to reduce the
   amount of reservation state needed, as well as, the processing load
   for signaling messages. Note that the QoS NSLP does not specify how
   reservations need to be combined in an aggregate or how end-to-end
   properties need to be computed but only provides signaling support
   for it.

   The essential difference with the layering approaches described in
   Section 3.2.8.1 and Section 3.2.8.2 is that the aggregate reservation
   needs a MRI that describes all traffic carried in the aggregate
   (e.g., a DSCP in case of IntServ over DiffServ). The need for a
   different MRI mandates the use of two different sessions, similar to
   Section 3.2.8.2 and to the RSVP aggregation solution in RFC 3175
   [RFC3175].

   Edge QNEs of the aggregation domain that want to maintain some end-
   to-end properties may establish a peering relation by sending the
   end-to-end message transparently over the domain (using the
   intermediate node bypass capability described above). Updating the
   end-to-end properties in this message may require some knowledge of
   the aggregated session (e.g., for updating delay values). For this
   purpose, the end-to-end session contains a BOUND_SESSION_ID carrying
   the SESSION_ID of the aggregate session.


3.2.9.  Support for Request Priorities

   This specification acknowledges the fact that in some situations,
   some messages or some reservations may be more important than others
   and therefore foresees mechanisms to give these messages or
   reservations priority.

   Priority of certain signaling messages over others may be required in
   mobile scenarios when a message loss during call set-up is less
   harmful than during handover. This situation only occurs when GIST or
   QoS NSLP processing is the congested part or scarce resource.

   Priority of certain reservations over others may be required when QoS
   resources are oversubscribed. In that case, existing reservations may
   be preempted in order to make room for new higher-priority
   reservations. A typical approach to deal with priority and preemption
   is through the specification of a setup priority and holding priority
   for each reservation. The resource management function at each QNE
   then keeps track of the resource consumption at each priority level.
   Reservations are established when resources, at their setup priority
   level, are still available. They may cause preemption of reservations
   with a lower holding priority than their setup priority.

   Support of reservation priority is a QSPEC parameter and therefore
   outside the scope of this specification. The GIST specification
   provides a mechanism to support a number of levels of message

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   priority that can be requested over the NSLP-GIST API.


3.2.10.  Rerouting

   The QoS NSLP needs to adapt to route changes in the data path. This
   assumes the capability to detect rerouting events, create a QoS
   reservation on the new path and optionally tear down reservations on
   the old path.

   From an NSLP perspective, rerouting detection can be performed in two
   ways. It can either come through NetworkNotification from GIST, or
   from information seen at the NSLP. In the latter case, the QoS NSLP
   node is able to detect changes in its QoS NSLP peers by keeping track
   of a Source Identification Information (SII) handle that provides
   information similar in nature to the RSVP_HOP object described in RFC
   2205 [RFC2205]. When a RESERVE message with an existing SESSION_ID
   and a different SII is received, the QNE knows its upstream or
   downstream peer has changed, for sender-oriented and receiver-
   oriented reservations, respectively.

   Reservation on the new path happens when a RESERVE message arrives at
   the QNE beyond the point where the old and new paths diverge. If the
   QoS NSLP suspects that a reroute has occurred, then a full RESERVE
   message (including the QSPEC) would be sent. A refreshing RESERVE
   (with no QSPEC) will be identified as an error by a QNE on the new
   path which does not have the reservation installed (i.e. it was not
   on the old path) or which previously had a different previous-hop
   QNE. It will send back an error message which results in a full
   RESERVE message being sent. Rapid recovery at the NSLP layer
   therefore requires short refresh periods. Detection before the next
   RESERVE message arrives is only possible at the IP layer or through
   monitoring of GIST peering relations (e.g., by TTL counting the
   number of GIST hops between NSLP peers or the observing changes in
   the outgoing interface towards GIST peer). These mechanisms can
   provide implementation specific optimizations, and are outside the
   scope of this specification.

   When the QoS NSLP is aware of the route change, it needs to set up
   the reservation on the new path. This is done by sending a new
   RESERVE message. If the next QNE is, in fact, unchanged then this
   will be used to refresh/update the existing reservation. Otherwise it
   will lead to the reservation being installed on the new path.

   After the reservation on the new path is set up, the branching node
   may want to tear down the reservation on the old path (sooner than
   would result from normal soft-state time-out). This functionality is
   supported by keeping track of the old SII-Handle provided over the
   GIST API. This handle can be used by the QoS NSLP to route messages
   explicitly to the next node.

   A QNI or a branch node may wish to keep the reservation on the old
   branch. This could for instance be the case when a mobile node has
   experienced a mobility event and wishes to keep reservation to its

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   old attachment point in case it moves back there. For this purpose, a
   REPLACE flag is provided in the QoS NSLP common header, which, when
   not set, indicates that the reservation on the old branch should be
   kept.

   Note that keeping old reservations affects the resources available to
   other nodes.  Thus, the operator of the access network must make the
   final decision on whether this behavior is allowed. Also, the QNEs in
   the access network may add this flag even if the mobile node has not
   used the flag initially.

   The design of the QoS NSLP allows reservations to be installed at a
   subset of the nodes along a path. In particular, usage scenarios
   include cases where the data flow endpoints do not support the QoS
   NSLP.


3.2.10.1.  Last Node Behavior

   In the case where the data flow receiver does not support the QoS
   NSLP, some particular considerations must be given to node discovery
   and rerouting at the end of the signaling path.

   There are three cases for the last node on the signaling path:
   1) Last node is the data receiver
   2) Last node is a configured proxy for the data receiver
   3) Last node is not the data receiver and is not explicitly
      configured to act as a signaling proxy on behalf of the data
      receiver.

   Cases (1) and (2) can be handled by the QoS NSLP itself during the
   initial path setup, since the QNE knows that it should terminate the
   signaling. Case (3) requires some assistance from GIST which provides
   messages across the API to indicate that no further QoS NSLP
   supporting GIST nodes are present downstream, and downstream route
   change probing needs to continue once the reservation is installed to
   detect any changes in this situation.

   Two particular scenarios need to be considered in this third case.
   In the first, referred to as "Path Extension", rerouting occurs such
   that an additional QNE is inserted into the signaling path between
   the old last node and the data receiver, as shown in Figure 4.













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             /-------\   Initial route
            /         v
                /-\
             /--|B|--\                +-+
            /   \-/   \               |x| = QoS NSLP aware
         +-+           /-\            +-+
     ----|A|           |D|
         +-+           \-/            /-\
            \   +-+   /               |x| = QoS NSLP unaware
             \--|C|--/                \-/
                +-+
            \         ^
             \-------/   Updated route
                         Figure 4: Path Extension

   When rerouting occurs, the data path changes from A-B-D to A-C-D.
   Initially the signaling path ends at A. Despite initially being the
   last node, node A needs to continue to attempt to send messages
   downstream to probe for path changes, unless it has been explicitly
   configured as a signaling proxy for the data flow receiver. This is
   required so that the signaling path change is detected, and C will
   become the new last QNE.

   In a second case, referred to as "Path Truncation", rerouting occurs
   such that the QNE that was the last node on the signaling path is no
   longer on the data path. This is shown in Figure 5.

             /-------\   Initial route
            /         v
                +-+
             /--|B|--\                 +-+
            /   +-+   \                |x| = QoS NSLP aware
         +-+           /-\             +-+
     ----|A|           |D|
         +-+           \-/             /-\
            \   /-\   /                |x| = QoS NSLP unaware
             \--|C|--/                 \-/
                \-/
            \         ^
             \-------/   Updated route
                         Figure 5: Path Truncation

   When rerouting occurs, the data path again changes from A-B-D to A-C-
   D. The signaling path initially ends at C, but this node is not on
   the new path. In this case, the normal GIST path change detection
   procedures at A will detect the path change and notify the QoS NSLP.
   GIST will also notify the signaling application that no downstream
   GIST nodes supporting the QoS NSLP are present. Node A will take over
   as the last node on the signaling path.






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3.2.10.2.  Handling Spurious Route Change Notifications

   The QoS NSLP is notified by GIST (with the NetworkNotification
   primitive) when GIST believes that a rerouting event may have
   occurred. In some cases, events that are detected as possible route
   changes will turn out not to be. The QoS NSLP will not always be able
   to detect this, even after receiving messages from the 'new' peer.

   As part of the RecvMessage API primitive, GIST provides an SII-Handle
   which can be used by the NSLP to direct a signaling message to a
   particular peer. The current SII-Handle will change if the signaling
   peer changes. However, it is not guaranteed to remain the same after
   a rerouting event where the peer does not change.  Therefore, the QoS
   NSLP mechanism for reservation maintenance after a route change
   includes robustness mechanisms to avoid accidentally tearing down a
   reservation in situations where the peer QNE has remained the same
   after a 'route change' notification from GIST.

   A simple example that illustrates the problem is shown in Figure 6
   below.

             (1)                         +-+
           /-----\                       |x| = QoS NSLP aware
         +-+     /-\ (3) +-+             +-+
     ----|A|     |B|-----|C|----
         +-+     \-/     +-+             /-\
           \-----/                       |x| = QoS NSLP unaware
             (2)                         \-/

             Figure 6: Spurious reroute alerting

   In this example the initial route A-B-C uses links (1) and (3). After
   link (1) fails, the path is rerouted using links (2) and (3). The set
   of QNEs along the path is unchanged (it is A-C in both cases, since B
   does not support the QoS NSLP).

   When the outgoing interface at A has changes, GIST may signal across
   its API to the NSLP with a NetworkNotification. The QoS NSLP at A
   will then attempt to repair the path by installing the reservation on
   the path'. In this case, however, the old and new paths are the same.

   To install the new reservation A will send a RESERVE message, which
   GIST will transport to C (discovering the new next peer as
   appropriate). The RESERVE also requests a RESPONSE from the QNR. When
   this RESERVE message is received through the RecvMessage API call
   from GIST at the QoS NSLP at C, the SII-Handle will be unchanged from
   its previous communications from A.

   A RESPONSE message will be sent by the QNR, and be forwarded from C
   to A. This confirms that the reservation was installed on the new
   path. The SII-Handle passed with the RecvMessage call from GIST to
   the QoS NSLP will be different to that seen previously, since the
   interface being used on A has changed.


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   At this point A can attempt to tear down the reservation on the old
   path. The RESERVE message with the TEAR flag set is sent down the old
   path by using the GIST explicit routing mechanism and specifying the
   SII-Handle relating to the 'old' peer QNE.

   If RSNs were being incremented for each of these RESERVE and RESERVE-
   with-TEAR messages the reservation would be torn down at C and any
   QNEs further along the path. To avoid this the RSN is used in a
   special way. The RESERVE down the new path is sent with the new
   current RSN set to the old RSN plus 2. The RESERVE-with-TEAR down the
   old path is sent with an RSN set to the new current RSN minus 1. This
   in the peer from which it was receiving RESERVE messages.


3.3.  GIST Interactions

   The QoS NSLP uses GIST for delivery of all its messages. Messages are
   passed from the NSLP to GIST via an API (defined in Appendix B of [I-
   D.ietf-nsis-ntlp]), which also specifies additional information,
   including an identifier for the signaling application (e.g., 'QoS
   NSLP'), session identifier, MRI, and an indication of the intended
   direction - towards data sender or receiver. On reception, GIST
   provides the same information to the QoS NSLP. In addition to the
   NSLP message data itself, other meta-data (e.g.  session identifier
   and MRI) can be transferred across this interface.

   The QoS NSLP keeps message and reservation state per session. A
   session is identified by a Session Identifier (SESSION_ID). The
   SESSION_ID is the primary index for stored NSLP state and needs to be
   constant and unique (with a sufficiently high probability) along a
   path through the network. The QoS NSLP picks a value for Session-ID.
   This value is subsequently used by GIST and the QoS NSLP to refer to
   this session.

   Currently, the QoS NSLP specification considers mainly the path-
   coupled MRM. However, extensions may specify how other types of MRMs
   may be applied in combination with the QoS NSLP.

   When GIST passes the QoS NSLP data to the NSLP for processing, it
   must also indicate the value of the 'D' (Direction) flag for that
   message in the MRI.

   The QoS NSLP does not provide any method of interacting with
   firewalls or Network Address Translators (NATs). It assumes that a
   basic NAT traversal service is provided by GIST.


3.3.1.  Support for Bypassing Intermediate Nodes

   The QoS NSLP may want to restrict the handling of its messages to
   specific nodes. This functionality is needed to support layering
   (explained in Section 3.2.8), when only the edge QNEs of a domain
   process the message. This requires a mechanism at GIST level (which
   can be invoked by the QoS NSLP) to bypass intermediate nodes between

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   the edges of the domain.

   The intermediate nodes are bypassed using multiple levels of the
   router alert option. In that case, internal routers are configured to
   handle only certain levels of router alerts. This is accomplished by
   marking the signaling messages, i.e., modifying the QoS NSLP default
   NSLP-ID value to another NSLP-ID predefined value. The marking is
   accomplished by the ingress edge by modifying the QoS NSLP default
   NSLP-ID value to a NSLP-ID predefined value, see Section 6.4. The
   egress stops this marking process by reassigning the QoS NSLP default
   NSLP-ID value to the original RESERVE message. The exact operation of
   modifying the NSLP-ID must be specified in the relevant QoS model
   specification.


3.3.2.  Support for Peer Change Identification

   There are several circumstances where it is necessary for a QNE to
   identify the adjacent QNE peer, which is the source of a signaling
   application message; e.g., it may be to apply the policy that "state
   can only be modified by messages from the node that created it" or it
   might be that keeping track of peer identity is used as a (fallback)
   mechanism for rerouting detection at the NSLP layer.

   This functionality is implemented in GIST service interface with SII-
   handle. As shown in the above example, we assume the SII- handling
   will support both own SII and peer SII.

   Keeping track of the SII of a certain reservation also provides a
   means for the QoS NSLP to detect route changes. When a QNE receives a
   RESERVE referring to existing state but with a different SII, it
   knows that its upstream peer has changed. It can then use the old SII
   to initiate a teardown along the old section of the path. This
   functionality is supported in GIST service interface when the peer's
   SII which is stored on message reception is passed to GIST upon
   message transmission.


3.3.3.  Support for Stateless Operation

   Stateless or reduced state QoS NSLP operation makes the most sense
   when some nodes are able to operate in a stateless way at GIST level
   as well. Such nodes should not worry about keeping reverse state,
   message fragmentation and reassembly (at GIST), congestion control or
   security associations. A stateless or reduced state QNE will be able
   to inform the underlying GIST of this situation. GIST service
   interface supports this functionality with the Retain-State attribute
   in the MessageReceived primitive.


3.3.4.  Priority of Signaling Messages

   The QoS NSLP will generate messages with a range of performance
   requirements for GIST. These requirements may result from a

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   prioritization at the QoS NSLP (Section 3.2.9) or from the
   responsiveness expected by certain applications supported by the QoS
   NSLP. GIST service interface supports this with the 'priority'
   transfer attribute.


3.3.5.  Knowledge of Intermediate QoS NSLP Unaware Nodes

   In some cases it is useful to know that there are routers along the
   path where QoS cannot be provided. The GIST service interface
   supports this by keeping track of IP-TTL and Original-TTL in the
   RecvMessage primitive. A difference between the two indicates the
   number of QoS NSLP unaware nodes. In this case the QNE that detects
   this difference can set the "B" (BREAK) flag. If a QNE generates a
   QUERY, RESERVE or RESPONSE message, after receiving a QUERY or
   RESERVE message with a "Break" flag set, it can set the "B" (BREAK)
   flag in these messages. There are however, situations where the
   egress QNE in a local domain may have some other means to provide QoS
   [I-D.ietf-nsis-qspec]. For example, in a RMD-QOSM [RMD] (or RMD-QOSM
   like) aware local domain that uses either NTLP stateless nodes or
   NSIS unaware nodes the end to end RESERVE or QUERY message bypasses
   these NTLP stateless or NSIS unaware nodes.  However, the reservation
   within the local domain can be signaled by the RMD-QOSM (or RMD-QOSM
   like QOSM). In such situations, the "B" (BREAK) flag in the end to
   end RESERVE or QUERY message should not be set by the edges of the
   local domain.


4.  Examples of QoS NSLP Operation

   The QoS NSLP can be used in a number of ways. The examples given here
   give an indication of some of the basic processing. However, they are
   not exhaustive and do not attempt to cover the details of the
   protocol processing.


4.1.  Sender-initiated Reservation


                  QNI        QNE        QNE        QNR
                   |          |          |          |
                   | RESERVE  |          |          |
                   +--------->|          |          |
                   |          | RESERVE  |          |
                   |          +--------->|          |
                   |          |          | RESERVE  |
                   |          |          +--------->|
                   |          |          |          |
                   |          |          | RESPONSE |
                   |          |          |<---------+
                   |          | RESPONSE |          |
                   |          |<---------+          |
                   | RESPONSE |          |          |
                   |<---------+          |          |

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                   |          |          |          |
                   |          |          |          |
               Figure 7: Basic Sender Initiated Reservation

   To make a new reservation, the QNI constructs a RESERVE message
   containing a QSPEC object, from its chosen QoS model, which describes
   the required QoS parameters.

   The RESERVE message is passed to GIST which transports it to the next
   QNE. There it is delivered to the QoS NSLP processing which examines
   the message. Policy control and admission control decisions are made.
   The exact processing also takes into account the QoS model being
   used. The node performs appropriate actions (e.g., installing
   reservation) based on the QSPEC object in the message.

   The QoS NSLP then generates a new RESERVE message (usually based on
   the one received). This is passed to GIST, which forwards it to the
   next QNE.

   The same processing is performed at further QNEs along the path, up
   to the QNR. The determination that a node is the QNR may be made
   directly (e.g., that node is the destination for the data flow), or
   using GIST functionality to determine that there are no more QNEs
   between this node and the data flow destination.

   Any node may include a request for a RESPONSE in its RESERVE
   messages.  It does so by including a Request Identification
   Information (RII) object in the RESERVE message. If the message
   already includes an RII, an interested QNE must not add a new RII
   object nor replace the old RII object. Instead it needs to remember
   the RII value so that it can match a RESPONSE message belonging to
   the RESERVE. When it receives the RESPONSE, it forwards the RESPONSE
   upstream towards the RII originating node.

   In this example, the RESPONSE message is forwarded peer-to-peer along
   the reverse of the path that the RESERVE message took (using GIST
   path state), and so is seen by all the QNEs on this segment of the
   path. It is only forwarded as far as the node which requested the
   RESPONSE originally.

   The reservation can subsequently be refreshed by sending further
   RESERVE messages containing the complete reservation information, as
   for the initial reservation. The reservation can also be modified in
   the same way, by changing the QSPEC data to indicate a different set
   of resources to reserve.

   The overhead required to perform refreshes can be reduced, in a
   similar way to that proposed for RSVP in RFC 2961 [RFC2961]. Once a
   RESPONSE message has been received indicating the successful
   installation of a reservation, subsequent refreshing RESERVE messages
   can simply refer to the existing reservation, rather than including
   the complete reservation specification.



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4.2.  Sending a Query

   QUERY messages can be used to gather information from QNEs along the
   path. For example, they can be used to find out what resources are
   available before a reservation is made.

   In order to perform a query along a path, the QNE constructs a QUERY
   message. This message includes a QSPEC containing the actual query to
   be performed at QNEs along the path. It also contains an RII object
   used to match the response back to the query, and an indicator of the
   query scope (next node, whole path, proxy). The QUERY message is
   passed to GIST to forward it along the path.

   A QNE receiving a QUERY message should inspect it and create a new
   message, based on that received with the query objects modified as
   required. For example, the query may request information on whether a
   flow can be admitted, and so a node processing the query might record
   the available bandwidth. The new message is then passed to GIST for
   further forwarding (unless it knows it is the QNR, or is the limit
   for the scope in the QUERY).

   At the QNR, a RESPONSE message must be generated if the QUERY message
   includes a Request Identification Information (RII) object. Various
   objects from the received QUERY message have to be copied into the
   RESPONSE message. It is then passed to GIST to be forwarded peer-to-
   peer back along the path.

   Each QNE receiving the RESPONSE message should inspect the RII object
   to see if it 'belongs' to it (i.e., it was the one that originally
   created it). If it does not then it simply passes the message back to
   GIST to be forwarded back down the path.

   If there was an error in processing a RESERVE, instead of an RII, the
   RESPONSE may carry an RSN. Thus, a QNE must also be prepated to look
   for an RSN object if no RII was present, and act based on the error
   code set in the INFO_SPEC of the RESPONSE.


4.3.  Basic Receiver-initiated Reservation

   As described in the NSIS framework [RFC4080] in some signaling
   applications, a node at one end of the data flow takes responsibility
   for requesting special treatment - such as a resource reservation -
   from the network. Both ends then agree whether sender or receiver-
   initiated reservation is to be done. In case of a receiver initiated
   reservation, both ends agree whether a "One Pass With Advertising"
   (OPWA) [OPWA95] model is being used. This negotiation can be
   accomplished using mechanisms that are outside the scope of NSIS.

   To make a receiver-initiated reservation, the QNR constructs a QUERY
   message, which may contain a QSPEC object from its chosen QoS model
   (see Figure 8). The QUERY must have the RESERVE-INIT flag set. This
   QUERY message does not need to trigger a RESPONSE message and
   therefore, the QNI must not include the RII object (Section 5.4.2) in

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   the QUERY message. The QUERY message may be used to gather
   information along the path, which is carried by the QSPEC object. An
   example of such information is the "One Pass With Advertising" (OPWA)
   [OPWA95]. This QUERY message causes GIST reverse-path state to be
   installed.

                    QNR        QNE        QNE        QNI
                   sender                          receiver
                     |          |          |          |
                     | QUERY    |          |          |
                     +--------->|          |          |
                     |          | QUERY    |          |
                     |          +--------->|          |
                     |          |          | QUERY    |
                     |          |          +--------->|
                     |          |          |          |
                     |          |          | RESERVE  |
                     |          |          |<---------+
                     |          | RESERVE  |          |
                     |          |<---------+          |
                     | RESERVE  |          |          |
                     |<---------+          |          |
                     |          |          |          |
                     | RESPONSE |          |          |
                     +--------->|          |          |
                     |          | RESPONSE |          |
                     |          +--------->|          |
                     |          |          | RESPONSE |
                     |          |          +--------->|
                     |          |          |          |

              Figure 8: Basic Receiver Initiated Reservation

   The QUERY message is transported by GIST to the next downstream QoS
   NSLP node. There it is delivered to the QoS NSLP processing which
   examines the message. The exact processing also takes into account
   the QoS model being used and may include gathering information on
   path characteristics that may be used to predict the end-to-end QoS.

   The QNE generates a new QUERY message (usually based on the one
   received). This is passed to GIST, which forwards it to the next QNE.
   The same processing is performed at further QNEs along the path, up
   to the flow receiver. The receiver detects that this QUERY message
   carries the RESERVE-INIT flag and by using the information contained
   in the received QUERY message, such as the QSPEC, constructs a
   RESERVE message.

   The RESERVE is forwarded peer-to-peer along the reverse of the path
   that the QUERY message took (using GIST reverse path state). Similar
   to the sender-initiated approach, any node may include an RII in its
   RESERVE messages. The RESPONSE is sent back to confirm the resources
   are set up.  The reservation can subsequently be refreshed with
   RESERVE messages in the same way as for the sender-initiated
   approach.

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4.4.  Bidirectional Reservations

   The term "bidirectional reservation" refers to two different cases
   that are supported by this specification:

   o Binding two sender-initiated reservations together, e.g., one
   sender-initiated reservation from QNE A to QNE B and another one from
   QNE B to QNE A.

   o  Binding a sender-initiated and a receiver-initiated reservation
   together, e.g., a sender-initiated reservation from QNE A towards QNE
   B, and a receiver-initiated reservation from QNE A towards QNE B for
   the data flow in the opposite direction (from QNE B to QNE A). This
   case is particularly useful when one end of the communication has all
   required information to set up both sessions.

   Both ends have to agree on which bi-directional reservation type they
   need to use. This negotiation/agreement can be accomplished using
   mechanisms that are outside the scope of NSIS.

   The scenario with two sender-initiated reservations is shown in
   Figure 9. Note that RESERVE messages for both directions may visit
   different QNEs along the path because of asymmetric routing. Both
   directions of the flows are bound by inserting the BOUND_SESSION_ID
   object at the QNI and QNR. RESPONSE messages are optional and not
   shown in the picture for simplicity.

      A          QNE        QNE        B
      |          |  FLOW-1  |          |
      |===============================>|
      |RESERVE-1 |          |          |
   QNI+--------->|RESERVE-1 |          |
      |          +-------------------->|QNR
      |          |          |          |
      |          |  FLOW-2  |          |
      |<===============================|
      |          |          |RESERVE-2 |
      |  RESERVE-2          |<---------+QNI
   QNR|<--------------------+          |
      |          |          |          |

      Figure 9: Bi-directional reservation for sender+sender scenario

   The scenario with a sender-initiated and a receiver-initiated
   reservation is shown on Figure 10. In this case, QNI B sends out two
   RESERVE messages, one for the sender-initiated and one for the
   receiver-initiated reservation. Note that the sequence of the two
   RESERVE messages may be interleaved.







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      A          QNE        QNE        B
      |          |  FLOW-1  |          |
      |===============================>|
      |  QUERY-1 |          |          |
   QNI+--------->| QUERY-1  |          |
      |          +-------------------->|QNR
      |          |          |          |
      |          |RESERVE-1 |          |
      |RESERVE-1 +<--------------------|QNR
   QNI+<---------|          |          |
      |          |          |          |
      |          |  FLOW-2  |          |
      |<===============================|
      |          |          |RESERVE-2 |
      |RESERVE-2 |          |<---------+QNI
   QNR|<--------------------+          |
      |          |          |          |

    Figure 10: Bi-directional reservation for sender+receiver scenario


4.5.  Use of Local QoS Models

   In some cases it may be required to use a different QoS model along a
   particular segment of the signaling path. In this case a node at the
   edge of this region needs to add additional local QSPEC information,
   based on the end-to-end QSPEC. This allows the QoS description to be
   tailored to the QoS provisioning mechanism available in the network.

                    +-------- QoSM2 domain -------+
                    |                             |
                    |                             |
   +----+         +----+         +----+         +----+         +----+
   |QNI |         |edge|         |int.|         |edge|         |QNR |
   |    |========>|QNE |========>|QNE |========>|QNE |========>|    |
   +----+ RESERVE +----+ RESERVE +----+ RESERVE +----+ RESERVE +----+
          QSPEC1    |    QSPEC2         QSPEC2    |    QSPEC1
                    |   {QSPEC1}       {QSPEC1}   |
                    |                             |
                    +-----------------------------+

               Figure 11: Reservation with local QoS Models

   The QNI starts the signaling communication by sending a RESERVE
   message, which contains QSPEC1. However, within a region of the
   network a different QoS model (QoSM2) needs to be used. At the edge
   of this region the QNEs support both the end-to-end and local QoS
   models. When the RESERVE message reaches the QNE at the ingress, the
   initial processing of the RESERVE proceeds as normal. However, the
   QNE also determines the appropriate description using QoSM2. The
   RESERVE message to be sent out is constructed mostly as usual but
   with a second QSPEC object added on top, which becomes the 'current'
   one.


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   When this RESERVE message is received at an node internal to the
   QoSM2 domain the QoS NSLP only uses the local QSPEC, rather than the
   end-to-end QSPEC. Otherwise, processing proceeds as usual. The
   RESERVE message that it generates should include both of the QSPECs
   from the message it received.

   At the QNE at the egress of the region the local QSPEC is removed
   from the message so that subsequent QNEs receive only the end-to-end
   QSPEC.

   A message can contain at most two QSPEC objects, i.e., the end-to-end
   QSPEC and a local QSPEC.


4.6.  Aggregate Reservations

   In order to reduce signaling and per-flow state in the network, the
   reservations for a number of flows may be aggregated.

   QNI        QNE      QNE/QNI'     QNE'    QNR'/QNE      QNR
                     aggregator           deaggregator
    |          |          |          |          |          |
    | RESERVE  |          |          |          |          |
    +--------->|          |          |          |          |
    |          | RESERVE  |          |          |          |
    |          +--------->|          |          |          |
    |          |          | RESERVE  |          |          |
    |          |          +-------------------->|          |
    |          |          | RESERVE' |          |          |
    |          |          +=========>| RESERVE' |          |
    |          |          |          +=========>| RESERVE  |
    |          |          |          |          +--------->|
    |          |          |          | RESPONSE'|          |
    |          |          | RESPONSE'|<=========+          |
    |          |          |<=========+          |          |
    |          |          |          |          | RESPONSE |
    |          |          |          | RESPONSE |<---------+
    |          |          |<--------------------+          |
    |          | RESPONSE |          |          |          |
    |          |<---------+          |          |          |
    | RESPONSE |          |          |          |          |
    |<---------+          |          |          |          |
    |          |          |          |          |          |
    |          |          |          |          |          |

         Figure 12: Sender Initiated Reservation with Aggregation

   An end-to-end per-flow reservation is initiated with the messages
   shown in Figure 12 as "RESERVE".

   At the aggregator a reservation for the aggregated flow is initiated
   (shown in Figure 12 as "RESERVE'"). This may use the same QoS model
   as the end-to-end reservation but has an MRI identifying the
   aggregated flow (e.g., tunnel) instead of for the individual flows.

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   This document does not specify how the QSPEC of the aggregate session
   can be derived from the QSPECs of the end-to-end sessions.

   The messages used for the signaling of the individual reservation
   need to be marked such that the intermediate routers will not inspect
   them.  In the QoS NSLP the following marking possibility is applied,
   see also RFC3175.

   All routers use essentially the same algorithm for which messages
   they process, i.e. all messages at aggregation level 0. However,
   messages have their aggregation level incremented on entry to an
   aggregation region and decremented on exit. In this technique the
   interior routers are not required to do any rewriting of the RAO
   values. However, the aggregating/deaggregating routers must be
   configured with which of their interfaces lie at which aggregation
   level, and also requires consistent message rewriting at these
   boundaries.

   In particular, the Aggregator performs the marking by modifying the
   QoS NSLP default NSLP-ID value to a NSLP-ID predefined value, see
   Section 6.4. A RAO value is then uniquely derivable from each
   predefined NSLP-ID. However, the RAO does not have to have a one-to-
   one relation to a specific NSLP-ID.

          Aggregator                    Deaggregator

             +---+     +---+     +---+     +---+
             |QNI|-----|QNE|-----|QNE|-----|QNR|            aggregate
             +---+     +---+     +---+     +---+            reservation

   +---+     +---+     .....     .....     +---+     +---+
   |QNI|-----|QNE|-----.   .-----.   .-----|QNE|-----|QNR|  end-to-end
   +---+     +---+     .....     .....     +---+     +---+  reservation

                    Figure 13: Reservation aggregation.

   The deaggregator acts as the QNR for the aggregate reservation.

   Session binding information carried in the RESERVE message enables
   the deaggregator to associate the end-to-end and aggregate
   reservations with one another (using the BOUND_SESSION_ID).

   The key difference between this example and the one shown in Section
   4.5 is that the flow identifier for the aggregate is expected to be
   different to that for the end-to-end reservation. The aggregate
   reservation can be updated independently of the per-flow end-to-end
   reservations.


4.7.  Reduced State or Stateless Interior Nodes

   This example uses a different QoS model within a domain, in
   conjunction with GIST and NSLP functionality which allows the
   interior nodes to avoid storing GIST and QoS NSLP state. As a result

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   the interior nodes only store the QSPEC-related reservation state, or
   even no state at all. This allows the QoS model to use a form of
   "reduced-state" operation, where reservation states with a coarser
   granularity (e.g., per-class) are used, or a "stateless" operation
   where no QoS NSLP state is needed (or created).

   The key difference between this example and the use of different QoS
   models in Section 4.5 is that the transport characteristics for the
   reservation, i.e., GIST can be used in a different way for the edge-
   to-edge and hop-by-hop sessions. The reduced state reservation can be
   updated independently of the per-flow end-to-end reservations.


4.7.1.  Sender-initiated Reservation

   The QNI initiates a RESERVE message (see Fig. 14). At the QNEs on the
   edges of the stateless or reduced-state region the processing is
   different and the nodes support two QoS models. At the ingress the
   original RESERVE message is forwarded but ignored by the stateless or
   reduced-state nodes. This is accomplished by marking this message,
   i.e., modifying the QoS NSLP default NSLP-ID value to another NSLP-ID
   predefined value (see Section 4.6). The marking must be accomplished
   by the ingress by modifying the QoS_NSLP default NSLP-ID value to a
   NSLP-ID predefined value. The egress must reassign the QoS NSLP
   default NSLP-ID value to the original end-to-end RESERVE message. An
   example of such operation is given in [RMD].

   The egress node is the next QoS NSLP hop for the end-to-end RESERVE
   message. Reliable GIST transfer mode can be used between the ingress
   and egress without requiring GIST state in the interior. At the
   egress node the RESERVE message is then forwarded normally.

   At the ingress a second RESERVE' message is also built (Fig. 14).
   This makes use of a QoS model suitable for a reduced state or
   stateless form of operation (such as the RMD per hop reservation).
   Since the original RESERVE and the RESERVE' messages are addressed
   identically, the RESERVE' message also arrives at the same egress QNE
   that was also traversed by the RESERVE message.

   When processed by interior (stateless) nodes the QoS NSLP processing
   exercises its options to not keep state wherever possible, so that no
   per flow QoS NSLP state is stored. Some state, e.g., per class, for
   the QSPEC related data may be held at these interior nodes. The QoS
   NSLP also requests that GIST use different transport characteristics
   (e.g., sending of messages in unreliable GIST transfer mode). It also
   requests the local GIST processing not to retain messaging
   association state or reverse message routing state.

   Nodes, such as those in the interior of the stateless or reduced-
   state domain, that do not retain reservation state cannot send back
   RESPONSE messages (and so cannot use the refresh reduction
   extension).

   At the egress node the RESERVE' message is interpreted in conjunction

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   with the reservation state from the end-to-end RESERVE message (using
   information carried in the message to correlate the signaling flows).
   The RESERVE message is only forwarded further if the processing of
   the RESERVE' message was successful at all nodes in the local domain,
   otherwise the end-to-end reservation is regarded as having failed to
   be installed. Note that the egress should use a timer, with a
   preconfigured value, that can be used to synchronise the arrival of
   both messages, i.e., the end-to-end RESERVE message and the local
   RESERVE' message.

           QNE             QNE             QNE            QNE
         ingress         interior        interior        egress
     GIST stateful  GIST stateless  GIST stateless  GIST stateful
            |               |               |              |
    RESERVE |               |               |              |
   -------->| RESERVE       |               |              |
            +--------------------------------------------->|
            | RESERVE'      |               |              |
            +-------------->|               |              |
            |               | RESERVE'      |              |
            |               +-------------->|              |
            |               |               | RESERVE'     |
            |               |               +------------->|
            |               |               |              | RESERVE
            |               |               |              +-------->
            |               |               |              | RESPONSE
            |               |               |              |<--------
            |               |               |     RESPONSE |
            |<---------------------------------------------+
    RESPONSE|               |               |              |
   <--------|               |               |              |

    Figure 14: Sender-initiated reservation with Reduced State Interior
              Nodes


4.7.2.  Receiver-initiated Reservation

   Since NSLP neighbor relationships are not maintained in the reduced-
   state region, only sender-initiated signaling can be supported within
   the reduced state region. If a receiver-initiated reservation over a
   stateless or reduced state domain is required this can be implemented
   as shown in Figure 15.

              QNE            QNE            QNE
            ingress        interior        egress
        GIST stateful  GIST stateless  GIST stateful
               |               |               |
       QUERY   |               |               |
      -------->| QUERY         |               |
               +------------------------------>|
               |               |               | QUERY
               |               |               +-------->
               |               |               | RESERVE

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               |               |               |<--------
               |               |      RESERVE  |
               |<------------------------------+
               | RESERVE'      | RESERVE'      |
               |-------------->|-------------->|
               |               |     RESPONSE' |
               |<------------------------------+
       RESERVE |               |               |
      <--------|               |               |

   Figure 15: Receiver-initiated reservation with Reduced State Interior
              Nodes

   The RESERVE message that is received by the egress QNE of the
   stateless domain is sent transparently to the ingress QNE (known as
   the source of the QUERY message). When the RESERVE message reaches
   the ingress, the ingress QNE needs to send a sender- initiated
   RESERVE' over the stateless domain. The ingress QNE needs to wait for
   a RESPONSE'. If the RESPONSE' notifies that the reservation was
   accomplished successfully then the ingress QNE sends a RESERVE
   message further upstream.


4.8.  Proxy Mode

   Besides the sender- and receiver-initiated reservations, the QoS NSLP
   includes a functionality we refer to as Proxy Mode. Here a QNE is set
   by administrator assignment to work as a proxy QNE (P-QNE) for a
   certain region, e.g., for an administrative domain. A node initiating
   the signaling may set the PROXY scope flag to indicate that the
   signaling is meant to be confined within the area controlled by the
   proxy, e.g., the local access network.

   The Proxy Mode has two uses. First it allows to confine the QoS NSLP
   signaling to a pre-defined section of the path. Secondly, it allows a
   node to make reservations for an incoming data flow.

   For outgoing data flows and sender-initiated reservations, the end
   host is the QNI, and sends a RESERVE with the PROXY scope flag set.
   The P-QNE is the QNR, it will receive the RESERVE, notice the PROXY
   scope flag is set and reply with a RESPONSE (if requested). This
   operation is the same as illustrated in Figure 7. The receiver-
   oriented reservation for outgoing flows works the same way as in
   Figure 8, the P-QNE is the QNI.

   For incoming data flows, the end host is the QNI, and it sends a
   RESERVE towards the data sender with the PROXY scope flag set. Here
   the end host sets the MRI so that it indicates the end host as the
   receiver of the data, and the D-flag is set. If there is only one P-
   QNE in the domain, GIST gets the RESERVE to the P-QNE. If there are
   more than one P-QNEs, GIST will do its best, but may reply with an
   error indicating destination unreachable, e.g., if there are multiple
   inbound routes and the data flow may arrive from either route - GIST
   does not send the RESERVE to multiple P-QNEs.

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   Bi-directional reservations, as discussed in Section 4.4. The P-QNE
   will be the QNR or QNI for reservations.

   If the PROXY scope flag is set in an incoming QoS NSLP message, the
   QNE must set the same flag in all QoS NSLP messages it sends that are
   related to this session.


5.  QoS NSLP Functional Specification


5.1.  QoS NSLP Message and Object Formats

   A QoS NSLP message consists of a common header, followed by a body
   consisting of a variable number of variable-length, typed "objects".
   The common header and other objects are encapsulated together in a
   GIST NSLP-Data object. The following subsections define the formats
   of the common header and each of the QoS NSLP message types. In the
   message formats, the common header is denoted as COMMON_HEADER.

   For each QoS NSLP message type, there is a set of rules for the
   permissible choice of object types. These rules are specified using
   the Augmented Backus-Naur Form (ABNF) specified in RFC 4234
   [RFC4234]. The ABNF implies an order for the objects in a message.
   However, in many (but not all) cases, object order makes no logical
   difference. An implementation SHOULD create messages with the objects
   in the order shown here, but MUST accept the objects in any order.


5.1.1.  Common Header

   All GIST NSLP-Data objects for the QoS NSLP MUST contain this common
   header as the first 32 bits of the object (this is not the same as
   the GIST Common Header).

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   | Message Type  | Message Flags |      Generic Flags            |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The fields in the common header are as follows:

   Msg Type: 8 bits

      1 = RESERVE

      2 = QUERY

      3 = RESPONSE

      4 = NOTIFY

   Message-specific flags: 8 bits

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      These flags are defined as part of the specfication of individual
      messages, and, thus, are different with each message type.

   Generic flags: 16 bits

      Generic flags have the same meaning for all message types. There
      exists currently two generic flag, the (next hop) Scoping flag
      (S), and the Proxy scope flag (P).

      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |          Reserved         |P|S|
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      SCOPING (S) - when set, indicates that the message is scoped and
      should not travel down the entire path but only as far as the next
      QNE (scope="next hop"). By default, this flag is not set (default
      scope="whole path").

      PROXY (P) - when set, indicates that the message is scoped, and
      should not travel down the entire path but only as far as the P-
      QNE. By default, this flag is not set.

   The set of appropriate flags depends on the particular message being
   processed. Any bit not defined as a flag for a particular message
   MUST be set to zero on sending and MUST be ignored on receiving.


5.1.2.  Message Formats


5.1.2.1.  RESERVE

   The format of a RESERVE message is as follows:

   RESERVE = COMMON_HEADER
             RSN [ RII ] [ REFRESH_PERIOD ] [ *BOUND_SESSION_ID ]
             [ [ PACKET_CLASSIFIER ] QSPEC [ QSPEC ] ]

   The RSN is the only mandatory object and MUST always be present in
   all cases. At least one QSPEC MUST be included in the initial RESERVE
   sent towards the QNR. A PACKET_CLASSIFIER MAY be provided. If the
   PACKET_CLASSIFIER is not provided, then the full set of information
   provided in the GIST MRI for the session should be used for packet
   classification purposes.

   Subsequent RESERVE messages meant as reduced refreshes, where no
   QSPEC is provided, MUST NOT include a PACKET_CLASSIFIER either.

   There are no requirements on transmission order, although the above
   order is recommended.

   Four message-specific flags are defined for use in the common header
   with the RESERVE message. These are:


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   +-+-+-+-+-+-+-+-+
   |Rsrved |B|Q|T|R|
   +-+-+-+-+-+-+-+-+

      TEAR (T) - when set, indicates that reservation state and QoS NSLP
      operation state should be torn down. The former is indicated to
      the RMF.  Depending on the QoS model, the tear message may include
      a QSPEC to further specify state removal, e.g., for an
      aggregation, the QSPEC may specify the amount of resources removed
      from the aggregate.

      REPLACE (R) - when set the flag has two uses. First, it indicates
      that a RESERVE with different MRI (but same SID) replaces an
      existing one, so the old one MAY be torn down immediately. This is
      the default situation. This flag may be unset to indicate a desire
      from an upstream node to keep an existing reservation on an old
      branch in place. Second, this flag is also used to indicate
      whether the reserved resources on the old branch should be torn
      down or not when a data path change happens. In this case, the MRI
      is the same and only the route path changes.

      REQUEST REDUCED REFRESHES (Q) - when set, indicates the sender of
      the RESERVE proposes to use the reduced refresh for this session.

      BREAK (B) - when set, indicates that there are routers along the
      path where QoS cannot be provided.

   If the REFRESH_PERIOD is not present, a default value of 30 seconds
   is assumed.

   "If the session of this message is bound to another session, then the
   RESERVE message SHOULD include the SESSION_ID of that other session
   in a BOUND_SESSION_ID object. In the situation of aggregated tunnels,
   the aggregated session MAY not include the SESSION_ID of its bound
   sessions in BOUND_SESSION_ID(s).

   A "reservation collision" may occur if the sender believes that a
   sender-initiated reservation should be performed for a flow, whilst
   the other end believes that it should be starting a receiver-
   initiated reservation. If different session identifiers are used then
   this error condition is transparent to the QoS NSLP though it may
   result in an error from the RMF, otherwise the removal of the
   duplicate reservation is left to the QNIs/QNRs for the two sessions.

   If a reservation is already installed and a RESERVE message is
   received with the same session identifier from the other direction
   (i.e., going upstream where the reservation was installed by a
   downstream RESERVE message, or vice versa) then an error indicating
   "RESERVE received from wrong direction" MUST be sent in a RESPONSE
   message to the signaling message source for this second RESERVE.

   A refresh right along the path can be forced by requesting a RESPONSE
   from the far end (i.e., by including an RII object in the RESERVE
   message). Without this, a refresh RESERVE would not trigger RESERVE

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   messages to be sent further along the path, as each hop has its own
   refresh timer.

   A QNE may ask for confirmation of tear operation by including an RII
   object. Retransmissions should be disabled. A QNE sending a tearing
   RESERVE with an RII included MAY ask GIST to use reliable transport.

   When the QNE sends out a tearing RESERVE, it MUST stop refreshing the
   session state.

   If the routing path changed due to mobility, the mobile node's IP
   address changed, and it sent a Mobile IP binding update, the
   resulting refresh is a new RESERVE. This RESERVE includes a new MRI
   and will be propagated end-to-end without requesting a RESPONSE.

   Note: It is possible for a host to use this mechanism to constantly
   force the QNEs on the path to send refreshing RESERVE messages. It
   may, therefore, be appropriate for QNEs to perform rate limiting on
   the refresh messages that they send.


5.1.2.2.  QUERY

   The format of a QUERY message is as follows:

   QUERY = COMMON_HEADER
           [ RII ][ *BOUND_SESSION_ID ]
           [ PACKET_CLASSIFIER ] QSPEC [ QSPEC ]

   QUERY messages MUST always include at least one QSPEC. QUERY messages
   MAY include a PACKET_CLASSIFIER when the message is used to trigger a
   receiver-initiated reservation. If a PACKET_CLASSIFIER is not
   included then the full GIST MRI should be used for packet
   classification purposes in the subsequent RESERVE. A QUERY message
   MAY contain a second QSPEC object.

   A QUERY message for requesting information about network resources
   MUST contain an RII object to match an incoming RESPONSE to the
   QUERY.

   The QSPEC object describes what is being queried for and may contain
   objects that gather information along the data path. There are no
   requirements on transmission order, although the above order is
   recommended.

   Two message-specific flags are defined for use in the common header
   with the QUERY message. This is:

   +-+-+-+-+-+-+-+-+
   |Reserved   |B|R|
   +-+-+-+-+-+-+-+-+

   RESERVE-INIT (R) - when this is set, the QUERY is meant as a trigger
   for the recipient to make a resource reservation by sending a

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   RESERVE.

   BREAK (B) - when set, indicates that there are routers along the path
   where QoS cannot be provided.

   If the session of this message is bound to another session, then the
    RESERVE message SHOULD include the SESSION_ID of that other session
   in a BOUND_SESSION_ID object. In the situation of aggregated tunnels,
   the aggregated session MAY not include the SESSION_ID of its bound
   sessions in BOUND_SESSION_ID(s).


5.1.2.3.  RESPONSE

   The format of a RESPONSE message is as follows:

   RESPONSE = COMMON_HEADER
              [ RII / RSN ] INFO_SPEC [ QSPEC [ QSPEC ] ]

   A RESPONSE message MUST contain an INFO_SPEC object which indicates
   the success of a reservation installation or an error condition.
   Depending on the value of the INFO_SPEC, the RESPONSE MAY also
   contain a QSPEC object. The value of an RII or an RSN object was
   provided by some previous QNE. There are no requirement on
   transmission order, although the above order is recommended.

   One message-specific flag is defined for use in the common header
   with the RESPONSE message. This is:

   +-+-+-+-+-+-+-+-+
   |Reserved     |B|
   +-+-+-+-+-+-+-+-+

   BREAK (B) - when set, indicates that there are routers along the path
   where QoS cannot be provided.


5.1.2.4.  NOTIFY

   The format of a NOTIFY message is as follows:

   NOTIFY = COMMON_HEADER
            INFO_SPEC [ QSPEC [ QSPEC ] ]

   A NOTIFY message MUST contain an INFO_SPEC object indicating the
   reason for the notification. Depending on the INFO_SPEC value, it MAY
   contain one or two QSPEC objects providing additional information.

   No message-specific flags are defined for use with the NOTIFY
   message.





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5.1.3.  Object Formats

   The QoS NSLP uses a Type-Length-Value (TLV) object format similar to
   that used by GIST. Every object consists of one or more 32-bit words
   with a one-word header. For convenience the standard object header is
   shown here:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |A|B|r|r|         Type          |r|r|r|r|        Length         |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The value for the Type field comes from the shared NSLP object type
   space, the various objects are presented in subsequent sections. The
   Length field is given in units of 32 bit words and measures the
   length of the Value component of the TLV object (i.e., it does not
   include the standard header).

   The bits marked 'A' and 'B' are flags used to signal the desired
   treatment for objects whose treatment has not been defined in the
   protocol specification (i.e., whose Type field is unknown at the
   receiver). The following four categories of object have been
   identified, and are described here.


      AB=00 ("Mandatory"): If the object is not understood, the entire
        message containing it MUST be rejected, and an error message
        sent back.

      AB=01 ("Ignore"): If the object is not understood, it MUST be
        deleted and the rest of the message processed as usual.

      AB=10 ("Forward"): If the object is not understood, it MUST be
        retained unchanged in any message forwarded as a result of
        message processing, but not stored locally.

      AB=11 ("Refresh"): If the object is not understood, it should be
        incorporated into the locally stored QoS NSLP signaling
        application operational state for this flow/session, forwarded
        in any resulting message, and also used in any refresh or repair
        message which is generated locally. The contents of this object
        does not need to be interpreted, and should only be stored as
        bytes on the QNE.


   The remaining bits marked 'r' are reserved. The extensibility flags
   AB are similar to those used in the GIST specification. All objects
   defined in this specification MUST be understood by all QNEs, thus,
   they MUST have the AB-bits set to "00". A QoS NSLP implementation
   must recognize objects of the following types: RII, RSN,
   REFRESH_PERIOD, BOUND_SESSION_ID, INFO_SPEC, and QSPEC.

   The object header is followed by the Value field, which varies for

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   different objects. The format of the Value field for currently
   defined objects is specified below.

   The object diagrams here use '//' to indicate a variable sized field.


5.1.3.1.  Request Identification Information (RII)

   Type: 0x01

   Length: Fixed - 1 32-bit word

   Value: An identifier which MUST be (probabilistically) unique within
   the context of a SESSION_ID, and SHOULD be different every time a
   RESPONSE is desired. Used by a QNE to match back a RESPONSE to a
   request in a RESERVE or QUERY message.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |           Response Identification Information (RII)           |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.1.3.2.  Reservation Sequence Number (RSN)

   Type: 0x02

   Length: Fixed - 2 32-bit words

   Value: An incrementing sequence number that indicates the order in
   which state modifying actions are performed by a QNE, and an epoch
   identifier to allow the identification of peer restarts. The RSN has
   local significance only, i.e., between a QNE and its downstream
   stateful peers. The RSN is not reset when the downstream peer
   changes..

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |               Reservation Sequence Number (RSN)               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                       Epoch Identifier                        |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.1.3.3.  Refresh Period (REFRESH_PERIOD)

   Type: 0x03

   Length: Fixed - 1 32-bit word

   Value: The refresh timeout period R used to generate this message; in
   milliseconds.

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    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      Refresh Period (R)                       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.1.3.4.  Bound Session ID (BOUND_SESSION_ID)

   Type: 0x04

   Length: Fixed - 5 32-bit words

   Value: contains an 8-bit Binding_Code that indicates the nature of
   binding. The rest specifies the SESSION_ID (as specified in GIST [I-
   D.ietf-nsis-ntlp]) of the session that MUST be bound to the session
   associated with the message carrying this object.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                  RESERVED                     |  Binding Code |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   +                                                               +
   |                                                               |
   +                          Session ID                           +
   |                                                               |
   +                                                               +
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Currently defined Binding Codes are:

       o  0x01 - Tunnel and end-to-end sessions

       o  0x02 - Bi-directional sessions

       o  0x03 - Aggregate sessions

       o  0x04 - Dependent sessions (binding session is alive only if
                 the other session is also alive)

   More binding codes maybe defined based on the above four atomic
   binding actions. Note a message may include more than one
   BOUND_SESSION_ID object. This may be needed in case one needs to
   define more specifically the reason for binding, or if the session
   must on depend on more than one other session (with possibly
   different reasons). Note that a session with e.g., SID_A (the binding
   session) can express its unidirectional dependency relation to
   another session with e.g., SID_B (the bound session) by including a
   BOUND_SESSION_ID object containing SID_B in its messages.



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5.1.3.5.  Packet Classifier (PACKET_CLASSIFIER)

   Type: 0x05

   Length: Variable

   Value: Contains a variable length MRM-specific data

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //          Method-specific classifier data (variable)         //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   At this stage, the QoS NSLP only uses the path-coupled routing MRM.
   The method-specific classifier data is two bytes long and consists of
   a set of flags:

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |X|Y|P|T|F|S|A|B|                      Reserved                  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-++-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The flags are:

      X - Source Address and Prefix

      Y - Destination Address and Prefix

      P - Protocol

      T - DiffServ Code Point

      F - Flow Label

      S - SPI

      A - Source Port

      B - Destination Port


   The flags indicate which fields from the MRI MUST be used by the
   packet classifier. This allows a subset of the information in the MRI
   to be used for identifying the set of packets which are part of the
   reservation. Flags MUST only be set if the data is present in the MRI
   (i.e., where there is a corresponding flag in the GIST MRI, the flag
   can only be set if the corresponding GIST MRI flag is set). It should
   be noted that some flags in the PACKET_CLASSIFIER (X and Y) relate to
   data that is always present in the MRI, but are optional to use for
   QoS NSLP packet classification. The appropriate set of flags set may
   depend, to some extent, on the QoS model being used.


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   As mentioned earlier in this section, the QoS NSLP is currently only
   defined for use with the Path-Coupled Message Routing Mechanism (MRM)
   in GIST.  Future work may extend the QoS NSLP to additional routing
   mechanisms. Such MRMs must include sufficient information in the MRI
   to allow the subset of packets for which QoS is to be provided to be
   identified. When QoS NSLP is extended to support a new MRM,
   appropriate method-specific classifier data for the PACKET_CLASSIFIER
   object MUST be defined.


5.1.3.6.  Information Object (INFO_SPEC) and Error Codes

   Type: 0x06

   Length: Variable

   Value: Contains a 16-bit error code, a 4-bit error class, a 4-bit
   error source identifier type, and an 8-bit error source identifier
   length (in 32-bit words), an error source identifier and optionally
   variable length error-specific information.

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |          Error Code           |E-Class|ESI Typ|   ESI-Length  |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                   Error Source Identifier                   //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //             Optional error-specific information             //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Class Field:

   The four E-Class bits of the object indicate the error severity
   class. The currently defined severity classes are:

      o  0x01 - Informational

      o  0x02 - Success

      o  0x03 - Protocol Error

      o  0x04 - Transient Failure

      o  0x05 - Permanent Failure

      o  0x06 - QoS Model Error

   Error field:

   Within each error severity class a number of error values are
   defined.

      o  Informational:

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         *  0x01 - Unknown BOUND_SESSION_ID: the message refers to an
                   unknown SESSION_ID in its BOUND_SESSION_ID object.

         *  0x02 - Route Change: possible route change occurred on
                   downstream path.

         *  0x03 - Reduced refreshes supported

         *  0x04 - Reduced refreshes not supported

         *  0x05 - Congestion situation: Possible congestion situation
                   ocurred on downstream path.

      o  Success:

         *  0x01 - Reservation succesful

         *  0x02 - Tear down succesful
      o  Protocol Error:

         *  0x01 - Illegal message type: the type given in the Message
                   Type field of the common header is unknown.

         *  0x02 - Wrong message length: the length given for the
                   message does not match the length of the message
                   data.

         *  0x03 - Bad flags value: an undefined flag or combination
                   of flags was set in the generic flags

         *  0x04 - Bad flags value: an undefined flag or combination
                   of flags was set in the message-specific flags

         *  0x05 - Mandatory object missing: an object required in a
                   message of this type was missing.

         *  0x06 - Illegal object present: an object was present which
                   must not be used in a message of this type.

         *  0x07 - Unknown object present: an object of an unknown type
                   was present in the message.

         *  0x08 - Wrong object length: the length given for the object
                   did not match the length of the object data present.

         *  0x09 - RESERVE received from wrong direction.

         *  0x0a - Unknown object field value: a field in an object had
                   an unknown value.

         *  0x0b - Duplicate object present.

         *  0x0c - Malformed QSPEC.


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         *  0x0d - Unknown MRI.
      o  Transient Failure:

         *  0x01 - No GIST reverse-path forwarding state

         *  0x02 - No path state for RESERVE, when doing a receiver-
                   oriented reservation

         *  0x03 - RII conflict

         *  0x04 - Full QSPEC required

         *  0x05 - Mismatch synchronization between end-to-end RESERVE
                   and intra-domain RESERVE

         *  0x06 - Reservation preempted

         *  0x07 - Reservation failure

      o  Permanent Failure:

         *  0x01 - Internal or system error

         *  0x02 - Authorization failure

      o  QoS Model Error:


         This error class can be used by QoS Models to add error codes
         specific to the QoS Model being used. All these errors and
         events are created outside the QoS NSLP itself. The error codes
         in this class are defined in QoS model specifications. Note
         that this error class may also include codes that are not
         purely errors, but rather some non-fatal information.

   Error Source Identifier

      The Error Source Identifier is for diagnostic purposes and its
      inclusion is OPTIONAL. It is suggested that implementations use
      this for the IP address, host name or other identifier of the QNE
      generating the INFO_SPEC to aid diagnostic activities. A QNE
      SHOULD NOT be used in any other purpose other than error logging
      or presenting to the user as part of any diagnostic information. A
      QNE SHOULD NOT attempt to send a message to that address.

      If no Error Source Identifier is included, the Error Source
      Identifier Type field must be zero.

      Currently three Error Source Identifiers have been defined: IPv4,
      IPv6 and FQDN.

      Error Source Identifier: IPv4

      Error Source Identifier Type: 0x01

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        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                      32-bit IPv4 address                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Error Source Identifier: IPv6

      Error Source Identifier Type: 0x02

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       +                                                               +
       |                                                               |
       +                      128-bit IPv6 address                     +
       |                                                               |
       +                                                               +
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Error Source Identifier: FQDN name in UTF-8

      Error Source Identifier Type: 0x03

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                            FQDN Name                        //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      If the length of the FQDN name is not a multiple of 32-bits, the
      field is padded with zero octets to the next 32-bit boundary.

      If a QNE encounters protocol errors, it MAY include additional
      information, mainly for diagnostic purposes. Additional
      information MAY be included if the type of an object is erroneous,
      or a field has an erroneous value.

      If the type of an object is erroneous, the following optional
      error-specific information may be included at the end of the
      INFO_SPEC.

      Object Type Info:

        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |         Object Type           |           Reserved            |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      This object provides information about the type of object which
      caused the error.

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      If a field in an object had an incorrect value, the following
      optional error-specific information may be added at the end of the
      INFO_SPEC.

      Object Value Info:


        0                   1                   2                   3
        0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | Rsvd  |  Real Object Length   |            Offset             |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //                           Object                            //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Real Object Length: Since the length in the original TLV header
      may be inaccurate, this field provides the actual length of the
      object (including the TLV Header) included in the error message.

      Offset: The byte in the object at which the QNE found the error.
      When this byte is set to "0", the complete object is included.

      Object: The invalid TLV object (including the TLV Header).

      This object carries information about a TLV object which was found
      to be invalid in the original message. An error message may
      contain more than one Object Value Info object.


5.1.3.7.  QoS Specification (QSPEC)

   Type: 0x07

   Length: Variable

   Value: Variable length QSPEC (QoS specification) information, which
   is QoS Model dependent.

   The contents and encoding rules for this object are specified in
   other documents. See [I-D.ietf-nsis-qspec].

    0                   1                   2                   3
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                               |
   //                         QSPEC Data                          //
   |                                                               |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


5.2.  General Processing Rules




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5.2.1.  State Manipulation

   The processing of a message and its component objects involves
   manipulating the QoS NSLP and reservation state of a QNE.

   For each flow, a QNE stores (RMF-related) reservation state which
   depends on the QoS model / QSPEC used and QoS NSLP operation state
   which includes non-persistent state (e.g., the API parameters while a
   QNE is processing a message) and persistent state which is kept as
   long as the session is active.

   The persistent QoS NSLP state is conceptually organized in a table
   with the following structure. The primary key (index) for the table
   is the SESSION_ID:

   SESSION_ID

      A 128-bit identifier.

   The state information for a given key includes:

   Flow ID

      Based on GIST MRI. Several entries are possible in case of
      mobility events.

   SII-Handle for each upstream and downstream peer

      The SII-Handle is a local identifier generated by GIST and passed
      over the API.  It is a handle that allows to refer to a particular
      GIST next hop. See SII-Handle in [I-D.ietf-nsis-ntlp] for more
      information.

   RSN from the upstream peer

      The RSN is a 32 bit counter.

   The latest local RSN

      A 32 bit counter.

   List of RII for outstanding responses with processing information.

      The RII is a 32 bit number.

   State lifetime

      The state lifetime indicates how long the state that is being
      signaled for remains valid.

   List of bound sessions

      A list of BOUND_SESSION_ID 128-bit identifiers for each session
      bound to this state.

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   Scope of the signaling

      If the Proxy scope is used, a flag is needed to identify all
      signaling of this session as being scoped.

   Adding the state requirements of all these items gives an upper bound
   on the state to be kept by a QNE. The need to keep state depends on
   the desired functionality at the NSLP layer.


5.2.2.  Message Forwarding

   QoS NSLP messages are sent peer-to-peer along the path. The QoS NSLP
   does not have the concept of a message being sent directly to the end
   of the path. Instead, messages are received by a QNE, which may then
   send another message (which may be identical to the received message,
   or contain some subset of objects from it) to continue in the same
   direction (i.e., towards QNI or QNR) as the message received.

   The decision on whether to generate a message to forward may be
   affected by the value of the SCOPING or PROXY flags, or by the
   presence of an RII object.


5.2.3.  Standard Message Processing Rules

   If a mandatory object is missing from a message then the receiving
   QNE MUST NOT propagate the message any further. It MUST construct a
   RESPONSE message indicating the error condition and send it back to
   the peer QNE that sent the message.

   If a message contains an object of an unrecognised type, then the
   behavior depends on the AB extensibility flags.

   If the Proxy scope flag was set in an incoming QoS NSLP message, the
   QNE must set the same flag in all QoS NSLP messages it sends that are
   related to this session.


5.2.4.  Retransmissions

   Retransmissions may happen end-to-end, e.g., between QNI and QNR
   (using an RII object). In case a QNE transmits a RESERVE with an RII
   object set it waits for a RESPONSE from the responding QNE. QoS NSLP
   messages for which a response is requested by including an RII
   object, but fail to elicit a response are retransmitted. The initial
   retransmission occurs after a QOSNSLP_REQUEST_RETRY wait period.
   Retransmissions MUST be made with exponentially increasing wait
   intervals (doubling the wait each time). QoS NSLP messages SHOULD be
   retransmitted until either a response (which might be an error) has
   been obtained, or until QOSNSLP_RETRY_MAX seconds after the initial
   transmission. In the latter case, a failure SHOULD be indicated to
   the signaling application. The default values for the above-mentioned
   timers are:

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   QOSNSLP_REQUEST_RETRY: 2 seconds      Wait interval before initial
                                         retransmit of the message

   QOSNSLP_RETRY_MAX:    30 seconds      Give up retrying to send the
                                         message

   Retransmissions SHOULD be disabled for tear messages.


5.2.5.  Rerouting


5.2.5.1.  Last Node Behavior

   As discussed in Section 3.2.10 some care needs to be taken to handle
   cases where the last node on the path may change.

   A node that is the last node on the path, but not the data receiver
   (or an explicitly configured proxy for it), MUST continue to attempt
   to send messages downstream to probe for path changes. This must be
   done in order to handle the "Path Extension" case described in
   Section 3.2.10.1.

   A node on the path, that was not previously the last node, MUST take
   over as the last node on the signaling path if GIST path change
   detection identifies that there are no further downstream nodes on
   the path. This must be done in order to handle the "Path Truncation"
   case described in Section 3.2.10.1.


5.2.5.2.  Avoiding Mistaken Teardown

   In order to handle the spurious route change problem described in
   Section 3.2.10.2, the RSN must be used in a particular way when
   maintaining the reservation after a route change is believed to have
   occurred.

   We assume that the current RSN (RSN[current]) is initially RSN0.

   When a route change is believed to have occurred, the QNE SHOULD send
   a RESERVE message, including the full QSPEC. This must contain an RSN
   which is RSN[current] = RSN0 + 2. It MUST include an RII, to request
   a response from the QNR. An SII-Handle MUST NOT be specified when
   passing this message over the API to GIST, so that it is correctly
   routed to the new peer QNE.

   When the QNE receives the RESPONSE message that relates to the
   RESERVE message sent down the new path, it SHOULD send a RESERVE
   message with the TEAR flag sent down the old path. To do so, it MUST
   request GIST to use its explicit routing mechanism and the QoS NSLP
   MUST supply an SII-Handle relating to the old peer QNE. When sending
   this RESERVE message it MUST contain an RSN which is RSN[current] -
   1. (RSN[current] remains unchanged).


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5.2.5.3.  Upstream Route Change Notification

   GIST may notify the QoS NSLP that a possible upstream route change
   has occurred over the GIST API. On receiving such a notification, the
   QoS NSLP SHOULD send a NOTIFY message with Informational code 0x02
   for signaling sessions associated with the identified MRI. If this is
   sent, it MUST be sent to the old peer using the GIST explicit routing
   mechanism through the use of the SII-Handle.

   On receiving such a NOTIFY message, the QoS NSLP SHOULD use the
   InvalidateRoutingState API call to inform GIST that routing state may
   be out of date. The QoS NSLP SHOULD send a NOTIFY message upstream.
   The NOTIFY message should be propagated back to the QNI or QNR.


5.2.5.4.  Route Change Oscillation

   In some circumstances a route change may occur, but the path then
   falls back to the original route.

   After a route change the routers on the old path will continue to
   refresh the reservation until soft state times out, or an explicit
   TEAR is received.

   After detecting an upstream route change a QNE SHOULD consider the
   new upstream peer as current and not fall back to the old upstream
   peer unless:

   - it stops receiving refreshes from the old upstream peer for at
     least the soft state timeout period and then starts receiving
     messages from the old upstream peer again

   - or, it stops receiving refreshes from the new upstream peer for at
     least the soft state timeout period

   GIST routing state keeps track of the latest upstream peer it has
   seen, and so may spuriously indicate route changes occur when the old
   upstream peer refreshes its routing state until the state at that
   node is explicitly torn down or times out.


5.3.  Object Processing


5.3.1.  Reservation Sequence Number (RSN)

   A QNE's own RSN is a sequence number which applies to a particular
   signaling session (i.e., with a particular SESSION_ID). It MUST be
   incremented for each new RESERVE message where the reservation for
   the session changes. The RSN is manipulated using the serial number
   arithmetic rules from [RFC1982], which also defines wrapping rules
   and the meaning of 'equals', 'less than' and 'greater than' for
   comparing sequence numbers in a circular sequence space.


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   The RSN starts at zero. It is stored as part of the per-session state
   and it carries on incrementing (i.e., it is not reset to zero) when a
   downstream peer change occurs. (Note that section 5.2.5.2 provides
   some particular rules for use when a downstream peer changes.)

   The RSN object also contains an Epoch Identifier, which provides a
   method for determining when a peer has restarted (e.g., due to node
   reboot or software restart). The exact method for providing this
   value is implementation defined. Options include storing a serial
   number which is incremented on each restart, picking a random value
   on each restart or using the restart time.

   On receiving a RESERVE message a QNE examines the Epoch Identifier to
   determine if the peer sending the message has restarted. If the Epoch
   Identifier is different to that stored for the reservation then the
   RESERVE message MUST be treated as an updated reservation (even if
   the RSN is less than the current stored value), and the stored RSN
   and Epoch Identifier MUST be updated to the new values.

   When receiving a RESERVE message a QNE uses the RSN given in the
   message to determine whether the state being requested is different
   to that already stored. If the RSN is equal to that stored for the
   current reservation the current state MUST be refreshed. If the RSN
   is greater than the current stored value, the current reservation
   MUST be modified appropriately (provided that admission control and
   policy control succeed), and the stored RSN value updated to that for
   the new reservation. If the RSN is less than the current value, then
   it indicates an out-of-order message and the RESERVE message MUST be
   discarded.

   If the QNE does not store per-session state (and so does not keep any
   previous RSN values) then it MAY ignore the value of the RSN. It MUST
   also copy the same RSN into the RESERVE message (if any) it sends as
   a consequence of receiving this one.


5.3.2.  Request Identification Information (RII)

   A QNE sending QUERY or RESERVE messages may require a response to be
   sent. It does so by including a Request Identification Information
   (RII) object. When creating an RII object the QNE MUST select the
   value for the RII such that it is probabilistically unique within the
   given session. A RII object is typically set by the QNI.

   A number of choices are available when implementing this.
   Possibilities might include using a random value, or a node
   identifier together with a counter. If the value collides with one
   selected by another QNE for a different QUERY then RESPONSE messages
   may be incorrectly terminated, and may not be passed back to the node
   that requested them.

   The node that created the RII object MUST remember the value used in
   the RII to match back any RESPONSE it will receive. The node SHOULD
   use a timer to identify situations where it has taken too long to

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   receive the expected RESPONSE. If the timer expires without receiving
   a RESPONSE it MAY perform a retransmission as discussed in Section
   5.2.4.  In this case this QNE MUST not generate any RESPONSE or
   NOTIFY message to notify this error.

   If an intermediate QNE wants to receive a response for an outgoing
   message, but the message already included an RII when it arrived, the
   QNE MUST NOT add a new RII object nor replace the old RII object, but
   MUST simply remember this RII to match a later RESPONSE message.
   When it receives the RESPONSE, it forwards the RESPONSE upstream
   towards the RII originating node. Note that only the node that
   originally created the RII can set up a retransmission timer. Thus,
   if an intermediate QNE decides to use the RII already contained in
   the message, it MUST NOT set up a retransmission timer, but rely on
   the retransmission timer set up by the QNE that inserted the RII.

   When receiving a message containing an RII object the node MUST send
   a RESPONSE if

      o  The SCOPING flag is set ('next hop' scope),

      o The PROXY scope flag is set and the QNE is the P-QNE, or

      o  This QNE is the last one on the path for the given session.

   and the QNE keeps per-session state for the given session.

   In the rare event that the QNE wants to request a response for a
   message that already included an RII, and this RII value conflicts
   with an existing RII value on the QNE, the node should interrupt the
   processing the message, and send an error message upstream to
   indicate an RII collision, and request a retry with a new RII value.


5.3.3.  BOUND_SESSION_ID

   As shown in the examples in Section 4, the QoS NSLP can relate
   multiple sessions together. It does this by including the SESSION_ID
   from one session in a BOUND_SESSION_ID object in messages in another
   session.

   When receiving a message with a BOUND_SESSION_ID object, a QNE MUST
   copy the BOUND_SESSION_ID object into all messages it sends for the
   same session. A QNE that stores per-session state MUST store the
   value of the BOUND_SESSION_ID.

   The BOUND_SESSION_ID is only indicative in nature. However, a QNE
   implementation may use BOUND_SESSION_ID information to optimize
   resource allocation, e.g., for bidirectional reservations. When
   receiving a tear down message (e.g., a RESERVE message with tear down
   semantic) for an aggregate reservation, it may use this information
   to initiate a tear down for end-to-end sessions bound to the
   aggregate. A QoS NSLP implementation MUST be ready to process more
   than one BOUND_SESSION_ID object within a single message.

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5.3.4.  REFRESH_PERIOD

   Refresh timer management values are carried by the REFRESH_PERIOD
   object which has local significance only. At the expiration of a
   "refresh timeout" period, each QNE independently examines its state
   and sends a refreshing RESERVE message to the next QNE peer where it
   is absorbed. This peer-to-peer refreshing (as opposed to the QNI
   initiating a refresh which travels all the way to the QNR) allows
   QNEs to choose refresh intervals as appropriate for their
   environment. For example, it is conceivable that refreshing intervals
   in the backbone, where reservations are relatively stable, are much
   larger than in an access network. The "refresh timeout" is calculated
   within the QNE and is not part of the protocol; however, it must be
   chosen to be compatible with the reservation lifetime as expressed by
   the REFRESH_PERIOD, and an assessment of the reliability of message
   delivery.

   The details of timer management and timer changes (slew handling and
   so on) are identical to the ones specified in Section 3.7 of RFC 2205
   [RFC2205].

   There are two time parameters relevant to each QoS NSLP state in a
   node: the refresh period R between generation of successive refreshes
   for the state by the neighbor node, and the local state's lifetime L.
   Each RESERVE message may contain a REFRESH_PERIOD object specifying
   the R value that was used to generate this (refresh) message. This R
   value is then used to determine the value for L when the state is
   received and stored. The values for R and L may vary from peer to
   peer.

   In more detail (quoting directly from RFC2205):

      1. Floyd and Jacobson [FJ94] have shown that periodic messages
      generated by independent network nodes can become synchronized.
      This can lead to disruption in network services as the periodic
      messages contend with other network traffic for link and
      forwarding resources. Since the QoS NSLP sends periodic refresh
      messages, it must avoid message synchronization and ensure that
      any synchronization that may occur is not stable. For this reason,
      it is recommended that the refresh timer should be randomly set to
      a value in the range [0.5R, 1.5R].

      2. To avoid premature loss of state, L must satisfy L >= (K +
      0.5)*1.5*R, where K is a small integer. Then in the worst case,
      K-1 successive messages may be lost without state being deleted.
      To compute a lifetime L for a collection of state with different R
      values R0, R1, ..., replace R by max(Ri).

      Currently K = 3 is suggested as the default. However, it may be
      necessary to set a larger K value for hops with high loss rate. K
      may be set either by manual configuration per interface, or by
      some adaptive technique that has not yet been specified.

      3. Each RESERVE message carries a REFRESH_PERIOD object containing

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      the refresh time R used to generate refreshes. The recipient node
      uses this R to determine the lifetime L of the stored state
      created or refreshed by the message.

      4. The refresh time R is chosen locally by each node. If the node
      does not implement local repair of reservations disrupted by route
      changes, a smaller R speeds up adaptation to routing changes,
      while increasing the QoS NSLP overhead. With local repair, a
      router can be more relaxed about R since the periodic refresh
      becomes only a backstop robustness mechanism. A node may therefore
      adjust the effective R dynamically to control the amount of
      overhead due to refresh messages.

      The current suggested default for R is 30 seconds. However, the
      default value Rdef should be configurable per interface.

      5. When R is changed dynamically, there is a limit on how fast it
      may increase. Specifically, the ratio of two successive values
      R2/R1 must not exceed 1 + Slew.Max.

      Currently, Slew.Max is 0.30. With K = 3, one packet may be lost
      without state timeout while R is increasing 30 percent per refresh
      cycle.

      6. To improve robustness, a node may temporarily send refreshes
      more often than R after a state change (including initial state
      establishment).

      7. The values of Rdef, K, and Slew.Max used in an implementation
      should be easily modifiable per interface, as experience may lead
      to different values. The possibility of dynamically adapting K
      and/or Slew.Max in response to measured loss rates is for future
      study.


5.3.5.  INFO_SPEC

   The INFO_SPEC object is carried by the RESPONSE and NOTIFY messages
   and it is used to report a successful, an unsuccessful, or an error
   situation. In case of an error situation the error messages SHOULD be
   generated even if no RII object is included in the RESERVE or in the
   QUERY messages. Note that when the TEAR flag is set in the RESERVE
   message an error situation SHOULD NOT trigger the generation of a
   RESPONSE message.

   Six classes of INFO_SPEC objects are identified and specified in
   Section 5.1.3.6. The message processing rules for each class are
   defined below.

   A RESPONSE message MUST carry INFO_SPEC objects towards the QNI. The
   RESPONSE message MUST be forwarded unconditionally up to the QNI. The
   actions that SHOULD be undertaken by the QNI that receives the
   INFO_SPEC object are specified by the local policy of the QoS model
   supported by this QNE. The default action is that the QNI that

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   receives the INFO_SPEC object SHOULD not trigger any other QoS NSLP
   procedure.

   The Informational INFO_SPEC class MUST be generated by a by a
   stateful QoS NSLP QNE when an Informational error class is caught.
   The Informational INFO-SPEC object MUST be carried by a RESPONSE or a
   NOTIFY message.

   In case of an unidirectional reservation, the Success INFO_SPEC class
   MUST be generated by a stateful QoS NSLP QNR when a RESERVE message
   is received and the reservation state installation or refresh
   succeeded. In case of a bi-directional reservation the INFO-SPEC
   object SHOULD be generated by a stateful QoS NSLP QNE when a RESERVE
   message is received and the reservation state installation or refresh
   succeeded. The Success INFO-SPEC object MUST be carried by a RESPONSE
   or a NOTIFY message.

   In case of an unidirectional reservation, the Protocol Error
   INFO_SPEC class MUST be generated by a stateful QoS NSLP QNE when a
   RESERVE or QUERY message is received by the QNE and a protocol error
   is caught. In case of a bi-directional reservation, the Protocol
   Error INFO_SPEC class SHOULD be generated by a stateful QoS NSLP QNE
   when a RESERVE or QUERY message is received by the QNE and a protocol
   error is caught. A RESPONSE message MUST carry this object, which
   MUST be forwarded unconditionally towards the upstream QNE that
   generated the RESERVE or QUERY message that triggered the generation
   of this INFO_SPEC object.  The default action for a stateless QoS
   NSLP QNE that detects such an error is that none of the QoS NSLP
   objects SHOULD be processed and the RESERVE or QUERY message SHOULD
   be forwarded downstream.

   In case of an unidirectional reservation, the Transient Failure
   INFO_SPEC class MUST be generated by a stateful QoS NSLP QNE when a
   RESERVE or QUERY message is received by the QNE and one Transient
   failure error code is caught, or when an event happens that causes a
   transient error. In case of a bi-directional reservation, the
   Transient Failure INFO_SPEC class SHOULD be generated by a stateful
   QoS NSLP QNE when a RESERVE or QUERY message is received by the QNE
   and one Transient failure error code is caught.

   A RESPONSE message MUST carry this object, which MUST be forwarded
   unconditionally towards the upstream QNE that generated the RESERVE
   or QUERY message that triggered the generation of this INFO_SPEC
   object.  The transient RMF-related error MAY also be carried by a
   NOTIFY message.  The default action is that the QNE that receives
   this INFO_SPEC object SHOULD re-trigger the retransmission of the
   RESERVE or QUERY message that triggered the generation of the
   INFO_SPEC object. The default action for a stateless QoS NSLP QNE
   that detects such an error is that none of the QoS NSLP objects
   SHOULD be processed and the RESERVE or QUERY message SHOULD be
   forwarded downstream.

   In case of an unidirectional reservation, the Permanent Failure
   INFO_SPEC class MUST be generated by a stateful QoS NSLP QNE when a

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   RESERVE or QUERY message is received by a QNE and an internal or
   system error occured, or authorization failed. In case of a bi-
   directional reservation, the Permanent Failure INFO_SPEC class SHOULD
   be generated by a stateful QoS NSLP QNE when a RESERVE or QUERY
   message is received by a QNE and an internal or system error occured,
   or authorization failed. A RESPONSE message MUST carry this object,
   which MUST be forwarded unconditionally towards the upstream QNE that
   generated the RESERVE or QUERY message that triggered this protocol
   error. The permanent RMF-related, the internal or system errors MAY
   also be carried by a NOTIFY message. The default action for a
   stateless QoS NSLP QNE that detects such an error is that none of the
   QoS NSLP objects SHOULD be processed and the RESERVE or QUERY message
   SHOULD be forwarded downstream.

   The QoS-specific error class may be used when errors outside the QoS
   NSLP itself occur that are related to the particular QoS Model being
   used. The processing rules of these errors are not specified in this
   document.


5.3.6.  QSPEC

   The contents of the QSPEC depends on the QoS model being used. A
   template for QSPEC objects can be found in [I-D.ietf-nsis-qspec].

   Upon reception, the complete QSPEC is passed to the Resource
   Management Function (RMF), along with other information from the
   message necessary for the RMF processing. A QNE may also receive an
   INFO_SPEC that includes a partial or full QSPEC. This will also be
   passed to the RMF.

   A QNE that receives a QSPEC stack may need to inspect the top most or
   both of the QSPEC objects in the stack, e.g., an domain edge QNE may
   need to add or remove a local QSPEC. The processing of the QSPEC is
   defined in [I-D.ietf-nsis-qspec].

   When a domain wants to apply a certain QoS Model to an incoming per-
   flow reservation request, each edge of the domain is configured to
   map the incoming QSPEC object to a local QSPEC object and push that
   object onto the stack of QSPEC objects (so that it becomes the first
   QSPEC in the message).

   A QNE that knows it is the last QNE to understand a local QSPEC
   object (e.g., by configuration of the egress QNEs of a domain) MUST
   remove the topmost QSPEC object from the stack. It SHOULD update the
   underlying QoS Model's writable parameters, e.g., QoS Available.


5.4.  Message Processing Rules

   This section provides rules for message processing. Not all possible
   error situations are considered. A general rule for dealing with
   erroneous messages is that a node should evaluate the situation
   before deciding how to react. There are two ways to react to

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   erroneous messages:

   a) Silently drop the message, or

   b) Drop the message, and reply with an error code to the sender.

   The default behavior, in order to protect the QNE from a possible DoS
   attack, is to silently drop the message. However, if the QNE is able
   to authenticate the sender, e.g., through GIST, the QNE may send a
   proper error message back to the neighbor QNE in order to let it know
   that there is an inconsistency in the states of adjacent QNEs.


5.4.1.  RESERVE Messages

   The RESERVE message is used to manipulate QoS reservation state in
   QNEs.  A RESERVE message may create, refresh, modify or remove such
   state. A QNE sending a RESERVE MAY require a response to be sent by
   including a Request Identification Information (RII) object, see
   Section 5.3.2.

   RESERVE messages MUST only be sent towards the QNR. A QNE that
   receives a RESERVE message checks the message format. In case of
   malformed messages, the QNE MAY send a RESPONSE message with the
   appropriate INFO_SPEC.

   Before performing any state changing actions a QNE MUST determine
   whether the request is authorized. The way to do this check depends
   on the authorization model being used.

   When the RESERVE is authorized, a QNE checks the COMMON_HEADER flags.
   If the TEAR flag is set, the message is a tearing RESERVE which
   indicates complete QoS NSLP state removal (as opposed to a
   reservation of zero resources). On receiving such a RESERVE message
   the QNE MUST inform the RMF that the reservation is no longer
   required. After this, there are two modes of operation:


      1. If the tearing RESERVE did not include an RII, i.e., the QNI
      did not want a confirmation, the QNE SHOULD remove the QoS NSLP
      state. It MAY signal to GIST (over the API) that reverse path
      state for this reservation is no longer required. Any errors in
      processing the tearing RESERVE SHOULD NOT be sent back towards the
      QNI since the downstream QNEs will already have removed their
      session states, thus, they are unable to do anything to the error.

      2. If an RII was included, the stateful QNE MUST still keep the
      NSLP operational state until a RESPONSE for the tear going towards
      the QNI is received. This operational state SHOULD be kept for one
      refresh interval, after which the NSLP operational state for the
      session is removed. Depending on the QoS model, the tear message
      MAY include a QSPEC to further specify state removal. If the QoS
      model requires a QSPEC, and none is provided, the QNE SHOULD reply
      with an error message, and SHOULD NOT remove the reservation.

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   If the tearing RESERVE includes a QSPEC, but none is required by the
   QoS model, the QNE MAY silently discard the QSPEC and proceed as if
   it did not exit in the message. In general, a QoS NSLP implementation
   should carefully consider, when an error message should be sent, and
   when not.  If the tearing RESERVE did not include an RII, then the
   downstream QNE has remove the RMF and NSLP states, and will not be
   able to do anything to the error. If an RII was included, the
   downstream QNE may still have the NSLP operational state, but no RMF
   state.

   If a QNE receives a tearing RESERVE for a session it still has the
   operational state, but the RMF state was removed, the QNE SHOULD
   accept the message and forward it upstream as if all is well.

   If a QNE receives a refreshing RESERVE for a session it still has the
   operational state, but the RMF state was removed, the QNE MUST
   silently drop the message and not forward it upstream.

   As discussed in Section 5.2.5.2, to avoid incorrect removal of state
   after a rerouting event, a node receiving a RESERVE message with the
   TEAR flag set which does not come from the current peer QNE,
   identified by its SII, MUST be ignored and MUST NOT be forwarded.

   If the QNE has reservations which are bound and dependent to this
   session (they contain the SESSION_ID of this session in their
   BOUND_SESSION_ID object and use Binding Code: 0x04), it MUST send a
   NOTIFY message for each of the reservations with an appropriate
   INFO_SPEC. If the QNE has reservations which are bound, but which
   they are not dependent to this session (the Binding Code in the
   BOUND_SESSION_ID object has one of the values: 0x01, 0x02, 0x03), it
   MAY send a NOTIFY message for each of the reservations with an
   appropriate INFO_SPEC. The QNE MAY elect to send RESERVE messages
   with the TEAR flag set for these reservations.

   The default behavior of a QNE that receives a RESERVE with a
   SESSION_ID for which it already has state installed but with a
   different flow ID is to replace the existing reservation (and tear
   down the reservation on the old branch if the RESERVE is received
   with a different SII).

   In some cases, this may not be the desired behavior. In that case,
   the QNI or a QNE MAY set the REPLACE flag in the common header to
   zero to indicate that the new session does not replace the existing
   one.

   A QNE that receives a RESERVE with the REPLACE flag set to zero but
   with the same SII, will indicate REPLACE=0 to the RMF (where it will
   be used for the resource handling). Furthermore, if the QNE maintains
   a QoS NSLP state then it will also add the new flow ID in the QoS
   NSLP state. If the SII is different, this means that the QNE is a
   merge point. In that case, in addition to the operations specified
   above, the value REPLACE=0 is also indicating that a tearing RESERVE
   SHOULD NOT be sent on the old branch.


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   When a QNE receives a RESERVE message with an unknown SESSION_ID and
   this message contains no QSPEC because it was meant as a refresh then
   the node MUST send a RESPONSE message with an INFO_SPEC that
   indicates a missing QSPEC to the upstream peer ("Full QSPEC
   required"). The upstream peer SHOULD send a complete RESERVE (i.e.,
   one containing a QSPEC) on the new path (new SII).

   At a QNE, resource handling is performed by the RMF. For sessions
   with the REPLACE flag set to zero, we assume that the QoS model
   includes directions to deal with resource sharing. This may include,
   adding the reservations, or taking the maximum of the two or more
   complex mathematical operations.

   This resource handling mechanism in the QoS Model is also applicable
   to sessions with different SESSION_ID but related through the
   BOUND_SESSION_ID object. Session replacement is not an issue here,
   but the QoS Model may specify whether to let the sessions that are
   bound together share resources on common links or not.

   Finally, it is possible that a RESERVE is received with no QSPEC at
   all. This is the case of a reduced refresh. In this case, rather than
   sending a refreshing RESERVE with the full QSPEC, only the SESSION_ID
   and the SII are sent to refresh the reservation. Note that this
   mechanism just reduces the message size (and probably eases
   processing). One RESERVE per session is still needed.

   If the REPLACE flag is set, the QNE SHOULD update the reservation
   state according to the QSPEC contained in the message (if the QSPEC
   is missing the QNE SHOULD indicate this error by replying with a
   RESPONSE containing the corresponding INFO_SPEC "Full QSPEC
   required"). It MUST update the lifetime of the reservation. If the
   REPLACE flag is not set, a QNE SHOULD NOT remove the old reservation
   state if the SII which is passed by GIST over the API is different
   than the SII that was stored for this reservation. The QNE MAY elect
   to keep sending refreshing RESERVE messages.

   If a stateful QoS NSLP QNE receives a RESERVE message with the BREAK
   flag set then the BREAK flag of new generated messages (e.g., RESERVE
   or RESPONSE) MUST be set. When a stateful QoS NSLP QNE receives a
   RESERVE message with the BREAK flag not set then the IP-TTL and
   Original-TTL values in GIST RecvMessage primitive MUST be monitored.
   If they differ then the BREAK flag of new generated messages (e.g.,
   RESERVE or RESPONSE) SHOULD be set. In situations where a QNE or a
   domain is able to provide QoS using other means, see Section 3.3.5,
   then the BREAK flag MUST not be set.

   If the RESERVE message included an RII, and any of the following are
   true, the QNE MUST send a RESPONSE message:

   o The SCOPING flag is set,

   o The Proxy scope flag is set and the QNE is a P-QNE, or

   o The QNE is the last QNE on the path to the destination.

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   When a QNE receives a RESERVE message, its processing may involve
   sending out another RESERVE message. When sending a RESERVE message,
   the QNE MAY insert or remove 'local' QSPEC objects from the message.
   If any QSPEC is present, the first QSPEC MUST NOT be removed when
   sending on the RESERVE message.

   It MUST NOT send a reduced overhead refresh message (i.e., a RESERVE
   with a non-incremented RSN and no QSPEC) unless it has received a
   RESPONSE message for that RESERVE message, and the downstream QNE has
   agreed to use reduced refreshes by sending a NOTIFY.

   If a QNE has not received a NOTIFY confirming the use of reduced
   refreshes from its downstream peer for a session, the QNE MUST
   continue to use full refresh messages. It MAY add the Q-bit (Request
   Reduced Refrehses) in subsequent refresh messages in order to
   continue asking the downstream QNE to use reduced refrehes.

   If the session of this message is bound to another session, then the
    RESERVE message SHOULD include the SESSION_ID of that other session
   in a BOUND_SESSION_ID object. In the situation of aggregated tunnels,
   the aggregated session MAY not include the SESSION_ID of its bound
   sessions in BOUND_SESSION_ID(s).

   In case of receiver-initiated reservations, the RESERVE message must
   follow the same path that has been followed by the QUERY message.
   Therefore, GIST is informed, over the QoS NSLP/GIST API, to pass the
   message upstream, i.e., by setting GIST "D" flag, see GIST [I-D.ietf-
   nsis-ntlp].

   The QNE MUST create a new RESERVE and send it to its next peer, when:

   - A new resource set up was done,

   - A new resource set up was not done, but the QOSM still defines that
     a RESERVE must be propagated,

   - The RESERVE is a refresh and includes new MRI, or

   - If the RESERVE-INIT flag is included in an arrived QUERY.


5.4.2.  QUERY Messages

   A QUERY message is used to request information about the data path
   without making a reservation. This functionality can be used to
   'probe' the network for path characteristics or for support of
   certain QoS models, or for initiating a receiver-initiated
   reservation.

   A QNE sending a QUERY indicates a request for a response by including
   a Request Identification Information (RII) object, see Section 5.3.2.
   A request to initiate a receiver-initiated reservation is done
   through the RESERVE-INIT flag, see Section 5.1.2.2.


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   When a QNE receives a QUERY message the QSPEC is passed to the RMF
   for processing. The RMF may return a modified QSPEC that is used in
   any QUERY or RESPONSE message sent out as a result of the QUERY
   processing.

   When processing a QUERY message, a QNE checks whether the RESERVE-
   INIT flag is set. If the flag is set, the QUERY is used to install
   reverse path state. In this case, if the QNE is not the QNI, it
   creates a new QUERY message to send downstream. If the QUERY
   contained a QSPEC, it MUST be passed to the RMF where it may be
   modified by the QoS Model specific QUERY processing. If the QNE is
   the QNI, the QNE creates a RESERVE message, which contains a QSPEC
   received from the RMF and which may be based on the received QSPEC.
   If this node was not expecting to perform a receiver-initiated
   reservation then an error MUST be sent back along the path.

   If an RII object is present, and if the QNE is the QNR, the SCOPING
   flag is set or the PROXY scope flag is set and the QNE is a p-QNE,
   the QNE MUST generate a RESPONSE message and pass it back along the
   reverse of the path used by the QUERY.

   In other cases, the QNE MUST generate a QUERY message which is then
   forwarded further along the path using the same MRI, Session ID and
   Direction as provided when the QUERY was received over the GIST API.
   The QSPEC to be used is that provided by the RMF as described
   previously. When generating a QUERY to send out to pass the query
   further along the path, the QNE MUST copy the RII object (if present)
   unchanged into the new QUERY message. A QNE that is also interested
   in the response to the query keeps track of the RII to identify the
   RESPONSE when it passes through it.

   Note that QUERY messages with the RESERVE-INIT flag set MUST be
   answered by the QNI. This feature may be used, e.g., following
   handovers, to set up new path state in GIST, and request the other
   party to send a RESERVE back on this new GIST path.

   If a stateful QoS NSLP QNE receives a QUERY message with the RESERVE-
   INIT flag and BREAK flag set then the BREAK flag of new generated
   messages (e.g., QUERY, RESERVE or RESPONSE) MUST be set. When a
   stateful QoS NSLP QNE receives a QUERY message with the the RESERVE-
   INIT flag set and BREAK flag not set then then the IP-TTL and
   Original-TTL values in GIST RecvMessage primitive MUST be monitored.
   If they differ then the BREAK flag of new generated messages (e.g.,
   QUERY, RESERVE or RESPONSE) SHOULD be set. In situations where a QNE
   or a domain is able to provide QoS using other means, see Section
   3.3.5, then the BREAK flag MUST not be set.


5.4.3.  RESPONSE Messages

   The RESPONSE message is used to provide information about the result
   of a previous QoS NSLP message, e.g., confirmation of a reservation
   or information resulting from a QUERY. The RESPONSE message does not
   cause any state to be installed, but may cause state(s) to be

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   modified, e.g., if the RESPONSE contains information about an error.

   A RESPONSE message MUST be sent when the QNR processes a RESERVE or
   QUERY message containing an RII object or if the QNE receives a
   scoped RESERVE or a scoped QUERY. In this case, the RESPONSE message
   MUST contain the RII object copied from the RESERVE or the QUERY.
   Also, if there is an error in processing a received RESERVE, a
   RESPONSE is sent indicating the nature of the error. In this case,
   the RII and RSN, if available, MUST be included in the RESPONSE.

   On receipt of a RESPONSE message containing an RII object, the
   stateful QoS NSLP QNE MUST attempt to match it to the outstanding
   response requests for that signaling session. If the match succeeds,
   then the RESPONSE MUST NOT be forwarded further along the path if it
   contains an INFO_SPEC class informational or success. If the QNE did
   not insert this RII itself, if must forward the RESPONSE to the next
   peer. Thus, for RESPONSES indicating success, forwarding should only
   stop if the QNE inserted the RII by itself, If the RESPONSE carries
   an INFO_SPEC indicating an error, forwarding SHOULD continue upstream
   towards the QNI by using RSNs as described in the next paragraph.

   On receipt of a RESPONSE message containing an RSN object, a stateful
   QoS NSLP QNE MUST compare the RSN to that of the appropriate
   signaling session. If the match succeeds then the INFO_SPEC MUST be
   processed. If the INFO_SPEC object is used to notify errors then the
   node MUST use the stored upstream peer RSN value, associated with the
   same session, and forward the RESPONSE message further along the path
   towards the QNI.

   If the INFO_SPEC is not used to notify error situations, see above,
   then if the RESPONSE message carries an RSN, the message MUST NOT be
   forwarded further along the path.

   If there is no match for RSN, the message SHOULD be silently dropped.

   On receipt of a RESPONSE message containing neither an RII nor an RSN
   object, the RESPONSE MUST NOT be forwarded further along the path.

   In the typical case RESPONSE messages do not change the states
   installed in intermediate QNEs. However, depending on the QoS model,
   there may be situations where states are affected, e.g.,

   - if the RESPONSE includes an INFO_SPEC describing an error situation
     resulting in reservations to be removed, or

   - the QoS model allows a QSPEC to define [min,max] limits on the
     resources requested, and downstream QNEs gave less resources than
     their upstream nodes, which means that the upstream nodes may
     release a part of the resource reservation.

   If a stateful QoS NSLP QNE receives a RESPONSE message with the BREAK
   flag set then the BREAK flag of new generated message (e.g.,
   RESPONSE) MUST be set.


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5.4.4.  NOTIFY Messages

   NOTIFY messages are used to convey information to a QNE
   asynchronously.  NOTIFY messages do not cause any state to be
   installed. The decision to remove state depends on the QoS model. The
   exact operation depends on the QoS model. A NOTIFY message does not
   directly cause other messages to be sent. NOTIFY messages are sent
   asynchronously, rather than in response to other messages. They may
   be sent in either direction (upstream or downstream).

   A special case of synchronous NOTIFY is when the upstream QNE asked
   to use reduced refresh by setting the appropriate flag in the
   RESERVE. The QNE receiving such a RESERVE MUST reply with a NOTIFY
   and a proper INFO_SPEC code whether the QNE agrees to use reduced
   refresh between the upstream QNE.

   The Transient error code 0x07 "Reservation preempted" is sent to the
   QNI whose resources were preempted. The NOTIFY message carries
   information to the QNI that one QNE no longer has a reservation for
   the session. It is up to the QNI to decice what to do based on the
   QoS Model being used.  The QNI would normally tear down the preempted
   reservation by sending a RESERVE with the TEAR flag set using the SII
   of the preempted reservation. However, the QNI can follow other
   procedures as specified in its QoS Model. More discussion on
   preemption can be found in the QSPEC Template [I-D.ietf-nsis-qspec]
   and the individual QoS Model specifications.


6.  IANA Considerations

   This section provides guidance to the Internet Assigned Numbers
   Authority (IANA) regarding registration of values related to the QoS
   NSLP, in accordance with BCP 26 RFC 2434 [RFC2434].

   The QoS NSLP requires IANA to create a number of new registries:
   - QoS NSLP Message Types
   - QoS NSLP Binding Codes
   - QoS NSLP Error Classes and Error Codes

   It also requires registration of new values in a number of
   registries:

   - NSLP Object Types
   - GIST NSLP-ID
   - Router Alert Option Values (IPv4 and IPv6)


6.1.  QoS NSLP Message Type

   The QoS NSLP Message Type is an 8 bit value. This specification
   defines four QoS NSLP message types, which form the initial contents
   of this registry: RESERVE (0x01), QUERY (0x02), RESPONSE (0x03) and
   NOTIFY (0x04).


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   The value 0 is reserved. Values 1-239 are to be allocated by
   Standards Action. Values 240 to 255 are for Experimental/Private Use.

   When a new message type is defined, any message flags used with it
   must also be defined.


6.2.  NSLP Message Objects

   [Delete this part if already done by another NSLP:

   A new registry is to be created for NSLP Message Objects. This is a
   12-bit field (giving values from 0 to 4095). This registry is
   shared between a number of NSLPs. Allocation policies are as follows:
   0-1023: Standards Action
   1024-1999: Specification Required
   2000-2047: Private/Experimental Use
   2048-4095: Reserved
   When a new object is defined, the extensbility bits (A/B) must also
   be defined.]

   This document defines seven new NSLP objects. These are described in
   Section 5.1.3: RII (0x01), RSN (0x02), REFRESH_PERIOD (0x03),
   BOUND_SESSION_ID (0x04), PACKET_CLASSIFIER (0x05), INFO_SPEC (0x06),
   and QSPEC (0x07).

   Values are to be assigned from the Standards Action required section
   of the NSLP Object Type registry.


6.3.  QoS NSLP Binding Codes

   A new registry is to be created for the 8-bit Binding Codes used in
   the BOUND_SESSION_ID object. The initial values for this registry are
   listed in Section 5.1.3.4.

   Value 0 is reserved. Values 1 to 127 are to be assigned based on a
   policy of Specification Required. Values 128 to 159 are for
   Exerimental/Private Use. Other values are Reserved.


6.4.  QoS NSLP Error Classes and Error Codes

   In addition Error Classes and Error Codes for the INFO_SPEC object
   are defined. These are described in Section 5.1.3.6.

      The Error Class is 4-bits in length. The initial values are:
      0: Reserved
      1: Informational
      2: Success
      3: Protocol Error
      4: Transient Failure
      5: Permanent Failure
      6: QoS Model Error

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      7-15: Reserved

   The Error Code is 16 bits in length. Each Error Codes are assigned
   within a particular Error Class. This requires the creation of a
   registry for Error Codes in each Error Class. The error code 0 in
   each class is Reserved.

   Policies for the error code registries are as follows:
   0-8191: Standards Action
   8192-12287: Specification Required
   12288-16383: Experimental/Private Use
   16384-65536: Reserved

   The initial assignments for the Error Code registries are given in
   section 5.1.3.6.


6.5.  QoS NSLP Error Source Identifiers

   Section 5.1.3.4 defines Error Source Identifiers, the type of which
   is identified by a 4 bit value. The value 0 is reserved, all other
   values are assigned on a basis of Specification Required, except for
   14 and 15 which are for Experimental/Private Use.

   Initial assignments are given in section 5.1.3.4.


6.6.  NSLP IDs and Router Alert Option Values

   This specification defines an NSLP for use with GIST. Furthermore it
   specifies that a number of NSLP-ID values are used for the support of
   bypassing intermediary nodes (see Section [FIXME]). Consequently, new
   identifiers must be assigned for them from the GIST NSLP identifier
   registry. The QoS NSLP requires that 32 NSLP-ID values be assigned,
   corresponding to QoS NSLP Aggregation Levels 0 to 31.

   The GIST specification also requires that NSLP-IDs be associated with
   specific Router Alert Option (RAO) values (although multiple NSLP-IDs
   may be associated with the same value). For the purposes of the QoS
   NSLP, each of its NSLP-ID values should be associated with a
   different RAO value. This requires that a block of 32 new IPv4 RAO
   values and a block of 32 new IPv6 RAO values be assigned,
   corresponding to QoS NSLP Aggregation Levels 0 to 31.


7.  Security Considerations

   The security requirement for the QoS NSLP is to protect the signaling
   exchange for establishing QoS reservations against identified
   security threats. For the signaling problem as a whole, these threats
   have been outlined in NSIS threats [RFC4081]; the NSIS framework
   [RFC4080] assigns a subset of the responsibility to GIST and the
   remaining threats need to be addressed by NSLPs. The main issues to
   be handled can be summarized as:

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   Authorization:

   The QoS NSLP must assure that the network is protected against theft-
   of-service by offering mechanisms to authorize the QoS reservation
   requester. A user requesting a QoS reservation might want proper
   resource accounting and protection against spoofing and other
   security vulnerabilities which lead to denial of service and
   financial loss. In many cases authorization is based on the
   authenticated identity. The authorization solution must provide
   guarantees that replay attacks are either not possible or limited to
   a certain extent. Authorization can also be based on traits which
   enables the user to remain anonymous. Support for user identity
   confidentiality can be accomplished.

   Message Protection:

   Signaling message content should be protected against modification,
   replay, injection and eavesdropping while in transit. Authorization
   information, such as authorization tokens, need protection. This type
   of protection at the NSLP layer is necessary to protect messages
   between NSLP nodes.

   Rate Limitation:

   QNEs should perform rate limiting on the refresh messages that they
   send. An attacker could send erroneous messages on purpose, forcing
   the QNE to constantly reply with an error message. Authentication
   mechanisms would help in figuring out if error situations should be
   reported to the sender, or silently ignored. If the sender is
   authenticated, the QNE should reply promptly.

   Prevention of Denial of Service Attacks:

   GIST and QoS NSLP nodes have finite resources (state storage,
   processing power, bandwidth). The protocol mechanisms s in this
   document try to minimize exhaustion attacks against these resources
   when performing authentication and authorization for QoS resources.

   To some extent the QoS NSLP relies on the security mechanisms
   provided by GIST which by itself relies on existing authentication
   and key exchange protocols. Some signaling messages cannot be
   protected by GIST and hence should be used with care by the QoS NSLP.
   An API must ensure that the QoS NSLP implementation is aware of the
   underlying security mechanisms and must be able to indicate which
   degree of security is provided between two GIST peers. If a level of
   security protection for QoS NSLP messages is required which goes
   beyond the security offered by GIST or underlying security
   mechanisms, additional security mechanisms described in this document
   must be used. The different usage environments and the different
   scenarios where NSIS is used make it very difficult to make general
   statements without reducing its flexibility.




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7.1.  Trust Relationship Model

   This specification is based on a model which requires trust between
   neighboring NSLP nodes to establish a chain-of-trust along the QoS
   signaling path. The model is simple to deploy, was used in previous
   QoS authorization environments (such as RSVP) and seems to provide
   sufficiently strong security properties. We refer to this model as
   the New Jersey Turnpike.

   On the New Jersey Turnpike, motorists pick up a ticket at a toll
   booth when entering the highway. At the highway exit the ticket is
   presented and payment is made at the toll booth for the distance
   driven. For QoS signaling in the Internet this procedure is roughly
   similar. In most cases the data sender is charged for transmitted
   data traffic where charging is provided only between neighboring
   entities.

   +------------------+  +------------------+  +------------------+
   |          Network |  |          Network |  |          Network |
   |             X    |  |             Y    |  |             Z    |
   |                  |  |                  |  |                  |
   |              ----------->          ----------->              |
   |                  |  |                  |  |                  |
   |                  |  |                  |  |                  |
   +--------^---------+  +------------------+  +-------+----------+
            |                                          .
            |                                          .
            |                                          v
         +--+---+  Data                   Data      +--+---+
         | Node |  ==============================>  | Node |
         |  A   |  Sender                Receiver   |  B   |
         +------+                                   +------+

     Legend:

     ----> Peering relationship which allows neighboring
           networks/entities to charge each other for the
           QoS reservation and data traffic

     ====> Data flow

     ..... Communication to the end host

                   Figure 16: New Jersey Turnpike Model

   The model shown in Figure 16 uses peer-to-peer relationships between
   different administrative domains as a basis for accounting and
   charging. As mentioned above, based on the peering relationship a
   chain-of-trust is established. There are several issues which come to
   mind when considering this type of model:

      o The model allows authorization on a request basis or on a per-
      session basis. Authorization mechanisms are elaborated in Section
      4.9. The duration for which the QoS authorization is valid needs

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      to be controlled. Combining the interval with the soft-state
      interval is possible. Notifications from the networks also seem to
      be viable approach.

      o The price for a QoS reservation needs to be determined somehow
      and communicated to the charged entity and to the network where
      the charged entity is attached. Protocols providing Advice of
      Charge functionality are out of scope.

      o This architecture is simple enough to allow a scalable solution
      (ignoring reverse charging, multicast issues and price
      distribution).

   Charging the data sender as performed in the model simplifies
   security handling by demanding only peer-to-peer security protection.
   Node A would perform authentication and key establishment. The
   established security association (together with the session key)
   would allow the user to protect QoS signaling messages. The identity
   used during the authentication and key establishment phase would be
   used by Network X (see Figure 16) to perform the so-called policy-
   based admission control procedure. In our context this user
   identifier would be used to establish the necessary infrastructure to
   provide authorization and charging. Signaling messages later
   exchanged between the different networks are then also subject to
   authentication and authorization. The authenticated entity thereby
   is, however, the neighboring network and not the end host.

   The New Jersey Turnpike model is attractive because of its
   simplicity. S. Schenker et. al. [shenker-pricing] discuss various
   accounting implications and introduced the edge pricing model. The
   edge pricing model shows similarity to the model described in this
   section with the exception that mobility and the security
   implications itself are not addressed.


7.2.  Authorization Model Examples

   Various authorization models can be used in conjunction with the QoS
   NSLP.


7.2.1.  Authorization for the Two Party Approach

   The two party approach is conceptually the simplest authorization
   model.










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   +-------------+  QoS request     +--------------+
   |  Entity     |----------------->| Entity       |
   |  requesting |                  | authorizing  |
   |  resource   |granted / rejected| resource     |
   |             |<-----------------| request      |
   +-------------+                  +--------------+
             ^                           ^
             +...........................+
                     compensation

                       Figure 17: Two party approach

   In this example the authorization decision only involves the two
   entities, or makes use of previous authorization using an out-of-band
   mechanism to avoid the need for active participation of an external
   entity during the NSIS protocol execution.

   This type of model may be applicable, e.g., between two neighboring
   networks (inter-domain signaling) where a long-term contract (or
   other out-of-band mechanisms) exists to manage charging and provides
   sufficient information to authorize individual requests.


7.2.2.  Token-based Three Party Approach

   An alternative approach makes use of tokens, such as those described
   in RFC 3520 [RFC3520] and RFC 3521 [RFC3521] or used as part of the
   Open Settlement Protocol [OSP]. Authorization tokens are used to
   associate two different signaling protocols runs (e.g., SIP and NSIS)
   and their authorization decision with each other. The latter is a
   form of assertion or trait. As an example, with the authorization
   token mechanism, some form of authorization is provided by the SIP
   proxy, which acts as the resource authorizing entity in Figure 18. If
   the request is authorized, then the SIP signaling returns an
   authorization token which can be included in the QoS signaling
   protocol messages to refer to the previous authorization decision.
   The tokens themselves may take a number of different forms, some of
   which may require the entity performing the QoS reservation to query
   external state.
















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     Authorization
     Token Request   +--------------+
     +-------------->| Entity  C    | financial settlement
     |               | authorizing  | <..................+
     |               | resource     |                    .
     |        +------+ request      |                    .
     |        |      +--------------+                    .
     |        |                                          .
     |        |Authorization                             .
     |        |Token                                     .
     |        |                                          .
     |        |                                          .
     |        |                                          .
     |        |      QoS request                         .
   +-------------+ + Authz. Token   +--------------+     .
   |  Entity     |----------------->| Entity B     |     .
   |  requesting |                  | performing   |     .
   |  resource   |granted / rejected| QoS          |  <..+
   |      A      |<-----------------| reservation  |
   +-------------+                  +--------------+

                Figure 18: Token based three party approach

   For the digital money type of systems (e.g., OSP tokens), the token
   represents a limited amount of credit. So, new tokens must be sent
   with later refresh messages once the credit is exhausted.


7.2.3.  Generic Three Party Approach

   Another method is for the node performing the QoS reservation to
   delegate the authorization decision to a third party, as illustrated
   in Figure 19. The authorization decision may be performed on a per-
   request basis, periodically, or on a per-session basis.

                                        +--------------+
                                        | Entity C     |
                                        | authorizing  |
                                        | resource     |
                                        | request      |
                                        +-----------+--+
                                           ^        |
                                       QoS |        | QoS
                                      authz|        |authz
                                       req.|        | res.
                          QoS              |        v
       +-------------+    request       +--+-----------+
       |  Entity     |----------------->| Entity B     |
       |  requesting |                  | performing   |
       |  resource   |granted / rejected| QoS          |
       |      A      |<-----------------| reservation  |
       +-------------+                  +--------------+

                      Figure 19: Three party approach

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7.3.  Computing the Authorization Decision

   Whenever an authorization decision has to be made then there is the
   question which information serves as an input to the authorizing
   entity. The following information items have been mentioned in the
   past for computing the authorization decision (in addition to the
   authenticated identity):

      Price

      QoS objects

      Policy rules

   Policy rules include attributes like time of day, subscription to
   certain services, membership, etc. into consideration when computing
   an authorization decision.

   The policies used to make the authorization are outside the scope of
   this document and implementation/deployment specific.


8.  Acknowledgments

   The authors would like to thank Eleanor Hepworth, Ruediger Geib,
   Roland Bless, Nemeth Krisztian, Markus Ott, Mayi Zoumaro-Djayoon,
   Martijn Swanink, and Ruud Klaver for their useful comments. Roland,
   especially, has done deep reviews of the document, making sure the
   protocol is well defined. Bob Braden provided helpful comments and
   guidance which were gratefully received.


9.  Contributors

   This draft combines work from three individual drafts. The following
   authors from these drafts also contributed to this document: Robert
   Hancock (Siemens/Roke Manor Research), Hannes Tschofenig and Cornelia
   Kappler (Siemens AG), Lars Westberg and Attila Bader (Ericsson) and
   Maarten Buechli (Dante) and Eric Waegeman (Alcatel).

   Sven Van den Bosch was the first editor of the draft. Since version
   06 of the draft, Jukka Manner has taken the editorship. Yacine El
   Mghazli (Alcatel) contributed text on AAA. Charles Shen and Henning
   Schulzrinne suggested the use of the reason field in the
   BOUND_SESSION_ID.


10.  References


10.1.  Normative References

   [I-D.ietf-nsis-ntlp] Schulzrinne, H., and R. Hancock, "GIST: General
   Internet Messaging Protocol for Signaling", Work in Progress.

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   [I-D.ietf-nsis-qspec] Ash, J., "QoS NSLP QSPEC Template", Work in
   Progress.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
   Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC2234]  Crocker, D., Ed. and P. Overell, "Augmented BNF for Syntax
   Specifications: ABNF", RFC 2234, November 1997.


10.2.  Informative References

   [LRSVP] Manner, J., and Raatikainen, K., "Localized QoS Management
   for Multimedia Applications in Wireless Access Networks". IASTED
   IMSA, August, 2003, pp. 193 - 200.

   [NSIS-EXT] Loughney, J. "NSIS Extensibility Model", Work in Progress.

   [NSLP-AUTH] Manner, J., Stiemerling, M., Tschofenig, H.,
   "Authorization for NSIS Signaling Layer Protocols", Work in Progress.

   [OSP] ETSI, "Telecommunications and Internet protocol harmonization
   over networks (tiphon); open settlement protocol (osp) for inter-
   domain pricing, authorization, and usage exchange", Technical
   Specification 101 321, version 2.1.0.

   [QOS-AUTH] Tschofenig, H., "QoS NSLP Authorization Issues", Work in
   Progress.

   [QOSM-CL] Kappler, C., "A QoS Model for Signaling IntServ Controlled-
   Load Service with NSIS", Work in Progress.

   [RFC1633]  Braden, B., Clark, D., and S. Shenker, "Integrated
   Services in the Internet Architecture: an Overview", RFC 1633, June
   1994.

   [RFC2205]  Braden, B., Zhang, L., Berson, S., Herzog, S., and S.
   Jamin, "Resource ReSerVation Protocol (RSVP) -- Version 1 Functional
   Specification", RFC 2205, September 1997.

   [RFC2210]  Wroclawski, J., "The Use of RSVP with IETF Integrated
   Services", RFC 2210, September 1997.

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
   IANA Considerations Section in RFCs", BCP 26, RFC 2434, October 1998.

   [RFC2475]  Blake, S., Black, D., Carlson, M., Davies, E., Wang, Z.,
   and W. Weiss, "An Architecture for Differentiated Services", RFC
   2475, December 1998.

   [RFC2961]  Berger, L., Gan, D., Swallow, G., Pan, P., Tommasi, F.,
   and S. Molendini, "RSVP Refresh Overhead Reduction Extensions", RFC
   2961, April 2001.


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   [RFC3175]  Baker, F., Iturralde, C., Le Faucheur, F., and B. Davie,
   "Aggregation of RSVP for IPv4 and IPv6 Reservations", RFC 3175,
   September 2001.

   [RFC3520]  Hamer, L-N., Gage, B., Kosinski, B., and H. Shieh,
   "Session Authorization Policy Element", RFC 3520, April 2003.

   [RFC3521]  Hamer, L-N., Gage, B., and H. Shieh, "Framework for
   Session Set-up with Media Authorization", RFC 3521, April 2003.

   [RFC3583]  Chaskar, H., "Requirements of a Quality of Service (QoS)
   Solution for Mobile IP", RFC 3583, September 2003.

   [RFC3726]  Brunner, M., "Requirements for Signaling Protocols", RFC
   3726, April 2004.

   [RFC4080] Hancock, R., "Next Steps in Signaling: Framework", RFC
   4080, December 2004.

   [RFC4081] Tschofenig, H. and D. Kroeselberg, "Security Threats for
   NSIS", RFC 4081, October 2004.

   [RFC4234] Crocker, D., and Overell, P., "Augmented BNF for Syntax
   Specifications: ABNF". RFC 4234, October, 2005.

   [RMD] Bader, A., "RMD-QOSM - The Resource Management in DiffServ QoS
   model", Work in Progress.

   [shenker-pricing] Shenker, S., Clark, D., Estrin, D., and S. Herzog,
   "Pricing in computer networks: Reshaping the research agenda", Proc.
   of TPRC 1995, 1995.

   [Y.1541] Ash, J., "Y.1541 QoS Model for Networks Using Y.1541 QoS
   Classes", Work in Progress.

   [FJ94] Jacobson, V., "Synchronization of Periodic Routing Messages",
   IEEE/ACM Transactions on Networking , Vol. 2 , No. 2 , April 1994.

   [OPWA95] Breslau, L., "Two Issues in Reservation Establishment",
   Proc. ACM SIGCOMM '95 , Cambridge , MA , August 1995.

   Authors' Addresses

   Jukka Manner
   Department of Computer Science University of Helsinki
   P.O. Box 68 (Gustav Hallstromin katu 2b)
   HELSINKI,   FIN-00014
   Finland
   Phone: +358-9-191-51298
   Email: jmanner@cs.helsinki.fi

   Georgios Karagiannis
   University of Twente/Ericsson
   P.O. Box 217

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   Enschede  7500 AE
   The Netherlands
   Email: karagian@cs.utwente.nl

   Andrew McDonald
   Siemens/Roke Manor Research
   Roke Manor Research Ltd.
   Romsey, Hants  SO51 0ZN
   UK
   Email: andrew.mcdonald@roke.co.uk

Appendix A. Glossary

   AAA: Authentication, Authorization and Accounting

   EAP: Extensible Authentication Protocol

   MRI: Message Routing Information (see [I-D.ietf-nsis-ntlp])

   NAT: Network Address Translator

   NSLP: NSIS Signaling Layer Protocol (see [RFC4080])

   NTLP: NSIS Transport Layer Protocol (see [RFC4080])

   OPWA: One Pass With Advertising

   OSP: Open Settlement Protocol

   PIN: Policy Ignorant Node

   QNE: an NSIS Entity (NE), which supports the QoS NSLP (see Section 2)

   QNI: the first node in the sequence of QNEs that issues a reservation
   request for a session (see Section 2)

   QNR: the last node in the sequence of QNEs that receives a
   reservation request for a session (see Section 2)

   QSPEC: Quality of Service Specification

   RII: Request Identification Information

   RMD: Resource Management for DiffServ

   RMF: Resource Management Function

   RSN: Reservation Sequence Number

   RSVP: Resource Reservation Protocol (see [RFC2205])

   SII: Source Identification Information

   SIP: Session Initiation Protocol

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   SLA: Service Level Agreement






















































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