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Versions: (draft-shen-nsis-tunnel) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 RFC 5979

IETF Next Steps in Signaling                                     C. Shen
Internet-Draft                                            H. Schulzrinne
Expires: December 21, 2006                                   Columbia U.
                                                                  S. Lee
                                                                 J. Bang
                                                             Samsung AIT
                                                           June 19, 2006


                     NSIS Operation Over IP Tunnels
                     draft-ietf-nsis-tunnel-00.txt

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This draft presents an NSIS operation over IP tunnel scheme using QoS
   NSLP as the NSIS signaling application.  Both sender-initiated and
   receiver-initiated NSIS signaling modes are discussed.  The scheme
   creates individual or aggregate tunnel sessions for end-to-end
   sessions traversing the tunnel.  Packets belonging to qualified end-



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   to-end sessions are mapped to corresponding tunnel sessions and
   assigned special flow IDs to be distinguished from the rest of the
   tunnel traffic.  Tunnel endpoints keep the association of the end-to-
   end and tunnel session mapping, so that adjustment in one session can
   be reflected in the other.


Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  4
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     2.1.  IP Tunneling Mechanisms and Tunnel Signaling Capability  .  4
     2.2.  NSIS Tunnel Operation Overview . . . . . . . . . . . . . .  5
   3.  Protocol Design Decisions  . . . . . . . . . . . . . . . . . .  6
     3.1.  Flow Packet Classification over the Tunnel . . . . . . . .  6
     3.2.  Tunnel Signaling and its Association with End-to-end
           Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  7
   4.  Protocol Operation with Dynamically Created Tunnel Sessions  .  8
     4.1.  Operation Scenarios  . . . . . . . . . . . . . . . . . . .  8
       4.1.1.  Sender-initiated Reservation for both End-to-end
               and Tunnel Signaling . . . . . . . . . . . . . . . . .  9
       4.1.2.  Receiver-initiated Reservation for both End-to-end
               and Tunnel Signaling . . . . . . . . . . . . . . . . . 11
       4.1.3.  Sender-initiated Reservation for End-to-end and
               Receiver-initiated Reservation for Tunnel Signaling  . 12
       4.1.4.  Receiver-initiated Reservation for End-to-end and
               Sender-initiated Reservation for Tunnel Signaling  . . 14
     4.2.  Implementation Specific Issues . . . . . . . . . . . . . . 15
       4.2.1.  End-to-end and Tunnel Signaling Interaction  . . . . . 15
       4.2.2.  Aggregate vs. Individual Tunnel Session Setup  . . . . 17
   5.  Protocol Operation with Pre-configured Tunnel Sessions . . . . 17
     5.1.  Tunnel with Exactly One Pre-configured Aggregate
           Session  . . . . . . . . . . . . . . . . . . . . . . . . . 18
     5.2.  Tunnel with Multiple Pre-configured Aggregate Sessions . . 18
     5.3.  Adjustment of Pre-configured Tunnel Sessions . . . . . . . 18
   6.  Processing Rules for Selected End-to-end QoS NSLP Messages . . 19
     6.1.  End-to-end QUERY Message at Tentry . . . . . . . . . . . . 19
     6.2.  End-to-end QUERY Message at Texit  . . . . . . . . . . . . 19
     6.3.  End-to-end RESERVE Message at Tentry . . . . . . . . . . . 19
       6.3.1.  Sender-initiated RESERVE Message . . . . . . . . . . . 19
       6.3.2.  Receiver-initiated RESERVE Message . . . . . . . . . . 20
     6.4.  End-to-end RESERVE Message at Texit  . . . . . . . . . . . 21
       6.4.1.  Sender-initiated RESERVE Message . . . . . . . . . . . 21
       6.4.2.  Receiver-initiated RESERVE Message . . . . . . . . . . 22
     6.5.  Special Processing Rules for Tunnels with Aggregate
           Sessions . . . . . . . . . . . . . . . . . . . . . . . . . 22
   7.  Tunnel Signaling Capability Discovery  . . . . . . . . . . . . 23
   8.  Other Considerations . . . . . . . . . . . . . . . . . . . . . 25



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     8.1.  Other Types of NSLP  . . . . . . . . . . . . . . . . . . . 25
     8.2.  IPSEC Flows  . . . . . . . . . . . . . . . . . . . . . . . 26
     8.3.  NSIS-tunnel Operation and Mobility . . . . . . . . . . . . 26
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 27
   10. Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . 27
     10.1. Various Design Alternatives  . . . . . . . . . . . . . . . 27
       10.1.1. End-to-end and Tunnel Signaling Interaction Model  . . 27
       10.1.2. Packet Classification over the Tunnel  . . . . . . . . 28
       10.1.3. Tunnel Binding Methods . . . . . . . . . . . . . . . . 28
   11. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 29
   12. References . . . . . . . . . . . . . . . . . . . . . . . . . . 29
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 29
     12.2. Informative References . . . . . . . . . . . . . . . . . . 30
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 32
   Intellectual Property and Copyright Statements . . . . . . . . . . 33




































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1.  Requirements notation

   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 [1].


2.  Introduction

   When IP tunnel mechanism is used to transfer signaling messages,
   e.g., NSIS messages, the signaling messages usually become hidden
   inside the tunnel and are not known to the tunnel intermediate nodes.
   In other words, the IP tunnel behaves as a logical link that does not
   support signaling in the end-to-end path.  If true end-to-end
   signaling support is desired, there needs to be a scheme to enable
   signaling at the tunnel segment of the end-to-end signaling path.
   This draft describes such a scheme for NSIS operation over IP
   tunnels.  We assume QoS NSLP as the NSIS signaling application.

2.1.  IP Tunneling Mechanisms and Tunnel Signaling Capability

   There are a number of common IP tunneling mechanisms, such as Generic
   Routing Encapsulation (GRE) [4][15], Generic Routing Encapsulation
   over IPv4 Networks (GREIP4) [5] , IP Encapsulation within IP
   (IP4INIP4) [7], Minimal Encapsulation within IP (MINENC) [8], Generic
   Packet Tunneling in IPv6 Specification (IP6GEN) [11], IPv6 over IPv4
   tunneling (IP6INIP4) [9], IPSEC tunneling mode [19][10].  These
   mechanisms can be differentiated according to the format of the
   tunnel encapsulation header.  IP4INIP4, IP6INIP4 and IP6GENIP4 can be
   seen as normal IP in IP tunnel encapsulation because their tunnel
   encapsulation headers are in the form of a standard IP header.  All
   GRE-related IP tunneling (GRE,GREIP4), MINENC and IPSEC tunneling
   mode can be seen as modified IP in IP tunnel encapsulation because
   the tunnel encapsulation header contains additional information
   fields besides a standard IP header.  The additional information
   fields are the GRE header for GRE and GREIP4, the minimum
   encapsulation header for MINENC and the Encapsulation Security
   Payload (ESP) header for IPSEC tunneling mode.

   By default any end-to-end signaling messages arriving at the tunnel
   endpoint will be encapsulated the same way as data packets.  Tunnel
   intermediate nodes do not identify them as signaling messages.  A
   signaling-aware IP tunnel can participate in a signaling network in
   various ways.  Prior work on RSVP operation over IP tunnles (RSVP-
   TUNNEL) [16] identifies two types of QoS-aware tunnels: a tunnel that
   can promise some overall level of resources but cannot allocate
   resources specifically to individual data flows, or a tunnel that can
   make reservations for individual end-to-end data flows.  This



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   classification leads to two types of tunnel signaling sessions:
   individual tunnel signaling sessions that are created and torn down
   dynamically as end-to-end session come and go, and aggregate tunnel
   sessions that can either be fixed, or dynamically adjusted as the
   actually used session resources increase or decrease.  Aggregate
   tunnel sessions are usually pre-configured but can also be
   dynamically created.  A tunnel MAY contain only individual tunnel
   sessions or aggregate tunnel sessions or both.

2.2.  NSIS Tunnel Operation Overview

   This NSIP operation over IP tunnel scheme is designed to work with
   most, if not all, existing IP in IP tunneling mechanisms.  The scheme
   requires the tunnel endpoints to support specific tunnel related
   functionalities.  Such tunnel endpoints are called NSIS-tunnel
   capable endpoints.  Tunnel intermediate nodes do not need to have
   special knowledge about this scheme.  When tunnel endpoints are NSIS-
   tunnel capable, this scheme enables the proper signaling initiation
   and adjustment inside the tunnel to match the requests of the
   corresponding end-to-end session.  In cases when tunnel session
   signaling status is uncertain or not successful, the end-to-end
   session will be notified about the existence of possible NSIS-unaware
   links in the end-to-end path.

   The overall design of this NSIS operation over IP tunnel scheme is
   conceptually similar to RSVP-TUNNEL [16].  However, the details of
   the scheme address all the important differences of NSIS from RSVP.
   For example,

   o  NSIS is based on a two-layer architecture, namely a signaling
      transport layer and a signaling application layer.  It is designed
      as a generic framework to accommodate various signaling
      application needs.  The basic RSVP protocol does not have a layer
      split and is only for QoS signaling.
   o  NSIS QoS NSLP allows both sender-initiated and receiver-initiated
      reservations; RSVP only supports receiver-initiated reservations.
   o  NSIS deals only with unicast; RSVP also supports multicast.
   o  NSIS integrates new features, such as the Session ID, to
      facilitate operation in specific environments (e.g. mobility and
      multi-homing).

   From a high level point of view, there are two main issues in a
   signaling operation over IP tunnel scheme.  First, how packet
   classification is performed inside the tunnel.  Second, how signaling
   is carried out inside the tunnel.

   Packets belonging to qualified data flows need to be recognized by
   tunnel intermediate nodes to receive special treatment.  Packet



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   classification is traditionally based on flow ID.  After a typical
   IP-in-IP tunnel encapsulation, packets from different flows appear as
   having the same flow ID which usually consists of the Tunnel Entry
   (Tentry) address and Tunnel Exit (Texit) address.  Therefore, the
   flow ID for a signaled flow needs to contain further demultiplexing
   information to make it distinguishable from non-signaled flows, and
   also from other different signaled flows.

   The special flow ID for signaled flows inside the tunnel needs to be
   carried in tunnel signaling messages, along with tunnel adjusted QoS
   parameters, to set up or modify the state information in tunnel
   intermediate nodes.  This process creates separate tunnel signaling
   sessions between the tunnel endpoints.  In most cases, it is
   necessary to maintain the state association between an end-to-end
   session and its corresponding tunnel session so that any change to
   one session MAY be reflected in the other.

   In the next section, we will illustrate details on packet
   classification over the tunnel, signaling over the tunnel as well as
   association of end-to-end and tunnel signaling.


3.  Protocol Design Decisions

3.1.  Flow Packet Classification over the Tunnel

   A flow can be an individual flow or an aggregate flow.  Flow ID
   formats that MAY be used to identify packets in individual tunnel
   flows are listed below.

   o  Selected fields from the base IP header portion of the tunnel
      encapsulation header.  For example, the IP source and destination
      address fields, which contain the IP addresses of Tentry and
      Texit, together with another field for tunnel-wide demultiplexing.
      This could be the IPv6 flow label field [6], or the Traffic Class,
      also known as DiffServ Code Point (DSCP) field.  Note that the
      DSCP field can also be used to represent an aggregate DiffServ
      flow.  As long as individual flow classification is processed
      before aggregate flow classification, or a longest match kind of
      packet classifier is used, this individual tunnel flow
      demultiplexing with DSCP field can work.  In the rare cases where
      these conditions cannot be satisfied, it is still possible to
      choose different range of DSCP values so that the values used for
      individual tunnel flow demultiplexing do not collide with those
      used for DiffServ aggregate flows.  Compared to the IPv6 flow
      label approach, using DSCP field as part of the tunnel flow ID can
      be applied to both IPv4 and IPv6 and is probably easier to deploy.
      The drawback is that the small number of bits in the DSCP field



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      limits the total number of individual flows that can be
      distinguished in the tunnel.  Overall, this group of flow ID
      formats enable efficient packet classification over the tunnel
      without introducing additional processing requirements on the
      existing infrastructure.  They are also easy to deploy.

   o  Selected fields from the base IP header portion of the tunnel
      encapsulation header, combined with fields from the addtional
      infromation in the tunnel encapsulation header.  This applies to
      modified IP-in-IP encapsulation as we mentioned in Section 2.1.
      An example of the additional information field is the Security
      Prameter Index (SPI) field for IPSEC tunnels.  Comparing with the
      flow ID formats in the first group, these flow ID formats might
      pose more requirements at the NSIS protocol side if the addition
      information field is unique to the specific tunnel mechanism and
      not already recognized in basic NSIS specification.

   o  UDP header insertion.  Inserting an extra UDP header between the
      tunnel encapsulation IP header and the tunnel payload provides
      additional demultiplexing information for a tunnelled flow.  The
      drawback of this flow ID format, as compared to the above two
      format groups, is the additional UDP header overhead both for
      bandwidth and processing.  Moreover, this approach modifies the
      basic tunneling mechanism at the Tentry, so Texit MUST also be
      aware of the special UDP insertion in order to correctly
      decapsulate and forward original packets further along the path.


   The above three groups of flow ID formats MAY also be used for
   aggregate tunnel flows.  For example, a common aggregate flow ID
   contains the addresses of tunnel endpoints and a DSCP value.  There
   are other options for aggregate flows.  For example, When additional
   interfaces at tunnel endpoints are available, the IP address of an
   additional interface at Tentry plus the IP address of the Texit, MAY
   constitute an aggregate flow ID.

   The decision of using a specific flow ID format is left to a policy
   mechanism outside the scope of this document.  Tunnel signaling is
   performed based on the chosen flow ID.  As long as the flow ID format
   is supported, Tentry SHOULD encapsulate all incoming packets for the
   specific data flows according to the chosen flow ID format.  Texit
   SHOULD be able to decapsulate the packets if any special tunnel flow
   encapsulation is performed at the Tentry.

3.2.  Tunnel Signaling and its Association with End-to-end Signaling

   Tunnel signaling messages contain tunnel specific parameters such as
   tunnel Message Routing Information (MRI) and tunnel adjusted QoS



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   parameters.  But in general, the formats of tunnel signaling messages
   are the same as end-to-end signaling messages.  Tunnel signaling is
   carried out according to the same signaling rules as for end-to-end
   signaling.  The main challenge is, therefore, the interaction between
   tunnel signaling and end-to-end signaling.  The interaction is
   achieved by special functionalities supported in the NSIS-tunnel
   aware tunnel endpoints.  These special functionalities include
   assigning tunnel flow IDs, creating tunnel session association,
   notifying the other endpoint about tunnel association, adjusting one
   session based on change of the other session, encapsulating
   (decapsulating) packets according to the chosen tunnel flow ID at
   Tentry (Texit), and etc.  In most cases, we expect to have bi-
   directional tunnels, where both tunnel endpoints are NSIS-tunnel
   aware.

   When both Tentry and Texit are NSIS-tunnel aware, the endpoint that
   creates the tunnel session MAY need to notify the other endpoint of
   the association between the end-to-end and tunnel session.  This is
   achieved by using the QoS NSLP BOUND_SESSION_ID object with a binding
   code indicating tunnel handling as the reason for binding.  In the
   rest of this document, we refer to a BOUND_SESSION_ID object with its
   tunnel binding_code set as a tunnel BOUND_SESSION_ID object or a
   tunnel binding object.  The tunnel binding object is carried in the
   end-to-end signaling messages and contains the session ID of the
   corresponding tunnel session.  NSIS-tunnel aware endpoints that
   receive this tunnel BOUND_SESSION_ID object SHOULD perform tunnel
   related procedures and then remove it from any end-to-end signaling
   messages sent out of the tunnel.


4.  Protocol Operation with Dynamically Created Tunnel Sessions

   The operation details for NSIS signaling over IP tunnels are more
   complicated if the tunnel session needs to be dynamically created,
   comparing to the case when tunnel sessions are pre-configured.  We
   discuss these two cases in this and the subsequent section,
   respectively.  If a tunnel contains both dynamic and pre-configured
   tunnel sessions, it can be handled by the combination of the
   corresponding mechanism for each type of tunnel sessions.  The choice
   of mapping an end-to-end session to a specific type of tunnel session
   is up to policy control.

4.1.  Operation Scenarios

   To dynamically create a mapping tunnel session upon receiving an end-
   to-end session, we identify four scenarios based on the sender-
   initiated and receiver-initiated reservation modes of NSIS QoS NSLP:




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   o  End-to-end session is sender-initiated; tunnel session is sender-
      initiated.
   o  End-to-end session is receiver-initiated; tunnel session is
      receiver-initiated.
   o  End-to-end session is sender-initiated; tunnel session is
      receiver-initiated.
   o  End-to-end session is receiver-initiated; tunnel session is
      sender-initiated.

   In the following we describe a typical NSIS end-to-end and tunnel
   signaling interaction process during the tunnel setup phase in each
   of these four scenarios.  The end-to-end QoS flow is assumed to be
   one that qualifies an individual dynamic tunnel session, whose tunnel
   reservation MUST be confirmed before the end-to-end reservation can
   proceed further outside the tunnel.

   It SHOULD be noted that different flow QoS requirements and policy
   assumptions MAY cause the timing sequence of the messaging flow to be
   slightly different.  This will be discussed in Section 4.2.

   Once the tunnel session has been created and associated with the end-
   to-end session, any subsequent changes (modification or termination)
   to either session MAY be communicated to the other one by the binding
   endpoint so the state of the two binding sessions can keep
   consistent.  The exception is when the tunnel session is an aggregate
   session.  In that case, after setup, the adjustment of the tunnel
   session SHOULD follow the rules for pre-configured aggregate tunnel
   adjustment in Section 5.

4.1.1.  Sender-initiated Reservation for both End-to-end and Tunnel
        Signaling



     Sender    Tentry      Tnode      Texit     Receiver

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



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       |          |<=========+          |          |
       |          |          |          | RESPONSE |
       |          |          |          |<---------+
       |          |       RESPONSE      |          |
       |          |<--------------------+          |
       | RESPONSE |          |          |          |
       |<---------+          |          |          |
       |          |          |          |          |
       |          |          |          |          |




   Figure 1: Sender-initiated Reservation for both End-to-end and Tunnel
   Signaling

   This scenario assumes both end-to-end and tunnel sessions are sender-
   initiated.  Figure 1 shows the messaging flow of NSIS operation over
   IP tunnels in this case.  Tunnel signaling messages are distinguished
   from end-to-end messages by a "'" after the message name.  Tnode
   denotes an intermediate tunnel node that participates in tunnel
   signaling.  The sender first sends an end-to-end RESERVE message
   which arrives at Tentry.  If Tentry supports tunnel signaling and
   determines that an individual tunnel session needs to be established
   for the end-to-end session, it chooses the tunnel flow ID, creates
   the tunnel session and associates the end-to-end session with the
   tunnel session.  It then sends a tunnel RESERVE' message matching the
   requests of the end-to-end session toward the Texit to reserve tunnel
   resources.  Tentry also appends to the original RESERVE message a
   tunnel BOUND_SESSION_ID object containing the session ID of the
   tunnel session and sends it toward Texit using normal tunnel
   encapsulation.

   The tunnel RESERVE' message is processed hop by hop inside the tunnel
   for the flow identified by the chosen tunnel flow ID.  When Texit
   receives the tunnel RESERVE' message, a reservation state for the
   tunnel session will be created.  Texit MAY also send a tunnel
   RESPONSE' message to Tentry.  On the other hand, the end-to-end
   RESERVE message passes through the tunnel intermediate nodes just
   like any other tunneled packets.  When Texit receives the end-to-end
   RESERVE message, it notices the binding of a tunnel session and
   checks the state for the tunnel session.  When the tunnel session
   state is available, it updates the end-to-end reservation state using
   the tunnel session state, removes the tunnel BOUND_SESSION_ID object
   and forwards the end-to-end RESERVE message further along the path
   towards the receiver.  When the end-to-end reservation finishes, an
   end-to-end RESPONSE MAY be sent back from the receiver to the sender.




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4.1.2.  Receiver-initiated Reservation for both End-to-end and Tunnel
        Signaling


     Sender    Tentry      Tnode      Texit     Receiver

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


   Figure 2: Receiver-initiated Reservation for both End-to-end and
   Tunnel Signaling

   This scenario assumes both end-to-end and tunnel sessions are
   receiver-initiated.  Figure 2 shows the messaging flow of NSIS
   operation over IP tunnels in this case.  When Tentry receives the
   first end-to-end QUERY message from the sender, it chooses the tunnel
   flow ID, creates the tunnel session and sends a tunnel QUERY' message
   matching the request of the end-to-end session toward the Texit.



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   Tentry also appends to the original QUERY message with a tunnel
   BOUND_SESSION_ID object containing the session ID of the tunnel
   session and sends it toward the Texit using normal tunnel
   encapsulation.

   The tunnel QUERY' message is processed hop by hop inside the tunnel
   for the flow identified by the chosen tunnel flow ID.  When Texit
   receives the tunnel QUERY' message, it creates a reservation state
   for the tunnel session without sending out a tunnel RESERVE' message
   immediately.

   The end-to-end QUERY message passes along tunnel intermediate nodes
   just like any other tunneled packets.  When Texit receives the end-
   to-end QUERY message, it notices the binding of a tunnel session and
   checks the state for the tunnel session.  When the tunnel session
   state is available, Texit updates the end-to-end QUERY message using
   the tunnel session state, removes the tunnel BOUND_SESSION_ID object
   and forwards the end-to-end QUERY message further along the path.

   When Texit receives the first end-to-end RESERVE message issued by
   the receiver, it finds the reservation state of the tunnel session
   and triggers a tunnel RESERVE' message for that session.  Meanwhile
   the end-to-end RESERVE message will be appended with a tunnel
   BOUND_SESSION_ID object and forwarded towards Tentry.  When Tentry
   receives the tunnel RESERVE', it creates the reservation state for
   the tunnel session and MAY send a tunnel RESPONSE' back to Texit.
   When Tentry receives the end-to-end RESERVE, it creates the end-to-
   end reservation state and updates it with information from the
   associated tunnel session reservation state.  Then Tentry further
   forwards the end-to-end RESERVE upstream toward the sender.

4.1.3.  Sender-initiated Reservation for End-to-end and Receiver-
        initiated Reservation for Tunnel Signaling


     Sender    Tentry      Tnode      Texit     Receiver
     |          |          |          |          |
     | RESERVE  |          |          |          |
     +--------->|          |          |          |
     |          |  QUERY'  |          |          |
     |          +=========>|          |          |
     |          |          |  QUERY'  |          |
     |          |          +=========>|          |
     |          |        RESERVE      |          |
     |          +-------------------->|          |
     |          |          | RESERVE' |          |
     |          |          |<=========+          |
     |          | RESERVE' |          |          |



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


   Figure 3: Sender-initiated Reservation for End-to-end and Receiver-
   initiated Reservation for Tunnel Signaling

   This scenario assumes the end-to-end signaling mode is sender-
   initiated and the tunnel signaling mode is receiver-initiated.
   Figure 3 shows the messaging flow of NSIS operation over IP tunnels
   in this case.  When Tentry receives the first end-to-end RESERVE
   message from the sender, it chooses the tunnel flow ID, creates the
   tunnel session and sends a tunnel QUERY' message matching the
   requests of the end-to-end session toward the Texit.  This Tunnel
   QUERY' message SHOULD have the "RESERVE-INIT" bit set.  Tentry also
   appends to the original RESERVE message a tunnel BOUND_SESSION_ID
   object containing the session ID of the tunnel session and sends it
   toward Texit using normal tunnel encapsulation.

   The tunnel QUERY' message is processed hop by hop inside the tunnel
   for the flow identified by the chosen tunnel flow ID.  When Texit
   receives the tunnel QUERY' message, it creates a reservation state
   for the tunnel session and immediately sends out a tunnel RESERVE'
   message back to Tentry.  When Tentry receives the tunnel RESERVE'
   message it learns the outcome of the tunnel reservation and sends a
   tunnel RESPONSE' message to Texit.

   When Texit receives the end-to-end RESERVE message, it notices the
   binding of a tunnel session and checks the state for the tunnel
   session.  It learns the outcome of tunnel session reservation from
   the tunnel RESPONSE' message.  Then it updates the end-to-end
   reservation state using the tunnel session state, removes the tunnel
   BOUND_SESSION_ID object and forwards the end-to-end RESERVE message
   further along the path towards the receiver.  When the end-to-end
   reservation finishes, an end-to-end RESPONSE MAY be sent back from



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   the receiver to the sender.

4.1.4.  Receiver-initiated Reservation for End-to-end and Sender-
        initiated Reservation for Tunnel Signaling



     Sender    Tentry      Tnode      Texit     Receiver
     |          |          |          |          |
     |  QUERY   |          |          |          |
     +--------->|          |          |          |
     |          |  QUERY'  |          |          |
     |          +=========>|          |          |
     |          |          |  QUERY'  |          |
     |          |          +=========>|          |
     |          |        QUERY        |          |
     |          +-------------------->|          |
     |          |          |          |  QUERY   |
     |          |          |          +--------->|
     |          |          |          | RESERVE  |
     |          |          |          |<---------+
     |          |       RESERVE       |          |
     |          |<--------------------+          |
     |          |          | RESERVE' |          |
     |          |          +=========>|          |
     |          | RESERVE' |          |          |
     |          +=========>|          |          |
     |          |          | RESPONSE'|          |
     |          |          |<=========|          |
     |          | RESPONSE'|          |          |
     |          |<=========|          |          |
     | RESERVE  |          |          |          |
     |<---------|          |          |          |
     | RESPONSE |          |          |          |
     +--------->|          |          |          |
     |          |       RESPONSE      |          |
     |          +-------------------->|          |
     |          |          |          | RESPONSE |
     |          |          |          +--------->|
     |          |          |          |          |
     |          |          |          |          |



   Figure 4: Receiver-initiated Reservation for End-to-end and Sender-
   initiated Reservation for Tunnel Signaling

   This scenario assumes the end-to-end signaling mode is receiver-



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   initiated and the tunnel signaling mode is sender-initiated.
   Figure 4 shows the messaging flow of NSIS operation over IP tunnels
   in this case.  When Tentry receives the first end-to-end QUERY
   message from the sender, it chooses the tunnel flow ID, creates the
   tunnel session and sends a tunnel QUERY' message matching the request
   of the end-to-end session toward the Texit.  Tentry also appends to
   the original QUERY message a tunnel BOUND_SESSION_ID object
   containing the session ID of the tunnel session and sends it toward
   the Texit using normal tunnel encapsulation.

   The tunnel QUERY' message is processed hop by hop inside the tunnel
   for the flow identified by the chosen tunnel flow ID.  When Texit
   receives the tunnel QUERY' message, it creates a reservation state
   for the tunnel session without sending out a tunnel RESERVE' message
   immediately.

   The end-to-end QUERY message passes along tunnel intermediate nodes
   just like any other tunneled packets.  When Texit receives the end-
   to-end QUERY message, it notices the binding of a tunnel session and
   checks the state for the tunnel session.  When the tunnel session
   state is available, Texit updates the end-to-end QUERY message using
   the tunnel session state, removes the tunnel BOUND_SESSION_ID object
   and forwards the end-to-end QUERY message further along the path.

   When Texit receives the first end-to-end RESERVE message issued by
   the receiver, it finds the reservation state of the tunnel session.
   Texit appends to the end-to-end RESERVE message a tunnel
   BOUND_SESSION_ID object containing the matching tunnel session ID and
   sends it upstream to Tentry.

   When Tentry receives the end-to-end RESERVE message, it notices the
   binding and immediately sends out a tunnel RESERVE' message matching
   the end-to-end RESERVE request over the tunnel.  This RESERVE'
   message SHOULD include the Request Identification Information (RII)
   to trigger a RESPONSE' from Texit.

   When Tentry receives the result of tunnel reservation from the tunnel
   RESPONSE' message, it updates the end-to-end RESERVE message and
   forwards the end-to-end RESERVE message upstream to the Sender.  The
   Sender MAY send an end-to-end RESPONSE message to the receiver when
   the whole process completes.

4.2.  Implementation Specific Issues

4.2.1.  End-to-end and Tunnel Signaling Interaction

   Given the two separate end-to-end and tunnel signaling sessions,
   there are many ways of integrating the signaling of each session.  In



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   general, different interaction approaches can be grouped into
   sequential mode and parallel mode.  In sequential mode, end-to-end
   signaling pauses when it is waiting for results of tunnel signaling,
   and resumes upon receipt of the tunnel signaling outcome.  In
   parallel mode, end-to-end signaling continues outside the tunnel
   while tunnel signaling is still in process and its outcome is
   unknown.  The operation outlined in Section 4.1 shows the sequential
   mode.  While this mode is suitable for a flow that requires hard
   guarantee of tunnel reservation, it MAY not be the best choice for a
   flow that can tolerate some QoS uncertainty but wants to complete the
   signaling on the path as fast as possible.  The parallel mode is
   clearly for the latter case.

   Having two separate signaling sessions also causes a possible race
   condition.  When an end-to-end session message carrying tunnel
   binding object arrives at one of the tunnel endpoints, if the
   corresponding tunnel session state has already been created, then the
   tunnel endpoint can refer to information in the tunnel session state
   (e.g., about tunnel reservation status, or tunnel resource
   availability) and construct an end-to-end signaling message to be
   sent out of the tunnel immediately.  On the other hand, if the tunnel
   endpoint receives an end-to-end signaling message carrying tunnel
   binding referring to a tunnel session that does not yet exist, it MAY
   either wait until the tunnel session information is ready, or forward
   the end-to-end session signaling without waiting for the tunnel
   session.  If the end-to-end signaling indeed proceeds in the absence
   of the tunnel session, the tunnel session MAY still be established
   after some delay.  Since the tunnel signaling message does not
   contain its associated end-to-end session's session ID, it cannot
   immediately change the state of its associated end-to-end session.
   However, the next refresh of the corresponding end-to-end session
   will carry the tunnel binding information and thus will update the
   association of the end-to-end and the tunnel session state.  If the
   period waiting for the end-to-end signaling refresh is considered too
   long, the tunnel endpoint MAY choose to actively poll the session
   state table about the existence of tunnel session before the refresh
   timer expires.  In any case, once the end-to-end signaling session
   learns about the tunnel signaling it can send an immediate refresh
   out of the tunnel with knowledge of tunnel session.

   The decision on whether and how long to wait for the corresponding
   tunnel session information is implementation specific and controlled
   by the tunnel endpoints.  This document only requires that if an
   NSIS-tunnel aware endpoint decides to go forward with the end-to-end
   signaling outside the tunnel with an uncertain tunnel session
   condition, it SHOULD indicate this in the corresponding end-to-end
   signaling messages.  As far as QoS NSLP is concerned, this means the
   NON-QoSM Hop field [12] SHOULD be set to one.  Note that in some



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   cases, the application using NSIS signaling MAY wish to indicate the
   preferred way of end-to-end and tunnel signaling interaction.  For
   example, an application that can not tolerate any QoS uncertainty
   will prefer the sequential mode of operation; an application that has
   a looser QoS requirement MAY prefer the parallel mode of operation
   for faster signaling speed.  Current NSIS specification does not
   contain fields to convey this preference.  New objects or flags will
   need to be defined if this behavior is considered necessary.

4.2.2.  Aggregate vs. Individual Tunnel Session Setup

   The operation outlined in Section 4.1 applies to a flow that
   qualifies an individual dynamic tunnel session.  For a tunnel that
   MAY contain multiple end-to-end sessions, it is more efficient to
   keep aggregate tunnel sessions rather than individual tunnel sessions
   whenever possible.  This will save the cost of setting up a new
   session and avoid the setup latency as well as the session
   establishment race conditions mentioned above.  Therefore, when the
   tunnel endpoint creates a reservation for a tunnel session based on
   the individual end-to-end session, it is up to local policy whether
   it wants to actually create an aggregate session by requesting more
   resources than the current end-to-end session requires.  If it does,
   other end-to-end sessions arrived later MAY make use of this
   aggregate tunnel session.  The tunnel endpoint will also need to
   determine how long to keep the tunnel session if no active end-to-end
   session is currently mapped to the aggregate tunnel session.  The
   decision MAY be based on knowledge of likelihood of traffic in the
   future.  It SHOULD be noted that once these kinds of on-demand
   aggregate tunnel sessions are set up, they are treated the same as
   pre-configured tunnel sessions to future end-to-end sessions.
   Therefore, the adjustment of such aggregate sessions SHOULD follow
   Section 5.

   Note that the session ID of an aggregate tunnel session SHOULD be
   different from that of the end-to-end session because they usually
   have separate lifetime.  If the tunnel endpoint is certain that the
   tunnel session is for an individual end-to-end session alone, it MAY
   in some cases want to reuse the same session ID for both sessions.
   This will require additional manipulation of the NSLP state at the
   tunnel endpoints, since the NSLP state is usually keyed based on the
   session ID.


5.  Protocol Operation with Pre-configured Tunnel Sessions

   This section discusses NSIS operation over tunnels that are pre-
   configured through management interface with one or more tunnel
   sessions.  A pre-configured tunnel sessions MAY be mapped to one



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   session as an individual tunnel session but are usually mapped to
   multiple end-to-end sessions as an aggregate tunnel session.

5.1.  Tunnel with Exactly One Pre-configured Aggregate Session

   If only one aggregate session is configured in the tunnel and all
   traffic will receive the reserved tunnel resources, all packets just
   need to be IP-in-IP encapsulated as usual.  If there is only one
   aggregate session configured in the tunnel but only some traffic
   SHOULD receive the reserved tunnel resources through the aggregate
   tunnel session, then the aggregate tunnel session SHOULD be assigned
   an appropriate flow ID.  Qualified packets need to be encapsulated
   with this special flow ID.  The rest of the traffic will be IP-in-IP
   encapsulated as usual.

5.2.  Tunnel with Multiple Pre-configured Aggregate Sessions

   If there are multiple pre-configured aggregate sessions over a tunnel
   set up, these sessions MUST be distinguished by their different
   aggregate tunnel flow IDs.  In this case it is necessary to
   explicitly bind the end-to-end sessions with specific tunnel
   sessions.  This binding is conveyed between tunnel endpoints by the
   tunnel BOUND_SESSION_ID object.  Once the binding has been
   established, Tentry SHOULD encapsulate qualified data packets
   according to the associated aggregate tunnel flow ID.  Intermediate
   nodes in the tunnel will then be able to filter these packets to
   receive reserved tunnel resources.

5.3.  Adjustment of Pre-configured Tunnel Sessions

   Adjustment of pre-configured tunnel sessions upon the change of its
   mapped end-to-end sessions is related is up to local policy
   mechanisms.  RSVP-TUNNEL [16] described multiple choices to
   accomplish this.  First, the tunnel reservation is never adjusted,
   which makes the tunnel a rough equivalent of a fixed-capacity
   hardware link ("hard pipe").  Second, the tunnel reservation is
   adjusted whenever a new end-to-end reservation arrives or an old one
   is torn down ("soft pipe").  Doing this will require the Texit to
   keep track of the resources allocated to the tunnel and the resources
   actually in use by end-to-end reservations separately.  The third
   approach adopts some hysteresis in the adjustment of the tunnel
   reservation parameters.  The tunnel reservation is adjusted upwards
   or downwards occasionally, whenever the end-to-end reservation level
   has changed enough to warrant the adjustment.  This trades off extra
   resource usage in the tunnel for reduced control traffic and
   overhead.





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6.  Processing Rules for Selected End-to-end QoS NSLP Messages

   The following lists basic tunnel related message processing rules for
   selected end-to-end QoS NSLP messages working in the sequential
   interaction mode.  They are provided as references for implementors
   to insure minimal interoperability.

6.1.  End-to-end QUERY Message at Tentry

   When an end-to-end QUERY message is received at Tentry, Tentry checks
   whether the end-to-end session is entitled to tunnel resources.

   If the end-to-end session SHOULD be bound to a tunnel session yet to
   be created.  Tentry creates a tunnel QUERY' message and sends it to
   Texit.  Tentry also appends a tunnel BOUND_SESSION_ID object to the
   end-to-end QUERY message.  The tunnel BOUND_SESSION_ID object
   contains the session ID of the tunnel session.  The end-to-end QUERY
   message is then encapsulated and sent out through the tunnel
   interface.

   If the end-to-end session SHOULD be bound to an existing tunnel
   session (whether aggregate or individual), Tentry appends a tunnel
   BOUND_SESSION_ID object to the end-to-end tunnel QUERY message and
   sends it toward Texit through the tunnel interface.

6.2.  End-to-end QUERY Message at Texit

   When an end-to-end QUERY message containing a tunnel BOUND_SESSION_ID
   object is received, Texit creates a conditional reservation state for
   the end-to-end session (i.e., a state is created but the related
   outgoing signaling message, in this case the QUERY message, is held
   until further information is available).  It also checks to see if a
   conditional reservation state for the associated tunnel session is
   available.  If yes, it reads information from the tunnel session
   state and sends the end-to-end QUERY downstream.  If the conditional
   reservation state for tunnel session is not yet available, it will be
   created upon receiving the tunnel QUERY', and then Texit SHOULD
   forward the end-to-end QUERY downstream with information from results
   of the tunnel QUERY'.

6.3.  End-to-end RESERVE Message at Tentry

6.3.1.  Sender-initiated RESERVE Message

   If the RESERVE message is received with its T-bit set (RESERVE tear),
   Tentry removes the local state, then encapsulates the RESERVE message
   and tunnels it to Texit.  If there is a tunnel session associated
   with this end-to-end session, Tentry also sends a tunnel RESERVE with



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   T-bit set for that tunnel session.

   If the end-to-end RESERVE message is a refresh for an existing end-
   to-end session and this session is associated with a tunnel session,
   the RESERVE message refreshes both two sessions.  If the RESERVE
   message causes changes in resources reserved for the end-to-end
   session, depending on whether the tunnel signaling is sender
   initiated or receiver initiated, Tentry SHOULD create a new tunnel
   RESERVE' message or tunnel QUERY' message to start changing the
   tunnel reservation as well.  At the same time, Tentry appends a
   tunnel BOUND_SESSION_ID object to the end-to-end RESERVE message and
   sends it to Texit through the tunnel interface.

   If the message is the first RESERVE message for an end-to-end
   session, Tentry determines whether the end-to-end session is entitled
   to tunnel resources based on policy control mechanisms outside the
   scope of this document.  If not, no special tunnel related processing
   is needed.  Otherwise, if this session SHOULD be bound to an existing
   tunnel session (whether aggregate or individual), Tentry creates the
   association between the end-to-end session and the tunnel session.
   Then it appends a tunnel BOUND_SESSION_ID object to the end-to-end
   RESERVE message and sends it through the tunnel interface (i.e. the
   message is encapsulated and tunneled to Texit as normal).

   If the end-to-end session SHOULD be bound to a tunnel session yet to
   be created, Tentry assigns the tunnel flow ID, and constructs a
   tunnel RESERVE' or QUERY' message, depending on whether the tunnel
   signaling is sender initiated or receiver initiated.  The QSPEC in
   this tunnel message MAY be different from the original QSPEC, taking
   into consideration the tunnel overhead of the encapsulation of data
   packets.  Tentry then associates the tunnel session with the end-to-
   end session in the NSLP state and sends the tunnel message toward
   Texit to start reserving resources over the tunnel.  At the same
   time, Tentry appends a tunnel BOUND_SESSION_ID object to the end-to-
   end RESERVE message and sends it through the tunnel interface.

6.3.2.  Receiver-initiated RESERVE Message

   If the RESERVE message is received with its T-bit set (RESERVE tear),
   Tentry removes the local state and forwards the message upstream.  If
   the tunnel signaling is sender initiated, Tentry also sends a tunnel
   RESERVE' message to tear down the tunnel session.

   If the end-to-end RESERVE message contains a tunnel BOUND_SESSION_ID
   and is the first end-to-end RESERVE message, Tentry checks whether
   the tunnel session bound to the end-to-end session indicated by the
   RESERVE message already exists.  If yes, Tentry records the
   association between the end-to-end and the tunnel session, reads



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   information from the tunnel session to create the end-to-end RESERVE
   message to be forwarded upstream.  If the state for the tunnel
   session is not available yet, Tentry SHOULD create state information
   for the tunnel session and indicate that a conditional reservation is
   pending.  If tunnel signaling is sender initiated, Tentry also sends
   a tunnel RESERVE' message toward Texit to reserve tunnel resources.
   When the actual tunnel session status is known at Tentry (from a
   tunnel RESERVE' if tunnel signaling is receiver initiated or at
   tunnel RESPONSE' if tunnel signaling is sender initiated) and if at
   this time there is a pending reservation, Tentry SHOULD generate an
   end-to-end RESERVE message and forward it upstream.

   If the end-to-end RESERVE message contains a tunnel BOUND_SESSION_ID
   and is a refresh, Texit refreshes the end-to-end session.  If the
   RESERVE message causes changes in resources reserved for the end-to-
   end session and if tunnel signaling is sender initiated, Tentry sends
   a tunnel RESERVE' message to Texit to change the reservation.  In any
   case, Texit checks the state information of the tunnel session.  If
   it finds that the reservation has been updated inside the tunnel,
   Texit forwards the changed RESERVE message toward the sender.  If the
   tunnel reservation update failed, Texit MUST send a RESPONSE with
   appropriate Error_Spec to the originator of the end-to-end RESERVE
   message.

6.4.  End-to-end RESERVE Message at Texit

6.4.1.  Sender-initiated RESERVE Message

   If the end-to-end RESERVE message is received with its T-bit set
   (RESERVE tear), Texit removes the local state, then forwards the
   RESERVE message downstream.  If tunnel signaling is receiver-
   initiated, Texit also sends a tunnel RESERVE tear upstream toward
   Tentry to tear down the tunnel session.

   If the end-to-end RESERVE message contains a tunnel BOUND_SESSION_ID
   and is the first end-to-end RESERVE message, Texit checks whether the
   state for the tunnel session indicated by the RESERVE message already
   exists.  If yes, Texit records the association between the end-to-end
   and the tunnel session and reads information from the tunnel session
   to create the end-to-end RESERVE message to be forwarded downstream.
   If the state for the tunnel session is not available yet, Texit
   SHOULD create state information for the tunnel session and indicate
   that a conditional reservation is pending.  When the actual tunnel
   RESERVE' or RESPONSE' message arrives, the tunnel session state will
   be updated.  If at this time there is a pending reservation, Texit
   will generate an end-to-end RESERVE message and forwards it
   downstream.




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   If the end-to-end RESERVE message contains a tunnel BOUND_SESSION_ID
   and is a refresh, Texit refreshes the end-to-end session.  If the
   RESERVE message causes changes in resources reserved for the end-to-
   end session, Texit checks the state information of the tunnel
   session.  If the reservation has been updated inside the tunnel,
   Texit forwards the RESERVE message toward the receiver.  If the
   tunnel reservation update failed, Texit MUST send a RESPONSE with
   appropriate Error_Spec to the originator of the end-to-end RESERVE
   message.

   Note that the processing rules for end-to-end RESERVE at Texit in
   end-to-end sender-initiated case is similar to those for end-to-end
   RESERVE at Tentry in end-to-end receiver-initiated case.

6.4.2.  Receiver-initiated RESERVE Message

   If the RESERVE message is received with its T-bit set (RESERVE tear),
   Texit removes the local state, then forwards the RESERVE message
   upstream.  If there is an individual tunnel session associated with
   this end-to-end session, Texit also sends a tunnel RESERVE' with
   T-bit set for that tunnel session.

   Otherwise Texit checks to see if the end-to-end session is associated
   with a tunnel session.  If only conditional reservation state is
   found and no actual reservation has been made, this RESERVE is the
   first end-to-end RESERVE message.  Texit appends a tunnel
   BOUND_SESSION_ID object to this end-to-end RESERVE message and sends
   it toward Tentry through the tunnel interface.  Meanwhile if tunnel
   signaling is receiver initiated Texit sends tunnel RESERVE' message
   toward Tentry to reserve tunnel resources.

   If the end-to-end session is bound to a tunnel session and the
   RESERVE message is a refresh, it refreshes both the end-to-end
   session and tunnel session.  If the RESERVE message causes changes in
   resources reserved for the end-to-end session and if tunnel signaling
   is receiver initiated, Texit MAY create a new tunnel RESERVE' message
   to change the tunnel reservation as well.  Meanwhile, the end-to-end
   RESERVE is appended with the tunnel BOUND_SESSION_ID object and sent
   to Tentry through the reverse path.

6.5.  Special Processing Rules for Tunnels with Aggregate Sessions

   In situations where the end-to-end session is bound to aggregate
   tunnel sessions, the handling is similar to that of RSVP-TUNNEL [16].

   If the associated tunnel session is a "hard pipe" session, arrival of
   a new end-to-end reservation or adjustment of an existing end-to-end
   session MAY cause the overall resources needed in the tunnel session



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   to exceed its capacity, this case is treated as admission control
   failure same as that of a tunnel reservation failure.  Tentry SHOULD
   create a RESPONSE message with appropriate INFO_SPEC and send it to
   the originator of the RESERVE message.

   If the associated tunnel session is a "soft pipe" session, arrival of
   a new end-to-end reservation or adjustment of existing sessions MAY
   cause the tunnel session to be modified.  It is recommended that some
   hysteresis is enforced in the adjustment of the tunnel reservation
   parameters.  This requires tunnel endpoint to keep track of both the
   allocated tunnel session resources and the resources actually used by
   end-to-end sessions bound to that tunnel session.


7.  Tunnel Signaling Capability Discovery

   The NSIS-tunnel signaling operations described in this document
   assume both Tentry and Texit are NSIS-tunnel capable.  If prior
   knowledge of the other endpoint's NSIS-tunnel capability is not
   available, we need a discovery mechanism to find that out.  For this
   purpose, we define a new NODE_CHAR object.

   The format of the NODE_CHAR object follows the general object
   definition in GIST [2].  It contains a fixed header giving the object
   Type and object Length, followed by the object Value as shown below.


       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         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      //                             Value                           //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


   Type: NODE_CHAR

   Length: Fixed (1 32-bit word)

   Value:

       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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |T|                            Reserved                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+




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   The Value field currently contains a single 'T' bit, indicating the
   basic NSIS-tunnel scheme defined in this document.  It is also
   possible to use multiple bits to define NSIS-tunnel capability in
   finer granularity.  We have adopted the simplest approach by using
   only one bit.  The remaining reserved bits can be used to signal
   other node characteristics in the future.

   The bits marked 'A' and 'B' define the desired behavior for objects
   whose Type field is not recognized.  If a node does not recognize the
   NODE_CHAR object, the desired behavior is "Ignore".  That is, the
   object MUST be deleted and the rest of the message processed as
   usual.  This can be satisfied by setting 'AB' to '01' according to
   GIST specification .

   This NODE_CHAR object is included in a QUERY or RESERVE message by a
   tunnel endpoint who wishes to learn about the other endpoint's tunnel
   handling capability.  The other endpoint that receives this object
   will know that the sending endpoint is NSIS-tunnel capable, and place
   the same object in a RESPONSE message to inform the sending endpoint
   of its own tunnel handling capability.  The procedures for using
   NODE_CHAR object in the four dynamically created tunnel session
   scenarios are further detailed below.

   If both end-to-end and tunnel sessions are sender-initiated
   (Section 4.1.1) and Tentry is NSIS-tunnel capable, the Tentry
   includes an RII object and a NODE_CHAR object with T bit set in the
   first end-to-end RESERVE message sent to Texit.  When Texit receives
   this RESERVE message, if it supports NSIS tunneling, it learns that
   Tentry is NSIS-tunnel capable and includes the same object with T bit
   set in the RESPONSE message sent back to Tentry.  Otherwise, Texit
   ignores the NODE_CHAR object.  When Tentry receives the RESPONSE
   message, it learns whether Texit is NSIS-tunnel capable by examining
   the existence of the NODE_CHAR object and its T-bit.  If both tunnel
   endpoints are NSIS-tunnel capable, the rest of the procedures will
   follow those defined in Section 4.1.1.  Alternatively, Tentry MAY
   send out tunnel RESERVE message before the RESPONSE message
   confirming the NSIS-tunnel capability of Texit is received.  If later
   it learns that the Texit is not NSIS-tunnel capable, it SHOULD send
   out teardown messages to cancel the tunnel session reservation that
   has already been made.  This way the signaling process is faster when
   Texit is NSIS-tunnel capable, but it can lead to temporary waste of
   tunnel resources if Texit is not NSIS-tunnel capable.

   If both end-to-end and tunnel sessions are receiver-initiated
   (Section 4.1.2) and Tentry is NSIS-tunnel capable, the Tentry
   includes an RII object and a NODE_CHAR object with T bit set in the
   first end-to-end QUERY message sent toward Texit.  An NSIS-tunnel
   capable Texit learns from the NODE_CHAR object whether Tentry is



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   NSIS-tunnel capable.  In reply to this end-to-end QUERY message, the
   NSIS-tunnel capable Texit includes a NODE_CHAR object with T bit set
   in its RESPONSE message to notify Tentry of its own tunnel
   capability.  If both tunnel endpoints are NSIS-tunnel capable, the
   rest of the procedures will follow those defined in Section 4.1.2.
   Otherwise, Texit will not initiate tunnel session reservations.

   If the end-to-end session is sender-initiated, the tunnel session is
   receiver-initiated (Section 4.1.3), and Tentry is NSIS-tunnel
   capable, the Tentry includes an RII object and a NODE_CHAR object
   with T bit set in the first end-to-end RESERVE message sent toward
   Texit.  An NSIS-tunnel capable Texit learns from the NODE_CHAR object
   whether Tentry is NSIS-tunnel capable.  In reply to this end-to-end
   QUERY message, the NSIS-tunnel capable Texit includes a NODE_CHAR
   object with T bit set in its RESPONSE message to notify Tentry of its
   own tunnel capability.  If both tunnel endpoints are NSIS-tunnel
   capable, the rest of the procedures will follow those defined in
   Section 4.1.3.  Otherwise, Texit will not initiate tunnel session
   reservations.

   If the end-to-end session is receiver-initiated, the tunnel session
   is sender-initiated (Section 4.1.4), and Tentry is NSIS-tunnel
   capable, the operation is similar to the case where both sessions are
   receiver-initiated.  The Tentry includes an RII object and a
   NODE_CHAR object with T bit set in the first end-to-end QUERY message
   sent toward Texit.  An NSIS-tunnel capable Texit learns from the
   NODE_CHAR object whether Tentry is also NSIS-tunnel capable.  In
   reply to this end-to-end QUERY message, the NSIS-tunnel capable Texit
   includes a NODE_CHAR object with T bit set in its RESPONSE message to
   notify Tentry of its own tunnel capability.  If both tunnel endpoints
   are NSIS tunnel capable, the rest procedures follow those defined in
   Section 4.1.4.  Otherwise, Tentry will not initiate further NSIS
   tunnel session reservations.


8.  Other Considerations

8.1.  Other Types of NSLP

   This document discusses tunnel operation using QoS NSLP.  It will be
   desirable to have the scheme work with other NSLPs as well.  Since
   NSIS-tunnel operation involves specific NSLP itself and different
   NSLPs have different message exchange semantics, the NSIS-tunnel
   specification would not be the same for all NSLPs.  However the basic
   aspects behind NSIS-tunnel operation could indeed be similar for
   different types of NSLPs.  For example, in the case of NATFW NSLP
   [13], the most important signaling operation is CREATE.  Assuming
   Tentry is a NATFW NSLP, the tunnel handling for the CREATE operation



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   is expected to be very similar to the sender-initiated QoS
   reservation case.  There are also a number of reverse directional
   operations in NATFW NSLP, such as RESERVE_EXTERNAL_ADDRESS and
   UCREATE.  It is not very clear whether IP tunnel will cause problems
   with these messages in general.  But they are likely easier to deal
   with than the receiver-initiated reservation case in QoS NSLP.  This
   topic will be discussed in future version of this document if
   necessary.

8.2.  IPSEC Flows

   If the tunnel supports IPSEC (especially ESP in Tunnel-Mode with or
   without AH), it MAY use the flow label, DSCP field, or IPSEC SPI
   along with the tunnel source and destination address, as discussed in
   Section 3.1 to form the tunnel Flow ID.  All these are standard NSIS
   MRI fields that can be matched by the NSIS packet classifier.
   Virtual destination ports as in RSVP-IPSEC [17] MAY be defined for
   further flow demultiplexing capability at the destination side if
   necessary.

8.3.  NSIS-tunnel Operation and Mobility

   NSIS-tunnel operation needs to interact with IP mobility in an
   efficient way.  In places where pre-configured tunnel sessions are
   available, the process is relatively straightforward.  For dynamic
   individual signaling tunnel sessions, one way to improve NSIS
   mobility efficiency in the tunnel is to reuse the session ID of the
   tunnel session when tunnel flow ID changes during mobility.  This
   works as follows.  With a mobile IP tunnel, one tunnel endpoint is
   the Home Agent (HA), and the other endpoint is the Mobile Node (MN)
   if collocated Care-of-Address (CoA) is used, or the Foreign Agent
   (FA) if FA CoA is used.  When MN is a receiver, Tentry is the HA and
   Texit is the MN or FA.  In a mobility event, handoff tunnel signaling
   messages will start from HA, which MAY use the same session ID for
   the new tunnel session.  When MN is a sender and collocated CoA is
   used, Tentry is the MN and Texit is the HA.  Handoff tunnel signaling
   is started at the MN.  It MAY also use the session ID of the previous
   tunnel session for the new tunnel session.  When MN is a sender and
   FA CoA is used, the situation is complicated because Tentry has
   changed from the old FA to the new FA.  In this case the new FA does
   not have the session ID of the previous tunnel session.

   When mobile IP is operating on a bi-directional tunneling mode, NSIS-
   tunnel operation with mobility MAY be further improved by localizing
   the handoff tunnel signaling process by bypassing the path between HA
   and CN.

   General aspects of NSIS interaction with mobility are discussed in



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   [14].


9.  Security Considerations

   This draft does not draw new security threats.  Security
   considerations for NSIS NTLP and QoS NSLP are discussed in [2] and
   [3], respectively.  General threats for NSIS can be found in [18].


10.  Appendix

10.1.  Various Design Alternatives

10.1.1.  End-to-end and Tunnel Signaling Interaction Model

   The contents of original end-to-end singling messages are not
   directly examined by tunnel intermediate nodes.  To carry out tunnel
   signaling we choose to maintain a separate tunnel session for the
   end-to-end session by generating tunnel specific signaling messages.
   An alternative approach is to stack tunnel specific objects on top of
   the original end-to-end messages and make these messages visible to
   tunnel intermediate nodes.  Thus, these new messages serve both the
   end-to-end session and tunnel session.  This approach turns out to be
   difficult because the actual tunnel signaling messages differ from
   the end-to-end signaling message both in GIST layer and NSLP layer
   information, such as MRI, PACKET CLASSIFIER and QSPEC.  Although
   QSPEC can be stacked in an NSLP message, there doesn't seem to be a
   handy way to stack MRI and the PACKET CLASSIFIER in the NSLP layer.
   In addition, the stacking method only applies to individual signaling
   tunnels.

   The separate end-to-end tunnel session signaling model adopted in
   this document handles both individual and aggregate signaling tunnels
   in a consistent way.  Its major drawback is the race condition we
   mentioned in Section 4.2.  However, we defined simple rules to solve
   this problem while maintaining interoperability.

   This document defines the sequential and parallel modes of end-to-end
   and tunnel signaling interaction.  There are a number of different
   aspects that can result in variations in carrying out the actual
   interaction.  One aspect is the tunnel session initiation location.
   For example, it is possible to initiate the tunnel session from
   Texit, instead of Tentry as in the proposed scheme.  A second aspect
   is the tunnel session initiation time point.  For example, in cases
   when both end-to-end session and tunnel session are receiver-
   initiated, it is possible to start the tunnel session when Tentry
   receives the first end-to-end RESERVE message, instead of when Tentry



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   receives the first end-to-end QUERY message, as in the proposed
   scheme.  The advantage of our adopted approach is that it will allow
   the first end-to-end QUERY message to also gather tunnel
   characteristics along with the rest of the end-to-end path.  A third
   aspect is how the tunnel signaling messages are used.  For example,
   in the case where end-to-end session is receiver initiated and tunnel
   session is sender initiated (Section 4.1.4), the first tunnel QUERY'
   message sent after receiving the end-to-end QUERY message by Tentry
   can be replaced by a tunnel RESERVE' message, if the application
   wants to trade temporary oversized or wasted (if the end-to-end
   reservation turns out to be unsatisfied) tunnel resource reservations
   for faster signaling setup delay.  All these aspects are local
   optimization issues.  We require any implementation to support the
   basic scheme defined in the main text of document to allow
   interoperability.

10.1.2.  Packet Classification over the Tunnel

   Packet classification over the tunnel MAY be done in either of the
   two ways: first, retaining the end-to-end packet classification
   rules; Second, using tunnel specific classification rules.  In the
   first approach, tunnel packet classification is not tied with tunnel
   MRI.  This is a useful property especially in handling tunnel
   mobility.  Mobility changes the tunnel MRI, if at the same time the
   packet classification rule does not change, the common path after a
   handoff does not need to be updated about the packet classification,
   which results in a better handoff performance.  The main problem with
   this approach is that most existing routers do not support inspection
   of inner IP headers in an IP tunnel, where the tunnel independent
   packet classification fields usually reside.  Therefore this document
   adopts the second approach which does not pose special classification
   requirements on intermediate tunnel nodes.

10.1.3.  Tunnel Binding Methods

   In this document, the end-to-end session and its mapping tunnel
   session use different session IDs and they are associated with each
   other using the BOUND_SESSION_ID object.  This choice is obvious for
   aggregate tunnels sessions because in that case the original end-to-
   end session and the corresponding aggregate tunnel session require
   independent control.

   Sessions in individual signaling tunnels are created and deleted
   along with the related end-to-end session.  So association between
   the end-to-end session and the corresponding individual tunnel
   session has another choice: the two sessions MAY share the same
   session ID.  Instead of sending a BOUND_SESSION_ID object, it MAY be
   possible to define a BOUND_FLOW_ID object, to bind the flow ID of the



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   end-to-end session to the flow ID of the tunnel session at the tunnel
   endpoints.  However, since flow ID is usually derived from MRI, if a
   NAT is present in the tunnel, this BOUND_FLOW_ID object will have to
   be modified in the middle, which makes the process fairly
   complicated.  Furthermore, it is not desirable to have different
   session association mechanisms for aggregate signaling tunnels and
   individual signaling tunnels.  Therefore, we decide to use the same
   tunnel BOUND_SESSION_ID mechanism for both individual and aggregation
   tunnel sessions.  Note that in this case the mobility handling inside
   the tunnel can still be optimized in certain situations as discussed
   in Section 8.3.

   In this document we used the existing BOUND_SESSION_ID object with a
   tunnel Binding_code to indicate the reason of binding.  Two other
   options were considered.

   1.  Define a designated "tunnel object" to be included when the
       tunnel binding needs to be conveyed.
   2.  Define a "tunnel bit" in corresponding NSLP message headers.

   These options are not chosen because they either requires the
   creation of an entirely new object, or the change of basic message
   headers.  They are also not generic solutions that can cover other
   binding causes.

   There are basically three ways to carry the binding object between
   Tentry and Texit, using (a) end-to-end signaling messages, (b) tunnel
   signaling messages, (c) both end-to-end and tunnel signaling
   messages.  In option (a) only tunnel endpoints see the tunnel binding
   information.  In option (b), every tunnel intermediate node sees the
   binding information.  Since there will be no state for the end-to-end
   session in tunnel intermediate nodes, they will all generate a
   message containing an "INFO_SPEC" object indicating no bound session
   found according to [3], which is not desirable.  Option (c) has an
   advantage that if both end-to-end and tunnel signaling messages have
   tunnel binding information, the racing condition will be resolved
   faster.  However it suffers the same problem as in (b).  Therefore
   the choice in this document for carrying the tunnel binding object is
   option (a).


11.  Acknowledgements


12.  References

12.1.  Normative References




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

   [2]  Schulzrinne, H. and R. Hancock, "GIST: General Internet
        Signaling Transport", draft-ietf-nsis-ntlp-09 (work in
        progress), February 2006.

   [3]  Manner, J., "NSLP for Quality-of-Service Signaling",
        draft-ietf-nsis-qos-nslp-10 (work in progress), March 2006.

12.2.  Informative References

   [4]   Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
         Routing Encapsulation (GRE)", RFC 1701, October 1994.

   [5]   Hanks, S., Li, T., Farinacci, D., and P. Traina, "Generic
         Routing Encapsulation over IPv4 networks", RFC 1702,
         October 1994.

   [6]   Rajahalme, J., Conta, A., Carpenter, B., and S. Deering, "IPv6
         Flow Label Specification", RFC 3697, March 2004.

   [7]   Perkins, C., "IP Encapsulation within IP", RFC 2003,
         October 1996.

   [8]   Perkins, C., "Minimal Encapsulation within IP", RFC 2004,
         October 1996.

   [9]   Nordmark, E. and R. Gilligan, "Basic Transition Mechanisms for
         IPv6 Hosts and Routers", RFC 4213, October 2005.

   [10]  Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303,
         December 2005.

   [11]  Conta, A. and S. Deering, "Generic Packet Tunneling in IPv6
         Specification", RFC 2473, December 1998.

   [12]  Ash, J., "QoS-NSLP QSPEC Template", draft-ietf-nsis-qspec-09
         (work in progress), March 2006.

   [13]  Stiemerling, M., "NAT/Firewall NSIS Signaling Layer Protocol
         (NSLP)", draft-ietf-nsis-nslp-natfw-11 (work in progress),
         April 2006.

   [14]  Lee, S., "Applicability Statement of NSIS Protocols in Mobile
         Environments",
         draft-ietf-nsis-applicability-mobility-signaling-04 (work in
         progress), March 2006.



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   [15]  Farinacci, D., Li, T., Hanks, S., Meyer, D., and P. Traina,
         "Generic Routing Encapsulation (GRE)", RFC 2784, March 2000.

   [16]  Terzis, A., Krawczyk, J., Wroclawski, J., and L. Zhang, "RSVP
         Operation Over IP Tunnels", RFC 2746, January 2000.

   [17]  Berger, L. and T. O'Malley, "RSVP Extensions for IPSEC Data
         Flows", RFC 2207, September 1997.

   [18]  Tschofenig, H. and D. Kroeselberg, "Security Threats for Next
         Steps in Signaling (NSIS)", RFC 4081, June 2005.

   [19]  Kent, S. and K. Seo, "Security Architecture for the Internet
         Protocol", RFC 4301, December 2005.





































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Authors' Addresses

   Charles Shen
   Columbia University
   Department of Computer Science
   1214 Amsterdam Avenue, MC 0401
   New York, NY  10027
   USA

   Phone: +1 212 854 3109
   Email: charles@cs.columbia.edu


   Henning Schulzrinne
   Columbia University
   Department of Computer Science
   1214 Amsterdam Avenue, MC 0401
   New York, NY  10027
   USA

   Phone: +1 212 939 7004
   Email: schulzrinne@cs.columbia.edu


   Sung-Hyuck Lee
   SAMSUNG Advanced Institute of Technology
   San 14-1, Nongseo-ri, Giheung-eup
   Yongin-si, Gyeonggi-do  449-712
   KOREA

   Phone: +82 31 280 9552
   Email: starsu.lee@samsung.com


   Jong Ho Bang
   SAMSUNG Advanced Institute of Technology
   San 14-1, Nongseo-ri, Giheung-eup
   Yongin-si, Gyeonggi-do  449-712
   KOREA

   Phone: +82 31 280 9585
   Email: jh0278.bang@samsung.com









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