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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
Intended status: Informational                               Columbia U.
Expires: December 25, 2009                                        S. Lee
                                                                 J. Bang
                                                             Samsung AIT
                                                           June 23, 2009


                     NSIS Operation Over IP Tunnels
                     draft-ietf-nsis-tunnel-06.txt

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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-
   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.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
     1.1.  IP Tunneling Mechanisms and Tunnel Signaling Capability  .  4
     1.2.  NSIS Tunnel Operation Overview . . . . . . . . . . . . . .  5
   2.  Protocol Design Decisions  . . . . . . . . . . . . . . . . . .  6
     2.1.  Flow Packet Classification over the Tunnel . . . . . . . .  6
     2.2.  Tunnel Signaling and its Association with End-to-end
           Signaling  . . . . . . . . . . . . . . . . . . . . . . . .  7
   3.  Protocol Operation with Dynamically Created Tunnel Sessions  .  7
     3.1.  Operation Scenarios  . . . . . . . . . . . . . . . . . . .  7
       3.1.1.  Sender-initiated Reservation for both End-to-end
               and Tunnel Signaling . . . . . . . . . . . . . . . . .  8
       3.1.2.  Receiver-initiated Reservation for both End-to-end
               and Tunnel Signaling . . . . . . . . . . . . . . . . . 10
     3.2.  Implementation Specific Issues . . . . . . . . . . . . . . 11
       3.2.1.  End-to-end and Tunnel Signaling Interaction  . . . . . 11
       3.2.2.  Aggregate vs. Individual Tunnel Session Setup  . . . . 12
   4.  Protocol Operation with Pre-configured Tunnel Sessions . . . . 13
     4.1.  Tunnel with Exactly One Pre-configured Aggregate
           Session  . . . . . . . . . . . . . . . . . . . . . . . . . 13
     4.2.  Tunnel with Multiple Pre-configured Aggregate Sessions . . 13
     4.3.  Adjustment of Pre-configured Tunnel Sessions . . . . . . . 14
   5.  NSIS-Tunnel Signaling Capability Discovery . . . . . . . . . . 14
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 16
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . . 16
   8.  Appendix . . . . . . . . . . . . . . . . . . . . . . . . . . . 17
     8.1.  NSIS-tunnel Operation for other Types of NSLP  . . . . . . 17
     8.2.  NSIS-tunnel Operation and Mobility . . . . . . . . . . . . 17
     8.3.  Various Design Alternatives  . . . . . . . . . . . . . . . 18
       8.3.1.  End-to-end and Tunnel Signaling Integration Model  . . 18
       8.3.2.  Packet Classification over the Tunnel  . . . . . . . . 18
       8.3.3.  Tunnel Binding Methods . . . . . . . . . . . . . . . . 18
   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 19



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   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 20
     10.2. Informative References . . . . . . . . . . . . . . . . . . 20
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 21















































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1.  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.

1.1.  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 tunnels (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
   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



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   sessions or aggregate tunnel sessions or both.

1.2.  NSIS Tunnel Operation Overview

   This NSIS 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 sessions.  In cases where 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
   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
   from other signaled flows.



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   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.


2.  Protocol Design Decisions

2.1.  Flow Packet Classification over the Tunnel

   A flow can be an individual flow, or an aggregate flow consisting of
   multiple individual flows.

   For individual flows that need to be distinguished from each other
   inside the tunnel, by default an additional UDP header is inserted
   during the tunnel IP encapsulation.  The resulting UDP encapsulated
   flow will then use the Tentry IP address, Texit IP address along with
   the source port number in the additional UDP header as flow ID inside
   the tunnel.  To ensure this mechanism work, the Tentry doing UDP
   encapsulation needs to know the Texit has the corresponding UDP
   decapsulation capability.  Tentry knows the capability of the Text
   either by pre-configuration or through tunnel signaling capability
   discovery defined in Section 5.

   Not all individual flows must use the UDP encapsulation to form the
   tunnel flow ID.  In particular, for an IPv6 flow with unique flow
   label [6], the tunnel signaling can use the Tentry and Texit IP
   addresses plus the IPv6 flow label as the flow ID; for an IPSEC flow
   with Security Parameter Index (SPI), the tunnel signaling can use the
   Tentry and Texit IP addresses plus the SPI as the tunnel flow ID.

   For aggregate flows, the tunnel signaling can still use UDP
   encapsulation for flow ID; when the DiffServ Code Point (DSCP) field
   is in use, the aggregate tunnel flow ID can also be Tentry and Texit
   IP addresses plus the DSCP value; when additional interfaces are
   available, the tunnel signaling may also use the IP address of an
   additional interface at Tentry plus the IP address of the Texit as
   the aggregate flow ID.

   The choice of the tunnel flow ID format is made by the tunnel
   signaling initiator and then conveyed to the other end of the tunnel
   as part of Message Routing Information (MRI, see [2]) in regular NSIS
   signaling messages.




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

   Tunnel signaling messages contain tunnel specific parameters such as
   tunnel MRI and tunnel adjusted QoS 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 notifies the other endpoint of the
   association between the end-to-end and tunnel session 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.  This
   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.


3.  Protocol Operation with Dynamically Created Tunnel Sessions

   The tunnel session corresponding to the end-to-end session can be
   dynamically created or pre-configured, the former case is much more
   complicated.  It is a policy decision over which method should be
   used.  We discuss the dynamically created tunnel session case in this
   section and then the pre-configured tunnel session case in the next.

3.1.  Operation Scenarios

   When tunnel sessions are dynamically created for end-to-end sessions,
   there could be 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.

   Whether sender-initiated or receiver-initiated reservation should be
   used is determined by the signaling initiator.  When both the end-to-
   end session and the tunnel session are concerned, this decision will
   need to be made twice.  In order to reduce complexity, we decide that
   both the end-to-end session and the tunnel session should use the
   same initiation mode.  Since the end-to-end session is the originator
   that causes the establishment of the tunnel session, we use the
   decision made by the end-to-end session as a reference.
   Specifically, when the end-to-end session is sender-initiated, then
   the tunnel session should be sender-initiated too.  If the end-to-end
   session is receiver-initiated, then the tunnel session should be
   receiver-initiated too.

   In the following we describe the typical NSIS end-to-end and tunnel
   signaling interaction process during the tunnel setup phase in each
   of the two recommended scenarios.  The end-to-end QoS flow is assumed
   to be one that qualifies an individual dynamic tunnel session.

3.1.1.  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 prime symbol 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 towards 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 towards Texit using normal tunnel
   encapsulation.

   The tunnel RESERVE' message is processed hop-by-hop inside the tunnel



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   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
   updates the end-to-end RESERVE message based on the result of the
   tunnel session reservation.  Then Texit 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, the receiver may send an end-to-end RESPONSE
   back to the sender.



     Sender    Tentry      Tnode      Texit     Receiver

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




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






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3.1.2.  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' message, it creates the reservation
   state for the tunnel session and may send a tunnel RESPONSE' message
   back to Texit.  When Tentry receives the end-to-end RESERVE message,
   it updates the end-to-end RESERVE message with the result of the
   corresponding tunnel session reservation.  Then it removes the
   BOUND_SESSION_ID object and forwards the end-to-end RESERVE message
   upstream toward the sender.  When the end-to-end signaling finishes,
   the sender may send a RESPONSE message to the receiver.

3.2.  Implementation Specific Issues

3.2.1.  End-to-end and Tunnel Signaling Interaction

   There could be many ways through which the end-to-end signaling and
   tunnel signaling may interact with each other.  In 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.  Our design decision in
   this document is a hybrid model.  The rule is that the end-to-end
   signaling waits for tunnel signaling only if pre-conditions is needed
   to initiate the end-to-end session reservation.  The example of this



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   is the end-to-end QUERY message in Section 3.1.2, which needs to wait
   for the QUERY' message about the tunnel information and then be
   forwarded further.  This ensures that the first end-to-end RESERVE
   message originated from the receiver will have the correct view of
   the whole path.  After that, as long as the amount of resources the
   end-to-end session requests for has been decided, the end-to-end
   reservation and tunnel reservation go parallel to speed up the whole
   process, as illustrated in both Section 3.1.1 and Section 3.1.2.

   When the RESERVE messages of the end-to-end session and the tunnel
   session are propagated in parallel, if by the time an end-to-end
   RESERVE message carrying tunnel binding object arrives at the exit
   endpoint of the tunnel (which could be the Texit in Section 3.1.1 or
   the Tentry in Section 3.1.2), the results of the corresponding tunnel
   session reservation is already available, then the tunnel exit
   endpoint can remove the tunnel BOUND_SESSION_ID object, update the
   end-to-end RESERVE message accordingly and send it out of the tunnel
   immediately.  However, it is also possible that the tunnel session
   state is not yet available when the end-to-end RESERVE message with a
   tunnel binding object is received.  In the latter case, the exit
   tunnel endpoint should still remove the tunnel BOUND_SESSION_ID
   object, but sets the NON-QoSM Hop field [12] to indicate the possible
   existence of non-QoS link and then forward the message out
   immediately.  The exit tunnel endpoint should then try to learn the
   results of the corresponding tunnel session reservation.  This could
   be done by proactive polling after a specific amount of time, or when
   a refresh message is scheduled to send.  In any case, once the state
   of the tunnel session is available, the exit tunnel endpoint should
   immediately trigger an end-to-end RESERVE message subject to the
   results of the tunnel reservation.  If the tunnel reservation is
   successfully confirmed, the message would be a normal RESERVE refresh
   but with the NON-QoSM Hop field reset.  Otherwise, the QSPEC in the
   RESERVE message should indicate error happened in the reservation.

3.2.2.  Aggregate vs. Individual Tunnel Session Setup

   The operation outlined in Section 3.1 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 avoid the new tunnel session setup
   overhead.  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



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   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 4.

   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.


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

4.1.  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.

4.2.  Tunnel with Multiple Pre-configured Aggregate Sessions

   If there are multiple pre-configured aggregate sessions over a tunnel
   setup, 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



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   nodes in the tunnel will then be able to filter these packets to
   receive reserved tunnel resources.

4.3.  Adjustment of Pre-configured Tunnel Sessions

   Adjustment of pre-configured tunnel sessions upon the change of its
   mapped end-to-end sessions 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.


5.  NSIS-Tunnel Signaling Capability Discovery

   There are several reasons why NSIS-tunnel signaling capability
   discovery is needed.  First, when the Tentry decides to use UDP
   encapsulation to distinguish the tunnel flows, it needs to make sure
   the Texit is capable of doing UDP decapsulation when the flows leave
   the tunnel.  Second, full operations of the NSIS tunnel mechanism,
   such as association of the end-to-end and tunnel session and
   adjustment of one session based on the state change of the other
   session, require the involvement of both Tentry and Texit.
   Therefore, one tunnel endpoint wants to know whether the other
   endpoint is also NSIS-tunnel signaling capable in deciding whether or
   not to initiate the related operations.

   Manual configuration is one possible solution to the NSIS-tunnel
   signaling capability discovery problem.  This section defines a
   NODE_CHAR object for GIST to automate the NSIS-tunnel capability
   discovery process.

   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 in
   Figure 3 and Figure 4.

   The Value field contains a single 'T' bit, indicating the NSIS-tunnel
   scheme defined in this document.  It is also possible to use multiple



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   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 .


       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                           //
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 3: NODE_CHAR Object Format

   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                         |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


                     Figure 4: NODE_CHAR Object Value

   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 two dynamically created tunnel session
   scenarios are further detailed below.




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   When both the end-to-end and the tunnel session are sender-initiated
   (Section 3.1.1) and Tentry is NSIS-tunnel capable, the Tentry
   includes a Request Identification Information (RII) object (see [3])
   (if it is not present already) 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 following end-to-end 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 3.1.1.  Alternatively, Tentry may send out tunnel RESERVE
   message before the RESPONSE message confirming the NSIS-tunnel
   capability of Texit is received.  If later it deduces 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 3.1.2) and Tentry is NSIS-tunnel capable, the Tentry
   includes an RII object (if it is not present already) 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 NSIS-tunnel capable.  In the later end-to-
   end RESPONSE message to this QUERY message, the NSIS-tunnel capable
   Texit includes a NODE_CHAR object with T bit set 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 3.1.2.  Otherwise, Texit will not initiate tunnel session
   reservations.


6.  IANA Considerations

   This document defines a new object type called NODE_CHAR for GIST.
   Its OType value needs to be assigned by IANA.  The object format and
   the setting of the extensibility bits are defined in Section 5.


7.  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].



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8.  Appendix

8.1.  NSIS-tunnel Operation for 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], one of the most important signaling operations is CREATE.
   Assuming Tentry is a NATFW NSLP, the tunnel handling for the CREATE
   operation 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.  Detailed discussion of their operations inside the tunnel
   will be the scope of a separate document.

8.2.  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
   [14].



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8.3.  Various Design Alternatives

8.3.1.  End-to-end and Tunnel Signaling Integration Model

   The contents of the 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.  The latter 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 and tunnel session
   signaling model adopted in this document handles both individual and
   aggregate signaling tunnels in a consistent way.

8.3.2.  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 the
   tunnel MRI.  This is a useful property especially in handling tunnel
   mobility.  Mobility causes changes in 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.

8.3.3.  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 tunnel sessions because in those cases the original end-to-
   end session and the corresponding aggregate tunnel session require
   independent control.



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   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
   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 8.2.

   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 tunnel
       binding needs to be conveyed.
   2.  Define a "tunnel bit" in corresponding NSLP message headers.

   These options are not chosen because they either require the creation
   of an entirely new object, or 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) suffers
   the same problem as in (b).  Therefore the choice in this document
   for carrying the tunnel binding object is option (a).


9.  Acknowledgements


10.  References




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10.1.  Normative References

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

   [2]   Schulzrinne, H. and M. Stiemerling, "GIST: General Internet
         Signalling Transport", draft-ietf-nsis-ntlp-20 (work in
         progress), June 2009.

   [3]   Manner, J., Karagiannis, G., and A. McDonald, "NSLP for
         Quality-of-Service Signaling", draft-ietf-nsis-qos-nslp-16
         (work in progress), February 2008.

10.2.  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]  Bader, A., Kappler, C., and D. Oran, "QoS NSLP QSPEC Template",
         draft-ietf-nsis-qspec-21 (work in progress), November 2008.

   [13]  Stiemerling, M., Tschofenig, H., Aoun, C., and E. Davies, "NAT/
         Firewall NSIS Signaling Layer Protocol (NSLP)",
         draft-ietf-nsis-nslp-natfw-20 (work in progress),
         November 2008.




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   [14]  Sanda, T., Fu, X., Jeong, S., Manner, J., and H. Tschofenig,
         "Applicability Statement of NSIS Protocols in Mobile
         Environments",
         draft-ietf-nsis-applicability-mobility-signaling-12 (work in
         progress), March 2009.

   [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.


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







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   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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