NSIS Working Group
   Internet Draft                               Robert Hancock (editor)
                                            Siemens/Roke Manor Research
                                                          Ilya Freytsis
                                                      Cetacean Networks
                                                   Georgios Karagiannis
                                                          John Loughney
                                                     Sven Van den Bosch
   Document: draft-ietf-nsis-fw-01.txt
   Expires: May 2003                                      November 2002

                    Next Steps in Signaling: Framework

Status of this Memo

   This document is an Internet-Draft and is in full conformance with
   all provisions of Section 10 of RFC2026 [1].

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF), its areas, and its working groups. Note that
   other groups may also distribute working documents as Internet-

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time. It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at
   The list of Internet-Draft Shadow Directories can be accessed at


   The NSIS working group is considering protocols for signaling for
   resources for a traffic flow along its path in the network. The
   requirements for such signaling are being developed in [2]; this
   Internet Draft will propose a framework for such signaling.

   This initial version provides a model of the entities that take part
   in the signaling. It discusses the considerations that must be taken
   into account in developing the framework, particularly the options
   for the structure of such a protocol, and the interactions between
   NSIS and other protocols and functions, including security issues.

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   Finally, it includes background material on how NSIS could support
   particular signaling applications.

   It is expected that future versions of this document will distill
   these structural options into a concrete technical framework, and
   material on particular signaling applications and deployment
   scenarios will be moved into separate NSIS applicability statements.

Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119 [3].

Table of Contents

   1. Introduction...................................................3
     1.1 Scope of the NSIS Framework ................................4
   2. Terminology....................................................5
   3. Overall Framework Structure....................................6
     3.1 Basic Signaling Entities and Interfaces ....................6
     3.1.1   NSIS Entities ..........................................6
     3.1.2   Placement of NSIS Entities .............................8
     3.1.3   NSIS Protocol Components ...............................9
     3.2 Options for Modes of NSIS Operation .......................10
     3.2.1   Path-Coupled and Path-Decoupled Signaling .............10
     3.2.2   Inter-domain and Intra-domain Signaling ...............11
     3.2.3   End-to-End, Edge-to-Edge, and End-to-Edge .............12
     3.2.4   Global and Local Operation ............................12
     3.2.5   Multicast versus Unicast ..............................13
     3.2.6   Sender versus Receiver Initiated Signaling ............13
     3.2.7   Uni-Directional and Bi-Directional Reservations .......14
     3.3 Basic Assumptions and Conceptual Issues ...................15
     3.3.1   Basic Assumptions .....................................15
     3.3.2   NI, NF, NR functionality ..............................15
     3.3.3   NI, NF, NR relationship ...............................16
     3.3.4   NSIS Addressing .......................................16
     3.3.5   NSIS Layer Boundaries .................................17
     3.3.6   NSIS Acknowledgement and Notification Semantics .......17
   4. Protocol Components...........................................18
     4.1 Lower Layer Interfaces ....................................18
     4.2 Upper Layer Services ......................................18
     4.3 Protocol Structure ........................................20
     4.3.1   Internal Layering .....................................20
     4.3.2   Protocol Messages .....................................21
     4.4 State Management ..........................................22
     4.5 Identity Elements .........................................24
     4.5.1   Flow Identification ...................................24

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     4.5.2   Reservation Identification ............................24
     4.5.3   NSLP Identification ...................................25
   5. NSIS Protocol Interactions....................................25
     5.1 Resource Management Interactions ..........................25
     5.2 IP Routing Interactions ...................................27
     5.2.1   Load Sharing ..........................................27
     5.2.2   QoS Routing ...........................................28
     5.2.3   Route pinning .........................................28
     5.2.4   Route Changes .........................................28
     5.2.5   Router Redundancy .....................................30
     5.3 Mobility Interactions .....................................30
     5.3.1   Addressing and Encapsulation ..........................30
     5.3.2   Localized Path Repair .................................31
     5.3.3   Reservation Update on the Unchanged Path ..............32
     5.3.4   Interaction with Mobility Signaling ...................32
     5.3.5   Interaction with Fast Handoff Support Protocols .......34
     5.4 NSIS Interacting with NATs ................................35
   6. Security and AAA Considerations...............................36
     6.1 Authentication ............................................36
     6.2 Authorization .............................................37
     6.3 Accounting ................................................38
     6.4 End-to-End vs. Peer Relationship Protection ...............39
   7. NSIS Application Scenarios....................................40
     7.1 NSIS and Existing Resource Signaling Protocols ............40
     7.2 NSIS Supporting Centralized QoS Resource Management .......41
     7.3 NSIS Supporting Distributed Resource Management ...........43
     7.4 NSIS for Middlebox Signaling ..............................43
     7.5 Multi-Level NSIS Signaling ................................44
   8. Open Issues...................................................45
   9. Change History................................................47
     9.1 Changes from draft-ietf-nsis-fw-00.txt ....................47
     9.2 Changes from draft-hancock-nsis-fw-00.txt .................47
   Author's Addresses...............................................51
   Full Copyright Statement.........................................52

1. Introduction

   NSIS will work on signaling from an end point that follows a path
   through the net that is determined by layer 3 routing and is used to
   convey information to the devices the signals pass through - the
   signaling can, for example, install soft state in the devices it
   passes through. A signaling end point could be a device along the
   path, which signals for a data flow that passes through it.

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   The intention is to allow for the NSIS protocol to be deployed in
   different parts of the Internet, for different needs, without
   requiring a complete end-to-end deployment.

   There is no requirement that the per-flow information be QoS related.
   NSIS should only worry about how to do the signaling - what the
   signaling conveys should be opaque to NSIS. This document discusses
   'where' the signaling takes place, with some discussion on 'how' the
   signaling can be done.

1.1 Scope of the NSIS Framework

   The scope of this document will be to provide a framework for where a
   NSIS protocol can be used and deployed. It is not intended that NSIS
   will define an over-arching architecture for carrying out resource
   management in the Internet, nor is this intended to be used as a
   detailed protocol design document.

   The framework is not about what NSIS should do but how it should do
   it. It is not intended that this places requirements on a future NSIS
   protocol, since requirements are already defined in [2]. The document
   discusses important protocol considerations, such as mobility,
   security, and interworking with resource management (in a broad
   sense). Discussions about lessons to be learned from existing
   signaling and resource protocols are contained in a separate analysis
   document [4].

   This initial version provides a model of the entities that take part
   in the signaling. It discusses the considerations that must be taken
   into account in developing the framework, particularly the options
   for the structure of such a protocol, and the interactions between
   NSIS and other protocols and functions, including security issues.
   Finally, it includes background material on how NSIS could support
   particular signaling applications.

   It is expected that future versions of this document will distill
   these structural options into a concrete technical framework, and
   material on particular signaling applications and deployment
   scenarios will be moved into separate NSIS applicability statements.

   The purpose of this document is to develop the realms, domains and
   modes of operation where an NSIS protocol can be used; identify the
   relationship of an NSIS protocol to other protocols; and identify
   areas for future work.

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2. Terminology

   Classifier - an entity which selects packets based on their contents
   according to defined rules.

   Interdomain traffic - Traffic that passes from one NSIS domain to

   NSIS Domain (ND) - Administrative domain where an NSIS protocol
   signals for a resource or set of resources.

   NSIS Entity (NE) - the function within a node which implements an
   NSIS protocol. In the case of path-coupled signaling, the NE will
   always be on the data path.

   NSIS Forwarder (NF) - NSIS Entity between a NI and NR which may
   interact with local resource management function (RMF). It also
   propagates NSIS signaling further through the network.

   NSIS Initiator (NI) - NSIS Entity that initiates NSIS signaling for a
   network resource.

   NSIS Responder (NR) - NSIS Entity that terminates NSIS signaling and
   can optionally interact with applications as well.

   NSIS Signaling Layer Protocol (NSLP) - generic term for an NSIS
   protocol component that supports a specific signaling application.
   See also section 3.1.3.

   NSIS Transport Layer Protocol (NTLP) - placeholder name for the NSIS
   protocol component that will support lower layer (signaling
   application independent) functions. See also section 3.1.3.

   Path-coupled signaling - a mode of signaling where the signaling
   messages follow a path that is tied to the data messages. See also
   section 3.2.1.

   Path-decoupled signaling - signaling with independent data and
   signaling paths.

   Peer determination - the act of locating and/or selecting which NSIS
   peer to carry out signaling exchanges with for a specific data flow.

   Peer relationship - signaling relationship between two adjacent NSIS
   entities (i.e. NEs with no other NEs between them).

   Receiver - the node in the network which is receiving the data
   packets in a flow.

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   Resource - something of value in a network infrastructure to which
   rules or policy criteria are first applied before access is granted.
   Examples of resources include the buffers in a router and bandwidth
   on an interface.

   Resource Management Function (RMF) - an abstract concept,
   representing the management of resources in a domain or a node.

   Sender - the node in the network which is sending the data packets in
   a flow.

   Service Level Agreement (SLA) - a service contract between a customer
   and a service provider that specifies the forwarding service a
   customer should receive.

   [NSIS] Signaling application - the purpose of the NSIS signaling: a
   service could be QoS management, firewall control, and so on. Totally
   distinct from any specific user application.

   Traffic characteristic - a description of the temporal behavior or a
   description of the attributes of a given traffic flow or traffic

   Traffic flow - a stream of packets between two end-points that can be
   characterized in a certain way.

3. Overall Framework Structure

3.1 Basic Signaling Entities and Interfaces

3.1.1  NSIS Entities

   The NSIS protocol is intended to be used as a signaling control plane
   for the variety of network resources required for data traffic across
   the Internet. The most common NSIS signaling applications are QoS
   resources, firewalls and NATs resources, etc. The NSIS signaling
   itself does not depend on the signaling application it is used for
   but the information it carries does. This section discusses the basic
   signaling entities of the protocol as well as interfaces between

   We can identify three different roles in the NSIS signaling for
   resources: initiator, forwarder and responder.

   The NSIS Initiator (NI) is an entity that initiates NSIS signaling
   (request) for the network resource. The NSIS initiator can be
   triggered by the different "sources" - user applications, an instance
   of NSIS Forwarder, other protocols, network management etc. - that

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   need network resources for a data flow. For the purpose of the NSIS
   discussion all these sources can be called "applications" (note that
   this is entirely distinct from the specific term "signaling
   application"). The NSIS initiator can provide feedback information to
   the triggering application in respect to the requested network
   resources. The NSIS initiator uses NSIS signaling to interact with
   other NSIS entities (NFs and NRs).

   The NSIS Forwarder (NF) is an entity that services NSIS resource
   requests from NSIS initiators and other NSIS forwarders. It may
   interact with local resource management function (RMF). How and if
   this interaction takes place depends on the deployed resource
   management mechanism and the specific role of the NF. The NSIS
   forwarder propagates NSIS signaling further through the network.

   The NSIS Responder (NR) is an entity that terminates NSIS signaling
   and can optionally interact with local applications as well e.g. for
   the purpose of notification when network resources get allocated etc.

   The signaling relationship between two NSIS entities (with no other
   NSIS entities between them) is called simply a 'peer relationship'.
   This concept might loosely be described as an 'NSIS hop'; however,
   there is no implication that it corresponds to a single IP hop.
   Either or both NEs might store some state information about the
   other, but there is no assumption that they establish a long-term
   signaling session between themselves.

   Figure 1 depicts simplified interactions/interfaces between NI, NFs
   and NR as well as local applications and RMFs. Note that the NI and
   NR could also interact with an RMF; additionally, this could be
   modeled as co-location of NI&NF and NR&NF. This distinction should
   have no impact on the operation of the protocol. Also, there is no
   bar on placing an NI or NR in the interior of the network, to
   initiate and terminate NSIS signaling independently of the ultimate
   endpoints of the end to end flow, and NI and NR do not have to talk
   via intervening NFs. An example of NSIS being used in this way is
   given in section 7.5.

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   +-----------+                                        +-----------+
   |Application|                                        |Application|
   +-----------+                                        +-----------+
        ^                                                      ^
        |                                                      |
        |  |____________|                      |____________|  |
        V  |            |                      |            |  V
       +----+          +----+              +----+          +----+
       | NI |==========| NF |=====....=====| NF |==========| NR |
       +----+          +----+              +----+          +----+
                         ^                    ^
                         |                    |
                         V                    V
                       +----+              +----+
                       |RMF |              | RMF|
                       +----+              +----+

                   ===========  = NSIS signaling messages

                   |_________|  = Scope of single NSIS
                   |         |    "peer relationship"

                  Figure 1: Basic NI/NF/NR Relationships

3.1.2  Placement of NSIS Entities

   The NI, NF and NR definitions do not make any assumptions about
   placements of NSIS signaling entities in respect to the particular
   part of the network or data-forwarding path.

   They can be located along the data path (hosts generating and
   receiving data flows, edge routers, intermediate routers etc.) but it
   may not be the only one desirable location.

   In some cases it is desired to be able to initiate and/or terminate
   NSIS signaling not from the end host that generates/receives the data
   flow, but from the some other entities on the network that can be
   called NSIS signaling application proxies. There could be various
   reasons for this: signaling on behalf of the end hosts that are not
   enabled with NSIS, consolidation of the customer accounting
   (authentication, authorization) in respect to consumed application
   and transport resources, security considerations, limitation of the
   physical connection between host and network etc. The proxy can
   communicate the relevant information to the host in the application
   specific, maybe compressed, form.

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   Support for NSIS proxies affects the protocol in the following way:
    *) The protocol should accommodate signaling with the scope of a
   single NSIS peer relationship; the signaling could be propagated over
   multiple peer relationships all the way toward the destination (end-
    *) In the particular case where the proxy is not on the data path,
   NSIS might have to be extended to allow separated data and signaling
   paths, although this analysis is not initially in scope.

   Further discussion of these issues is given in sections 3.2.1 and

   As it can be seen from the usage cases presented in the NSIS
   requirements draft [2] the NSIS signaling procedures may depend on
   the part/type of the network where NSIS is used. In fact to satisfy
   sometimes-conflicting requirements in [2], different procedures and
   possibly different kinds of the NSIS protocol can be used on
   different parts/types of the network. Sections 3.2 and 7.5 provide
   more details on this topic.

3.1.3  NSIS Protocol Components

   In order to achieve a modular solution for the NSIS requirements, it
   is proposed to structure what we refer to overall as 'the NSIS
   protocol' into 2 layers, similarly to the original proposal in [8]:
    *) a 'signaling transport' layer, responsible for moving signaling
   messages around, which should be independent of any particular
   signaling application; and
    *) a 'signaling application' layer, which contains functionality
   such as message formats and sequences, specific to a particular
   signaling application.

   For the purpose of this document, we use the term 'NSIS Transport
   Layer Protocol' (NTLP) to refer to the component that will be used in
   the transport layer; it may or may not be based on the use of
   existing transport protocols. We also use the term 'NSIS Signaling
   Layer Protocol' (NSLP) to refer generically to any protocol component
   within the signaling application layer; in the end, there will be
   several NSLPs. These relationships are illustrated in Figure 2.

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                 ^                     +-----------------+
                 |                     | NSIS Signaling  |
                 |                     | Layer Protocol  |
          NSIS   |    +----------------| for middleboxes |
       Signaling |    | NSIS Signaling |        +-----------------+
         Layer   |    | Layer Protocol +--------| NSIS Signaling  |
                 |    |     for QoS     |       | Layer Protocol  |
                 |    |                 |       | for something   |
                 |    +-----------------+       |     else        |
                 V                              +-----------------+
                 ^         +--------------------------------+
                 |         | NSIS Transport Layer Protocol  |
          NSIS   |         |       ....................     |
       Transport |         |       .Standard transport.     |
         Layer   |         |       . protocol (maybe) .     |
                 |         |       ....................     |
                 V         +--------------------------------+

                    Figure 2: NSIS Protocol Components

   The precise boundary between these layers is not defined at this
   stage; see section 3.3.5 for some initial discussion of this point.

3.2 Options for Modes of NSIS Operation

   This section discusses several possible modes of NSIS operation. Each
   mode of NSIS operation is briefly introduced and where needed
   analyzed and compared with the alternatives. It is not assumed that
   NSIS will support all the mode variants described in these
   subsections; after the tradeoffs described here have been evaluated,
   some might be excluded from further consideration.

3.2.1  Path-Coupled and Path-Decoupled Signaling

   We can consider two basic paradigms for resource reservation
   signaling, which we refer to as "path-coupled" and "path-decoupled".

   In the path-coupled case, signaling messages are routed only through
   nodes (NEs) that are in the data path. They do not have to reach all
   the nodes on the data path (for example, there could be proxies
   distinct from the sender and receiver as described in section 3.1.2,
   or intermediate signaling-unaware nodes); and between adjacent NEs,
   the route taken by signaling and data might diverge. The path-coupled
   case can be supported by various addressing styles, with messages
   either explicitly addressed to the neighbor on-path NE, or routed
   identically to the data packets and intercepted. These cases are

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   considered in section 3.3.4. In the second case, some network
   configurations may split the signaling and data paths (see section
   5.2); this is considered an error case for path-coupled signaling.

   In the path-decoupled case, signaling messages are routed to nodes
   (NEs) which are not assumed to be on the data path, but which are
   (presumably) aware of it. Signaling messages will always be directly
   addressed to the neighbor NE, and the NI/NR may have no relation at
   all with the ultimate data sender or receiver.

   There are potentially significant differences in the way that the two
   signaling paradigms should be analyzed, for example in terms of
   scaling behavior, failure recovery, security properties, mechanism
   for NSIS peer determination, and so on. These differences might or
   might not cause changes in the way that the NSIS protocol operates.

   The initial goal of NSIS and this framework is to concentrate mainly
   on the path-coupled case.

3.2.2  Inter-domain and Intra-domain Signaling

   Inter-domain NSIS signaling is where the NSIS signaling messages are
   originated in one NSIS domain and are terminated in another NSIS

   In the path-coupled case, inter-domain NSIS signaling can be used to
   signal NSIS information to the edge nodes of one or more NSIS

   In the path-decoupled case, inter-domain NSIS signaling can be used
   to signal NSIS information to entities that are not on the data path
   (i.e., "out-of-band" NFs), and additionally to signal from off-path
   entities to on-path edge nodes .

   NSIS inter-domain signaling has to fulfill several requirements, such
    *) Basic functionality, such as scalable, simple and fast signaling.
   Because different networks have different resource management
   characteristics, such as cost of bandwidth and performance, this
   basic functionality may differ from one NSIS domain to another.
    *) All other requirements specified in [2].

   Intra-domain NSIS signaling is where the NSIS signaling messages are
   originated, processed and terminated within the same NSIS domain.
   Note that these messages could be handled within a local instance of
   NSIS signaling; another possibility could be to piggyback them on
   inter-domain NSIS messages.

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   Intra-domain signaling can be used to signal NSIS information to the
   edge nodes (i.e., routers located at the border of the NSIS domain)
   and to the interior nodes (i.e., routers located within the NSIS
   domain that are not edge nodes).

   The NSIS intra-domain signaling approach has to fulfill fewer
   requirements than inter-domain signaling. These are:
    *) Basic functionality, such as scalable, simple and fast signaling.
   Due to the fact that different networks have different resource
   management characteristics, this basic functionality may differ from
   one NSIS domain to another.
    *) Provides the necessary functionality to interact between inter-
   domain signaling and intra-domain signaling.

3.2.3  End-to-End, Edge-to-Edge, and End-to-Edge

   End-to-end: When used end-to-end, the NSIS protocol is initiated by
   an end host and is terminated by another end host. In this context,
   NSIS can be applied as needed within all of the NSIS domains between
   the end hosts. In the end-to-end path, NSIS may be used both for
   intra-domain NSIS signaling, as well as for inter-domain signaling.

   Edge-to-edge: In this scenario the NSIS protocol is initiated by an
   edge node of a NSIS domain and is terminated by another edge node of
   the same (or possibly different) NSIS domain. NSIS can be applied
   either within one single NSIS domain, which is denoted as edge-to-
   edge in a single domain, or within a concatenated number of NSIS
   domains, which is denoted as edge-to-edge in a multi-domain. When an
   appropriate security trust relation exists between two or more
   concatenated NSIS domains, these concatenated NSIS domains are
   considered, in terms of NSIS, to be a single, larger NSIS domain.

   End-to-edge: In this scenario the NSIS protocol is either initiated
   by an end host and is terminated by an edge node or is initiated by
   an edge node and is terminated by an end host. In the path-coupled
   case, the edge node may be a proxy that is located on a boundary node
   of a NSIS domain. In the path-decoupled case, the edge node may be a
   proxy that is located on an off-path node that controls, or is
   associated with, a NSIS domain.

3.2.4  Global and Local Operation

   It is likely that the appropriate way to describe the resources NSIS
   is signaling for will vary from one part of the network to another.
   In particular, resource descriptions that are valid for inter-domain
   links will probably be different from those useful for intra-domain
   operation (and the latter will differ from one NSIS domain to

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   One way to describe this issue is to consider the resource
   description objects carried by NSIS (typically within the signaling
   application layer) as divided in globally-understood objects ("global
   objects") and locally-understood objects ("local objects"). The local
   objects are only applicable for intra-domain signaling, while the
   global objects are mainly used in inter-domain signaling. Note that
   such local objects are still part of the NSIS protocol, unlike opaque
   data which would be invisible to the protocol; local objects can be
   inserted, used and removed by one single domain.

   The purpose of this division is to provide additional flexibility in
   defining the objects carried by the NSIS protocol such that only
   those objects that are applicable in a particular setting are used.
   An example approach for reflecting the distinction in the signaling
   is that local objects could be put into separate local messages that
   are initiated and terminated within one single NSIS domain and/or
   they could be "stacked" within the NSIS messages that are used for
   inter-domain signaling. These possibilities will be considered
   further during the protocol design activity.

3.2.5  Multicast versus Unicast

   Multicast support, compared to unicast support, would introduce a
   level of complexity into the NSIS protocol mainly related to:
    *) complex state maintenance to support dynamic membership changes
   in the multicast groups, such as reservation state merging and
    *) a state per flow has to be maintained that is used during
   backward routing.

3.2.6  Sender versus Receiver Initiated Signaling

   A sender-initiated approach is when the sender of the data flow
   initiates and maintains the resource reservation used for that flow.
   In a receiver-initiated approach the receiver of the data flow
   initiates and maintains the resource reservation used for the data

   In the path-coupled case, and in the absence of NSIS proxies, the
   following relationships apply:
    *) in the sender initiated case, the sender of the data is the NSIS
   Initiator, while the receiver of the data is the NSIS Responder;
    *) in the receiver initiated case, the receiver of the data is the
   NSIS Initiator, while the sender of the data is the NSIS Responder.
   In the path-decoupled case, the mapping is not necessarily clear cut
   (for example, if the NI and NR are not located at the end systems

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   The main differences between the sender-initiated and receiver-
   initiated approaches are the following:
    *) Compared with the receiver-initiated approach, a sender using a
   sender-initiated approach can be informed faster when the reservation
   request is rejected. In other words, when using a sender-initiated
   approach, the reservation request response time can be shorter in the
   case of an unsuccessful reservation than with a receiver-initiated
    *) In a receiver-initiated approach, the signaling messages
   traveling from the receiver to the sender must be backward routed
   such that they follow exactly the same path as was followed by the
   signaling messages belonging to the same flow traveling from the
   sender to the receiver. This implies that a backward routing state
   per flow must be maintained. When using a sender-initiated approach,
   provided acknowledgements and notifications can be securely delivered
   to the sending node, backward routing is not necessary, and nodes do
   not have to maintain backward routing states.
    *) In a sender-initiated approach, a mobile node can initiate a
   reservation for its outgoing flows as soon as it has moved to another
   roaming subnetwork. In a receiver-initiated approach, a mobile node
   has to inform the receiver about its handover procedure, thus
   allowing the receiver to initiate a reservation for these flows.
    *) Where the signaling is looking for the last (nearest to receiver)
   NE on the data path, receiver oriented signaling is most efficient;
   sender orientation would be possible, but take more messages.

3.2.7  Uni-Directional and Bi-Directional Reservations

   It is possible that a resource will only be required for one
   direction of traffic, for example for a media stream with no feedback
   channel. Reservations for both directions of traffic may be required
   for other applications, for example a voice call. Therefore, the NSIS
   signaling protocol must allow for both uni- and bi-directional
   resource reservations.

   The most basic method for bi-directional reservations is based on
   combining two uni-directional reservations. This allows that the
   signaling messages for one direction of the bi-directional
   reservation are able to follow a different path from messages
   traveling in the opposite direction, which is necessary for path-
   coupled signaling in the presence of asymmetric routing. (Other more
   integrated approaches may be possible in constrained network
   topologies where parts of the route are symmetric.) The bi-
   directional reservations can, for example, be used to make the NSIS
   signaling procedure required after a handover procedure more

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3.3 Basic Assumptions and Conceptual Issues

3.3.1  Basic Assumptions

   The following assumptions have been made during prior NSIS
   requirements work and initial framework discussions. They are
   summarized here for completeness. The subsequent subsections describe
   more generic conceptual assumptions and issues. Note that a complete
   overview of current open issues is contained in section 8.

    *) The solution developed by NSIS must be sufficiently flexible and
   modular that it can be efficiently deployed and used with
   functionality appropriate to the part/type of the network. (Sections
   3.2.2 and 3.2.3.)

    *) The protocol developed by the NSIS working group will be path-
   coupled. Considerations related to a potential path-decoupled
   solution are part of this framework, because they are also needed in
   order to co-exist with existing solutions; however, the NSIS working
   group currently has no plans to develop path-decoupled signaling
   protocol. (Section 3.2.1.)

    *) End-to-end message routing will be achieved by each NE
   determining the next appropriate NSIS peer, based on the flow in
   question and information within the NTLP layer, not requiring any
   node or the upper layers to acquire end-to-end topology information.
   (Section 3.2.4.)

    *) Multicast support introduces a level of complexity into the NSIS
   protocol that is not needed in support of unicast applications.
   Therefore, a working assumption is be that the NSIS protocol should
   be optimized for unicast. (Section 3.2.5.)

    *) The NSIS protocol can be used for setup of both uni-directional
   and bi-directional reservations. (Section 3.2.7.)

3.3.2  NI, NF, NR functionality

   The basic functions that can be fulfilled by an NSIS entity are
   request, accept, notify, modify and release of a reservation. At this
   point, it is not clear which responsibilities can be assumed by each
   of the NSIS entities. More in particular, it is not clear whether:
    *) an NF can request, modify or release a reservation. If it cannot,
   it needs to notify the NI in order to perform these functions.
    *) an NR can modify and release a reservation. Even if the NR can
   reject or accept the reservation with modification, it might still be
   required to notify the NI to signal the release or modification.

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3.3.3  NI, NF, NR relationship

   An important open issue is related to the way in which NSIS entities
   maintain relations between each other. These relations could be
   purely local, where an NSIS entity only maintains relations with its
   direct neighbors (peers). In that case, messages will be sent to and
   accepted from these neighbors only. Alternatively, the relations
   between NSIS entities could have a more global scope.

   The type of NSIS peering relations may have an impact on the
   complexity involved with protocol security. In case of inter-domain
   signaling, the security relations are likely to be built between
   neighboring NSIS entities only for scalability reasons. In that case,
   each NSIS entity will establish and maintain a security relation with
   each of its peers and accept only messages from these peers.

   Conversely, there may exist larger domains of NSIS entities that have
   a trust relationship (trusted domains). This may be the case for
   intra-domain signaling. In this case, an NE may accept messages from
   all other NSIS entities in the domain. Both alternatives need not be
   mutually exclusive. It is conceivable that different instances of the
   NSIS protocol (or different NSIS protocols) use the NSIS security
   model to a larger or lesser extent, provided that overall security is
   not impacted. An analysis of NSIS threats is available from [5].

   The NSIS peering relations may also have an impact on the required
   amount of state at each NSIS entity. When direct interaction with
   remote NSIS peers is not allowed, it may be required to keep track of
   the path that an NSIS message has followed through the network. This
   can be achieved by keeping per-flow state at the NSIS entities or by
   maintaining a record route object in the NSIS messages.

   An initial working assumption is that the NTLP will operate
   'locally', that is, just over the scope of a single peer
   relationship. End-to-end operation is built up by simply
   concatenating these relationships. Any non-local operation (if any)
   will take place only in particular NSLPs.

3.3.4  NSIS Addressing

   The are potentially two ways to establish a signaling connection by
   means of the NSIS protocol. On the one hand, the NSIS message could
   be addressed to a neighboring NSIS entity (NE) that is known to be
   closer to the destination NE. On the other hand, the NSIS message
   could be addressed to the destination directly, and intercepted by an
   intervening NE. We denote the latter approach as end-to-end
   addressing and the former as peer-peer addressing.

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   With peer-peer addressing, an NE will determine the address of the
   next NE based on the payload of the NSIS message (and potentially
   also on the previous NE). This requires the address of the
   destination NE to be derivable from information present in the
   payload. This can be achieved through the availability of a local
   routing table or through participation in the routing protocol. Peer-
   peer addressing inherently supports tunneling of NSIS signaling
   messages between NEs, and is equally applicable to the path-coupled
   and path-decoupled cases.

   In case of end-to-end addressing, the NSIS message will be sent with
   the address of the NR, which then necessarily needs to be on the data
   path. This requires (some of) the data-path entities to be upgraded
   (NSIS-aware) in order to be able to intercept the NSIS messages. The
   routing of the NSIS signaling should follow exactly the same path as
   the data flow for which the reservation is requested.

3.3.5  NSIS Layer Boundaries

   The detailed boundary between the NTLP and NSLPs is an area for
   (considerable) further analysis. In particular, it is not clear how
   the key issues described earlier (such as sender/receiver
   orientation) are allocated to the different layers. However, some
   initial assumptions have been made about the functionality in
   different layers.

   *) It is assumed that some flow description information is part of
   the NTLP (see section 4.3.1 and 4.5.1). This might be needed by
   signaling application unaware entities located at address boundaries.
   It is not clear to which level of complexity the flow description
   needs to be available at this level.
    *) It is not assumed that the operation of an NSLP is totally
   independent of the NTLP; for example, the appropriate interpretation
   of an NSLP message might depend on the local status of the NTLP.

3.3.6  NSIS Acknowledgement and Notification Semantics

   The semantics of the acknowledgement and notification messages are of
   particular importance. An NE sending a message can assume
   responsibility for the entire downstream chain of NEs, indicating for
   instance the availability of reserved resources for the entire
   downstream path. Alternatively, the message could have a more local
   meaning, indicating for instance that a certain failure or
   degradation occurred at a particular NSIS entity.

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4. Protocol Components

4.1 Lower Layer Interfaces

   Within a signaling entity, NSIS interacts with the 'lower layers' of
   the protocol stack for two nearly independent purposes: sending and
   receiving signaling messages; and configuring the operation of the
   lower layers themselves.

   For sending and receiving messages, this framework places the lower
   boundary of the NTLP at the IP layer. (It is possible that NSIS could
   use a standard transport protocol above the IP layer to provide some
   of its functionality; this is discussed in section 4.3.1.) The
   interface with the lower layers is therefore very simple:
    *) The NTLP sends raw IP packets
    *) The NTLP receives raw IP packets. In the case of peer-peer
   addressing, they have been addressed directly to it. In the case of
   end-to-end addressing, this will be by intercepting packets that have
   been marked in some special way (by special protocol number or by
   some option interpreted within the IP layer, such as the Router Alert
   option [6] and [7].)

   For correct message routing, the NTLP needs to have some information
   about the link and IP layer configuration of the local networking
   stack. For example, it needs to know:
    *) [in general] how to select the outgoing interface for a signaling
   message, in case this needs to match the interface that will be used
   by the corresponding flow. This might be as simple as just allowing
   the IP layer to handle the message using its own routing table.
    *) [in the case of IPv6] what address scopes are associated with the
   interfaces that messages are sent and received on (to interpret
   scoped addresses in flow identification, if these are to be allowed).

   The way in which the lower layers are actually configured to handle
   the flow depends on the particular NSIS signaling application; for
   example, if NSIS is being used for QoS signaling, this might involve
   configuration of traffic classification and conditioning parameters,
   for example local packet queues, type of filters, type of scheduling,
   and so on. However, none of this is directly related to the NTLP or
   indeed any NSLP; therefore, this interaction is handled indirectly
   via a resource management function, as described in section 5.1.

4.2 Upper Layer Services

   The combination of the NTLP and an NSLP provides a signaling service,
   appropriate for a particular signaling application. We can describe
   such a signaling service as an abstract set of capabilities, provided
   at a service interface, defined from three perspectives:

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    *) What basic control primitives are available at the interface;
    *) What information is exchanged within these primitives;
    *) What assumptions are made about operations carried out above the

   The set of control primitives required is quite small.
   At the initiating (NI) end:
    *) Signaling application requests signaling for a new resource;
    *) Signaling application requests modification or removal of an
   existing resource.
    *) Signaling application receives progress indications (minimally,
   success or failure).
   At the responding (NR) end:
    *) Notification to signaling application that a resource has been
   set up.
   At either end:
    *) Notification to signaling application that something has changed
   about the available resource and other error conditions.

   This description is in terms of a 'hard state' interface, without
   explicit refresh messages between the signaling application and NSIS,
   although this is an implementation issue. In any case,
   implementations will need to be able to detect conditions when
   instances of signaling applications fail without issuing explicit
   resource removal requests.

   The information in the control primitives consists essentially of two
   parts. The first is the definition of the data flow for which the
   resource is being signaled. The format (e.g. socket id or packet
   fields or whatever) is an implementation issue; it has to be
   interpreted into a 'wire format' (as in section 4.5). Since NSIS
   could support both sender and receiver initiation, the flow
   definition must also state whether it is incoming or outgoing over a
   particular interface (this can be inferred when the initiator is
   colocated with the flow endpoint). The second part of the information
   exchanged is the service definition (e.g. QoS description in the case
   of a QoS request). This will be opaque at least to the NTLP, which
   only knows the specific NSLP being used.

   We have a basic design goal not to duplicate functionality that is
   already present in (or most naturally part of) existing signaling
   protocols which could be used by the upper layers. Therefore NSIS
   (implicitly) assumes that certain procedures are carried out
   'externally'. The main aspects of this are:
    *) Negotiation of service configuration (e.g. discovering what
   services are available to be requested);
    *) Agreement to use NSIS for signaling, and coordination of which
   end will be the initiator.

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   In addition, as well as NSIS (presumably the NTLP) providing a
   'native' capability to determine the peer to carry out signaling
   with, it is possible that this information could be provided from
   some external source (which might be helpful in some access
   scenarios, or in the path-decoupled case). See also the security
   discussion in section 6.

   Actually providing these functions might require enhancements to
   these other protocols. These are still to be identified.

4.3 Protocol Structure

4.3.1  Internal Layering

   We can model NSIS in two layers, as shown in Figure 3. This is
   initially just a way of grouping associated functionality, and does
   not mean that all these layers could necessarily operate or even be
   implemented independently.

                    .     Signaling Application      .
                    .        (section 4.2)           .
                    .                                .
                    | NSIS Signaling Layer Protocol  |
                    |  (for some specific signaling  |
                    |          application)          |
                    |                                |
                    | NSIS Transport Layer Protocol  |
                    |      ....................      |
                    |      .Standard transport.      |
                    |      . protocol (maybe) .      |
                    |      ....................      |
                    .     Interface to IP layer      .
                    .         (section 4.1)          .
                    .                                .

                      Figure 3: NSIS Layer Structure

   The lower layer interface (to IP) has been described in section 4.1.
   The support of the signaling application is as described in section
   4.2. The degree of independence between the NTLP and NSLP is unclear
   and might depend on the particular signaling application. To make the
   NTLP independent of the signaling application, we must allow that

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   NSLPs could be explicitly dependent on the layer below. This is
   similar to the ALSP/CSTP coupling described in [8].

   The distinction between the NTLP and any 'Standard Transport
   Protocol' is not functionally clear cut, but one of convenience. In
    *) The 'standard' protocol could provide (at most) functionality
   which might be available from existing protocols, such as SCTP [9] or
   IPSec [10]. An extreme case could be the binding update messages of
   mobility signaling (section 5.3.4).
    *) The NTLP provides (at least) functionality which is somehow
   specific to path-coupled signaling.

   Functionality reasonable to re-use from existing protocols might
   include reliability and re-ordering protection, dead peer detection
   (keepalive), multihoming support, payload multiplexing
   (piggybacking), and security services, such as establishment of
   security contexts and carrying out key exchange.

   Functionality which would probably have to be in the NTLP would
   include flow and reservation identification, some error handling,
   demultiplexing between different NSLPs, as well as possibly the basic
   NSIS messages. More details on the messages are in section 4.3.2 and
   the identifier aspects in section 4.5.

   The choice of using functionality from an existing protocol or re-
   specifying it as part of the NTLP is for further analysis. It
   probably depends on the function in question, and in the end might be
   left flexible to allow optimization to local circumstances. (For
   example, Diameter allows the use of IPSec for security services, but
   also includes its own CMS application as an alternative.) Whichever
   approach is taken, the combination of NTLP and supporting transport
   protocol must provide a uniform protocol capability to the NSLPs
   which support the actual signaling applications.

4.3.2  Protocol Messages

   The NSIS protocols will include a set of messages to carry out
   particular operations along the signaling path. Initial work for RSVP
   concentrated on the particular case of QoS signaling, although the
   implication of the analysis in [8] is that this message set
   generalizes to a wide variety of signaling applications and so we use
   it as a starting point. (A very similar set of messages was generated
   in [11].) However, in principle, the necessary basic messages could
   depend on the signaling application that NSIS is being used for,
   which means that we are not specific here about whether these
   messages are visible within the NTLP or only NSLP.

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   Note that the 'direction' column in the table below only indicates
   the 'orientation' of the message. The messages can be originated and
   absorbed at NF nodes as well as the NI or NR; an example might be NFs
   at the edge of a domain exchanging NSIS messages to set up resources
   for a flow across a it.

   Note the working assumption that responder as well as the initiator
   can release a reservation (comparable to rejecting it in the first
   place). It is left open if the responder can modify a reservation,
   during or after setup. This seems mainly a matter of assumptions
   about authorization, and the possibilities might depend on resource
   type specifics.

   | Name  |Direction|                  Semantics                  |
   |Request| I-->R   |     Create a new reservation for a flow     |
   |Modify | I-->R   |        Modify an existing reservation       |
   |       |(&R-->I?)|                                             |
   |Release| I-->R & |  Delete (tear down) an existing reservation |
   |       |  R-->I  |                                             |
   |Accept/| R-->I   |  Confirm (possibly modified?) or reject a   |
   | Reject|         |             reservation request             |
   |Notify | I-->R & |     Report an event detected within the     |
   |       |  R-->I  |  network (e.g. congestion condition or end  |
   |       |         |                of condition)                |
   |Refresh| I-->R   |      State management (see section 4.4)     |

   The table also explicitly includes a refresh message. This does
   nothing to a reservation except extend its lifetime, and is one
   possible state management mechanism for NSIS. This is considered in
   more detail in section 4.4.

4.4 State Management

   The prime purpose of NSIS is to manage state information along the
   path taken by a data flow. There two critical issues to be considered
   in building a robust protocol to handle this problem:
    *) The protocol must be scalable. It should minimize the state
   storage demands that it makes on intermediate nodes; in particular,
   storage of state per 'micro' flow is likely to be impossible except
   at the very edge of the network.

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    *) The protocol must be robust against failure and other conditions,
   which imply that the stored state has to be moved or removed.

   The total amount of state that has to be stored depends both on NSIS
   and on the specific signaling application in use. The signaling
   application might require per flow or lower granularity state;
   examples of each for the case of QoS would be IntServ or RMD (per
   'class' state) respectively. The NSIS protocol should not overburden
   an application that was otherwise lightweight in state requirement.
   However, depending on design details, it might require storage of
   per-flow state including reverse path peer addressing, simply for
   sending NSIS messages themselves.

   There are several robustness problems, which roughly align with the
   'layers' of the NSIS protocols of Figure 3, that can be handled by
   the soft state principle. (Independence of these layers therefore
   implies the danger of duplication of functionality.) This relies on
   periodic refresh of the state information with the current context,
   relying on invalid state being timed out. Soft state can be used
   either as the primary mechanism to handle the problem, or sometimes
   as a backup to some other approach.

    *) At the lowest level, soft state can be used to detect dead NSIS
   peers - loss of several periodic messages implies termination of the
   signaling. (The same inference can be made e.g. if failure is
   detected at the link layer.) The assumption is then that the
   corresponding reservation should be automatically deleted, and the
   deletion propagated along the remainder of the path.

    *) At the next level, in the event of a routing change (for example
   caused by network changes or end host mobility), reservation state
   should be removed from the old path and added to the new one. This
   will be handled automatically by periodic messaging, provided that
   the entities on the new path accept a Refresh message to install a
   new reservation. (A partial alternative is to have a routing-aware
   NSIS implementation, if the route change takes place at an NSIS-aware

    *) At the highest level, a particular signaling application might
   have timing limits associated with a particular reservation (e.g.
   credit limited network access). Periodic re-authorized requests can
   be used as part of the time control.

   All of these can be handled with a single soft state mechanism,
   although it may be hard to choose a single refresh interval and
   message loss threshold appropriate for all of them. Even where
   alternative approaches are possible, for example using knowledge of
   the fact that a routing change has occurred to trigger an explicit

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   release message, it seems that a soft state mechanism is always
   necessary as a backup.

4.5 Identity Elements

   NSIS will carry certain identifiers within the NTLP. The most
   significant identifier needs seem to be the following.

4.5.1  Flow Identification

   The flow identification is a method of identifying a flow in a unique
   way. All packets and/or messages that are associated with the same
   flow will be identified by the same flow identifier. In principle, it
   could be a combination of the following information (note that this
   is not an exclusive list of information that could be used for flow
    *) source IP address;
    *) destination IP address;
    *) protocol identifier and higher layer (port) addressing;
    *) flow label (typical for IPv6);
    *) SPI field for IPSec encapsulated traffic;
    *) DSCP/TOS field

   We've assumed here that the flow identification is not hidden within
   the NSLP, but is explicitly part of the NTLP. The justification for
   this is that it might be valuable to be able to do NSIS processing
   even at a node which was unaware of the specific signaling
   application; this would be a case of an NSIS forwarder with no
   interface to any resource management function. An example scenario
   would be NSIS messages passing through an addressing boundary where
   the flow identification had to be re-written.

   The very flexibility possible in flow classification is a possible
   source of difficulties: when wildcards or ranges are included, it is
   probably unreasonable to assume a standard classification capability
   in routers; on the other hand, negotiating this capability would be a
   significant protocol complexity.

4.5.2  Reservation Identification

   There are several circumstances where it is important to be able to
   refer to a reservation independently of whatever other information is
   associated with it. The prime example is a mobility-induced address
   change (handover) which required the flow identifier associated with
   a reservation to be rewritten without installing a totally new
   reservation (see section 5.3.1 for some security and scoping
   implications of this use). The same capability could also be used to
   simplify refresh or release messages in some circumstances, and might

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   be useful within the protocol to resolve reservation collisions
   (where both sender and receiver initiate for the same flow).

   A reservation identifier performs these roles. It is open how the
   reservation identifier space should be defined and managed, and what
   the scope of the identifier should be (only peer-peer, or end-end,
   when interpreted in conjunction with some of the addressing
   information). Some of the necessary identifier functions, especially
   to do with local operation of NSIS, may also be provided by lower
   layer signaling transport protocols.

4.5.3  NSLP Identification

   Since the NTLP can be used to support several NSLPs, there is a need
   to identify which one a particular NSIS message is being used for:
    *) processing incoming messages at a responder - the NTLP should be
   able to demultiplex these towards the appropriate signaling
    *) processing general NSIS messages at an NSIS aware intermediate
   node - if the node does not handle the specific signaling
   application, it should be able to make a forwarding decision without
   having to parse the upper layer information.

   Signaling application identifiers would probably require an IANA

5. NSIS Protocol Interactions

   So far as possible, the NSIS protocol should be usable in isolation,
   without explicitly depending on other protocols to operate. However,
   in many cases, NSIS functionality overlaps with the problem spaces of
   other protocols. In order to determine the boundaries which minimize
   any explicit interdependencies, these protocol interactions must be

   This is different from considering the use of NSIS protocols to
   support a particular signaling application, or example configurations
   in which NSIS might be deployed. These subjects are discussed in
   section 7.

5.1 Resource Management Interactions

   The NSIS protocol is used for signaling resource requests from an
   NSIS Initiator to an NSIS Responder. The NSIS protocol should be
   useful for many signaling applications, but should not be involved in
   any specific resource allocation or management techniques. As such,
   we need to define the interaction between an NSIS entity and what we
   will call the Resource Management Function (RMF). The RMF is

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   responsible for all resource provisioning, monitoring and assurance
   functions in the network.

   The RMF may interact with NSIS entities in two different ways: as a
   client or as a server.

   First, the RMF can act as a client towards the NSIS protocol, as a
   particular application triggering NSIS signaling for resources in the
   network. This is a special case of general NSIS triggering and will
   not be elaborated here. This case could for instance apply with
   multi-level NSIS signaling (section 7.5).

   Second, the RMF can act as a server towards the NSIS protocol. In
   that case, the signaling decision taken by the NF may depend on the
   content or processing of the NSIS payload.

   The RMF may or may not be co-located with the NSIS protocol
   processing. To cater for both cases, we define a (possibly logical)
   NF-RMF interface, see Figure 4. (As mentioned in section 3.1.1, the
   NI and NR could also interact with an RMF. Note that this could also
   be modeled as co-location of the NI&NF and NR&NF. This distinction
   should have no impact on the operation of the protocol.) Over this
   interface, information may be provided from the RMF about monitoring,
   resource availability, topology, configuration, and so on.
   Additionally, resource provisioning requests may be issued towards
   the RMF. Note that the actual implications for NSIS as a protocol are
   the same, regardless of whether the RMF is centralized or
   distributed, since NSIS sees the same interface towards the RMF in
   each case.

           +----+   NSIS   +----+   NSIS    +----+   NSIS   +----+
           | NI |==========| NF |====...====| NF |==========| NR |
           +----+          +----+           +----+          +----+
                              ^                ^
                              |                |
                              V                V
                           +----+           +----+
                           | RMF|           | RMF|
                           +----+           +----+

                   Figure 4: Basic NSIS-RMF Relationship

   One way to formalize the interface between the NF and the RMF is via
   a Service Level Agreement (SLA). The SLA may be static or it may be
   dynamically updated by means of a negotiation protocol. Such a
   protocol is outside the scope of NSIS.

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5.2 IP Routing Interactions

   Several situations may occur when routing diverges from standard
   layer 3 routing. These are summarized in the sections below.

5.2.1  Load Sharing

   Load sharing or load balancing is a network optimization technique
   that exploits the existence of multiple paths to the same destination
   in order to obtain benefits in terms of protection, resource
   efficiency or network stability. The significance of load sharing in
   the context of NSIS is that, if the load sharing mechanism in use
   will forward packets on any basis other than source and destination
   address, routing of NSIS messages using end-to-end addressing does
   not guarantee that the messages will follow the data path. In this
   section, we briefly survey what standard methods have been used for
   load sharing within standard routing protocols.

   In OSPF, load balancing can be used between equal cost paths [12] or
   unequal cost paths. An example of the latter approach is Optimized
   Multi Path (OMP). OMP discovers multiple paths, not necessarily equal
   cost paths, to any destinations in the network, but based on the load
   reported from a particular path, it determines which fraction of the
   traffic to direct to the given path. Incoming packets are subject to
   a (source, destination address) hash computation, and effective load
   sharing is accomplished by means of adjusting the hash thresholds.

   BGP [13][14] advertises the routes chosen by the BGP decision process
   to other BGP speakers. In the basic specification, routes with the
   same Network Layer reachability information (NLRI) as previously
   advertised routes implicitly replace the original advertisement,
   which means that multiple paths for the same prefix cannot exist.
   Recently, however, a new mechanism was defined that will allow the
   advertisement of multiple paths for the same prefix without the new
   paths implicitly replacing any previous ones [15]. The essence of the
   mechanism is that each path is identified by an arbitrary identifier
   in addition to its prefix.

   The distribution of traffic over the available path may be done per
   destination, per message in a round-robin fashion or with a
   predefined hashing function. The determination of the hashing image
   may take into account the source/destination IP address, QoS
   information such as the DSCP or protocol ID. When the routing
   decision is no longer based on the destination address only, however,
   there is a risk that data plane messages and control plane messages
   will not follow the same route.

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5.2.2  QoS Routing

   The are several proposals for the introduction of QoS awareness in
   the routing protocols. All of these essentially lead to the existence
   of multiple paths (with different QoS) towards the same destination.
   As such, they also contain an inherent risk for a divergence between
   control plane and data plane, similar to the load sharing case.

   For intra-domain traffic, the difference in routing may result from a
   QoS-aware traffic engineering scheme, that e.g. maps incoming traffic
   to LSPs based on multi-field classification. In BGP, several
   techniques for including QoS information in the routing decision are
   currently proposed. A first proposal is based on a newly defined
   BGP-4 attribute, the QoS_NLRI attribute [16]. The QoS_NLRI attribute
   is an optional transitive attribute that can be used to advertise a
   QoS route to a peer or to provide QoS information in along with the
   Network Layer Reachability Information (NLRI) in a single BGP update.
   A second proposal is based on controlled redistribution of AS routes
   [17]. It defines a new extended community (the redistribution
   extended community) that allows a router to influence how a specific
   route should be redistributed towards a specified set of eBGP
   speakers. The types of redistribution communities may result in a
   specific route not being announced to a specified set of eBGP
   speakers, that it should not be exported or that the route should be
   prepended n times.

5.2.3  Route pinning

   Route pinning refers to the independence of the path taken by certain
   data packets from reachability changes caused by routing updates from
   an Interior Gateway Protocol (OSPF, IS-IS) or an Exterior Gateway
   Protocol (BGP). This independence may for instance be caused by the
   configuration of static LSPs or by the establishment of explicitly
   routed LSPs by means of a signaling protocol (RSVP-TE or CR-LDP). If
   the NSIS signaling messages follow standard Layer 3 routing, this may
   cause a divergence between control plane and data plane. If
   reservations are made on the control plane, this may result in
   sending data along an unreserved path while maintaining a reservation
   on a path that is not used.

5.2.4  Route Changes

   In this section, we will explore the expected interworking between a
   signaling for resource BGP routing updates, although the same applies
   for any source of routing updates. The normal operation of the NSIS
   protocol will lead to the situation depicted in Figure 5, where the
   reserved resources match the data path.

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                    reserved +----+  reserved  +----+
                     ------->| NF |----------->| NF |
                             +----+            +----+
                                data path

                 Figure 5: Normal NSIS protocol operation

   A route change (triggered by a BGP routing update for instance) can
   occur while such a reservation is in place. In case of RSVP, the
   route change will be installed immediately and any data that is sent
   will be forwarded on the new path. This situation is depicted
   Figure 6.

                           Route update
                    reserved +----+  reserved  +----+
                     ------->| NF |----------->| NF |
                             +----+            +----+
                     ========== |
                             || |           +----+
                             || +---------->| NF |
                             ||             +----+
                               data path

                          Figure 6: Route Change

   Resource reservation on the new path will only be started once the
   next control message is routed along the new path. This means that
   there is a certain time interval during which resources are not
   reserved on (part of) the data path. To minimize this time interval
   several techniques could be considered. As an example, RSVP [18] has
   the concept of local repair, where the router may be triggered by a
   route change. In that case the RSVP node can start sending PATH
   messages directly after the route has been changed. Note that this
   option may not be available for NSIS if no per-flow state is kept in
   the NF.

   It is not guaranteed that the new path will be able to provide the
   same guarantees that were available on the old path. Therefore, in a
   more desirable scenario, the NF should wait until resources have been
   reserved on the new path before installing the route change. The
   route change procedure then consists of the following steps:
    1. NF receives a route announcement,
    2. Refresh messages are forwarded along the current path,

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    3. A copy of the refresh message is remarked as request and send
   along the new path that was announced,
    4. When the NF has been acknowledged about the reservations on the
   new path the route will be installed and the traffic will flow along
   the new path.

   Another example related to route changes is denoted as severe
   congestion and is explained in [19]. This solution adapts to a route
   change, when a route change creates a congestion on the new routed

5.2.5  Router Redundancy

   In some environments, it is desired to provide connectivity and per
   flow or per class resource management with high-availability
   characteristics, i.e. with rapid transparent recovery even in the
   presence of route changes. This may involve interactions with the
   basic protocols which are used to manage the routing in this case,
   such as VRRP [20]. A future version of this document may consider
   interactions between NSIS and such protocols in support of high
   availability functionality.

5.3 Mobility Interactions

   The interactions between mobility and resource signaling protocols
   have been extensively analyzed in recent years, primarily in the
   context of RSVP and Mobile IP interaction (e.g. [21]), but also in
   the context of other types of network (e.g. [22]). This analysis work
   has shown that some difficulties in the interactions are quite deep
   seated in the detailed design of these protocols; however, the
   problems and their possible solutions fall under five broad headings.
   The main issue is to limit the period after handovers during which
   the resource state has not been installed on the path, in particular
   the new part of the path.

   We can use this work as the starting point for considering the
   framework aspects of a new signaling protocol like NSIS, which will
   need to interwork with mobility signaling, from Mobile IP to mobility
   paradigms based on micromobility or application layer approaches.

5.3.1  Addressing and Encapsulation

   A mobility solution typically involves address reallocation on
   handover (unless a network supports per host routing) and may involve
   special packet formats (e.g. the routing header and Home Address
   option of MIPv6). Since NSIS may depend on end system addresses for
   forwarding signaling messages and defining flows (section 4.5.1), the
   special implications of mobility for addressing need to be

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   considered. Examples of possible approaches that could be used to
   solve the addressing and encapsulation problem are as follows:
    *) Use a flow identification based on low level IP addresses (e.g.
   the Care of Address) and other 'standard' fields in the IP header.
   This makes least demands on the packet classification engines within
   the network. However, it means that even on a part of the flow path
   which is unchanged, the reservation will need to be modified to
   reflect the changed flow identification (see section 5.3.3).
    *) Use a flow identification that does not change (e.g. based on
   Home Address); this is the approach assumed in [23]. This simplifies
   the problem of reservation update, at the likely cost of considerably
   complicating the flow identification requirements.

   In the first approach, to prevent double reservation, NSIS nodes need
   to be able to recognize that a reservation with the new flow
   identifier is to be correlated with an existing one. The reservation
   identifier (section 4.5.2) was introduced for exactly this purpose.
   Note that this would require the reservation identifier to have
   (secure) end to end significance. (An additional optimization here
   would be use a local mobility management scheme to localize the
   visibility of the address change.)

   The feasibility and performance of this first approach needs to be
   assessed, including a detailed analysis of the signaling scenarios
   after a handover. However, given the high impact of requiring more
   sophisticated packet classifiers, initially it still seems more
   plausible than the second approach. This implies that the NSIS
   initiator should define flows in terms of real (care of) addresses
   rather than virtual (home) addresses. Thus, it would have detailed
   access to lower layer interface configuration (cf. section 4.1),
   rather than operating as a pure application level daemon as is
   commonplace with current RSVP implementations.

5.3.2  Localized Path Repair

   In any mobility approach, a handover will cause at least some changes
   in the path of upstream and downstream packets. NSIS needs to install
   new state on the new path, and remove it on the old. Provided that
   some NSIS node on the joined path - the crossover router - can
   recognize this situation (which again depends on reservation
   identification), state installation and teardown can be done locally
   between it and the mobile node. (This may have implications for which
   entities are allowed to generate which message types, see section
   4.3.2). It seems that the basic NSIS framework already contains the
   fundamental components necessary for this.

   A critical point here is the signaling that is used to discover the
   crossover router. This is a generalization of the problem of finding

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   next-NSIS-hop nodes: it requires extending the new path over several
   hops until it intersects the old one. This is easy for uplink traffic
   (where the mobile is the sender), but much harder for downlink
   traffic without signaling via the correspondent. There is no reason
   for the crossover routers for uplink and downlink flows to be the
   same, even for the same correspondent. The problem is discussed
   further in [24].

5.3.3  Reservation Update on the Unchanged Path

   On the path between the crossover router(s) and the correspondent, it
   is necessary to avoid, if possible, double reservations, but rather
   to update the reservation state to reflect new flow identification
   (if this is needed, which is the default assumption of section
   5.3.1). Examples of approaches that could be used to solve this
   problem are the following:
    *) Use a reservation state definition that does not change even if
   the flow definition changes (see Section 4.5.2). In this case this
   problem is solved.
    *) Use signaling all the way to the correspondent node (receiver end
   host), accepting the additional latency that this might impose.
    *) Use an NSIS-capable crossover router that manages this
   reservation update autonomously (more efficiently than the end
   nodes), with similar considerations to the local path repair case.

5.3.4  Interaction with Mobility Signaling

   In existing work on mobility protocol and resource signaling protocol
   interactions, several framework proposals describing the protocol
   interactions have been made. Usually they have taken existing
   protocols (Mobile IP and RSVP respectively) as the starting point; it
   should be noted that an NSIS protocol might operate in quite a
   different way. In this section, we provide an overview of how these
   proposals would be reflected in framework of NSIS. The mobility
   aspects are described using Mobile IP terminology, but are generally
   applicable to other network layer mobility solutions. The purpose of
   this overview is not to select or prioritise any particular approach,
   but simply to point out how they would fit into our framework and any
   major issues with them.

   We can consider that two signaling processes are active: mobility
   signaling (e.g. binding updates or local micromobility signals) and
   NSIS. The discussion so far considered how NSIS should operate. There
   is still a question of how the interactions between the NSIS and
   mobility signaling should be considered.

   The basic case of totally independent specification and
   implementation seems likely to lead to ambiguities and even

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   interoperability problems (see [23]). At least, the addressing and
   encapsulation issues for mobility solutions that use virtual links or
   their equivalents need to be specified in an implementation-neutral

   A type of 'loose' integration is to have independent protocol
   definitions, but to define how they trigger each other - in
   particular, how the mobility protocol triggers NSIS to send
   refresh/modify/tear messages. A pair of implementations could use
   these triggers to improve performance, primarily reducing latency.
   (Existing RSVP modification consider the closer interaction of making
   the RSVP implementation mobility-routing aware, e.g. so it is able to
   localize refresh signaling; this would be a self contained aspect of
   NSIS.) This information could be developed for NSIS by analyzing
   message flows for various mobility signaling scenarios as was done
   in [21].

   An even tighter level of integration is to consider a single protocol
   carrying both mobility and resource information. Logically, there are
   two cases:
    1. Carry mobility routing information (a 'mobility object') in the
   resource messages, as is done in [23]. (The prime purpose in this
   approach is to enable crossover router discovery.)
    2. Carry resource signaling in the mobility messages, typically as a
   new extension header. This was proposed in [25] and followed up
   in [26]; [27] also anticipates this approach. In our framework, we
   could consider this a special case of NSIS layering, with the
   mobility protocol playing the role of the signaling transport (as
   in 4.3.1).
   The usefulness of this class of approach depends on a tradeoff
   between specification simplicity and performance. Simulation work is
   under way to compare the performance of the two approaches in the
   case of RSVP and micromobility protocols.

   Other modes of interaction might also be possible. The critical point
   with all these models is that the general solutions developed by NSIS
   should not depend fundamentally on the choice of any particular
   mobility protocol. Especially if it has interdomain scope, tight
   integration would have major deployment issues (even loose
   integration could require NSIS implementations to hook into multiple
   different mobility protocols). Therefore, any tightly integrated
   solution should be considered out of scope of initial NSIS
   development, and even in the long term is probably only applicable if
   it can be localized within a particular part of the network.

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5.3.5  Interaction with Fast Handoff Support Protocols

   In the context of mobility between different access routers, it is
   common to consider performance optimizations in two areas: selection
   of the optimal access router to handover to, and transfer of state
   information between the access routers to avoid having to regenerate
   it in the new access router after handover. The seamoby working group
   is developing solutions for these protocols for pure IP based
   networks (CARD[28] and CT[29] respectively); other networks, which
   use NSIS for resource signaling within the network, may use different
   types of solution.

   In this section, we consider how NSIS should interact with these
   functions, however they are implemented. Detailed solutions are not
   proposed, but the way in which interaction these functions is seen
   within the NSIS framework is described. NSIS should be able to
   operate independently of these protocols. However, significant
   performance gains could be achieved if they could be made to
   cooperate. In addition, the resource signaling aspects of these
   protocols could profitably use a common set of resource types and
   definitions, since they will probably be supporting the same overall
   signaling application.

   The question arises, what the mode of interaction should be:
   independent operation, NSIS triggering access router discovery and
   state transfer, or vice versa. The questions for the two cases seem
   to be independent.

   For access router discovery, a typical model of operation is that the
   mobile carries out an information gathering exercise about a range of
   capabilities. In addition, where those capabilities relate purely to
   the AR and mobile, there is no role for NSIS (its special
   functionality is not relevant). However, considering resource
   aspects, one aspect of the AR 'capability' is resource availability
   on the path between it and the correspondent, and NSIS should be able
   to fulfill this part. Indeed, this is effectively precisely the
   application considered in [26], where it is a sort of special case of
   resource signaling during handover.

   Therefore, a possible model of access router discovery/NSIS
   relationship is that some entity in a candidate AR triggers NSIS
   using resource and reservation information (including reservation id)
   from the current AR to find out about what would be available on the
   new path. Note that this should be a query rather than an actual
   reservation; this semantic could be included either in the NTLP or

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   The case of state transfer is more complex. There are two obvious
   options, corresponding to whether one transfers just signaling
   application state or NSIS state as well:
    1. "State transfer triggering NSIS": A state transfer process passes
   the 'raw' resource state to the new AR. This triggers a new instance
   of NSIS to request that resource.
    2. "NSIS using state transfer": NSIS transfers its own state
   information from the old to the new AR. It can then carry out the
   same update signaling as though it was a single 'virtual AR' which
   had just had a topology change towards the correspondent. (This is
   essentially the conceptual model of [21].)

   The first model is simpler, and maybe more in line with the basic
   state transfer expectation; however, it seems hard to avoid double
   reservations since the two NSIS protocol instances are not
   coordinated. Therefore, the second model seems more appropriate. An
   advantage of the 'virtual AR' model is that it ensures that the
   impact of the interaction is limited to the NSIS instances at ARs
   themselves, since the rest of the network must be able to handle a
   topology change anyway.

   Note that there is an open issue of who is responsible between the
   mobile and AR to decide that the state transfer procedures have not
   happened for whatever reason - e.g. because they were not even
   implemented - and take recovery action to have the mobile refresh
   reservations promptly. It appears this has to be an NSIS
   responsibility in the AR, and probably requires a custom notification
   message for this circumstance.

5.4 NSIS Interacting with NATs

   Because at least some NSIS messages will almost inevitably contain
   address and possibly higher layer information as payload (see section
   4.5.1), we must consider the interaction between NSIS and address
   translation devices (NATs). As well as 'traditional' NATs of various
   types (as defined in [30]) very similar considerations would apply to
   some IPv4/v6 transition mechanisms such as SIIT [31].

   In the simplest case of an NSIS unaware NAT in the signaling path,
   payloads will be uncorrected and the signaling will be for the
   incorrect flow. Applications could attempt to use STUN [32] or
   similar techniques to detect and recover from the presence of the
   NAT. Even then, NSIS would have to use a well known encapsulation
   (TCP/UDP/ICMP) to avoid being dropped by the more cautious low-end
   NAT devices.

   A simple 'NSIS-aware' NAT would require flow identification
   information to be in the clear and not integrity protected. An

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   alternative conceptual approach is to consider the NAT functionality
   being part of NSIS message processing itself, in which case the
   translating node can take part natively in any NSIS security
   mechanisms. Depending on NSIS layering, it could be possible for this
   processing to be done in an NSIS node which was otherwise ignorant of
   any particular NSIS signaling applications.

   Note that all of this discussion is independent of the use of NSIS
   for general control of NATs (and firewalls). This is considered in
   section 7.4.

6. Security and AAA Considerations

   A framework is meant to create boundaries for a later protocol and to
   describe the interaction between the protocol and its environment.
   Security issues usually turn out to have impacts in the interaction
   of these protocols and must therefore be appropriately addressed in
   such a framework. This section describes these general security
   issues, and in particular considers the interactions between NSIS and
   authentication, authorization and accounting. Together with
   authentication the protection of the signaling messages is addressed
   - namely replay and integrity protection.

   An initial analysis of the major security threats that apply in the
   typical of scenario where NSIS is expected to be used is given in
   [5]; these threats are described at the overall scenario level, in
   terms of the impact on users and networks. However, in any given
   scenario, NSIS will be just one part of the overall solution.
   Ultimately, the framework will need to define which of these threats
   need to be handled by NSIS (and which parts of NSIS) and which by the
   other components. Currently, we can only make initial scoping
   assumptions of this sort.

6.1 Authentication

   Authentication and key establishment for a signaling protocol should
   be seen as a two-phase process. The first-phase is usually more
   performance intensive because of a larger number of roundtrips,
   denial of service protection, cross-realm handling, interaction with
   other protocols and the likely larger cryptographic computation
   associated with it. As stated in section 4.3, this functionality
   could be provided externally to NSIS, e.g. by reusing a standard
   protocol which already included this functionality.

   At the end of this phase it should be possible to create or derive
   security associations that are usable for the protection of the NSIS
   signaling messages themselves. The functionality required here
   relates to (data origin) authentication (including integrity and

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   replay protection) of individual signaling messages. Key
   establishment, rekeying, synchronization issues are issue that may be
   addressed here depending on the specific method. In any case the
   protection applied to each signaling message must be fast and

   When using cryptography to protect signaling messages, it is obvious
   that a node must be able to select the appropriate security
   association in order to be able to apply signaling message
   protection. This should just be a general point about endpoint
   identity issues. Hence the identifier must be available to the
   transmitting node. Regarding identities there is a need to support
   different identity types to enable the flexible usage of several
   signaling initiators and receivers. Supporting static configuration
   and dynamic learning of these identities should be provided.

6.2 Authorization

   Authorization information can be seen in an abstract form as "Can the
   resource requestor be trusted to pay for the reservation?". This
   abstraction is supported by the fact that reservations require some
   form of incentive to use some 'default' resource (or vice versa -
   penalty for not reserving too many resources). In general, the
   semantics of the authorisation will depend on the signaling
   application in use. The implication of this is that NSIS will not
   directly make authorisation decisions; instead, the authorisation
   information must be fed into the resource management function
   (section 5.1) which actually decides on the request.

   Some negotiation needs to take place to determine which node will
   take responsibility for authorising a resource request, the
   implication being that the same node will ultimately be accounted to
   for it. Such a negotiation needs to be flexible enough to support
   most currently deployed schemes (e.g. reverse charging, etc.) while
   keeping efficiency and simplicity in mind. This negotiation might be
   executed before starting resource signaling (assumed in section 4.2),
   although it could also be part of the NSIS signaling messages (as in
   some proposals dealing with charging and RSVP). Since information
   needs to be sent to the networks, some information needs to be
   included to provide the network with the necessary information to
   start the authorisation process. Hence fully opaque objects might not
   always be the proper choice.

   It is not clear if 'initiation' of a reservation is related to
   willingness to accept authorisation responsibility. (Current
   practices tend to assume that flow originators are responsible.) In
   any case, it seems unlikely that a domain will make a cost-incurring
   request of a peer domain without already having received a matching

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   request from the peer in the other direction - in other words,
   requests must propagate between domains in the same direction as
   authorisation responsibility.

   If this argument is correct, and if NSIS initiation and authorisation
   responsibility are decoupled, it must be possible for the
   authorisation responsibility to propagate both in the direction
   initiator->responder and vice versa. Also, if both [flow] sender and
   receiver initiation are possible, service descriptions must include
   information about the authorisation policy to be applied, which must
   be imposed consistently along the whole path. These issues should be
   analyzed to determine if 1, 2 or 4 alternative scenarios are possible
   and realistic.

   A second question is that of which entities actually authorise which.
   One end user must ultimately get authorisation for the request (this
   may or may not be assumed to be the NSIS initiator, see below). There
   are then two possible models for how this authorisation is done
   throughout the path.

   The first model assumes that each network along the path is able to
   authenticate and authorise the user directly. The implication for a
   signaling protocol is that the user credentials cannot be removed
   after the first hop and have to be further included in the message
   when forwarded to other networks. Every node along the path is then
   able to verify the user and to provide policy based admission

   The second model assumes that the user credentials are removed at the
   first hop. The first network knows the user identity requesting the
   resources but does not include this information further along the
   path. The first network can therefore be seen as acting on behalf of
   the originator to take responsibility to enable further reservations
   to be done along the path i.e. in particular to the next network
   only. This procedure is then applied on a hop-by-hop basis.

   Note that both models are independent of whether a traditional
   subscription based approach or an alternative means of payment (such
   as pre-pay on on-line charging by the visited network) is used. These
   issues only have an impact for the transmission of accounting records
   and for a requirement to execute an online verification whether a
   user still has sufficient credits/funds; therefore, these details do
   not affect NSIS operation.

6.3 Accounting

   It is obvious that accounting/charging is an important part for the
   success and the acceptance of a resource signaling protocol. Most of

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   the thinking in this area is derived from the specific case of
   signaling for QoS; however, we make an initial working assumption
   that the same paradigm should apply to any signaling application for
   which accounting is necessary. We make the general assumption here
   that accounting records are generated by the resource management
   function based entirely on traffic measurements and processed in
   accordance with the authorisation information that was used in
   deciding to grant the request in the first place.

   Therefore, NSIS plays no further part in this activity; the
   accounting records are transmitted using the AAA infrastructure, and
   charging and billing for the overall service is carried out at some
   higher layer. This would include feedback to applications (and users)
   about total session cost (of which the network resource cost might be
   only a part). An open issue is whether a query (without actually
   making a reservation) to the network should also generate a
   chargeable event; this could be considered as an aspect of the
   service definition.

6.4 End-to-End vs. Peer Relationship Protection

   It is reasonable to assume that peer relationship security (with
   chain-of-trust) is used for most signaling environments relevant to
   NSIS. Especially the separation of signaling into different network
   parts (intra-domain within the access network, end-node to access
   network, intra-domain, and so on) and new proposals regarding
   mobility and proxy support show that traditional end-to-end signaling
   is not applicable in every environment (or possibly only in a minor
   number of environments). End-to-end security in a signaling protocol
   is actually problematic for two reasons:

    1. Even if the messages use the address of the end-host (to support
   routing), the messages still have to be interpreted and modified
   along the path.

    2. The only property that can be achieved by using end-to-end
   security is that one end-host can be assured that the other end-host
   included some parameters (possibly resource parameters) that have not
   been modified along the path. Nodes along the path usually do not
   have the possibility to cryptographically verify the protected
   message parts. If the two end-points negotiate which side has to pay
   for the reservation (or possibly how much and other parameters)
   within the signaling protocol then there is a need to protect this
   information. This leads to the question which protocols are executed
   before the signaling message exchange starts. If resource parameters
   and payment/charging related information are already exchanged
   beforehand as part of a separate protocol (possibly SIP) then there
   is little need to protect (and possibly retransmit) this information

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   at the NSIS level basis. In most cases an opaque token to link the
   different protocols may be sufficient.

7. NSIS Application Scenarios

   This section considers various application scenarios or deployment
   configurations for NSIS. Our goal is that an NSIS protocol designed
   according to the framework presented in the previous sections should
   be able to support these scenarios if implemented appropriately;
   therefore, this section does not form part of the framework
   definition, but rather provides examples of how NSIS can be used to
   do something interesting. In the long term, some of this material may
   be contained in specific NSIS applicability statements.

7.1 NSIS and Existing Resource Signaling Protocols

   It is hoped that NSIS could eventually achieve widespread use for
   resource signaling. However, it is bound to have to inter-operate
   with existing resource signaling protocols at least during transition
   and possibly long term. The prime example for QoS is RSVP, although
   other proprietary or domain specific protocols (e.g. bandwidth broker
   related) may also be considered. A related issue is that NSIS will be
   only one part of the solution: it will always need to interwork with
   other resource-related protocols (e.g. COPS).

   Analyzing the constraints on NSIS that come from these requirements
   is hard before further refinement of the framework has been carried
   out and critical assumptions pinned down. However, we can identify
   various modes of interoperation, and the attributes of the framework
   that will make them easy.

   Firstly, we allow for NSIS use over a 'long range', in conjunction
   with a different protocol locally (e.g. intra-domain); or, the two
   roles could be reversed. This is actually very similar to the case of
   use of NSIS layered over itself (section 7.5). In the case where the
   'inter-layer' interaction is mediated via resource management, the
   same should approach should work with non-NSIS protocols. What needs
   to be validated here is whether NSIS layering requires the exchange
   of NSIS specific information between the layers.

   A second issue is that NSIS should be deployable within an
   environment without radical changes to supporting resource (or AAA)
   related protocols. The main issue here is that NSIS should be
   flexible in its ability to support different service definitions (and
   possibly flow classifications). This is already one of the main goals
   of the framework presented here.

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   The final point is that it should be possible to use NSIS over one
   network region, concatenated with another protocol over an adjacent
   region. The main issue here, apart from the flexible service and flow
   capabilities already mentioned, is that NSIS should be adaptable in
   what it assumes about signaling paths (e.g. to interwork with both
   path-coupled and decoupled solutions), and in initiation paradigms
   (e.g. to interwork with sender and receiver initiated solutions).

7.2 NSIS Supporting Centralized QoS Resource Management

   One area of application for the NSIS protocol is for QoS resource
   reservation and provisioning. The NSIS protocol may be used to
   provide intra-domain or inter-domain QoS bandwidth reservation setup
   by means of its interaction with the RMF. In what follows we assume
   that the NEs are colocated with an admission control entity that has
   a logical (abstract) view on the resources managed by the RMF, as
   described in section 5.1.

   The NEs in a domain can interface with an RMF managing the complete
   domain, in which case, the abstract topology view provided between
   NSIS and RMF can be formalized as a Service Level Agreement (SLA).
   This situation is depicted schematically in Figure 7.

             +----+   NSIS     +-----+    NSIS     +----+
             | NI |============| NF  |=============| NR |
             +----+            +-----+             +----+
                                  | SLA
                               | RMF  |

       Figure 7: Resource Reservation using RMF as a Server to NSIS

   In case of centralized RMF, the SLA or its technical part, the
   Service Level Specification (SLS) [33] specifies the resource
   guarantees that the RMF needs to provide to the NF. These guarantees
   apply between one or more ingress and egress points of the network.
   The SLS also specifies the availability and reliability of the
   service. In the case of QoS signaling, it may refer to a bandwidth
   service with certain performance guarantees regarding delay, jitter
   or packet loss. The SLS interface can be automated by means of an SLS
   negotiation protocol. This allows for more dynamical SLS
   modifications and the exchange of notification messages with the NF.
   These can for instance be used to provide monitoring feedback from
   the RFM to the NF.

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   The decoupling of NSIS signaling and network management by means of
   an SLS has some attractive properties:
    *) It allows a Network Provider to easily share the use of its
   infrastructure between several Service Providers using NSIS signaling
   to provide their service.
    *) It allows a clear separation between resource provisioning and
   management and reservation signaling and admission control.
    *) It relieves the NF from several tasks, making it potentially more
   scalable in the core of the network.

   The NF can perform either per-flow or per-class admission control
   decisions based on the requested QoS information and on the
   reservation state it keeps regarding active flows (or classes).
   Keeping per-flow state may be required for policing,
   accounting/billing and explicit reservation teardown. These functions
   are mandatory in the access or edge of the network. Conveniently,
   this is also where the processing needed to maintain per-flow state
   will remain manageable. In the core, this approach may not scale very
   well and per-class state may be used as an alternative that is very
   scalable and allows for a lightweight processing of signaling
   messages. With per-class state, however, we lose the ability to
   directly notify the NI in case of unsolicited network events because
   the affected flows cannot be identified. Instead, the NI needs to be
   indirectly notified in response to a refresh message which in turn
   mandates the use of soft-state with separate messages or message
   structure for requests and refreshes.

   The RMF can execute its network provisioning functions according to
   its internal policies. In the easiest case, it may run an
   overprovisioned network with only monitoring capabilities in order to
   follow up on the delivered performance. In more complex scenarios, it
   may use a whole array of network optimization tools in order to
   deliver and maintain service quality according to the SLS. This may
   require network monitoring, the installation and use of appropriate
   protection mechanisms and providing feedback regarding actual traffic
   performance to the NSIS entity.

   Alternatively, the NSIS protocol may be used for resource
   provisioning. In that case, the RMF acts as a client towards the NSIS
   protocol, as a particular "application" triggering an NI for
   resources in the network. This situation is depicted in Figure 8.

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                    +----------| RMF  |----------+
                   /           +------+           \
                  /                                \
                 /                                  \
                /                                    \
             +----+   NSIS     +-----+    NSIS     +----+
             | NI |============| NF  |=============| NR |
             +----+            +-----+             +----+

                 Figure 8: NSIS for Resource Provisioning

   In this case the RMF is providing traffic classification and
   conditioning functions. An example of such functionality is described
   in [34]. The packet "classifiers" select the packets in a traffic
   stream based on the content of some portion of the packet header. The
   traffic "conditioner" performs metering, shaping, policing,
   scheduling and/or re- marking of packets to ensure that the traffic
   entering a node conforms to a certain predefined policy.

7.3 NSIS Supporting Distributed Resource Management

   Section 7.2 described the situation where NSIS is supporting a
   centralized RMF. This section introduces the situation where NSIS is
   supporting a distributed RMF. When the RMF is distributed in the
   network, a protocol for communication with the NI, NF, NR may not be
   required. In this case the RMF is providing traffic classification
   and conditioning functions; an example of such functionality is
   described in [34]. Figure 9 shows how a distributed RMF could
   interact with the NSIS protocol.

     +----+   NSIS   +-----+    NSIS   +-----+   NSIS   +----+
     | NI |==========| NF  |====...====| NF  |==========| NR |
     +----+          +-----+           +-----+          +----+
     +----+          +-----+           +-----+          +----+
     |RMF |          | RMF |           | RMF |          |RMF |
     +----+          +-----+           +-----+          +----+

              Figure 9: Distributed RMF as a server for NSIS

7.4 NSIS for Middlebox Signaling

   As well as the use for 'traditional' QoS signaling, it should be
   possible to use NSIS to set up flow-related state in middleboxes
   (firewalls, NATs, and so on). Requirements for such communication are
   given in [35], and initial discussions of NSIS-like solutions are
   contained in [36], [37] and [38]. A future version of this document

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   may contain more details on how an NSIS should be used for this type
   of signaling application.

7.5 Multi-Level NSIS Signaling

   This section describes a way of separating the NSIS signaling
   protocol into more than one hierarchical level. In this section three
   levels of hierarchy are considered (see Figure 10); however, the
   approach is quite general to more (or fewer) levels: the important
   issue is the use of NSIS at more than one level at all.

   The lowest hierarchical level ("level 1") provides basic resource
   management functionality related to scalable, simple and fast soft
   state maintenance and to transport functions, such as reliable
   delivery of signaling messages, congestion control notification and
   load sharing adaptation. Soft state that is maintained by this level
   is usually per traffic class based.

   The second hierarchical level ("level 2") is more complex than level
   1 as regards soft state maintenance. Soft state maintained by this
   hierarchical level is usually per flow. Note that this level, like
   level 1, also supports transport functions. When an NSIS edge-to-edge
   multi-domain protocol is used, level 2 stretches beyond domain
   boundaries and is applied on all the edges of the domains that are
   included in the multidomain region.

   The third hierarchical level ("level 3") includes a set of upper-
   level signaling functions that are specific to particular signaling
   applications. Such functions could, for example, be security, policy,
   billing, etc.

   As shown in Figure 10, the three hierarchical levels might be applied
   on different NSIS entities.

   This three-level architecture for NSIS signaling can be provided by
    *) a single end-to-end NSIS protocol that supports all three
   hierarchical levels
    *) two independent NSIS protocols: Level 3 is supported by an end-
   to-end NSIS protocol, and levels 1 and 2 are supported by another
   edge-to-edge NSIS protocol.

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   |-----|   |-------|                           |-------|   |-----|
   |level|<--| level |<--------------------------| level |<->|level|
   |  3  |<--|   3   |                           |   3   |<->|  3  |
   |-----|   |-------|                           |-------|   |-----|
   |     |   |       |                           |       |   |     |
   |     |   |-------|                           |-------|   |     |
   |     |   | level |<------------------------->| level |   |     |
   |     |   |   2   |                           |   2   |   |     |
   |     |   |-------|                           |-------|   |     |
   |     |   |       |                           |       |   |     |
   |-----|   |       |   |
              -------     -------|   |-------|   |-------|   |-----|
   |level|<->| level |<->| level |<->| level |<->| level |<->|level|
   |  1  |<->|   1   |<->|   1   |<->|   1   |<->|   1   |<->|  1  |
   |-----|   |-------|   |-------|   |-------|   |-------|   |-----|
     NI         NF          NF          NF          NF         NR
              (edge)     (interior)  (interior)   (edge)

          Figure 10: Three level architecture for NSIS signaling

   The components in the scenario are as follows:
    *) NI (NSIS Initiator): can be an end-host or a proxy and can
   process and use the "level 1" and "level 3" protocol components
    *) NR (NSIS Responder): can be an end-host or a proxy and can
   process and use the "level 1" and "level 3" protocol components
    *) NF (NSIS Forwarder) (edge): can be a Diffserv edge, MPLS edge,
   etc. It can process and use the "level 3", "level 2" and "level 1"
   protocol components. Usually, "level 2" provides an interworking
   between "level 1" and "level 3" protocol components.
    *) NF (interior): can be any router within a domain. It can process
   and use only the "level 1" protocol component. The "level 3" and
   "level 2" protocol components are not processed (used or checked).

   The hierarchical level separation can be provided by supporting a
   hierarchical object structure. In other words, the NSIS protocol
   objects should be structured and positioned within the NSIS messages
   in a hierarchical way, i.e., first the "level 1" objects, then the
   "level 2" objects and finally the "level 3" objects.

8. Open Issues

   The following issues are currently open points within the framework.
   They are summarized here to provide a single overview.

    1. It is not clear which of the NI, NF and NR can modify or release
   existing reservations (this is essentially an authorisation issue).
   (Section 3.3.2.)

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    2. It is not clear whether NSIS entities relate to each other only
   locally (peer-peer) or whether longer distance, non-local
   interactions and state have to be managed and stored. (Section

    3. NSIS messages could be addressed either explicitly (to the
   neighboring peer) or implicitly, using the flow endpoint addresses.
   (Section 3.3.4.)

    4. It is not clear where to draw the boundaries between the NTLP and
   NSIS signaling layer, and how to establish the extent to which the
   requirements of the diverse signaling applications considered for
   NSIS should influence NTLP functionality. (Section 3.3.5.)

    5. If NSIS has explicit acknowledgement and notification messages,
   it is open whether they should relate to anything beyond the
   immediate peer relationship. (Section 3.3.6.)

    6. To function as part of a complete system, the NSIS protocol may
   need to be supported by extensions to other protocols. These
   extensions are still to be identified. (Section 4.2.)

    7. The NSIS protocol could be constructed on the services offered by
   lower layer protocols, but the dividing line between NSIS and these
   lower layers is not fixed. Use of standard lower layer protocols may
   be difficult if 'end-to-end addressing' (see section 3.3.4) is used.
   (Section 4.3.1.)

    8. It is commonly expected that a future resource signaling protocol
   would need to use abstract reservation identifiers. However, the
   precise properties needed of these identifiers are unclear, and
   enabling their secure use may be hard. (Sections 4.5.2 and 5.3.2.)

    9. Use of some routing techniques (e.g. load sharing or QoS
   routing), even in remote parts of the network, could be incompatible
   with naive use of end-to-end addressing. (Sections 5.2.1 and 5.2.2.)

    10. The correct flow identification semantics need to be defined in
   the case where mobility encapsulations might make it ambiguous which
   addresses to use. (Section 5.3.1.)

    11. The interactions between mobility and resource signaling during
   path updating need to be further analyzed, especially from the point
   of view of combined overall latency. (Section 5.3.2 and 5.3.3.)

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9. Change History

9.1 Changes from draft-ietf-nsis-fw-00.txt

   1. Editorial fix in 'classifier' definition (section 2).
   2. Added definition of 'peer determination' (finding the right peer
      for a given flow) (section 2).
   3. Added definitions for 'sender' and 'receiver' refers to role
      relative to data packets always (section 2, and minor fixes in
      sections 3.2.6 and 3.2.7).
   4. Updated references.
   5. Replaced 'peer session' with 'peer relationship' and 'peer
      session addressing' with 'peer-peer addressing' (throughout), and
      attempted redraw of Figure 1 to make it less session-like
      (corresponding changes in Figure 4, Figure 7, Figure 8, and
      Figure 9).
   6. Added terms for transport and signaling layer protocols
      (NTLP/NSLP) and explanation in new section 3.1.3. New terms used
      throughout (significant rewrites to section 4, although this
      should be at most a change of emphasis rather than technical
   7. Clarified that section 3.2 is about possible modes of operation
      (listing alternatives, not all to be supported).
   8. Clarified 'local object' definition in 3.2.4.
   9. Added working assumption in 3.3.1 that end-to-end routing is done
      by sequentially determining the right peer in the NTLP, and no-
      one discovers or uses global topology information for this.
   10.Added working assumption in 3.3.3 that NTLP operates only
   11.Slightly trimmed 3.3.5 in preparation for turning it into a
      discussion about NSIS layering boundaries.
   12.Clarified in section 4.2 that peer determination doesn't have to
      be a separate capability, just that it could additionally be done
   13.Fixed some flow identification terminology inconsistencies in
      section 5.3.1.

9.2 Changes from draft-hancock-nsis-fw-00.txt

    1. Changed title, document name and dates.
    2. Updated references.
    3. Editorial fix in NSIS Forwarder definition (section 2).
    4. Revised section 3.2.1 (path-coupled terminology), now used
   consistently in the rest of the document. Likewise, 'signaling
   application' terminology used consistently in remainder of document.
    5. Split old section 5 into new sections (new 5 "real interactions",
   new 7 "how to use NSIS to do something useful").

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    6. Added new resource management text for section 5.1; slight
   smoothing to balance centralized and distributed, and comment on
   NI/NF/NR distinction.
    7. Added VRRP placeholder in routing section of section 5 (5.2.5).
    8. Added section 5.4 on NSIS/NAT interactions based on Melinda's
    9. Added new text for resource management in section 7.2; slightly
   trimmed and made clearer that it is mainly discussing the centralized
   case (and isn't specific to the inter-domain case). Comment that it's
   OK to use the Q-word here since we aren't talking about the NSIS
   protocol but a use of the NSIS protocol.
    10. Added section 7.3 for discussion of how NSIS can be used in a
   distributed resource management environment.
    11. Added a placeholder in section 7.4 for use of NSIS for midcom
   (no technical content, but references to the midcom requirements and
   the TIST and NEC drafts).
    12. Moved open issues from section 3.3.1 to new section 8 (left
   assumptions behind).
    13. Added this changes section 9.


   1  Bradner, S., "The Internet Standards Process -- Revision 3", BCP
      9, RFC 2026, October 1996.

   2  Brunner, M., "Requirements for QoS Signaling Protocols", draft-
      ietf-nsis-req-05.txt (work in progress), November 2002

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

   4  Manner, J. and X. Fu, "Analysis of Existing Quality of Service
      Signaling Protocols", draft-ietf-nsis-signalling-analysis-00.txt
      (work in progress), October 2002

   5  Tschofenig, H., "NSIS Threats", draft-ietf-nsis-threats-00.txt
      (work in progress), October 2002

   6  Katz, D., "IP Router Alert Option", RFC 2113, February 1997

   7  Partridge, C., A. Jackson, "IPv6 Router Alert Option", RFC 2711,
      October 1999

   8  Braden, R., and B. Lindell, "A Two-Level Architecture for Internet
      Signaling", draft-braden-2level-signaling-01.txt (work in
      progress), November 2002

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                  Next Steps in Signaling: Framework     November 2002

   9  Stewart, R., Q. Xie, K. Morneault, C. Sharp, H. Schwarzbauer,
      T. Taylor, I. Rytina, M. Kalla, L. Zhang, V. Paxson, "Stream
      Control Transmission Protocol", RFC 2960, October 2000

   10 Kent, S., R. Atkinson, "Security Architecture for the Internet
      Protocol", RFC 2401, November 1998

   11 Westberg, L., G. Karagiannis, D. Partain, V. Rexhepi., "Framework
      for Edge-to Edge NSIS Signaling", draft
                 -                           -westberg-nsis-edge-edge-
      framework-00.txt (work in progress), May 2002

   12 Apostolopoulos, G., D. Williams, S. Kamat, R. Guerin, A. Orda,
      T. Przygienda, "QoS Routing Mechanisms and OSPF Extensions", RFC
      2676, August 1999

   13 Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)", RFC
      1771, March 1995

   14 Rekhter, Y. and T. Li, "A Border Gateway Protocol 4 (BGP-4)",
      draft-ietf-idr-bgp4-17.txt (work in progress), January 2002

   15 Walton, D., D. Cook, A. Retana and J. Scudder, "Advertisement of
      Multiple Paths in BGP", draft-walton-bgp-add-paths-00.txt (work in
      progress), May 2002

   16 Cristallo, G., C. Jacquenet, "Providing Quality-of-Service
      Indication by the BGP-4 Protocol: the QoS_NLRI Attribute", draft-
      jacquenet-qos-nlri-04.txt (work in progress), March 2002 (expired)

   17 Bonaventure, O., S. De Cnodder, J. Haas, B. Quoitin and R. White,
      "Controlling the redistribution of BGP Routes", draft-bonaventure-
      bgp-redistribution-02.txt (work in progress), February 2002

   18 Braden, R., L. Zhang, S. Berson, S. Herzog, S. Jamin, "Resource
      ReSerVation Protocol (RSVP) -- Version 1 Functional
      Specification", RFC 2205, September 1997

   19 Westberg, L., M. Jacobsson, G. Karagiannis, S. Oosthoek, D.
      Partain, V. Rexhepi, R. Szabo, P. Wallentin, "Resource Management
      in Diffserv (RMD) Framework", draft-westberg-rmd-framework-02.txt
      (work in progress), October 2002

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   20 Knight, S., D. Weaver, D. Whipple, R. Hinden, D. Mitzel, P. Hunt,
      P. Higginson, M. Shand, A. Lindem, "Virtual Router Redundancy
      Protocol", RFC2338, April 1998

   21 Thomas, M., "Analysis of Mobile IP and RSVP Interactions", draft-
      thomas-nsis-rsvp-analysis-00.txt (work in progress), October 2002

   22 Partain, D., G. Karagiannis, P. Wallentin, L. Westberg, "Resource
      Reservation Issues in Cellular Radio Access Networks", draft-
      westberg-rmd-cellular-issues-01.txt (work in progress), June 2002

   23 Shen, C. et al., "An Interoperation Framework for Using RSVP in
      Mobile IPv6 Networks", draft-shen-rsvp-mobileipv6-interop-00.txt
      (work in progress), July 2001 (expired)

   24 Manner, J., et al., "Localized RSVP", draft-manner-lrsvp-00.txt
      (work in progress), May 2002

   25 Chaskar, H. and R. Koodli, "A Framework for QoS Support in Mobile
      IPv6", draft-chaskar-mobileip-qos-01.txt (work in progress), March
      2001 (expired)

   26 Fu, X., et al, "QoS-Conditionalized Binding Update in Mobile
      IPv6", draft-tkn-nsis-qosbinding-mipv6-00.txt (work in progress),
      January 2002 (expired)

   27 Kan, Z., "Two-plane and Three-tier QoS Framework for Mobile IPv6
      Networks", draft-kan-qos-framework-01.txt (work in progress), July

   28 Trossen, D., G. Krishnamurthi, H. Chaskar, J. Kempf, "Issues in
      candidate access router discovery for seamless IP-level handoffs",
      draft-ietf-seamoby-cardiscovery-issues-04.txt (work in progress),
      October 2002

   29 Kempf, J., "Problem Description: Reasons For Performing Context
      Transfers Between Nodes in an IP Access Network", RFC3374,
      September 2002

   30 Srisuresh, P. and M. Holdrege, "IP Network Address Translator
      (NAT) Terminology and Considerations", RFC2663, August 1999

   31 Nordmark, E., "Stateless IP/ICMP Translation Algorithm (SIIT)",
      RFC2765, February 2000

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   32 Rosenberg, J., J. Weinberger, C. Huitema, R. Mahy, "STUN - Simple
      Traversal of UDP Through Network Address Translators", draft-ietf-
      midcom-stun-03.txt (work in progress), October 2002

   33 Danny Goderis, et al. "Service Level Specification Semantics and
      Parameters", draft-tequila-sls-02.txt (work in progress), February
      2002 (expired)

   34 Blake, S., D. Black, M. Carlson, E. Davies, Z. Wang, W. Weiss, "An
      Architecture for Differentiated Services", RFC2475, December 1998

   35 Swale, R. P., P. A. Mart, P. Sijben, S. Brim, M. Shore, "Middlebox
      Communications (midcom) Protocol Requirements", RFC3304, August

   36 Shore, M., "Towards a Network-friendlier Midcom", draft-shore-
      friendly-midcom-01.txt (work in progress), June 2002

   37 Shore, M., "The TIST (Topology-Insensitive Service Traversal)
      Protocol", draft-shore-tist-prot-00.txt (work in progress), May

   38 Brunner, M. and M. Stiemerling, "Middlebox Signaling in a NSIS
      Framework", draft-brunner-nsis-mbox-fmwk-00.txt (work in
      progress), June 2002


   The authors would like to thank Anders Bergsten, Bob Braden, Maarten
   Buchli, Melinda Shore and Hannes Tschofenig for significant
   contributions in particular areas of this draft. In addition, the
   authors would like to acknowledge Marcus Brunner, Danny Goderis,
   Eleanor Hepworth, Cornelia Kappler, Hans De Neve, David Partain,
   Vlora Rexhepi, and Lars Westberg for insights and inputs during this
   and previous framework activities.

Author's Addresses

   Ilya Freytsis
   Cetacean Networks Inc.
   100 Arboretum Drive
   Portsmouth, NH 03801
   email: ifreytsis@cetacean.com

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                  Next Steps in Signaling: Framework     November 2002

   Robert Hancock
   Roke Manor Research
   Old Salisbury Lane
   SO51 0ZN
   United Kingdom
   email: robert.hancock@roke.co.uk

   Georgios Karagiannis
   Ericsson EuroLab Netherlands B.V.
   Institutenweg 25
   P.O.Box 645
   7500 AP Enschede
   The Netherlands
   email: georgios.karagiannis@eln.ericsson.se

   John Loughney
   Nokia Research Center
   11-13 Italahdenkatu
   00180 Helsinki
   email: john.loughney@nokia.com

   Sven Van den Bosch
   Francis Wellesplein 1
   B-2018 Antwerpen
   email: sven.van_den_bosch@alcatel.be

Full Copyright Statement

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                  Next Steps in Signaling: Framework     November 2002

   The limited permissions granted above are perpetual and will not be
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