Internet Engineering Task Force                              J. Loughney
Internet-Draft                                                     Nokia
Expires: September 7, 2006                                 March 6, 2006

                        NSIS Extensibility Model

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Copyright Notice

   Copyright (C) The Internet Society (2006).


   This document discusses the Next Steps in Signaling extensibility
   model.  This model is based upon a two-layer model, where there is a
   transport layer and a signaling application model.  This two-layer
   provides the ability to develope new signaling applications, while
   retaining the use of a common transport layer.  This document will
   serve as guidence on how the NSIS architecture can be extended.

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Table of Contents

   1.  Requirements notation  . . . . . . . . . . . . . . . . . . . .  3
   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
     2.1.  NSIS Extensibility Types . . . . . . . . . . . . . . . . .  3
   3.  GIST Extensibility . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  NSLP Identifiers . . . . . . . . . . . . . . . . . . . . .  4
     3.2.  Message Routing Methods  . . . . . . . . . . . . . . . . .  4
     3.3.  Protocol Indicators  . . . . . . . . . . . . . . . . . . .  5
     3.4.  Router Alert Values  . . . . . . . . . . . . . . . . . . .  5
   4.  NSLP Extensibility . . . . . . . . . . . . . . . . . . . . . .  6
     4.1.  Common Functionality Among Signaling Applications  . . . .  7
   5.  QoS Model Extensibility  . . . . . . . . . . . . . . . . . . .  7
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . .  7
   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  7
   8.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . .  7
   9.  References . . . . . . . . . . . . . . . . . . . . . . . . . .  8
     9.1.  Normative References . . . . . . . . . . . . . . . . . . .  8
     9.2.  Informative References . . . . . . . . . . . . . . . . . .  8
   Author's Address . . . . . . . . . . . . . . . . . . . . . . . . .  9
   Intellectual Property and Copyright Statements . . . . . . . . . . 10

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1.  Requirements notation

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in [1].

2.  Introduction

   The Next Steps in Signaling Framework NSIS Framework [2] details a
   basic two-layer framework for signaling on the Internet.  The
   document decomposes signaling into a two-layer model, into a generic
   transport layer and specific signaling layers.

   This model allows for an extensible model for different signaling
   needs on the the Internet.  Currently, the NSIS working group is
   working on two main signaling applications - QoS signaling [3] and
   NAT/Firewall signaling [4].  It is expected that there will be more
   signaling applications.

   The NSIS Transport Layer Protocol, GIST (General Internet Signaling
   Transport) GIST [5] defines a basic protocol for routing and
   transport of per-flow signaling along the path taken by that flow
   through the network; managing the underlying transport and security

   Above GIST can one or more NSIS Signaling Layer protocols, which can
   signal for things such as QoS, firewall control and NAT signaling.QoS
   NSLP [3], NAT/FW NSLP [4].  These signaling applications manage their
   state by using the services that the GIST provides them for

   This two layer approach allows for signaling applications to be
   developed indepently of the transport.  As it is likely that the
   functionality entities for different signaling applications will be
   distinct, not all path elements support NSIS signaling will require
   that a specific signaling application is present - only those nodes
   that will be maintaining some signaling application state need to
   support the signaling application.

2.1.  NSIS Extensibility Types

   Generally, NSIS protocols can be extended in multiple ways.  This
   secition is and overview of the mechansims used.  The extensibility
   rules are based upon the procedures by which IANA assigns values:
   "Standards Action" (as defined in [IANA]), "IETF Action", "Expert
   Review", and "Organization/Vendor Private", defined below.

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   Extensions subject to "IETF Action" require either a Standards Track
   RFC, Experimental RFC or an Information RFC.

   Extensions subject to "Expert Review" refer to values that are to be
   reviewed by an Expert designated by the IESG.  The code points from
   these ranges are typically used for experimental extensions; such
   assignments MUST be requested by either Experimental or Information
   RFCs that document their use and processing, and the actual
   assignments made during the IANA actions for the document.  Values
   from "Expert Review" ranges MUST be registered with IANA.

   "Organization/Vendor Private" ranges refer to values that are
   enterprise-specific.  In this way, different enterprises, vendors, or
   Standards Development Organizations (SDOs) can use the same code
   point without fear of collision.

   In the NSIS protocols, experimental code points are allocated for
   experimentation, usually within closed networks, as explained in RFC
   3692.[7].  If these experiments yield useful results, it is assumed
   that they will be formally allocated by one of the above mechanisms.

3.  GIST Extensibility

   GIST is Major extensibility options for GIST are:

3.1.  NSLP Identifiers

   Each signaling application requires one of more NSLPIDs (different
   NSLPIDs may be used to distinguish different classes of signaling
   node, for example to handle different aggregation levels or different
   processing subsets).  An NSLPID must be associated with a unique RAO
   value.  IETF Action is required to allocate a new NSLP Identifier.

3.2.  Message Routing Methods

   GIST allows the idea of multiple Message Routing Methods (MRM).  The
   message routing method is indicated in the leading 2 bytes of the MRI
   object.  GIST allocates 2 bits for experimental Routing Methods, for
   use in closed networks for experimentation purposes.  Standards
   Action is required to allocate new Routing Methods.

   Experimental NSLPs are required to be able to use experimental MRMs,
   and the experimental NSLP is not supported, then the MRM is ignored.
   The expectation is that the experimental MRM is used within a closed
   network, for experimental purposes, as explained in RFC 3692.[7]

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3.3.  Protocol Indicators

   The GIMPS design allows the set of possible protocols to be used in a
   messaging association to be extended.  Every new mode of using a
   protocol is given by a Protocol Indicator, which is used as a tag in
   the Node Addressing and Stack Proposal objects.  New protocol
   indicators require IETF Action.  Allocating a new protocol indicator
   requires defining the higher layer addressing information in the Node
   Addressing Object that is needed to define its configuration.

3.4.  Router Alert Values

   Router Alert Option (RAO) values are allocated on the basis of IETF
   consensis.  However, new RAO values SHOULD NOT be allocated for each
   new NSLP.  Careful consideration needs to be exercised when choosing
   to allocate a new RAO value.  This section discusses some
   considerations on how to choose if an existing RAO option should be
   chosen or a new RAO should be allocated for an NSLP

   The use of the RAO is the primary mechanism to indicate that an GIST
   message should be intercepted by a particular node.  There are two
   basic reasons why a GIST node might wish not to intercept a
   particular message.  The first reason would be because the message is
   for a signaling application that the node does not process.  The
   second reason would be because the node is processes signaling
   messages at the aggregate level, not for individual flow, even though
   the signaling application is present on the node.  However, these
   reasons do not preclude a node processing several RAO values,
   implying it supports several different signaling applications.

   Some of this information can be encoded in the RAO value field, which
   then allows messages to be filtered on the fast path.  There is a
   tradeoff between two approaches here, whose evaluation depends on
   whether the processing node is specialised or general purpose:

   Fine-Grained: The signaling application (including specific version)
   and aggregation level are directly identified in the RAO value.  A
   specialised node which handles only a single NSLP can efficiently
   ignore all other messages; a general purpose node may have to match
   the RAO value in a message against a long list of possible values.

   Coarse-Grained> RAO values are allocated are ased on common
   applications or sets of applications (such as 'All QoS Signaling
   Applications').  This speeds up the processing in a general purpose
   node, but a specialised node may have to carry out further processing
   on the GIST common header to identify the precise messages it needs
   to consider.

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   These considerations imply that the RAO value should not be tied
   directly to the NSLPID, but should be selected for the application on
   broader considerations of likely deployment scenarios.  Note that the
   exact NSLP is given in the GIMPS common header, and some
   implementations may still be able to process it on the fast path.
   The semantics of the node dropping out of the signaling path are the
   same however the filtering is done.  Which is to say that the RAO
   does not have to have a one-to-one relation to a specific NSLPID, the
   RAO must be uniquely derivable from the NSLPID.

   There is a special consideration in the case of the aggregation
   level.  In this case, whether a message should be processed depends
   on the network region it is in (specifically, the link it is on).
   There are then two basic possibilities:

   All routers have essentially the same algorithm for which messages
   they process, i.e. all messages at aggregation level 0.  However,
   messages have their aggregation level incremented on entry to an
   aggregation region and decremented on exit.

   Router interfaces are configured to process messages only above a
   certain aggregation level and ignore all others.  The aggregation
   level of a message is never changed; signaling messages for end to
   end flows have level 0, but signaling messages for aggregates are
   generated with a higher level.

   The first technique requires aggregating/deaggregating routers to be
   configured with which of their interfaces lie at which aggregation
   level, and also requires consistent message rewriting at these
   boundaries.  The second technique eliminates the rewriting, but
   requires interior routers to be configured also.  It is not clear
   what the right trade-off between these options is.

4.  NSLP Extensibility

   An NSLP roughly should correspond to a class of signaling
   application, which requires some state maintenance along a network
   path.  Signaling applications should be generic enough to allow for
   state manipulation for a common set of funtions.  This allows for an
   architecture which allows for flexible network deployment, without
   over-burdening nodes with extra signaling applications.

   New NSLPs should be created when there is a new signaling
   application.  Creating new NSLPs which only slightly modify existing
   NSLPs is not recommended as it will increase deployment complexity
   (common nodes would need to support multiple NSLPs for similar

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4.1.  Common Functionality Among Signaling Applications

   While NSIS has adopted a two-layer signaling approach, in practice,
   there is much in common between different NSLPs.  Efforts should be
   made to ensure some high-level of compatibililty among signaling
   applications, which could be reused by some implementations in order
   to combine multiple signaling applications into one implementation,
   but that is an implementation decision.

5.  QoS Model Extensibility

   The QoS NSLP provides signaling for QoS reservations on the Internet.
   The QoS NSLP decouples the resource reservation model or architecture
   from the signaling.  The QoS specification is defined in QSpec [6].
   New QoS Models require IETF action, which defines the elements within
   the QSpec.  See QSpec [6] for details.

   A key part of the QoS model is support a common language, which can
   be shared among several QOSMs.  These QSPEC parameters ensure a
   certain level of interoperability of QOSMs.  Optional QSPEC
   parameters support the extensibility of the QoS NSLP to other QOSMs
   in the future.  The node initiating the NSIS signaling adds an
   Initiator QSPEC that must not be removed, thereby ensuring the
   intention of the NSIS initiator is preserved along the signaling

6.  IANA Considerations

   This document outlines the basic rules for extending NSIS protocols.
   This instructions IANA on allocation policies for NSIS protocols.

7.  Security Considerations

   This document is an informational document, outlining the
   extensibility model of the NSIS protocol suite.  As such, this
   document does not impact the security of the Internet directly.

8.  Acknowledgements

   This document borrows some ideas and some text from RFC3936 [8],
   Procedures for Modifying the Resource reSerVation Protocol (RSVP).

   Robert Hancock provided text for much of the GIST section.  Claudia
   Keppler have provided feedback on this draft.

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   Allison Mankin and Bob Braden suggest that this draft be worked on.

9.  References

9.1.  Normative References

   [2]  Hancock, R., "Next Steps in Signaling: Framework",
        draft-ietf-nsis-fw-07 (work in progress), December 2004.

   [4]  Stiemerling, M., "NAT/Firewall NSIS Signaling Layer Protocol
        (NSLP)", draft-ietf-nsis-nslp-natfw-09 (work in progress),
        February 2006.

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

   [3]  Manner, J., "NSLP for Quality-of-Service signalling",
        draft-ietf-nsis-qos-nslp-09 (work in progress), February 2006.

   [6]  Ash, J., "QoS-NSLP QSPEC Template", draft-ietf-nsis-qspec-08
        (work in progress), December 2005.

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

9.2.  Informative References

   [7]  Narten, T., "Assigning Experimental and Testing Numbers
        Considered Useful", BCP 82, RFC 3692, January 2004.

   [8]  Kompella, K. and J. Lang, "Procedures for Modifying the Resource
        reSerVation Protocol (RSVP)", BCP 96, RFC 3936, October 2004.

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Author's Address

   John Loughney
   Itamerenkatu 11-13
   Helsinki  00180

   Phone: +358504836242

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