draft-willis-p2psip-concepts-02(1012).txt

IETF12号的文档

SIPPING Working Group                                     D. Willis, Ed.
Internet-Draft                                             Cisco Systems
Intended status: Experimental                                   D. Bryan
Expires: April 15, 2007               SIPeerior Technologies and William
                                                                  & Mary
                                                             P. Matthews
                                                                   Avaya
                                                                 E. Shim
                                            Panasonic Digital Networking
                                                              Laboratory
                                                        October 12, 2006


             Concepts and Terminology for Peer to Peer SIP
                    draft-willis-p2psip-concepts-02

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   This Internet-Draft will expire on April 15, 2007.

Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines concepts and terminology for use of the Session



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   Initiation Protocol in a peer-to-peer environment where the
   traditional proxy-registrar function is replaced by a distributed
   mechanism that might be implemented using a distributed hash table or
   other distributed data mechanism with similar external properties.
   This document includes a high-level view of the functional
   relationships between the network elements defined herein, a
   conceptual model of operations, and an outline of the related open
   problems that might be addressed by an IETF working group.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [1].





































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Table of Contents

   1.  Background . . . . . . . . . . . . . . . . . . . . . . . . . .  5

   2.  Definitions  . . . . . . . . . . . . . . . . . . . . . . . . .  5

   3.  Discussion . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     3.1.  What Kinds of P2PSIP Peers and Clients Might Exist?  . . . 10
     3.2.  Reference Model  . . . . . . . . . . . . . . . . . . . . . 10
     3.3.  Example Signalling Message Flows . . . . . . . . . . . . . 13
       3.3.1.  P2PSIP Peer contacts P2PSIP Peer . . . . . . . . . . . 13
       3.3.2.  P2PSIP Client contacts P2PSIP Peer . . . . . . . . . . 14
       3.3.3.  Conventional SIP Device using a Proxy Peer . . . . . . 15
       3.3.4.  Conventional SIP Device Using a Redirect Peer  . . . . 16
     3.4.  Conceptual Outline of Operations . . . . . . . . . . . . . 18
       3.4.1.  Enrolling and Inserting an P2PSIP Peer . . . . . . . . 18
       3.4.2.  More on The Difference Between a Peer, Client, and
               User Agent . . . . . . . . . . . . . . . . . . . . . . 18
       3.4.3.  Enrolling a User and Inserting a P2PSIP User Agent . . 19
       3.4.4.  Bootstrapping  . . . . . . . . . . . . . . . . . . . . 19

   4.  Questions  . . . . . . . . . . . . . . . . . . . . . . . . . . 20
     4.1.  PP2PSIP Peer Protocol  . . . . . . . . . . . . . . . . . . 20
     4.2.  P2PSIP Client Protocol . . . . . . . . . . . . . . . . . . 20
     4.3.  How To Find Media Relays?  . . . . . . . . . . . . . . . . 20
     4.4.  How Do We Find Gateways? . . . . . . . . . . . . . . . . . 21
     4.5.  Peer-Adjacency Through NATs  . . . . . . . . . . . . . . . 21
     4.6.  Cryptotransparency . . . . . . . . . . . . . . . . . . . . 21
     4.7.  Record Formats . . . . . . . . . . . . . . . . . . . . . . 21
     4.8.  Peer and Client Enrollment Protocols . . . . . . . . . . . 21
     4.9.  Peer and User Credentials  . . . . . . . . . . . . . . . . 21
     4.10. Bootstrapping  . . . . . . . . . . . . . . . . . . . . . . 21
     4.11. Credential Recovery  . . . . . . . . . . . . . . . . . . . 22
     4.12. Overlapping Domains  . . . . . . . . . . . . . . . . . . . 22
     4.13. Hybrid Domains . . . . . . . . . . . . . . . . . . . . . . 22
     4.14. Admissions Control . . . . . . . . . . . . . . . . . . . . 22
     4.15. Users versus Resources . . . . . . . . . . . . . . . . . . 22

   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 23

   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 23

   7.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 23

   8.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
     8.1.  Normative References . . . . . . . . . . . . . . . . . . . 23
     8.2.  Informative References . . . . . . . . . . . . . . . . . . 24




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   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
   Intellectual Property and Copyright Statements . . . . . . . . . . 26

















































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1.  Background

   One of the fundamental problems in multimedia communications between
   Internet nodes is that of a discovering the IP address at which a
   given correspondent can be reached.  Correspondents are frequently
   identified by distinguished names, perhaps represented in the form of
   a universal resource indicator (URI) [2].

   The Session Initiation Protocol (SIP) [3] commonly addresses this
   task assuming that the domain part of the URI indicates an internet
   host address or internet domain name using the Domain Name System
   (DNS) [4].  SIP's location process [5] assumes that host part of the
   URI indicates either the target SIP user agent (UA), or a proxy that
   has knowledge of how to to reach the target UA, presumably gained
   through SIP's registration process.

   This approach, referred to herein as "Conventional SIP" or "Client/
   Server SIP", assumes a relatively fixed hierarchy of SIP routing
   proxies (servers) and SIP user agents (clients).  The routing proxies
   are typically resolvable using conventional Internet mechanisms with
   static IP addresses and associated DNS entries.  This structure may
   not be ideal in all cases, including specifically ad-hoc, serverless,
   and reduced-administration scenarios.  As an alternative, several
   authors [7] [8] [9] [10] have proposed using peer-to-peer (P2P) [11]
   approaches to solving the correspondent discovery problem.  The
   motivations for a P2P approach in SIP have been documented in [12].

   This document offers a consolidation of the more important terms and
   concepts from several of the above documents, presented in the
   context of a reference model for peer-to-peer SIP (P2PSIP).  It is
   intended that this document serve as a starting point for describing
   the work needed to resolve a number of open questions such that an
   IETF working group could be chartered to do the work needed to
   resolve these questions and present a standard solution.  The authors
   believe that this goal is roughly consistent with that of a Protocol
   Model as defined in [13].


2.  Definitions

   We provide a list of terms used, as well as alternate forms that have
   been used for these in drafts or discussions.  In general, the
   thought is to use the primary suggested form for clarity -- we have
   included the other forms for simplicity and to provide a "mapping" to
   existing drafts.  Defined terms include:






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   Overlay Network:  An overlay network is a computer network which is
      built on top of another network.  Nodes in the overlay can be
      thought of as being connected by virtual or logical links, each of
      which corresponds to a path, perhaps through many physical links,
      in the underlying network.  For example, many peer-to-peer
      networks are overlay networks because they run on top of the
      Internet.  Dial-up Internet is an overlay upon the telephone
      network. <http://en.wikipedia.org/wiki/P2P_overlay>

   P2P Network:  A peer-to-peer (or P2P) computer network is a network
      that relies primarily on the computing power and bandwidth of the
      participants in the network rather than concentrating it in a
      relatively low number of servers.  P2P networks are typically used
      for connecting nodes via largely ad hoc connections.  Such
      networks are useful for many purposes.  Sharing content files (see
      file sharing [16]) containing audio, video, data or anything in
      digital format is very common, and realtime data, such as
      telephony traffic, is also passed using P2P technology.
      <http://en.wikipedia.org/wiki/Peer-to-peer>.  A P2P Network may
      also be called a "P2P Overlay" or "P2P Overlay Network" or "P2P
      Network Overlay" , since its organization is not at the physical
      layer, but is instead "on top of" an existing Internet Protocol
      network.

   P2PSIP:  A communications protocol related to the Session Initiation
      Protocol (sip) [3] that extends SIP by using peer-to-peer
      techniques for resolving the targets of SIP requests.

   P2PSIP Overlay:  A P2PSIP Overlay is an association, collection, or
      federation of nodes that provides SIP registration, SIP request
      routing, and similar functions using a P2P organization, as
      defined by "P2P Network" above.  Other forms: overlay.

   P2PSIP Peer:  A node participating in a P2PSIP Overlay that provides
      storage and routing services (fully participates in the P2P
      routing) to other nodes in that P2PSIP Overlay.  Each P2PSIP Peer
      is presumed to have a unique identifier within the P2PSIP Overlay.
      Each P2PSIP Peer may or may not be coupled to one or more P2PSIP
      User Agents.  Within the P2PSIP Overlay, the peer is capable of
      performing several different operations, including: joining and
      leaving the overlay, routing requests within the overlay, storing
      information on behalf of the overlay, putting information into the
      overlay, and getting information from the overlay.  Other forms:
      overlay peer or node, peer or node, superpeer or supernode (in
      systems with peers and clients), peer.






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   P2PSIP Client:  A node participating in a P2PSIP Overlay that
      provides neither routing nor route storage and retrieval functions
      to that P2PSIP Overlay.  The P2PSIP Client interacts with the
      P2PSIP Overlay only to request the insertion of routing
      information (put in a Contact), request the retrieval of routing
      information (get a Contact), or to request the routing of a
      message to elsewhere in the P2PSIP Overlay.  Unlike the P2PSIP
      Peer, the client is presumed not to have a unique identifier
      within the overlay.  In cases where conventional SIP is used for
      the P2PSIP Client protocol, this entity could be identical to a
      standard SIP user agent.  A P2PSIP Client may be coupled to one or
      more P2PSIP Overlay User Agents.  A P2PSIP Client is a logical
      subset of a P2PSIP Peer; anything a P2PSIP Client can do, a P2PSIP
      Peer can do as well.  Other forms: overlay client, client.

   P2PSIP Resource (User):  An addressable user endpoint, entity,
      service, or function within a P2PSIP Overlay.  Examples include
      but are not limited to humans, automata, bridges, mixers, media
      relays, gateways, and media storage.  Other forms: resource
      (user).

   P2PSIP Overlay Identifier:  Information that identifies a specific
      P2PSIP Overlay.  All the P2PSIP Peers in a particular P2PSIP
      Overlay have the same P2PSIP Overlay Identifier.  This is may be
      scoped to a name within the DNS, but other scopes may apply,
      particularly in ad-hoc environments.  Short forms: overlay name,