Peer-to-Peer Session Initiation Protocol
Peer-to-Peer Session Initiation Protocol WG
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The Peer-to-Peer (P2P) Session Initiation Protocol working group
(P2PSIP WG) is chartered to develop protocols and mechanisms for the
use of the Session Initiation Protocol (SIP) in settings where the
service of establishing and managing sessions is principally handled
by a collection of intelligent endpoints, rather than centralized
servers as in SIP as currently deployed. A number of cases where such
an architecture is desirable have been documented.
The work focuses on collections of nodes called "P2PSIP peers" and
"P2PSIP clients". P2PSIP peers manifest a distributed namespace in
which overlay users are identified and provides mechanisms for
locating users or resources within the P2PSIP overlay. P2PSIP clients
differ from P2PSIP peers primarily in that they do not store
information in the overlay, but only use it to locate users and
resources. P2PSIP clients and peers use the resolution services of the
peers as an alternative to the SIP discovery process of RFC 3263. In
this way, P2PSIP offers an alternative mechanism for determining the
correct destination for SIP requests. The working group's initial
charter scope will be to produce protocols to enable this alternate
mechanism for RFC 3263 functionality. Session management, messaging,
and presence functions are performed using conventional SIP.
This group's primary tasks are to produce:
1. An overview document explaining concepts, terminology, rationale,
and illustrative use cases for the remaining work.
2. A proposed standard defining a P2PSIP Peer Protocol. This protocol
is used between P2PSIP overlay peers, some of which may be behind
NATs. This protocol will define how the P2PSIP peers collectively
provide for user and resource location in a SIP environment with no or
minimal centralized servers. This protocol may or may not be
syntactically based on SIP, a decision to be made by the WG. The group
will identify and require one base P2P algorithm (likely a particular
Distributed Hash Table (DHT) algorithm), while allowing for additional
optional algorithms in the future.
3. Optionally, a proposed standard defining a P2PSIP Client Protocol
for use by P2PSIP clients, some of which may be behind NATs. This
protocol will define how the P2PSIP clients query and/or modify, the
resource location information of the overlay. While clearly a logical
subset of the P2PSIP Protocol, the WG will determine if the P2PSIP
Client Protocol is a syntactic subset of the P2PSIP Peer Protocol, and
whether the P2PSIP Client Protocol builds on the SIP protocol.
4. A usage document. This document will address how the protocols
defined above, along with existing IETF protocols, can be used to
produce systems to locate a P2PSIP peer or client, identify appropriate
resources to facilitate communications (for example media relays), and
establish communications between the users of these P2PSIP peers or
clients, without relying on centralized servers. Additionally, the
document will explain how P2PSIP and conventional SIP entities can
The initial work will assume the existence of some enrollment process
that provides a unique user name, credentials, and an initial set of
bootstrap nodes if that is required by the protocols. Developing a
non-centralized enrollment process is not in scope.
The work planned for the P2PSIP working group is distinct from, but
requires close participation with other IETF WGs, particularly SIP,
SIPPING, SIMPLE, BEHAVE and MMUSIC. The group cannot modify the
baseline SIP behavior, define a new version of SIP, or attempt to
produce a parallel protocol for session establishment. If the group
determines that any capabilities requiring an extension to SIP are
needed, the group will seek to define such extensions within the SIP
working group using the SIP change process (RFC 3427). Similarly,
existing tools developed in the BEHAVE and MMUSIC groups will be used
for NAT traversal, with extensions or changes desired to support P2PSIP
presented to the BEHAVE or MMUSIC working groups.
The working group will assume that NATs and firewalls exist in the
Internet, and will ensure that the protocols produced work in their
presence as much as possible. Similarly, the WG will avoid making
protocol design decisions that would preclude the creation of anonymous
communications systems using techniques such as onion routing to
conceal the IP addresses of P2PSIP peers.
P2P networks pose unique security and privacy problems because an
adversarial relationship may exist between nodes. Attackers can mount
both integrity attacks on the stored data and denial of service
attacks on the system as a whole. The WG will not attempt a solution
to these issues for P2P networks in general. In order to simplify this
problem, the WG will assume that all participants in the system are
issued unique identities and credentials through some mechanism not in
the scope of this working group, such as a centralized server, and
that the data stored in the network will be authenticated by the
storing entity in order to address the integrity issue and to some
extent alleviate the DoS issue. Because signaling dialogs may be
routed through intermediate P2PSIP peers which may be untrusted by the
originating SIP UA, the WG will address the issue of establishing
authenticated signaling dialogs through such untrusted relays.
P2P systems also have privacy issues because the nodes that store data
objects and route requests are unrelated to the clients which want to
communicate. In the design of the P2PSIP protocol, the WG will assess
these privacy issues and determine to what extent they need to be
alleviated. The protocol document will contain a complete description
of the privacy properties of P2PSIP.
The following topics are excluded from the Working Group's scope:
1. Issues specific to applications other than locating users and
resources for SIP-based communications and presence.
2. Solving "research" type questions related to P2PSIP or P2P in
general. The WG will instead forward such work to the IRTF P2PRG or
other RG as appropriate. Examples include fully distributed schemes for
assuring unique user identities and the development of P2P-based
replacements for DNS.
3. Locating resources based on something other than URIs. In other
words, arbitrary search of attributes is out of scope, but locating
resources based on their URIs is in scope. Using URIs need not imply
using the DNS or having a record in the DNS for the URI.
4. Multicast and dynamic DNS based approaches as the core lookup
mechanism for locating users and resources. Approaches based on these
technologies may be reasonable ways to solve similar problems but that
is not the focus of this WG. These techniques may be in-scope for
locating bootstrap peers/servers or for interoperation with