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P2PSIP                                                          D. Bryan
Internet-Draft                              SIPeerior Technologies, Inc.
Intended status: Informational                                   E. Shim
Expires: January 3, 2008                                   Locus Telecom
                                                             B. Lowekamp
                                               SIPeerior; William & Mary
                                                            July 2, 2007

    Use Cases for Peer-to-Peer Session Initiation Protocol (P2P SIP)

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Copyright Notice

   Copyright (C) The IETF Trust (2007).


   This document attempts to identify and classify use cases of P2P
   based SIP.  It does not attempt to exhaustively enumerate these
   cases, and is focused exclusively on cases related to real-time IP

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3
   3.  Use Cases  . . . . . . . . . . . . . . . . . . . . . . . . . .  4
     3.1.  Global Internet Environment  . . . . . . . . . . . . . . .  4
       3.1.1.  Public P2P VoIP Service Providers  . . . . . . . . . .  4
       3.1.2.  Open Global P2P VoIP Network . . . . . . . . . . . . .  4
       3.1.3.  Presence Using Multimedia Consumer Electronics
               Devices  . . . . . . . . . . . . . . . . . . . . . . .  5
       3.1.4.  Multimedia content sharing via Application Layer
               Multicasting . . . . . . . . . . . . . . . . . . . . .  5
     3.2.  Security Demanding Environments  . . . . . . . . . . . . .  5
       3.2.1.  Impeded Access . . . . . . . . . . . . . . . . . . . .  5
       3.2.2.  Anonymous Communications . . . . . . . . . . . . . . .  6
       3.2.3.  Security Conscious Small Organizations . . . . . . . .  6
     3.3.  Environments with Limited Connectivity to the Internet
           or Infrastructure  . . . . . . . . . . . . . . . . . . . .  6
       3.3.1.  Ad-Hoc and Ephemeral Groups  . . . . . . . . . . . . .  7
       3.3.2.  Emergency First Responder Networks . . . . . . . . . .  7
       3.3.3.  Extending the Reach of Mobile Devices  . . . . . . . .  8
       3.3.4.  Deployments in the Developing World  . . . . . . . . .  8
     3.4.  Managed, Private Network Environments  . . . . . . . . . .  8
       3.4.1.  Serverless or Small Scale IP-PBX . . . . . . . . . . .  8
       3.4.2.  P2P for Redundant SIP Proxies  . . . . . . . . . . . .  9
       3.4.3.  Failover for Centralized Systems . . . . . . . . . . .  9
   4.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . .  9
   5.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   6.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   7.  References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     7.1.  Normative References . . . . . . . . . . . . . . . . . . . 10
     7.2.  Informative References . . . . . . . . . . . . . . . . . . 10
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 10
   Intellectual Property and Copyright Statements . . . . . . . . . . 12

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1.  Introduction

   This document attempts to identify and classify use cases for Peer-
   to-Peer (P2P) based Session Initiation Protocol (SIP)[RFC3261].
   Identifying use cases will help to understand and clarify
   requirements of P2P SIP.  In particular, these use cases will assist
   in identifying commonalities and differences between requirements for
   P2P SIP for different use cases, which in turn will help define the
   near-term scope of specifications and provide a perspective on future

   Only use cases related to real-time IP communications, such as VoIP,
   Instant Messaging (IM), and presence are considered in this document.
   Use cases of other kinds, even if interesting and possibly useful
   applications of P2P SIP, are out of scope for this document.  Thus,
   use cases described herein are use cases of P2P IP real-time
   communications, and P2P SIP is a protocol choice rather than a
   constraining factor for most of them.  In describing use cases, no
   deliberation on implementation is provided.  Some of the use cases
   presented may already be implemented or deployed, possibly using
   proprietary technology.

   Some of these use cases, while difficult to implement using a
   traditional client server SIP (CS SIP) architecture may not require
   P2P and could be implemented in other ways.  While these have often
   been presented as scenarios calling for P2P communication, the
   authors recognize that other technologies may also be applicable to
   these use cases.

   Since the original iteration of this document, the P2PSIP WG has been
   formed and numerous documents have been submitted that include some
   number of use cases.  We will not try to enumerate them here.  This
   draft draws from these documents, as well as discussions at the P2P
   SIP ad-hoc and WG meetings and numerous mailing list and personal
   conversations of the authors.  The list of use cases compiled here is
   by no means a complete list of uses cases of P2P SIP, and further
   cases would be limited only by the imagination.

2.  Terminology

   In this document, words which are normally key words, such as "MUST",
   COLLOQUIALLY and are not intended to be interpreted as described in
   RFC2119 [RFC2119].

   We use the terminology and definitions from the Concepts and

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   Terminology for Peer to Peer SIP [I-D.willis-p2psip-concepts] draft
   in this document without further definition.  Terminology defined in
   RFC3261 [RFC3261] is used without definition.

3.  Use Cases

   Use cases are grouped according to the characteristics of the network
   environment in which the end users or devices participating in the
   P2P overlay are communicating with each other.

3.1.  Global Internet Environment

   The global Internet environment consists of a large number of
   autonomous networks with diverse characteristics.  Thus, there is no
   central administration or network control of the physical network on
   a global scale.  Communication paths between two remote devices may
   span multiple administrative domains and should be assumed to be
   insecure.  Note that most well-known P2P file sharing overlay
   networks have operated in this environment.

3.1.1.  Public P2P VoIP Service Providers

   Skype is an outstanding example of a public VoIP service provider
   using P2P technology among end user devices, although using a
   proprietary protocol.  Recent research has shown [skypestudy]that
   Skype uses a central login server, responsible for management of
   registered user names.  End users are authenticated via certificate
   signed by a central server.  End user devices are distributed across
   the global Internet.  The number of participating end user devices is
   very large.  A major motivation of using P2P between end user devices
   for a commercial VoIP service is a reduction in infrastructure and
   operational costs.

3.1.2.  Open Global P2P VoIP Network

   This is a global P2P VoIP network in which there is no central
   authority such as a single service provider.  Anyone can join and
   leave the network freely and anyone can implement the software to
   participate in the overlay network.  In such a system, the protocols
   used must be based on open standards.  This P2P VoIP network
   resembles the global Internet itself in that it has distributed
   management and growth, enables anyone to reach anyone else in the
   overlay network, and any device supporting the standard protocols can
   be used.

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3.1.3.  Presence Using Multimedia Consumer Electronics Devices

   Presence is a useful and important feature for instant messaging and
   VoIP applications.  Well-known instant messaging application software
   provides presence, text and media messaging, and supports file
   transfer between online users.  As more and more multimedia consumer
   electronics devices such as cameras, camcorders and televisions
   become network aware, instant sharing of multimedia content such as
   photos and video clips between family members and friends will be
   desirable.  VoIP may not be needed on some of these consumer
   electronics devices, however presence that enables instant content
   sharing will be required for many types of consumer electronics
   devices.  A global P2P network supporting presence is an important
   infrastructure component for this use case.

3.1.4.  Multimedia content sharing via Application Layer Multicasting

   IP-layer multicasting is not generally available beyond the boundary
   of single IP subnet.  Application layer multicasting has become a
   fausible alternative to IP-layer multicasting.  In application layer
   multicasting, the nodes that need to receive the content from the
   same source form a distribution network, typically of a tree-like
   topology, and relay the received content to other nodes in the
   distribution network.  This technique can be used to multicasting
   video or audio stream to a number of nodes distributed over the
   Internet (or across multiple IP subnets).  This can be used to
   realize large-scale commercial audio or video distribution/
   broadcasting services such as Internet radio or TV services or to ad-
   hoc video sharing among a group of friends.

3.2.  Security Demanding Environments

   There are situations where, despite having connectivity to the
   Internet or even to client server SIP infrastructure such as SIP
   proxies, users may not like to use the infrastructure because of
   security concerns or may not be allowed to use the infrastructure.
   Such situations are referred to here as involving a security
   demanding environment.  Maintaining privacy of communication and
   secrecy of identities are important in this environment and the P2P
   architecture's distributed nature may be more attractive than a
   client server approach.

3.2.1.  Impeded Access

   Certain groups may have their ability to communicate impeded.  These
   users should be able to communicate without the need to connect to
   any centralized servers, which may be blocked by providers upstream
   of the user.  A fully decentralized system cannot be completely

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   disconnected without removing connectivity at the basic Internet

   Examples: A user wishes to use an IP telephony service to communicate
   PC to PC with a friend, but the ports commonly used by these
   services, or the the servers used for authentication, are blocked by
   the ISP because the ISP also offers communications systems and have a
   vested interest in denying access.

   A user with an Internet enabled PDA devices wishes to connect with
   colleagues, but traditional services are blocked to ensure that SMS
   or voice minutes are used (at additional cost) instead.

3.2.2.  Anonymous Communications

   Users occasionally have need to communicate among themselves in a
   completely anonymous fashion, whether due to political persecution,
   need for secrecy for commercial reasons, or threats of violence.  In
   such a case, the need for a self organizing, server-less system is
   imperative.  Users on such a system could communicate with reduced
   risk of the system being monitored or their identities discovered.
   As with the impeded access scenario, the only way to disable such
   networks would be to completely disable Internet connectivity.

3.2.3.  Security Conscious Small Organizations

   Certain security conscious small organizations may have need for
   communications systems that allow members of the organization to
   communicate directly with one another regardless of their location,
   with encryption, and without any connectivity to or use of servers,
   either internal or external to the organization.  For these
   organizations, traditional client-server SIP implementations and more
   importantly hosted solutions for communications are unacceptable.
   These entities need a system to facilitate such communications
   without central servers.  Note that these users may overlap with the
   anonymized communications case also described in this document.

   Examples: Organizations who are developing technology that might be
   of interest to a hosted service provider, but because of small size
   may have no desire or time to maintain centralized servers.
   Organizations with security needs that preclude any traffic flowing
   through a central server such as military, national security, or
   intelligence organizations.

3.3.  Environments with Limited Connectivity to the Internet or

   When there is no physical network available for stable deployment of

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   client server SIP or an instant deployment of real-time communication
   systems is required, the P2P approach may be the only feasible
   solution.  Examples of such environment are isolated wireless ad-hoc
   networks with no connection to the Internet or ad-hoc networks with
   limited connectivity to the Internet in situations like outdoor
   public events, emergencies, and battlefields.  Any type of manual
   configuration is difficult to achieve because technical support is
   not readily available in such environment.  In some cases,
   connectivity to the global Internet may be available, but be very
   expensive, of limited capacity, or unstable, such as satellite
   connections.  In such cases, it is preferable to localize
   communications as much as possible, reducing dependency on any
   infrastructure in the global Internet.

3.3.1.  Ad-Hoc and Ephemeral Groups

   Groups of individuals meeting together have need for collaborative
   communications systems that are ephemeral in nature, have minimum
   (ideally zero) configuration, and do not depend on connectivity to
   the Internet.  These scenarios require an arbitrary number of users
   to connect communications devices.

   Example: A group gets together for a meeting, but there is no
   Internet connectivity.  If the users establish a wireless ad hoc
   network or have a base station, all users may connect and establish
   chat sessions using an IM protocol with no need for server

3.3.2.  Emergency First Responder Networks

   Following a large scale disaster such as a tsunami, earthquake,
   hurricane, or terrorist attack, access to traditional communications
   devices of any kind -- Internet, cellular, or traditional PSTN -- may
   be compromised.  Recent events have shown that current first
   responder radio systems cannot be relied upon to interoperate
   effectively.  A network of devices that can grow organically as
   responders arrive, requiring only wireless access, is required.  As
   more personnel show up, they should be able to join the network,
   locate other personnel, and communicate without any centralized
   configuration required.

   Example: Following a disaster, the local fire department arrives.
   Each fire fighter has a wireless handset, and one or more trucks have
   wireless base stations.  When a nearby locality sends additional
   rescuers, their wireless handsets should be able to instantly join
   the communications network and communicate.

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3.3.3.  Extending the Reach of Mobile Devices

   A network of mobile devices can relay traffic between themselves to
   reach a base station, even if the base station is out of reach of
   that device.

   Example: A user has a handset for communication that cannot reach a
   base station.  Some other user is within range of both that user and
   a base station.  This intermediate user can serve as a relay for the
   caller who is out of range.  A system might make this feature
   optional for standard communication and mandatory for E911.

3.3.4.  Deployments in the Developing World

   Certain locations in the developing world have limited, intermittent,
   or non-existent connectivity to the Internet.  These locations also
   typically lack experienced people with the specialized skills needed
   to administer or maintain centralized SIP proxies.  Even DNS servers
   may not exist.  A communications system that is able to function
   reliably for internal communications, even in the presence of
   degraded or absent connectivity, is clearly needed.  Such a system
   must also scale easily with little or no configuration and ideally
   should interface easily to existing communications systems when
   connectivity is available.

   Example: A village in the developing world has connectivity that is
   limited by weather (microwave connection) or is solar powered.  It
   would be desirable for intra-village communication to continue to
   function in the absence of Internet connectivity.

3.4.  Managed, Private Network Environments

   A corporate network or a school campus network is an example of the
   managed, private network environment.  Most likely client server SIP
   can be used and managed for real-time communication applications in
   these environment.  However, in certain scenarios, P2P SIP may be
   used instead or as a complementary means, to achieve various goals
   such as cost and management overhead reduction, scalability, and
   system robustness.

3.4.1.  Serverless or Small Scale IP-PBX

   Many small enterprises have a need for integrated communications
   systems.  These systems have slightly different requirements than
   more traditional IP PBXs.  For small enterprises, there may be no
   administrator for these systems, requiring the systems to be
   essentially self-configuring and/or self-organizing.  Additional
   endpoints should be able to be added with no requirements for

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   configuration on central devices.

   These systems should offer the feature sets similar to those of
   client server type PBX systems.  Connectivity to the PSTN is an
   important feature for these systems.  In addition, they may support
   features such as call transfer, voice mail, and possibly even other
   communications modes such as instant messaging or media features such
   as video or conference services.  There are already commercial
   products of this type.

   Example: Small organizations without centralized IT

3.4.2.  P2P for Redundant SIP Proxies

   Service providers may wish to connect a farm of proxies together in a
   transparent way, passing resources (user registrations or other call
   information) between themselves with as little configuration or
   traffic as possible.  Ideally, the redundancy and exchange of
   information should require a minimum of configuration between the
   devices.  A P2P architecture between the proxies allows proxy farms
   to be organizing and operated in this way.  With this approach, it is
   easy to add more proxies with minimal service disruptions and
   increases the robustness of the system.

3.4.3.  Failover for Centralized Systems

   A traditional centralized SIP server, such as used in an IP-PBX,
   forms a single point of failure of an otherwise fault-independent
   network.  Relying on P2P SIP as a backup to the centralized server
   allows the communications system to continue functioning normally in
   the event of planned or unplanned service interruptions of the
   central IP-PBX.

   Example: A small company has a central IP-PBX.  When that device
   experiences a failure, the handsets are able to transparently
   continue operation for the 24 hours it takes to obtain a replacement

4.  Acknowledgments

   The following persons have contributed use case suggestions or ideas
   to this document:

   Cullen Jennings, Philip Matthews, Henry Sinnreich, Adam Roach, Robert
   Sparks, Kundan Singh, Henning Schulzrinne, K. Kishore Dhara, and
   Salman A. Baset.

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5.  Security Considerations

   The security requirements of the various use-cases vary tremendously.
   They should be discussed in more detail in this document.

6.  IANA Considerations

   This document has no IANA Considerations.

7.  References

7.1.  Normative References

              Willis, D., "Concepts and Terminology for Peer to Peer
              SIP", draft-willis-p2psip-concepts-04 (work in progress),
              March 2007.

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119, March 1997.

   [RFC3261]  Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
              A., Peterson, J., Sparks, R., Handley, M., and E.
              Schooler, "SIP: Session Initiation Protocol", RFC 3261,
              June 2002.

7.2.  Informative References

              Baset, S. and H. Schulzrinne, "An Analysis of the Skype
              Peer-to-Peer Internet Telephony Protocol", Technical
              Report, Department of Computer Science, Columbia
              University 0309-04, September 2004.

Authors' Addresses

   David A. Bryan
   SIPeerior Technologies, Inc.
   3000 Easter Circle
   Williamsburg, VA  23188

   Phone: +1 757 565 0101
   Email: dbryan@sipeerior.com

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   Eunsoo Shim
   Locus Telecommunications, Inc.
   2200 Fletcher Ave. 6th FL
   Fort Lee, NJ  07024

   Email: eunsoo@locus.net

   Bruce B. Lowekamp
   SIPeerior; William & Mary
   3000 Easter Circle
   Williamsburg, VA  23188

   Phone: +1 757 565 0101
   Email: lowekamp@sipeerior.com

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