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Network Working Group                                      D. Malas, Ed.Request for Comments: 5486                                     CableLabsCategory: Informational                                    D. Meyer, Ed.                                                              March 2009Session Peering for Multimedia Interconnect (SPEERMINT) TerminologyStatus of This Memo   This memo provides information for the Internet community.  It does   not specify an Internet standard of any kind.  Distribution of this   memo is unlimited.Copyright Notice   Copyright (c) 2009 IETF Trust and the persons identified as the   document authors.  All rights reserved.   This document is subject toBCP 78 and the IETF Trust's Legal   Provisions Relating to IETF Documents in effect on the date of   publication of this document (http://trustee.ietf.org/license-info).   Please review these documents carefully, as they describe your rights   and restrictions with respect to this document.   This document may contain material from IETF Documents or IETF   Contributions published or made publicly available before November   10, 2008.  The person(s) controlling the copyright in some of this   material may not have granted the IETF Trust the right to allow   modifications of such material outside the IETF Standards Process.   Without obtaining an adequate license from the person(s) controlling   the copyright in such materials, this document may not be modified   outside the IETF Standards Process, and derivative works of it may   not be created outside the IETF Standards Process, except to format   it for publication as an RFC or to translate it into languages other   than English.Abstract   This document defines the terminology that is to be used in   describing Session PEERing for Multimedia INTerconnect (SPEERMINT).Malas & Meyer                Informational                      [Page 1]

RFC 5486                 SPEERMINT Terminology                March 2009Table of Contents1. Introduction ....................................................22. SPEERMINT Context ...............................................33. General Definitions .............................................43.1. Signaling Path Border Element ..............................43.2. Data Path Border Element ...................................43.3. Session Establishment Data .................................43.4. Call Routing ...............................................53.5. PSTN .......................................................53.6. IP Path ....................................................53.7. Peer Network ...............................................53.8. Service Provider ...........................................53.9. SIP Service Provider .......................................64. Peering .........................................................64.1. Layer 3 Peering ............................................64.2. Layer 5 Peering ............................................64.2.1. Direct Peering ......................................74.2.2. Indirect Peering ....................................74.2.3. On-Demand Peering ...................................74.2.4. Static Peering ......................................74.3. Functions ..................................................74.3.1. Signaling Function ..................................74.3.2. Media Function ......................................84.3.3. Look-Up Function ....................................84.3.4. Location Routing Function ...........................85. Federations .....................................................86. Security Considerations .........................................97. Acknowledgments .................................................98. Informative References .........................................101.  Introduction   The term "Voice over IP Peering" (VoIP Peering) has historically been   used to describe a wide variety of practices pertaining to the   interconnection of service provider networks and to the delivery of   Session Initiation Protocol (SIP [2]) call termination over those   interconnections.   The discussion of these interconnections has at times been confused   by the fact that the term "peering" is used in various contexts to   describe interconnection at different levels in a protocol stack.   Session Peering for Multimedia Interconnect focuses on how to   identify and route real-time sessions (such as VoIP calls) at the   session layer, and it does not (necessarily) cover the exchange of   packet-routing data or media sessions.  In particular, "layer 5   network" is used here to refer to the interconnection between SIPMalas & Meyer                Informational                      [Page 2]

RFC 5486                 SPEERMINT Terminology                March 2009   servers, as opposed to interconnection at the IP layer ("layer 3").   The term "peering" will be used throughout the remainder of the   document for the purpose of indicating a layer 5 interconnection.   This document introduces standard terminology for use in   characterizing real-time session peering.  Note however, that while   this document is primarily targeted at the VoIP peering case, the   terminology described here is applicable to those cases in which   service providers peer using SIP signaling (defined as SIP Service   Providers; seeSection 3.9) for non-voice or quasi-real-time   communications like instant messaging.   The remainder of this document is organized as follows:Section 2   provides the general context for the Session PEERing for Multimedia   INTerconnect working group (SPEERMINT).Section 3 provides the   general definitions for real-time, SIP-based communication, with   initial focus on the VoIP peering case, andSection 4 defines the   terminology describing the various forms of peering.  Finally,Section 5 introduces the concept of federations.2.  SPEERMINT Context   SPEERMINT provides a peering framework that leverages the building   blocks of existing IETF-defined protocols such as SIP [2] and ENUM   [4].  While the SPEERMINT working group describes the use of these   protocols in peering, it does not redefine how these protocols use   input or output variables necessary for creating Session   Establishment Data (SED) or the methods in which this data will be   used during the peering process.  SeeSection 3.3 for additional   detail on SED and its principal variables such as Uniform Resource   Identifiers (URIs) [3] and telephone numbers of E.164 numbers [5].   For example, while the SPEERMINT working group is not limited to the   use of telephone numbers, an E.164 number may be used as a key in an   E.164-to-URI mapping using ENUM.  This mapping involves looking up   Naming Authority Pointer (NAPTR) records in the DNS, and results in a   SIP URI.  The process for deriving this information has already been   defined in [4], but is used as a building block for SPEERMINT SED, on   which the subsequent call routing is based.  Note that the call-   routing step does not depend on the presence of an E.164 number.   Indeed, the URI resulting from an ENUM query may no longer even   contain numbers of any type.  In particular, the SIP URI can be   advertised in various other ways, such as on a web page.   Finally, note that the term "call" is being used here in the most   general sense, i.e., call routing and session routing are used   interchangeably.Malas & Meyer                Informational                      [Page 3]

RFC 5486                 SPEERMINT Terminology                March 20093.  General Definitions3.1.  Signaling Path Border Element   A signaling path border element (SBE) is located on the   administrative border of a domain through which inter-domain session   layer messages will flow.  It typically provides signaling functions   such as protocol inter-working (for example, H.323 to SIP), identity   and topology hiding, and Session Admission Control for a domain.3.2.  Data Path Border Element   A data path border element (DBE) is located on the administrative   border of a domain through which flows the media associated with an   inter-domain session.  It typically provides media-related functions   such as deep packet inspection and modification, media relay, and   firewall-traversal support.  The DBE may be controlled by the SBE.3.3.  Session Establishment Data   Session Establishment Data, or SED, is the data used to route a call   to the next hop associated with the called domain's ingress point.  A   domain's ingress point might, for example, be the location derived   from various types of DNS records (NAPTR, SRV, or A record) [1] that   resulted from the resolution of the SIP URI.   More specifically, the SED is the set of parameters that the outgoing   SBEs need to complete the call, and may include:      o  A destination SIP URI      o  A SIP proxy or ingress SBE to send the INVITE to, including:         -  Fully Qualified Domain Name (FQDN)         -  Port         -  Transport Protocol (UDP [8], TCP [9], and TLS [7])      o Security parameters, including:         -  TLS certificate to use         -  TLS certificate to expect         -  TLS certificate verification settingMalas & Meyer                Informational                      [Page 4]

RFC 5486                 SPEERMINT Terminology                March 2009      o  Optional resource control parameters such as:         -  Limits on the total number of call initiations to a peer         -  Limits on SIP transactions per second3.4.  Call Routing   Call routing is the set of processes and rules used to route a call   and any subsequent mid-dialog SIP requests to their proper (SIP)   destination.  More generally, call routing can be thought of as the   set of processes and rules that are used to route a real-time session   to its termination point.3.5.  PSTN   The term "PSTN" refers to the Public Switched Telephone Network.  In   particular, the PSTN refers to the collection of interconnected,   circuit-switched, voice-oriented public telephone networks, both   commercial and government-owned.  In general, PSTN terminals are   addressed using E.164 numbers; however, various dial-plans (such as   emergency services dial-plans) may not directly use E.164 numbers.3.6.  IP Path   For the purposes of this document, an IP path is defined to be a   sequence of zero or more IP router hops.3.7.  Peer Network   This document defines a peer network as the set of SIP user agents   (UAs) (customers) that are associated with a single administrative   domain and can be reached via some IP path.  Note that such a peer   network may also contain end-users who are located on the PSTN (and   hence may also be interconnected with the PSTN) as long as they are   also reachable via some IP path.3.8.  Service Provider   A Service Provider (SP) is defined to be an entity that provides   layer 3 (IP) transport of SIP signaling and media packets.  Example   services may include, but are not limited to, Ethernet Private Line   (EPL), Frame Relay, and IP Virtual Private Network (VPN).  An example   of this may be an Internet Service Provider (ISP).Malas & Meyer                Informational                      [Page 5]

RFC 5486                 SPEERMINT Terminology                March 20093.9.  SIP Service Provider   A SIP Service Provider (SSP) is an entity that provides session   services utilizing SIP signaling to its customers.  In the event that   the SSP is also a function of the SP, it may also provide media   streams to its customers.  Such an SSP may additionally be peered   with other SSPs.  An SSP may also interconnect with the PSTN.  An SSP   may also be referred to as an Internet Telephony Service Provider   (ITSP).  While the terms ITSP and SSP are frequently used   interchangeably, this document and other subsequent SIP peering-   related documents should use the term SSP.  SSP more accurately   depicts the use of SIP as the underlying layer 5 signaling protocol.4.  Peering   While the precise definition of the term "peering" is the subject of   considerable debate, peering in general refers to the negotiation of   reciprocal interconnection arrangements, settlement-free or   otherwise, between operationally independent service providers.   This document distinguishes two types of peering, layer 3 peering and   layer 5 peering, which are described below.4.1.  Layer 3 Peering   Layer 3 peering refers to interconnection of two service providers'   networks for the purposes of exchanging IP packets that are destined   for one (or both) of the peer's networks.  Layer 3 peering is   generally agnostic to the IP payload, and is frequently achieved   using a routing protocol such as the Border Gateway Protocol (BGP)   [6] to exchange the required routing information.   An alternate, perhaps more operational, definition of layer 3 peering   is that two peers exchange only customer routes, and hence any   traffic between peers terminates on one of the peers' networks or the   peer's customer's network.4.2.  Layer 5 Peering   Layer 5 (session) peering refers to interconnection of two SSPs for   the purposes of routing real-time (or quasi-real-time) call signaling   between their respective customers using SIP methods.  Such peering   may be direct or indirect (seeSection 4.2.1 andSection 4.2.2   below).  Note that media streams associated with this signaling (if   any) are not constrained to follow the same set of IP paths.Malas & Meyer                Informational                      [Page 6]

RFC 5486                 SPEERMINT Terminology                March 20094.2.1.  Direct Peering   Direct peering describes those cases in which two SSPs peer without   using an intervening layer 5 network.4.2.2.  Indirect Peering   Indirect, or transit, peering refers to the establishment of either a   signaling and media path or a signaling path alone via one (or more)   layer 5 transit network(s).  In this case, it is generally required   that a trust relationship is established between the originating SSP   and the transit SSP on one side, and between the transit SSP and the   termination SSP on the other side.4.2.3.  On-Demand Peering   SSPs are said to peer on-demand when they are able to exchange SIP   traffic without any pre-association prior to the origination of a   real-time transaction (like a SIP message) between the domains.  Any   information that needs to be exchanged between domains in support of   peering can be learned through a dynamic protocol mechanism.  On-   demand peering can occur as direct or indirect.4.2.4.  Static Peering   SSPs are said to peer statically when pre-association between   providers is required for the initiation of any real-time   transactions (like a SIP message).  Static peering can occur as   direct or indirect.  An example of static peering is a federation.   Each of the peers within the federation must first agree on a common   set of rules and guidelines for peering, thus pre-associating with   each other prior to initiating session requests.4.3.  Functions   The following are terms associated with the functions required for   peering.4.3.1.  Signaling Function   The Signaling Function (SF) performs routing of SIP requests for   establishing and maintaining calls, and to assist in the discovery or   exchange of parameters to be used by the Media Function (MF).  The SF   is a capability of SIP processing elements such as SIP proxies, SBEs,   and user agents.Malas & Meyer                Informational                      [Page 7]

RFC 5486                 SPEERMINT Terminology                March 20094.3.2.  Media Function   The Media Function (MF) performs media-related functions such as   media transcoding and media security implementation between two SSPs.   The MF is a capability of SIP-session-associated media end-points   such as DBEs and user agents.4.3.3.  Look-Up Function   The Look-Up Function (LUF) determines for a given request the target   domain to which the request should be routed.  An example of an LUF   is an ENUM [4] look-up or a SIP INVITE request to a SIP proxy   providing redirect responses for peers.   In some cases, some entity (usually a 3rd party or federation)   provides peering assistance to the originating SSP by providing this   function.  The assisting entity may provide information relating to   direct (Section 4.2.1) or indirect (Section 4.2.2) peering as   necessary.4.3.4.  Location Routing Function   The Location Routing Function (LRF) determines for the target domain   of a given request the location of the SF in that domain, and   optionally develops other SED required to route the request to that   domain.  An example of the LRF may be applied to either example inSection 4.3.3.  Once the ENUM response or SIP 302 redirect is   received with the destination's SIP URI, the LRF must derive the   destination peer's SF from the FQDN in the domain portion of the URI.   In some cases, some entity (usually a 3rd party or federation)   provides peering assistance to the originating SSP by providing this   function.  The assisting entity may provide information relating to   direct (Section 4.2.1) or indirect (Section 4.2.2) peering as   necessary.5.  Federations   A federation is a group of SSPs that agree to exchange calls with   each other via SIP and who agree on a set of administrative rules for   such calls (settlement, abuse-handling, etc.) and specific rules for   the technical details of the peering.   The following provides examples of rules that the peers of a   federation may agree to and enforce upon all participants:      o  Common domain for all federation peers (e.g.,         bob@peer1.federation.example.com)Malas & Meyer                Informational                      [Page 8]

RFC 5486                 SPEERMINT Terminology                March 2009      o  Codec rules (e.g., all peers must use the ITU-T G.711 codec         [10])      o  Authentication preference (e.g., all peers must use TLS when         requesting to establish sessions with other peers)      o  Transport protocol (e.g., all peers must use TCP)      o  SIP address resolution mechanisms (e.g., all peers must use         ENUM for resolving telephone numbers to SIP URIs)   Finally, note that an SSP can be a member of:      -  No federation (e.g., the SSP has only bilateral peering         agreements)      -  A single federation      -  Multiple federations   Also, an SSP can have any combination of bilateral and multilateral   (i.e., federated) peers.6.  Security Considerations   This document introduces no new security considerations.  However, it   is important to note that session peering, as described in this   document, has a wide variety of security issues that should be   considered in documents addressing both protocol and use-case   analysis.7.  Acknowledgments   Many of the definitions were gleaned from detailed discussions on the   SPEERMINT, ENUM, and SIPPING mailing lists.  Scott Brim, John Elwell,   Mike Hammer, Eli Katz, Gaurav Kulshreshtha, Otmar Lendl, Jason   Livingood, Alexander Mayrhofer, Jean-Francois Mule, Jonathan   Rosenberg, David Schwartz, Richard Shockey, Henry Sinnreich, Richard   Stastny, Hannes Tschofenig, Adam Uzelac, and Dan Wing all made   valuable contributions to early versions of this document.  Patrik   Faltstrom also made many insightful comments to early versions of   this document.Malas & Meyer                Informational                      [Page 9]

RFC 5486                 SPEERMINT Terminology                March 20098.  Informative References   [1]   Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for         specifying the location of services (DNS SRV)",RFC 2782,         February 2000.   [2]   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.   [3]   Mealling, M., "Dynamic Delegation Discovery System (DDDS) Part         Four: The Uniform Resource Identifiers (URI)",RFC 3404,         October 2002.   [4]   Faltstrom, P. and M. Mealling, "The E.164 to Uniform Resource         Identifiers (URI) Dynamic Delegation Discovery System (DDDS)         Application (ENUM)",RFC 3761, April 2004.   [5]   International Telecommunications Union, "The International         Public Telecommunication Numbering Plan", ITU-T Recommendation         E.164, February 2005.   [6]   Rekhter, Y., Ed., Li, T., Ed., and S. Hares, Ed., "A Border         Gateway Protocol 4 (BGP-4)",RFC 4271, January 2006.   [7]  Dierks, T. and E. Rescorla, "The Transport Layer Security (TLS)         Protocol Version 1.2",RFC 5246, August 2008.   [8]  Postel, J., "User Datagram Protocol", STD 6,RFC 768, August         1980.   [9]  Postel, J., "DoD standard Transmission Control Protocol",RFC761, January 1980.   [10]  ITU Recommendation G.711 (11/88) - Pulse code modulation (PCM)         of voice frequencies.Authors' Addresses   Daryl Malas (editor)   CableLabs   858 Coal Creek Circle   Louisville, CO  80027   USA   EMail: d.malas@cablelabs.com   David Meyer (editor)   EMail: dmm@1-4-5.netMalas & Meyer                Informational                     [Page 10]