\
SPEERMINT                                                  D. Malas, Ed.
Internet-Draft                                                 CableLabs
Intended status: Informational                         J. Livingood, Ed.
Expires: March 3, 2011                                           Comcast
                                                         August 30, 2010


                     SPEERMINT Peering Architecture
                  draft-ietf-speermint-architecture-11

Abstract

   This document defines a peering architecture for the Session
   Initiation Protocol (SIP) [RFC3261], it's functional components and
   interfaces.  It also describes the components and the steps necessary
   to establish a session between two SIP Service Provider (SSP) peering
   domains.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on March 3, 2011.

Copyright Notice

   Copyright (c) 2010 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as



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   described in the Simplified BSD License.


Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3
   2.  Reference Architecture . . . . . . . . . . . . . . . . . . . .  3
   3.  Procedures of Inter-domain SSP Session Establishment . . . . .  4
   4.  Relationships Between Functions/Elements . . . . . . . . . . .  5
   5.  Recommended SSP Procedures . . . . . . . . . . . . . . . . . .  5
     5.1.  Originating SSP Procedures . . . . . . . . . . . . . . . .  5
       5.1.1.  The Look-Up Function (LUF) . . . . . . . . . . . . . .  5
         5.1.1.1.  Target Address Analysis  . . . . . . . . . . . . .  6
         5.1.1.2.  ENUM Lookup  . . . . . . . . . . . . . . . . . . .  6
       5.1.2.  Location Routing Function (LRF)  . . . . . . . . . . .  7
         5.1.2.1.  DNS resolution . . . . . . . . . . . . . . . . . .  7
         5.1.2.2.  Routing Table  . . . . . . . . . . . . . . . . . .  7
         5.1.2.3.  LRF to LRF Routing . . . . . . . . . . . . . . . .  7
       5.1.3.  The Signaling Path Border Element (SBE)  . . . . . . .  7
         5.1.3.1.  Establishing a Trusted Relationship  . . . . . . .  8
         5.1.3.2.  IPSec  . . . . . . . . . . . . . . . . . . . . . .  8
         5.1.3.3.  Co-Location  . . . . . . . . . . . . . . . . . . .  8
         5.1.3.4.  Sending the SIP Request  . . . . . . . . . . . . .  8
     5.2.  Target SSP Procedures  . . . . . . . . . . . . . . . . . .  8
       5.2.1.  The Ingress SBE  . . . . . . . . . . . . . . . . . . .  8
         5.2.1.1.  TLS  . . . . . . . . . . . . . . . . . . . . . . .  9
         5.2.1.2.  Receive SIP Requests . . . . . . . . . . . . . . .  9
     5.3.  Data Path Border Element (DBE) . . . . . . . . . . . . . .  9
   6.  Address Space Considerations . . . . . . . . . . . . . . . . .  9
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 10
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 10
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
   11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 11
   12. Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 11
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
     13.1. Normative References . . . . . . . . . . . . . . . . . . . 11
     13.2. Informative References . . . . . . . . . . . . . . . . . . 12
   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13












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1.  Introduction

   This document defines a reference peering architecture in the context
   of session peering for multimedia interconnects.  In this process, we
   define the peering reference architecture, its functional components,
   and peering interface functions from the perspective of a SIP Service
   providers [RFC5486] network.

   This architecture allows the interconnection of two SSPs in layer 5
   peering as defined in the SIP-based session peering requirements
   [I-D.draft-ietf-speermint-requirements-09].

   Layer 3 peering is outside the scope of this document.  Hence, the
   figures in this document do not show routers so that the focus is on
   Layer 5 protocol aspects.

   This document uses terminology defined in the Session Peering for
   Multimedia Interconnect Terminology document [RFC5486].


2.  Reference Architecture

   The following figure depicts the architecture and logical functions
   that form peering between two SSPs.



























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        +=============++                          ++==============+
                      ||                          ||
                +-----------+                +-----------+
                |    SBE    |       +-----+  |    SBE    |
                |  +-----+  | SIP   |Proxy|  |  +-----+  |
                |  | LUF |<-|------>|ENUM |  |  | LUF |  |
                |  +-----+  | ENUM  |TN DB|  |  +-----+  |
           SIP  |           |       +-----+  |           |
         ------>|  +-----+  | DNS   +-----+  |  +-----+  |
                |  | LRF |<-|------>|FQDN |  |  | LRF |  |
                |  +-----+  |       |IP   |  |  +-----+  |
                |  +-----+  | SIP   +-----+  |  +-----+  |
                |  | SF  |<-|----------------|->|  SF |  |
                |  +-----+  |                |  +-----+  |
                +-----------+                +-----------+
                     ||                           ||
                +-----------+                +-----------+
           RTP  |    DBE    | RTP            |    DBE    |
         ------>|           |--------------->|           |
                +-----------+                +-----------+
                      ||                           ||
        SSP1 Network  ||                           ||  SSP2 Network
        +=============++                           ++=============+


   Reference Architecture

                                 Figure 1

   For further details on the elements and functions described in this
   figure, please refer to [RFC5486].


3.  Procedures of Inter-domain SSP Session Establishment

   This document assumes that in order for a session to be established
   from a UA in the Originating SSP's network to an UA in the Target
   SSP's network the following steps are taken:

   1.  Determine the target SSP via the LUF.  (Note: If the target
       address represents an intra-SSP resource, the behavior is out-of-
       scope with respect to this draft.)

   2.  Determine the address of the SF of the target SSP via the LRF.

   3.  Establish the session





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   4.  Exchange the media, which could include voice, video, text, etc.

   5.  End the session (BYE)

   The originating SSP would likely perform steps 1-4, and the target
   SSP would likely perform steps 4-5.

   In the case the target SSP changes, then steps 1-4 would be repeated.
   This is reflected in Figure 1 that shows the target SSP with its own
   peering functions.


4.  Relationships Between Functions/Elements

   o  An SBE can contain a SF function.

   o  An SF can perform LUF and LRF functions.

   o  As an additional consideration, a Session Border Controller, can
      contain an SF, SBE and DBE, and may perform the LUF and LRF
      functions.

   o  The following functions can communicate as follows, depending upon
      various real-world implementations:

      *  SF can communicate with LUF, LRF, SBE and SF

      *  LUF can communicator with SF and SBE

      *  LRF can communicate with SF and SBE


5.  Recommended SSP Procedures

   This section describes the functions in more detail and provides some
   recommendations on the role they would play in a SIP call in a Layer
   5 peering scenario.

   Some of the information in the section is taken from
   [I-D.draft-ietf-speermint-requirements-09] and is put here for
   continuity purposes.

5.1.  Originating SSP Procedures

5.1.1.  The Look-Up Function (LUF)

   Purpose is to determine the SF of the target domain of a given
   request and optionally develop Session Establishment Data.



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5.1.1.1.  Target Address Analysis

   When the originating SSP receives a request to communicate, it
   analyzes the target URI to determine whether the call needs to be
   routed internal or external to its network.  The analysis method is
   internal to the SSP; thus, outside the scope of SPEERMINT.

   If the target address does not represent a resource inside the
   originating SSP?s administrative domain or federation of domains,
   then the originating SSP performs a Lookup Function (LUF) to
   determine a target address, and then is resolves the call routing
   data by using the Location routing Function (LRF).

   For example, if the request to communicate is for an im: or pres: URI
   type, the originating SSP follows the procedures in [8].  If the
   highest priority supported URI scheme is sip: or sips: the
   originating SSP skips to SIP DNS resolution in Section 5.1.3.
   Likewise, if the target address is already a sip: or sips: URI in an
   external domain, the originating SSP skips to SIP DNS resolution in
   Section 4.1.2.1.

   If the target address corresponds to a specific E.164 address, the
   SSP may need to perform some form of number plan mapping according to
   local policy.  For example, in the United States, a dial string
   beginning "011 44" could be converted to "+44", or in the United
   Kingdom "00 1" could be converted to "+1".  Once the SSP has an E.164
   address, it can use ENUM.

5.1.1.2.  ENUM Lookup

   If an external E.164 address is the target, the originating SSP
   consults the public "User ENUM" rooted at e164.arpa, according to the
   procedures described in RFC 3761.  The SSP must query for the "E2U+
   sip" enumservice as described in RFC 3764 [11], but MAY check for
   other enumservices.  The originating SSP MAY consult a cache or
   alternate representation of the ENUM data rather than actual DNS
   queries.  Also, the SSP may skip actual DNS queries if the
   originating SSP is sure that the target address country code is not
   represented in e164.arpa.  If a sip: or sips: URI is chosen the SSP
   skips to Section 5.1.6.

   If an im: or pres: URI is chosen for based on an "E2U+im" [8] or
   "E2U+pres" [9] enumserver, the SSP follows the procedures for
   resolving these URIs to URIs for specific protocols such a SIP or
   XMPP as described in the previous section.






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5.1.2.  Location Routing Function (LRF)

   The LRF of an Originating SSP analyzes target address and target
   domain identified by the LUF, and discovers the next hop signaling
   function (SF) in a peering relationship.  The resource to determine
   the SF of the target domain might be provided by a third-party as in
   the assisted-peering case.  The following sections define mechanisms
   which may be used by the LRF.  These are not in any particular order
   and, importantly, not all of them may be used.

5.1.2.1.  DNS resolution

   The originating SSP uses the procedures in RFC 3263 [4] Section 4 to
   determine how to contact the receiving SSP.  To summarize the RFC
   3263 procedure: unless these are explicitly encoded in the target
   URI, a transport is chosen using NAPTR records, a port is chosen
   using SRV records, and an address is chosen using A or AAAA records.

   When communicating with another SSP, entities compliant to this
   document should select a TLS-protected transport for communication
   from the originating SSP to the receiving SSP if available.

5.1.2.2.  Routing Table

   If there are no End User ENUM records and the Originating SSP cannot
   discover the carrier-of-record or if the Originating SSP cannot reach
   the carrier-of-record via SIP peering, the Originating SSP may
   deliver the call to the PSTN or reject it.  Note that the originating
   SSP may forward the call to another SSP for PSTN gateway termination
   by prior arrangement using the routing table.

   If so, the originating SSP rewrites the Request-URI to address the
   gateway resource in the target SSP's domain and MAY forward the
   request on to that SSP using the procedures described in the
   remainder of these steps.

5.1.2.3.  LRF to LRF Routing

   Communications between the LRF of two interconnecting SSPs may use
   DNS or statically provisioned IP Addresses for reachability.  Other
   inputs to determine the path may be code-based routing, method-based
   routing, Time of day, least cost and/or source-based routing.

5.1.3.  The Signaling Path Border Element (SBE)

   The purpose of signaling function is to perform routing of SIP
   messages as well as optionally implement security and policies on SIP
   messages, and to assist in discovery/exchange of parameters to be



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   used by the Media Function (MF).

   The signaling function performs the routing of SIP messages.  The
   optional termination and re-initiation of calls may be performed by
   the signaling path Session Border Element (SBE), or other signaling
   elements.

   Optionally, a SF may perform additional functions such as Session
   Admission Control, SIP Denial of Service protection, SIP Topology
   Hiding, SIP header normalization, SIP security, privacy, and
   encryption.

   The SF of a SBE can also process SDP payloads for media information
   such as media type, bandwidth, and type of codec; then, communicate
   this information to the media function.  Signaling function may
   optionally communicate with the network to pass Layer 3 related
   policies [10].

5.1.3.1.  Establishing a Trusted Relationship

   Depending on the security needs and trust relationships between SSPs,
   different security mechanism can be used to establish SIP calls.
   These are discussed in the following subsections.

5.1.3.2.  IPSec

   In certain deployments the use of IPSec between the signaling
   functions of the originating and terminating domains can be used as a
   security mechanism instead of TLS.

5.1.3.3.  Co-Location

   In this scenario the SFs are co-located in a physically secure
   location and/or are members of a segregated network.  In this case
   messages between the originating and terminating SSPs would be sent
   as clear text.

5.1.3.4.  Sending the SIP Request

   Once a trust relationship between the peers is established, the
   originating SSP sends the request.

5.2.  Target SSP Procedures

5.2.1.  The Ingress SBE






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5.2.1.1.  TLS

   When the receiving SSP receives a TLS client hello, it responds with
   its certificate.  The Target SSP certificate should be valid and
   rooted in a well-known certificate authority.  The procedures to
   authenticate the SSP?s originating domain are specified in [24].

   The SF of the Target SSP verifies that the Identity header is valid,
   corresponds to the message, corresponds to the Identity-Info header,
   and that the domain in the From header corresponds to one of the
   domains in the TLS client certificate.

5.2.1.2.  Receive SIP Requests

   Once a trust relationship is established, the Target SSP is prepared
   to receive incoming SIP requests.  For new requests (dialog forming
   or not) the receiving SSP verifies if the target (request-URI) is a
   domain that for which it is responsible.  For these requests, there
   should be no remaining Route header field values.  For in-dialog
   requests, the receiving SSP can verify that it corresponds to the
   top-most Route header field value.

   The receiving SSP may reject incoming requests due to local policy.
   When a request is rejected because the originating SSP is not
   authorized to peer, the receiving SSP should respond with a 403
   response with the reason phrase "Unsupported Peer".

5.3.  Data Path Border Element (DBE)

   The purpose of the DBE [RFC 5486] is to perform media related
   functions such as media transcoding and media security implementation
   between two SSPs.

   An Example of this is to transform a voice payload from one codec
   (e.g., G.711) to another (e.g., EvRC).  Additionally, the MF may
   perform media relaying, media security, privacy, and encryption.


6.  Address Space Considerations

   Peering must occur in a common IP address space, which is defined by
   the federation, which may be entirely on the public Internet, or some
   private address space.  The origination or termination networks may
   or may not entirely be in the same address space.  If they are not,
   then a network address translation (NAT) or similar may be needed
   before the signaling or media is presented correctly to the
   federation.  The only requirement is that all associated entities
   across the peering interface are reachable.



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7.  Acknowledgments

   The working group thanks Sohel Khan for his initial architecture
   draft that helped to initiate work on this draft.  John Elwell, Mike
   Hammer, Otmar Lendl, Jason Livingood, Alexander Mayrhofer, Jean-
   Francois Mule, Jonathan Rosenberg, David Schwartz, Richard Shockey,
   Jim McEachern, and Dan Wing all made valuable contributions to
   versions of this document.

   A significant portion of this draft is taken from
   [I-D.draft-mahy-speermint-direct-peering-02] with permission from the
   author R. Mahy.


8.  IANA Considerations

   This memo includes no request to IANA.


9.  Security Considerations

   In all cases, cryptographic-based security should be maintained as an
   optional requirement between peering providers conditioned on the
   presence or absence of underlying physical security of SSP
   connections, e.g. within the same secure physical building.

   In order to maintain a consistent approach, unique and specialized
   security requirements common for the majority of peering
   relationships, should be standardized within the IETF.  These
   standardized methods may enable capabilities such as dynamic peering
   relationships across publicly maintained interconnections.


10.  Contributors

   Adam Uzelac

   Reinadlo Penno

   Mike Hammer

   Sohel Khan

   Hadriel Kaplan

   David Schwartz

   Richard Shockey



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11.  Change Log

   NOTE TO RFC EDITOR: PLEASE REMOVE THIS SECTION PRIOR TO PUBLICATION.

   o  -11 - Quick update to refresh the I-D since it expired, and
      cleaned up some of the XML for references.  A real revision is
      coming soon.


12.  Open Issues

   NOTE TO RFC EDITOR: PLEASE REMOVE THIS SECTION PRIOR TO PUBLICATION.

   o  Cleanup odd spacing in XML

   o  Revise contributors list, which are really authors, due to
      document masthead constraint

   o  Lots of clean-up


13.  References

13.1.  Normative References

   [I-D.ietf-speermint-requirements]
              Mule, J., "SPEERMINT Requirements for SIP-based Session
              Peering", draft-ietf-speermint-requirements-09 (work in
              progress), October 2009.

   [I-D.lee-speermint-use-case-cable]
              Lee, Y., "Session Peering Use Case for Cable",
              draft-lee-speermint-use-case-cable-01 (work in progress),
              September 2006.

   [I-D.lendl-speermint-federations]
              Lendl, O., "A Federation based VoIP Peering Architecture",
              draft-lendl-speermint-federations-03 (work in progress),
              September 2006.

   [I-D.mahy-speermint-direct-peering]
              Mahy, R., "A Minimalist Approach to Direct Peering",
              draft-mahy-speermint-direct-peering-02 (work in progress),
              July 2007.

   [I-D.schwartz-speermint-use-cases-federations]
              Schwartz, D., "Session Peering Use Cases for Federations",
              draft-schwartz-speermint-use-cases-federations-00 (work in



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              progress), November 2006.

   [I-D.uzelac-speermint-use-cases]
              Uzelac, A., "SIP Peering Use Case for VSPs",
              draft-uzelac-speermint-use-cases-00 (work in progress),
              October 2006.

   [RFC1918]  Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
              E. Lear, "Address Allocation for Private Internets",
              BCP 5, RFC 1918, February 1996.

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

   [RFC2434]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 2434,
              October 1998.

   [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.

   [RFC3263]  Rosenberg, J. and H. Schulzrinne, "Session Initiation
              Protocol (SIP): Locating SIP Servers", RFC 3263,
              June 2002.

   [RFC3761]  Faltstrom, P. and M. Mealling, "The E.164 to Uniform
              Resource Identifiers (URI) Dynamic Delegation Discovery
              System (DDDS) Application (ENUM)", RFC 3761, April 2004.

   [RFC5486]  Malas, D. and D. Meyer, "Session Peering for Multimedia
              Interconnect (SPEERMINT) Terminology", RFC 5486,
              March 2009.

13.2.  Informative References

   [I-D.lewis-peppermint-enum-reg-if]
              Lewis, E., "ENUM Registry Interface Requirements",
              draft-lewis-peppermint-enum-reg-if-01 (work in progress),
              November 2007.

   [I-D.newton-peppermint-problem-statement]
              Newton, A., "Provisioning Extensions in Peering Registries
              for Multimedia Interconnection  (PEPPERMINT) Problem
              Statement", draft-newton-peppermint-problem-statement-00
              (work in progress), January 2007.




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   [RFC3546]  Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
              and T. Wright, "Transport Layer Security (TLS)
              Extensions", RFC 3546, June 2003.

   [RFC3711]  Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
              Norrman, "The Secure Real-time Transport Protocol (SRTP)",
              RFC 3711, March 2004.

   [RFC4483]  Burger, E., "A Mechanism for Content Indirection in
              Session Initiation Protocol (SIP) Messages", RFC 4483,
              May 2006.


Authors' Addresses

   Daryl Malas (editor)
   CableLabs
   Louisville, CO
   US

   Email: d.malas@cablelabs.com


   Jason Livingood (editor)
   Comcast
   Philadelphia, PA
   US

   Email: Jason_Livingood@cable.comcast.com






















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