Speermint Working Group                                   A.Uzelac(Ed.)
Internet Draft                                          Global Crossing
Intended status: Informational
Expires: May 2010
                                                       November 10, 2009

                       SPEERMINT Peering Architecture

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   are provided without warranty as described in the BSD License."


   This document defines the SPEERMINT peering architecture, its functional
   components and peering interface functions. It also describes the steps taken

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   to establish a session between two peering domains in the context of the
   functions defined.

Table of Contents

   1. Introduction...................................................2
   2. Reference SPEERMINT Architecture...............................4
   3. Procedures of Inter-domain SSP Session Establishment...........4
      3.1. Relationships between functions/elements..................5
   4. Recommended SSP Procedures.....................................5
      4.1. Originating SSP Procedures................................5
         4.1.1. The Look-Up Function (LUF)...........................5
   Target Address Analysis.........................6
   ENUM Lookup.....................................6
         4.1.2. Location Routing Function (LRF)......................6
   DNS Resolution..................................7
   Routing Table...................................7
   LRF to LRF Routing..............................7
         4.1.3. The Signaling Path Border Element (SBE)..............7
   Establishing a Trusted Relationship.............8
   Sending the SIP request.........................8
      4.2. Target SSP Procedures.....................................8
         4.2.1. The Ingress Signaling Path Border Element (SBE)......8
   Receive SIP requests............................9
      4.3. Data Path Border Element (DBE)............................9
   5. Address space considerations...................................9
   6. Security Considerations........................................9
   7. IANA Considerations...........................................10
   8. Acknowledgments...............................................10
   9. References....................................................11
      9.1. Normative References.....................................11
      9.2. Informative References...................................12
   Author's Addresses...............................................13

1. Introduction

   The objective of this document is to define a reference peering architecture in
   the context of Session PEERing for Multimedia INTerconnect (SPEERMINT). In this
   process, we define the peering reference architecture, its functional
   components, and peering interface functions from the perspective of a SIP
   Service provider's (SSP) network.

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   This architecture allows the interconnection of two SSPs in layer 5 peering as
   defined in the SPEERMINT Requirements [14] and Terminology [13] documents.

   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

   This document uses terminology defined in the SPEERMINT Terminology document
   [13], so the reader should be familiar with all the terms defined there.

   In this document, the key words "MUST", "MUST NOT", "REQUIRED",   "SHALL",
   to be interpreted as described in [RFC2119].

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2. Reference SPEERMINT Architecture

   Figure 2 depicts the SPEERMINT architecture and logical functions that form the
   peering between two SSPs.

              ---------------                          ---------------
             /               \                        /               \
           |    +--LUF-+     |       +------+       |     +--LUF-+    |
           | |->|      |     |       | ENUM |       |     |      |<-| |
           | |  |      +------------>| TN DB|<------------+      |  | |
           | |  |      |     |       +------+       |     |      |  | |
           | |  +------+     |                      |     +------+  | |
           | |               |                      |               | |
           | |  +--LRF-+     |      +--------+      |     +--LRF-+  | |
           | |->|      |     |      | DNS    |      |     |      |<-| |
           | |  |      +----------->|IP Addrs|<-----------+      |  | |
           | |  |      |     |      +--------+      |     |      |  | |
           | |  +------+     |                      |     +------+  | |
           | |               |                      |               | |
           | |               |                      |               | |
           | |           +-------+              +-------+           | |
           | ----------->|       |              |       |<----------- |
           |             |  SBE  |<------------>|  SBE  |             |
           |             |       |              |       |             |
           |             +-------+              +-------+             |
           |    SSP1         |                      |       SSP2      |
           |             +-------+              +-------+             |
           |             |       |              |       |             |
           |             |  DBE  |<------------>|  DBE  |             |
           |             |       |              |       |             |
           |             +-------+              +-------+             |
             \               /                        \               /
              ---------------                          ---------------
                  Figure 1: Reference SPEERMINT Architecture

   For further details on the elements and functions described in this figure,
   please refer to [RFC 5486].

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.

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          a.  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

     4. Exchange the media, which could include voice, video, tec, 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 2 that shows the target SSP with its own peering functions.

  3.1. Relationships between functions/elements

      -  An SBE can contain a SF function.
      -  An SF can perform LUF and LRF functions.
      -  As an additional consideration, a Session Border Controller [SBC RFC], can
        contain an SF, SBE and DBE, and may perform the LUF and LRF functions.
      -  The following functions can communicate as follows, depending upon various
        real-world implementations:
           o                  SF can communicate with LUF, LRF, SBE and SF
           o                  LUF can communicator with SF and SBE
           o                  LRF can communicate with SF and SBE

4. 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

   Some of the information in the section is taken from [14] and is put here for
   continuity purposes.

  4.1. Originating SSP Procedures

4.1.1. 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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   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

   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. 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.

4.1.2. 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

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   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. 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. 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. 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.

4.1.3. 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 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.

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   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] 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. 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. 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. Sending the SIP request

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

  4.2. Target SSP Procedures

4.2.1. The Ingress Signaling Path Border Element (SBE) 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

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   the domain in the From header corresponds to one of the domains in the TLS
   client certificate. 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".

  4.3. 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.

5. 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.

6. 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.

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   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

7. IANA Considerations

   There are no IANA considerations at this time.

8. Acknowledgments

   The working group thanks Sohel Khan for his initial architecture
   draft that helped to initiate work on this draft.

   A significant portion of this draft is taken from [14] with
   permission from the author R. Mahy. The other important contributor
   is Otmar Lendl. Special thanks to Jim McEachern for detailed comments and

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9. References

  9.1. Normative References

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

   [2]   Mealling, M. and R. Daniel, "The Naming Authority Pointer (NAPTR) DNS
         Resource Record", RFC 2915, September 2000.

   [3]   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.

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

   [5]   Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J., and T.
         Wright, "Transport Layer Security (TLS) Extensions", RFC 4366, April

   [6]   Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A
         Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July

   [7]   Peterson, J., Liu, H., Yu, J., and B. Campbell, "Using E.164 numbers
         with the Session Initiation Protocol (SIP)", RFC 3824, June 2004.

   [8]   Peterson, J., "Address Resolution for Instant Messaging and
         Presence",RFC 3861, August 2004.

   [9]   Peterson, J., "Telephone Number Mapping (ENUM) Service Registration for
         Presence Services", RFC 3953, January 2005.

   [10]  ETSI TS 102 333: " Telecommunications and Internet converged Services
         and Protocols for Advanced Networking (TISPAN); Gate control protocol".

   [11]  Peterson, J., "enumservice registration for Session Initiation Protocol
         (SIP) Addresses-of-Record", RFC 3764, April 2004.

   [12]  Livingood, J. and R. Shockey, "IANA Registration for an
         Enumservice Containing PSTN Signaling Information", RFC 4769, November

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  9.2. Informative References

   [13]  Malas, D., "SPEERMINT Terminology", draft-ietf-speermint-terminology-16
         (work in progress), February 2008.

   [14]  Mule, J-F., "SPEERMINT Requirements for SIP-based VoIP Interconnection",
         draft-ietf-speermint-requirements-04.txt, February 2008.

   [15]  Mahy, R., "A Minimalist Approach to Direct Peering", draft-
         mahy-speermint-direct-peering-02.txt, July 2007.

   [16]  Penno, R., et al., "SPEERMINT Routing Architecture Message
         Flows", draft-ietf-speermint-flows-02.txt", April 2007.

   [17]  Houri, A., et al., "RTC Provisioning Requirements", draft-
         houri-speermint-rtc-provisioning-reqs-00.txt, June, 2006.

   [18]  Habler, M., et al., "A Federation based VOIP Peering
         Architecture", draft-lendl-speermint-federations-03.txt, September 2006.

   [19]  Mahy, R., "A Telephone Number Mapping (ENUM) Service
         Registration for Instant Messaging (IM) Services", draft-ietf-
         enum-im-service-03 (work in progress), March 2006.

   [20]  Haberler, M. and R. Stastny, "Combined User and Carrier ENUM in the
         e164.arpa tree", draft-haberler-carrier-enum-03 (work in progress),
         March 2006.

   [21]  Penno, R., Malas D., and Melampy, P., "A Session Initiation
         Protocol (SIP) Event package for Peering", draft-penno-sipping-peering-
         package-00 (work in progress), September 2006.

   [22]  Hollander, D., Bray, T., and A. Layman, "Namespaces in XML", W3C REC
         REC-xml-names-19990114, January 1999.

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

   [24]  Gurbani, V., Lawrence, S., and B. Laboratories, "Domain Certificates in
         the Session Initiation Protocol (SIP)", draft-ietf-sip-domain-certs-00
         (work in progress), November 2007.

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Author's Addresses

   Adam Uzelac
   Global Crossing
   Rochester, NY - USA
   Email: adam.uzelac@globalcrossing.com

   Reinaldo Penno
   Juniper Networks
   Sunnyvale, CA - USA
   Email: rpenno@juniper.net

   Mike Hammer
   Cisco Systems
   Herndon, VA - USA
   Email: mhammer@cisco.com

   Sohel Khan, Ph.D.
   Comcast Cable Communications
   Email: sohel_khan@cable.comcast.com

   Daryl Malas
   Louisville, CO - USA
   Email: d.malas@cablelabs.com

   Hadriel Kaplan
   Acme Packet
   Email: hkaplan@acmepacket.com

   Jason Livingood
   Email: Jason_livingood@cable.comcast.com

   David Schwartz
   Kayote Systems
   Email: david.schwartz@kayote.com

   Rich Shockey
   Email: Richard@shockey.us

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