SPEERMINT                                                  D. Malas, Ed.
Internet-Draft                                                 CableLabs
Intended status: Informational                         J. Livingood, Ed.
Expires: May 12, June 23, 2011                                           Comcast
                                                        November 8,
                                                       December 20, 2010

                     SPEERMINT Peering

        Session PEERing for Multimedia INTerconnect Architecture
                  draft-ietf-speermint-architecture-16
                  draft-ietf-speermint-architecture-17

Abstract

   This document defines a peering architecture for the Session
   Initiation Protocol (SIP) [RFC3261], it's its 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.

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   This Internet-Draft will expire on May 12, June 23, 2011.

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Table of Contents

   1.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  4
   2.  Reference Architecture . . . . . . . . . . . . . . . . . . . .  4
   3.  Procedures of Inter-Domain SSP Session Establishment . . . . .  5  6
   4.  Relationships Between Functions/Elements . . . . . . . . . . .  6  7
   5.  Recommended SSP Procedures . . . . . . . . . . . . . . . . . .  6  7
     5.1.  Originating or Indirect SSP Procedures . . . . . . . . . .  6  8
       5.1.1.  The Look-Up Function (LUF) . . . . . . . . . . . . . .  7  8
         5.1.1.1.  Target Address Analysis  . . . . . . . . . . . . .  7  8
         5.1.1.2.  ENUM Lookup  . . . . . . . . . . . . . . . . . . .  7  9
       5.1.2.  Location Routing Function (LRF)  . . . . . . . . . . .  8  9
         5.1.2.1.  DNS Resolution . . . . . . . . . . . . . . . . . .  8  9
         5.1.2.2.  Routing Table  . . . . . . . . . . . . . . . . . .  8 10
         5.1.2.3.  LRF to LRF Routing . . . . . . . . . . . . . . . .  9 10
       5.1.3.  The Signaling Path Border Element (SBE)  . . . . . . .  9 10
         5.1.3.1.  Establishing a Trusted Relationship  . . . . . . .  9 10
         5.1.3.2.  IPSec  . . . . . . . . . . . . . . . . . . . . . .  9 10
         5.1.3.3.  Co-Location  . . . . . . . . . . . . . . . . . . .  9 11
         5.1.3.4.  Sending the SIP Request  . . . . . . . . . . . . . 10 11
     5.2.  Target SSP Procedures  . . . . . . . . . . . . . . . . . . 10 11
       5.2.1.  TLS  . . . . . . . . . . . . . . . . . . . . . . . . . 10 11
       5.2.2.  Receive SIP Requests . . . . . . . . . . . . . . . . . 10 11
     5.3.  Data Path Border Element (DBE) . . . . . . . . . . . . . . 10 12
   6.  Address Space Considerations . . . . . . . . . . . . . . . . . 11 12
   7.  Acknowledgments  . . . . . . . . . . . . . . . . . . . . . . . 11 12
   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 11 12
   9.  Security Considerations  . . . . . . . . . . . . . . . . . . . 11 12
   10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 11 13
   11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 13 14
   12. Open Issues  . . . . . . . . . . . . . . . . . . . . . . . . . 13
   13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 14
     13.1. 15
     12.1. Normative References . . . . . . . . . . . . . . . . . . . 14
     13.2. 15
     12.2. Informative References . . . . . . . . . . . . . . . . . . 15 16

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 15 16

1.  Introduction

   This document defines a reference peering architecture for the
   Session Initiation Protocol (SIP)[RFC3261], it's functional
   components and interfaces, 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 Provider's
   (SSP) [RFC5486] network.  Thus, it also describes the components and
   the
   steps necessary steps necessary to establish a session between two SSP peering
   domains.

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

   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 (SPEERMINT) Terminology document [RFC5486].
   Apart from normative references included herein, readers may also
   find [I-D.ietf-speermint-voip-consolidated-usecases] informative.

2.  Reference Architecture

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

   For further details on the elements and functions described in this
   figure, please refer to [RFC5486].  The following terms, which appear
   in Figure 1, which are documented in [RFC5486] are reproduced here
   for simplicity.

   - Data Path Border Element (DBE): 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.

   - E.164 Number Mapping (ENUM): See [RFC3761].

   - Fully Qualified Domain Name (FQDN): See Section 5.1 of [RFC1035].

   - Location Routing Function (LRF): 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 in Section 4.3.3 of [RFC5486].  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 of [RFC5486]) or indirect (Section 4.2.2 of [RFC5486]) peering
   as necessary.

   - Look-Up Function (LUF): 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 of [RFC5486]) or indirect (Section 4.2.2 of [RFC5486])
   peering as necessary.

   - Real-Time Transport Protocol (RTP): See [RFC3550].

   - Session Initiation Protocol (SIP): See [RFC3261].

   - Signaling Path Border Element (SBE): 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.

   - Signaling Function (SF): 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 establish be used by
   the Media Function (MF).  The SF is a session between two capability of SIP processing
   elements such as SIP proxies, SBEs, and user agents.

   - SIP Service Provider (SSP): A SIP Service Provider (SSP) peering domains.

   This architecture enables is an
   entity that provides session services utilizing SIP signaling to its
   customers.  In the interconnection of two SSPs in layer 5
   peering, as defined in event that the SIP-based session peering requirements
   [I-D.ietf-speermint-requirements].

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

   This document uses terminology defined in PSTN.  An SSP may also be referred to as an Internet
   Telephony Service Provider (ITSP).  While the Session Peering for
   Multimedia Interconnect (SPEERMINT) Terminology terms ITSP and SSP are
   frequently used interchangeably, this document [RFC5486].

2.  Reference Architecture

   The following figure and other subsequent
   SIP peering-related documents should use the term SSP.  SSP more
   accurately depicts the architecture and logical functions
   that form peering between two SSPs. use of SIP as the underlying layer 5 signaling
   protocol.

        +=============++                          ++==============+
                      ||                          ||
                +-----------+                +-----------+
                |    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 User Agent (UA) in the originating (or indirect) SSP's network
   to an UA in the Target SSP's network the following steps are taken:

   1.  Determine the target or indirect 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

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

   5.  End the session (BYE)

   The originating or indirect SSP would likely perform steps 1-4, and the
   target SSP would likely perform steps 4-5. 4, and either one is likely to
   perform step 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.ietf-speermint-requirements] and is put here for continuity
   purposes.

5.1.  Originating or Indirect SSP Procedures

   This section describes the procedures of the originating or indirect
   SSP.

5.1.1.  The Look-Up Function (LUF)

   The purpose of the LUF is to determine the SF of the target domain of
   a given request and optionally to develop Session Establishment Data.
   It is important to note that the LUF may utilize the public e164.arpa
   ENUM root, as well as one or more private roots.  When private roots
   are used specialized routing rules may be implemented, and these
   rules may vary depending upon whether an originating or indirect SSP
   is querying the LUF.

5.1.1.1.  Target Address Analysis

   When the originating (or indirect) 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 (or indirect) SSP's administrative domain or federation
   of domains, then the originating (or indirect) 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 [RFC3861] [RFC3953], the originating (or indirect) SSP follows
   the procedures in [RFC3861].  If the highest priority supported URI
   scheme is sip: or sips: the originating (or indirect) 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
   (or indirect) SSP skips to SIP DNS resolution in Section 5.1.2.1.
   This may be the case, to use one example, with
   "sips:bob@biloxi.example.com".

   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 (or
   indirect) SSP consults the public "User ENUM" rooted at e164.arpa,
   according to the procedures described in [RFC3761].  The SSP must
   query for the "E2U+sip" enumservice as described in [RFC3764], but
   may check for other enumservices.  The originating (or indirect) 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 (or indirect) SSP is sure that the target
   address country code is not represented in e164.arpa.

   If an im: or pres: URI is chosen for based on an "E2U+im" [RFC3861] or
   "E2U+pres" [RFC3953] 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.

   The NAPTR response to the ENUM lookup may be a SIP AoR (such as
   "sips:bob@example.com") or SIP URI (such as
   "sips:bob@sbe1.biloxi.example.com").  In the case of when a SIP URI
   is returned, the originating (or indirect) SSP has sufficient routing
   information to locate the target SSP.  In the case of when a SIP AoR
   is returned, the SF then uses the LRF to determine the URI for more
   explicitly locating the target SSP.

5.1.2.  Location Routing Function (LRF)

   The LRF of an originating (or indirect) 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 (or indirect) SSP uses the procedures in Section 4 of
   [RFC3263] to determine how to contact the receiving SSP.  To
   summarize the [RFC3263] 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 (or indirect) SSP to the receiving SSP if
   available, as described further in Section 5.2.1.

5.1.2.2.  Routing Table

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

   If so, the originating (or indirect) 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
   used by the Media Function (MF).  The signaling function performs the
   routing of SIP messages.  The SBE may be a B2BUA or it may act as a
   SIP proxy.  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.

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 (or indirect) SSP sends the request.

5.2.  Target SSP Procedures

   This section describes the Target SSP Procedures.

5.2.1.  TLS

   The section defines uses of TLS between two SSPs [RFC5246] [RFC5746]
   [RFC5878].  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 [RFC5922].

   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.

5.2.2.  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 (or indirect) 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 [RFC5486] 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 [RFC3711], 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 [RFC1918].  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.

7.  Acknowledgments

   The working group would like to thank John Elwell, Otmar Lendl, Rohan
   Mahy, Alexander Mayrhofer, Jim McEachern, Jean-Francois Mule,
   Jonathan Rosenberg, and Dan Wing for their valuable contributions to
   various versions of this document.

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.

   Additional security considerations have been documented separately in
   [I-D.ietf-speermint-voipthreats].

10.  Contributors

   Mike Hammer

   Cisco Systems

   Herndon, VA - USA

   Email: mhammer@cisco.com

   --------------------------------------------------------------

   Hadriel Kaplan

   Acme Packet

   Burlington, MA - USA

   Email: hkaplan@acmepacket.com

   --------------------------------------------------------------

   Sohel Khan, Ph.D.

   Comcast Cable

   Philadelphia, PA - USA

   Email: sohel_khan@cable.comcast.com

   --------------------------------------------------------------

   Reinaldo Penno

   Juniper Networks

   Sunnyvale, CA - USA

   Email: rpenno@juniper.net

   --------------------------------------------------------------
   David Schwartz

   XConnect Global Networks

   Jerusalem - Israel

   Email: dschwartz@xconnnect.net

   --------------------------------------------------------------

   Rich Shockey

   Shockey Consulting

   USA

   Email: Richard@shockey.us

   --------------------------------------------------------------

   Adam Uzelac

   Global Crossing

   Rochester, NY - USA

   Email: adam.uzelac@globalcrossing.com

11.  Change Log

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

   o  17: Misc. updates at the request of Gonzalo, the RAI AD, in order
      to clear his review and move to the IESG.  This included adding
      terminology from RFC 5486 and expanding the document name.

   o  16: Yes, one final outdated reference to fix.

   o  15: Doh!  Uploaded the wrong doc to create -14.  Trying again. :-)

   o  14: WGLC ended.  Ran final nits check prior to sending proto to
      the AD and sending the doc to the IESG.  Found a few very minor
      nits, such as capitalization and replacement of an obsoleted RFC,
      which were corrected per nits tool recommendation.  The -14 now
      moves to the AD and the IESG.

   o  13: Closed out all remaining tickets, resolved all editorial
      notes.

   o  12: Closed out several open issues.  Properly XML-ized all
      references.  Updated contributors list.

   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  NONE!

13.  References

13.1.

12.1.  Normative References

   [I-D.ietf-speermint-requirements]
              Mule, J., "Requirements for SIP-based Session Peering",
              draft-ietf-speermint-requirements-10 (work in progress),
              October 2010.

   [I-D.ietf-speermint-voipthreats]
              Seedorf, J., Niccolini, S., Chen, E., and H. Scholz,
              "Session Peering for Multimedia Interconnect (SPEERMINT)
              Security Threats and Suggested Countermeasures",
              draft-ietf-speermint-voipthreats-06 (work in progress),
              November 2010.

   [RFC1035]  Mockapetris, P., "Domain names - implementation and
              specification", STD 13, RFC 1035, November 1987.

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

   [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.

   [RFC3550]  Schulzrinne, H., Casner, S., Frederick, R., and V.
              Jacobson, "RTP: A Transport Protocol for Real-Time
              Applications", STD 64, RFC 3550, July 2003.

   [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.

   [RFC3764]  Peterson, J., "enumservice registration for Session
              Initiation Protocol (SIP) Addresses-of-Record", RFC 3764,
              April 2004.

   [RFC3861]  Peterson, J., "Address Resolution for Instant Messaging
              and Presence", RFC 3861, August 2004.

   [RFC3953]  Peterson, J., "Telephone Number Mapping (ENUM) Service
              Registration for Presence Services", RFC 3953,
              January 2005.

   [RFC5246]  Dierks, T. and E. Rescorla, "The Transport Layer Security
              (TLS) Protocol Version 1.2", RFC 5246, August 2008.

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

   [RFC5746]  Rescorla, E., Ray, M., Dispensa, S., and N. Oskov,
              "Transport Layer Security (TLS) Renegotiation Indication
              Extension", RFC 5746, February 2010.

   [RFC5878]  Brown, M. and R. Housley, "Transport Layer Security (TLS)
              Authorization Extensions", RFC 5878, May 2010.

   [RFC5922]  Gurbani, V., Lawrence, S., and A. Jeffrey, "Domain
              Certificates in the Session Initiation Protocol (SIP)",
              RFC 5922, June 2010.

13.2.

12.2.  Informative References

   [I-D.ietf-speermint-voip-consolidated-usecases]
              Uzelac, A. and Y. Lee, "VoIP SIP Peering Use Cases",
              draft-ietf-speermint-voip-consolidated-usecases-18 (work
              in progress), April 2010.

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

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