Speermint Working Group A.Uzelac(Ed.) Internet Draft Global Crossing Intended status: Informational Expires: September 2009 March 2, 2009 SPEERMINT Peering Architecture draft-ietf-speermint-architecture-08 Status of this Memo This Internet-Draft is submitted to IETF in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF), its areas, and its working groups. Note that other groups may also distribute working documents as Internet- Drafts. 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." The list of current Internet-Drafts can be accessed at http://www.ietf.org/ietf/1id-abstracts.txt. The list of Internet-Draft Shadow Directories can be accessed at http://www.ietf.org/shadow.html. This Internet-Draft will expire on September 2, 2009. Copyright Notice Copyright (c) 2009 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 to this document. Abstract This document defines the SPEERMINT peering architecture, its functional components and peering interface functions. It also describes the steps taken to establish a session between two peering domains in the context of the functions defined. Uzelac Expires September 2, 2009 [Page 1] Internet-Draft SPEERMINT peering architecture February 2009 Table of Contents 1. Introduction...................................................3 2. Network Context................................................3 3. Reference SPEERMINT Architecture...............................4 4. Procedures of Interdomain SSP Session Establishment............6 5. Recommended SSP Procedures.....................................7 5.1. Originating SSP Procedures................................7 5.1.1. The Look-Up Function (LUF)...........................7 5.1.1.1. Target address analysis.........................7 5.1.1.2. End User ENUM Lookup............................8 5.1.1.3. Infrastructure ENUM lookup......................8 5.1.2. Location Routing Function (LRF)......................8 5.1.2.1. SIP DNS Resolution..............................8 5.1.2.2. Routing Table...................................9 5.1.2.3. SIP Redirect Server.............................9 5.1.3. The Signaling Function (SF)..........................9 5.1.3.1. Establishing a Trusted Relationship.............9 5.1.3.2. Sending the SIP request........................10 5.2. Terminating SSP Procedures...............................10 5.2.1. The Location Function (LF)..........................10 5.2.1.1. Publish ENUM records...........................10 5.2.1.2. Publish SIP DNS records........................11 5.2.1.3. Subscribe Notify...............................11 5.2.2. Signaling Function (SF).............................11 5.2.2.1. TLS............................................11 5.2.2.2. Receive SIP requests...........................11 5.3. Target SSP Procedures....................................12 5.3.1. Signaling Function (SF).............................12 5.3.1.1. TLS............................................12 5.3.1.2. Receive SIP requests...........................12 5.4. Media Function (MF)......................................12 5.5. Policy Considerations....................................12 6. Call Control and Media Control Deployment Options.............13 7. Address space considerations..................................14 8. Security Considerations.......................................15 9. IANA Considerations...........................................15 10. Acknowledgments..............................................15 11. References...................................................16 11.1. Normative References....................................16 11.2. Informative References..................................17 Author's Addresses...............................................18 Uzelac Expires September 2, 2009 [Page 2] Internet-Draft SPEERMINT peering architecture February 2009 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. 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 aspects. 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", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" are to be interpreted as described in [RFC2119]. 2. Network Context Figure 1 allows for the following potential SPEERMINT peering scenarios: o Enterprise to Enterprise across the public Internet o Enterprise to SSP across the public Internet o SSP to SSP across the public Internet o Enterprise to enterprise across a private Layer 3 network o Enterprise to SSP across a private Layer 3 network o SSP to SSP across a private Layer 3 network +-------------------+ | | | Public | | SIP | | Peering | | | +-------------------+ | ----- Uzelac Expires September 2, 2009 [Page 3] Internet-Draft SPEERMINT peering architecture February 2009 +-----------+ / \ +-----------+ |Enterprise | -- -- |Enterprise | |Provider A |-----------/ \-----------|Provider B | +-----------+ -- -- +-----------+ / Public \ | Internet | \ (Layer 3) / +-----------+ -- -- +-----------+ | SSP C |-----------\ /-----------| SSP D | | | -- -- | | +-----------+ \_____/ +-----------+ | Layer 3 Peering | Point (out of scope) ----- +-----------+ / \ +-----------+ |Enterprise | -- -- |Enterprise | |Provider E |-----------/ \-----------|Provider F | +-----------+ -- Private -- +-----------+ / Network \ | (Layer 3) | \ / +-----------+ -- -- +-----------+ | SSP G |-----------\ /-----------| SSP H | | | -- -- | | +-----------+ \____/ +-----------+ | +-------------------+ | Private | | SIP | | Peering | | | +-------------------+ Figure 1: SPEERMINT Network Context 3. Reference SPEERMINT Architecture Figure 2 depicts the SPEERMINT architecture and logical functions that form the peering between two SSPs. Uzelac Expires September 2, 2009 [Page 4] Internet-Draft SPEERMINT peering architecture February 2009 +------+ | DNS, | +---------->| Db, |<---------+ | | etc | | | +------+ | | | ------|-------- -------|------- / v \ / v \ | +--LUF-+ | | +--LUF-+ | | | | | | | | | | | | | | | | | | | | | | | | | | +------+ | | +------+ | | | | | | +--LRF-+ | | +--LRF-+ | | | | | | | | | | | | | | | | | | | | | | | | | | +------+ | | +------+ | | | | | | | | | | +---SF--+ +---SF--+ | | | | | | | | | SBE | | SBE | | | Originating | | | | Target | | +---SF--+ +---SF--+ | | SSP | | SSP | | +---MF--+ +---MF--+ | | | | | | | | | DBE | | DBE | | | | | | | | | +---MF--+ +---MF--+ | \ / \ / --------------- --------------- Figure 2: Reference SPEERMINT Architecture The following procedures are implemented by a set of peering functions: The Look-Up Function (LUF) provides a mechanism for determining for a given request the target domain to which the request should be routed. 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 Session Establishment Data (SED) required to route the request to that domain. Uzelac Expires September 2, 2009 [Page 5] Internet-Draft SPEERMINT peering architecture February 2009 The Signaling Function (SF) provides SIP call routing, to optionally perform termination and re-initiation of call, to 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 Media Function (MF) provides media related functions such as media transcoding, topology hiding and media security implementation between two SSPs. The intention of defining these functions is to provide a framework for design segmentation and allow each one to evolve independently. 4. Procedures of Interdomain 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. analyze the target address. a. If the target address represents an intra-SSP resource, the behavior is out-of-scope with respect to this draft. 2. determine the target SSP (LUF) 3. determine the SF next-hop in the target SSP (LRF) 4. enforce authentication and potentially other policies 5. determine of the UA 6. establish the session, 7. transfer of media which could include voice, video, text and others, 8. terminate 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. Uzelac Expires September 2, 2009 [Page 6] Internet-Draft SPEERMINT peering architecture February 2009 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 [14] 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. 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. Note that the SSP may also consult any manner of private data sources to make this determination. If the target address does not represent a resource inside the originating SSP's administrative domain or federation of domains, the originating SSP 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 5.1.2.1. 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. Uzelac Expires September 2, 2009 [Page 7] Internet-Draft SPEERMINT peering architecture February 2009 5.1.1.2. End User 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. 5.1.1.3. Infrastructure ENUM lookup An originating SSP may check for a carrier-of-record in an Infrastructure ENUM domain according to the procedures described in [12]. As in the previous step, the SSP may consult a cache or alternate representation of the ENUM data in lieu of actual DNS queries. The SSP first checks for records for the "E2U+sip" enumservice, then for the "E2U+pstn" enumservice as defined in [21]. If a terminal record is found with a sip: or sips: URI, the SSP skips to Section 5.1.2.1. , otherwise the SSP continues processing according to the next section. 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. 5.1.2.1. SIP DNS Resolution Once a sip: or sips: in an external domain is identified as the target, the originating SSP may apply local policy to decide whether forwarding requests to the target domain is acceptable. 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. Note that these are queries of records in the global DNS. Uzelac Expires September 2, 2009 [Page 8] Internet-Draft SPEERMINT peering architecture February 2009 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. SIP Redirect Server A SIP Redirect Server using 3XX SIP Redirect is another option in resolving the next-hop SF of the target domain. 5.1.3. The Signaling Function (SF) 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). Optionally, a SF may perform additional functions such as Session Admission Control, SIP Denial of Service protection, SIP Topology Hiding, SIP header normalization, and 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. Uzelac Expires September 2, 2009 [Page 9] Internet-Draft SPEERMINT peering architecture February 2009 5.1.3.1.1. TLS connection Once a transport, port, and address are found, the originating SSP will open or find a reusable TLS connection to the peer. The procedures to authenticate the SSP's target domain is specified in [24] 5.1.3.1.2. TLS If the trust relationship was established through TLS, the originating SSP can optionally verify and assert the senders identity using the SIP Identity mechanism. In addition, new requests should contain a valid Identity and Identity-Info header as described in [12]. The Identity-Info header must present a domain name that is represented in the certificate provided when establishing the TLS connection over which the request is sent. The originating SSP should include an Identity header on in-dialog requests as well if the From header field value matches an identity the originating SSP is willing to assert. 5.1.3.1.3. 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. 5.1.3.1.4. 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. 5.1.3.2. Sending the SIP request Once a trust relationship between the peers is established, the originating SSP sends the request. 5.2. Terminating SSP Procedures 5.2.1. The Location Function (LF) 5.2.1.1. Publish ENUM records The receiving SSP should participate by publishing "E2U+sip" and "E2U+pstn" records with sip: or sips: URIs wherever a public Infrastructure ENUM root is available. This assumes that the receiving SSP wants to peer by default. When Uzelac Expires September 2, 2009 [Page 10] Internet-Draft SPEERMINT peering architecture February 2009 the receiving SSP does not want to accept traffic from specific originating SSPs, it may still reject requests on a call-by-call basis. 5.2.1.2. Publish SIP DNS records To receive SSP requests, the receiving SSP must insure that it publishes appropriate NAPTR, SRV, and address (A and/or AAAA) records in the LF relevant to the SSP's SF. 5.2.1.3. Subscribe Notify Policies function may also be optionally implemented by dynamic subscribe, notify, and exchange of policy information and feature information among SSPs [21]. 5.2.2. Signaling Function (SF) 5.2.2.1. 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. 5.2.2.2. 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 SSP is not authorized to peer, the receiving SSP should respond with a 403 response with the reason phrase "Unsupported Peer". Uzelac Expires September 2, 2009 [Page 11] Internet-Draft SPEERMINT peering architecture February 2009 5.3. Target SSP Procedures 5.3.1. Signaling Function (SF) 5.3.1.1. TLS When the receiving SSP receives a TLS client hello, it responds with its certificate. The Target SSP's 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]. If the requests should contain a valid Identity and Identity-Info header as described in [24] the target SF 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. 5.3.1.2. Receive SIP requests The procedures of the SF of the target SSP are the same as the ones described in section 5.2.2.2 with the addition that it might establish a connection to another target SSP, and in this case use the procedures recommended to an originating SS (section 5.1). 5.4. Media Function (MF) The purpose of the MF 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. 5.5. Policy Considerations In the context of the SPEERMINT working group when two SSPs peer, there MAY be a desire to exchange peering policy information dynamically. There are specifications in progress in the SIPPING working group to define policy exchange between an UA and a domain [23] and providing profile data to SIP user agents [24] These considerations borrow from both. Following the terminology introduced in [12], this package uses the terms Peering Session-Independent and Session-Specific policies in the following context. o Peering Session-Independent policies include Diffserv Marking, Policing, Session Admission Control, and domain reachabilities, amongst others. The Uzelac Expires September 2, 2009 [Page 12] Internet-Draft SPEERMINT peering architecture February 2009 time period between Peering Session-Independent policy changes is much greater than the time it takes to establish a call. o Peering Session-Specific polices includes supported connection/call rate, total number of connections/calls available, current utilization, amongst others. Peering Session-specific policies can change within the time it takes to establish a call. These policies can be SSP dependent or independent, creating the following peering policy definition: o SSP Independent or Dependent Session dependent Session independent 6. Call Control and Media Control Deployment Options The peering functions can be deployed along the following two dimensions depending upon how the signaling and the media functions along with IP layer are implemented: Composed or Decomposed: Addresses the question whether the media must flow through the same physical and geographic elements as SIP dialogs and sessions. Centralized or Distributed: Addresses the question whether the logical and physical interconnections are in one geographical location or distributed to multiple physical locations on the SSP's network. In a composed model, SF and MF functions are implemented in one peering logical element. Uzelac Expires September 2, 2009 [Page 13] Internet-Draft SPEERMINT peering architecture February 2009 Provider A Provider B ---------- . . ---------- / \ . . / \ | | . _ . | | | +----+ . / \_ . +----+ | | | SF |<-----/ \------| SF | | | +-+--+ . /Transit\ . | | | | | | . / IP \ . | | | | +-+--+ . | Provider| . | | | | | MF |<~~~| (Option)|~~~~| MF | | | +----+ . \ / . +----+ | | | . \ __ _ / . | | \_________ / . . \________ _/ ---------- ---------- --- Signal (SIP) ~~~ Bearer (RTP/IP) ... Scope of peering Figure 3: Decomposed v. Collapsed Peering The advantage of a collapsed peering architecture is that one-element solves all peering issues. Disadvantage examples of this architecture are single point of failure, bottleneck, and complex scalability. In a decomposed model, SF and MF are implemented in separate peering logical elements. SFs are implemented in a proxy and MFs are implemented in another logical element. The scaling of signaling versus scaling of media may differ between applications. Decomposing allows each to follow a separate migration path. This model allows the implementation of M:N model where one SF is associated with multiple peering MF and one peering MF is associated with multiple SFs. Generally, a vertical protocol associates the relationship between a SF and a MF. This architecture reduces the potential of a single point of failure. It allows separation of the policy decision point and the policy enforcement point. An example of disadvantages is the scaling complexity because of the M:N relationship and latency due to the vertical control messages between entities. 7. 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 Uzelac Expires September 2, 2009 [Page 14] Internet-Draft SPEERMINT peering architecture February 2009 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. 8. 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. 9. IANA Considerations There are no IANA considerations at this time. 10. 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 feedback. Uzelac Expires September 2, 2009 [Page 15] Internet-Draft SPEERMINT peering architecture February 2009 11. References 11.1. 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 2006. [6] Schulzrinne, H., Casner, S., Frederick, R., and V. Jacobson, "RTP: A Transport Protocol for Real-Time Applications", STD 64, RFC 3550, July 2003. [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 2006. Uzelac Expires September 2, 2009 [Page 16] Internet-Draft SPEERMINT peering architecture February 2009 11.2. 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. Uzelac Expires September 2, 2009 [Page 17] Internet-Draft SPEERMINT peering architecture February 2009 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 USA Email: sohel_khan@cable.comcast.com Daryl Malas CableLabs Louisville, CO - USA Email: d.malas@cablelabs.com Uzelac Expires September 2, 2009 [Page 18]