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Versions: 00 01 02 03                                                   
Session PEERing for Multimedia                               M. Haberler
INTerconnect                                                         IPA
Internet-Draft                                                 M. Hammer
Expires: February 11, 2007                                         Cisco
                                                                O. Lendl
                                                                 enum.at
                                                         August 10, 2006


              A Federation based VoIP Peering Architecture
                  draft-lendl-speermint-federations-02

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Copyright Notice

   Copyright (C) The Internet Society (2006).

Abstract

   This document defines the federation concept and proposes a peering
   and routing architecture for SIP-based applications.  Federations can
   be used to establish selective peerings e.g. in the Voice over IP and
   Instant Messaging space.  Service providers may announce federation
   membership as domain attributes.  This document contains the policy-



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   type definition for federations within the Domain Policy DDDS
   Application.


Table of Contents

   1.  Terminology  . . . . . . . . . . . . . . . . . . . . . . . . .  3

   2.  Introduction . . . . . . . . . . . . . . . . . . . . . . . . .  3

   3.  Federations  . . . . . . . . . . . . . . . . . . . . . . . . .  3

   4.  Federation based Routing . . . . . . . . . . . . . . . . . . .  4
     4.1.  Assumptions  . . . . . . . . . . . . . . . . . . . . . . .  4
     4.2.  Call Flows . . . . . . . . . . . . . . . . . . . . . . . .  5
       4.2.1.  Direct Intra-federation calls  . . . . . . . . . . . .  6
       4.2.2.  Single-transit Inter-federation calls  . . . . . . . .  6
       4.2.3.  Multiple-Transit calls . . . . . . . . . . . . . . . .  6
     4.3.  Procedures . . . . . . . . . . . . . . . . . . . . . . . .  6
     4.4.  Routing Architecture . . . . . . . . . . . . . . . . . . .  7
       4.4.1.  Static configuration . . . . . . . . . . . . . . . . .  8
       4.4.2.  Forward Search . . . . . . . . . . . . . . . . . . . .  8
       4.4.3.  Route Announcements  . . . . . . . . . . . . . . . . .  8

   5.  Policy-Type template . . . . . . . . . . . . . . . . . . . . .  8

   6.  Examples . . . . . . . . . . . . . . . . . . . . . . . . . . .  9

   7.  Security Considerations  . . . . . . . . . . . . . . . . . . .  9

   8.  IANA Considerations  . . . . . . . . . . . . . . . . . . . . . 10

   9.  Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 10

   10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
     10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
     10.2. Informative References . . . . . . . . . . . . . . . . . . 10

   Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
   Intellectual Property and Copyright Statements . . . . . . . . . . 12











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1.  Terminology

   This document uses the terminology as defined in
   draft-ietf-speermint-terminology-00 [1].

   The acronym VSP will stand for "VoIP Service Provider".

   Our definition of VSP encompasses commercial service providers as
   well as enterprises and end user operating their own SIP [4] proxy.


2.  Introduction

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in [3].

   The domain policy DDDS application [2] defines a generic method how a
   domain owner may announce the conditions to accept incoming
   communications.  This documents defines the policy-type for
   publishing federation membership.

   This document focuses on the use of federations for SIP peering.  The
   same mechanism may be applied to other application protocols as well.
   The difference is in the protocol field of the service parameter in
   the NAPTR records.


3.  Federations

   The proposed method is based upon the concept of a "Federation".  A
   federation is defined as follows:

      A Federation is a group of VoIP service providers which
      *  agree to accept calls from each other via SIP,
      *  agree on a set of administrative rules for these calls
         (settlement, abuse-handling, ...), and
      *  agree on rules for the technical details of the
         interconnection.

   The actual rules are private to the federation and need not be
   published.  Federation members are expected to know and abide by
   these rules.

   Federations are identified by URIs.  It is RECOMMENDED that
   federations use URLs as identifiers which point to documents
   describing the federation.




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   For the purposes of the domain policy DDDS application, federation
   identifiers are opaque strings.  The only operations performed on
   these identifiers are string comparisons.  If the identifier is in
   the form of an URL, the document referred to by that URL is never
   evaluated during the basic peer discovery process.

   The federation named "urn:ietf:rfc:3261" stands for the public
   Internet.  A SIP service provider who announces his membership in
   "urn:ietf:rfc:3261" will accept calls as defined in the generic SIP
   RFC [4].

   Examples:

   o  A group of VoIP service providers forms an association and agrees
      to accept calls from each other via the public Internet provided
      the TLS transport is used for SIP signalling and members present a
      valid X.509 cert signed by the association's certificate
      authority.

   o  A group of VoIP service providers build a Layer 3 network for VoIP
      peering ("walled garden", e.g. similar to the 3GPP GRX network).
      They agree to accept calls from all participants in that network
      and settle through a clearinghouse.

   o  A group of VoIP service providers agree to accept calls
      originating from from each other.  They use firewall rules to
      block calls from all other networks.

   o  Peering fabric based on SIP: A SIP hub acts as a forwarding proxy
      between participants.  Intra-federation calls are to be routed
      through the SIP hub.

   o  Peer to Peer SIP clouds: P2P SIP proposes an alternative
      resolution method based on distributed hash tables (DHT).  The set
      participants in each such DHT can be seen as a federation whose
      technical rules stipulate the URI resolution via the DHT ring.


4.  Federation based Routing

   This section outlines how the federations concept relates to the
   Speermint routing architecture.

4.1.  Assumptions

   Many VSPs will prefer not to run open SIP proxies and accept calls
   from the public Internet.




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   Some VSPs will establish private peerings between each other.

   Groups of VSPs will enter into mutual peering agreements.  In other
   cases, third parties might build such peering fabrics as a service.

   Both private peerings and such peering fabrics are federations as
   defined by this document.

   VSPs might choose to join several federations if it suits their
   business strategy.  This set of federations defines the range of
   destination VSPs reachable with a direct SIP connection.

   VSPs which are members of multiple federations may choose to provide
   transit services to other VSPs.  Such VSPs act as bridges between
   federations.

   On the other hand, the VSPs who decline to join many federations
   might choose to buy transit from VSPs which offer such services.

4.2.  Call Flows

   To visualize the possible call flows we use the following set of VSPs
   and federations:

                    +-----+
                   /  FED  \
                   \   1   /
                    +-----+
                   /   |   \
                  /    |    \
                 /     |     \
             +---+   +---+   +---+
             | A |   | B |   | C | VSPs offering transit services
             +---+   +---+   +---+
                \     / \      /
                 \   /   \    /
                 +---+    +---+
                / FED \  / FED \
                \  2  /  \  3  /
                 +---+    +---+
                 /   \   /    \
                /     \ /      \
             +---+   +---+   +---+
             | X |   | Y |   | Z | VSPs
             +---+   +---+   +---+

   X, Y, and Z are terminating VSPs which serve as SIP providers for
   end-customers.  A, B, and C are VSPs offering transit into a



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   federation to members of other federations.

4.2.1.  Direct Intra-federation calls

   Calls from customers of X to customers of Y can be passed directly
   according to rules of federation 2.  Transit is not required.

   Details how X passes traffic to Y are internal to federation 2 - it
   could be end-to-end or, for example, through a SIP hub.

4.2.2.  Single-transit Inter-federation calls

   Calls from X to Z need to traverse a third VSP as X and Z do not
   share a common federation.  B shares federations with X and Z, thus
   it can bridge calls between X and Z. VSP X thus may elect to enlist
   the help of B to complete calls to Z.

   On a high level this call is the combination of two intra-federation
   call legs - one within FED2 from X to B, and one within FED3 from B
   to Z. If FED2 and FED3 share the same Layer 3 network, then the RTP
   stream may well be end to end (X to Z directly).  If not (e.g.  FED3
   employs a private network), then B needs to provide media relay
   service as well.

4.2.3.  Multiple-Transit calls

   If B is not available, calls from X to Z need to traverse via FED2 to
   A, then via FED1 to C, and finally via FED3 to Z. Now there are three
   segments in the call.

4.3.  Procedures

   The basic call flow is as follows (this is an extension to
   draft-mahy-speermint-direct-peering):

   1.  If number-based dialing is used, then the initiating VSP converts
       the dial-string to a fully qualified E.164 number and retrieves a
       SIP URI through User ENUM and/or Infrastructure ENUM.

   2.  The initiating VSP performs the Domain Policy DDDS Application
       [2] and thus retrieves the set of federation of the target VSP.
       If source and destination VSP share a federation then the call is
       established according to its rules.  The destination VSP can use
       non-terminal NAPTRs in his policy announcements to indicate that
       he has contracted another VSP to provide transit services towards
       him.  In that case, the originating VSP repeats this step in the
       algorithm in order to find shared federations with the transit
       providing VSP.



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   3.  If no common federation is found, the initiating VSP may choose
       to enlist the help of a transit VSP on his side.  The call to the
       transit VSP follows normal federation rules.  See the next
       section for details how a suitable transit VSP is selected.

   4.  For number-based dialing: if no path can be found through either
       a common federation or any transit VSP, then the originating VSP
       may fall back to PSTN delivery.  Thus, the PSTN may be viewed as
       just another "default" federation where all VSPs using E.164
       numbers and having PSTN connectivity are members.

4.4.  Routing Architecture

   For the direct intra-federation call, it is sufficient to match the
   federation memberships of the initiating and destination VSP.  This
   matching can be achieved through the domain policy DDDS application.
   While direct matching of federations enables direct peering, it does
   not solve the universal reachability problem.

   In the general case, a routing algorithm is needed: Once the source
   VSP does not share a common federation with the destination VSP the
   source VSP needs select a transit VSPs.  This transit VSP in turn
   needs to make a routing decision.

   The "next hop" selection is akin to other routing problems, thus
   similar approaches can be used.  In some way, topology information
   beyond the next hop needs to be communicated between VSPs.  Other
   than in IP (layer 3) routing, announcements need not exclusively be
   learned from adjacent nodes and can be published through other means
   since IP connectivity can be assumed.

   Non-terminal NAPTRs in the Domain Policy DDDS can be used by the
   destination VSP to publish a list of VSPs which provides transit
   services towards that network.  If one assumes that a multi-tier
   hierarchy of VSPs will emerge (similar to the current PSTN or
   Internet one), then such referrals point up the hierarchy on the
   destination side.  If the source VSP is a major carrier then climbing
   up the hierarchy ladder on the destination side will likely lead to a
   known peer.

   If the call originates within a small VSP then he might not find a
   common federation with one of the major VSPs the destination
   (directly or indirectly) refers to.  He will need to hand the call to
   some larger VSP which he pays to connect him to the major transit
   networks.

   This document does not propose a routing protocol for that.  The
   following options are intended to stimulate discussions in the



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   SPEERMINT working-group.

4.4.1.  Static configuration

   For small VSPs this can be simple choice: everything that cannot be
   handed off to the destination network directly is relayed to a
   default transit provider.

4.4.2.  Forward Search

   Another option is to follow the referrals up the hierarchy on the
   source side, too.  Any VSP can do this offline to learn the set of
   VSPs and thus the range of federations that are reachable via the
   VSPs it has contracted to provide transit service.

   Walking the domain policy referrals generates a tree of VSPs which
   are all willing to pass calls from/to the root of the tree.  Building
   these trees both for the source and the destination VSP and then
   checking for shared VSPs (or federations) between these two trees
   will find a valid path if the top-tier VSPs peer amongst each other.

4.4.3.  Route Announcements

   SIP messages between federation members could be used to distribute
   reachability information.  To use the above example:

   If X buys transit from B then X might subscribe to a "topology" event
   package with B. Using NOTIFIES, B may announce to X its reachable
   federations.

   The same mechanisms can be used amongst transit VSPs (e.g. in
   federation 1) to exchange reachability information.  VSP A could
   learn through a NOTIFY from C that C is a member of FED3.


5.  Policy-Type template















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      Policy Type: "fed"

      URI Scheme(s): Any URI is allowed.

      Functional Specification: The URI acts purely as an identifier
           of a federation.  If both the sender and the destination
           are members of the same federation then they can communicate
           using this federation's rules.

      Security considerations:

      Intended usage: COMMON

      Author: Otmar Lendl



6.  Examples

   The examples show the NAPTR records for some the VSPs from the
   diagram from section 4.2.  The VSPs shall use domains like vsp-
   X.example.com and federations use identifiers like
   "http://fed-1.example.org/".

   o  VSP X is only reachable through FED2, thus:

      $ORIGIN vsp-X.example.com
      @ IN NAPTR 10 50   "U"  "D2P+SIP:fed" (
                 "!^.*$!http://fed-2.example.org/!" . )


   o  VSP C is a member of both FED1 and FED3, thus:

      $ORIGIN vsp-C.example.com
      @ IN NAPTR 10 10   "U" "D2P+SIP:fed" (
                 "!^.*$!http://fed-1.example.org/!" . )
      @ IN NAPTR 20 10   "U" "D2P+SIP:fed" (
                 "!^.*$!http://fed-3.example.org/!" . )

   o  The lower order value indicate that C prefers to receive calls via
      FED1.  B, who is also a member of FED1 and FED3, can choose to
      honor that preference and use FED1 when contacting C.


7.  Security Considerations

   The publishing of the access policy via the DNS RR described in this
   draft will reduce the amount of unwanted communication attempts, as



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   all well-meaning clients will follow them, but these records cannot
   substitute measures to actually enforce the published policy.


8.  IANA Considerations

   This document registers the policy-type "fed" for the domain policy
   DDDS application.


9.  Acknowledgements

   The author would like to thank Alexander Mayrhofer, Henry Sinnreich,
   Eli Katz, Reinaldo Penno, Patrick Melampy, Daryl Malas and Richard
   Stastny for their contributions.


10.  References

10.1.  Normative References

   [1]  Meyer, D., "SPEERMINT Terminology",
        draft-ietf-speermint-terminology-00 (work in progress),
        May 2006.

   [2]  Lendl, O., "The Domain Policy DDDS Application",
        draft-lendl-domain-policy-ddds-00 (work in progress),
        February 2006.

10.2.  Informative References

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

   [4]  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.














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Authors' Addresses

   Michael Haberler
   Internet Foundation Austria
   Waehringerstrasse 3/19
   Wien  A-1090
   Austria

   Phone: +43 664 4213465
   Email: mah@inode.at
   URI:   http://www.nic.at/ipa/


   Mike Hammer
   Cisco Systems
   13615 Dulles Technology Drive
   Herndon  VA 20171
   USA

   Phone: +1-703-484-3069
   Email: mhammer@cisco.com


   Otmar Lendl
   enum.at GmbH
   Karlsplatz 1/9
   Wien  A-1010
   Austria

   Phone: +43 1 5056416 33
   Email: otmar.lendl@enum.at
   URI:   http://www.enum.at/



















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