Network Working Group D. Meyer
Internet-Draft February 14, 2006
Expires: August 18, 2006
SPEERMINT Requirements and Terminology
draft-ietf-speermint-reqs-and-terminology-00.txt
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Copyright (C) The Internet Society (2006).
Abstract
This document outlines the solutions space requirements and defines
the terminology that is to be used by the Session PEERing for
Multimedia INTerconnect Working Group (SPEERMINT). It has as its
primary objective to focus the working group during its discussions,
and when writing requirements, gap analysis and other solutions
oriented documents.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Context . . . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Requirements . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. Unified solution for all peering policies . . . . . . . . 4
3.2. Domain Based . . . . . . . . . . . . . . . . . . . . . . . 5
3.3. No blocked calls . . . . . . . . . . . . . . . . . . . . . 5
3.4. Scaling . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.5. Independence of lower layers . . . . . . . . . . . . . . . 5
3.6. Administrative and technical policies . . . . . . . . . . 5
3.7. Minimal additional cost on call initiation . . . . . . . . 6
3.8. Look beyond SIP . . . . . . . . . . . . . . . . . . . . . 6
4. General Definitions . . . . . . . . . . . . . . . . . . . . . 6
4.1. Call Routing Data . . . . . . . . . . . . . . . . . . . . 6
4.2. Call Routing . . . . . . . . . . . . . . . . . . . . . . . 6
4.3. PSTN . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.4. Network . . . . . . . . . . . . . . . . . . . . . . . . . 6
4.5. VoIP Service Provider . . . . . . . . . . . . . . . . . . 7
4.6. Peering . . . . . . . . . . . . . . . . . . . . . . . . . 7
4.6.1. Layer 3 Peering . . . . . . . . . . . . . . . . . . . 7
4.6.2. Layer 5 Peering . . . . . . . . . . . . . . . . . . . 7
4.7. VoIP Peering . . . . . . . . . . . . . . . . . . . . . . . 8
5. ENUM . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1. Carrier of Record . . . . . . . . . . . . . . . . . . . . 8
5.2. Public ENUM . . . . . . . . . . . . . . . . . . . . . . . 8
5.3. Private ENUM . . . . . . . . . . . . . . . . . . . . . . . 8
5.4. Carrier ENUM . . . . . . . . . . . . . . . . . . . . . . . 9
6. Conclusions . . . . . . . . . . . . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 9
8. Security Considerations . . . . . . . . . . . . . . . . . . . 9
9. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
10.1. Normative References . . . . . . . . . . . . . . . . . . . 10
10.2. Informative References . . . . . . . . . . . . . . . . . . 10
Author's Address . . . . . . . . . . . . . . . . . . . . . . . . . 10
Intellectual Property and Copyright Statements . . . . . . . . . . 11
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1. Introduction
The term "VoIP Peering" has historically been used to describe a wide
variety of aspects pertaining to the interconnection of service
provider networks and to the delivery of SIP call termination over
those interconnections. The discussion of these interconnections has
at times been confused by the fact that the term "peering" is used in
various contexts to relate to interconnection at different levels in
a protocol stack. Session Peering for Multimedia Interconnect
focuses on how to identify and route real-time sessions (such as VoIP
calls) at the application layer, and it does not (necessarily)
involve the exchange of packet routing data or media sessions. In
particular, "layer 5 network" is used here to refer to the
interconnection between SIP servers, as opposed to interconnection at
the IP layer ("layer 3"). Finally, the terms "peering" and
"interconnect" are used interchangeably throughout this document.
This document introduces standard terminology for use in
characterizing real-time session interconnection. Note however, that
while this document is primarily targeted at the VoIP interconnect
case, the terminology described here is applicable to those cases in
which service providers interconnect using SIP signaling for real-
time or quasi-real-time communications.
The remainder of this document is organized as follows: Section 3
provides the requirements for SPEERMINT working group solutions.
Section 2 provides the general context for the VOIPEER Working Group,
and Section 4 provides the general definitions for real-time SIP
based communication, with focus on the VoIP interconnect case.
Section 5 briefly touches on terms from the ENUM Working Group.
Finally, Section 6 provides comments on usage.
2. Context
Figure 1 depicts the general VoIP interconnect context. In this
case, the caller uses an E.164 number [ITU.E164.1991] as the "name"
of the called user. Note that this E.164 number is not an address,
since at this point we do not have information about where the named
endpoint is located. In the case shown here, an E.164 number is used
as a key to retrieve a NAPTR recored [RFC3404] from the DNS, which in
turn resolved into a SIP URI. Call routing is based on this SIP URI.
The call routing step does not depend on the presence of an E.164
number; the SIP URI can be advertised in various other ways, such as
on a web page. Finally, note that the subsequent lookup steps,
namely, lookup of SRV, A, and AAAA records (as well as any routing
steps below that) are outside the scope of VOIPEER.
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E.164 number <--- Peer Discovery
|
| <--- ENUM lookup of NAPTR in DNS
|
|
| ENUM Working Group Scope
=====+=======================================
| VOIPEER Working Group Scope
|
|
SIP URI <--- Call Routing Data (CRD)
|
| <--- Service Location (Lookup of SRV in DNS)
|
|
Hostname <--- VoIP addressing and session establishment
|
| <---- Lookup of A and AAAA in DNS
|
Ip address
|
| <---- Routing protocols, ARP etc
|
Mac-address
Figure 1: VoIP Interconnect Context
The ENUM Working Group is primarily concerned with the acquisition of
Call Routing Data, or CRD (i.e., above the double line in Figure 1),
while the VOIPEER Working Group is focused on the use of such CRD.
Importantly, the CRD can be derived from ENUM (i.e., an E.164 DNS
entry), or via any other mechanism available to the user.
3. Requirements
A system for real-time session interconnection must satisfy the
following requirements:
3.1. Unified solution for all peering policies
Policies developed in the context of the SPEERMINT working group must
be extensible and flexible enough to cover existing and future
peering policies. These start by a closed system which accepts only
incoming calls from selected peers (i.e. a set of bilateral peerings)
and include the model of membership in a number of peering fabrics or
carrier clubs. The case of an open SIP proxy should be covered as a
special case as well.
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3.2. Domain Based
Although the initial call routing may be based on E.164 numbers, a
generic peering methodology should not rely on such numbers. Rather,
call routing should rely on URIs. We assume that all SIP URIs with
the same domain-part share the same set of peering policies, thus the
domain of the SIP URI may be used as the primary key to any
information regarding the reachability of that SIP URI.
3.3. No blocked calls
An originating Voice Service Provider, or VSP, must be able to
determine whether a SIP URI is open for direct interconnection
without actually sending a SIP INVITE. This is important as
unsuccessful call attempts are highly undesirable since they can
introduce high delays due to timeouts and can act as an unintended
denial of service attack. (e.g., by repeated TLS handshakes).
3.4. Scaling
The maintenance of the system needs to scale beyond simple lists of
peering partners. In particular, it must incorporate aggregation
mechanisms which avoid O(n2) scaling (where n is the number of
participating VoIP services). Per-VSP opt-in without consultation of
a centralized 'peering registry', but rather by publishing local
configuration choices only is highly desirable. The distributed
management of the DNS is a good example for the scalability of this
approach.
3.5. Independence of lower layers
The system needs to be independent of details on what technologies
are used route the call and which are used to ensure that only
approved peering partner actually connect to the destination SIP
proxy. It should not matter whether restrictions are implemented by
private L3 connectivity ("walled gardens"), firewalls, TLS policies
or SIP proxy configuration.
3.6. Administrative and technical policies
The reasons for declining vs. accepting incoming calls from a
prospective peering partner can be both administrative (contractual,
legal, commercial, or business decisions) and technical (certain QoS
parameters, TLS keys, domain keys, ...). Methodologies developed by
the SPEERMINT working group should accommodate all policies.
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3.7. Minimal additional cost on call initiation
Since each call setup implies execution of any proposed algorithm it
should incur minimal overhead and delay, and employ caching wherever
possible to avoid extra protocol round trips.
3.8. Look beyond SIP
The problem of selective peering is not limited to SIP-based
communication. Other protocols may benefit from a generic framework
as well, such as SMTP mail. Any solutions proposed by the SPEERMINT
working group must be generic enough to encompass other protocols as
well.
4. General Definitions
4.1. Call Routing Data
Call Routing Data, or CRD, is a SIP URI used to route a call (real-
time, voice or other type) to the called domain's ingress point. A
domain's ingress point can be thought of as the location pointed to
by the SRV record that resulted from the resolution of the CRD (i.e.,
a SIP URI).
4.2. Call Routing
Call routing is the set of processes, rules, and CRD used to route a
VoIP call to its proper (SIP) destination. More generally, call
routing can be thought of as the set of processes, rules and CRD
which are used to route a real-time session to its termination
(ingress) point.
4.3. PSTN
The term "PSTN" refers to the Public Switched Telephone Network. In
particular, the PSTN refers to the collection of interconnected
circuit-switched voice-oriented public telephone networks, both
commercial and government-owned. In general, PSTN terminals are
addressed using E.164 numbers, noting that various dial-plans (such
as emergency services dial-plans) may not directly use E.164 numbers.
4.4. Network
For purposes of this document and the VOIPEER and ENUM Working
Groups, a network is defined to be the set of SIP servers and end-
users (customers) that are controlled by a single administrative
domain. The network may also contain end-users who are located on
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the PSTN.
4.5. VoIP Service Provider
A VoIP service provider is an entity that provides transport of SIP
signaling (and possibly media streams) to its customers. Such a
service provider may additionally be interconnected with other
service providers; that is, it may "peer" with other service
providers. A VoIP service provider may also interconnect with the
PSTN.
Note that as soon as a ingress point is advertised via a SRV record,
anyone can find that ingress point and hence can send calls there.
This is very similar to sending mail to a SMTP server based on the
existence of a MX record.
4.6. Peering
While the precise definition of the term "peering" is the subject of
some debate, peering in general refers to the negotiation of
reciprocal interconnection arrangements, settlement-free or
otherwise, between operationally independent service providers.
This document distinguishes two types of peering, Layer 3 Peering and
Layer 5 peering, which are described below.
4.6.1. Layer 3 Peering
Layer 3 peering refers to interconnection of two service providers
for the purposes of exchanging IP packets which destined for one (or
both) of the peer's networks. Layer 3 peering is generally agnostic
to the IP payload, and is frequently achieved using a routing
protocol such as BGP [RFC1771] to exchange the required routing
information.
An alternate, perhaps more operational definition of layer 3 peering
is that two peers exchange only customer routes, and hence any
traffic between peers terminates on one of the peer's network.
4.6.2. Layer 5 Peering
Layer 5 peering refers to interconnection of two service providers
for the purposes of SIP signaling. Note that in the layer 5 peering
case, there is no intervening network. That is, for purposes of this
discussion, there is no such thing as a "Layer 5 Transit Network".
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4.7. VoIP Peering
VoIP peering is defined to be a layer 5 peering between two VoIP
providers for purposes of routing real-time (or quasi-real time) call
signaling between their respective customers. Media streams
associated with this signaling (if any) are not constrained to follow
the same set of paths.
5. ENUM
ENUM [RFC3761] defines how the Domain Name System (DNS) can be used
for identifying available services connected to one E.164 number.
5.1. Carrier of Record
For purposes of this document, "Carrier of Record", or COR, refers to
the entity that provides PSTN service for an E.164 number
[I-D.lind-infrastructure-enum-reqs]. The exact definition of who and
what is a COR is ultimately the responsibility of the relevant
National Regulatory Authority.
5.2. Public ENUM
Public ENUM is generally defined as the set administrative policies
and procedures surrounding the use of the e164.arpa domain for
Telephone Number to URI resolution [RFC3761]. Policies and
procedures for the registration of telephone numbers within all
branches of the e164.arpa tree are Nation State issues by agreement
with the IAB and ITU. National Regulatory Authorities have generally
defined Public ENUM Registrants as the E.164 number holder as opposed
to the COR that issued the phone number.
5.3. Private ENUM
Private ENUM is generally regarded as one or more technologies
(including DNS and SIP Redirect) that service providers or
enterprises may use to exchange phone number to URI mappings in a
private secure manner. Private ENUM may be used in any mutually
agreed upon domain. Records in Private ENUM may be globally visible
but in most cases are not visible to the global Internet and are
protected using a variety of security technologies such as split-DNS,
VPN's or various forms or authentication and authorization.
Technical comments on issues surrounding split-DNS can be found in
[RFC2826].
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5.4. Carrier ENUM
Carrier ENUM is generally regarded as the use of a separate branch
the e164.arpa tree, such as 4.4.c.e164.arpa to permit service
providers to exchange phone number to URI data in order to find
points of interconnection. The current theory of Carrier ENUM is
that only the COR for a particular E.164 number is permitted to
provision data for that E.164 within that portion of the e164.arpa
tree.
In carrier ENUM case, only the COR may enter data in the
corresponding domain. The COR may also enter CRD (i.e., a SIP URI)
to allow other VoIP Service Providers to route calls to its network.
Finally, note that ENUM is not constrained to carry only data (CDR)
as defined by VOIPEER. In particular, an an important class of CRD,
the tel URIs [RFC3966] may be carried in ENUM. Such tel URIs are
most frequently used to interconnect with the PSTN directly, and are
out of scope for VOIPEER. On the other hand, PSTN endpoints served
by a COR and reachable via CDR and networks as defined in Section 4.1
and Section 4.4 are in scope for VOIPEER.
6. Conclusions
7. Acknowledgments
Many of the definitions were gleaned from detailed discussions on the
VOIPEER, ENUM, and SIPPING mailing lists. Scott Brim, Mike Hammer,
Jean-Francois Mule, Richard Shocky, Henry Sinnreich, and Richard
Stastny all made valuable contributions to early revisions of this
document. Patrik Faltstrom also made many insightful comments to
early versions of this draft, and contributed the basis of Figure 1.
Finally, Otmar Lendl contributed much of the text found in the
Requirements section.
8. Security Considerations
This document itself introduces no new security considerations.
However, it is important to note that VoIP interconnect has a wide
variety of security issues that should be considered in documents
addressing both protocol and use case analyzes.
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9. IANA Considerations
This document creates no new requirements on IANA namespaces
[RFC2434].
10. References
10.1. Normative References
[RFC3404] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part Four: The Uniform Resource Identifiers (URI)",
RFC 3404, October 2002.
[RFC3761] Faltstrom, P. and M. Mealling, "The E.164 to Uniform
Resource Identifiers (URI) Dynamic Delegation Discovery
System (DDDS) Application (ENUM)", RFC 3761, April 2004.
[ITU.E164.1991]
International Telecommunications Union, "The International
Public Telecommunication Numbering Plan", ITU-
T Recommendation E.164, 1991.
[RFC3966] Schulzrinne, H., "The tel URI for Telephone Numbers",
RFC 3966, December 2004.
10.2. Informative References
[RFC1771] Rekhter, Y. and T. Li, "A Border Gateway Protocol 4
(BGP-4)", RFC 1771, March 1995.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[RFC2826] Internet Architecture Board, "IAB Technical Comment on the
Unique DNS Root", RFC 2826, May 2000.
[I-D.lind-infrastructure-enum-reqs]
Lind, S., "Infrastructure ENUM Requirements",
draft-lind-infrastructure-enum-reqs-00 (work in progress),
July 2005.
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Author's Address
David Meyer
Email: dmm@1-4-5.net
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