SPEERMINT D. Malas, Ed.
Internet-Draft CableLabs
Intended status: Informational J. Livingood, Ed.
Expires: March 3, 2011 Comcast
August 30, 2010
SPEERMINT Peering Architecture
draft-ietf-speermint-architecture-11
Abstract
This document defines a peering architecture for the Session
Initiation Protocol (SIP) [RFC3261], it's 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.
Status of this Memo
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This Internet-Draft will expire on March 3, 2011.
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described in the Simplified BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Reference Architecture . . . . . . . . . . . . . . . . . . . . 3
3. Procedures of Inter-domain SSP Session Establishment . . . . . 4
4. Relationships Between Functions/Elements . . . . . . . . . . . 5
5. Recommended SSP Procedures . . . . . . . . . . . . . . . . . . 5
5.1. Originating SSP Procedures . . . . . . . . . . . . . . . . 5
5.1.1. The Look-Up Function (LUF) . . . . . . . . . . . . . . 5
5.1.1.1. Target Address Analysis . . . . . . . . . . . . . 6
5.1.1.2. ENUM Lookup . . . . . . . . . . . . . . . . . . . 6
5.1.2. Location Routing Function (LRF) . . . . . . . . . . . 7
5.1.2.1. DNS resolution . . . . . . . . . . . . . . . . . . 7
5.1.2.2. Routing Table . . . . . . . . . . . . . . . . . . 7
5.1.2.3. LRF to LRF Routing . . . . . . . . . . . . . . . . 7
5.1.3. The Signaling Path Border Element (SBE) . . . . . . . 7
5.1.3.1. Establishing a Trusted Relationship . . . . . . . 8
5.1.3.2. IPSec . . . . . . . . . . . . . . . . . . . . . . 8
5.1.3.3. Co-Location . . . . . . . . . . . . . . . . . . . 8
5.1.3.4. Sending the SIP Request . . . . . . . . . . . . . 8
5.2. Target SSP Procedures . . . . . . . . . . . . . . . . . . 8
5.2.1. The Ingress SBE . . . . . . . . . . . . . . . . . . . 8
5.2.1.1. TLS . . . . . . . . . . . . . . . . . . . . . . . 9
5.2.1.2. Receive SIP Requests . . . . . . . . . . . . . . . 9
5.3. Data Path Border Element (DBE) . . . . . . . . . . . . . . 9
6. Address Space Considerations . . . . . . . . . . . . . . . . . 9
7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
9. Security Considerations . . . . . . . . . . . . . . . . . . . 10
10. Contributors . . . . . . . . . . . . . . . . . . . . . . . . . 10
11. Change Log . . . . . . . . . . . . . . . . . . . . . . . . . . 11
12. Open Issues . . . . . . . . . . . . . . . . . . . . . . . . . 11
13. References . . . . . . . . . . . . . . . . . . . . . . . . . . 11
13.1. Normative References . . . . . . . . . . . . . . . . . . . 11
13.2. Informative References . . . . . . . . . . . . . . . . . . 12
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 13
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1. Introduction
This document defines a reference peering architecture 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 [RFC5486] network.
This architecture allows the interconnection of two SSPs in layer 5
peering as defined in the SIP-based session peering requirements
[I-D.draft-ietf-speermint-requirements-09].
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 Terminology document [RFC5486].
2. Reference Architecture
The following figure depicts the architecture and logical functions
that form peering between two SSPs.
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+=============++ ++==============+
|| ||
+-----------+ +-----------+
| 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 in the Originating SSP's network to an UA in the Target
SSP's network the following steps are taken:
1. Determine the target SSP via the LUF. (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
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4. Exchange the media, which could include voice, video, text, etc.
5. End the session (BYE)
The originating SSP would likely perform steps 1-4, and the target
SSP would likely perform steps 4-5.
In the case the target SSP changes, then steps 1-4 would be repeated.
This is reflected in Figure 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.draft-ietf-speermint-requirements-09] 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.
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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.
If the target address does not represent a resource inside the
originating SSP?s administrative domain or federation of domains,
then the originating SSP performs a Lookup Function (LUF) to
determine a target address, and then is resolves the call routing
data by using the Location routing Function (LRF).
For example, if the request to communicate is for an im: or pres: URI
type, the originating SSP follows the procedures in [8]. If the
highest priority supported URI scheme is sip: or sips: the
originating SSP skips to SIP DNS resolution in Section 5.1.3.
Likewise, if the target address is already a sip: or sips: URI in an
external domain, the originating SSP skips to SIP DNS resolution in
Section 4.1.2.1.
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.
5.1.1.2. 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.
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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. 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 SSP uses the procedures in RFC 3263 [4] Section 4 to
determine how to contact the receiving SSP. To summarize the RFC
3263 procedure: unless these are explicitly encoded in the target
URI, a transport is chosen using NAPTR records, a port is chosen
using SRV records, and an address is chosen using A or AAAA records.
When communicating with another SSP, entities compliant to this
document should select a TLS-protected transport for communication
from the originating SSP to the receiving SSP if available.
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. 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
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used by the Media Function (MF).
The signaling function performs the routing of SIP messages. The
optional termination and re-initiation of calls may be performed by
the signaling path Session Border Element (SBE), or other signaling
elements.
Optionally, a SF may perform additional functions such as Session
Admission Control, SIP Denial of Service protection, SIP Topology
Hiding, SIP header normalization, SIP security, privacy, and
encryption.
The SF of a SBE can also process SDP payloads for media information
such as media type, bandwidth, and type of codec; then, communicate
this information to the media function. Signaling function may
optionally communicate with the network to pass Layer 3 related
policies [10].
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 SSP sends the request.
5.2. Target SSP Procedures
5.2.1. The Ingress SBE
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5.2.1.1. 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.
5.2.1.2. 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".
5.3. Data Path Border Element (DBE)
The purpose of the DBE [RFC 5486] is to perform media related
functions such as media transcoding and media security implementation
between two SSPs.
An Example of this is to transform a voice payload from one codec
(e.g., G.711) to another (e.g., EvRC). Additionally, the MF may
perform media relaying, media security, privacy, and encryption.
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. 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.
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7. Acknowledgments
The working group thanks Sohel Khan for his initial architecture
draft that helped to initiate work on this draft. John Elwell, Mike
Hammer, Otmar Lendl, Jason Livingood, Alexander Mayrhofer, Jean-
Francois Mule, Jonathan Rosenberg, David Schwartz, Richard Shockey,
Jim McEachern, and Dan Wing all made valuable contributions to
versions of this document.
A significant portion of this draft is taken from
[I-D.draft-mahy-speermint-direct-peering-02] with permission from the
author R. Mahy.
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.
10. Contributors
Adam Uzelac
Reinadlo Penno
Mike Hammer
Sohel Khan
Hadriel Kaplan
David Schwartz
Richard Shockey
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11. Change Log
NOTE TO RFC EDITOR: PLEASE REMOVE THIS SECTION PRIOR TO PUBLICATION.
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 Cleanup odd spacing in XML
o Revise contributors list, which are really authors, due to
document masthead constraint
o Lots of clean-up
13. References
13.1. Normative References
[I-D.ietf-speermint-requirements]
Mule, J., "SPEERMINT Requirements for SIP-based Session
Peering", draft-ietf-speermint-requirements-09 (work in
progress), October 2009.
[I-D.lee-speermint-use-case-cable]
Lee, Y., "Session Peering Use Case for Cable",
draft-lee-speermint-use-case-cable-01 (work in progress),
September 2006.
[I-D.lendl-speermint-federations]
Lendl, O., "A Federation based VoIP Peering Architecture",
draft-lendl-speermint-federations-03 (work in progress),
September 2006.
[I-D.mahy-speermint-direct-peering]
Mahy, R., "A Minimalist Approach to Direct Peering",
draft-mahy-speermint-direct-peering-02 (work in progress),
July 2007.
[I-D.schwartz-speermint-use-cases-federations]
Schwartz, D., "Session Peering Use Cases for Federations",
draft-schwartz-speermint-use-cases-federations-00 (work in
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progress), November 2006.
[I-D.uzelac-speermint-use-cases]
Uzelac, A., "SIP Peering Use Case for VSPs",
draft-uzelac-speermint-use-cases-00 (work in progress),
October 2006.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2434] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
[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.
[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.
[RFC5486] Malas, D. and D. Meyer, "Session Peering for Multimedia
Interconnect (SPEERMINT) Terminology", RFC 5486,
March 2009.
13.2. Informative References
[I-D.lewis-peppermint-enum-reg-if]
Lewis, E., "ENUM Registry Interface Requirements",
draft-lewis-peppermint-enum-reg-if-01 (work in progress),
November 2007.
[I-D.newton-peppermint-problem-statement]
Newton, A., "Provisioning Extensions in Peering Registries
for Multimedia Interconnection (PEPPERMINT) Problem
Statement", draft-newton-peppermint-problem-statement-00
(work in progress), January 2007.
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[RFC3546] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 3546, June 2003.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC4483] Burger, E., "A Mechanism for Content Indirection in
Session Initiation Protocol (SIP) Messages", RFC 4483,
May 2006.
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
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