SPEERMINT A. Uzelac, Ed.
Internet-Draft Global Crossing
Intended status: Informational R. Penno
Expires: September 10, 2010 Juniper Networks
M. Hammer
Cisco Systems
D. Malas
CableLabs
S. Khan
Comcast
H. Kaplan
Acme Packet
J. Livingood
Comcast
D. Schwartz
XConnect Global Networks
R. Shockey
Shockey Consulting
March 9, 2010
SPEERMINT Peering Architecture
draft-ietf-speermint-architecture-10
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Abstract
This document defines a peering architecture for the Session
Initation Protocol (SIP) [RFC3261], it's functional components and
interfaces. It also describes the steps necessary to establish a
session between two peering domains in the context of the functions
defined.
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
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provisions of BCP 78 and BCP 79.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Reference Architecture . . . . . . . . . . . . . . . . . . . . 4
3. Procedures of Inter-domain SSP Session Establishment . . . . . 5
4. Relationships between functions/elements . . . . . . . . . . . 6
5. Recommended SSP Procedures . . . . . . . . . . . . . . . . . . 6
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. ENUM Lookup . . . . . . . . . . . . . . . . . . . 7
5.1.2. Location Routing Function (LRF) . . . . . . . . . . . 8
5.1.2.1. DNS resolution . . . . . . . . . . . . . . . . . . 8
5.1.2.2. Routing Table . . . . . . . . . . . . . . . . . . 8
5.1.2.3. LRF to LRF Routing . . . . . . . . . . . . . . . . 8
5.1.3. Signaling Path Border Element (SBE) . . . . . . . . . 8
5.1.4. Establishing a Trusted Relationship . . . . . . . . . 9
5.1.4.1. IPSec . . . . . . . . . . . . . . . . . . . . . . 9
5.1.4.2. Co-Location . . . . . . . . . . . . . . . . . . . 9
5.1.4.3. Sending the SIP Request . . . . . . . . . . . . . 9
5.2. Target SSP Procedures . . . . . . . . . . . . . . . . . . 9
5.2.1. The Ingress SBE . . . . . . . . . . . . . . . . . . . 10
5.2.1.1. TLS . . . . . . . . . . . . . . . . . . . . . . . 10
5.2.1.2. Receive SIP Requests . . . . . . . . . . . . . . . 10
5.3. Data Path Border Element (DBE) . . . . . . . . . . . . . . 10
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
8. Security Considerations . . . . . . . . . . . . . . . . . . . 11
9. Normative References . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 12
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1. Introduction
The objective of this document is to define 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 provider's (SSP)
[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.ietf-speermint-requirements].
Layer 3 peering is outside the scope of this document. Hence, the
figures in this document focus on Layer 5 protocol functions and
elements.
This document uses terminology defined in the Session Peering for
Multimedia Interconnect Terminology document [RFC5486].
2. Reference Architecture
Figure 1 depicts the architecture and logical functions that form
peering between two SSPs. The terms used in the diagram are expanded
here for reference:
o SBE - Signaling Path Border Element is described in Section 5.1.3
o LUF - Look-up Function is described in Section 5.1.1
o LRF - Location Routing Function is described in Section 5.1.2
o SF - Signaling Function is defined in [RFC5486]
o SIP - Session Initiation Protocol is defined in [RFC3261]
o DBE - Data Path Border Element is described in Section 5.3
o DNS - Domain Name Service is described in Section 5.1.2.1
o ENUM - E.164 Number Mapping is described in Section 5.1.1.2
o FQDN - Fully Qualified Domain Name
o TN DB - Telephone Number Database
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o IP - IPv4/v6 Address
o RTP - Real-time Transport Protocol is defined in [RFC3550]
+=============++ ++==============+
|| ||
+-----------+ +-----------+
| SBE | | SBE |
| +-----+ | SIP +-----+ | +-----+ |
| | LUF |<-|------>|ENUM | | | LUF | |
| +-----+ | ENUM |TN DB| | +-----+ |
SIP | | +-----+ | |
------>| +-----+ | DNS +-----+ | +-----+ |
| | LRF |<-|------>|FQDN | | | LRF | |
| +-----+ | |IP | | +-----+ |
| +-----+ | SIP +-----+ | +-----+ |
| | SF |<-|----------------|->| SF | |
| +-----+ | | +-----+ |
+-----------+ +-----------+
|| ||
+-----------+ +-----------+
RTP | DBE | RTP | DBE |
------>| |--------------->| |
+-----------+ +-----------+
|| ||
SSP1 Network || || SSP2 Network
+=============++ ++=============+
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 User Agent (UA) in the Originating SSP's network to a 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 a resource within the originating SSP, the
behavior is out-of-scope with respect to this draft.)
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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
The originating SSP would likely perform steps 1-4, and the target
SSP would likely perform steps 4-5.
If the target SSP is also an indirect peer, then steps 1-4 may 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, in current Session Border
Controller (SBC) implementations, an SBC 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 and another SF
* LUF can communicate with SF
* LRF can communicate with SF
5. Recommended SSP Procedures
This section describes the functions in more detail and provides some
recommendations on the role they would play in an example SIP
telephony call scenario.
Some of the information in the section is taken from
[I-D.ietf-speermint-requirements] and is put here for continuity
purposes.
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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 SIP request, it analyzes the
target URI to determine whether the call needs to be routed internal
or external to its network.
If the target address does not represent a resource inside the
originating SSP's administrative domain, then the originating SSP
performs a Lookup (LUF) to determine the target domain, and then it
resolves the call routing data by using Location Routing (LRF).
For example, if the request to communicate is for an im: or pres: URI
type, the originating SSP follows the procedures in [RFC3861]. If
the highest priority supported URI scheme is sip: or sips: the
originating SSP skips to SIP DNS resolution. 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.
5.1.1.2. ENUM Lookup
If an external E.164 address is the target, the originating SSP
consults a private or public ENUM server, 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 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 target domain is
represented as an IPv4/v6 address.
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.
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5.1.2. Location Routing Function (LRF)
The LRF of an Originating SSP analyzes the 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 indirect 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 [RFC3263] to determine how
to contact the target SSP. To summarize the RFC 3263 procedure:
unless these are explicitly encoded in the target URI, a transport is
chosen using Naming Authority Pointer (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 target 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
Communication 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. Signaling Path Border Element (SBE)
The purpose of signaling path border element is to perform routing of
SIP messages as well as optionally implement security and policies on
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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), or other signaling
elements.
Optionally, the SF of a SBE 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.
5.1.4. 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.
5.1.4.1. 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.
5.1.4.2. 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.
5.1.4.3. Sending the SIP Request
Once a trust relationship between the peers is established, the
originating SSP sends the request.
5.2. Target SSP Procedures
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5.2.1. The Ingress SBE
5.2.1.1. TLS
When the target SSP receives a TLS client hello, it responds with its
certificate. The Originating 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
[I-D.ietf-sip-domain-certs].
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 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 [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., Enhanced Variable Rate Codec (EvRC)).
Additionally, the MF may perform media relaying, media security,
privacy, and encryption.
6. Acknowledgments
The working group thanks Sohel Khan for his initial architecture
draft that helped to initiate work on this draft.
Other contributors include Rohan Mahy, Otmar Lendl, Jim McEachern and
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John Elwell for detailed comments and feedback.
7. IANA Considerations
This memo includes no request to IANA.
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. Normative References
[I-D.ietf-sip-domain-certs]
Gurbani, V., Lawrence, S., and B. Laboratories, "Domain
Certificates in the Session Initiation Protocol (SIP)",
draft-ietf-sip-domain-certs-05 (work in progress),
March 2010.
[I-D.ietf-speermint-requirements]
Mule, J., "SPEERMINT Requirements for SIP-based Session
Peering", draft-ietf-speermint-requirements-09 (work in
progress), October 2009.
[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.
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[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.
[RFC5486] Malas, D. and D. Meyer, "Session Peering for Multimedia
Interconnect (SPEERMINT) Terminology", RFC 5486,
March 2009.
Authors' Addresses
Adam Uzelac (editor)
Global Crossing
Rochester, NY
US
Email: adam.uzelac@globalcrossing.com
Reinadlo Penno
Juniper Networks
Sunnyvale, CA
US
Email: rpenno@juniper.net
Mike Hammer
Cisco Systems
Herndon, VA
US
Email: mhammer@cisco.com
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Daryl Malas
CableLabs
Louisville, CO
US
Email: d.malas@cablelabs.com
Sohel Khan
Comcast
Philadelphia, PA
US
Email: sohel_khan@cable.comcast.com
Hadriel Kaplan
Acme Packet
Burlington, MA
US
Email: hkaplan@acmepacket.com
Jason Livingood
Comcast
Philadelphia, PA
US
Email: Jason_Livingood@cable.comcast.com
David Schwartz
XConnect Global Networks
Jerusalem
Israel
Email: dschwartz@xconnnect.net
Richard Shockey
Shockey Consulting
US
Email: Richard@shockey.us
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