One document matched: draft-ietf-speermint-flows-00.txt
Speermint Working Group R. Penno
Internet Draft Juniper Networks
Expires: February 2007 D. Malas
Level 3
S. Khan
Sprint
A. Uzelac
Global Crossing
September 6, 2006
SPEERMINT Routing Architecture Message Flows
draft-ietf-speermint-flows-00
Status of this Memo
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This Internet-Draft will expire on March 6, 2007.
Abstract
This draft provides the message flows associated with the SPEERMINT,
SIP Peering and Multimedia Interconnect, routing architecture. This
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document provides examples of many different message flows relative
to varying peering scenarios.
Conventions used in this document
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 RFC-2119 [1].
Table of Contents
1. Introduction...................................................3
2. Peering Message flows..........................................7
3. On-Demand Peering..............................................9
3.1. Transport Layer Security..................................9
3.2. Proxy Authentication: Subscribe/Notify...................11
3.3. Proxy Authentication: Surrogate Registration.............12
4. Static Peering................................................15
4.1. IPSec....................................................15
4.2. Co-Location..............................................15
5. Federation Based Peering......................................16
5.1. Simple Federation Match..................................17
5.2. No federation match......................................17
5.3. Federation Referral......................................18
5.4. Federation Specific Call Processing......................19
5.4.1. Central Federation Proxy............................20
5.4.2. VPN Based Federations...............................21
5.4.3. TLS Based Federation................................21
6. Considerations on Private [13] IP addresses...................21
7. Considerations on Media Flows.................................22
7.1. Decomposition............................................22
7.2. Media Relay..............................................22
7.3. Media QoS................................................25
8. Considerations on Multilateral Peering........................26
9. SIP Priority and SPEERMINT QoS................................26
9.1. Problem Statement........................................27
9.2. Packet Recognition and Marking...........................27
9.2.1. Peering Classes of Service..........................27
9.2.2. Network Address Translation (NAT)...................29
9.3. Accounting...............................................29
9.4. Trust....................................................29
10. SIP Policy Enforcement and Definition........................29
10.1. Local SIP Policy........................................30
10.2. Remote SIP Policy.......................................30
10.3. SIP Proceed Policy......................................30
11. Peering Domain Information Exchange..........................31
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11.1. Domain Routes...........................................31
11.2. Authentication Credentials..............................32
12. Peering Message Flow Phases..................................33
12.1. Discovery Phase.........................................35
12.2. Policy Exchange Phase...................................36
12.3. Security Establishment Phase............................36
12.4. Signaling Exchange Phase................................37
12.5. Media Exchange Phase....................................38
13. Security Considerations......................................39
14. IANA Considerations..........................................39
15. Conclusions..................................................39
16. Acknowledgments..............................................39
17. References...................................................39
17.1. Normative References....................................39
17.2. Informative References..................................40
Author's Addresses...............................................41
Intellectual Property Statement..................................41
Disclaimer of Validity...........................................42
Copyright Statement..............................................42
Acknowledgment...................................................42
1. Introduction
This document shows the message flows associated with the most
relevant SPEERMINT routing architecture peering scenarios. Most of
the message diagrams were based on previous work described within
existing IETF standards documents.
The document focuses on the messages exchanged for the purpose of
Layer 5 peering [7] between two domains. Messages exchanged for the
purpose of setting up SIP sessions within a domain are considered out
of scope and were already defined in other IETF documents.
The draft separates the Layer 5 peering scenarios in two major
peering scenarios.
o On-demand: In this scenario the SIP proxies in domains A and B
establish a peering relationship driven by the necessity to
deliver a SIP message to another domain. This is sometimes
referred as the "email" model.
o Static: In this scenario the peering relationship between proxies
A and B is statically provisioned independent of the establishment
of any SIP session between users in different domains.
Normally, media for a given SIP session follows a different path,
traversing a different device (most commonly a router) when crossing
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peering domains. Alternatively, media for a given session can be
directed to traverse the same device used for Layer 5 peering, i.e.,
the same device that handles signaling when crossing domains. This
produces two different models:
o Decomposed: In this model SIP proxies perform Layer 5 peering and
media is sent directly between the User Agent's (UA's) involved in
the session. Signaling and media follow different paths.
o Collapsed: In this model the device that performs Layer 5 peering
also processes the associated media when crossing domains. In the
light of SPEERMINT these devices may need to process media mainly
when peering involves SIP entities in private address spaces. This
function is usually referred to as media relay and is usually
performed by a B2BUA or SBC (Session Border Controller). See [6]
for a complete discussion of SBC functions. The decomposed or
basic peering model picture is shown below. It is worth mentioning
that Proxy 1 and 2 can be separated by any number of layer 3 hops.
We will refer to this picture throughout this document.
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............................ ..............................
. . . .
. +-------+ . . +-------+ .
. | | . . | | .
. | DNS | . . | DNS | .
. | 1 | . . | 2 | .
. | | . . | | .
. +-------+ . . +-------+ .
. | . . | .
. | . . | .
. +-------+ . . +-------+ .
. | | . . | | .
. | Proxy |--------------| Proxy | .
. | 1 | . . | 2 | .
. | | . . | | .
. / +-------+ . . +-------+ \ .
. / . . \ .
. / . . \ .
. / . . \ .
. / . . \ .
. / . . \ .
. / . . \ .
. / . . \ .
. +-------+ . . +-------+ .
. | | . . | | .
. | | . Media . | | .
. | UA 1 |<========================================>| UA 2 | .
. | | . . | | .
. +-------+ . . +-------+ .
. Domain A . . Domain B .
............................ ..............................
Figure 1 Basic Peering Picture.
The collapsed model is shown below:
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............................ ..............................
. . . .
. +-------+ . . +-------+ .
. | | . . | | .
. | DNS | . . | DNS | .
. | 1 | . . | 2 | .
. | | . . | | .
. +-------+ . . +-------+ .
. | . . | .
. | . . | .
. +-------+ . . +-------+ .
. | B2BUA | . . | B2BUA | .
. | & |--------------| & | .
. | other |**************| other |\ .
. /| funct | . . | funct | \ .
. / +-------+ . . +-------+* \ signaling .
. / * . . * \ .
. / * . . * \ .
. / * . . * \ .
. / * media . . * \ .
. / * . . * \ .
. / * . . * \ .
. / * . . * \ .
. +-------+ . . +-------+ .
. | | . . | | .
. | | . . | | .
. | UA 1 | . . | UA 2 | .
. | | . . | | .
. +-------+ . . +-------+ .
. Domain A . . Domain B .
............................ ..............................
Figure 2 Collapsed Peering Picture.
In a decomposed model, the signaling function (SF) and the media
function (MF) are implemented in separate entities. A B2BUA is
generally on the SIP path in the SF. The vertical control protocol
between the SF and MF is out of the scope of this document. The
decomposed model is shown below:
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............................ ..............................
. . . .
. +-------+ . . +-------+ .
. | | . . | | .
. | DNS | . . | DNS | .
. | 1 | . . | 2 | .
. | | . . | | .
. +-------+ . . +-------+ .
. | . . | .
. | . . | .
. +-------+ . . +-------+ .
. /| B2BUA |--------------| B2BUA |\ .
. / +-------+ +-------+ \ .
. / +-------+ +-------+ \ .
. / | MF |**************| MF | \ .
. / +-------+ . . +-------+* \signaling .
. / * . . * \ .
. / * . . * \ .
. / * . . * \ .
. / * media . . * \ .
. / * . . * \ .
. / * . . * \ .
. / * . . * \ .
. +-------+ . . +-------+ .
. | | . . | | .
. | | . . | | .
. | UA 1 | . . | UA 2 | .
. | | . . | | .
. +-------+ . . +-------+ .
. Domain A . . Domain B .
............................ ..............................
Figure 3 Collapsed Peering Picture.
2. Peering Message flows
We first depict what we call the basic message flow. The various
scenarios differ mostly of how and when peering is implemented. As
mentioned earlier peering can be establish following the arrival of a
message at a border proxy or statically following an agreement
between both domains.
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Alice Proxy 1 DNS Proxy 2 Bob
| | | | |
| | | | |
| | Peering | |
| | Phase | |
| | [Static] | |
| |<------------------>| |
| INVITE | | | |
|------->| | | |
| 100 | | |
|<-------| | |
| | NAPTR | | |
| | Query | | |
| |--------->| | |
| | NAPTR | | |
| | Reply | | |
| |"SIPS+D2T"| | |
| |<---------| | |
| | SRV | | |
| | Query | | |
| |--------->| | |
| | SRV | | |
| | Reply | | |
| |<---------| | |
| | | |
| | Peering | |
| | Phase | |
| | [On-Demand] | |
| |<------------------>| |
| | INVITE | |
| |------------------->| INVITE |
| | 100 |---------->|
| |<-------------------| |
| | | 180 |
| | 180 |<----------|
| 180 |<-------------------| |
|<-------| | 200 |
| | 200 |<----------|
| 200 |<-------------------| |
|<-------| | |
| ACK | | |
|------->| ACK | |
| |------------------->| ACK |
| | |---------->|
| Both Way RTP Media |
|<=======================================>|
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| | | BYE |
| | BYE |<----------|
| BYE |<-------------------| |
|<-------| | |
| 200 | | |
|------->| 200 | |
| |------------------->| 200 |
| | |---------->|
| | | |
In the collapsed model, media would follow the path shown below. All
other signaling call flows remain the same, except a B2BUA is used
instead of a proxy.
Alice B2BUA 1 DNS B2BUA 2 Bob
| | | | |
| | | | |
| Both Way RTP Media |
|<======>|<==================>|<=========>|
| | | |
The following sections show the message flows in several different
scenarios broken in two categories, on-demand and static.
3. On-Demand Peering
In the on demand peering scenario, the relationship between proxies
in domains A and B is driven by the arrival of a SIP message at proxy
A directed to a user in domain B (or vice-versa).
3.1. Transport Layer Security
In the case this is in fact the first call between those two VSPs,
than this call will trigger the establishment of the TLS connection.
Otherwise we can assume the TLS connection has been established by
some other means.
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Alice Proxy 1 DNS Proxy 2 Bob
| | | | |
| | | | |
| INVITE | | | |
|------->| | | |
| 100 | | | |
|<-------| | | |
| | NAPTR | | |
| | Query | | |
| |--------->| | |
| | NAPTR | | |
| | Reply | | |
| |"SIPS+D2T"| | |
| |<---------| | |
| | SRV | | |
| | Query | | |
| |--------->| | |
| | SRV | | |
| | Reply | | |
| |<---------| | |
| | | | |
| | Peering | |
| | [TLS Connection] | |
| |<------------------>| |
| | | |
| | INVITE | |
| |------------------->| INVITE |
| | 100 |---------->|
| |<-------------------| |
| | | 180 |
| | 180 |<----------|
| 180 |<-------------------| |
|<-------| | 200 |
| | 200 |<----------|
| 200 |<-------------------| |
|<-------| | |
| ACK | | |
|------->| ACK | |
| |------------------->| ACK |
| | |---------->|
| Both Way RTP Media |
|<=======================================>|
| | | BYE |
| | BYE |<----------|
| BYE |<-------------------| |
|<-------| | |
| 200 | | |
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|------->| 200 | |
| |------------------->| 200 |
| | |---------->|
| | | |
TBD: DNS exchange could present proxy 1 with a set of peering
policies that need to be met for the peering with proxy 2 too
succeed.
3.2. Proxy Authentication: Subscribe/Notify
In the following example message flow, the authentication credentials
exchange method may take place before any INVITE is sent by ALICE.
The P2Key is sent by Proxy 2's NOTIFY and is included within
subsections of the peering policy event package (PeerPlcyEvtPkg).
The P2Key may be stored on Proxy 1 for the duration of the policy
subscription. When the subscription expires, the P2Key becomes
invalid. At any time before the subscription expires, the P2Key MAY
be updated or refreshed as described in [8]. The message flow and
authentication exchange may occur in either direction, but for
simplicity reasons is only shown unilaterally.
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ALICE Proxy 1(P1) Proxy 2(P2) Bob
| | | |
| INVITE | | |
|--------------->| | |
| 100 Trying | | |
|<---------------| | |
| | Subscribe w/ PeerPlcyEvtPkg | |
| |---------------------------->| |
| | 401 Unauthorized | |
| |<----------------------------| |
| |Subscribe w/Auth | |
| |---------------------------->| |
| | 202 Accepted | |
| |<----------------------------| |
| | Notify w/P2Key | |
| |<----------------------------| |
| | 200 OK | |
| |---------------------------->| |
| | INVITE | |
| |---------------------------->| |
| | 401 Unauthorized | |
| |<----------------------------| |
| | INVITE w/P2Key | |
| |---------------------------->| |
| | 100 Trying |INVITE |
| |<----------------------------|-----------> |
| | |180 Ringing |
| | 180 Ringing |<----------- |
| 180 Ringing|<----------------------------| |
|<---------------| |200 OK |
| | 200 OK |<----------- |
| 200 OK |<----------------------------| |
|<---------------| | |
| ACK | | |
|--------------->|ACK | |
| |---------------------------->|ACK |
| | |-----------> |
3.3. Proxy Authentication: Surrogate Registration
In this optional scenario we are assuming a new proxy authentication
method exists that allows mutual authentication between two proxies.
This authentication can be termed as the "Surrogate Authentication".
Generally, a proxy cannot register with another proxy because in
between two proxies there is not a child-parent relationship;
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however, an originating proxy can register with another proxy on
behalf of a UA.
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ALICE Proxy 1(P1) Proxy 2(P2) Bob
| | | |
| INVITE | | |
|--------------->| | |
| 100 Trying | | |
|<---------------| | |
| |REGISTER | |
| |------------------->| |
| | 401 Unauthorized | |
| |<-------------------| |
| |REGISTER w/Auth | |
| |------------------->| |
| | 100 Trying | |
| |<-------------------| |
| | 200 OK w/P2Key | |
| |<-------------------| |
| | REGISTER | |
| |<-------------------| |
| | 401 Unauthorized | |
| |------------------->| |
| | REGISTER w/Auth| |
| |<-------------------| |
| | 100 Trying | |
| |------------------->| |
| | 200 OK w/P1Key | |
| |------------------->| |
| | INVITE w/P2Key | |
| |------------------->| |
| | 100 Trying |INVITE |
| |<-------------------|-----------> |
| | |180 Ringing |
| | 180 Ringing |<----------- |
| 180 Ringing|<-------------------| |
|<---------------| |200 OK |
| | 200 OK |<----------- |
| 200 OK |<-------------------| |
|<---------------| | |
| ACK | | |
|--------------->|ACK | |
| |------------------->|ACK |
| | |-----------> |
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4. Static Peering
In the static peering scenario the relationship between proxies A and
B is not driven by a SIP session, but before hand through manual
provisioning.
4.1. IPSec
In this model an IPSec connection between proxies A and B is
provisioned following an agreement between the two domains.
Alice Proxy 1 DNS Proxy 2 Bob
| | | | |
| | | |
| | [Peering] | |
| | IPSec Connection | |
| |<------------------>| |
| | | | |
\ / \ / \
/ \ / \ /
| | | | |
| INVITE | | | |
|------->| | | |
| 100 | | | |
|<-------| | | |
\ / \ / \
/ \ / \ /
| | BYE |<----------|
| BYE |<-------------------| |
|<-------| | |
| 200 | | |
4.2. Co-Location
In this scenario the two proxies are co-located in a physically
secure location and/or are members of a segregated network. In this
case messages between Proxy 1 and Proxy 2 would be sent as clear
text.
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Alice Proxy 1 DNS Proxy 2 Bob
| | | | |
| | | |
| | [Peering] | |
| | Co-Location | |
| |<------------------>| |
| | | | |
\ / \ / \
/ \ / \ /
| | | | |
| INVITE | | | |
|------->| | | |
| 100 | | | |
|<-------| | | |
\ / \ / \
/ \ / \ /
| | BYE |<----------|
| BYE |<-------------------| |
|<-------| | |
| 200 | | |
5. Federation Based Peering
The Domain Policy DDDS framework [13] can be used to integrate on-
demand peering and static peering into one unified setup. The main
idea is that the target can use its domain to publish peering-related
information in the DNS. Federations as defined in [14] are one way
how source and destination network can find a common set of
procedures for the peering.
Federation based peering is thus not a substitute to the various
authentication, routing, and QoS procedures which are described in
this document.
The following examples demonstrate how Alice can use this scheme to
dynamically select the correct peering mechanisms when talking to
Bob.
The overall message flow is similar to the one from section 3.1. The
DP-DDDS queries the DNS for the same NAPTR records as the algorithm
from RFC 3263 [3]. While the originating network behavior according
to [3] depends solely on the results retrieved from DNS, the DP-DDDS
also uses a set of local configuration options to drive the source
network behavior. The following examples thus list both the sender
configuration and the answers from the DNS.
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5.1. Simple Federation Match
The simplest case is when Alice and Bob share membership in one
federation ("http://example.com/Wonderland") which stipulates further
call-setup according to section 3.1.
Configuration at Alice's DNS list Alice's federations (which includes
http://example.com/Wonderland) and rules what do to when a federation
is chosen for a call.
NAPTR RRset at Bob's domain includes:
IN NAPTR 10 50 "u" "D2P+SIP:fed" (
"!^.*$!http://example.com/small-federation!" . )
IN NAPTR 20 50 "u" "D2P+SIP:fed" (
"!^.*$!http://example.com/Wonderland!" . )
Alice Proxy 1 DNS Proxy 2 Bob
| | | | |
| | | | |
| INVITE | | | |
|------->| | | |
| 100 | | | |
|<-------| | | |
| | NAPTR | | |
| | Query | | |
| |--------->| | |
| | NAPTR | | |
| | Reply | | |
| |<---------| | |
| Parse D2P+SIP RRs | | |
| Federation match | | |
| successful | | |
| | | | |
| Parse NAPTR with | | |
| "SIPS+D2T" | | |
| | | | |
| | SRV | | |
| | Query | | |
| |--------->| | |
[Rest according to section 3.1]
5.2. No federation match
If Bob does not share a federation with Alice, e.g. by just being a
member of the "small-federation", then no direct peering is possible
between Alice and Bob.
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Bob's Domain contains:
IN NAPTR 10 50 "u" "D2P+SIP:fed" (
"!^.*$!http://example.com/small-federation!" . )
Alice Proxy 1 DNS Proxy 2 Bob
| | | | |
| | | | |
| INVITE | | | |
|------->| | | |
| 100 | | | |
|<-------| | | |
| | NAPTR | | |
| | Query | | |
| |--------->| | |
| | NAPTR | | |
| | Reply | | |
| |<---------| | |
| Parse D2P+SIP RRs | | |
| Federation match | | |
| failed. | | |
| | | | |
| Bob offers no alternative ways |
| No peering is possible. | |
| | | | |
If no matching federations or referrals are found, Alice can either
fall back to PSTN routing or use a transit VSP.
5.3. Federation Referral
If Bob buys transit services from Carol, he can announce this in a
"D2P+SIP" NAPTR record. We now have at Bob's domain:
IN NAPTR 10 50 "u" "D2P+SIP:fed" (
"!^.*$!http://example.com/small-federation!" . )
IN NAPTR 20 50 "u" "D2P+SIP" "" carol.example.com.
If Carol is a member of the Wonderland federation, then we have
$ORIGIN carol.example.com
IN NAPTR 10 50 "u" "D2P+SIP:fed" (
"!^.*$!http://example.com/Wonderland!" . )
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Alice Proxy 1 DNS Proxy 2 Bob
| | | | |
| | | | |
| INVITE | | | |
|------->| | | |
| 100 | | | |
|<-------| | | |
| | NAPTR | | |
| | Query | | |
| |--------->| | |
| | NAPTR | | |
| | Reply | | |
| |<---------| | |
| Parse D2P+SIP RRs | | |
| direct federation | | |
| match fails | | |
| Found non-terminal| | |
| | |Alice retargets to Carol
| | NAPTR | | |
| | Query | | |
| |--------->| | |
| | NAPTR | | |
| | Reply | | |
| |<---------| | |
| Parse D2P+SIP RRs | | |
| Federation match | | |
| successful | | |
| | | | |
| Parse NAPTR with | | |
| "SIPS+D2T" | | |
| | | | |
| | SRV | | |
| | Query | | |
| |--------->| | |
[Rest according to section 3.1]
5.4. Federation Specific Call Processing
The output of the federation matching step in the Domain Policy DDDS
application is a federation name and a destination domain (which
differs from the original destination domain if referrals were
followed).
Federations as defined in [14] can specify their own specific rules
on how the actual call-setup is to be performed between two
federation members. If Alice is a member of more than one federation
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then Alice's peering SIP proxy needs to adapt its behavior to the
rules of the federation this call is traversing.
The following subsections provide some examples of what a federation
could imply for the call processing.
5.4.1. Central Federation Proxy
Federation rules can dictate that calls are to be routed via a
federation-maintained central SIP proxy. In that case no further
NAPTR/SRV/A lookups are made. Instead, the INVITE will be sent
directly via a preconfigured TLS connection to that proxy. This proxy
acts as a redirect proxy.
The following message flow provides an example describing this
process:
Peer Proxy Federation Proxy Peer Proxy Bob
| | | |
| INVITE | | |
|--------------->| | |
| 302 | | |
|<---------------| | |
| ACK | | |
|--------------->| | |
| INVITE | |
|-------------------------------->| INVITE |
| 100 |--------------->|
|<--------------------------------| 180 |
| 180 |<---------------|
|<--------------------------------| |
| | 200 |
| 200 |<---------------|
|<--------------------------------| |
| ACK | |
|-------------------------------->| ACK |
| |--------------->|
| Both Way RTP Media |
|<================================================>|
| | BYE |
| BYE |<---------------|
|<--------------------------------| |
| 200 | |
|-------------------------------->| 200 |
| |--------------->|
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5.4.2. VPN Based Federations
If a federation has established some sort of VPN which connects the
SIP elements of all participating VSPs, then matching that federation
will cause:
Proxy1 to use e.g. a private DNS within that VPN for further lookups
and will direct all further traffic to be routed into that VPN.
IPsec based VPNs are a special case of this.
5.4.3. TLS Based Federation
One of the simplest cases is a TLS based federation.
In that case the federation rules may prescribe the default NAPTR/SRV
lookups and only affect the selection of the correct X.509
certificate for the TLS connection.
6. Considerations on Private [13] IP addresses
In Layer 5 peering scenarios, it does not really matter if the
peering fabric is public or private. What is relevant is if one of
the SIP devices participating in the session is in a public address
space and the other in a private.
In this case some observations should be made:
o A SIP device in a private address space can only communicate with
a device in a public address space if a NAT binding from private
to public address is provided.
o If a SIP device is in a private address space behind a legacy NAT
device and implements a NAT traversal method [8], media relay
might be needed for the successful establishment of the session.
Media relay is most commonly implemented by a B2BUA or SBC. A
legacy NAT is one that does not implement a SIP Application Level
Gateway (ALG).[4]
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7. Considerations on Media Flows
7.1. Decomposition
The scenarios in the previous sections show media flowing between the
endpoints involved in the SIP session, but it is important to
understand that the domains involved in peering might not carry the
media associated with such sessions.
Media associated with the sessions established across the peering
interface could be carried by a traditional ISP. The picture below
depicts such a scenario.
+---------+ _________
/--->| VSP |<-----\
/ | | \
| +---------+ |
Signaling | | Signaling
(peering) | | (peering)
| |
+------------+ | | +------------+
| |<-/ +-----------+_ \->| |
| | | | | |
| Domain A |>------->| ISP |>-------->| Domain B |
| |<-------<|___________|<--------<| |
|____________| Media | | Media |____________|
+------------+ +-----------+ +------------+
7.2. Media Relay
In the event that a calling and/or called entity are part of a
private network and the NAT/FW at the CPE is VoIP unaware or the
client uses a NAT traversal method, the SIP proxy must find a way to
modify the private addresses that remain in the signaling payload (in
addition to threading media through the NAT/FW). This modifying
process is sometimes referred to as Far-end NAT Traversal (FE-NTRV).
The core of the FE-NTRV process is media relaying. The signaling
entity relays media between the two endpoints as a result of the
repairing process and to guarantee NAT/FW traversal (symmetric RTP).
It is important to understand that media relay can be use independent
of NAT/FW as a way to direct media to a certain device for
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processing. In the context of SPEERMINT, media relay could be used to
enable the collapsed model and/or perform FE-NTRV.
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ALICE NAT/FW Media Relay Bob
10.10.1.2 Signaling:128.16.5.10 192.32.6.2
Media:168.12.1.8
| | | |
| INVITE | | |
|------------------>| INVITE | |
|s:10.10.1.2:9082 |------------------->| INVITE |
|d:128.16.5.10:5060 |s:140.1.1.1:23040 |------------------>|
|c= 10.10.1.2 |d:128.16.5.10:5060 |s:128.16.5.10:5060 |
|m= 11032 |c= 10.10.1.2 |d:192.32.6.2:5060 |
| |m= audio 11032 |c= 168.12.1.8 |
| | |m= audio 3600 |
| | | |
|
v
+---------------------------------------------------------------------+
| Media Relay creates a pair of media relay ports. The first port, |
| 3600, is for receiving media from the called party and the 2nd |
| port, 7600, is for receiving media from the calling party. As we do |
| not know what the transport address of the calling party will be |
| (post NAPT), any media received from the called party must be |
| dropped. |
+---------------------------------------------------------------------+
| | | 200 OK |
| | 200 OK |<------------------|
| 200 OK |<-------------------|s:192.32.6.2:5060 |
|<------------------|s:128.16.5.10:5060 |d:128.16.5.10:5060 |
|s:128.16.5.10:5060 |d:140.1.1.1:23040 |c= 192.32.6.2 |
|d:10.10.1.2:9082 |c= 168.12.1.8 |m= audio 9080 |
|c= 168.12.1.8 |m= audio 7600 | |
|m= audio 7600 | | |
| | | |
| | | |
|
V
+----------------------------+
| Media Relay updates remote |
| dest. as 192.32.6.2:9080 |
+----------------------------+
| | | |
| ACK (...) | | |
|------------------>| | |
| | | Media |
| | X<==================|
| | |s:168.12.1.8:3600 |
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| | |d:192.32.6.2:9080 |
| | | |
| | v |
Discarded
| Media | |
|=======================================>|==================>|
|s:10.10.1.2:11032 |s:140.1.1.1:16220 |s:168.12.1.8:3600 |
|d:168.12.1.8:7600 |d:168.12.1.8:7600 |d:192.32.6.2:9080 |
| | | |
| | v |
+---------------------------+
| Update remote destination |
+---------------------------+
| | | |
| Media | |
|<=======================================|<==================|
|s:168.12.1.8:7600 |s:168.12.1.8:7600 |s:192.32.6.2:9080 |
|d:10.10.1.2:11032 |d:140.1.1.1:16220 |d:168.12.1.8:3600 |
| | | |
| | | |
| | | |
| | | |
| | | |
| | | |
7.3. Media QoS
Media flows for real time communication usually need strict
scheduling guarantees in order to not degrade the service. The
problem of QoS within an independent administratively managed domain
and across independent domains is quite different.
In the case of L5 peering several issues arise around QoS for media
flows, especially in the case of on-demand peering. Some of these
issues are listed below.
o How to reconcile general QoS parameters used in domain A across
the peering interface with those announced by domain B's peering
policy?
o How domain B can identify media flows crossing the peering
interface coming from domain A (and vice-versa) in order to
provide the agreed upon QoS treatment? We could potentially be
talking about hundreds of calls (and consequently new media flows)
per second.
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o Moreover, in a decomposed scenario, how the SIP proxy can let the
router know the identity of such media flows and the QoS
parameters associated with it? This problem was discussed under
the TISPAN umbrella related to NGN networks [6].
o Alternatively or in conjunction with dynamic identification there
is the issue of trust. Possibly domain B could trust domain A to
mark all media packets appropriately. Domain B would honor such
markings and give the appropriate treatment announced on its
peering policy
8. Considerations on Multilateral Peering
Some of the difficulties discussed in previous sections would be
aggravated in the case of multilateral on-demand peering where
potentially more than one VSP could carry signaling (and possibly
media) to reach a specific endpoint.
How could peer policies be compared to find out the best one for a
specific case? In the case of routing protocols a combination of
metrics, route filtering, and other techniques provide a solution.
+---------+
| |
/ | Domain |\
/ | C | \
/ | | \
/ +---------+ \
/ \
+--------+ / +---------+ \ +--------+ +-----+
| |---/ | | \----| | | |
| Domain | | Domain | | Domain | | UA |
| A |-----------| B |-----------| D |-------| |
| | | | | | +-----+
+--------+ +---------+ +--------+
9. SIP Priority and SPEERMINT QoS
There are various QoS aspects that need to be taken into account in
the context of SPEERMINT. These contexts include, but are not limited
to, Signaling and Media QOS. The following subsections discuss those
aspects by first laying out some groundwork and then going through
scenarios.
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9.1. Problem Statement
When SIP signaling and media packets from UA 1 arrive at peering
point destined to UA 2, the Layer 5 peering functions need to make
sure those packets receive the proper treatment when crossing the
peering fabric into another domain. Proper treatment involves three
aspects: packet recognition and marking, accounting, and trust. The
scope of resource allocation to ensure predictive per hop behaviors,
or QOS, is a matter of local policy within an administrative domain.
More often than not, a SIP Session traverses multiple administrative
domains. A subset scope of QOS local policies can be shared within a
direct or transit peering arrangement.
9.2. Packet Recognition and Marking
If the layer 5 peering devices (referred to as SIP proxies) are going
to mark signaling and media packets, they need to first be able to
recognize them. Recognizing and marking SIP signaling is not
problematic since we assume the Layer 5 peering devices perform SIP
proxy functions. The primary source of confusion is in the
recognition and marking of the media (RTP, etc) packets.
If the SIP Proxy performs SDP inspection, it will be able to
recognize media packets based on the contents of the c and m lines.
It is important to notice that there is an implicit assumption of
what will be negotiated, and also that this proxy stays in the
signaling call flow for the duration of the call - and therefore be
aware of mid-call events.
Now we come to the problem of which device will mark the packets. In
a decomposed scenario, the SIP proxy needs to let the router know how
to identify media packets and which marking to use. One possible
solution is the use of a Gate Control Protocol [6].
9.2.1. Peering Classes of Service
In the simplest case the peering fabric will have a set of classes of
service that serve as a translation table from one domain to another.
So, a domain A only needs to know how to map the classes of service
used internally to the ones used in the peering point (and vice-
versa).
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In the simplest case the peering fabric will have a set of classes of
service that serve as a translation table from one domain to another.
So, domain A only needs to know how to map the classes of service
used internally to the ones used in the peering point (and vice-
versa). This could be independent or above and beyond any QoS policy
exchanges. We should read "a packet received with an EF DSCP should
be marked with AF41".
-------------------------
| Ingress | Egress |
| DSCP | DSCP |
| name | name |
+=========+=============+
| EF | AF41 |
+---------+-------------+
| CS5 | CS5 |
+---------+-------------+
|AF41,AF42| AF41 |
| AF43 | |
+---------+-------------+
| CS4 | CS4 |
+---------+-------------+
In the transit VoIP peering model, in order to maintain some
consistency with classification of packets, there needs to be a
common denominator for originating and terminating domains to
understand. This only pertains to a transit peering model as a
direct peering strategy does not have an abstracting 3rd party to the
ultimate terminating domain.
_Origin. Domain__,___Transit Domain_,_Termin. Domain___
| | | |
| EF | "Highest" | EF |
| | | |
| AF1 | "High" | AF |
| | | |
| AF2 | "Medium" | AF2 |
| | | |
| BE | "Low" | BE |
| | | |
| BE | "Who Cares?" | BE |
|_________________|__________________|_________________|
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9.2.2. Network Address Translation (NAT)
The use of NAT media makes packet recognition problem more severe. As
discussed in section 6, in certain scenarios the identification of
the media flows require special processing.
9.3. Accounting
Accounting refers to the tracking consumption of network resources by
sessions. In order to accomplish inter-domain accounting, it is
required to know the exchanged policies, resources available and
reachability. Within the information gathered, it is important to
know the identity of the session, the nature of the service
delivered, when the service began, and when it ended.
9.4. Trust
If Proxy 1 trusts that its users will mark packets correctly, the
issue of packet recognition and marking can be mitigated. Of course
that does not imply that Proxy 2 trusts Domain 1 to mark packets
correctly. That is where a QoS policy exchange comes into play.
10. SIP Policy Enforcement and Definition
Within the following description, there is an assumption that the SIP
proxy will know via policy exchange, variables that will weigh
potentially in routing decisions from Proxy A to Proxy B, (e.g.
defined relationship, trust established, etc).
In the inter-domain exchange of SIP signaled real-time sessions, the
SIP proxy will be the policy decision point that enforces exchanged
session policies. In this signaling plane enforcement model, all
bearer traffic will receive the same level of QoS (e.g. EF). Real-
time traffic (voice, video, etc) share the same sensitivity to
latency, jitter, and packet loss. Therefore any direct inter-domain
QoS mapping of service levels is not needed. Should one type of
traffic (Video) have more significance than another (voice) then the
SIP proxy will enforce that policy, possible preempting existing
sessions if required.
In both the collapsed and decomposed inter-domain call models, the
SIP proxies of both the originating and terminating domains have the
authority to permit, deny, preempt and throttle sessions. Inspecting
and classifying at the SIP layer brings an added differentiation
superseding Layer 3 policies.
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10.1. Local SIP Policy
Local SIP Policy is defined as that which has local significance, or
not appropriate to exchange beyond administrative domains. Examples
of local policies would be preferential treatment of sessions based
on hierarchical subscriber groupings ("gold level" subscribers), path
selection based on time of day, or presence.
10.2. Remote SIP Policy
Remote SIP policy is defined as policies that are learned via
exchange mechanism with a peer in a remote administrative domain.
Examples of a remote policy would be the preferred codec, or number
of sessions permitted.
10.3. SIP Proceed Policy
The SIP Proceed policy is used to determine if a session attempt
should be permitted to continue or not. The SIP Proceed policy is
constructed from a merging of local and remote policies learned via
an exchange mechanism. Permitting of a session to proceed or not can
be done by any SIP proxy involved in inter-domain signaling of the
session.
The need for a scalable/fast implementation that will track current
state information in real-time can be achieved by RADIUS. A real-
time and historical session activity database will have a full
history of all active sessions. When a session attempt is made from
an UA, it will be accounted for on a session accounting element of
the SIP proxy. The accounting element(s) can maintain data on
whatever criteria pertinent to track (codec, domain, timestamps
etc...) When a new session attempt is made, an accounting look-up is
done and a search on whatever criteria of interest is done to
determine if session signaling can proceed. See the Policy Decision
Point (PDP) in the following call flow:
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Alice Proxy 1 Radius Proxy 2 Bob
| | | | |
|INVITE | | | |
|------->| | | |
| 100 | | | |
|<-------| Session | | |
| | Attempt | | |
| |---------->| | |
| | Current | | |
| | Peer Stats| | |
| |<----------| | |
| (PDP) | | |
| | INVITE | | |
| |--------------------->| INVITE |
| | 100 | |--------->|
| |<---------------------|180 |
| | 180 | |<---------|
| 180 |<---------------------| |
|<-------| | |200 |
| | 200 | |<---------|
| 200 |<---------------------| |
|<-------| | | |
| ACK | | | |
|------->| ACK | | |
| |--------------------->|ACK |
| | | |--------->|
| | | | |
SIP proxies talk to a list of radius servers for accounting purposes.
The radius servers should be on a local network to the proxy.
Prior to Proxy 1 sending INVITE to Proxy 2, a determination will be
made based on the exchanged policies if the attempt at session
establishment should be permitted.
11. Peering Domain Information Exchange
11.1. Domain Routes
In some cases, it may be required to exchange specific domain route
information between peers. The following describes a method for a
relationship between proxies in domains A and B to exchange domain
routes using a SIP peering policy event package. This event package
may contain specific sections, which will provide routing information
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for the peering proxy server to update its routing table with new
peering routes. This method utilizes a SUBSCRIBE method, and routes
may be updated through expiry timers and subscription refreshes as
defined in [8].
Proxy 1 Proxy 2
| |
|Subscribe w/PeerPlcyEvtPkg |
|---------------------------->|
| 401 Unauthorized |
|<----------------------------|
|Subscribe w/Auth |
|---------------------------->|
| 202 Accepted |
|<----------------------------|
| Notify |
|<----------------------------|
| 200 OK |
|---------------------------->|
11.2. Authentication Credentials
In some cases, authorization credentials for authentication methods
such as HTTP digest may want to be exchanged and utilized by domain
proxies for authenticating new message requests from subscribers
intended for a UA in another domain. The following describes a
method for a relationship between proxies in domains A and B to
exchange authentication information using a SIP peering policy event
package. This event package may contain specific sections, which
will provide authentication methods to be used for authenticating to
the peer's proxy. This method utilizes a SUBSCRIBE method similar to
the method described in section 3.2.
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Proxy 1 Proxy 2
| |
|Subscribe w/ PeerPlcyEvtPkg |
|---------------------------->|
| 401 Unauthorized |
|<----------------------------|
|Subscribe w/Auth |
|---------------------------->|
| 202 Accepted |
|<----------------------------|
| Notify |
|<----------------------------|
| 200 OK |
|---------------------------->|
12. Peering Message Flow Phases
The message flow phases are Discovery, Policy Exchange, Security
Establishment, Signaling Exchange, and Media Exchange. The following
flow provides an overview of the phases. Each of the phases is
described individually in the following subsections. In the
following flow, the policy and peering proxy have been combined;
however, these two functions may be separated. Also, the signaling
and media exchange phase descriptions have been omitted for clarity
purposes, because their functionality has not changed for the
purposes of peering. However, they have been explained further in
the following subsections.
Alice Peer Proxy DNS Peer Policy/Proxy Bob
| | | | |
|INVITE | | | |
|----------->| | | |
| 100| | | |
|<-----------| | | |
|NAPTR Query | | |
+---->|--------------->| | |
| | NAPTR Reply| | |
Discovery Phase | |<---------------| | |
----------------| |SRV Query | | |
| |--------------->| | |
| | SRV Reply| | |
+---->|<---------------| | |
| | | |
| INVITE | |
|---------------------------->| |
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| 401 Unauthorized | |
|<----------------------------| |
| | |
| SUBSCRIBE | |
+---->|---------------------------->| |
| | 202 Accepted | |
Policy Exchange | |<----------------------------| |
----------------| | Notify | |
Phase | |<----------------------------| |
| | 200 OK | |
+---->|---------------------------->| |
| INVITE | |
+---->|---------------------------->| |
| | [TLS Connection] | |
Security Exch. | |<--------------------------->| |
----------------| | 401 Unauthorized | |
Phase | |<----------------------------| |
| | INVITE | |
+---->|---------------------------->|INVITE |
| | 100 Trying |------------->|
| |<----------------------------| 180 Ringing|
| | 180 Ringing |<-------------|
| 180 Ringing|<----------------------------| 200OK |
|<------------| 200OK |<-------------|
| 200OK |<----------------------------| |
|<------------| | |
| ACK | | |
|------------>| ACK | |
| |---------------------------->|ACK |
| | |------------->|
| | Both Way RTP Media | |
|<========================================================>|
| | | BYE |
| | BYE |<-------------|
| BYE |<----------------------------| |
|<------------| | |
| 200OK | | |
|------------>| 200OK | |
| |---------------------------->|200OK |
| | |------------->|
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12.1. Discovery Phase
The first phase of static or dynamic peering requests is discovery.
The discovery process can be summarized by querying the Location
Function to determine the next phase in the message flow. The
discovery phase can take place via a local or external federation
location function. Examples of the function may be comprised of an
ENUM/DNS or redirect server. After the discovery phase has
completed, the peering process will progress to a subsequent phase,
usually the policy or authentication phase. The following message
flows provide examples of the discovery phase.
Discovery phase utilizing an ENUM/DNS server as a location function:
Alice Peer Proxy DNS Peer Proxy
| | | |
|INVITE | | |
|----------->| | |
| 100| | |
|<-----------| | |
|NAPTR Query | |
+---->|--------------->| |
| | NAPTR Reply| |
Discovery Phase | |<---------------| |
-----------------| |SRV Query | |
| |--------------->| |
| | SRV Reply| |
+---->|<---------------| |
|INVITE |
|------------------------------->|
Discovery phase utilizing a REDIRECT server as a location function:
Peer Proxy Federation Proxy Peer Proxy
| | |
| INVITE | |
+---->|--------------->| |
Discovery Phase | | 302 | |
-----------------| |<---------------| |
| | ACK | |
+---->|--------------->| |
| INVITE |
|------------------------------->|
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12.2. Policy Exchange Phase
Since the originating peer proxy does not know if the destination AOR
is a PF or a SF, it must progress with a normal dialog request with
the assumption it is a SF. In the event a request fails due to an
authentication failure (401 Unauthorized), and no known
authentication credentials exist or no longer appear to be working,
the requesting proxy may issue a SUBSCRIBE [8] request to the
attempted peer's AOR received through the discovery phase. The
SUBSCRIBE request should be a request to attain a, currently,
undefined peering policy event package. In some cases, the
requesting proxy already knows it must attain the peering policy
event package, and may forego the initial INVITE attempt and issue a
SUBSCRIBE request instead. Once this phase is completed, after
extracting and following any specific received policies, the
authentication phase is attempted as the policy permits or requires.
The following message flow provides an example of the policy exchange
phase. The following message flow assumes the discovery phase has
already completed using one of the methods described in section 12.1.
Peer Proxy Policy Server
| |
| INVITE |
|------------------------------->|
| 401 Unauthorized |
|<-------------------------------|
| |
| SUBSCRIBE |
+---->|------------------------------->|
| | 202 Accepted |
Policy Exchange | |<-------------------------------|
-----------------| | Notify |
Phase | |<-------------------------------|
| | 200 OK |
+---->|------------------------------->|
| INVITE |
|------------------------------->|
12.3. Security Establishment Phase
The security establishment phase follows the described methods in
previous sections of this document. After the originating proxy
receives the policy event package, it extracts the necessary security
policy information. The security policy may contain many different
combinations of security requirements. For example, it may contain a
simple digest authentication method or may require TLS with digest
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authentication. This is determined by the destination peer, and must
be followed to successfully complete this phase. This phase follows
standard methods described in [2], so the following flow provides an
example of this phase, but does not incorporate all possibilities.
This phase assumes the previous phases were successfully completed or
purposefully omitted per peering implementation.
Peer Proxy Peer Proxy
| |
| INVITE |
+---->|------------------------------->|
| | [TLS Connection] |
Security Exch. | |<------------------------------>|
----------------| | 401 Unauthorized |
Phase | |<-------------------------------|
| | INVITE |
+---->|------------------------------->|
| 100 Trying |
|<-------------------------------|
| 180 Ringing |
|<-------------------------------|
12.4. Signaling Exchange Phase
The signaling exchange phase is a necessary step to progress towards
establishing peering. This phase may incorporate the security
exchange phase, but it is not required. This phase follows standard
methods described in [2], so the following flow provides an example
of this phase, but does not incorporate all possibilities.
Peer Proxy Peer Proxy
| |
| INVITE |
+---->|------------------------------->|
| | [TLS Connection] |
| |<------------------------------>|
| | 401 Unauthorized |
| |<-------------------------------|
| | INVITE |
| |------------------------------->|
Signaling Exch. | | 100 Trying |
-----------------| |<-------------------------------|
Phase | | 180 Ringing |
| |<-------------------------------|
| | 200 OK |
| |<-------------------------------|
| | ACK |
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| |------------------------------->|
| | BYE |
| |<-------------------------------|
| | 200 OK |
+---->|------------------------------->|
| |
12.5. Media Exchange Phase
The media exchange phase is negotiated and established during the
signaling exchange phase. This phase follows standard methods
described in [2], so the following flow provides an example of this
phase, but does not incorporate all possibilities.
Alice Peer Proxy Peer Proxy Bob
+---->|INVITE | | |
| |----------->| INVITE | |
| | 100 |------------------>| |
| |<-----------| [TLS Connection] | |
| | |<----------------->| |
| | | 401 Unauthorized | |
| | |<------------------| |
Media Exch. | | | INVITE | |
---------------| | |------------------>|INVITE |
Phase | | | 100 Trying |----------->|
| | |<------------------| 180 |
| | | 180 Ringing |<-----------|
| | 180 |<------------------| 200 |
| |<-----------| 200 OK |<-----------|
| | 200 |<------------------| |
| |<-----------| | |
| |ACK | | |
+---->|----------->|ACK | |
| |------------------>|ACK |
| | |----------->|
| Both Way RTP Media | |
|<===========================================>|
| | | |
| | | BYE |
| | BYE |<-----------|
| BYE|<------------------| |
|<-----------| | |
|200 | | |
|----------->|200 | |
| |------------------>|200 |
| | |----------->|
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13. Security Considerations
The level of security required during the establishment and
maintenance of a SIP peering relationship between two proxies can
vary greatly. In general all security considerations related to the
SIP protocol are also applicable in a peering relationship.
If the two proxies communicate over an insecure network, and
consequently are subject to attacks, the use of TLS or IPSec would be
advisable.
If there is physical security and the proxies are co-located, or the
proxies are situated in a segregated network (such as a VPN), one
could argue that basic filtering based on IP address is enough.
14. IANA Considerations
N/A
15. Conclusions
The purpose of this draft is to show SPEERMINT message flows but also
to raise awareness through questions and detailed considerations of
several issues the industry might have to deal with in different
peering scenarios.
16. Acknowledgments
Thanks to Otmar Lendl for the Federation Call flows
17. References
17.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] 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.
[3] Rosenberg, J. and H. Schulzrinne, "Session Initiation Protocol
(SIP): Locating SIP Servers", RFC 3263, June 2002.
[4] Srisuresh, P. and K. Egevang, "Traditional IP Network Address
Translator (Traditional NAT)", RFC 3022, January 2001.
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[5] Johnston, A., Donovan, S., Sparks, R., Cunningham, C., and K.
Summers, "Session Initiation Protocol (SIP) Basic Call
Flow Examples", BCP 75, RFC 3665, December 2003.
[6] ETSI TS 102 333: " Telecommunications and Internet converged
Services and Protocols for Advanced Networking (TISPAN); Gate
control protocol".
[7] Babiarz, J., "Configuration Guidelines for DiffServ Service
Classes", draft-ietf-tsvwg-diffserv-service-classes-02 (work in
progress), February,2006.
[8] Roach, A., "Session Initiation Protocol (SIP)-Specific Event
Notification", RFC 3265, June 2002.
[9] Crocker, D. and Overell, P.(Editors), "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, Internet Mail Consortium and
Demon Internet Ltd., November 1997.
[10] Rekhter, Y., Moskowitz, B., Karrenberg, D., de Groot, G., and
E. Lear, "Address Allocation for Private Internets", RFC 1918,
February 1996.
17.2. Informative References
[11] Meyer, D., "SPEERMINT Requirements and Terminology", Internet
Draft, draft-ietf-speermint-reqs-and-terminology-01
[12] Boulton, C., Rosenberg, J., Camarillo, G., "Best Current
Practices for NAT Traversal for SIP", Internet Draft, draft-
ietf-sipping-nat-scenarios-04
[13] Lendl, O., "The Domain Policy DDDS Application", draft-lendl-
domain-policy-ddds-00 (work in progress), February 2006.
[14] Lendl, O., "A Federation based VoIP Peering Architecture",
draft-lendl-speermint-federations-02 (work in progress), August
2006.
[15] Camarillo, G., Penfield, R., Hawrylyshen, A., "Requirements
from SIP (Session Initiation Protocol) Session Border
Controller Deployments", Internet Draft, draft-camarillo-
sipping-sbc-funcs-03
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Author's Addresses
Daryl Malas
Level 3 Communications LLC
1025 Eldorado Blvd.
Broomfield, CO 80021
USA
EMail: daryl.malas@level3.com
Sohel Khan, Ph.D.
Technology Strategist
Sprint
6220 Sprint Parkway
Overland Park, KS 66251
U.S.A
Email: Sohel.Q.Khan@sprint.com
Reinaldo Penno
Juniper Networks
1194 N Mathilda Avenue
Sunnyvale, CA
USA
Email: rpenno@juniper.net
Adam Uzelac
Global Crossing
1120 Pittsford Victor Road
PITTSFORD, NY 14534
USA
Email: adam.uzelac@globalcrossing.com
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