Speermint Working Group R. Penno
Internet Draft Juniper Networks
Expires: February 2007 D. Malas
Level 3
S. Khan
Sprint
A. Uzelac
Global Crossing
September 19, 2006
SPEERMINT Routing Architecture Message Flows
draft-ietf-speermint-flows-01
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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..........................................6
3. On-Demand Peering..............................................8
3.1. Transport Layer Security..................................8
3.2. Proxy Authentication: Subscribe/Notify...................10
4. Static Peering................................................11
4.1. IPSec....................................................12
4.2. Co-Location..............................................12
5. Federation Based Peering......................................13
5.1. Simple Federation Match..................................14
5.2. No federation match......................................14
5.3. Federation Referral......................................15
5.4. Federation Specific Call Processing......................16
5.4.1. Central Federation Proxy............................17
5.4.2. VPN Based Federations...............................18
5.4.3. TLS Based Federation................................18
6. Peering Domain Information Exchange...........................18
6.1. Domain Routes............................................18
6.2. Authentication Credentials...............................19
7. Peering Message Flow Phases...................................20
7.1. Discovery Phase..........................................21
7.2. Policy Exchange Phase....................................22
7.3. Security Establishment Phase.............................23
7.4. Signaling Exchange Phase.................................24
7.5. Media Exchange Phase.....................................24
8. Security Considerations.......................................25
9. IANA Considerations...........................................25
10. Acknowledgments..............................................26
11. References...................................................26
11.1. Normative References....................................26
11.2. Informative References..................................27
Author's Addresses...............................................28
Intellectual Property Statement..................................28
Disclaimer of Validity...........................................29
Copyright Statement..............................................29
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Acknowledgment...................................................29
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
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.
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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.
............................ ..............................
. . . .
. +-------+ . . +-------+ .
. | | . . | | .
. | DNS | . . | DNS | .
. | 1 | . . | 2 | .
. | | . . | | .
. +-------+ . . +-------+ .
. | . . | .
. | . . | .
. +-------+ . . +-------+ .
. | | . . | | .
. | Proxy |--------------| Proxy | .
. | 1 | . . | 2 | .
. | | . . | | .
. / +-------+ . . +-------+ \ .
. / . . \ .
. / . . \ .
. / . . \ .
. / . . \ .
. / . . \ .
. / . . \ .
. / . . \ .
. +-------+ . . +-------+ .
. | | . . | | .
. | | . Media . | | .
. | UA 1 |<========================================>| UA 2 | .
. | | . . | | .
. +-------+ . . +-------+ .
. Domain A . . Domain B .
............................ ..............................
Figure 1 Basic Peering Picture.
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The collapsed model is shown below:
............................ ..............................
. . . .
. +-------+ . . +-------+ .
. | | . . | | .
. | 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 |
| | |-----------> |
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.
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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. Peering Domain Information Exchange
6.1. 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
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].
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Proxy 1 Proxy 2
| |
|Subscribe w/PeerPlcyEvtPkg |
|---------------------------->|
| 401 Unauthorized |
|<----------------------------|
|Subscribe w/Auth |
|---------------------------->|
| 202 Accepted |
|<----------------------------|
| Notify |
|<----------------------------|
| 200 OK |
|---------------------------->|
6.2. 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.
Proxy 1 Proxy 2
| |
|Subscribe w/ PeerPlcyEvtPkg |
|---------------------------->|
| 401 Unauthorized |
|<----------------------------|
|Subscribe w/Auth |
|---------------------------->|
| 202 Accepted |
|<----------------------------|
| Notify |
|<----------------------------|
| 200 OK |
|---------------------------->|
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7. 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 | |
|---------------------------->| |
| 401 Unauthorized | |
|<----------------------------| |
| | |
| SUBSCRIBE | |
+---->|---------------------------->| |
| | 202 Accepted | |
Policy Exchange | |<----------------------------| |
----------------| | Notify | |
Phase | |<----------------------------| |
| | 200 OK | |
+---->|---------------------------->| |
| INVITE | |
+---->|---------------------------->| |
| | [TLS Connection] | |
Security Exch. | |<--------------------------->| |
----------------| | 401 Unauthorized | |
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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 |
| | |------------->|
7.1. 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| | |
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|<-----------| | |
|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 |
|------------------------------->|
7.2. 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
| |
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| INVITE |
|------------------------------->|
| 401 Unauthorized |
|<-------------------------------|
| |
| SUBSCRIBE |
+---->|------------------------------->|
| | 202 Accepted |
Policy Exchange | |<-------------------------------|
-----------------| | Notify |
Phase | |<-------------------------------|
| | 200 OK |
+---->|------------------------------->|
| INVITE |
|------------------------------->|
7.3. 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
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 |
|<-------------------------------|
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7.4. 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 |
| |------------------------------->|
| | BYE |
| |<-------------------------------|
| | 200 OK |
+---->|------------------------------->|
| |
7.5. 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 | |
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| | |<------------------| |
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 |
| | |----------->|
8. 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.
9. IANA Considerations
N/A
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10. Acknowledgments
Thanks to Otmar Lendl for the federation call flows.
11. References
11.1. 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.
[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.
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11.2. 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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