One document matched: draft-ietf-speermint-voip-consolidated-usecases-12.txt
Differences from draft-ietf-speermint-voip-consolidated-usecases-11.txt
SPEERMING Working Group A. Uzelac, Ed.
Internet-Draft Global Crossing
Intended status: Informational Y. Lee, Ed.
Expires: November 28, 2009 Comcast Cable
May 27, 2009
VoIP SIP Peering Use Cases
draft-ietf-speermint-voip-consolidated-usecases-12
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Abstract
This document depicts many common Voice over IP (VoIP) use cases for
Session Initiation Protocol (SIP) Peering. These use cases are
categorized into static and on-demand, and then further sub-
categorized into direct and indirect. These use cases are not an
exhaustive set, but rather the most common use cases deployed today.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 4
3. Reference Architecture . . . . . . . . . . . . . . . . . . . . 4
4. Contexts of Use Cases . . . . . . . . . . . . . . . . . . . . 5
5. Use Cases . . . . . . . . . . . . . . . . . . . . . . . . . . 6
5.1. Static Peering Use Cases . . . . . . . . . . . . . . . . . 6
5.2. Static Direct Peering Use Case . . . . . . . . . . . . . . 6
5.2.1. Administrative characteristics . . . . . . . . . . . . 11
5.2.2. Options and Nuances . . . . . . . . . . . . . . . . . 11
5.3. Static Direct Peering Use Case - Assisting LUF and LRF . . 12
5.3.1. Administrative Characteristics . . . . . . . . . . . . 13
5.3.2. Options and Nuances . . . . . . . . . . . . . . . . . 14
5.4. Static Indirect Peering Use Case - Assisting LUF and
LRF . . . . . . . . . . . . . . . . . . . . . . . . . . . 14
5.4.1. Administrative characteristics . . . . . . . . . . . . 20
5.4.2. Options and Nuances . . . . . . . . . . . . . . . . . 20
5.5. Static Indirect Peering Use Case . . . . . . . . . . . . . 21
5.5.1. Administrative characteristics . . . . . . . . . . . . 21
5.5.2. Options and Nuances . . . . . . . . . . . . . . . . . 22
5.6. On-demand Peering Use Cases . . . . . . . . . . . . . . . 22
5.6.1. Administrative characteristics . . . . . . . . . . . . 22
5.6.2. Options and Nuances . . . . . . . . . . . . . . . . . 22
6. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 23
7. Security Considerations . . . . . . . . . . . . . . . . . . . 23
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8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 23
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 23
9.1. Normative References . . . . . . . . . . . . . . . . . . . 23
9.2. Informative References . . . . . . . . . . . . . . . . . . 24
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 24
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1. Introduction
This document attempts to capture Voice over IP (VoIP) use cases for
Session Initiation Protocol (SIP) [RFC3261] based peering. These use
cases will assist in identifying requirements and other issues to be
considered for future resolution by the working group.
Only use cases related to VoIP are considered in this document.
Other real-time SIP communications use cases, like Instant Messaging
(IM) and presence are out of scope for this document. In describing
use cases, the intent is descriptive, not prescriptive.
The use cases contained in this document attempts to be as
comprehensive as possible, but should not be considered the exclusive
set of use cases.
2. Terminology
This document uses terms defined in [RFC5486]. Please refer to it
for definitions.
3. Reference Architecture
The diagram below provides the reader with a context for the VoIP use
cases in this document. Terms such as Sip Service Provider (SSP),
Look-Up Function (LUF), Location Routing Function (LRF), Signaling
Path Border Element (SBE) and Data Path Border Element (DBE) are
defined in [RFC5486].
Originating SSP (O-SSP) is the SSP originating a request.
Terminating SSP (T-SSP) is the SSP terminating the request
originating from O-SSP. Assisting LUF and LRF Provider offers LUF
and LRF services to O-SSP. Indirect SSP (I-SSP) is the SSP providing
indirect peering service(s) to O-SSP to connect to T-SSP.
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+--------------------+------------------------+--------------------+
| Originating SSP | Assisting LUF and LRF | Terminating SSP |
| Domain | Provider Domain | Domain |
| | | |
| +-----+ +-----+ | +------+ +------+ | +-----+ +-----+ |
| |O-LUF| |O-LRF| | |A-LUF | | A-LRF| | |T-LUF| |T-LRF| |
| +-----+ +-----+ | +------+ +------+ | +-----+ +-----+ |
| | | |
| +-------+ +-----+ +------------------------+ +-----+ +-------+ |
| |O-Proxy| |O-SBE| | Indirect SSP Domain | |T-SBE| |T-Proxy| |
| +-------+ +-----+ | | +-----+ +-------+ |
| | +-----+ +-----+ | |
| +---+ +-----+ | |O-SBE| |O-DBE| | +-----+ +---+ |
| |UAC| |O-DBE| | +-----+ +-----+ | |T-DBE| |UAS| |
| +---+ +-----+ | | +-----+ +---+ |
| | | |
+--------------------+------------------------+--------------------+
General Overview
Figure 1
Note that in Figure 1 - some elements defined are optional in many
use cases.
4. Contexts of Use Cases
Use cases are sorted into two general groups: Static and On-demand
Peering [RFC5486]. Each group can be further sub-divided into Direct
Peering and Indirect Peering [RFC5486]. Although there may be some
overlap among the use cases in these categories, there are different
requirements between the scenarios. Each use case must specify a
basic set of required operations to be performed by each SSP when
peering.
These can include:
o Peer Discovery - Peer discovery via a Look-Up Function (LUF) to
determine the Session Establishment Data (SED) [RFC5486] of the
request. In VoIP use cases, a request normally contains a phone
number. The O-SSP will input the phone number to the LUF and the
LUF will normally return a SIP AOR [RFC3261] which contains a
domain name.
o Next Hop Routing Determination - Resolving the SED information is
necessary to route the request to the T-SSP. The LRF is used for
this determination. The O-SSP may also use the standard procedure
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defined in [RFC3263] to discover the next hop.
o Call setup - SSPs that are interconnecting to one another may also
define specifics on what SIP features need to be used when
contacting the next hop in order to a) reach the next hop at all
and b) to prove that the sender is a legitimate peering partner.
Examples: hard-code transport (TCP/UDP/TLS), non-standard port
number, specific source IP address (e.g. in a private Layer-3
network), which TLS client certificate [RFC4366] to use, and other
authentication schemes.
o Call reception - This step serves to ensure that the type of
relationship (static or on-demand, indirect or direct) is
understood and acceptable. For example, the receiving SBE needs
to determine whether the INVITE it received really came from a
trusted member possibly via an access control list entry.
5. Use Cases
Please note there are intra-domain message flows within the use cases
to serve as supporting background information. Only inter-domain
communications are germane to Speermint.
5.1. Static Peering Use Cases
Static Peering [RFC5486] describes the use case when two SSPs form a
peering relationship with some form of association established prior
to the exchange of traffic. Pre-association is a prerequisite to
static peering. Static peering is used in cases when two peers want
a consistent and tightly controlled approach to peering. In this
scenario, a number of variables, such as an identification method
(remote proxy IP address) and Quality of Service (QoS) parameters,
can be defined upfront and known by each SSP prior to peering.
5.2. Static Direct Peering Use Case
This is the simplest form of a peering use case. Two SSPs negotiate
and agree to establish a SIP peering relationship. The peer
connection is statically configured and is direct between the
connected SSPs. The peers may exchange interconnection parameters
such as DSCP [RFC2474] policies, the maximum number of requests per
second and proxy location prior to establishing the interconnection.
Typically, the T-SSP only accepts traffic originating directly from
the trusted peer.
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+--------------------+ +---------------------+
| O-SSP | | T-SSP |
| +-----+ | | +-----+ |
| |O-LUF| | | |T-LUF| |
| |O-LRF| | | /|T-LRF| |
| /+-----+\ | | / +-----+ |
| (2) (4,5,6) | | / |
| / \ | | /(8,9) |
|+-------+ +-----+ +-----+ +-------+|
||O-Proxy|-(3)-|O-SBE+-----(7)-----+T-SBE|-(10)-|T-Proxy||
|+-------+ +-----+ +-----+ +-------+|
| | | | | |
| (1) | | (11) |
| | | | | |
| +-----+ +-----+ +-----+ +-----+ |
| | UAC +======|O-DBE+=====(12)====+T-DBE|=======+ UAS | |
| +-----+ +-----+ +-----+ +-----+ |
+--------------------+ +---------------------+
example.com example.net
Static Direct Peering Use Case
Figure 2
The following is a high-level depiction of the use case:
1. UAC initiates a call via SIP INVITE to O-Proxy. O-Proxy is the
home proxy for UAC.
INVITE sip:+19175550100@example.com;user=phone SIP/2.0
Via: SIP/2.0/TCP client.example.com:5060
;branch=z9hG4bK74bf9
Max-Forwards: 10
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=12345
To: Bob <sip+19175550100@example.com;user=phone>
Call-ID: abcde
CSeq: 1 INVITE
Contact: <sip:+19175550100@client.example.com;user=phone
;transport=tcp>
Note that UAC inserted its Fully Qualified Domain Name (FQDN) in
the VIA and CONTACT headers. This example assumes that UAC has
its own FQDN. In the deployment where UAC does not have its own
FQDN, UAC may insert an IP address into the headers.
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2. UAC only knows UAS's TN but not UAS's domain. It appends its
own domain to generate the SIP URI in Request-URI and TO header.
O-Proxy checks the Request-URI and discovers that the Request-
URI contains user parameter "user=phone". This parameter
indicates that the Request-URI is a phone number. So O-Proxy
will extract the TN from the Request-URI and query LUF for SED
information from a routing database. In this example, the LUF
is an ENUM [RFC3761] database. The ENUM entry looks similar to
this:
$ORIGIN 0.0.1.0.5.5.5.7.1.9.1.e164.arpa.
IN NAPTR (
10
100
"u"
"E2U+SIP"
"!^.*$!sip:+19175550100@example.net!"
. )
This SED data can be provisioned by O-SSP or populated by the
T-SSP.
3. O-Proxy examines the SED and discovers the domain is external.
Given the O-Proxy's internal routing policy, O-Proxy decides to
use O-SBE to reach T-SBE. O-Proxy routes the INVITE request to
O-SBE and adds a Route header which contains O-SBE.
INVITE sip:+19175550100@example.net;user=phone SIP/2.0
Via: SIP/2.0/TCP o-proxy.example.com:5060
;branch=z9hG4bKye8ad
Via: SIP/2.0/TCP client.example.com:5060
;branch=z9hG4bK74bf9;received=192.0.1.1
Max-Forwards: 9
Route: <sip:o-sbe1.example.com;lr>
Record-Route: <sip:o-proxy.example.com;lr>
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=12345
To: Bob s<ip+19175550100@example.com;user=phone>
Call-ID: abcde
CSeq: 1 INVITE
Contact: <sip:+19175550100@client.example.com;user=phone
;transport=tcp>
4. O-SBE receives the requests and pops the top entry of the Route
header which contains "o-sbe1.exapmle.com". O-SBE examines the
Request-URI and does a LRF for "example.net". In this example,
the LRF is a NAPTR DNS query [RFC3403] of the domain name.
O-SBE receives a NAPTR response from LRF. The response looks
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similar to this:
IN NAPTR (
50
50
"S"
"SIP+D2T"
""
_sip._tcp.t-sbe.example.net. )
IN NAPTR (
90
50
"S"
"SIP+D2U"
""
_sip._udp.t-sbe.example.net. )
5. Given the lower order for TCP in the NAPTR response, O-SBE
decides to use TCP as the transport protocol, so it sends a SRV
DNS query for the SRV record [RFC2782] for "_sip._tcp.t-
sbe.example.net".
;; priority weight port target
IN SRV 0 2 5060 t-sbe1.example.net.
IN SRV 0 1 5060 t-sbe2.example.net.
6. Given the higher weight for "t-sbe1.example.net", O-SBE sends an
A record DNS query for "t-sbe1.example.net." to get the A
record:
;; DNS ANSWER
t-sbe1.example.net. IN A 192.0.2.100
t-sbe1.example.net. IN A 192.0.2.101
7. O-SBE sends the INVITE to T-SBE. O-SBE is the egress point to
the O-SSP domain, so it should ensure subsequent mid-dialog
requests traverse via itself. If O-SBE chooses to act as a
Back-to-Back User Agent (B2BUA) [RFC3261], it will terminate the
call and generate a new INVITE request. If O-SBC chooses to act
as a proxy, it should record-route to stay in the call path. In
this example, O-SBE is a B2BUA.
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INVITE sip:+19175550100@example.net;user=phone SIP/2.0
Via: SIP/2.0/TCP o-sbe1.example.com:5060
;branch= z9hG4bK2d4zzz;
Max-Forwards: 10
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=54321
To: Bob <sip:+19175550100@example.net;user=phone>
Call-ID: abcde-osbe1
CSeq: 1 INVITE
Contact: <sip:+19175550100@o-sbe1.example.com;user=phone
;transport=tcp>
Note that O-SBE may re-write the Request-URI with the target
domain in the SIP URI. Some proxy implementations will only
accept the request if the Request-URI contains their own
domains.
8. T-SBE determines the called party home proxy and directs the
call to the called party. T-SBE may use ENUM or other internal
mechanism to locate the home proxy. If T-SSP uses ENUM, this
internal ENUM entry is different from the external ENUM entry
populated for O-SSP. In this example, the internal ENUM query
returns the UAS's home proxy.
$ORIGIN 0.0.1.0.5.5.5.7.1.9.1.e164.arpa.
IN NAPTR (
10
100
"u"
"E2U+SIP"
"!^.*$!sip:+19175550100@t-proxy.example.net!"
. )
9. T-SBE receives the NAPTR record and query DNS for the A record
of domain "t-proxy.example.net.". The DNS returns an A record:
;; DNS ANSWER
t-proxy.example.net. IN A 192.0.2.2
10. T-SBE is a B2BUA, so it generates a new INVITE and sends it to
UAS's home proxy:
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INVITE sip:bob@t-proxy.example.net;user=phone SIP/2.0
Via: SIP/2.0/TCP t-sbe1.example.net:5060
;branch= z9hG4bK28uyyy;
Max-Forwards: 10
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=54321
To: Bob <sip:+19175550100@t-proxy.example.net;user=phone>
Call-ID: abcde-tsbe1
CSeq: 1 INVITE
Contact: <sip:+19175550100@t-sbe1.example.net;user=phone
;transport=tcp>
11. Finally, UAS's home proxy forwards the INVITE request to the
UAS.
INVITE sip:+19175550100@server.example.net;user=phone SIP/2.0
Via: SIP/2.0/TCP t-proxy.example.net:5060
;branch= z9hG4bK28u111;
Via: SIP/2.0/TCP t-sbe1.example.net:5060
;branch= z9hG4bK28uyyy; received=192.2.0.100
Max-Forwards: 9
Record-Route: <sip:t-proxy.example.net:5060;lr>,
<sip:t-sbe1.example.net:5060;lr>
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=54321
To: Bob <sip:+19175550100@t-proxy.example.net;user=phone>
Call-ID: abcde-tsbe1
CSeq: 1 INVITE
Contact: <sip:+19175550100@t-sbe1.example.net;user=phone
;transport=tcp>
12. RTP is established between the UAC and UAS. Note that the media
passes through O-DBE and T-DBE.
5.2.1. Administrative characteristics
The static direct peering use case is typically implemented in a
scenario where there is a strong degree of trust between the two
administrative domains. Both administrative domains typically sign a
peering agreement which state clearly the policies and terms.
5.2.2. Options and Nuances
In Figure 2 O-SSP and T-SSP peer via SBEs. Normally, the operator
will deploy the SBE at the edge of its administrative domain. The
signaling traffic will pass between two networks through the SBEs.
The operator has many reasons to deploy a SBE. For example, either
proxy and UA may use [RFC1918] addresses that are not routable in the
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target network. The SBE can perform a NAT function. Also, the SBE
eases the operation cost for deploying or removing Layer-5 network
elements. Consider the deployment architecture where multiple
proxies connect to a single SBE. An operator can add or remove a
proxy without coordinating with the peer operator. The peer operator
"sees" only the SBE. As long as the SBE is maintained in the path,
the peer operator does not need to be notified.
When an operator deploys SBEs, the operator is required to advertise
the SBE to the peer LRF so that the peer operator can locate the SBE
and route the traffic to the SBE accordingly.
SBE deployment is a decision within an administrative domain. Either
one or both administrative domains can decide to deploy SBE(s). To
the peer network, most important is to identify the next-hop address.
Whether the next-hop is a proxy or SBE, the peer network will not see
any difference.
5.3. Static Direct Peering Use Case - Assisting LUF and LRF
This use case shares many properties with the static direct use case.
There must exist a pre-association between the O-SSP and T-SSP. The
difference is O-SSP will use the Assisting LUF/LRF Provider for LUF
and LRF. The LUF/LRF provider stores the SED to reach T-SSP and
provides it to O-SSP when O-SSP requests it.
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+-----------------+
|LUF/LRF Provider |
| |
| +-------+ |
| +-+ A-LUF | |
| / | A-LRF | |
+--------------------+ / ++-------+ +---------------------+
| O-SSP |/ / | T-SSP |
| +------------/(4,5,6) | +-----+ |
| / | / | |T-LUF| |
| (2) +-+/ | +-|T-LRF| |
| / / | | / +-----+ |
| / / | | /(8,9) |
|+-------+ +-----+ +-----+ +-------+|
||O-Proxy|-(3)-|O-SBE+-------(7)-------+T-SBE|-(10)-|T-Proxy||
|+-------+ +-----+ +-----+ +-------+|
| | | | | |
| (1) | | (11) |
| | | | | |
| +-----+ +-----+ +-----+ +-----+ |
| | UAC +======|O-DBE+=======(12)======+T-DBE+=======+ UAS | |
| +-----+ +-----+ +-----+ +-----+ |
+--------------------+ +---------------------+
example.com example.net
Static Direct Peering with Assisting LUF and LRF
Figure 3
The call flow looks almost identical to Static Direct Peering Use
Case except Step 2,4,5 and 6 which happen in LUF/LRF provider
remotely instead of happening in O-SSP domain.
Similar to Static Direct Peering Use case, O-DBE and T-DBE in the
Figure 3 are optional.
5.3.1. Administrative Characteristics
The LUF/LRF provider provides the LUF and LRF services for the O-SSP.
As such, LUF/LRF provider, O-SSP and T-SSP form a trusted
administrative domain. To reach T-SSP, O-SSP must still require pre-
arranged agreements for the peer relationship with T-SSP. The
Layer-5 policy is maintained in the O-SSP and T-SSP domains, and the
LUF/LRF provider may not be aware of any Layer-5 policy between the
O-SSP and T-SSP.
A LUF/LRF provider can serve multiple administrative domains. The
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LUF/LRF provider typically does not share SED from one administrative
domain to another administrative domain without appropriate
permission granted.
5.3.2. Options and Nuances
The LRF/LRF provider can use multiple methods to provide SED to
O-SSP. The most commonly used are an ENUM and a SIP Redirect. The
O-SSP should negotiate with the LUF/LRF provider which query method
it will use prior to sending request to LUF/LRF provider.
The T-SSP needs to populate its users' AORs and SED to the LUF/LRF
provider. Currently, this procedure is non-standardized and labor
intensive. A more detailed description of this problem has been
documented in the work in progress [I-D.ietf-drinks-cons-rqts].
5.4. Static Indirect Peering Use Case - Assisting LUF and LRF
The difference between a Static Direct Use Case and a Static Indirect
Use Case lies within the Layer-5 relationship of which O-SSP and
T-SSP maintain. In the Indirect use case, the O-SSP and T-SSP do not
have direct Layer-5 connectivity. They require one or multiple
Indirect Domains to assist routing the SIP messages and possibly the
associated media.
In this use case, the O-SSP and T-SSP want to form a peer
relationship. For some reason, the O-SSP and T-SSP do not have
direct Layer-5 connectivity. The reasons may vary, for example
business demands and/or domain policy controls. Due to this indirect
relationship the signaling will traverse from O-SSP to one or
multiple I-SSP(s) to reach T-SSP.
In addition, O-SSP decides to use a LUF/LRF provider. This LUF/LRF
provider stores the T-SSP's SED pre-populated by T-SSP. One
important motivation to use the LUF/LRF provider is that T-SSP only
needs to populate its SED once to the provider. Any O-SSP who wants
to query T-SSP's SED can use this LUF/LRF provider. Current practice
has shown that it is rather difficult for the T-SSP to populate its
SED to every O-SSP who likes to reach the T-SSP's subscribers. This
is especially true in the Enterprise environment.
Note that the LUF/LRF provider and I-SSP can be the same provider or
different providers.
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+------------------+
| LUF/LRF Provider |
| I-SSP |
| +-------+ |
| ---+ A-LUF | |
| / | A-LRF | |
+--------------------+ / +-------+ +---------------------+
| O-SSP |/ / | T-SSP |
| +-------------/ / | +-----+ |
| / |(4,5,6) | |T-LUF| |
| / | / | +----+T-LRF| |
| (2) + +--- | / +-----+ |
| / / | | /(9,10) |
|+-------+ +-----+ +-----+ +-----+ +-------+|
||O-Proxy|-(3)-|O-SBE+-(7)-+I-SBE+-(8)--+T-SBE+-(11)-|T-Proxy||
|+-------+ +-----+ +-----+ +-----+ +-------+|
| | | | | |
| (1) | | (12) |
| | | | | |
| +-----+ +-----+ +-----+ +-----+ +-----+ |
| | UAC +=(13)=|O-DBE+=====+I-DBE+======+T-DBE+=======+ UAS | |
| +-----+ +-----+ +-----+ +-----+ +-----+ |
+-------------------------------------------------------------+
example.com example.org example.net
Indirect Peering via LUF/LRF provider and I-SSP (SIP and media)
Figure 4
The following is a high-level depiction of the use case:
1. UAC initiates a call via SIP INVITE to O-Proxy. O-Proxy is the
home proxy for UAC.
INVITE sip:+19175550100@example.com;user=phone SIP/2.0
Via: SIP/2.0/TCP client.example.com:5060
;branch=z9hG4bK74bf9
Max-Forwards: 10
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=12345
To: Bob <sip+19175550100@example.com;user=phone>
Call-ID: abcde
CSeq: 1 INVITE
Contact: <sip:+19175550100@client.example.com;user=phone
;transport=tcp>
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2. UAC only knows UAS's TN but not UAS's domain. It appends its
own domain to generate the SIP URI in Request-URI and TO header.
O-Proxy checks the Request-URI and discovers that the Request-
URI contains user parameter "user=phone". This parameter
indicates that the Request-URI is a phone number. So O-Proxy
will extract the TN from the Request-URI and query LUF for SED
information from a routing database. In this example, the LUF
is an ENUM database. The ENUM entry looks similar to this:
$ORIGIN 0.0.1.0.5.5.5.7.1.9.1.e164.arpa.
IN NAPTR (
10
100
"u"
"E2U+SIP"
"!^.*$!sip:+19175550100@example.org!"
. )
Note that the response shows the next-hop is the SBE in Indirect
SSP.
Alternatively, O-SSP may have a pre-association with I-SSP. As
such, O-SSP will forward all requests which contains an external
domain in the Request-URI or unknown TN to I-SSP. The O-SSP
will rely on the I-SSP to determine the T-SSP and route the
request correctly. In this configuration, the O-SSP can skip
Steps 2,4,5 and 6 and forward the request directly to the I-SBE.
This configuration is commonly used in the Enterprise
environment.
3. Given the O-Proxy's internal routing policy, O-Proxy decides to
use O-SBE to reach I-SBE. O-Proxy routes the INVITE request to
O-SBE and adds a Route header which contains the O-SBE.
INVITE sip:+19175550100@example.org;user=phone SIP/2.0
Via: SIP/2.0/TCP o-proxy.example.com:5060
;branch=z9hG4bKye8ad
Via: SIP/2.0/TCP client.example.com:5060
;branch=z9hG4bK74bf9;received=192.0.1.1
Max-Forwards: 9
Route: <sip:o-sbe1.example.com;lr>
Record-Route: <sip:o-proxy.example.com;lr>
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=12345
To: Bob <sip+19175550100@example.net;user=phone>
Call-ID: abcde
CSeq: 1 INVITE
Contact: <sip:+19175550100@client.example.com;user=phone
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;transport=tcp>
4. O-SBE receives the requests and pops the top entry of the Route
header which contains "sip:o-sbe1.example.com". O-SBE examines
the Request-URI and does a LRF for "example.org". In this
example, the LRF is a NAPTR DNS query of the domain. O-SBE
receives a response similar to this:
IN NAPTR (
50
50
"S"
"SIP+D2T"
""
_sip._tcp.i-sbe.example.org. )
IN NAPTR (
90
50
"S"
"SIP+D2U"
""
_sip._udp.i-sbe.example.org. )
5. Given the lower order for TCP in the NAPTR response, O-SBE
decides to use TCP for transport protocol, so it sends a SRV DNS
query for the SRV record for "_sip._tcp.i-sbe.example.org.".
;; priority weight port target
IN SRV 0 2 5060 i-sbe1.example.org.
IN SRV 0 1 5060 i-sbe2.example.org.
6. Given the higher weight for "i-sbe1.example.org", O-SBE sends a
DNS query for A record of "i-sbe1.example.org." to get the A
record:
;; DNS ANSWER
i-sbe1.example.org. IN A 192.0.2.200
i-sbe1.example.org. IN A 192.0.2.201
7. O-SBE sends the INVITE to I-SBE. O-SBE is the entry point to
the O-SSP domain, so it should ensure subsequent mid-dialog
requests traverse via itself. If O-SBE chooses to act as a
B2BUA, it will terminate the call and generate a new back-to-
back INVITE request. If O-SBC chooses to act as proxy, it
should record-route to stay in the call path. In this example,
O-SBE is a B2BUA.
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INVITE sip:+19175550100@example.org;user=phone SIP/2.0
Via: SIP/2.0/TCP o-sbe1.example.com:5060
;branch= z9hG4bK2d4zzz;
Max-Forwards: 10
Route: <sip:i-sbe1.example.org;lr>
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=54321
To: Bob <sip:+19175550100@example.net;user=phone>
Call-ID: abcde-osbe1
CSeq: 1 INVITE
Contact: <sip:+19175550100@o-sbe1.example.com;user=phone
transport=tcp>
8. I-SBE receives the request and queries its internal routing
database on the TN. It determines the target belongs to T-SSP.
Since I-SBE is a B2BUA, I-SBE generates a new INVITE request to
T-SSP.
INVITE sip:+19175550100@.example.net;user=phone SIP/2.0
Via: SIP/2.0/TCP i-sbe1.example.org:5060
;branch= z9hG4bK2d4777;
Max-Forwards: 10
Route: <sip:t-sbe1.example.net;lr>
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=54321
To: Bob <sip:+19175550100@example.net;user=phone>
Call-ID: abcde-isbe1
CSeq: 1 INVITE
Contact: <sip:+19175550100@i-sbe1.example.org;user=phone
transport=tcp>
Note that if I-SSP wants the media to traverse through the
I-DBE, I-SBE must modify the SDP in the Offer to point to its
DBE.
9. T-SBE determines the called party home proxy and directs the
call to the called party. T-SBE may use ENUM or other internal
mechanism to locate the home proxy. If T-SSP uses ENUM, this
internal ENUM entry is different from the external ENUM entry
populated for O-SSP. This internal ENUM entry will contain the
information to identify the next-hop to reach the called party.
In this example, the internal ENUM query returns the UAS's home
proxy.
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$ORIGIN 0.0.1.0.5.5.5.7.1.9.1.e164.arpa.
IN NAPTR (
10
100
"u"
"E2U+SIP"
"!^.*$!sip:+19175550100@t-proxy.example.net!"
. )
Note that this step is optional. If T-SBE has other ways to
locate the UAS home proxy, T-SBE can skip this step and send the
request to the UAS's home proxy. We show this step to
illustrate one of the many possible ways to locate UAS's home
proxy.
10. T-SBE receives the NAPTR record and query DNS for the A record
of "t-proxy.example.net". The DNS returns an A record:
;; DNS ANSWER
t-proxy.example.net. IN A 192.0.2.2
11. T-SBE sends the INVITE to UAS's home proxy:
INVITE sip:+19175550100@t-proxy.example.net;user=phone SIP/2.0
Via: SIP/2.0/TCP t-sbe1.example.net:5060
;branch= z9hG4bK28uyyy;
Max-Forwards: 10
Record-Route: <sip:t-sbe1.example.net:5060;lr>
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=54321
To: Bob <sip:+19175550100@example.net;user=phone>
Call-ID: abcde-tsbe1
CSeq: 1 INVITE
Contact: <sip:+19175550100@t-sbe1.example.com;user=phone
transport=tcp>
12. Finally, UAS's home proxy forwards the INVITE request to UAS.
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INVITE sip:+19175550100@server.example.net;user=phone SIP/2.0
Via: SIP/2.0/TCP t-proxy.example.net:5060
;branch= z9hG4bK28u111;
Via: SIP/2.0/TCP t-sbe1.example.net:5060
;branch= z9hG4bK28uyyy; received=192.2.0.100
Max-Forwards: 9
Record-Route: <sip:t-proxy.example.net:5060;lr>,
<sip:t-sbe1.example.net:5060;lr>
From: Alice <sip:+14085550101@example.com;user=phone>
;tag=54321
To: Bob <sip:+19175550100@example.net;user=phone>
Call-ID: abcde-tsbe1
CSeq: 1 INVITE
Contact: <sip:+19175550100@t-sbe1.example.com;user=phone
transport=tcp>
13. RTP is established between UAC and UAS.
5.4.1. Administrative characteristics
This use case looks very similar to the Static Direct Peering with
Assisting LUF and LRF. The major difference is the O-SSP and T-SSP
do not have direct Layer-5 connectivity. Instead, O-SSP connects to
T-SSP indirectly via I-SSP.
Typically, a LUF/LRF provider serves multiple O-SSPs. Two O-SSPs may
use different I-SSP to reach the same T-SSP. For example, O-SSP1 may
use I-SSP1 to reach T-SSP, but O-SSP2 may use I-SSP2 to reach T-SSP.
Given the O-SSP and T-SSP pair as input, the LUF/LRF provider will
return the SED of I-SSP that is trusted by O-SSP to forward the
request to T-SSP.
In this use case. there are two levels of trust relationship. First
trust relationship is between the O-SSP and LUF/LRF provider. The
O-SSP trusts the LUF/LRF to provide the T-SSP's SED. Second trust
relationship is between O-SSP and I-SSP. The O-SSP trusts the I-SSP
to provide Layer-5 connectivity to assist the O-SSP to reach T-SSP.
The O-SSP and I-SSP have a pre-arranged agreement for policy. Note
that Figure 4 shows a single provider to provide both LUF/LRF and
I-SSP, O-SSP can choose two different providers.
5.4.2. Options and Nuances
Similar to the Static Direct Peering Use Case, the O-SSP and T-SSP
may deploy SBE and DBE for NAT traversal, security, transcoding, etc.
I-SSP can also deploy SBE and DBE for similar reasons. (as depicted
in Figure 4)
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5.5. Static Indirect Peering Use Case
This use case O-SSP uses its internal LUF/LRF. One of the reasons of
using internal LUF/LRF is to control the routing database. By
controlling the database, O-SSP can apply different routing rules and
policies to different T-SSPs. For example, O-SSP can use I-SSP1 and
Policy-1 to reach T-SSP1, and use I-SSP2 and Policy-2 to reach
T-SSP2. Note that there could be multiple I-SSPs and multiple SIP
routes to reach the same T-SSP; this is out of scope of Speermint and
has become a focus in the IETF DRINKS working group.
+--------------------+-------------------+---------------------+
| O-SSP | I-SSP | T-SSP |
| +-----+ | | +-----+ |
| -+O-LUF| | | |T-LUF| |
| / |O-LRF+\ | | +----+T-LRF| |
| / +-----+ \ | | / +-----+ |
| /(2) \(4,5,6) | /(9,10) |
|+-------+ +-----+ +-----+ +-----+ +-------+|
||O-Proxy|-(3)-|O-SBE+--(7)-+I-SBE+-(8)--+T-SBE+-(11)-|T-Proxy||
|+-------+ +-----+ +-----+ +-----+ +-------+|
| | | | | |
| (1) | | (12) |
| | | | | |
| +-----+ +-----+ +-----+ +-----+ +-----+ |
| | UAC +=(13)=+O-DBE+======+I-DBE+======+T-DBE+=======+ UAS | |
| +-----+ +-----+ +-----+ +-----+ +-----+ |
+--------------------------------------------------------------+
example.com example.org example.net
Indirect Peering via I-SSP (SIP and media)
Figure 5
5.5.1. Administrative characteristics
The Static Indirect Use Case is implemented in cases where no direct
interconnection exists between the originating and terminating
domains due to either business or physical constraints.
O-SSP <---> I-SSP = Relationship O-I
In the O-I relationship, typical policies, features or functions that
deem this relationship necessary are number portability, Ubiquity of
termination options, security certificate management and masquerading
of originating VoIP network gear.
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T-SSP <---> I-SSP = Relationship T-I
In the T-I relationship, typical policies, features or functions
observed consist of codec "scrubbing", anonymizing, and transcoding.
I-SSP must record-route and stay in the signaling path. T-SSP will
not accept message directly sent from O-SSP.
5.5.2. Options and Nuances
In Figure 5, we show I-DBE. Using I-DBE is optional. One scenario
the I-DBE can be used is when the O-SSP and T-SSP do not have a
common codec. To involve I-DBE, I-SSP should know the list of codec
supported by O-SSP and T-SSP. When I-SBE receives the INVITE
request, it will make a decision to invoke the I-DBE. Another
scenario an I-DBE can be used is if O-SSP uses SRTP [RFC3711] for
media and T-SSP does not support SRTP.
5.6. On-demand Peering Use Cases
On-demand Peering [RFC5486] describes two SSPs form the peering
relationship without a pre-arranged agreement.
The basis of this use case is built on the fact that there is no pre-
established relationship between the O-SSP and T-SSP. The O-SSP and
T-SSP does not share any information prior to the dialog initiation
request. When the O-Proxy invokes the LUF and LRF on the Request-
URI, the terminating user information must be publicly available.
Besides, when the O-Proxy routes the request to the T-Proxy, the
T-Proxy must accept the request without any pre-arranged agreement
with O-SSP.
5.6.1. Administrative characteristics
The On-demand Direct Peering Use Case is typically implemented in a
scenario where the T-SSP allows any O-SSP to reach its serving
subscribers. T-SSP administrative domain does not require any pre-
arranged agreement to accept the call. The T-SSP makes its
subscribers information available in public. This model mimics the
Internet email model. Sender does not need an pre-arranged agreement
to send email to the receiver.
5.6.2. Options and Nuances
Similar to the Static Direct Peering Use Case, the O-SSP and T-SSP
can decide to deploy SBE. Since T-SSP is open to the public, T-SSP
is considered to be in higher security risk than static model because
there is no trusted relationship between O-SSP and T-SSP. T-SSP
should protect itself from any attack launch by untrusted O-SSP.
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6. Acknowledgments
Michael Haberler, Mike Mammer, Otmar Lendl, Rohan Mahy, David
Schwartz, Eli Katz and Jeremy Barkan are the authors of the early
individual drafts. Their use cases are captured in this document.
Besides, Jason Livingood, Daryl Malas, David Meyer, Hadriel kaplan,
John Elwell, Reinaldo Penno, Sohel Khan, James McEachern, Jon
Peterson, Alexander Mayrhofer, and Jean-Francois Mule made many
valuable comments to this document.
7. Security Considerations
This document introduces no new security consideration. However, it
is important to note that session interconnect, as described in this
document, has a wide variety of security issues that should be
considered in documents addressing both protocol and use case
analyzes. [I-D.niccolini-speermint-voipthreats] discuss the
different security threats related to VoIP peering.
8. IANA Considerations
This document creates no new requirements on IANA namespaces
[RFC5226].
9. References
9.1. Normative References
[I-D.niccolini-speermint-voipthreats]
Niccolini, S., Chen, E., Seedorf, J., and H. Scholz,
"SPEERMINT Security Threats and Suggested
Countermeasures", draft-niccolini-speermint-voipthreats-05
(work in progress), October 2008.
[RFC1918] Rekhter, Y., Moskowitz, R., Karrenberg, D., Groot, G., and
E. Lear, "Address Allocation for Private Internets",
BCP 5, RFC 1918, February 1996.
[RFC2782] Gulbrandsen, A., Vixie, P., and L. Esibov, "A DNS RR for
specifying the location of services (DNS SRV)", RFC 2782,
February 2000.
[RFC3261] Rosenberg, J., Schulzrinne, H., Camarillo, G., Johnston,
A., Peterson, J., Sparks, R., Handley, M., and E.
Schooler, "SIP: Session Initiation Protocol", RFC 3261,
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June 2002.
[RFC3263] Rosenberg, J. and H. Schulzrinne, "Session Initiation
Protocol (SIP): Locating SIP Servers", RFC 3263,
June 2002.
[RFC3403] Mealling, M., "Dynamic Delegation Discovery System (DDDS)
Part Three: The Domain Name System (DNS) Database",
RFC 3403, October 2002.
[RFC3761] Faltstrom, P. and M. Mealling, "The E.164 to Uniform
Resource Identifiers (URI) Dynamic Delegation Discovery
System (DDDS) Application (ENUM)", RFC 3761, April 2004.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
May 2008.
[RFC5486] Malas, D. and D. Meyer, "Session Peering for Multimedia
Interconnect (SPEERMINT) Terminology", RFC 5486,
March 2009.
9.2. Informative References
[I-D.ietf-drinks-cons-rqts]
Schwartz, D., Mahy, R., Duric, A., and E. Lewis,
"Consolidated Provisioning Problem Statement",
draft-ietf-drinks-cons-rqts-00 (work in progress),
July 2008.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
December 1998.
[RFC3711] Baugher, M., McGrew, D., Naslund, M., Carrara, E., and K.
Norrman, "The Secure Real-time Transport Protocol (SRTP)",
RFC 3711, March 2004.
[RFC4366] Blake-Wilson, S., Nystrom, M., Hopwood, D., Mikkelsen, J.,
and T. Wright, "Transport Layer Security (TLS)
Extensions", RFC 4366, April 2006.
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Authors' Addresses
Adam Uzelac (editor)
Global Crossing
U.S.A.
Phone:
Email: adam.uzelac@globalcrossing.com
URI: http://www.globalcrossing.com
Yiu L.Lee (editor)
Comcast Cable
U.S.A.
Phone:
Email: yiu_lee@cable.comcast.com
URI: http://www.comcast.com
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