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Versions: (draft-ietf-iptel-trip-gw) 00 01 02
03 04 05 06 07 08 09 RFC 5140
IPTEL Working Group Manjunath Bangalore, Cisco Systems Inc.
Internet Draft Rajneesh Kumar, Cisco Systems Inc.
draft-ietf-iptel-tgrep-06.txt Hussein Salama, MenaNet Communications S.A.E.
July 2005 Jonathan Rosenberg, Cisco Systems Inc.
Expiration Date: January 2006 Dhaval N. Shah, Cisco Systems Inc.
A Telephony Gateway REgistration Protocol (TGREP)
Status of this Memo
This document is an Internet-Draft and is subject to all provisions
of section 3 of RFC 3667. By submitting this Internet-Draft, each
author represents that any applicable patent or other IPR claims of
which he or she is aware have been or will be disclosed, and any of
which he or she becomes aware will be disclosed, in accordance with
Section 6 of BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
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Internet-Drafts are draft documents valid for a maximum of six months
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time. It is inappropriate to use Internet-Drafts as reference
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The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
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This Internet-Draft will expire on January 16, 2005.
Copyright Notice
Copyright (C) The Internet Society (2005).
Abstract
This document describes the Telephony Gateway Registration Protocol
(TGREP) for registration of telephony prefixes supported by telephony
gateways and soft switches. The registration mechanism can also be
used to export resource information. The prefix and resource
information can then be passed on to a Telephony Routing over IP
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(TRIP) Location Server, which in turn can propagate that routing
information within and between internet telephony administrative
domains (ITAD). TGREP shares a lot of similarities with the TRIP
Protocol. It has similar procedures and Finite State Machine for
session establishment. It also shares the same format for messages
and a subset of attributes with TRIP.
TGREP entities are valid trip implementations, but they do only a
subset of what they otherwise could. In particular, a gateway is
always in Send mode, the LS peering with it is always in Receive
mode.
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Table of Contents
1 Terminology and Definitions .............................. 4
2 Introduction ............................................. 4
3 TGREP: Overview of operation ............................. 6
4 TGREP Attributes ......................................... 7
4.1 TotalCircuitCapacity Attribute ........................... 7
4.2 AvailableCircuits Attribute .............................. 9
4.3 CallSuccess Attribute .................................... 10
4.4 Prefix Attributes ........................................ 12
4.5 TrunkGroup Attribute ..................................... 13
4.6 Carrier Attribute ........................................ 15
4.7 TrunkGroup and Carrier Address Families .................. 16
4.8 Gateway Operation ........................................ 18
4.9 LS/Proxy Behavior ........................................ 21
5 Security Considerations .................................. 25
6 IANA Considerations ...................................... 26
6.1 Attribute Codes .......................................... 26
6.2 Address Family Codes ..................................... 26
7 Change history ........................................... 27
7.1 Changes since draft-ietf-iptel-tgrep-03.txt .............. 27
7.2 Changes since draft-ietf-iptel-tgrep-02.txt .............. 27
7.3 Changes since draft-ietf-iptel-tgrep-01.txt .............. 27
7.4 Changes since draft-ietf-iptel-tgrep-00.txt .............. 27
7.5 Changes since draft-ietf-iptel-trip-gw-00.txt ............ 28
7.6 Changes since -03 ........................................ 28
7.7 Changes since -02 ........................................ 28
7.8 Changes since -01 ........................................ 29
7.9 Changes since -00 ........................................ 29
8 Acknowledgments .......................................... 29
9 References ............................................... 29
9.1 Normative References ..................................... 29
9.2 Informative References ................................... 30
Authors' Addresses ....................................... 30
Intellectual Property Statement .......................... 31
Disclaimer of Validity ................................... 32
Copyright Statement ...................................... 32
Acknowledgment ........................................... 32
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1. Terminology and Definitions
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].
Some other useful definitions are:
Circuit: A circuit is a discrete (specific) path between two or more
points along which signals can be carried. In this context, a circuit
is a physical path, consisting of one or more wires and possibly
intermediate switching points.
Trunk: In a network, a communication path connecting two switching
systems used in the establishment of an end-to-end connection. In
selected applications, it may have both its terminations in the same
switching system.
TrunkGroup: A set of trunks, traffic engineered as a unit, for the
establishment of connections within or between switching systems in
which all of the paths are interchangeable except where subgrouped.
Carrier: A company offering telephone and data communications between
points (end-users and/or exchanges).
2. Introduction
It is assumed that reader of this has already gone through TRIP [4].
In typical VoIP networks, Internet Telephony Administrative Domains
(ITADs) will deploy numerous gateways for the purposes of
geographical diversity, capacity, and redundancy. When a call arrives
at the domain, it must be routed to one of those gateways.
Frequently, an ITAD will break their network into geographic Points
of Presence (POP), with each POP containing some number of gateways,
and a proxy server element that fronts those gateways. The proxy
server is responsible for managing the access to the POP, and also
for determining which of the gateways will receive any given call
that arrives at the POP. In conjunction with the proxy server that
routes the call signaling, there are two TRIP Speaker components, the
"Ingress LS" and the "Egress LS". The Ingress LS maintains TGREP
peering relationship with one or more gateways. The routing
information received from the gateways are further injected into the
Egress LS, which in turn disseminates into the rest of the network on
TRIP.
This configuration is depicted graphically in Figure 1.
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+---------+
| |
| GW |
> +---------+
//
//
// +---------+
// | |
+-------------------------+ // | GW |
| | // +---------+
| +-------------+ |/
| | | |
| | Routing | | +---------+ TO PSTN
| | Proxy | | | |
---> | | |-----------> | GW | ----->
|+---+-----+ +-----+----+ | +---------+
|| | | | |
|| <+-+ | |--
||Egress LS| |Ingress LS| | --- +---------+
|| | | | | -- | |
|+---------+ +----------+ | -- | GW |
| | -- +---------+
| | -->
+-------------------------+
+---------+
| |
| GW |
+---------+
Figure 1: Gateway and LS Configuration
The decision about which gateway to use depends on many factors,
including their availability, remaining call capacity and call
success statistics to a particular PSTN destination. For the proxy to
do this adequately, it needs to have access to this information in
real-time, as it changes. This means there must be some kind of
communications between the proxy and the gateways to convey this
information.
In this document, we specify a protocol for registration of routes
(destinations) supported by the gateway to the TRIP Location Server
[4], known as Telephony Gateway REgistration Protocol (TGREP). TGREP
Protocol can be considered an auxiliary protocol to TRIP. Routes
learnt through TGREP can be injected into and further processed
and/or propagated by the TRIP Location Server.
TGREP shares a lot of commonality with TRIP in various aspects.
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Particularly, TGREP and TRIP have the same session establishment
procedures, state machine, etc. TGREP also makes use of a similar
UPDATE message to propagate the routes supported. It uses
Notification, Keepalive and OPEN message in the same essence as TRIP.
TGREP defines few new attributes that are needed to specify certain
characteristics of gateways, like Available Capacity for a
destination. The document aims at specifying all the attributes
related to the TGREP session. This document also specifies some new
address families which can be useful in advertising the information
on the GWs.
As a general rule, because of lot of similarities between TRIP and
TGREP, frequent reference will be made to the terminologies and
formats defined in TRIP [4]. It is suggested that the reader be
familiar with the concepts of TRIP like attributes, flags, route
types, address families, etc.
3. TGREP: Overview of operation
TGREP is a route registration protocol for telephony destinations on
a gateway. These telephony destinations could be prefixes, trunk
groups or Carriers. The Speaker of TGREP resides on the GW and
gathers all the information from the GW to relay to the TRIP Location
Server. A TGREP Receiver is defined, which receives this information
and after certain optional operations like consolidation and
aggregation. (defined in Sections 3.10.1 and 3.10.2) hands over the
reachability information a to TRIP Location Server.
The TGREP speaker establishes a session to the TGREP Receiver using
the procedures similar to session establishment in TRIP. The TGREP
Speaker is however, in "Send only" mode and the receiver is in the
"Receive only" mode. After the session establishment the TGREP
speaker sends the reachibility information in the UPDATE messages.
The UPDATE messages have the same format as in TRIP. However, certain
TRIP attributes are not relevant in TGREP; a TGREP speaker MAY ignore
them if they are present in a TGREP message. The following TRIP
attributes do not apply to TGREP:
1. AdvertisementPath
2. RoutedPath
3. AtomicAggregate
4. LocalPreference
5. MultiExitDisc
6. ITADTopology
7. ConvertedRoute
In addition, TGREP defines the following new attributes in this
document that can be carried in a TGREP UPDATE message.
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1. TotalCircuitCapacity
2. AvailableCircuits
3. CallSuccess
4. Prefix (E164)
5. Prefix (Decimal Routing Number)
6. Prefix (Hexadecimal Routing Number)
7. TrunkGroup
8. Carrier
In the rest of the document we specify attributes and address
families used in TGREP. We also specify the operations of
consolidation and aggregation as they apply to the UPDATEs received
from the TGREP Gateway by the TGREP Receiver.
4. TGREP Attributes
A TGREP UPDATE supports the following attributes:
1. WithdrawnRoutes (as defined in TRIP)
2. ReachableRoutes (as defined in TRIP)
3. NexthopServer (as defined in TRIP)
4. TotalCircuitCapacity
5. AvailableCircuits
6. CallSuccess
7. Prefix (E.164, Pentadecimal routing number, Decimal routing number)
8. TrunkGroup
9. Carrier
10. Communities
4.1. TotalCircuitCapacity Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 13.
The TotalCircuitCapacity identifies the total number of PSTN circuits
that are available on a route to complete calls. It is used in
conjunction with the AvailableCircuits attribute in gateway selection
by the LS. The total number of calls sent to the specified route on
the gateway cannot exceed this total circuit capacity under steady
state conditions.
The TotalCircuitCapacity attribute is used to reflect the
administratively provisioned capacity as opposed to the availability
at a given point in time as provided by the AvailableCircuits
attribute. Because of its relatively static nature, this attribute
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MAY be propagated beyond the LS that receives it.
TotalCircuitCapacity represents the total number of active calls at
any instant. This is not expected to change frequently. This can
change, for instance, when certain telephony trunks on the gateway
are taken out of service for maintenance purposes.
4.1.1. TotalCircuitCapacity Syntax
The TotalCircuitCapacity attribute is a 4-octet unsigned integer. It
represents the total number of circuits available for terminating
calls through this advertised route. This attribute represents a
potentially achievable upper bound on the number of calls which can
be terminated on this route in total.
4.1.2. Route Origination and TotalCircuitCapacity
Routes MAY be originated containing the TotalCircuitCapacity
attribute.
4.1.3. Route Selection and TotalCircuitCapacity
The TotalCircuitCapacity attribute MAY be used for route selection.
Since one of its primary applications is load balancing, an LS will
wish to choose a potentially different route (amongst a set of routes
for the same destination), on a call by call basis. This can be
modeled as re-running the decision process on the arrival of each
call. The aggregation and dissemination rules for routes with this
attribute ensure that re-running this selection process never results
in propagation of a new route to other peers.
4.1.4. Aggregation and TotalCircuitCapacity
An LS MAY aggregate routes to the same prefix which contain a
TotalCircuitCapacity attribute. It SHOULD add the values of the
individual routes to determine the value for the aggregated route in
the same ITAD.
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4.1.5. Route Dissemination and TotalCircuitCapacity
Since this attribute reflects the static capacity of the gateway's
circuit resources, it is not expected to change frequently. Hence the
LS receiving this attribute MAY disseminate it to other peers, both
internal and external to the ITAD.
4.2. AvailableCircuits Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 14.
The AvailableCircuits identifies the number of PSTN circuits that are
currently available on a route to complete calls. The number of
additional calls sent to that gateway for that route cannot exceed
the circuit capacity. If it does, the signaling protocol will likely
generate errors, and calls will be rejected.
The AvailableCircuits attribute is used ONLY between a gateway and
its peer LS responsible for managing that gateway. If it is received
in a route, it is not propagated.
4.2.1. AvailableCircuits Syntax
The AvailableCircuits attribute is a 4-octet unsigned integer. It
represents the number of circuits remaining for terminating calls to
this route.
4.2.2. Route Origination and AvailableCircuits
Routes MAY be originated containing the AvailableCircuits attribute.
Since this attribute is highly dynamic, changing with every call,
updates MAY be sent as it changes. However, it is RECOMMENDED that
measures be taken to help reduce the messaging load from route
origination. It is further RECOMMENDED that a sufficiently large
window of time be used to provide a useful aggregated statistic.
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4.2.3. Route Selection and AvailableCircuits
The AvailableCircuits attribute MAY be used for route selection.
Since one of its primary applications is load balancing, an LS will
wish to choose a potentially different route (amongst a set of routes
for the same prefix) on a call by call basis. This can be modeled as
re-running the decision process on the arrival of each call. The
aggregation and dissemination rules for routes with this attribute
ensure that re-running this selection process never results in
propagation of a new route to other peers.
4.2.4. Aggregation and AvailableCircuits
Not applicable
4.2.5. Route Dissemination and AvailableCircuits
Routes MUST NOT be disseminated with the AvailableCircuits attribute.
The attribute is meant to reflect capacity at the originating gateway
only. Its highly dynamic nature makes it inappropriate to disseminate
in most cases.
4.3. CallSuccess Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 15.
The CallSuccess attribute is an attribute used ONLY between a gateway
and its peer LS responsible for managing that gateway. If it is
received in a route, it is not propagated.
The CallSuccess attribute provides information about the number of
normally terminated calls out of a total number of attempted calls.
CallSuccess is to be determined by the gateway based on the
Disconnect cause code at call termination. For example, a call that
reaches the Alerting stage but does not get connected due to the
unavailability of the called party, or the called party being busy,
is conventionally considered a successful call. On the other hand, a
call that gets disconnected because of a Circuit or Resource being
unavailable is conventionally considered a failed call. The exact
mapping of disconnect causes to CallSuccess is at the discretion of
the gateway reporting the attribute.
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The CallSuccess attribute is used by the LS to keep track of failures
in reaching certain telephony destinations through a gateway(s) and
use that information in the gateway selection process to enhance the
probability of successful call termination.
This information can be used by the LS to consider alternative
gateways to terminate calls to those destinations with a better
likelihood of success.
4.3.1. CallSuccess Syntax
The CallSuccess attribute is comprised of two component fields - each
represented as an unsigned 4-octet unsigned integer. The first
component field represents the total number of calls terminated
successfully for the advertised destination on a given address family
over a given window of time. The second component field represents
the total number of attempted calls for the advertised destination
within the same window of time.
4.3.2. Route Origination and CallSuccess
Routes MAY be originated containing the CallSuccess attribute. This
attribute is expected to get statistically significant with passage
of time as more calls are attempted. It is RECOMMENDED that
sufficiently large windows be used to provide a useful aggregated
statistic.
4.3.3. Route Selection and CallSuccess
The CallSuccess attribute MAY be used for route selection. This
attribute represents a measure of success of terminating calls to the
advertised destination(s). This information MAY be used to select
from amongst a set of alternative routes to increase the probability
of successful call termination.
4.3.4. Aggregation and CallSuccess
Not applicable
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4.3.5. Route Dissemination and CallSuccess
Routes MUST NOT be disseminated with the CallSuccess attribute. Its
potential to change dynamically does not make it suitable to
disseminate.
4.4. Prefix Attributes
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Codes: 16 for E164 prefix, 17 for Pentadecimal routing number prefix
and 18 for Decimal routing number prefix.
The Prefix attribute is used to represent the list of prefixes that
the respective route can complete calls to. This attribute is
intended to be used with the Carrier or Trunkgroup address family
(discussed in Section 3.7).
Though it is possible that all prefix ranges may be reachable
through a given Carrier, administrative issues could make certain
ranges preferable to others.
4.4.1. Prefix Attribute Syntax
The Prefix attribute could be E.164, Decimal or PentaDecimal (refer
to TRIP [4]), each of them having it's own type code. The Prefix
attribute is encoded as a sequence of prefix values in the attribute
value field. The prefixes are listed sequentially with no padding as
shown in Figure 2. Each prefix includes a 2-octet length field that
represents the length of the address field in octets. The order of
prefixes in the attribute is not significant.
The presence of Prefix Attribute with the length field of the
attribute as 0 signifies that the TGREP GW can terminate ALL prefixes
of that prefix type (E.164, Decimal or Pentadecimal) for the given
Reachable route(s). This is not equivalent to excluding the Prefix
attribute in the TGREP update.
1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 . . . 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4
+-------------------------------+-----------+----------------------------------+-----------
| Length | Prefix1...| Length | Prefix2...
+-------------------------------+-----------+----------------------------------+-----------
Figure 2: Prefix Format
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4.4.2. Route Origination and Prefix
Routes MAY be originated containing the Prefix attribute.
4.4.3. Route Selection and Prefix
The Prefix attribute MAY be used for route selection.
4.4.4. Aggregation and Prefix
Routes with differing Prefix attribute MUST NOT be aggregated.
Routes with the same value in the Prefix attribute MAY be aggregated
and the same Prefix attribute attached to the aggregated object.
4.4.5. Route Dissemination and Prefix
The LS receiving this attribute should disseminate to other peers,
both internal and external to the ITAD.
4.5. TrunkGroup Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 20.
The TrunkGroup attribute is used to represent the list of trunkgroups
on the gateway used to complete calls. It enables providers to route
calls to destinations through preferred trunks. This attribute is
relatively static.
4.5.1. TrunkGroup Syntax
The TrunkGroup attribute is a variable length attribute that is
composed of a sequence of trunkgroup identifiers. It indicates that
the gateway can complete the call through any trunkgroup identifier
indicated in the sequence.
Each trunkgroup identifier is encoded as a length-value field (shown
in Figure 3 below). The length field is a 1-octet unsigned numeric
value. The value field is a variable length field consisting of two
sub-fields, a trunk group label followed by a trunk context, the two
sub-fields separated by the delimiter ";" (semicolon). Both the trunk
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group label and the trunk context sub-fields are of variable length.
The length field represents the total size of the value field
including the delimiter.
The permissible character set for the trunk group label and the trunk
group context sub-fields and the associated ABNF [10] is per rules
outlined in [13].
The presence of TrunkGroup attribute with the length field of the
attribute as 0 signifies that the TGREP GW can terminate ALL
trunkgroup for the given Reachable route(s).
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 ... 7 8 9 0 1 2 3 4 5 ...
+---------------+--------------------+---------------+---------------------
| Length | TrunkGroup 1... | Length | TrunkGroup 2...
+---------------+--------------------+---------------+---------------------
Figure 3: TrunkGroup Syntax
4.5.2. Route Origination and TrunkGroup
Routes MAY be originated containing the TrunkGroupattribute.
4.5.3. Route Selection and TrunkGroup
The TrunkGroup attribute MAY be used for route selection. Certain
trunkgroups MAY be preferred over others based on provider policy.
4.5.4. Aggregation and TrunkGroup
Routes with differing TrunkGroup attribute MUST NOT be aggregated.
Routes with the same value in the TrunkGroup attribute MAY be
aggregated and the same TrunkGroup attribute attached to the
aggregated object.
4.5.5. Route Dissemination and TrunkGroup
This attribute is not expected to change frequently. Hence, the LS
receiving this attribute MAY disseminate it to other peers, internal
to ITAD. Routes SHOULD not be disseminated external to the ITAD, with
TrunkGroup attribute.
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4.6. Carrier Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 19.
The Carrier attribute is used to represent the list of carriers that
the gateway uses to complete calls. It enables providers to route
calls to destinations through preferred carriers. This attribute is
relatively static.
4.6.1. Carrier Syntax
The Carrier attribute is a variable length attribute that is composed
of a sequence of carrier identifiers. It indicates that the route
can complete the call to any of the carriers represented in the
sequence of carrier identifiers.
Each carrier identifier is encoded as a length-value field (shown in
Figure 4 below). The length field is a 1-octet unsigned numeric
value. The value field is a variable length field.
The permissible character set for the value field and the associated
ABNF [10] is per rules outlined in [15]. Specifically, it carries
"global-cic" or "local-cic"[15]. In case of "local-cic", the
"phonedigit-hex" part and the "cic-context" part would be separated
by the delimiter ";". Hence absence or presence of the delimiter can
be used to determine if the value is a "global-cic" or a "local-cic".
The length field represents the total size of the value field
including the delimiter.
The presence of Carrier Attribute with the length field of the
attribute as 0 signifies that the TGREP GW can terminate ALL Carriers
for the given Reachable route(s).
0 1
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 ... 7 8 9 0 1 2 3 4 5 ...
+---------------+--------------------+---------------+---------------------
| Length | Carrier 1... | Length | Carrier 2...
+---------------+--------------------+---------------+---------------------
Figure 4: Carrier Syntax
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4.6.2. Route Origination and Carrier
Routes MAY be originated containing the Carrier attribute.
4.6.3. Route Selection and Carrier
The Carrier attribute MAY be used for route selection. Certain
carriers MAY be preferred over others based on provider policy.
4.6.4. Aggregation and Carrier
Routes with differing Carrier attribute MUST NOT be aggregated.
Routes with the same value in the Carrier attribute MAY be aggregated
and the same Carrier attribute attached to the aggregated object.
4.6.5. Route Dissemination and Carrier
This attribute is not expected to change frequently. Hence, the LS
receiving this attribute MAY disseminate it to other peers, both
internal and external to the ITAD.
4.7. TrunkGroup and Carrier Address Families
As described in TRIP [4], the address family field gives the type of
address for the route. Two new address families and their codes are
defined in this Section:
Code Address Family
4 TrunkGroup
5 Carrier
When a set of GWs are to managed at the granularity of carriers or
trunkgroups then it may be more appropriate for a GW to advertise
routes using the Carrier address family or trunkgroup address family
respectively. Also, in a TGREP association between the gateway and
the LS responsible for managing that gateway, there are some
attributes that more naturally fit in as advertised properties of
trunkgroups or carriers rather than that of advertised prefixes; for
example, the AvailableCircuit information on a particular trunkgroup
or a particular carrier. To express this relationship, the existing
TRIP address families are inadequate. We need separate address
families that can associate certain properties like AvailableCircuits
information to trunkgroups or carriers.
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The primary benefits of this model are as follows:
- It allows a service provider to route calls based strictly on the
trunkGroups or carriers.
- it facilitates more accurate reporting of attributes of a dynamic
nature like AvailableCircuits by providing the ability to manage
resources at the granularity of a trunkgroup or a carrier.
- Gateways can get really large with the ability to provision
hundreds or a few thousand circuits and this can increase the
potential for traffic that reports dynamic resource information
between the gateway and the LS. The model introduced can
potentially alleviate this UPDATE traffic hence increasing
efficiency and providing a scalable gateway registration model.
4.7.1. Address Family Syntax
Consider the generic TRIP route format from TRIP[4] shown below.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+---------------+---------------+--------------+----------------+
| Address Family | Application Protocol |
+---------------+---------------+--------------+----------------+----
| Length | Address (variable) ....
+---------------+---------------+--------------+----------------+----
Figure 5: Generic TRIP Route Format
The Address Family field will be used to represent the type of the
address associated for this family, which is based on the TrunkGroup
or Carrier. The codes for the new address families will be allocated
by IANA.
The code for the trunk group address family is XX [[NOTE TO RFC-ED:
Please replace XX with the IANA assigned value for the trunk group
address family]] and the code for the carrier address family is XXX
[[NOTE TO RFC-ED: Please replace XX with the IANA assigned value for
the carrier address family]].
The Application Protocol field is same as the one for the Decimal,
PentaDecimal and E.164 address families defined in TRIP[4]. The
Length field represents the total size of the Address field in bytes.
The value in the Address field represents either the TrunkGroup or
the Carrier address families and the syntax is as follows:
For the TrunkGroup Address Family, the Address field represents a
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Internet Draft draft-ietf-iptel-tgrep-05.txt July 2005
Trunkgroup value that is defined as specified in an
earlier Section 4.5.1 about the TrunkGroup Attribute.
For the Carrier Address Family, the Address field represents a
Carrier value that is defined as specified in an
earlier Section 4.6.1 about the Carrier Attribute.
If a gateway supports any of these address families, it should
include that address family as one of the Route types supported in
the OPEN message capability negotiation phase.
The following attributes are currently defined to be used with all
the address families including the TrunkGroup and Carrier address
families.
- AvailableCircuits Attribute
- TotalCircuitCapacity Attribute
- CallSuccess Attribute
It is recommended that the above three attributes be used by the
gateway with the TrunkGroup or Carrier address families, if possible.
This will potentially offer a more efficient resource reporting
framework, and a scalable model for gateway provisioning.
However, when the gateway is not using TrunkGroup or Carrier address
family, it MAY use the above attributes with the Decimal,
PentaDecimal and E.164 address families.
The prefix attribute cannot be used when the address family is E164
numbers, Pentadecimal routing numbers or Decimal routing numbers.
The Carrier attribute cannot be used if the address family type is
Carrier
The TrunkGroup attribute cannot be used if the address family type is
TrunkGroup
4.8. Gateway Operation
A gateway uses TGREP to advertise its reachability to its domain's
Location Server(s) (LS, which are closely coupled with proxies). The
gateway operates in TGREP Send Only mode since it is only interested
in advertising its reachability, but is not interested in learning
about the reachability of other gateways and other domains. Also, the
gateway will not create its own call routing database. In this
section we describe the operation of TGREP on a gateway.
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4.8.1. Session Establishment
When opening a peering session with a TGREP Receiver, a TGREP gateway
follows exactly the same procedures as any other TRIP speaker. The
TGREP gateway sends an OPEN message which includes a Send Receive
Capability in the Optional Parameters. The Send Receive Capability is
set by the gateway to Send Only. The OPEN message also contains the
address families supported by the gateway. The remainder of the peer
session establishment is identical to TRIP.
4.8.2. UPDATE Messages
Once the peer session has been established, the gateway sends UPDATE
messages to the TRIP LS with the gateway's entire reachability. The
Gateway also sends any attributes associated with the routes.
If the gateway's reachability changes at any point in time, the
gateway MUST generate UPDATE message(s) with the change. The
frequency of successive UPDATE messages MUST follow the same rules
specified for TRIP[4]. The TGREP gateway MUST support all mandatory
TRIP attributes.
If the gateway receives an UPDATE message from the TRIP LS, it MUST
silently discard it as specified for TRIP[4]. No further action
should be taken.
4.8.3. KEEPALIVE Messages
KEEPALIVE messages are periodically exchanged over the peering
session between the TGREP gateway and the TRIP LS as specified in
Section 4.4 of TRIP [4].
4.8.4. Error Handling and NOTIFICATION Messages
The same procedures used with TRIP, are used with TGREP for error
handling and generating NOTIFICATION messages. The only difference is
that a TGREP gateway will never generate a NOTIFICATION message in
response to an UPDATE message, irrespective of the contents of the
UPDATE message. Any UPDATE message is silently discarded.
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4.8.5. TGREP Finite State Machine
When the TGREP finite state machine is in the Established state and
an UPDATE message is received, the UPDATE message is silently
discarded and the TGREP gateway remains in the Established state.
Other than that the TRIP finite state machine and the TGREP finite
state machine are identical.
4.8.6. Call Routing Databases
A TGREP gateway may maintain simultaneous sessions with more than one
TRIP LSs. A TGREP gateway maintains one call routing database per
peer TRIP LS. These databases are equivalent to TRIP's Adj-TRIBs-Out,
and hence we will call them Adj-TRIB-GWs-Out. An Adj-TRIB-GW-Out
contains the gateway's reachability information advertised to its
peer TRIP LS. How an Adj-TRIB-GW-Out database gets populated is
outside the scope of this draft (possibly by manual configuration).
The TGREP gateway does not have databases equivalent to TRIP's Adj-
TRIBs-In and Loc-TRIB, because the TGREP gateway does not learn
routes from its peer TRIP LSs, and hence it does not run call route
selection.
4.8.7. Multiple Address Families
As mentioned above, TGREP supports various address families in order
to convey the reachabilty of telephony destinations. A TGREP session
MUST NOT send UPDATEs of more than one of the following categories
(a) Prefix Address families (E164, Pentadecimal and decimal) (b)
Trunkgroup address family (c) Carrier Address family for a given
established session. TGREP should specify it's choice address family
through the route-type capability in the OPEN message. And route-type
specification in the OPEN message violating the above rule should be
rejected with a NOTIFICATION message.
4.8.8. Route Selection and Aggregation
TRIP's route selection and aggregation operations MUST NOT be
implemented by TGREP gateways.
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4.9. LS/Proxy Behavior
As mentioned earlier, TGREP can be considered as a protocol
complimentary to TRIP in providing reachability information that can
then be further fed into the Location Server. The architecture of an
LS/Proxy system is as follows: There exists a TRIP LS application
that functions as a speaker in the I-TRIP/E-TRIP network as
documented in TRIP [4]. This component is termed as "LS-Egress" for
the purposes of this discussion. Then, there is a signaling server
fronting a set of gateways. In conjunction with this signaling
server, is also a second TRIP LS component operating in receive mode,
that peers with one more gateways, each of them using TGREP to
advertise routing information. This TRIP LS component on the
receiving end of one or more TGREP sessions is termed as the "LS-
Ingress" or "TGREP Receiver" for the purposes of this discussion. The
LS-Ingress receiving the TRIP messages takes the resulting routing
information from each gateway, and "exports" it to another process we
are defining that performs consolidation and aggregation, in that
order. These operations would take as input the collective set of
routes from all the gateways. Subsequently, the resulting TRIB is
passed as input into the LS-Egress process as shown below, that can
then disseminate these via TRIP. The interface between the LS-Ingress
peering with the GW(s) and the TRIP LS (LS-Egress) is entirely a
local matter.
The nature of the Consolidation and Aggregation operations and the
accompanying motivation are described in the subsections below. The
order in which the operations are listed represents an implicit
logical sequence in which they are applied. The architecture for an
LS/Proxy entity is shown in Figure 7 below.
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+-------------------------------------------------------+
| +-------------------------------+ |
| | +-+ +-+ | |
| | |A| |C| | | +-----+
| | |g| |o| | | TGREP | |
| +-------------+ | |g| |n| +-------------+ | | -- | GW |
| | | | |r| |s| | | | | -- +-----+
| | TRIP | | |e| |o| | | | +--
| | LS <----------|g<--|l<--- TGREP |-++-| +-----+
| | | | |a| |i| | Session | | | | |
| | (I-TRIP/ | | |t| |d| | Management |-++-+-------| GW |
| | E-TRIP) | | |i| |a| | | | | +-----+
| | (LS-Egress) | | |o| |t| | |-+ -+-
| +-----------/-+ | |n| |i| +-------------+ | | --- +-----+
| / | | | |o| | | -- | |
| / | | | |n| (LS-Ingress) | | | GW |
| / | +-+ +-+ | | +-----+
| / | TGREP Receiver | |
| / +-------------------------------+ |
| / |
| / |
+-------/-----------------------------------------------+
/ LS/Proxy
/
/
/
/
/
+/----------------+
| |
| |
| |
| LS |
| |
| |
| |
| |
| |
+\---------------+
\
\
\
\
\
\
\
+--------\---------------------------------------------+
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| \ +-------------------------------+ |
| \ | +-+ +-+ | |
| \ | |A| |C| | | +-----+
| \ | |g| |o| | | TGREP | |
| +---------\---+ | |g| |n| +-------------+ | | -- | GW |
| | | | |r| |s| | | | | -- +-----+
| | TRIP | | |e| |o| | | | +--
| | LS <----------|g<--|l<--- TGREP |-++-| +-----+
| | | | |a| |i| | Session | | | | |
| | (I-TRIP/ | | |t| |d| | Management |-++-+-------| GW |
| | E-TRIP) | | |i| |a| | | | | +-----+
| | (LS-Egress) | | |o| |t| | |-+ -+-
| +-------------+ | |n| |i| +-------------+ | | --- +-----+
| | | | |o| | | -- | |
| | | | |n| | | | GW |
| | +-+ +-+ (LS-Ingress) | | +-----+
| | TGREP Receiver | |
| +-------------------------------+ |
| |
| |
+-------------------------------------------------------+
LS/Proxy
Figure 7: LS Architecture for TRIP-GW
4.9.1. Route consolidation
The TGREP receiver (LS-Ingress) may receive routing information from
one or more gateways. It is possible that multiple routes are
available for the same destination. These different alternative
routes may be received from the same gateway, or from multiple
gateways. It is RECOMMENDED that the set of gateway routes for each
destination be consolidated, before presenting a candidate route, to
the LS-Egress entity. The motivation for this operation should be to
define a route that can maximally represent the collective routing
capabilities of the set of gateways, managed by this TGREP receiver.
Let us take an example scenario in order to bring out the motivation
for this operation. Let us say, the TGREP receiver maintains peering
sessions with gateways A, and B.
- Gateway A advertises a route for destination "SIP 408" on the
E.164 address family with the Carrier attribute value C1.
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- Gateway B advertises a route for destination "SIP 408" on the
E.164 address family with Carrier attribute value C2.
The TGREP receiver that receives these routes can consolidate
these constituent routes into a single route for destination "SIP
408" with its Carrier attribute being a union of the the Carrier
attribute values of the individual routes, namely, "C1 C2". This
operation is referred to as Consolidation. In the above example,
it is possible that a route to the destination "SIP 408" through
one or more carriers may have been lost if the individual routes
were not consolidated.
Another example is to consolidate the Prefix attribute from
multiple Carrier or Trunkgroup updates received from different
gateways for the same destination. Let us say, there are Carrier
AF updates from two gateways for Carrier destination X, and the
prefix attribute values are {408, 650} from one update and {919,
973} from the other. The prefix values from these two updates can
be consolidated into a single Carrier AF route advertisement with
prefix value {408, 650, 919, 973}.
In general, there is a potential for loss of gateway routing
information, when TGREP routes from a set of gateways are not
consolidated, when a candidate route is presented to the TRIP LS.
The specifics of applying the consolidation operation to
different attributes and routes from different address families,
is left to the individual TGREP receiver implementations.
4.9.2. Aggregation
The set of gateway routes, that are in a consolidated form or
otherwise, may be aggregated before importing it to the LS instance
that is responsible for I-TRIP/E-TRIP processing (LS-Egress). This
operation follows the standard aggregation procedures described in
the TRIP [4], while adhering to the aggregation rules for each route
attribute.
4.9.3. Consolidation v/s Aggregation
To highlight the difference between the two operations discussed
above, "Consolidation" combines multiple routes for the same route
destination, whereas "Aggregation" combines routes for different
route destinations that qualify as candidates to be summarized
resulting in route information reduction.
To take an example, if there are multiple gateways offering routes to
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an E.164 destination "408" but with possibly different attributes
(Eg: Carrier), the LS/Proxy can combine these to form one route for
"408" but representing the attribute information collectively. This
process is Consolidation
If, for example, the LS/Proxy receives routes for 4080, 4081, 4082,
... 4089 from amongst a set of gateways, it could aggregate these
different candidate routes to have a summarized route destination
"408" with each of the attributes computed using the Aggregation
procedures defined in the TRIP.
5. Security Considerations
The Security considerations defined in the TRIP [4] apply to TGREP
sessions between Gateways and TGREP Receivers (TRIP LS).
The security mechanism for the peering session between TGREP GW and a
TRIP LS, in an IP network, is IPsec [6]. IPsec uses two protocols to
provide traffic security: Authentication Header (AH) [7] and
Encapsulating Security Payload (ESP) [8].
The AH header affords data origin authentication, connectionless
integrity and optional anti-replay protection of messages passed
between the peer LSs. The ESP header provides origin authentication,
connectionless integrity, anti-replay protection, and confidentiality
of messages.
Implementations of the protocol defined in this document employing
the ESP header SHALL comply with section 5 of [8], which defines a
minimum set of algorithms for integrity checking and encryption.
Similarly, implementations employing the AH header SHALL comply with
section 5 of [7], which defines a minimum set of algorithms for
integrity checking using manual keys.
Implementations SHOULD use IKE [9] to permit more robust keying
options. Implementations employing IKE SHOULD support authentication
with RSA signatures and RSA public key encryption.
A Security Association (SA) [6] is a simplex "connection" that
affords security services to the traffic carried by it. Security
services are afforded to a SA by the use of AH, or ESP, but not both.
Two types of SAs are defined: transport mode and tunnel mode [12]. A
transport mode SA is a security association between two hosts, and is
appropriate for protecting the TRIP session between two peer LSs.
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6. IANA Considerations
Both TRIP[4] and TGREP share the same IANA registry for Capabilities,
Attributes, Address Families, and Application Protocols.
6.1. Attribute Codes
The Attribute Type Codes to be assigned for the new attributes
defined in this document are listed below:
| Code Attribute Reference
| ---- --------- ---------
| 13 TotalCircuitCapacity [RFCXXXX]
| 14 AvailableCircuits [RFCXXXX]
| 15 CallSuccess [RFCXXXX]
| 16 E.164 Prefix [RFCXXXX]
| 17 Pentadecimal Routing Number Prefix [RFCXXXX]
| 18 Decimal Routing Number Prefix [RFCXXXX]
| 19 TrunkGroup [RFCXXXX]
| 19 Carrier [RFCXXXX]
[NOTE TO RFC-ED: please replace XXXX with the rfc number of this
specification ]
6.2. Address Family Codes
The following subsections show the codes to be assigned for the two
new address families introduced in this document
6.2.1. TrunkGroup Address Family
| Code Address Family Reference
| ---- -------------- ---------
| 4 TrunkGroup [RFCXXXX]
[NOTE TO RFC-ED: please replace XXXX with the rfc number of this
specification ]
6.2.2. Carrier Address Family
| Code Address Family Reference
| ---- -------------- ---------
| 5 Carrier [RFCXXXX]
[NOTE TO RFC-ED: please replace XXXX with the rfc number of this
specification ]
Bangalore, Kumar, Rosenberg, Salama, Shah [Page 26]
Internet Draft draft-ietf-iptel-tgrep-05.txt July 2005
7. Change history
[[NOTE TO RFC-ED: Please remove this section prior to publication]]
7.1. Changes since draft-ietf-iptel-tgrep-03.txt
- No change in content. Releasing a new revision for renewal of
draft.
7.2. Changes since draft-ietf-iptel-tgrep-02.txt
- No change in content. Releasing a new revision for renewal of
draft.
7.3. Changes since draft-ietf-iptel-tgrep-01.txt
- Added a "Security Considerations" Section to the document.
- Strengthened the text under "LS/Proxy Behavior" regarding
Consolidation and Aggregation with additional examples for better
clarity.
- Removed the section "Other Attributes" including its subsection
on the "Pricing" attribute.
- Modified the definition of Carrier in the "Carrier attribute" and
"TrunkGroup and Carrier Address Families" sections respectively.
Pz - Rectified the section number references in the "IANA
Considerations" Section.
- Strengthened the text in the attribute sections regarding
dissemination of attributes received on TGREP.
- Updated the "References" section.
- Corrected typos, nits, grammatical errors, and language of the
text throughout the document based on feedback from the iptel
community.
7.4. Changes since draft-ietf-iptel-tgrep-00.txt
- Added recommendations for AvailableCircuits and CallSuccess
attributes.
- Updated Carrier Attribute with ASCII syntax.
- Removed thresholding scheme description.
- Updated author addresses.
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Internet Draft draft-ietf-iptel-tgrep-05.txt July 2005
7.5. Changes since draft-ietf-iptel-trip-gw-00.txt
- Changed title of the document to TGREP (Telephony Gateway
REgistration Protocol).
- Changed name of protocol described in this document to TGREP.
- Changed Abstract and Introduction sections to position TGREP as
an auxiliary protocol to TRIP (as opposed to a "subset" of TRIP).
- Modified the section on LS/Proxy Behavior including the diagram.
- Added an additional example to the Route Consolidation section.
- Changed the format of Carrier (both as an attribute and as an AF)
to accommodate representation of Country codes in association
with CICs.
- Updated text to allow Carrier attribute in TrunkGroup address
family and TrunkGroup attribute in Carrier address family.
7.6. Changes since -03
- Removed Carrier-Trunkgroup attribute and address family and
references to it.
- Added Terminology and Definitions section.
- Updated CallSuccess attribute.
- Added Prefix attribute.
- Added Carrier attribute.
- Added TrunkGroup attribute.
- Added TrunkGroup Address Family.
- Added Carrier Address Family.
- Added some more references.
7.7. Changes since -02
- Removed the requirements section.
- Discussed the motivation for introducing Carrier information into
TRIP.
- Defined a new attribute for the E.164 address family.
- Defined a new address family for CarrierCode-TrunkGroup
combination .
- Defined new attributes to advertise dynamic gateway
characteristics like resource availability, and call success
rate.
- Added as section to validate the TGREP solution against the
requirements in [7].
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Internet Draft draft-ietf-iptel-tgrep-05.txt July 2005
7.8. Changes since -01
- Added requirements.
- Added more formal analysis of REGISTER and added analysis of SLP.
- Removed circuit capacity attribute.
7.9. Changes since -00
- Added text to stress the value of this proposal for managing a
gateway cluster.
- Added attributes for circuit capacity and DSP capacity.
- Added section on LS operation, discussing aggregation issue.
8. Acknowledgments
We wish to thank Vijay Gurbani, Li Li, Kevin McDermott, David Oran,
Bob Penfield, Jon Peterson, Anirudh Sahoo and James Yu for their
insightful comments and suggestions.
9. References
9.1. Normative References
[1] Bradner, S., "Keywords for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
session initiation protocol," Request for Comments 3261, Internet
Engineering Task Force, Mar. 1999.
[3] E. Guttman, C. Perkins, J. Veizades, and M. Day, "Service
location protocol, version 2," Request for Comments 2608, Internet
Engineering Task Force, June 1999.
[4] J. Rosenberg, H. Salama, and M. Squire, "Telephony routing over
IP (TRIP)," Request for Comments 3219, Internet Engineering Task
Force, January 2002.
[5] J. Rosenberg and H. Schulzrinne, "A framework for telephony
routing over IP," Request for Comments 2871, Internet Engineering
Task Force, June 2000.
[6] Kent, S. and R. Atkinson, "Security Architecture for the
Internet Protocol", RFC 2401, November 1998.
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[7] Kent, S. and R. Atkinson, "IP Authentication Header", RFC 2402,
November 1998.
[8] Kent, S. and R. Atkinson, "IP Encapsulating Security Payload
(ESP)", RFC 2406, November 1998.
[9] Harkins, D. and D. Carrel, "The Internet Key Exchange (IKE)",
RFC 2409, November 1998.
[10] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 2234, November 1997.
9.2. Informative References
[11] ITU-T List of ITU Carrier Codes (published periodically in the
ITU-T Operational Bulletin).
[12] J. Peterson, "An Architecture for Gateway Registration Based on
Trunk Groups," Internet Draft, Internet Engineering Task Force, Feb.
2002. Work in progress.
[13] V. Gurbani and C. Jennings, "Representing trunk groups in
tel/sip Uniform Resource Identifiers (URIs)," Internet Draft,
Internet Engineering Task Force, May 2005.
[14] J. Rosenberg, "Requirements for Gateway Registration," Internet
Draft, Internet Engineering Task Force, Nov. 2001. Work in progress.
[15] J. Yu, "New Parameters for the "tel" URI to Support Number
Portability," Internet Draft, Internet Engineering Task Force, July
2005.
Authors' Addresses
Manjunath Bangalore
Cisco Systems Inc.
Mail Stop SJC-21/2/2
170 W. Tasman Drive
San Jose, CA 95134
Phone: +1-408-853-3239
email: manjax@cisco.com
Bangalore, Kumar, Rosenberg, Salama, Shah [Page 30]
Internet Draft draft-ietf-iptel-tgrep-05.txt July 2005
Rajneesh Kumar
Cisco Systems Inc.
Mail Stop SJC-14/4/2
170 W. Tasman Drive
San Jose, CA 95134
Phone: +1-408-527-6148
email: rajneesh@cisco.com
Jonathan Rosenberg
Cisco Systems Inc.
Mail Stop PPY02/2
600 Lanidex Plaza
Parsippany
NJ 07054
Phone: +1-973-952-5060
email: jdrosen@cisco.com
Hussein F. Salama
Cisco Systems Inc.
Mail Stop CAI1
135 Abdel Aziz Fahmy Street
2nd Floor Apartment #3, Heliopolis
Cairo, Egypt
Phone: +202-4166200
email: hsalama@sysdsoft.com
Dhaval N. Shah
Cisco Systems Inc.
Mail Stop SJC-20/3/3
170 W. Tasman Drive
San Jose, CA 95134
Phone: +1-408-527-0436
email: dhaval@cisco.com
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Bangalore, Kumar, Rosenberg, Salama, Shah [Page 31]
Internet Draft draft-ietf-iptel-tgrep-05.txt July 2005
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