IPTEL Working Group Manjunath Bangalore, Cisco Systems
Internet Draft Rajneesh Kumar, Cisco Systems
draft-ietf-iptel-tgrep-09.txt Hussein Salama, Citex Software
September 2007 Jonathan Rosenberg, Cisco Systems
Expiration Date: March 2008 Dhaval Shah, Moowee Inc.
A Telephony Gateway REgistration Protocol (TGREP)
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Copyright Notice
Copyright (C) The IETF Trust (2007).
Abstract
This document describes the Telephony Gateway Registration Protocol
(TGREP) for registration of telephony prefixes supported by telephony
gateways and soft switches [12]. 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
(TRIP) Location Server, which in turn can propagate that routing
information within and between Internet telephony administrative
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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.
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Table of Contents
1 Terminology and Definitions .............................. 4
2 Introduction ............................................. 4
3 TGREP: Overview of operation ............................. 6
4 TGREP Attributes ......................................... 8
4.1 TotalCircuitCapacity Attribute ........................... 9
4.2 AvailableCircuits Attribute .............................. 10
4.3 CallSuccess Attribute .................................... 11
4.4 Prefix Attributes ........................................ 13
4.5 TrunkGroup Attribute ..................................... 14
4.6 Carrier Attribute ........................................ 16
5 TrunkGroup and Carrier Address Families .................. 17
5.1 Address Family Syntax .................................... 18
6 Gateway Operation ........................................ 20
6.1 Session Establishment .................................... 20
6.2 UPDATE Messages .......................................... 20
6.3 KEEPALIVE Messages ....................................... 20
6.4 Error Handling and NOTIFICATION Messages ................. 21
6.5 TGREP Finite State Machine ............................... 21
6.6 Call Routing Databases ................................... 21
6.7 Multiple Address Families ................................ 21
6.8 Route Selection and Aggregation .......................... 22
7 LS/Proxy Behavior ........................................ 22
7.1 Route consolidation ...................................... 24
7.2 Aggregation .............................................. 25
7.3 Consolidation v/s Aggregation ............................ 25
8 Security Considerations .................................. 25
9 IANA Considerations ...................................... 26
9.1 Attribute Codes .......................................... 26
9.2 Address Family Codes ..................................... 27
10 Change history ........................................... 27
10.1 Changes since draft-ietf-iptel-tgrep-03.txt .............. 27
10.2 Changes since draft-ietf-iptel-tgrep-02.txt .............. 27
10.3 Changes since draft-ietf-iptel-tgrep-01.txt .............. 28
10.4 Changes since draft-ietf-iptel-tgrep-00.txt .............. 28
10.5 Changes since draft-ietf-iptel-trip-gw-00.txt ............ 28
10.6 Changes since -03 ........................................ 29
10.7 Changes since -02 ........................................ 29
10.8 Changes since -01 ........................................ 29
10.9 Changes since -00 ........................................ 29
11 Acknowledgments .......................................... 30
12 References ............................................... 30
12.1 Normative References ..................................... 30
12.2 Informative References ................................... 30
Authors' Addresses ....................................... 31
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Intellectual Property Statement .......................... 32
Copyright Statement ...................................... 32
Acknowledgment ........................................... 33
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 trunk is 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 is familiar with TRIP [2,10]. 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
element is a SIP Proxy [9] or H.323 Gatekeeper. 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
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the call signaling, there are two components, the "Ingress LS"
(a.k.a. "TGREP Receiver" and the "Egress LS". The "TGREP Receiver"
component 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. For convenience, gateway and GW are
used interchangably.
This configuration is depicted graphically in Figure 1.
Signalling TGREP
-------------> <----------------
+---------+
| |
| GW |
> +---------+
//
//
SIP // +---------+
<----> // | |
+-------------------------+ // | GW |
| | // +---------+
| +-------------+ |/
| | | |
| | Routing | | +---------+ TO PSTN
| | Proxy | | | |
---> | | |-----------> | GW | ----->
|+---+-----+ +-----+----+ | +---------+
|| | | | |
|| <+-+ | |--
||Egress LS| |Ingress LS| | --- +---------+
|| | | | | -- | |
|+---------+ +----------+ | -- | GW |
| | -- +---------+
| | -->
+-------------------------+
TRIP +---------+
<----> | |
| 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
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real-time, as it changes. This means there must be some kind of
communications between the proxy and the gateways to convey this
information.
The TRIP protocol [2] is defined for carrying telephony routing
information between providers, for the purposes of getting a call
routed to the right provider for termination to the PSTN. However,
there is no mechanism defined in TRIP that defines how routes get
injected into the TRIP protocol from within the network. Nor does it
define mechanisms which would allow the provider to select the
specific gateway for terminating a call when it arrives. Those gaps
are filled by TGREP.
TGREP allows PSTN gateways or softswitches to inform a signaling
server, such as a SIP proxy server or H.323 gatekeeper, of routes it
has to the PSTN. These advertisements include fairly dynamic
information, such as the remaining capacity in a particular trunk,
which is essential for selecting the right gateway.
TGREP is identical in syntax and overall operation to TRIP. However,
it differs in the route processing rules followed by the TGREP
receiver, allowing for a route processing function called
"Consolidation". Consolidation combines multiple routes for the same
route destination with different attributes to a single route to
prevent loss of routing information. TGREP also defines a set of new
attributes, usable by TGREP or TRIP. Finally, TGREP only utilizes a
subset of overall TRIP capabilities. Specifically, certain
attributes are not utilized (as described below), and the TGREP
entities (the sender and receiver) operate in an asymmetric
relationship, whereas TRIP allows symmetric and asymmetric.
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 [2]. 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 TGREP sender 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
optionally performs operations like consolidation and aggregation,
hands over the reachability information to a TRIP Location Server.
The routing proxy also uses the information to select the gateway for
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incoming calls.
"Consolidation" combines multiple routes for the same route
destination, whereas "Aggregation" combines routes for different
route destinations that qualify as candidate routes to be summarized
resulting in route information reduction. To take an example, if
there are multiple gateways offering routes to an E.164 destination
"408" but with possibly different attributes (e.g.: 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.
The TGREP Sender establishes a session to the TGREP Receiver using a
procedure similar to session establishment in TRIP. After the
session establishment, the TGREP Sender sends the reachability
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 Receiver 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.
- TotalCircuitCapacity: This attribute identifies the total number
of PSTN circuits that are available on a route to complete calls.
- AvailableCircuits: This attribute identifies the number of PSTN
circuits that are currently available on a route to complete
calls.
- CallSuccess: This attribute represents information about the
number of normally terminated calls out of a total number of
attempted calls.
- Prefix (E164): This attribute is used to represent the list of
E164 prefixes that the respective route can complete calls to.
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- Prefix (Decimal Routing Number): This attribute is used to
represent the list of Decimal prefixes that the respective route
can complete calls to.
- Prefix (Hexadecimal Routing Number): This attribute is used to
represent the list of Hexadecimal prefixes that the respective
route can complete calls to.
- TrunkGroup: This attribute enables providers to route calls to
destinations through preferred trunks.
- Carrier: This attribute enables providers to route calls to
destinations through preferred carriers.
In the rest of the document we specify attributes and address
families used in TGREP. The new attributes and Address families
introduced are also applicable for general usage in TRIP except
where noted (AvailableCircuits attribute for example)
4. TGREP Attributes
Due to its usage within a service provider network, TGREP makes use
of a subset of the attributes defined for TRIP, in addition to
defining several new ones. In particular, the following attributes
from TRIP are applicable to TGREP:
1. WithdrawnRoutes 2. ReachableRoutes 3. NexthopServer 4. Prefix 5.
Communities
TGREP also defines several new attributes, described in this section.
These are TotalCircuitCapacity, AvailableCircuits, CallSuccess,
TrunkGroup and Carrier. As mentioned above, these new attributes are
usable by TRIP unless noted otherwise.
A TGREP UPDATE supports the following attributes:
1. TotalCircuitCapacity
2. AvailableCircuits
3. CallSuccess
4. Prefix (E.164, Pentadecimal routing number, Decimal routing
number)
5. TrunkGroup
6. Carrier
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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
MAY be propagated beyond the LS that receives it.
TotalCircuitCapacity represents the total number of possible 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
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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.
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.
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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.
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.
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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.
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.
When the value for the total number of attempted calls wraps around,
the counter value for the number of successful calls is reset to keep
it aligned with the other component over a given window of time. The
TGREP receiver using this information should obtain this information
frequently enough to prevent loss of significance.
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.
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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
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 [2]), 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.
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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.
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 . . .
+-------------------------------+-----------+------------------------
| Length | Prefix1...| Length |Prefix2
+-------------------------------+-----------+------------------------
Figure 2: Prefix Format
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
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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
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 [8] is per rules
outlined in [4].
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.
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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.
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 [11].
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 [9] is per rules outlined in [5]. Specifically, it carries
"global-cic" or "local-cic" [5]. 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.
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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
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.
5. TrunkGroup and Carrier Address Families
As described in TRIP [2], 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
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Internet Draft draft-ietf-iptel-tgrep-09.txt September 2007
When a set of GWs are to be 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.
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.
- It enables scalability as 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.
5.1. Address Family Syntax
Consider the generic TRIP route format from TRIP[2] 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.
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The code for the trunk group address family is 4 and the code for the
carrier address family is 5.
The Application Protocol field is the same as the one for the
Decimal, Pentadecimal and E.164 address families defined in TRIP[2].
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
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. This is the same as the value field specified in an
earlier Section 4.6.1 about the Carrier Attribute.
The above mentioned address families are not hierarchical, but flat.
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
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TrunkGroup.
6. 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 TRIP 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.
6.1. Session Establishment
When opening a peering session with a TGREP Receiver, a TGREP gateway
follows exactly the same procedures as any other TRIP entity. 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.
6.2. 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.
TGREP processing of the UPDATE message at the gateway is identical to
UPDATE processing in TRIP[2]. A TGREP sender MUST support all
mandatory TRIP attributes.
6.3. 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 [2].
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6.4. 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.
6.5. 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.
6.6. 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.
6.7. Multiple Address Families
As mentioned above, TGREP supports various address families in order
to convey the reachability 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 its 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.
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6.8. Route Selection and Aggregation
TRIP's route selection and aggregation operations MUST NOT be
implemented by TGREP gateways.
7. LS/Proxy Behavior
As mentioned earlier, TGREP can be considered as a protocol
complimentary to TRIP in providing reachability information which 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 [2]. 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 component operating in receive mode, that
peers with one more gateways, each of them using TGREP to advertise
routing information. This 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. Also, the entity (typically, a
Gateway) advertising the routes on the TGREP session is termed as the
"TGREP Sender". The "TGREP Receiver" receiving the TRIP messages
takes the resulting routing information from each gateway, and
"exports" it to another process we define below, 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 TGREP Receiver(aka. 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 6 below.
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+-------------------------------------------------------+
| +-------------------------------+ |
| | +-+ +-+ | | TGREP
| | |A| |C| | | +-----+
| | |g| |o| | | | |
| +-------------+ | |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 |
| |
| |
| |
| |
| |
+-----------------+
Figure 6: LS Architecture for TRIP-GW
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7.1. 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.
- 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 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.
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7.2. Aggregation
The set of gateway routes, that are in a consolidated form or
otherwise, may be aggregated before importing it to the LS instance
which is responsible for I-TRIP/E-TRIP processing (LS-Egress). This
operation follows the standard aggregation procedures described in
the TRIP [2], while adhering to the aggregation rules for each route
attribute.
7.3. 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
an E.164 destination "408" but with possibly different attributes
(e.g.: 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.
8. Security Considerations
The Security considerations for TGREP are identical to that
identified in TRIP [2] and are just restated here for the purposes of
clarity.
The security mechanism for the peering session between TGREP GW and a
TRIP LS, in an IP network, is IPsec [3]. IPsec uses two protocols to
provide traffic security: Authentication Header (AH) [6] and
Encapsulating Security Payload (ESP) [7].
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.
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Implementations of the protocol defined in this document employing
the ESP header SHALL comply with section 3.1.1 of [13], which defines
a minimum set of algorithms for integrity checking and encryption.
Similarly, implementations employing the AH header SHALL comply with
section 3.2 of [13], which defines a minimum set of algorithms for
integrity checking.
Implementations SHOULD use IKEv2 [7] to permit more robust keying
options. Implementations employing IKEv2 SHOULD support 3DES-CBC for
confidentiality and HMAC-SHA1 for integrity.
A Security Association (SA) [3] 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. A
transport mode SA is a security association between two hosts, and is
appropriate for protecting the TRIP session between two peer LSs.
9. IANA Considerations
Both TRIP[2] and TGREP share the same IANA registry for Capabilities,
Attributes, Address Families, and Application Protocols. This
specification requests that IANA add the following attribute codes
and address family codes to the TRIP [2] registries.
9.1. 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 [5]
[NOTE TO RFC-ED: please replace XXXX with the rfc number of this
specification ]
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9.2. Address Family Codes
The following subsections show the codes to be assigned for the two
new address families introduced in this document
9.2.1. TrunkGroup Address Family
| Code Address Family Reference
| ---- -------------- ---------
| 4 TrunkGroup [RFCXXXX]
[NOTE TO RFC-ED: please replace XXXX with the rfc number of this
specification ]
9.2.2. Carrier Address Family
| Code Address Family Reference
| ---- -------------- ---------
| 5 Carrier [RFCXXXX]
[NOTE TO RFC-ED: please replace XXXX with the rfc number of this
specification ]
10. Change history
[[NOTE TO RFC-ED: Please remove this section prior to publication]]
10.1. Changes since draft-ietf-iptel-tgrep-03.txt
- No change in content. Releasing a new revision for renewal of
draft.
10.2. Changes since draft-ietf-iptel-tgrep-02.txt
- No change in content. Releasing a new revision for renewal of
draft.
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Internet Draft draft-ietf-iptel-tgrep-09.txt September 2007
10.3. 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.
- 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.
10.4. 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.
10.5. 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.
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Internet Draft draft-ietf-iptel-tgrep-09.txt September 2007
10.6. 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.
10.7. 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 [6].
10.8. Changes since -01
- Added requirements.
- Added more formal analysis of REGISTER and added analysis of SLP.
- Removed circuit capacity attribute.
10.9. 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.
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11. 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.
12. References
12.1. Normative References
[1] Bradner, S., "Keywords for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[2] J. Rosenberg, H. Salama, and M. Squire, "Telephony routing over
IP (TRIP)," Request for Comments 3219, Internet Engineering Task
Force, January 2002.
[3] Kent, S. and Seo K., "Security Architecture for the Internet
Protocol", RFC 4301, December 2005.
[4] V. Gurbani and C. Jennings, "Representing trunk groups in tel/sip
Uniform Resource Identifiers (URIs)," Internet Draft, Internet
Engineering Task Force, August 2006.
[5] J. Yu, "Number Portability Parameters for the "tel" URI", RFC
4694, October 2006.
[6] Kent, S., "IP Authentication Header", RFC 4302, December 2005.
[7] Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303,
December 2005.
[8] Crocker, D. and P. Overell, "Augmented BNF for Syntax
Specifications: ABNF", RFC 4234, October 2005.
12.2. Informative References
[9] M. Handley, H. Schulzrinne, E. Schooler, and J. Rosenberg, "SIP:
session initiation protocol," Request for Comments 3261, Internet
Engineering Task Force, Mar. 1999.
[10] J. Rosenberg and H. Schulzrinne, "A framework for telephony
routing over IP," Request for Comments 2871, Internet Engineering
Task Force, June 2000.
[11] ITU-T List of ITU Carrier Codes (published periodically in the
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Internet Draft draft-ietf-iptel-tgrep-09.txt September 2007
ITU-T Operational Bulletin).
[12] J. Rosenberg, "Requirements for Gateway Registration," Internet
Draft, Internet Engineering Task Force, Nov. 2001. Work in progress.
[13] D. Eastlake, "Cryptographic Algorithm Implementation
Requirements for Encapsulating Security Payload (ESP) and
Authentication Header (AH)", RFC 4305, December 2005.
Authors' Addresses
Manjunath Bangalore
Cisco Systems Inc.
Mail Stop SJC-14/2/1
3625 Cisco Way
San Jose, CA 95134
Phone: +1-408-525-7555
email: manjax@cisco.com
Rajneesh Kumar
Cisco Systems Inc.
Mail Stop SJC-14/4/2
3625 Cisco Way
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
Citex Software Ltd.
4 Dr. Soliman Square
Dokki, Giza 12311
Egypt
Phone: +20-2-33371672/+1-425-7497286
email: h.f.salama@ieee.org
Bangalore, Kumar, Rosenberg, Salama, Shah [Page 31]
Internet Draft draft-ietf-iptel-tgrep-09.txt September 2007
Dhaval N. Shah
Moowee Inc.
4920 El Camino Real,
Los Altos
CA 94022
Phone: +1-408-307-7455
email: dhaval@moowee.tv
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Bangalore, Kumar, Rosenberg, Salama, Shah [Page 32]
Internet Draft draft-ietf-iptel-tgrep-09.txt September 2007
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
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Bangalore, Kumar, Rosenberg, Salama, Shah [Page 33]