One document matched: draft-ietf-iptel-tgrep-01.txt
Differences from draft-ietf-iptel-tgrep-00.txt
IPTEL Working Group Manjunath Bangalore, Cisco Systems
Internet Draft Rajneesh Kumar, Cisco Systems
draft-ietf-iptel-tgrep-01.txt Jonathan Rosenberg, dynamicsoft
October 2002 Hussein Salama, Cisco Systems
Expiration Date: August 2003 Dhaval N. Shah, Cisco Systems
A Telephony Gateway REgistration Protocol (TGREP)
Status of this Memo
This document is an Internet-Draft and is in full conformance with
all provisions of Section 10 of RFC2026.
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-Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
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 TRIP Location Server, which in
turn can propogate that routing information within the same, and
other internet telephony administrative domains (ITAD). TGREP shares
a lot of similarites with the TRIP Protocol. It has similar
procedures and Finite State Machine for session establishment. It
also shares the same format for messaages and a subset of attributes
with TRIP.
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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:
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: An organization that provides connections for telephony
services between end-users and/or exchanges.
2. Introduction
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 POPs,
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.
This configuration is depicted graphically in Figure 1.
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+---------+
| |
| GW |
-> +---------+
//
//
// +---------+
// | |
// | GW |
// +---------+
//
+----------+ // TO PSTN
| | / +---------+
| Routing | ---------------> | | ----->
-------->| Proxy | | GW |
| | -- +---------+
| | --
+----------+ --
--- +---------+
-- | |
-- | 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 particular POTS 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,
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 propogated by the TRIP Location Server.
TGREP shares a lot of commonality with the 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 propogate 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
characterstics of gateways, like Available Capacity for a destination
etc. The document aims at specifying all the attributes that can go
in on the TGREP session. The document also specified some new address
families which can be useful in advertising the information on the
GWs. The type codes for the new attributes and address families are
yet to be obtained from IANA. An attempt will be made to assign the
codes in such a way that they are in continuation with the codes
assigned for attributes and families defined in the the TRIP RFC[4].
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 RFC[4]. It is suggested that the reader be
familiar with the concepts of TRIP like attributes, flags, route
types, address families etc.
3. Defining TGREP
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 other side. A
TGREP Receiver is defined, which receives this information and after
certain optional operations like consolidation, aggregation etc.
(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 informaton in the UPDATE messages. The
UPDATE messages have the same format as in TRIP. However, there are
certain attributes that are not relevant in TGREP. TGREP also defines
certain new attributes that find a use in a TGREP update.
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.
A TGREP UPDATE supports the following attributes:
1. WithdrawnRoutes (as defined in TRIP)
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2. ReachableRoutes (as defined in TRIP)
3. NexthopServer (as defined in TRIP)
4. TotalCircuitCapacity
5. AvailableCircuits
6. CallSuccess
7. Prefix
8. TrunkGroup
9. Carrier
3.1. TotalCircuitCapacity Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 13 (To be assigned by IANA)
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 propogated beyond the LS that receives it.
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.
TotalCircuitCapacity is measured in integral number of calls. 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.
3.1.1. TotalCircuitCapacity Syntax
The TotalCircuitCapacity attribute is a 4-octet unsigned numeric
value. 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.
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3.1.2. Route Origination and TotalCircuitCapacity
Routes MAY be originated containing the TotalCircuitCapacity
attribute.
3.1.3. 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.
3.1.4. 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.
3.1.5. 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.
3.2. AvailableCircuits Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 14. (To be assigned by IANA)
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 MUST NOT be propagated unless the LS is sure that it
is relatively static.
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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.
AvailableCircuits is measured in integral number of calls. It is very
dynamic.
3.2.1. AvailableCircuits Syntax
The AvailableCircuits attribute is a 4-octet unsigned numeric value.
It represents the number of circuits remaining for terminating calls
to this route.
3.2.2. 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 sufficiently large
windows be used to provide a useful aggregated statistic.
3.2.3. 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.
3.2.4. Aggregation and AvailableCircuits
Not applicable
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3.2.5. 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.
3.3. CallSuccess Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 15. (To be assigned by IANA)
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 MUST NOT be 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 because of
called party being unavailable is conventionally considered a
successful call. Similar is the case when the called party is busy.
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.
3.3.1. CallSuccess Syntax
The CallSuccess attribute is comprised of two component fields - each
represented as an unsigned 4-octet numeric value. The first
component field represents the total number of calls terminated
normally for the advertised destination on a given address family.
The second component field represents the total number of attempted
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calls for the advertised destination.
3.3.2. 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.
3.3.3. 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.
3.3.4. Aggregation and CallSuccess
Not applicable
3.3.5. 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 in most cases.
3.4. Prefix Attributes
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Codes: 16 for E164 prefix, 17 for pentadecimal prefix and
18 for decimal prefix (To be assigned by IANA)
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
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ranges preferable to others.
3.4.1. Prefix Attribute Syntax
The Prefix attribute could be E.164, Decimal or PentaDecimal (refer
to TRIP RFC [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
for the given Reachable route(s).
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
3.4.2. Route Origination and Prefix
Routes MAY be originated containing the Prefix attribute.
3.4.3. Route Selection and Prefix
The Prefix attribute MAY be used for route selection.
3.4.4. 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.
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3.4.5. Route Dissemination and Prefix
The LS receiving this attribute should disseminate it to other peers,
both internal and external to the ITAD.
3.5. TrunkGroup Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 20 (To be assigned by IANA)
The TrunkGroup attribute is used to represent the list of trunkgroups
on the gateway that the gateway can complete the calls to. It enables
providers to route calls to destinations through preferred trunks.
This attribute is relatively static.
3.5.1. TrunkGroup Syntax
The TrunkGroup attribute is a variable length attribute that is
composed of a sequence of trunkgroup length-value fields. It
indicates that the gateway can complete the call through any
trunkgroup (represented by the trunkgroup label) in the sequence.
Each trunkgroup is 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 alphanumeric field and is also called the
trunkgroup label field. The length field represents the size of the
trunkgroup label in number of octets. The maximum length is 128
octets.
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 Label1..| Length | TrunkGroup Label2..
+---------------+--------------------+---------------+---------------------
Figure 3: TrunkGroup Syntax
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3.5.2. Route Origination and TrunkGroup
Routes MAY be originated containing the TrunkGroupattribute.
3.5.3. Route Selection and TrunkGroup
The TrunkGroup attribute MAY be used for route selection. Certain
trunkgroups MAY be preferred over others based on provider policy.
3.5.4. 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.
3.5.5. 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 MUST not be disseminated external to the ITAD, with
TrunkGroup attribute.
3.6. Carrier Attribute
Mandatory: False.
Required Flags: Not well-known.
Potential Flags: None.
TRIP Type Code: 19 (To be assigned by IANA)
The Carrier attribute is used to represent the list of carriers that
the gateway can complete calls to. It enables providers to route
calls to destinations through preferred carriers. This attribute is
relatively static.
3.6.1. Carrier Syntax
The Carrier attribute is a variable length attribute that is composed
of a sequence of carrier values. It indicates that the route can
complete the call to any of the carriers represented in the sequence
of carrier values.
Each carrier value has two ASCII fields, a 3-octet CountryCode, and a 4-
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octet CarrierIdCode. The CountryCode field represents the country
that corresponds to the Carrier identified by CarrierIdCode. It is
the same as the E.164 country code used to dial internal telephony
destinations. The CarrierIdCode or CIC represents a unique code
assigned to the Carrier or Telephony service provider offering the
service by an administrative body operating in that region.
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 2 3 5
0 1 2 3 4 5 6 7 8 9 0 .... 0 1 2 3 4 5 6 7 8 9 0 1 2 3 .... 0 1 2 3 4 5
+----------------------------------+------------------------------------+-----
| CountryCode | CarrierIdCode .... | ....
+----------------------------------+------------------------------------+-----
Figure 4: Carrier Syntax
3.6.2. Route Origination and Carrier
Routes MAY be originated containing the Carrier attribute.
3.6.3. Route Selection and Carrier
The Carrier attribute MAY be used for route selection. Certain
carriers MAY be preferred over others based on provider policy.
3.6.4. 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.
3.6.5. 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.
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3.7. TrunkGroup and Carrier Address Families
When a set of GWs are to managed at the granularity of carriers or
trunkgroups then it may be more appropriate for a GW can 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.
- 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.
3.7.1. 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.
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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 is a variable
length alphanumeric field (trunkgroup label), where length is
determined by the length field of the route. The maximum value of the
length field for this Address Family is 128 bytes.
For the Carrier Address Family, the length field represents the
length of the Address field in bytes. The Address field is a fixed
length field representing Carrier value. It is encoded as a fixed
length 4-octet value consisting of two fields : Country code and the
CarrierId.
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, Carrier and TrunkGroup attributes MUST NOT be used
with their respective address families.
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3.8. Other attribute considerations
3.8.1. Cost/Pricing attribute
In exploring attributes suitable for the GW-LS communications,
Pricing is another attribute that was considered. Though at first
glance, it seems like a useful piece of information to be advertised
by the gateway to express the price offered by carriers to different
destinations, in reality, the computation of pricing can get quite
complex. For example, the price offered by a provider can vary by
time of day, it can be based on an agreement between two service
providers interconnecting with each other, it could be based on one
price for the first 'n' minutes and a different price after that,
Least Cost routing choices and Grades of service offered by a carrier
can affect pricing. There could be other factors as well. Expressing
this complex interplay between different factors that determine
pricing is non-trivial to represent. It will be a subject of further
investigation to determine whether advertising pricing associated
with carriers in its simple form without any dependencies adds value
to be included as an attribute in the TGREP communications.
3.9. Gateway Operation
A gateway uses TRIP 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. Therefore, the
gateway does not need a complete implementation of TRIP. A
lightweight version of the protocol is sufficient. In this section we
describe the operation of TRIP on a gateway.
3.9.1. 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.
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3.9.2. 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.
3.9.3. 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 RFC[4].
3.9.4. 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.
3.9.5. 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.
3.9.6. 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
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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.
3.9.7. Multiple Address Families
As mentioned above, TGREP supports various address families in order
to convey the reachibilty of telephony destinations. A TGREP session
MUST NOT send UPDATEs of more than one of the following catagories
(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.
3.9.8. Route Selection and Aggregation
TRIP's route selection and aggregation operations MUST NOT be
implemented by TGREP gateways.
3.10. 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 for propogation. 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 the TRIP RFC [4]. Then, there is a signaling
server fronting a set of gateways and receives routing information on
one or more TGREP sessions. This routing information from the
gateways is received and processed by a TGREP receiver application.
Subsequently, this routing information is presented as candidate
routes (possibly as local routes) to the TRIP LS. The interface
between these two applications is entirely a local matter. However,
before importing these routes into the TRIP LS, certain operations
may optionally be performed on these routes. The nature of these
operations and the accompanying motivation are described in the
subsections below. The order in which the operations are listed
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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| | Mangement |-++-+-------| GW |
| | E-TRIP) | | |i| |a| | | | | +-----+
| | | | |o| |t| | |-+ -+-
| +-----------/-+ | |n| |i| +-------------+ | | --- +-----+
| / | | | |o| | | -- | |
| / | | | |n| | | | 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| | Mangement |-++-+-------| GW |
| | E-TRIP) | | |i| |a| | | | | +-----+
| | | | |o| |t| | |-+ -+-
| +-------------+ | |n| |i| +-------------+ | | --- +-----+
| | | | |o| | | -- | |
| | | | |n| | | | GW |
| | +-+ +-+ | | +-----+
| | TGREP Receiver | |
| +-------------------------------+ |
| |
| |
+-------------------------------------------------------+
LS/Proxy
Figure 7: LS Architecture for TRIP-GW
3.10.1. Route consolidation
The TGREP receiver 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 TRIP LS. 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.
o Gateway A advertises a route for destination "SIP 408" on the E.164
address
family with the Carrier attribute value C1.
o Gateway B advertises a route for destination "SIP 408" on the E.164
address
family with Carrier attribute value C2.
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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
refered 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.
3.10.2. 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. This operation
follows the standard aggregation procedures described in the TRIP RFC
[4], while adhering to the aggregation rules for each route
attribute.
4. IANA Considerations
- The Attribute Type Codes for the new attributes:
AvailableCircuits, TotalCircuitCapacity, CallSuccess, Prefix,
TrunkGroup and Carrier described in Sections 4.1, 4.2, 4.3, 4.4,
4.5 and 4.6 above, respectively, are to be assigned by IANA.
- The Address Family Codes for the new address families: TrunkGroup
and Carrier described in Section 4.7, are to be assigned by IANA.
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5. Changes since draft-ietf-iptel-tgrep-00.txt
- Added recommendation for AvailableCircuits and CallSuccess
attributes.
- Updated Carrier Attribute with ASCII syntax.
- Removed thresholding scheme description.
- Updated author addresses.
6. 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 accomodate 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. 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.
8. 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.
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- 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].
9. Changes since -01
- Added requirements.
- Added more formal analysis of REGISTER and added analysis of SLP.
- Removed circuit capacity attribute.
10. 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.
Authors' Addresses
Manjunath Bangalore
Cisco Systems
Mail Stop SJC-21/2/2
170 W. Tasman Drive
San Jose, CA 95134
email: manjax@cisco.com
Rajneesh Kumar
Cisco Systems
Mail Stop SJC-21/2/2
170 W. Tasman Drive
San Jose, CA 95134
email: rajneesh@cisco.com
Bangalore, Kumar, Rosenberg, Salama, Shah [Page 24]
Internet Draft draft-ietf-iptel-tgrep-00.txt May 2002
Jonathan Rosenberg
dynamicsoft
72 Eagle Rock Avenue
First Floor
East Hanover, NJ 07936
email: jdrosen@dynamicsoft.com
Hussein F. Salama
Cisco Systems
Mail Stop CAI1
135 Abdel Aziz Fahmy Street
2nd Floor Apartment #3, Heliopolis
Cairo, Egypt
email: hsalama@cisco.com
Dhaval N. Shah
Cisco Systems
Mail Stop SJC-06/4/3
170 W. Tasman Drive
San Jose, CA 95134
email: dhaval@cisco.com
Acknowledgments
We wish to thank David Oran, Anirudh Sahoo, Kevin McDermott, Jon
Peterson, Li Li and Bob Penfield for their insightful comments and
suggestions.
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 2543, 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
Bangalore, Kumar, Rosenberg, Salama, Shah [Page 25]
Internet Draft draft-ietf-iptel-tgrep-00.txt May 2002
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] International Telecommunication Union, "Packet based multimedia
communication systems," Recommendation H.323, Telecommunication
Standardization Sector of ITU, Geneva, Switzerland, Feb. 1998.
[7] J. Rosenberg, "Requirements for Gateway Registration," Internet
Draft, Internet Engineering Task Force, Nov. 2001. Work in progress.
[8] ITU-T List of ITU Carrier Codes (published periodically in the
ITU-T Operational Bulletin).
[9] J. Peterson, "An Architecture for Gateway Registration Based on
Trunk Groups," Internet Draft, Internet Engineering Task Force, Feb.
2002. Work in progress.
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