TR30/02-09-025
UIT - Secteur de la normalisation des télécommunications
ITU - Telecommunication Standardization Sector
UIT - Sector de Normalización de las Telecomunicaciones
Study Period 2001-2004
Commission d' études 

Study Group
 16
Comisión de Estudio 

Contributi on tardive 

Delayed Contributi on  D.xxx (WP1/16)
Contribuci ón tardía 
Geneva, 15-25 October 2002
Texte disponible seulement en 

Text available only in
 E
Texto disponible solamente en 

Question:
11/16
SOURCE*:
Cisco Systems
TITLE:
External Signaling and Trans-compression for Virtual Gateways
___________________
ABSTRACT
This contribution provides clarification for the PSTN-IP modem relay scenario. It has been
previously agreed to that this scenario will be part of the V.MoIP standard. This contribution
also proposes modifications to external signaling and trans-compression rules in support of the
PSTN-IP Modem Relay Scenario.
* Contact:
Herb Wildfeuer
Tel:
+1 805 961 3620
Fax:
E-mail: hwildfeu@cisco.com
Attention: This is not a publication made available to the public, but an internal ITU-T Document intended only for use by the
Member States of the ITU, by ITU-T Sector Members and Associates, and their respective staff and collaborators in their ITU
related work. It shall not be made available to, and used by, any other persons or entities without the prior written consent of the
ITU-T.
1
Introduction
Agreed issue 2.1 of the V.MoIP issues list [1] states that IP-PSTN architecture should be supported. This
contribution proposes external signalling and trans-compression rules for “Modem Relay Virtual
Gateway” (MRVG) in support of the IP-PSTN V.MoIP architecture.
The MRVG can either initiate or terminate a call through a V.MoIP compliant gateway in order to
communicating with an end-modem that is connected to the gateway. Figure 1 provides an example of an
application of the MRVG.
kets
Pac
li n g
ig n a
23 S
T
SPR
MRVG
PSTN
V.MoIP
Compliant
Gateway
IP
End
Modem
Pa
cke
ts
H.3
IP Network
Figure 1: Example application of Modem Relay Virtual Gateway (MRVG)
In the example application, if the MRVG is to interoperate with a calling end-modem, the V.MoIP
compliant gateway will initiate an H.323 V.MoIP compliant call to the MRVG. The MRVG will
negotiate with the gateway using external signalling to setup the necessary sessions through the IP
network for the data traffic. These sessions might include an SSE channel, SPRT channel, and VBD
channel.
For examples where the MRVG is initiating a call to an end-modem, the MRVG will initiate a H.323
V.MoIP compliant call to the gateway, negotiating the setup of the required sessions through the IP
network with the gateway using external signalling as per V.MoIP standards.
2
Gateway Type Extensions
MRVG’s do not need to implement trans-compression, as they are not directly interoperating with an endmodem. Since MRVG’s differ from gateways in this regard, a new set of trans-compression rules are
needed to fully define MRVG for V.MoIP.
The entire list of MRVG’s that can be specified (analogous to the current definition of V.MoIP gateways)
include those that have no compression or decompression capability (analogous to NTCX gateway),
either compression or decompression (but not both) capability (analogous to STCX gateway), or both
compression and decompression capability (analogous to DTCX gateway). This contribution proposes to
simplify the interoperability of V.MoIP compliant gateways with MRVG by assuming all MRVG’s
support compression and decompression. This assumption is based on the expectation that the MRVG’s
are centralized network resources and therefore do not have scalability and resource allocation concerns
which would limit their ability to support modem compression standards. (A standard network topology
strategy is to centralize the high resource usage applications in the network.)
Table 3 of V.MoIP draft [2] should be modified to add the MRVG gateway type to the existing list of
V.MoIP gateway types:
TABLE 1/V.MOIP (PROPOSED CHANGE)
Supported TCX capability Values
Parameter
Value
Supported TCX capability
Non-TCX/
Single-TCX/
Double-TCX/
MRVG
Table 1 of V.MoIP draft [2] should be modified to add the transcompression mode selection when the
MRVG gateway is involved in the call. Note that there is no need to consider MRVG to MRVG
connectivity since this is not in the scope of V.MoIP. A MRVG gateway will terminate a call to another
MRVG gateway upon determination of its type.
TABLE 2/V.MOIP (PROPOSED CHANGE)
Trans-Compression Mode Selection
Trans-Compression Mode
Capabilities Exchanged
3
Resultant Trans-Compression Mode
Selected by Gateways
G1
G2
G1
G2
No
No
No
No
No
Single
No
No
No
Double
No
Double
Single
No
No
No
Single
Single
Single
Single
Single
Double
Single
Single
Double
No
Double
None
Double
Single
Single
Single
Double
Double
Single/Double*
Single/Double*
MRVG
-
N/A
None
-
MRVG
None
N/A
References
[1] “V.MoIP Issues List”, TR-30.1/02-09-113, TR.30.1 Committee Meeting, McLean, VA; September 9th
–12th, 2002
[2] “Proposed Draft Text for D-008 version of V.MoIP”, TR-30.1/02-09-114, TR.30.1 Committee
Meeting, McLean, VA; September 9th –12th, 2002