ITU - Telecommunication Standardization Sector
PCM02-018
STUDY GROUP 16
Mississauga, Canada, May 14th – 17th 2002
QUESTIONS:
Q.11/16
SOURCE:
Cisco Systems
CONTACT:
Herb Wildfeuer
Phone: +1 805 961 3620
Fax:
+1 805 961 3600
Email: [email protected]
TITLE:
V.MoIP Trans-Compression Configuration Rules
__________________
ABSTRACT
This document presents section 2 of TR30.1 document 102040.doc which some clarifications and
modification of scenario 4 rules to include range of maximum compression.
PCM02-018
Abbreviations used in this contribution
G1
On-ramp Gateway on calling leg
G2
Off-ramp Gateway on called leg
M1
Originating Modem on calling leg
M2
Answering Modem on called leg
MoIP
Modem over IP
PSTN Public Switched Telephone Network
MR
Modem Relay
TLP
Transport Layer Protocol
XIDdef XID corresponding to the default compression parameters
1
CPoff-ramp
Denotes compression parameters negotiated locally on the off-ramp leg
CPon-ramp
Denotes compression parameters negotiated locally on the on-ramp leg
Introduction
Generic framework for compression negotiation was laid out in Ref. [1]. This contribution presents the
procedures for selecting the trans-compression parameters for V.MoIP.
2
Transcompression Configuration for Scenarios 3c, 4, and 5
G1P: Represents negotiation posture of G1 when it performs XID negotiation with M1. This is the
“maximum” compression options that can be specified by the gateway in XID frames for negotiation
with M1.
G2P: Represents negotiation posture of G2 when it performs XID negotiation with M2. This is the
“maximum” compression options that can be specified by the gateway in XID frames for negotiation
with M2.
Negotiation posture can be represented as a vector as follows:
GxP=(GxV44TxDictionary, GxV44TxStringLength, GxV44TxHistory, GxV44RxDictionary,
GxV44RxStringLength, GxV44RxHistory, GxV42bisDictionary, GxV42bisStringLength,
GxMNP5Support)
Consider vectors G1 and G2 representing the trans-compression capability of a gateway as follows:
G1 = (G1V44TxDictionary, G1V44TxStringLength, G1V44TxHistory, G1V44RxDictionary,
G1V44RxStringLength, G1V44RxHistory, G1V42bisDictionary, G1V42bisStringLength,
G1MNP5Support)
G2 = (G2V44TxDictionary, G2V44TxStringLength, G2V44TxHistory, G2V44RxDictionary,
PCM02-018
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G2V44RxStringLength, G2V44RxHistory, G2V42bisDictionary, G2V42bisStringLength,
G2MNP5Support)
If a compression functionality is not supported, its corresponding parameters would be set to zero in
above vector. When the values are non-zero, transcoding may occur from any supported compression
type (up to supported values) to any other supported compression type. Furthermore, transcoding
capabilities are symmetric, meaning that when a transcoding capability is indicated, the gateway may
transcode from a supported compression type to another supported compression type regardless of
whether the conversion is for data flow from telephony to IP side or in the reverse direction.
Consider vector operation MIN defined as follows:
V = (v1, v2, v3, ….)
U = (u1, u2, u3, ….)
MIN(V, U) = (min(v1, u1), min(v2, u2), min(v3, u3), ….)
For the various scenarios, the compression function shall be setup as follows:
Scenario 3c:
G1P = G1
G2P = G2
GIP = MIN (G1, G2)
Compression coding on IP leg would be symmetric (same by either gateway) and based on GIP
element values and would use the set of GIP elements corresponding to V44 if available, else V42bis,
else MNP, else NONE in this specified order.
Scenario 4:
For V44 elements:
G1tx >= G1Ptx >= MIN(G1tx, G2rx)
G2rx >= G1Prx >= MIN(G1tx, G2rx)
G2tx >= G2Ptx >= MIN(G2tx, G1rx)
G1rx >= G2Prx >= MIN(G2tx, G1rx)
For V42bis and MNP5 elements:
G1P = MIN (G1, G2)
G2P = MIN (G1, G2)
Scenario 5:
G1P = Gd
G2P = Gd
Where Gd is the capability vector of the double transcompression gateway.
The above procedures for configuring transcoding function applies only when both on-ramp and offramp telephony links are using V42 link layer.
PCM02-0XX
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3
References
[1]
A. Zakrzewski et. al., “Compression Negotiation for V.MoIP”, Albuquerque TIA TR30.1
contribution
[2]
M. Garakani et. al., “Configuration of Transcompression Function”, Albuquerque TIA TR30.1
contribution
PCM02-0XX