Telecommunications Industry Association (TIA)
TR-30.1/01-05-0
Wilmington, Delaware, 30th April - 4th May 2001
COMMITTEE CONTRIBUTION
Technical Committee TR30 Meeting
SOURCE:
Conexant Systems Inc.
TITLE:
Flow Control for Non-controlled Links
DISTRIBUTION:
TR30.1 Meeting attendees
CONTACT:
Keith Chu
Voice: +1 (949) 435-3163
Fax:
+1 (949) 483-3667
Email: keith.chu@mindspeed.com
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Abstract
This contribution describes how MoIP modem pairs can provide a rudimentary type of flow control for the
situation where the end-point modems have elected not to enable this function.
Copyright Statement
The contributors grant a free, irrevocable license to the Telecommunications Industry Association (TIA) to
incorporate text contained in this contribution and any modifications thereof in the creation of a TIA standards
publication, to copyright in TIA's name any standards publication even though it may include portions of this
contribution, and at TIA's sole discretion to permit others to reproduce in whole or in part the resulting TIA
standards publication.
Introduction
This contribution describes how MoIP modem pairs can provide a rudimentary type of flow control for the
situation where the end-point modems have elected not to enable this function.
For MoIP scenarios 2a, 3, 4 and 5 the link layer flow control is negotiated locally between the modem/gateway
pairs. In each of these cases it is the flow control function that determines the throughput of data end to end.
Flow control is important if the modem pairs connect at either different modulations or data rates. An application
that makes extensive use of proprietary or even no link layer protocols is that of gaming. Her in order to save on
end-to-end latency flow control, ARQ and compression may be disabled. This contribution provides two
mechanisms by which if no protocol is negotiated between the gateway/modem pairs that the throughput
problem can be significantly mitigated.
Possible methods of mitigating lack of protocol
1. After full data mode is established, the gateways examine the data rates and rate renegotiate (or retrain
if necessary) such that the M1 transmit data rate is ≤ than M2 receive data rate and M2 transmit data
rate is less than M1 receive data rate.
2. Flow control between modems can be achieved by using rate renegotiations as a mechanism to slow
down a remote transmitter.
Both of the above techniques described above can be used either independently or together to mitigate the net
effects of no flow control.
If no data compression is negotiated across the link, then the simplest solution is maintain this status quo. There
does not seem to be any additional advantage of adding compression just for the gateway to gateway portion
and it only adds to the latency, which is against the intent for not enabling it in the first case.
Summary
This contribution provides some ideas on how to handle situations whereby no link layer protocol is negotiated
between gateway/modem pairs.
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