Dale L. Skran wrote:
Sec. 3.4 - Flow Control when using UDP The formal liaison comments on maxBitRate. This represents the maximum (peak) fax bit rate that the unit can absorb, and should not be exceeded over a period of time.
maxBitRate is an extremal-bound peak-rate traffic descriptor which provides a crude form of open-loop flow control. It is really only useful across networks where traffic is very smooth and predictable. Across a small corporate WAN, maybe; the Internet, no. :-) It should therefore be set to as large a value as is sensible, based on what the endpoint knows of the connection, which is usually just the speed of the first segment, if it even knows that much.
It is interesting that you are concerned about UDP flow control as this is a major issue with UDP. TCP can be relied on to throttle a high-speed internet fax device to match a 4.8 kbps G3 device, but with UDP it is unclear how this will happen.
Here's an interesting paper by Jamshid Mahdavi and Sally Floyd on UDP rate control: TCP-Friendly Unicast Rate-Based Flow Control http://www.psc.edu/networking/papers/tcp_friendly.html
Compliant terminals should not need a UDP throttle.
I don't understand this. Are you assuming that the gatekeeper will perform explicit network-state measurement and rate control using ACF and BRQ, therefore taking the responsibility for UDP flow control completely away from the endpoint, or are you referring to some kind of currently nonexistent message that directly throttles the transmitter (I haven't seen the Liaison report)? Otherwise, assuming we're talking about an RTP/RTCP stream here, RTCP and a few other measurements provide sufficient feedback for an endpoint to perform implicit measurement and control of its transmission rate.
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