On Wed, 17 Mar 1999, Henrik Olsen wrote:
> With a switch you really really want to use Half Duplex anyway, since full
> duplex has no congestion control, so will grind to uselessness once your
> load increases.
There is a technical fix to this.
Most newer Ethernet adapters support Flow Control packets. These packets
look like multicast packets with a unique protocol type. The payload is
a pause value, and they act to shut off the transmitter for the specified
period (usually the maximum period, 0xffff). If the pause value is '0' the
transmitter resumes activity.
A link partner that has flow control capability advertises the 0x0400 bit
during autonegotiation (e.g. 0x05e1 instead of 0x01e1).
Most of the flow control functionality must be implemented in hardware, as
the transmitter must be stopped within a packet or two. Typically the
driver needs only to enable the feature, and there is no harm in always
enabling it.
Donald Becker [EMAIL PROTECTED]
USRA-CESDIS, Center of Excellence in Space Data and Information Sciences.
Code 930.5, Goddard Space Flight Center, Greenbelt, MD. 20771
301-286-0882 http://cesdis.gsfc.nasa.gov/people/becker/whoiam.html
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