Trailer protocol on 4.2BSD

[walsh%bbn-labs-b at sri-unix.UUCP]

From:  Bob Walsh <walsh at bbn-labs-b>


I would like to find out if anyone has used trailers and found them
beneficial.  My own tests have shown that they have little effect on
throughput.

My tests used a VAX 780 and a VAX 750 connected to an ethernet
by Interlan controllers.  I have tried two programs. The first is my own
benchmarking program to measure bit rates.  The other is ftp.  I used the
benchmarking program to measure bit rates when writing 1, 2, 4, 8, 16, 32,
64, 128, 256, 512, 1024, and 2048 byte sized buffers onto a TCP connection.
For the different sized buffers, sometimes trailers produced higher bit rates
and sometimes trailers produced lower bit rates.  Trailer throughput was
always within 3% the throughput achieved without trailers.  Similar results
were found with ftp.  During these tests, socket send and receive
buffering high water marks were set at 4096 bytes.

Does a different hardware configuration bring forth the 200Kb/sec gain
mentioned in the "Networking Implementation" paper found in volume 2C?
Yes, I had remembered to turn trailers on for both VAXes.

bob walsh