Ref: 03250425
Title: IB/3 Serial Link Overhead & Buffer Space Overflow
Date: 6/2/88

Copyright 3Com Corporation, 1991.  All rights reserved.

The following answers questions about IB/3 serial link overhead
and buffer space overflow.

Q: How much packet overhead (that's always present) is there on the serial
link between IB/3's?

A: For a minimum size packet (60 bytes), the overhead is around
10%.  For probe packets, the overhead is approximately 20%.

For a maximum sized packet, the overhead is approximately .5%.
For probe packets, the overhead is about .9%.

Overhead is larger if you take into account bit-stuffing.


Q: How large are the buffers in the IB/3's?

A: 1500 bytes, excluding headers and CRC.


Q: How many bytes may be sent to a pair of IB/3's linked by a 9600 baud
line before buffer overflow occurs?

A: For 60 bytes packets, 960 bytes.  For 1500 bytes packets, 24000 bytes.


Q: If traffic is NFS, can we determine the number of packets which may be
sent before buffer overflow occurs?

A: No.  The answer depends on the NFS packet size, which itself depends
on the application.
