Browse Prior Art Database

Low Latency Flow Control for Multistage Switches

IP.com Disclosure Number: IPCOM000109583D
Original Publication Date: 1992-Sep-01
Included in the Prior Art Database: 2005-Mar-24
Document File: 1 page(s) / 65K

Publishing Venue

IBM

Related People

Finney, DW: AUTHOR

Abstract

Described is a method of controlling the forwarding of messages when the network is busy (the output port is not available) without adding latency to the normal case when the network is free.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 58% of the total text.

Low Latency Flow Control for Multistage Switches

       Described is a method of controlling the forwarding of
messages when the network is busy (the output port is not available)
without adding latency to the normal case when the network is free.

      The method is based on the network always sending messages in
bursts of N bytes between switches (no idle cycles between the first
and last bytes) and each input port having the capability to buffer
at least one complete burst.

      The main concept is that as soon as the input port receives the
first byte of a burst, it indicates the associated buffer is full
(since it knows the remaining bytes will be received immediately).
Also, as soon as a connection is made through the switch to the next
output port, the buffer is considered empty, since all bytes will be
immediately transferred.  This allows a buffer to be considered first
full and then empty before the last byte of the burst has been
received, because the port knows the last byte will be transferred to
the next stage before it could be overwritten by a second burst (even
in a one-buffer port).

      Any time the input port does not have any empty buffers, it
sets its flow control signal active, which inhibits the previous
stage from beginning the next burst.

      If the number of clocks required to transmit one burst is
greater than the arbitration time for the next output stage plus the
maximum cable delay (to transmit the flow control si...