Browse Prior Art Database

3990 Serial Input/output Distance Measurement

IP.com Disclosure Number: IPCOM000105673D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-20
Document File: 2 page(s) / 29K

Publishing Venue

IBM

Related People

Beardsley, BC: AUTHOR [+6]

Abstract

The Input/Output (I/O) controllers of today support channel-to-control unit distances of several kilometers. At these distances, the precise timing of the reconnect during a channel program is very important in that it has a substantial effect on the performance of the operation.

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3990 Serial Input/output Distance Measurement

      The Input/Output (I/O) controllers of today support
channel-to-control unit distances of several kilometers.  At these
distances, the precise timing of the reconnect during a channel
program is very important in that it has a substantial effect on the
performance of the operation.

      The controller uses the time delay of the cables in order to
accurately calculate the reconnection time after an operation in
order to minimize the amount of time that data is stored in the data
transfer buffer.  This is important since the data transfer buffer
cannot be used for any data transfers to or from the channel during
this time.  Using the maximum cable length delay causes unnecessary
delays when a shorter cable is actually used.

      The usage is maximized since the cable delay can be accurately
calculated for each cable.  The control unit determines the distance
between the channel and the control unit be measuring the time
between when a disconnection status signal is sent and the accept
signal is received.  Some processing time at the channel is assumed.
The propagation delay of signals on the link is known.  The cable
distance can then be calculated.