Browse Prior Art Database

Channel To Channel Computer Communications Without a Separate Adapter

IP.com Disclosure Number: IPCOM000121890D
Original Publication Date: 1991-Oct-01
Included in the Prior Art Database: 2005-Apr-03
Document File: 3 page(s) / 157K

Publishing Venue

IBM

Related People

Sachs, MW: AUTHOR

Abstract

A technique is described whereby channel-to-channel communications between computer systems, using serial input/output (I/O) architecture, is provided without the need for a separate channel-to-channel adapter or multi-systems communications unit. The same channel is used for both channel-to-channel communications and normal I/O operations. Channel microcode is utilized which contains a section to execute normal channel I/O functions as well as a section which executes channel-to-channel functions.

This text was extracted from an ASCII text file.
This is the abbreviated version, containing approximately 38% of the total text.

Channel To Channel Computer Communications Without a Separate Adapter

      A technique is described whereby channel-to-channel
communications between computer systems, using serial input/output
(I/O) architecture, is provided without the need for a separate
channel-to-channel adapter or multi-systems communications unit.  The
same channel is used for both channel-to-channel communications and
normal I/O operations.  Channel microcode is utilized which contains
a section to execute normal channel I/O functions as well as a
section which executes channel-to-channel functions.

      In prior art, such as used in IBM System/360* or System/370*
computer systems, the parallel channel to control unit interface
(OEMI) is not symmetrical between channels and control units at the
physical link level. Therefore, it is not possible to cable two
channels together and have them communicate, even if the
channel-to-channel communications function were incorporated into the
channels, without the use of a channel-to-channel control unit
adapter for both channels.  In contrast, the link level of serial I/O
architecture is completely symmetrical, both physically and
logically.  If two channels are cabled together, exchange of
link-level communications is possible.  However, neither the device
level of the serial I/O architecture nor higher levels of channels
and software are symmetrical. Therefore, for two channels to
communicate, one of them must take on the appearance of a control
unit.  The concept described herein provides the channel-to-channel
communications without a physically distinct channel-to-channel
adapter.

      The essence of the concept is to provide a means of channel
determination, for each I/O operation, whether the operation is to a
normal I/O device or to a channel-to-channel function.  Channel
microcode contains a section which executes normal channel functions
and a section which executes channel-to-channel functions.  A
computer may direct each operation at a subchannel, which is a
logical representation of the device.  Associated with the
architected subchannel is an unarchitected area, frequently called a
unit control word (UCW), which contains internal channel control
information associated with the device and current I/O operations.
The technique utilized to eliminate a separate adapter adds an
indicator to the UCW which indicates whether the associated
subchannel represents channel-to-channel function.  This is called a
CTC subchannel.

      For communications between channels on two systems, a pair of
subchannels, one in each system, is assigned and designated a CTC
subchannel and a normal subchannel. Reference to the CTC subchannel,
either by subchannel identification (ID) in its own system or by
device address from the other system causes the CTC function to be
executed.  A particular channel can be used for channel-to-control
unit communications, channel-to-channel communications in which the
subc...