Serial Message Architecture
Original Publication Date: 1995-Apr-01
Included in the Prior Art Database: 2005-Mar-30
Isenberg, JF: AUTHOR [+3]
Certain computer applications require a means for rapidly exchanging a program-supplied request message and a response message from a control unit. Using conventional I/O for this purpose is too slow because it involves multiple round trip delays on the link connecting the channel and the control unit.
Serial Message Architecture
computer applications require a means for rapidly
exchanging a program-supplied request message and a response message
from a control unit. Using conventional I/O for this purpose is too
slow because it involves multiple round trip delays on the link
connecting the channel and the control unit.
System/390* systems, the needed message exchange could
be accomplished using the channel program protocol equivalent to a
channel program consisting of a write command (to write out the
request message) command-chained to a read command (to store the
response message). However, this method does not provide sufficient
performance for applications for which the message exchange is
required to be synchronous with the issuing CPUs instruction stream.
With the IBM ESCON I/O Interface, using the channel program protocol
to accomplish the message exchange requires 4 round trips on the
link, 11 transmission frames, and 212 bytes of overhead in the
information on the link. The combined length of the request and
response messages is as short as 30 bytes. At a distance of 50
meters, assuming a 200-Mbit/s ESCON link, the time consumed by this
overhead is 12.6 microseconds, compared to a transmission time of 1.5
microseconds for the 30 bytes of useful information. In addition,
there is channel and control unit overhead associated with each
disclosed herein accomplishes the same message
exchange with only one round trip on the link, two transmission
frames, and 26 bytes of overhead. The overhead time is thus reduced
to only 1.8 microseconds at 50 meters distance. Since there are only
two transmission frames in this exchange, compared to 11 frames using
the channel program protocol, this invention substantially reduces
the channel and control unit time to process the transmission frames.
invention provides a mechanism which allows a generalized
(multipath, multidestination, multidevice) interface to be used
synchronously to a new processor instruction which guarantees, in a
recoverable fashion, interprocessor serialization. The mechanism is
based on the synchronous exchange of a request message and a response
message between a message channel and a message control unit which
are interconnected by a point-to-point link or switched
point-to-point interconnect which conforms to the ESCON link level.
exchange protocol of this invention is defined as a
new device level which uses the ESCON link level. Message exchanges
can be carried out on the same switched interconnect concurrently
with channel program execution by other channel and control unit
pairs. The ESCON device-level descriptor field is the means for
allowing multiple device levels to coexist on the same interconnect.
The messages of this invention have a device-level descriptor whose
value differs from that used in frames associated with the no...