Browse Prior Art Database

Input/Output Link Architecture Extensibility

IP.com Disclosure Number: IPCOM000105442D
Original Publication Date: 1993-Aug-01
Included in the Prior Art Database: 2005-Mar-19
Document File: 2 page(s) / 131K

Publishing Venue

IBM

Related People

Elliott, JC: AUTHOR [+4]

Abstract

An Input/Output (I/O) link architecture may be divided into two levels of function: the link level and the device level. The link level describes the physical characteristics and associated functions and protocols for the transmission and reception of frames. The device level deals with higher level functions and protocols; for example, one type of device level may support a channel-to-control-unit model, with commands, status, data transfer, etc. while another type of device level might support a general message passing function, with totally different protocols, such as a simple request-response protocol.

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This is the abbreviated version, containing approximately 41% of the total text.

Input/Output Link Architecture Extensibility

      An Input/Output (I/O) link architecture may be divided into two
levels of function:  the link level and the device level.  The link
level describes the physical characteristics and associated functions
and protocols for the transmission and reception of frames.  The
device level deals with higher level functions and protocols; for
example, one type of device level may support a
channel-to-control-unit model, with commands, status, data transfer,
etc. while another type of device level might support a general
message passing function, with totally different protocols, such as a
simple request-response protocol.

      It is desirable that units which obey different protocols or
have differing transmission frame formats to be able to coexist on a
single instance of an I/O interconnection network.  It is also
desirable that there be a means of introducing extensions to existing
protocols in a way which provides for coexistence between older and
newer units.

      A significant problem arises when units which obey different
protocols or have different frame formats are connected to the same
network.  Due to a configuration error or other kind of error, a
connection may be inadvertently created between two units which have
incompatible frame formats and protocols.  When the connection is
created, it is essential that the recipient of the frame which
created the connection be able to detect this incompatibility and to
signal the error to the sender.  This error signal must be
understandable by all units, regardless of which protocol set they
obey and regardless of their frame format.

      Described is a means for identifying the specific device-level
protocol which a unit uses, the specific link-level address format
being used, and the specific link-level frame format being used.
Also described is a means for enabling units with different protocols
and frame formats to coexists on the same I/O interconnection
network.  The approach described is specifically applicable to a
circuit-switched interconnection network although some aspects of it
are also applicable to other types of interconnection network.

      The specific device-level frame format and protocol which are
being used are identified by a device-level identifier field which is
part of the link header of every frame containing device-level
information.  Since the device-level identifier is in the link
header, it is always in the same place in every frame which has the
same link-level format and is defined in the same way, regardless of
the device-level protocol and frame format used by the sender of the
frame.  The device-level identifier is a key indication, because it
fundamentally describes both how the recipient must interpret various
fields within the frame and the protocols to be used in dealing with
the frame.

      Defining the device-level identifier as part of the link-level
information, r...