Dynamic Switch Cascading
Original Publication Date: 1995-Mar-01
Included in the Prior Art Database: 2005-Mar-30
Franaszek, PA: AUTHOR [+1]
Disclosed is a means of extending the connectivity of a switched I/O configuration.
Dynamic Switch Cascading
a means of extending the connectivity of a
switched I/O configuration.
invention applies to a computer system in which processors
and I/O devices are interconnected by means of dynamic switches.
Each processor memory has a number of channels through which data are
passed through and from the switches. Groups of I/O devices are
managed by control units. Each control unit has some number of
interfaces to connections to the switch. For each I/O operation, a
connection through the switch is established between a channel and a
control unit interface. The switch contains a number of ports
interconnected by a connection matrix. Each channel and each control
unit interface in the system is connected to one port on the switch.
Each channel and each control unit interface is assigned a unique
link address. A unit (channel or control unit) wishing to make a
connection to a destination unit sends a connect request message
containing the link address of the desired destination. The switch
matrix controller uses the link address to determine the port to
which the desired destination unit is attached and makes a connection
between the port of the requesting unit and the port of the
destination unit. It then sends the connection request message to
the destination. The connection remains until it is explicitly
broken by a disconnect message. The switch maintains awareness, at
all times, of which ports are involved in connections. If the port
corresponding to the desired destination is already connected to
another port, the switch sends a switch-busy message to the unit
which requested the connection and no connection is made.
There may be
system configurations which require greater
connectivity than can be provided by a single switch. Connectivity
can be increased by using multistage networks of switches. This
invention is the means to create a connection through two or more
switches. The Figure shows an example of such a network, containing
invention, the link address supplied and recognized by
channels and control units continues to be the address of the
destination unit as it is with a single switch. Each switch between
the source and the destination of a message has to translate the
address to determine the correct outgoing port but the endpoint
channel and control unit do not have to know or care whether zero,
one, or more switches are on the way.
invention, each switch treats the destination link
address in the connection request message as composed of an area code
and a unit link address. Each switch is assigned a unique area code
value and all channels and control units attached directly to that
switch have the same area code value as part of their link addresses.
In the Figure, the two switches have area code values 1 and 2. Each
switch is given its area code value as part of the system