Routing switch

Details Routing switch Routing switch

1997-08-21

2001-08-21

Nguyen, Chau (Department: 2663)

Multiplex communications

Pathfinding or routing

Switching a message which includes an address header

C370S393000

Reexamination Certificate

active

06278709

ABSTRACT:

FIELD OF THE INVENTION
The present invention relates to a routing switch for use in a network for transmitting serial message packets between a source node and a destination node. The invention relates particularly, but not exclusively, to such a network where message packets are transmitted from a single source node to a single destination node, and where packets are also transmitted from a single source node to multiple destination nodes.
BACKGROUND OF THE INVENTION
For high speed networks, particularly in the home, there is a need for a communication system which is efficient, which minimises the bandwidth required in the cables (and the corresponding radiation from the cables), and which minimises the cost and complexity of any repeaters, bridges, or routing switches in the network, and which places no constraint on the topology required of a network in order that the network functions.
A number of bridging, routing and switching technologies exist which have some, but not all, of the desirable properties required for a high speed network.
IEEE 1394 does not have a routing network, but is logically a bus with every node seeing every bit. Many of the packets are asynchronous packets which go from one source to one destination, and this is very wasteful of cable bandwidth. IEEE 1394 has bridges to isolate logical buses, but the bridges are not simple devices and are likely to be expensive.
ATM uses switches and makes efficient use of bandwidth. However, ATM is designed for a global network, and consequently has complications therein far beyond what is necessary for a high speed network in the home.
The STC
104
, used for IEEE 1355, is much simpler than ATM and this makes it possible to build the STC
104
with 32 full-duplex serial ports. The chip is, however, one of the largest chips made, and has around 28 k bits of memory—memory all made up of special registers. The STC
104
only provides for unicast packets, i.e. where message packets are transmitted from a single source to a single destination. Multicast packets where transmissions from a single source to multiple destinations or broadcast where transmission is from a single source to all destinations is desirable for a home network.
The ICR C
416
is a simple routing switch, with physical routing which requires no initialisation. The ICR C
416
uses one byte of header for each routing switch between source and destination, stripping the header at each switch. Like the STC
104
, output ports can be grouped, so that several ports become logically a single port with higher bandwidth. Again, however, like the STC
104
it supports only unicast, (and not multicasting or broadcasting of packets).
Thus, it would be desirable to provide a routing switch suitable for a high speed network, particularly in the home, which was capable of routing packets or cells from a source to a single destination (i.e. unicast), to multiple destinations (i.e. multicast) and to all destinations (i.e. broadcast). In addition, for use in a home network, any routing switch must be compatible with any topology the untrained user arbitrarily constructs.
The routing switch must be capable, for use in a home network, of minimising bandwidth, power consumption, and RFI emissions, so that traffic should only travel on links necessary for the connection. In addition, it is essential that costs must be minimised, within the constraint of providing the necessary functionality and efficiency.
SUMMARY OF THE INVENTION
Thus, it is an object of the present invention to provide a routing switch which enables headers associated with message packets to be used efficiently to determine which input port is to be connected to which output port for a given input packet message or cell.
Thus according to an aspect of the present invention there is provided a method of routing a message packet including a header from an input to an output of a routing switch, the method comprising the steps of storing a plurality of sets of routing information, each set being associated with one value of the header, accessing a stored set of routing information in dependence on the header of the message packet to be routed and routing the message packet to one of a plurality of outputs of the routing switch in dependence on the accessed set of routing information.
This aspect of the invention also provides a routing switch having a plurality of inputs for receiving message packets each including a header comprising storage circuitry for storing a plurality of sets of routing information, each set being associated with one value of the header, address circuitry responsive to the header of the message packet to be routed and for accessing the stored set of routing information associated therewith and connection circuitry for routing the message packet to the at least one of the plurality of outputs in dependence on the accessed set of routing information.
Once the decision on which output port the input message or packet is to be directed to is made, the ports are connected by a connection mechanism such as a cross bar switch.
The present invention allows the use of only a small amount of memory for each output port, and uses that memory to determine whether that port is associated with the incoming routing information given by a single byte, in the preferable embodiment, of routing header. The memory is initialised for physical routing of unicast packet/cells only, so that a network mapping program, running from one (or more) nodes of the network can determine the network and set up the sets of routing information in the routing tables accordingly.
In a routing network, there are sometimes provided multiple parallel collections between different routing switches, and also it may well be that it is possible to transmit a message packet from one routing switch to another routing switch via more than one output path. It may well be that multiple routing paths are provided between two routing switches because there is sufficient traffic between the routing switches to warrant multiple connections. A technique used both in the STC
104
and the ICR C
416
is known as grouped adaptive routing, whereby if there are several connections between two switches, a packet/cell addressed to one of them can use any other group of links which is available, rather than having to wait for the addressed link to become available.
On the STC
104
and ICR C
416
, grouped routing is used for unicast. However, grouped routing would be even more useful in the home network if used for multicast. This is because a multicast packet/cell has to wait until all the addressed output ports to which it is to be output from are available, and there is a much better chance of one of a group being available than of a particular link being available.
It is thus another object of the present invention to provide a routing switch in which grouping can be used with both unicast and multicast packet/cells.
According to an aspect of the present invention there is provided a method of routing a message packet from an input to an output of a routing switch, the message packet including a header indicative of the output of the routing switch to which the message packet is to be routed, wherein the routing switch has a plurality of outputs suitable for transmitting the message packet, the method comprising the step of routing the message packet to any one of the plurality of outputs if the header indicates the message packet is to be routed to a particular one of the plurality of outputs.
This aspect of the invention also provides a routing switch having a plurality of inputs for receiving message packets each message packet including a header indicative of at least one of a plurality of outputs of the routing switch to which the message packet is to be routed, the routing switch comprising storage circuitry for storing a plurality of sets of grouping information, each set being associated with one output of the routing switch, wherein for each output the set of grouping information groups other outputs of the routing switch addit

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