WO1996038959A1

WO1996038959A1 - Network and method for implementing a workgroup

Info

Publication number: WO1996038959A1
Application number: PCT/EP1996/002339
Authority: WO
Inventors: Tadhg Creedon; Anne O'connell; Eugene O'neill; Vincent Gavin; Ciaran Murphy; John Hickey
Original assignee: 3Com Ireland
Priority date: 1995-05-31
Filing date: 1996-05-30
Publication date: 1996-12-05
Also published as: GB2316281A; GB9510933D0; AU7513896A; GB9725273D0

Abstract

Each port in a switch or bridge is provided with an additional identifier whereby ports may be grouped together to create a separate virtual network. Each source port adds additional addressing bits to a packet, which addressing bits are indicative of the work group of the source port. This is preferably done as the packets enter a switch or bridge. Each destination port has logic which checks its own additional addressing bits against the additional addressing bits in the packet and if there is disparity at that stage it ignores the packet. The efficiency of data handling is thus greatly improved.

Description

NETWORK AND METHOD FOR IMPLEMENTING A WORKGROUP

The present invention relates to computer networks and more particularly networks which are usually known as local area networks (LANs).

Local area networks are now well known and can vary in size considerably. With a network of anything more than a few ports, it is customary to separate the network into operational areas so that those devices which will normally wish to share information and/or send information to each other are grouped together but are able to communicate with other portions of the network via a device known variously as a bridge or switch. One of the features of a bridge or switch is that it contains an up-to-date list of all device addresses and the ports to which those devices are connected.

For large networks, the network is separated not only notionally by the bridges and switches and even by routers but also physically into a plurality of separate housings which are interconnected in order to form the network. Even with this degree of physical separation of parts of the network, it is not possible to efficiently handle all the traffic which may occur with large networks particularly when multicasts or broadcasts are being transmitted. The present invention provides a method whereby each port in a switch or bridge is provided with an additional identifier whereby ports may be grouped together, to create a separable network.

In our preferred embodiment, the grouping of the ports is in fact achieved by adding additional addressing bits to a packet, which additional addressing bits are indicative of the work group of the source port. The destination port logic checks its own additional addressing bits against the additional addressing bits in the packet and if there is a disparity at that stage it ignores the packet.

It is intended that the additional addressing bits be added by the port logic as the packets enter a switch or bridge so that the extra addressing bits do not appear on the network and thus the packets as seen by the network conform with the normal network standard.

In order that the present invention be more readily understood, an embodiment thereof will now be described by way of example with reference to the accompanying drawing, in which:-

Fig. 1 shows diagrammatically a computer network inco orating a number of bridges or structures; and

Fig. 2 shows one embodiment of a bridge or switch used in the network shown in Fig. 1;

The preferred embodiment of the present invention assumes that a local area network will be separated up into a number of discrete areas using bridges or switches and that the ports incorporated within one or more areas will be provided as ports on a box which is also provided with its own microprocessor and CAM. This is shown in Fig. 1 where a network is shown as being formed by a main network 1 to which is attached bridges or switches 2 and 3. Each switch supports a number of devices attached to ports of the switch in a conventional manner. It is common to supply multi-port bridges or switches with a predetermined number of ports but problems arise when a user wishes to connect more devices to a bridge than there are ports available. In the past this has required replacing the multi-port bridge with another having a greater number of ports or adding another complete bridge.

Users are not always happy with this approach as it tends to increase the cost to them. We propose that a bridge or switch be assembled from one or more identical modules and for the sake of this example we will use four identical modules ABCD as shown in Fig. 2 which when connected together will function as a single bridge or switch as far as the network is concerned. Each module is provided with a number of ports to which devices can be connected. In Fig. 2 we show that there are ten ports numbered 0-9 for each module for this purpose although it will be noted that port 0 of module A is in fact the port which connects to the rest of the network.

Each module is also provided with an additional port 10 which is used as a communications port with access to a local bus 11 so that data can be transferred from module to module. In this any additional ports can be provided for a bridge or switch simply by supplying one or more modules and connecting them to the data bus 11.

As is customary with local area networks, the microprocessor and CAM of each module knows the relationship between all ports and the MAC addresses of all devices attached thereto for its own module.

In this embodiment, the microprocessor and CAM of each module has built up a table of port and device addresses in the normal fashion. In addition to this normal information, we propose each entry in the table indicative of the device MAC address and its associated port will also contain additional addressing information which will be used to associate ports with each other even though they may be separated from each other by a bridge or switch. The amount of additional addressing required is a function of the number of work groups. For the purposes of this example we will assume that the additional addressing is in the form of a four bit word. A four bit word will allow up to 16 work groups. Other sizes of word from a single bit to a much larger word could also be used depending on the user's requirements. In this way, when a packet is received by a box and inspected by the microprocessor, the microprocessor inspects the destination address in the packet for additional addressing information in the form of a four bit word which is indicative of the work group of the source port. Packets with no known destination address for that box can be switched based on the additional addressing information to one of a number of down links no matter where they are on the stack.

With this system, multicast packets going across work groups are discarded by destination ports simply by checking the additional addressing information of the packet with the additional addressing information relative to the port and if there is disparity the port ignores the packet. This has particular advantages in the case of broadcast and multicast packets. These are made visible to all destination ports in accordance with the rules of the network but only those transmitters within the same work group i.e. those with the same additional addressing information take the packets. In this way, the efficiency of the network can be improved.

The use of additional addressing bits indicating the work group of a port allows ports to be grouped together functionally but each group of ports to be separable from each other although all ports will be on the same bridge or switch. It also allows devices connected to ports of one bridge or switch to be functionally associated with devices or another bridge or switch. Each work group on a switch is provided with its own port for communicating with the rest of the network and in this way virtual networks can be created. The communications port need not be port 0 as shown in the drawings. This is shown in Fig. 1 where the switch or bridge 2 has only one down link to the rest of the network whereas switch 3 has two down links one from module A and one from module D indicating two work groups present in switch 3. In this example, since a four bit word is being used as additional addressing it will be appreciated that up to 16 down links would be present from just one switch.

The above described arrangement works well with an ethernet network. It is possible to modify the arrangement in order to enable a switch such as the one described in relation to Fig. 2 to be used in an Asynchronous Transfer Mode (ATM) network. In other words, the main network 1 in Fig. 1 could be either an ethernet network or an ATM network.

An ATM network takes a packet and breaks it up into smaller blocks each with its own header. The blocks are then sent down a single down link together with blocks from the parts of the network in a multiplexed fashion. By relating the work group identifiers mentioned above to virtual circuit identifiers in the headers of the ATM blocks one could supply data from switch to switch via an ATM network.

One could supply data from switch to switch via a ATM network mamtaining several different networks but with only one connection rather than one connection per network.

Work groups can also be used to improve the security of unicast traffic and there is no need to construct a switch or bridge from a number of modules. The general principles outlined apply to all bridges and switches.

Claims

CLAIMS :

1. A network wherein each port can be provided with additional addressing information allocating said port a workgroup, whereby transmissions addressed to a specific workgroup or workgroups can be discarded by switches and ports not associated with said workgroup or workgroups.

2. The network of claim 1, wherein each switch is linked to the network by one port for each workgroup associated with said switch, whereby a transmission intended for a specific workgroup is only permitted to enter said switch via a port associated with said workgroup.

3. A method for increasing efficiency in a network, whereby additional information can be added to port addresses corresponding to a workgroup for said port, whereby transmissions addressed to a specific workgroup or workgroups can be discarded by switches and ports not associated with said workgroup or workgroups.

4. The method of claim 3, wherein each switch is linked to the network by one port for each workgroup associated with said switch, whereby a transmission intended for a specific workgroup is only permitted to enter said switch via a port associated with said workgroup.