WO1998004070A1

WO1998004070A1 - Multisegment repeater

Info

Publication number: WO1998004070A1
Application number: PCT/GB1997/001996
Authority: WO
Inventors: Nicholas Stapleton; Peter Wilson; David R. Smith; Patrick Overs; Steven Brewer
Original assignee: 3Com Ireland
Priority date: 1996-07-23
Filing date: 1997-07-23
Publication date: 1998-01-29
Also published as: GB9615421D0; EP0931400A1; GB2332840A; GB9904154D0

Abstract

A repeater device for a communications network comprising a plurality of input and output ports, a core means for repeating a data signal received by an input port of the device to one or more of the output ports of the device, port logic circuitry for providing port configuration control and a media access control means for controlling the transmission and reception of data by the device characterised in that the core means is in the form of a plurality of core elements each for receiving a data signal for an input port, and in that there is a single port logic control circuit which is shared by all core elements.

Description

Multisegment Repeater

The present invention relates to computer networks or local area networks (LANs) in which a plurality of users are connected together to enable them to communicate with each other.

In LANs there are provided devices known as repeaters which enable the users of the network to communicate with each other. In particular, repeaters comprise a number of ports, to each of which a user may be connected. The repeater functions to receive communications on each of its ports and to output each received communication on all of its other ports. In this manner, each communication transmitted by each user on the network is received by each other user, which can either act on or ignore the received communication as appropriate.

In a repeater device, in addition to the repeater core which performs the repeating function, there are provided a number of other devices. Firstly, associated with each port there is provided port logic which implements a number of functions, for instance it acts to detect collisions at the port. Also, there is provided a media access control (MAC) unit which controls the transmission and reception of data by the repeater and in particular acts to receive communications directed to the repeater itself by the management of the network. Further there is provided in a typical repeater devices which function in conjunction with the MAC to record statistics concerning the communications which pass through the repeater. Such statistics when gathered can be downloaded by the network management and give an indication to management of how the repeater and the network overall are functioning.

Because a repeater as described above plays such a central function in the operation of a network, the repeater is commonly the limiting factor in the volume of communication which can be carried by the network. In order to increase the capacity of the network for carrying communications it would be possible to have a plurality of repeaters operating in parallel . However such an arrangement would be inefficient and would be open to error if the plurality of repeaters were not properly managed. Also, this would be inefficient as all of the above mentioned associated devices would be duplicated with each repeater.

The present invention provides an arrangement in which a plurality of repeater cores are integrated onto a single integrated circuit and a reduced number of at least some of the types of peripheral device is provided in association with the repeater.

The present invention therefore provides the above mentioned increase in network capacity, while avoiding potential redundancy and inefficiency in the operation of the plurality of repeater cores.

In particular in a preferred embodiment the overall repeater device which includes the plurality of repeater cores has a plurality of ports each of which may be connected to any one of the repeater cores. There is provided however only one set of port logic of the type mentioned above rather than there being a plurality of sets of port logic corresponding to the plurality of receiver cores.

Additionally, in the preferred arrangement, there is provided only one transmit MAC (hereafter Tx MAC) while there are provided a plurality of receive

MACs (Rx MACs) in an arrangement as is described in a copending application.

It is necessary to provide a plurality of Rx MACs corresponding to the plurality of receiver cores in order to cope with the fact that any receiver core may receive a communication at any time. However, it is possible to provide only one Tx MAC, as the interaction between the plurality of receiver cores can be managed overall.

Further, in the preferred arrangement, the statistics collection for the overall repeater device is integrated as much as possible into a single unit dealing with the statistics associated with all of the plurality of receiver cores.

The present invention will be better understood from the following description of a preferred embodiment given by way of example with reference to the accompanying drawings in which:-

Figure 1 illustrates in schematic form a repeater arrangement embodying the invention;

Figure 2 illustrates the repeater management system of Figure 1;

Figure 3 is a schematic illustration of the operation of Figure 2; and

Figure 4 illustrates the collection of statistics in memory. Figure 1 illustrates in schematic form a repeater arrangement embodying this invention. In this embodiment there are four repeater kernals 1 which are all integrated onto a single application specific integrated circuit (ASIC). Associated with the plurality of repeater 1 are repeater management subsystems 2 which will be described in further detail below. The overall device is provided with a plurality of ports 5, to which network users can connect in order to communicate with each other. The plurality of ports

5 are connected with the plurality of repeaters 1 by way of a switch matrix 6, which is configured to enable any of ports 5 to be connected to any of repeaters 1. There is provided a single Tx MAC 3 which is enabled, by way of switching means 4, to act as the Tx MAC for all of repeaters 1. T e mechanism by way of which only one

Tx MAC is required while a separate Rx MAC is provided for each repeater as is mentioned below, is described in more detail in a copending application and will not be described in detail here.

The devices according to this embodiment are designed to be cascade connected to enable additional users to be connected to the network and therefore in this embodiment there are additionally provided network cascade ports 10 by way of which users connected to one repeater device can communicate with users connected to another repeater device. There is also provided in this embodiment a management cascade port 9 by way of which management communications can be passed up the stack. Details of these features are described in copending applications and are not repeated here.

The device according to this embodiment comprises port logic associated with ports 5 in the normal way. As mentioned above, there is provided only a single set of port logic for die whole of the device illustrated in Figure 1, despite the fact that there are a plurality of repeaters 1. This is possible because however many repeaters it is possible to connect each of ports 5 to, it is only necessary to provide one means for detecting carrier collisions etc. and providing port configuration control on any one port 5.

Figure 2 illustrates in more detail the repeater management system 2 illustrated in Figure 1. Figure 2 illustrates how some portions of the repeater device are duplicated- in accordance with the number of repeater kernals there are present in the device, while other portions of the repeated device are not duplicated at all. In Figure 2 this is illustrated by the dashed line dividing the figure top and bottom, and as indicated the items in the top half of Figure 2 are provided one for each repeater, while those items illustrated in the lower half of Figure 2 are common to all of repeaters 1.

As shown in Figure 2 there is one Rx MAC 2.3 provided for each repeater 1 while there is only a single Rx MAC ring 2.4 provided for all the Rx MACs 2.3. The Rx MAC ring is a buffer memory for storing communication packets addressed to the receiver device and, as mentioned above, details of the operation of these items are described in a copending application.

The apparatus illustrated in Figure 2 comprises a statistics engine 2.1 corresponding to each repeater 1. The statistics engine is responsible for analysing each frame received by its associated repeater, together with status information made available by the repeater, as it arrives from the network and constructing a set of information summarising that frame. This operation is illustrated schematically in Figure 3 and as illustrated, for each frame the statistics engine constructs, in a working register, all the necessary status information and the source address/destination address pair. At the end of the frame the information required to update the statistics counters described below is copied to a holding register. Once the statistics engine has gathered all the statistics relating to a particular frame, it notifies the statistics update system 2.2 illustrated in Figure 2 that a new frame has been summarised.

As can be seen in Figure 2 there is a single statistics update system 2.2 provided for all of the repeaters and statistics engines described above. The statistics update system 2.2 therefore services the plurality of statistics engines 2.1 as it receives the above mentioned notifications. The statistics update system 2.2 maintains a number of statistics blocks in the system RAM. In the RAM there is a separate statistics block for each of the ports on the receiver device and within each of these blocks there are a plurality of counters, each of which counts the statistics relating to a particular aspect of the operation of the device.

The implementation of the statistics update system is a particularly preferred feature of this embodiment of the invention as it operates particularly efficiently. In previous systems there was simply provided a register, for example a 32 bit register, for each of the statistics to be counted. Once a number of ports and a number of different types of statistic are required to be collected, this approach leads to a very high gate count in order to provide the required number of registers.

The approach for collecting statistics according to the present embodiment is illustrated in Figure 4. In this figure there is illustrated a portion of memory 40. Within memory 40 there are a plurality of memory locations 41 each having an address. Within each memory location there is stored the current number representing a particular statistic for a particular port number and repeater number. The different types of statistic which may be collected for each packet which passes through the repeater device include the frame length, the port number which received a frame, die segment from which the frame was received, the status of the frame (good/bad) and other parameters.

As illustrated in Figure 4 there is associated with the memory 40 a state machine 42 which receives as inputs signals indicating the particular counter to increment (that is the particular type of statistic which is being provided), the current repeater number and the current port number. On the basis of the information, state machine 42 calculates the relevant memory address in memory 40 and reads out the present value from that address as illustrated by 44. State machine 42 then increments this value and writes the new value back to the same address in memory means 40 as illustrated at 46. The advantage of this particular arrangement is that a single state machine can be used to update any number of counters. Each memory location in memory means 40 is effectively functioning as a counter for a particular statistic but it is not required to provide a separate incrementing machine for each statistic. It is simply necessary to provide sufficient memory 40 to accommodate all the statistics necessary. This means the size of the state machine 42 is independent of the number of repeaters and ports which it monitors and this is advantageous from the point of view of implementing the device in hardware.

Referring back to Figure 2 it will be seen that there is additionally provided a security engine 2.8 for each repeater 1. As is well known there may be provided in repeaters schemes for ensuring that received data packets are transmitted only to permitted ports in an unscrambled fashion, that is only to ports having users which are allowed to receive the data package in question. Such repeaters therefore have an address table to store details of permitted communications. In the present embodiment a single address table 2.7 and loockup mechanism is provided which caters both for the security engines 2.8 of all the repeaters 1, and for the reception of packets by the repeater management system. Ordinarily at least two different address tables would be required and thus this reduces redundancy in the system. Further, the security scrambling mechanism is simplified by including it in the port logic, avoiding replicating it for each repeater.

Claims

CLAIMS:

1. A repeater device for a communications network comprising a plurality of input and output ports, a core means for repeating a data signal received by an input port of the device to one or more of the output ports of the device, port logic circuitry for providing port configuration control and a media access control means for controlling the transmission and reception of data by the device characterised in that the core means is in the form of a plurality of core elements each for receiving a data signal for an input port, and in that there is a single port logic control circuit which is shared by all core elements.

2. A repeater device according to claim 1, wherein the media access control means is in the form of transmit and receive control circuits with there being more receive control circuits than transmit control circuits.

3. A device according to claim 2, wherein mere is a single transmit control circuit associated with a plurality of receive control circuits.

4. A device according to claim 2 or 3, wherein there are the same number of receive control circuits as there are core elements.

5. A device according to any one of the preceding claims, wherein there is a statistics engine corresponding to each core element for analysing data received by its associated core element.

6. A device according to claim 5, wherein there is a single statistics update means for all of the statistics engines.