Network communication device

Details Network communication device Network communication device

1998-11-30

2003-07-15

Kizou, Hassan (Department: 2662)

Multiplex communications

Communication techniques for information carried in plural...

Combining or distributing information via time channels

C370S389000, C370S425000, C370S446000

Reexamination Certificate

active

06594283

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to computer networking technology and in particular to communication devices such as Repeaters for interconnecting network devices in such networks.
2. The Prior Art
A Repeater is a very important component of computer networks such as local area networks as it provides the medium through which other devices can communicate with each other. In particular, a Repeater is provided with a number of communications ports and in the simplest configuration an end station, such as a computer is attached to each of the ports. A repeater functions such that any communication which is received on one port is retransmitted on all of the other ports, so that a communication sent out by any one device attached to the network is received by all of the others. In principle, the retransmission by a Repeater of a communication should be simultaneous with its reception at the receiving port. In this ideal situation, it will therefore be understood that a common communications medium is provided between all of the computers attached to the network via which communications can be sent between any of the devices. However, it is of course the case that, owing to the physical characteristics of the construction of the Repeater, the retransmission of a received communication is not instantaneous and the speed at which data can be passed through a Repeater has effects on the operation of the network as will be explained in the following.
One very common type of communications protocol in such networks is a carrier sense multiple access protocol of which Ethernet is a well known example. In such a protocol communications between computers attached to the network are by way of data packets having a pre defined format. Whenever a network user wishes to transmit a communications packet it simply attempts to access the communications medium provided by the Repeater or interconnected Repeaters and transmits the packet. The repeating function of the Repeater device mentioned above means that the communication packet reaches all of the other users on the network including the intended destination. In the event that another user is attempting to transmit a packet at the same time, the two or more transmitting units sense that a collision has occurred on the network and therefore that the transmitted data packet will not have been successfully received. In order for the collision to be sensed and properly acted upon, the collision must be sensed by the transmitting station before it has completed the transmission of a packet. If this occurs, the transmitting station will simply attempt, at the end of a predetermined period to retransmit the packet. If it completes transmission of the packet without receiving a collision detector signal, it will assume that the transmission was successful.
The above mentioned physical characteristics of the Repeater device have an impact on the operation of such protocol for the following reasons. In order for a collision to be properly sensed by a transmitting station, the transmitted packet must be received by the Repeaters and repeated to all segments of the network quickly enough so that if a collision occurs on any one of the network segments this can be relayed back, via the Repeaters, to the transmitting station before the end of the transmission of the packet in order that the collision can be properly sensed. It has been known that computer networks such as local area networks operating the Ethernet protocol can handle communications at 10 megabits per second (Mbps) for some while and it has been relatively easy to implement Repeaters for such network speeds which propagate data quickly enough so that up to approximately five Repeaters could be connected together and still obtain satisfactory network performance.
More recently there have been new standards set to increase the speed of communication over local area networks. In particular standards have been set defining network communication speeds of 100 Mbps. With communications occurring at such increased speeds, it clearly takes less time for a transmitting station to complete the transmission of a packet. It is therefore necessary that the packet should be more quickly repeated to all of the network segments in order that any collisions can be detected and returned to the transmitting station before the completion of the transmission of the packet.
One standard for Repeaters which has been defined for 100 Mbps networks is the Class I Repeater. With a Class I Repeater it is not permitted to connect two Repeaters together and so it is essentially necessary that each port on a Class I Repeater is directly connected to an end station or to a bridge or switch, which are other well known types of communications hub.
There is also more recently defined a standard of a Class II Repeater according to which standard, two Class II Repeaters may be connected together in the configuration of a network. With such a configuration it is of course the case that a transmitted packet must be propagated through two Repeaters to enable it to reach all of the network segments. To achieve this within the time constraints for detecting collisions as explained above, a Class II 100 Mbps Repeater must propagate received data to its other ports significantly quicker than Class I Repeaters.
Also, for 100 Mbps Repeaters, the communication standards do not allow any alterations in the lengths of the preambles to the data packets passing through the network. Therefore, as well as re-transmitting the packets quickly, a Class II Repeater must take considerable care to ensure that the whole of any received data packet, including the preamble, is accounted for and properly handled.
These constraints place considerable strain on the design of a Class II 100 Mbps Repeater. The implications of this are discussed further below.
Within a Repeater device, there is of course a certain architecture of the various parts of the Repeater to enable the ports to be connected to the Repeater core which will be on ASIC or other chip. In particular, there is provided within a Repeater device a physical layer device (PHY) provided for each port and the PHYs are then connected to the Repeater core. In one configuration it has been known to connect all of the PHYs directly to the Repeater core in a star configuration but this entails a large number of connections to the core.
A preferred Repeater architecture provides a receive data bus to which each PHY device is connected and which has a single connection to the Repeater core. Such an arrangement involving a data bus is advantageous as it reduces the number of connections, and therefore physical pins, which must be made on the ASIC. This architecture is further explained, insofar as it is relevant to the present invention, with reference to
FIG. 2
which shows the interconnections made between ASIC
1
and PHY devices
2
in order to enable the reception of data. A Repeater device would of course also include interconnections for the retransmission of the received data but the present invention is related principally to the receive side of a Repeater device and therefore the relevant portions of the receive side are shown.
As shown in
FIG. 2
, there is provided a bus
10
to which all of the PHY devices
2
may put their received data (RXD) in order that the received data can be received at ASIC
1
. There is of course present some bus control arrangements such that only one PHY device at a time is accessing the bus
10
and this will be outlined in the following, also with reference to the timing diagram of FIG.
3
.
FIG. 3
b
illustrates the start of a received data packet and in particular is illustrated according to the known defined 100 Mbps protocol. The communications packet begins with a predetermined sequence of symbols (in particular J, K followed by a plurality of 5s) which are present to enable functions such as synchronising with the packet to be done before the information bearing portion of the packet arrives, and oth

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