Multiplex communications – Pathfinding or routing – Switching a message which includes an address header
Reexamination Certificate
1998-06-17
2001-04-17
Kizou, Hassan (Department: 2662)
Multiplex communications
Pathfinding or routing
Switching a message which includes an address header
C370S446000, C370S462000
Reexamination Certificate
active
06219353
ABSTRACT:
This invention relates to a message hub for messaging between a plurality of nodes connected by a data communication medium, and a message communication system using the message hub.
BACKGROUND OF THE INVENTION
There are many of different Local Area Network (LAN) technologies. Ethernet is one of the most commonly used LAN technologies. Ethernet uses hub/bus topology. In those systems using bus topology, a plurality of processor based circuit packs or nodes share a common data communication medium, and accordingly, some form of mechanism is required for controlling access to the data communication medium by each node.
The medium access control protocol used by Ethernet is Carrier Sense Multiple Access/Collision Detection (CSMA/CD), in which each node monitors the data communication medium and transmits a message when the medium is idle. If two or more nodes attempt to transmit at the same time, a collision occurs. If a collision is detected during the transmission, each node ceases transmission and re-transmit after waiting for random amount of time.
This CSMA/CD system works well while the medium is relatively quiet and there are relatively a few collisions occurring. However, when the medium becomes busy, excessive collisions reduce the overall throughput of the network. Although this system does not favour any node and all nodes can have access to the medium in theory, in worst cases, some nodes may not be able to access the medium due to excessive collisions.
In addition, Ethernet uses transformers to exchange data between nodes, which is extra circuitry not needed for intra system communication.
U.S. Pat. No. 5,479,395 issued on Dec. 26, 1995 to Goodman et al and assigned to the same assignee as the present invention discloses a serial bus system which operates in an arbitration or scheduling phase and a transmission phase. The system uses a set of four signals, an arbitration clock, a data clock, an arbitration signal and a slot signal. All nodes are connected to those four signals. In order to ensure equal access to all nodes wishing to transmit, each node is provided with an access control means which uses the arbitration signal to ensure only one node accesses the bus, and uses the slot signal to identify the point at which a node has “won” control of the bus so that the other nodes can “win” before the node which has “won”. Use of four signals and the access control means add complexity in each node. Also, this system does not allow different levels of priority in transmission requests.
Accordingly, there is a need for an improved message communication system which is simple and provides reliable access for each node to the medium, and which allows use of different levels of priority and easy communication with nodes in other network systems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a message communication system which performs efficient scheduling of access to a data communication medium by a plurality of nodes connected to the medium using simple signals and circuitry.
To this end, the present invention uses a message hub which operates in a scheduling phase and a transmission phase. The system schedules the access of each node to a data communication medium without requiring any special scheduling signal.
In accordance with an aspect of the present invention, there is provided a message hub for use in a message communication system having a plurality of nodes connected to the message hub by a data communication medium for inter-node messaging. The message hub operates in a scheduling phase and a transmission phase. In the scheduling phase, request receiving means receives a messaging request signal is received from each node. In accordance with the messaging request signal, selecting means selects a selected node in the scheduling phase. Granting means generates a grant signal to the selected node for allowing the selected node to transmit a message to the message hub on the data communication medium. The granting means also generates a listen signal to the other nodes for commanding the other nodes to listen to the data communication medium. The message hub enters in the transmission phase in which message receiving means receives a message transmitted from the selected node on the data communication medium. The message includes an end of message signal at the end of the message. The message is broadcasted by broadcasting means to all nodes on the data communication medium so as to enter into the scheduling phase by broadcasting the end of message signal.
REFERENCES:
patent: 4628311 (1986-12-01), Milling
patent: 4630254 (1986-12-01), Tseng
patent: 4656627 (1987-04-01), Hasley et al.
patent: 4982400 (1991-01-01), Elbersole
patent: 4998244 (1991-03-01), Lee et al.
patent: 5005167 (1991-04-01), Arthurs et al.
patent: 5469439 (1995-11-01), Thaler et al.
patent: 5479395 (1995-12-01), Goodman et al.
patent: 5550836 (1996-08-01), Albrecht et al.
patent: 2015217 (1979-09-01), None
Barry Peter J.
Gagnon Stephane
Masonde Kalamaljit S.
Tatar Mohammed I.
Wight Mark Stephen
Kizou Hassan
Nortel Networks Limited
Tran Thien
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