Multiplex communications – Channel assignment techniques – Polling
Patent
1995-07-07
1998-05-19
Chin, Wellington
Multiplex communications
Channel assignment techniques
Polling
370223, 370403, 370404, 34082502, H04L 12403, H04L 1242
Patent
active
057545510
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The invention relates to a method of operating a ring communication system, for example based on a token ring or FDDI communication protocol.
DESCRIPTION OF THE BACKGROUND ART
In a conventional ring based data communication system a token passing or similar scheme is used to control access to the ring by end stations. These end stations are typically then connected together via a hub containing control systems and the like.
Ring communication systems can support large numbers of end stations but for small numbers of end stations, particularly two end stations, the communication protocol can slow down network throughput.
Where only two end stations are communicating in the network, it is preferable to establish two way communication between them (known as "full duplex mode").
EP-A-0439008 discloses a method of operating a token ring network. In a first "full duplex auto-configuration" mode the ring is initialized in conventional token ring mode, followed by a "2-station test" which ascertains whether only two stations are active in the network. If more than two stations are active in the network, token ring operation is maintained. If only two stations are active, the network switches to full duplex mode. This is an inefficient way of operating the network, and does not allow a new end station to enter the network in full duplex mode. In a second "full duplex fixed" mode, the network is initialized in full duplex mode without any "2-station test", and without reverting to token ring mode in the event of a third station's presence or cessation of full duplex operation by the other station. This is a fairly crude method, which does not allow conventional token ring operation.
SUMMARY OF THE INVENTION
In accordance with one aspect of the present invention, a method of connecting a new end station to a ring communication system for connecting a number of end stations comprises: ring; and, ring, allowing the new end station to attach to the ring and maintaining the ring communication configuration; or breaking the ring configuration and setting up two separate communication paths between the new end station and the existing end station.
In accordance with a second aspect of the present invention, a ring communication system comprises communication means for connecting a number of end stations together in a ring configuration; and control means for carrying out a method according to the first aspect of the invention.
This invention specifically addresses the case where a new end station wishes to join a ring having only a single end station and enables the aggregate bandwidth of the network in that case to be doubled by setting up two separate or independent communication links between the stations. The negotiation allowing full duplex operation is undertaken before the end station has entered the ring.
In some cases, the use of two separate or independent communication links can be used to enable relatively long cables or poorer quality cables to be used. Thus, crosstalk and other interference which can occur between adjacent links in a cable can be minimized by arranging for only one of the communication paths to be active at any one time.
If the system is operating in the "separate path" or full duplex mode, then an additional station can only attach if the system reverts to normal ring based operation. For example, if one of the stations operating in full duplex mode detects an initialization frame from a third station then it will cause communication to revert to a ring configuration.
In many such systems, a hub unit is provided typically with an end station located within the hub unit. In that case, the end station within the hub unit will constitute the existing end station.
Preferably, the method further comprises causing the new end station to emit data indicating whether it is capable of operating in the "separate path" mode. This then enables the system to decide whether it should then carry out steps ii) and iii). The present invention allows the hub unit to be a dual mod
REFERENCES:
patent: 5155726 (1992-10-01), Spinney et al.
patent: 5337311 (1994-08-01), Herzberg et al.
patent: 5414700 (1995-05-01), Yang et al.
patent: 5490145 (1996-02-01), Tanabe et al.
Claridge Philip G.
Pearce David A. J.
Carman Melissa Kay
Chin Wellington
Madge Networks Limited
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