Multiplex communications – Channel assignment techniques – Using time slots
Patent
1998-04-06
2000-12-05
Ngo, Ricky
Multiplex communications
Channel assignment techniques
Using time slots
370437, 370439, 370468, H04L 12407, H04J 316
Patent
active
061576565
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD OF INVENTION
The present invention relates to a method and an arrangement for dynamic signalling in a time multiplexed network, such as a Dynamic Synchronous Transfer Mode (DTM) network.
DESCRIPTION OF RELATED ART
DTM is a broadband network architecture (see e.g. "The DTM Gigabit Network" by Christer Bohm, Per Lindgren, Lars Ramfelt and Peter Sjodin, published in Journal of High Speed Networks, Vol. 3, No. 2, pp. 109-126, 1994, and "Multi-gigabit networking based on DTM" by Lars Gauffin, Lars Hakansson and Bjorn Pehrson, published in Computer Networks and ISDN Systems, Vol. 24, No. 2, pp. 119-139, April, 1992).
DTM is a circuit switched network intended to be used in public networks as well as in local area networks (LAN's). It uses channels as the communication abstraction. The channels differ from telephony circuits in various ways. First, the establishment delay is short so that resources can be allocated/reallocated dynamically as fast as user requirements change. Second, they are simple and so minimise overhead when the communication is unidirectional. Third, they offer multiple bit-rates to support large variations in user capacity requirements. Finally, they are multicast, allowing several destinations.
DTM channels share many beneficial properties with circuits. There is no transfer of control information after channel establishment, resulting in very high utilisation of network resources for large data transfers. Support of real-time traffic is natural; there is no need for policing, congestion control or flow control within the network. The control information is separated from data information, making the data flow swiftly through the network without being manipulated in network switches. The switching delay is negligible (i.e. less than 125 .mu.s) and there is no potential for data loss because of buffer overflow as in ATM (ATM--Asynchronous Transfer Mode). Bit error rates depend on the underlying media technologies, and switches are simple and fast due to strict reservation of resources at channel setup. DTM can show good performance in areas where traditional circuit-switched networks fall short: dynamic bandwidth allocation, channel establishment delay, and as shared media networks.
The basic topology of a DTM network preferably comprises a bus with two unidirectional optical fibers connecting all nodes, but can also be realised by any other kind of structure, e.g. a ring or hub structure. The DTM medium access protocol is a time-division multiplexing scheme. The bandwidth of the bus is divided into 125 .mu.s cycles, which in turn are divided into 64-bit time slots. The number of slots in a cycle thus depends on the network's bit-rate.
The time slots are divided into two groups, control slots and data slots. Control slots are used to carry messages for the network's internal operation. The data slots are used to transfer user data.
Generally, in each network node there is a node controller, which preferably controls the access to data slots and performs network management operations.
Control slots are used exclusively for messages between node controllers. Each node controller preferably has write permission to at least one control slot in each cycle that it uses to broadcast control messages to other nodes. Here, broadcast refers to sending information to all downstream nodes on a bus as the transmission medium is unidirectional. Since write access to control slots is exclusive, the node controller has always access to its control slots regardless of other nodes and network load.
However, if there are many nodes on the same bus, the signalling overhead represented by the control slots may constitute a large part of the total capacity. It is therefore desirable to keep the control signalling capacity as low as possible. On the other hand, the control signalling capacity determines much of the performance of the network, both for access delay and utilisation. During periods of much control signalling, it is consequently advantageous to have a high control signalling capaci
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Computer Networks and ISDN Systems, vol. 24, No. 2, Apr. 1992, pp. 119-130, "Multi-gigabit networking based on DTN", Lars Gauffin.
Journal of High Speed Networks 3, 1994, IOS Press, pp. 109-126, "The DTM Gigabit Network".
Bohm Christer
Gauffin Lars
Lindgren Per
Ramfelt Lars
Net Insight AB
Ngo Ricky
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