Multiplex communications – Wide area network – Packet switching
Patent
1994-09-09
1996-08-13
Hsu, Alpus H.
Multiplex communications
Wide area network
Packet switching
370 681, 370 79, 370 857, 370 8511, 370 942, 370 951, 3701101, 370118, H04L 1240, H04L 1264
Patent
active
055463924
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
This invention relates generally to the field of communication buses and bus controllers and more particularly, this invention relates to a communication bus and bus controller which can handle multiple communication modes.
BACKGROUND OF THE INVENTION
Many communications buses and controllers have been developed using a number of communications modes on either parallel or serial buses depending on suitability for given applications.
Isochronous or Circuit Switched Services and Packet or Framed services are already widely used and Asynchronous Transfer Mode (ATM) or Cell services are being introduced. These three communications modes are briefly characterised as follows.
Isochronous Services require guaranteed synchronous access to the bearer--e.g. receipt or delivery of an octet at precisely 125 .mu.secs. Their most typical usage is to convey voice information at 64 Kb/s, however they are often used for data services to take advantage of the flexible and cost-effective switching and routing capabilities incorporated in the globally connected telephony networks. Historically these services were very prone to errors and thus voice services were typically noisy and data often unreliable. More recently network bearers have become much less error prone.
Cells are employed in the so called Asynchronous Transfer Mode (ATM) technology embodied in CCITT's B-ISDN, Bell Corp's Switched Multi-Megabit Data Service (SMDS), and IEEE 802.6 Metropolitan Area Network (MAN) standard. Cells are comprised of fixed length packets or frames, 53 octets long, of which 48 octets are user data created by a source user and then rapidly routed on the fly through ATM switches to their destination. To assure that acceptable end user service delay criteria are met, cells require either Deterministic Guaranteed Access to match some maximum value, or Statistical Access with a tolerable Quality of Service, or some combination of these.
Packet Services are by comparison with Isochronous and Cell services very delay tolerant, and typically an end user's real time usage of such services is very peaky. By serially multiplexing the needs of many users a more consistent level of traffic is usually supported over a fixed bandwidth channel. Thus a Packet bearer service must offer a Multi-User (and therefore arbitrated) statistically queued (and therefore delayed) Service. Packet services grew out of a need for more reliable transfer of data in spite of poor lines. Information integrity remains a major requirement of Packet services.
These three services can be ranked in terms of their access priority demands as: Isochronous, Cell and Packet. Thus Isochronous must take precedence over Cell, and Cell over Packet.
SUMMARY OF THE INVENTION
A communications controller in accordance with the invention advantageously controls communications in more than one communication mode on a TDM bus by inhibiting or interrupting communication in a first mode during communication in a second mode. This is particularly advantageous if the first mode is tolerant of delays and the second requires more rapid, guaranteed access to the bus. The controller according to the invention is therefore particularly advantageous if the first mode is a packet mode and the second is a cell mode.
In a particularly preferred embodiment the controller of the invention controls communication on an OSI physical layer TDM (time division multiplexed) bus in circuit, cell or packet modes in which, each TDM slot on the bearer may be associated with one of the three modes.
A physical layer multiplexed scheme offers relatively simple interfacing because above the TDM multiplexer, the packet, ATM (cell) and circuit services, can be seen as entirely independent of each other. In addition it will be shown that it requires very little additional logic to optionally support a simple node maintenance capability using the packet bus framing service.
Compared, for example, to three separate co-resident packet, cell and isochronous buses the combined bus offers considerable
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Boal John H.
Newton Mark K.
Hernandez Pedro P.
Hsu Alpus H.
Racal-Datacom Limited
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