Multiplex communications – Communication techniques for information carried in plural... – Combining or distributing information via time channels
Reexamination Certificate
2000-12-21
2004-12-28
Phan, Man U. (Department: 2665)
Multiplex communications
Communication techniques for information carried in plural...
Combining or distributing information via time channels
C370S430000, C370S540000, C370S384000, C370S248000
Reexamination Certificate
active
06836486
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to the switching of low order data structures. In particular, the invention relates to switching an SDH low order VC-3 using a high order switching apparatus.
BACKGROUND TO THE INVENTION
The SONET (Synchronous Optical Network) Standard defined by ANSI (American National Standards Institute) is similar in many respects to the SDH (Synchronous Digital Hierarchy) standard defined by the ITU-T (International Telecommunications Union Telecommunications Standardization Sector). One key difference, however, is the respective basic unit of payload. In SONET, the basic unit is an STS-1, which offers a bandwidth of approximately 50 Mbit/s. With SDH, the basic unit is an AU-4, which offers a bandwidth of approximately 150 Mbit/s. SDH channels with smaller bandwidths are available and are provided by, for example, basic units known as VC-12 (approximately 2 Mbit/s) and VC-3 (approximately 50 Mbit/s). However, VC-12s and VC-3s are carried within VC-4s which, in turn, are carried within AU-4s. The VC-12s and VC-3s are therefore referred to as low order data structures, the VC-4 being a high order data structure. Switching a low order data structure within a network element, such as a multiplexer, is relatively complex and requires relatively expensive equipment.
Increasingly, telecommunications customers are able to make use of 50 Mbit/s bandwidth. In a SONET network, this bandwidth can conveniently be provided by the STS-1, which is a high order data structure. As a result, the infrastructure for SONET networks can be built using primarily STS, or STS-1, switches i.e. high order switches. High order switches are simpler and cheaper than low order switches.
With an SDH network, the 150 Mbit/s bandwidth provided by the AU-4 is more than most customers require. Accordingly, most SDH network infrastructures must support low order payloads such as the VC-12 and VC-3. This in turn means that the SDH network elements must support low order data switching.
In view of the increasing popularity of 50 Mbit/s services in particular, it is desirable to be able to switch low order VC-3s using a high order switch and so to reduce the complexity and cost of the required network infrastructure.
SUMMARY OF THE INVENTION
Accordingly, a first aspect of the invention provides a method of switching a TU-3 data structure contained in an AU-4 data structure, the TU-3 data structure including a TU-3 pointer, the AU-4 data structure including an AU-4 pointer and two pointer locations comprising concatenation indicators, the method comprising:
converting the AU-4 data structure into three AU-3 type data structures each having a respective AU-3 pointer;
switching at least one of said AU-3 type data structures using a high order data switching apparatus;
associating said at least one switched AU-3 type data structure with two further AU-3 type data structures; and
converting said associated AU-3 type data structures into an AU-4 data structure,
wherein said at least one AU-3 type data structure contains said TU-3 data structure associated with an AU-3 pointer, and the method further includes:
pointer processing said TU-3 pointer and said AU-3 pointers so that said AU-3 pointers are set to a common fixed value, and wherein the conversion of said associated AU-3 type data structures is performed by replacing said AU-3 pointers with a single AU-4 pointer and two concatenation indicators.
The method of the invention enables low order VC-3 data structures (which are included in respective TU-3 data structures) to be switched as a high order data structure using a high order data switch. This is advantageous since high order data switches are inherently less complex, and therefore less expensive, than the low order data switches that are conventionally required to switch low order VC-3s. Thus the overall complexity and cost of the network equipment is reduced.
Preferably, the conversion of said AU-4 data structure is performed by replicating the AU-4 pointer into each of said pointer locations comprising concatenation indicators to produce three AU-3 pointers.
Preferably, said pointer processing includes performing a high order pointer termination function on said AU-3 pointers; performing a low order pointer termination function on said TU-3 pointer; performing a low order pointer generation function to regenerate said TU-3 pointer; performing a high order frame generation function to generate a data frame structure comprising three corresponding AU-3 type data structures including said three AU-3 pointers set to said common fixed value.
At least some of said AU-3 type structures may comprise respective STS-1 type structures including STS-1 pointers.
The pointer processing may be performed before or after switching.
A second aspect of the invention provides a network element, or network node, arranged to perform the method of the first aspect of the invention.
A third aspect of the invention provides a data communications network comprising one or more network elements according to the second aspect of the invention.
A fourth aspect of the invention provides a method of switching a TU-3 data structure, the method comprising:
mapping the TU-3 into a high order VC-3 type data structure; aligning the high order VC-3 type data structure with a fixed AU-3 pointer to form an AU-3 type structure; causing the high order VC-3 type data structure to be switched by a high order switching apparatus; associating said switched VC-3 type data structure with two further VC-3 type data structures, each associated VC-3 type structure being aligned with a respective fixed AU-3 pointer having a common value; and replacing the AU-3 pointers with an AU-4 pointer and two concatenation indicators to produce an AU-4 data structure.
Further advantageous aspects of the present invention will become apparent to those ordinarily skilled in the art upon review of the following description of a preferred embodiment of the invention and with reference to the accompanying drawings, in which like numerals are used to represent like parts.
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Carson Mark
Courtney John
Kelly Cormac
Barnes & Thornburg LLP
Nortel Networks Limited
Phan Man U.
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