Multiplex communications – Communication techniques for information carried in plural... – Adaptive
Reexamination Certificate
1998-12-21
2003-10-14
Yao, Kwang Bin (Department: 2664)
Multiplex communications
Communication techniques for information carried in plural...
Adaptive
Reexamination Certificate
active
06633584
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to synchronous digital networks and particularly, although not exclusively to conversion of payload data between ETSI derived containers and SONET containers within synchronous digital hierarchy networks.
BACKGROUND TO THE INVENTION
In the applicants co-pending U.S. patent applications Ser. No. 09/143466 entitled “Frame Based Data Transmission Over Synchronous Digital Hierarchy Network”, and Ser. No. 09/143465 entitled “Payload Mapping In Synchronous Networks”, and the applicant's U.S. patent application Ser. No. 09/166,184 entitled “Concatenation of Containers in Synchronous Digital Hierarchy Network”, copies of which are filed herewith and the contents of which are incorporated herein, there is disclosed a method and apparatus for carrying frame based data over synchronous digital hierarchy (SDH) transport networks wherein the frame based data eg Ethernet data according to IEEE Standard 802.3, has an inherent data rate which does not conveniently match the telecoms data rates specified in ITU-T recommendations G.707 and G.708 for containers and tributary unit groups (TUGS). In the applicant's previous disclosures, frame based data packets at a first (higher) data rate are mapped into a plurality of virtual container (VC) streams, each operating at a second (lower) data rate. For example a stream of 10 Mbits/s Ethernet data frames may be mapped into a plurality of five 2 Mbits/s virtual container streams and transported across a network to a destination in five parallel transmitted virtual container stream channels. On reaching the destination, the data frames are reconstructed from a plurality of payloads of the virtual container streams.
By incorporating the frame based data directly into synchronous transmission channels, the above disclosed methods may provide a functionality which has previously been available over a limited distance in a local area network, but extended over distances which have previously been regarded as being wide area networks, for example over networks spanning between different continents. Conventionally, a feature of SDH networks which span across the Atlantic ocean is that different transmission rates exist between Europe and North America. The known synchronous digital hierarchy multiplexing scheme has developed historically by incorporation of both European multiplexing standards (ETSI standards), and North American synchronous optical network (SONET) standards and Bellcore GR 253 standard, and is derived from a combination of different bit rate multiplex schemes. Large amounts of legacy network equipment exist in Europe, operating at the ETSI derived bit rates within the synchronous digital hierarchy, and in North America, operating at SONET bit rates within the synchronous digital hierarchy. In most cases a global network operator would wish to use either ETSI derived SDH equipment within a single territory, or SONET based SDH equipment and not convert data traffic between two different systems within a same territory, but only convert between ETSI and SONET data rates when spanning between networks across international boundaries. Within the synchronous digital hierarchy regime there are points of equivalence between the ETSI derived bit rates and the SONET derived bit rates. For example a VC-4 container is of equivalent bit rate and bit capacity to a SONET STS-3C frame. However, the VC4/STS-3C bit rate of approximately 155 MBits/s is too large for global network operators to offer to their customers for provision of individual globalized circuit and trunk services spanning across national borders and across both European and North American territories.
The practical problems of providing a frame based data network carried over a synchronous network across national boundaries include interfacing between ETSI and SONET options for most data traffic types within SDH, which involves provision of different equipment types which operate at ETSI and SONET data rates, as well as providing equipment and protocols to convert from ETSI derived synchronous bit rates, via plesiochronous bit rates to SONET bit rates and vice versa.
In order to implement the applicant's above disclosed frame based data communications system in an SDH network spanning between ETSI and SONET domains, there is a requirement for translation of payload between ETSI and SONET frame options within SDH.
Although specific implementations of the present invention have arisen from addressing the problem of carrying frame based data over SDH networks, the implementations address a more general need for provision of translation of data between ETSI and SONET options within SDH, without having to convert through an intermediate plesiochronous mode.
SUMMARY OF THE INVENTION
One object in the present invention is to provide a method and apparatus for converting data between ETSI derived and SONET derived data rates within a synchronous digital hierarchy network in an efficient manner.
Another object of specific implementations of the present invention is to minimize an amount of latency within a data network.
A further object of specific implementations of the present invention is to provide efficient conversion between ETSI and SONET data rates at a lower level of granularity than is available by translating between the VC-4 and STS-3C containers.
Specific implementations of the present invention may convert between SONET and ETSI derived data rates without recourse to plesiochronous digital hierarchy data rates.
According to a first aspect of the present invention there is provided a method of converting payload data between a VC-3 virtual container and an STS-1 synchronous payload envelope, said method comprising the steps of reading a first set of pointer bytes, said first set of pointer bytes pointing to a position within said VC-4 virtual container of each of a plurality of VC-3 virtual containers; reading bytes of first, second and third VC-3 virtual containers from positions within said VC-4 virtual container indicated by said first set of pointer bytes; generating an STS-3C synchronous payload envelope; determining start positions within an STS-3C synchronous payload envelope of each of a plurality of STS-1 synchronous payload envelopes; determining positions within said STS-1 synchronous payload envelopes of each of a plurality of redundant stuff bytes; determining a set of STS-1 synchronous payload envelopes pointer byte values for pointing to said start positions of said plurality of STS-1 synchronous payload envelopes within said STS-3C synchronous payload envelopes; determining a set of pointer byte values for pointing to said positions of said redundant stuff bytes within said STS-1 synchronous payload envelopes; and writing said bytes of said first, second and third VC-3 virtual containers into positions within said STS-3C synchronous payload envelopes allocated for said plurality of said STS-1 SPEs.
Said method may further comprise the steps of reading a second set of pointer bytes, said second set of pointer bytes indicating a start of said VC-4 virtual container within an STM-1 frame.
Said step of determining positions within an STS-1 synchronous payload envelope of each of a plurality of redundant stuff bytes preferably comprises writing a said STS-1 synchronous payload envelope as a 9 byte row×87 byte column array; and setting said plurality of redundant stuff bytes as occupying a 30
th
said column of bytes and a 59
th
said column of bytes.
Preferably said step of determining a set of pointer byte values for pointing to said positions of said redundant stuff bytes within a said STS-1 synchronous payload envelope comprises writing said STS-1 synchronous payload envelope as a 9 byte row×87 byte column array, and setting said pointer byte values to point to a first byte of a 30
th
said column and to a first byte of a 59
th
said column.
Said step of determining start positions within the STS-3C synchronous payload envelope of each of a plurality of STS-1 synchronous payload envelopes ma
Goodman David Michael
Murton Christopher David
Ramsden Christopher Thomas William
Russell John Paul
Shields James
Barnes & Thornburg
Jones Prenell
Nortel Networks Limited
Yao Kwang Bin
LandOfFree
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