Method for transmitting concatenated data signals

A method for transmitting concatenated data signals wherein an STM-256/OC-768 signal is divided into four concatenated signals which are inserted into modified STM-64/OC-192 pulse frames. The bytes of the unused information and the frame alignment words of the STM-256/OC-768 signal are not transmitted so that the total content of the STM-256/OC-768 signal, reduced by this redundant information, can be transmitted transparently in the modified STM-64/OC-192 pulse frames. The concatenated signals can be regenerated without problems.

BACKGROUND OF THE INVENTION

In synchronous data systems such as the synchronous digital hierarchy SDH and a corresponding system SONET, used in North America, binary data are inserted into pulse frames and transmitted. So that signals having relatively high data rates also can be transmitted via systems which only have a restricted transmission capacity, these signals are divided into a number of subsignals having a lower data rate. A corresponding arrangement is described as “inverse multiplexers” and is known, for example, from European patent application EP 0 429 888.

In the near future, it can be expected that there will be devices, for example routers, which will deliver STM-256/OC-768 signals with about 40 Gbit/s. At present, wavelength-division multiplexer systems, the individual channels of which are designed for transmission rates of 10 Gbit/s, are still being used in optical transmission technology.

It is an object of the present invention to specify a method which enables STM-256/OC-768 signals to be transmitted via 10 Gbit/s channels.

SUMMARY OF THE INVENTION

An advantage of the method according to the present invention is that pulse frames which essentially correspond to a standardized pulse frame are used for the transmission. It is only the number of frame alignment bytes which is reduced. As such, existing transmission devices only need to be modified slightly, or not at all. The pulse frame is designed in such a manner that the operation of electric regenerative repeaters is not impaired. A uniform type of regenerative repeater therefore can be provided in the network. The original signal is transmitted transparently.

Numbering of the concatenated pulse frames is also advantageous. This enables the subsignals to be detected in a simple manner at the receiving end and to be combined in an error-free manner to form the original signal.

To ensure error-free transmission even with relatively large delay differences, it is advantageous to form a superframe. This can be done by marking, for example, the first concatenated pulse frames of a superframe or by numbering all concatenated pulse frames of a superframe.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 1shows a possible use of the method according to the present invention. A first router ROUT1inserts an STM-256/OC-768 signal DSA into a pulse frame PR256 (FIG. 2), delivered with a bit rate of approx. 40 Gbit/s. This signal is divided byte by byte into four concatenated subsignals IMA1to IMA4, after omission of bytes NU, A1, A2, NU according toFIG. 2, in a demultiplexer DMUX (inverse multiplexer) so that bytes I11, I21, I31, I41, I12, I22, . . . of the original 256/OC-768 signal DSA are evenly allocated to pulse frames PR64.1 to PR64.4.

The precise structure of the pulse frames STM-64/OC-192 is described in ITU recommendation G.707, page 42 and pages 54 and 55. The pulse frames PR64.1 to PR64.4 used here correspond to those of the STM-64/OC-192 pulse frames completely in format and largely in content as is shown in the right-hand half ofFIG. 2. The representation is not true to scale. Each of these pulse frames has nine rows Z1to Z9and 17,280 columns S1, S2, . . . and the time slots formed in this manner, in each case, accommodate one byte. The ITU-conformal overhead of the pulse frames PR64.1 to PR64.4, in each case, has 576 columns. A traditional overhead includes 576 columns.

In the first row of each pulse frame PR64.1 to PR64.4, frame markings A1and A2are transmitted, the number of A2bytes having been reduced by 8 bytes and the frame alignment bytes A2having been replaced by information bytes I11, I12, . . . Only 384 time slots are reserved for the overhead information OH; in the remaining time slots, data of, in each case, one subsignal or, respectively, the STM-256/OC-768 signal DSA1are transmitted as also in the (original) payload PL.

The first payload byte1537of the STM-256/OC-768 signal or, respectively, the first byte of the subsignal IMA1, is inserted as byte I11at position377in the first STM64/OC-192 pulse frame PR64.1; the payload byte1538of the STM-256/OC-768 signal located at position1538or, respectively, the first byte of subsignal IMA2, is inserted as byte I21at position377of the second STM64/OC-192 pulse frame PR64.2 etc. until the byte of position1541is again inserted as byte I12at position378of the first pulse frame PR64.1 etc. Other bytes of the signal IMA1are inserted in the first row Z1from column379to column384and again from column387etc. of pulse frame PR64.1. After that, further bytes of subsignal IMA1are inserted in the second row from column2to column192, from column194to column384and from column386as can be seen inFIG. 2.

The regenerative repeaters RE1to RE4shown inFIG. 1only analyze the transitions between A1and A2for synchronization so that the reduction in the number of A2bytes does not impair their operation. The reduction in the number of frame alignment bytes is necessary since 9×69.120–1536 bytes=620 544 bytes in total must be inserted into the four pulse frames PR64.1 to PR64.4 from the pulse frame PR256 and, in addition, eight additional bytes J0, C, B1, E1, F1, D1, D2, D3also must be inserted into the overhead in order to generate a compatible STM-64/OC-192 pulse frame. The STM-64/OC-192 signals allocated to the concatenated subsignals IMA1to IMA4are additionally identified by #1 to #4.

In the basic block diagram ofFIG. 1, the concatenated signals IMA1to IMA4, together with other signals, are combined to form a transmission signal WS1in a first wavelength-division multiplexer WDM1and transmitted. As a rule, the transmission link contains optical amplifiers OA1and electric regenerative repeaters RE1to REn. The regeneration (still) requires an initial division of the transmission signal by a first wavelength-division demultiplexer WDD1into the corresponding 10-Gbit/s signals followed by an opto-electric conversion (not shown here). After the signals have been regenerated, they are electro-optically converted and combined in a second wavelength-division multiplexer WDM2to form the transmission signal WS2which is forwarded via a further optical amplifier OA2to a second wavelength-division demultiplexer WDD2where it is reconverted into concatenated subsignals IME1to IME4which correspond to the subsignals IMA1to IMA4at the transmitting end.

In the multiplexer MUX, the regenerator section overhead inserted in the demultiplexer, bytes J0, C, B1, E1, F1, D1, D2, D3of the concatenated signals, are in each case removed and the subsignals are mapped into the corresponding pulse frame PR256 and supplied to a second router ROUT2, again as STM-256/OC-768 signal DSE.

To be able to identify the pulse frames, they are suitably numbered which takes place in byte C. In addition, a superframe marking which can be a special binary combination can be transmitted in the C byte. Similarly, it is possible to extend consecutive numbering to the superframe. Pursuant to these measures, delay differences greater than one half frame period also can be detected and compensated for by buffers in the multiplexer MUX. An analogous facility is provided for transmitting signals in the reverse direction.

Although the present invention has been described with reference to specific embodiments, those of skill in the art will recognize that changes may be made thereto without departing from the spirit and scope of the invention as set forth in the hereafter appended claims.