DE2814259A1 - Frame structure for third order digital TDM system - has every 512 signal bits preceded by 25 additional bits for synchronisation, timing and alarm signals - Google Patents

Abstract

The frame is suitable for transmission and switching, with information for synchronisation and signalling timing deviations, containing two timing adjustment commands, alternating in case of synchronism. In order to combine 16 wideband channels or PCM-30- basic systems, each with 2.048 Mbit/s into a signal flow of 34.368 Mbit/s, each 512 information bits are preceded by 25 additional bits. The first 12 bits serve for synchronisation, 13th to 16th bits allocate timing deviation signals to a subsystem, 17th bit signals positive timing deviation, 18th bit a not urgent alarm, 19th bit an urgent alarm, and remaining bits are reserved for international problems.

Description

The invention relates to a frame structure for a digital

Time division multiplex system, with the help of which both in a plesiochronous Communication network bundling the information from broadband channels with 2.048 Mbit / s for transmission purposes, as well as in a synchronous network at clock frequencies from 34.368 z a bundling for communicating information with the baseband 32 times a telephone channel is possible.

For solving the switching problem of broadband channels with 2,048 Mbit / s is so far no concept, although in all major institutes at the Problems of coding image signals for narrowband systems is being worked on (NTZ, 1977, no. 3, pp. 245-250). As an alternative to multiple room switching, the a complete demultiplexing of time division bundles with e.g. 4, 16 or 64 broadband channels would only require the creation of synchronous multiplexing systems that both are suitable for transmission as well as switching tasks (NTZ, 1976, no. 3, pp. 190-210).

That time-division exchanges can also be implemented at higher clock frequencies shows the development and commissioning of the time division multiple switching system in 1976 ESS-No. 4 from the Beil Telephone Company. The ESS-No. 4 works internally with bundles of 120 voice channels in time division multiplex (tone conference report ISS. 1972, OHO 617-1-COM, Pp. 19-25). Frameworks are also specified internationally.

structures for digital synchronous multiplex devices for 120 voice channels (CCI21, 1976, Rec. 741, Annex 1).

However, this is not the end of the development, as well as from publications from other European countries emerges (Eurocon, 1971, paper no. B 8-3; Commutation + Electronique, 1973, p. 14).

The object of the invention is derived from the following considerations: While of the transmission technology essentially the clock bit rates and frame structures for digital systems up to the fourth level of the digital hierarchy are, on the part of switching technology, the move to development is independent of this and to recognize the use of multi-channel time multiplexing systems. So through the introduction the greatest possible benefit can be achieved in digital technology should be achieved with the Selection of the multiplex method, both for switching and transmission technology must be taken into account. Time division exchanges place at the involved input clock the demand for synchronicity, if not parts of information are lost should go.

For transmission systems of higher order, however, this requirement can are then weakened if tolerance limits are defined for the clocks of the subsystems If they are observed, the information can be transferred without loss.

When using certain timing adjustment methods in multiplex technology both demands could be met in the long run. So is through that CCITT document, TD No. 19, Nov. 1971, a clock adjustment method known which is used for Signaling of clock deviations with two states (positive-negative) gets by and transmits the two commands alternately in the synchronous case. It is further known in plesiochronous systems, the additional information both for the purpose of Use synchronization as well as clock adjustment (Review of the Electrical Communication Laboratories, year 1971, no. 9 - 10, p. 1055 - 1059).

For a very long introductory period and for particularly high-channel Transmission systems could clock tolerances be allowed without a change synchronous operation would be excluded from the outset. Switching to a synchronous network makes not only the solution of the synchronization problem, but also the introduction elastic storage (so-called phase compensator) required.

This connection has already been discussed in detail (Proceedings of the IEE, Vol 60, No. 5, May 1972, p. 594 - 601) and it was also on the noted relatively large memory requirements at higher clock frequencies.

Theoretically, the feasibility seems to be a global one synchronous network possible (IEEE Transactions on Communications, June 1974, p. 839 - 845) and the question of the manufacturability of inexpensive elastic stores, too for larger content, solvable in a few years.

The invention is based on the object by specifying an alternative Frame structure for the third level of the digital multiplex hierarchy a time diversity to enable the switching and transmission of broadband channels with 2.048 Mbit / s, without the need for several multiplexing and demultiplexing devices that would otherwise be necessary required are.

The solution assumes that both the flow of information of the input systems with 2.048 Ybit / s each as well as the bit rate at the output of the Multiplexers with 34.368 Mbit / s are fixed and no longer by international Committees can be changed.

Another requirement is that everyone involved in the setpoint frequencies The pulse frame clocks exactly all incoming information from the information flows of the lower class can absorb without being in the impulse frame of the higher class Stuffing bits arise.

If you take the theory of block synchronization through the work of Häberle binary transmission systems "Dissertation TH Munich, 1966, known requirement for an optimal length of the synchronization pattern in the requirements catalog, 80 one arrives at the table shown in FIG. 1. In this table are the Each possible bit number for the useful information, the additional information, the by the sum of the two resulting block length and the optimal length of the synchronization word and the number of channels to be transmitted or switched one below the other arranged. All frame structures resulting there from the columns are fulfilled the requirements listed above.

In addition to the requirements met by this table, one ascertains short synchronization time the further demands for insensitivity to Bit errors, a sufficiently large permissible clock deviation of the input and Output information flows as well as a channel or block-wise nestability of the input information, it can be seen that these requirements are only common to one column of the table are met.

The invention therefore proposes to combine 16 6 broadband channels in each case or PCM-30 basic systems with 2.048 Mblt / s each to an information flow of 34.368 Mbit / s before, *) it clock adjustment synchronization word that each 512 information bits are preceded by 25 bits of additional information, the first 12 bit of synchronization and signaling of clock discrepancies, the 13th up to 16th bit for assigning the clock deviation signaling to the respective subsystem, the 17th bit as an information bit in the event of a positive clock deviation of the input, the 18th bit Bit for signaling a non-urgent alarm, the 19th bit for signaling of an urgent alarm and the 20th to 25th bits as reserve bits for international ones Serving tasks.

The frame structure according to the invention is applicable when broadband channels to be transmitted or switched at 2.048 Mbit / s, or for automatic Changeovers or substitute circuits if the influence of faults or overloads in a digital telephone network are to be mitigated.

So could in the future, similar to today for F long-distance systems usual (Siemens-Zeitschrift, 48th year (1974), supplement p. 283 - 289 and p. 308 - 312) via special remote or

Computer-controlled time-division switching fields PCM basic systems switched in replacement without the need for expensive demultiplexing and multiplexing devices would be.

However, the frame structure according to the invention can, without change, by Additional effort in the stop records of the exchange for switching individual telephone channels or of channels with two, three, two, six or ten times the capacity of one Telephone channel can be used.

Fig. 2 shows the frame structure according to the invention for these two Cases under a to combine 16 broadband channels, for example in their original data rate the known means of redundancy and irrelevance reduction reduced picture telephone channels with 2.048 Mbit / s each and under b for the union of 16 PCM-30 basic systems with also 2.048 Mbit / s and under c the breakdown of the additional information preceding the information to be combined.

The frame structure of Fig. 2 was chosen from the multitude of possible Frame structures according to Fig. 1 selected to have a short synchronization time between To ensure sender and recipient and to achieve that for a transitional period, in the one with plesiochronous clocks of all input information flows and in the multiplex device must be expected, both a clock adjustment (justification) and a signaling urgent or non-urgent alarms must be possible.

The frame structure according to the invention makes this on the one hand of the method mentioned in the prior art, the additional information for both Purpose of synchronization as well as to use clock adjustment, as well as of the also mentioned known clock adjustment method with two in synchronous Case use of clock adjustment commands transmitted alternately.

This includes the synchronous operating state of the network from the start.

In order to retain the frame structure later also for time division multiplex switches to be able to, the additional information of 1600 kblt / s in the form of four blocks 25 bits used in each case.

Essential parts of the additional information (13 of 25 bits) of a such Blocks are used for the purpose of signaling clock adjustment commands and for the transmission of excess bits from the respective information flows of the lower Class assigned to a specific subsystem.

Claims (2)

Equally suitable for transmission and mediation tasks Frame structure for a third-order digital time division multiplex system (2) claims Framework structure that is equally suitable for bank transfer and mediation tasks for a third order digital time division multiplex system with either synchronization as well as the signaling of clock discrepancies serving additional information, the contains two clock adjustment commands transmitted alternately in the synchronous case, gekenneeichnet that for the union of 16 broadband channels or PCM-30 basic systems with j 2.048 Mbit / s each to an information flow of 34.368 Mbit / s 512 information bits are preceded by 25 bits of additional information, where the first 12 bits of synchronization and signaling of clock deviations, the 13th to the 16th bit to assign the clock deviation signaling to the respective one Subsystem, the 17th bit as an information bit in the event of a positive clock deviation of the respective Input, the 18th bit to signal a non-urgent alarm, the 19th bit Bit for signaling an urgent alarm and the 20th to 25th bit as reserve bits serve for international tasks. 2. Frame structure according to claim 1, characterized in that it without change for switching individual voice channels or channels with two, three, five, six or ten times the capacity of a telephone channel is usable.