Method of providing a frame clock for data signals in a communic

Details Method of providing a frame clock for data signals in a communic Method of providing a frame clock for data signals in a communic

1995-11-20

1997-11-04

Olms, Douglas W.

Multiplex communications

Fault recovery

370503, 375356, 39520019, 331 11, H04J 306, H03L 7087

Patent

active

056847882

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

The invention is based on a method of providing a frame clock for data signals in a communications network.
Transmission channels with constant propagation delays are required, in particular for feed lines of centralized multi-station control signals or synchronized broadcasting. In connection with carrier frequency systems and simple point-to-point connections, this requirement was, as a rule, met without additional effort by digital transmission systems. The user was able to set a desired total propagation delay by means of adjustable phase setting members at the end of the transmission channel. In modern digital transmission systems with branching, cross-connecting or relaying capabilities, FIFOs are used, as a rule, at the digital inputs in order to adapt all multiplex signals to a common, usually random, phase position. The propagation delays resulting from this do not have a constant value, in particular after a restart.
To obtain a constant propagation delay, it is possible to couple the phase positions of all outgoing multiplex signals to that of a selected incoming signal. In a transmission system in accordance with the pamphlet "Gerate und Anlagen der Nachrichtentechnik 2 Industrielle Netze der ANT and Installations of Communications Technology 2, Industrial Networks of ANT Communications Technology, pages 6 and 7, in particular Flex Plex XMP1!, the frame identification word is employed as reference.
This solution is sufficient for line- or star-shaped networks. However with meshed network structures it is unsatisfactory, because net interferences result in changes in propagation delay.
Meshed transmission networks with Flex Plex XMP1 offer an integrated cycle synchronization of the entire network which reacts flexibly to network interferences and maintains the desirable synchronization in the entire network (or within partial networks if the entire network disintegrates because of interference). However, the solution for constant propagation delay transmission known so far is not compatible with this because of the required locked fixing of the reference signal.
With phase-locked transmission a clock reference tree is manually preset. All desired nodes form a rigid partial network offering stable propagation times between arbitrary points. The concept is not compatible with replacement circuits.
Partial networks which are separated from the preset clock reference tree by interference have no defined cycle reference with the remaining network, even if cycle synchronization were possible via 2 MBit/s connections not contained in the clock reference tree. In particular, centralized multi-station control channels run through such connections are no longer stable in their propagation delay.
A bus system for a local operating system is known from DE 42 24 339 A1. The communication transmitted by a subscriber is sent to all subscribers via a star coupler. A frame clock signal is generated by a frame clock signal generator and sent to the star coupler, wherein the chronological sequence of the frame data of the frame clock in the star coupler define a reference frame clock. The further subscribers define an individual frame transmission cycle, taking into consideration the propagation delay to the star coupler.
In German Patent DE 41 34 360 C1, different propagation delays in partial networks are compensated by appropriate propagation delay compensating units. In German Patent DE 42 07 675 C1, bus stations are equipped with frame generators and control devices, which take over the central cycle supply in case of loss or interference. This solution is also phase-locked.


SUMMARY OF THE INVENTION

It is the object of the instant invention to provide a method for providing a frame clock for data signals in which propagation delay stability continues to be maintained, in particular in case of loss or interference.
It is another object of the present invention to provide a switching device in a communication network by means of which propagation time stability can be maintained,

REFERENCES:
patent: 4600896 (1986-07-01), Cellerino
patent: 4914404 (1990-04-01), Ernst
patent: 5184350 (1993-02-01), Dara
patent: 5373537 (1994-12-01), Oberhauser
patent: 5475717 (1995-12-01), Cordonnier et al.

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