Multiplex communications – Wide area network – Packet switching
Patent
1984-05-04
1986-11-11
Olms, Douglas W.
Multiplex communications
Wide area network
Packet switching
375110, H04J 306
Patent
active
046226656
DESCRIPTION:
BRIEF SUMMARY
FIELD OF INVENTION
The present invention relates to a synchronizing system for synchronizing stored program controlled digital telecommunication stations, according to a synchronizing method selected from a plurality of methods known per se. The stations are interconnected by means of time-division-multiplex (TDM) links. Each station includes an oscillator provided with a frequency regulation input, for generating a transmission pulse swinging about a normal clock pulse, a plurality of adjacent clocks for generating bit pulses at which the station receives information transferred on associated TDM links, a phase difference meter for determining, in accordance with one of said synchronizing methods, phase differences, between the oscillator transmission pulse and the bit pulses of the clocks, and a regulation value generator for converting said phase differences to values for regulating the oscillator frequency.
BACKGROUND
U.S. Pat. No. 4,075,428 describes an apparatus, in a stored program controlled telecommunication station, for generating regulation values according to a given synchronizing method, said values being transmitted to the frequency regulation input of the station oscillator. The known apparatus includes a digital filter and a memory which stores weight factors, each of which is assigned to one of a number of clocks as well as an algorithm for averaging with the aid of the filter and the weight factors, a number of phase differences between pulses from the station oscillator and the clocks. A change of the network synchronizing method is obtained by changing the memory contents.
It is also known, e.g. from a paper No. 132-1 "Transition to a digital telephone network" which was read at the 1976 International Switching Symposium in Kyoto, Japan, to synchronize a digital stored program controlled telecommunication network with the aid of a method suited to the size of the network and the standard of communication, and to change the synchronizing method at certain occasions, e.g. in conjunction with extending the network or improving its standard. Such a synchronizing method change affects the whole network in question and has so far required rather extensive alterations in all the stations of thereof. Even though apparatus according to said U.S. patent are used, a synchronizing method change includes altering the extensive contents in the program memories of the communication network. Such alterations are difficult to carry out without disturbing network operation.
SUMMARY OF INVENTION
It is an object of the invention to provide an improved synchronizing system for telecommunication systems.
As will be shown in greater detail hereinafter synchronizing system provided in accordance with the invention enables changing between a plurality of network synchronizing methods known per se without suffering operational disturbances. Digital stored program controlled stations are provided with a standard such that various synchronizing principles are feasible at any time. In each station there is arranged a plurality of regulation value generators each associated with its own principle. During each network operational period, the synchronizing method best suited to the occasion is selected with the aid of a few specifications characteristic of the principle. In addition to the regulation value generator in question, these specifications indicate the clocks affecting the phase difference averaging according to the selected principle, and are stored as control information in the program memory of the network.
BRIEF DESCRIPTION OF DRAWING
The invention will be explained hereinafter with reference to the appended drawing, wherein the sole FIGURE illustrates part of a network synchronizing system provided in accordance with the invention and included in a stored program controlled digital telecommunication station having a plurality of adjacent clocks and a master clock.
DETAILED DESCRIPTION OF THE INVENTION
An individual station included in a digital telecommunication network does not need to kno
REFERENCES:
patent: 3869579 (1975-03-01), Karl
patent: 3936604 (1976-02-01), Pommerening
patent: 4042781 (1977-08-01), Dragotinov
patent: 4074080 (1978-02-01), Dragotinov et al.
patent: 4075428 (1978-02-01), Ghisler et al.
patent: 4339817 (1982-07-01), Hata et al.
Jonsson Stig R. E.
Larsson Lars-Erik A.
Olms Douglas W.
Rokoff Kenneth I.
Telefonaktiebolaget LM Ericsson
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