Pulse or digital communications – Synchronizers – Phase displacement – slip or jitter correction
Patent
1993-05-28
1995-11-28
Chin, Stephen
Pulse or digital communications
Synchronizers
Phase displacement, slip or jitter correction
375326, 375376, 3701053, 370108, H04L 2536, H04L 700
Patent
active
054715105
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention concerns telecommunications.
It is more particularly concerned with an asynchronous transfer mode digital telecommunication network terminal equipment synchronization device.
These networks are well known and will not be described again here. Suffice to say that in a network of this kind the data is structured into fixed length packets or cells each comprising one part reserved for data to be transmitted by the network and a header which includes parameters needed to route the cell through the network and that the cells are routed through the network utilizing the virtual circuit technique, a hybrid of circuit switching and packet switching well suited to transmission through a telecommunication network at various bit rates, including very high bit rates and bit rates that vary irregularly with time.
The transfer time-delays introduced by these networks are variable in time for the same call depending on the instantaneous load at the network nodes.
For some applications including telephony where it is necessary to achieve some degree of synchronism between terminals connected by the network it is then necessary to synchronize the terminals in order to achieve in each terminal correct recovery of data received from the network.
A known way of synchronizing a terminal is to retrieve the transmit clock at the receiving end simply by filtering the transfer jitter introduced by the network.
For example, the transfer jitter can be filtered by continuously varying the frequency of a local clock signal according to measured differences between how much of a buffer is filled by the received data and how full this buffer is expected to be, this corresponding to the current frequency state of this signal.
The drawback of this method is that it is not totally effective in the presence of relatively severe constraints on obtaining the filtered clock signal because, failing improvements which would inevitably render it more complex to implement, it cannot react smoothly and smooth action is essential in some applications.
One such application, for example, involves setting up a call between two terminals one of which is connected to an asynchronous transfer mode network such as the broadband ISDN and the other of which is connected to a synchronous transfer mode digital telecommunication network such as the narrowband ISDN, each of these networks having access points to the other.
An application of this kind therefore raises the problem of the compatibility of the two networks, which are by definition based on different principles, in particular using different interfaces with the terminals connected to them.
The term "interface" encompasses all the concepts relating to the nature of the signals exchanged on the medium connecting the terminal in question to the network in question and the procedures for setting up, maintaining and clearing down a call via the network concerned. The interfaces for each type of network are covered by standards.
The standard defining the So interface between a subscriber and the asynchronous transfer mode ISDN requires each call set-up phase to include, prior to the signalling phase relating to the call, a phase for synchronizing the terminals in question to the network reference clock by sending specific signals to the terminals via the network from which they can recover the reference clock. The signalling and data sent to this interface are structured into frames comprising locations with a fixed assignment either to signalling or to data.
In the case considered here of connecting a terminal to this network via an asynchronous transfer mode network, the standard defining the So interface has to be complied with and the terminal is associated with an adapter and the reference clock signal applied to the terminal outside the synchronized phase is produced by a local clock internal to the adapter.
The clock signal from this local clock enables exchange of signalling and therefore call set-up. Unlike data, signalling is generated sporadical
REFERENCES:
patent: 4759041 (1988-07-01), Anderson et al.
patent: 4841550 (1989-06-01), George et al.
patent: 4945548 (1990-07-01), Iannarone et al.
patent: 5146477 (1992-09-01), Cantoni et al.
patent: 5239544 (1993-08-01), Balzano et al.
patent: 5245636 (1993-09-01), Sari et al.
patent: 5268936 (1993-12-01), Bernardy
patent: 5274680 (1993-12-01), Sorton et al.
patent: 5283787 (1994-02-01), Fletcher et al.
patent: 5291483 (1994-03-01), Nagai et al.
Campana Roland
Renault Denis
Alcatel Cit
Chin Stephen
Le Amanda T.
LandOfFree
Asynchronous transfer mode digital telecommunication network ter does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Asynchronous transfer mode digital telecommunication network ter, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Asynchronous transfer mode digital telecommunication network ter will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2019361