Multiplex communications – Wide area network – Packet switching
Patent
1993-10-05
1996-01-23
Marcelo, Melvin
Multiplex communications
Wide area network
Packet switching
455 68, 370 14, H04J 314
Patent
active
054870712
DESCRIPTION:
BRIEF SUMMARY
TECHNICAL FIELD
The present invention relates to an improvement in a cellular TDMA (time division multiple access) mobile telephone system which uses multi-layer protocol in accordance with the so-called OSI-model for the transmission of information.
BACKGROUND
In the European cellular mobile telephone system GSM, all traffic and signalling is transmitted digitally and in accordance with the TDMA method. Signalling and traffic information are both transmitted in radio channels between base stations (BTS) and mobile stations (MS) in the form of bursts (NB) which include, for instance, 156.25 bits, as illustrated in FIG. 1a. A burst (NB) is begun with three start bits (TB) which are followed sequentially by 58 message bits (encrypted), 26 bits included in a training sequence, 58 new message bits (encrypted) and three stop bits (TB). A guard space (GP) corresponding to 8.25 bits is provided between two mutually sequential bursts. A burst will therefore have a total length of 156.25 bits, corresponding to a time period of 0.577 ms. Bursts from different channels are placed sequentially on a radio channel frequency where they form TDMA frames each of 8 bursts, as illustrated in FIG. 1b. Mutually sequential frames in one and the same time slot, e.g. time slot 2, form a channel, for instance a traffic channel (TCH). These bursts contain, for instance, speech information in a digital compressed form, although one burst among 26 bursts in a channel is reserved for a control channel SACCH (slow access control channel) and has been referenced A in FIG. 1c.
As illustrated in FIG. 2, the transmission of information in accordance with the above description can take place either solely between MS (mobile station) and BTS (base station), for instance when transmitting speech information which is coded/decoded in MS and BTS, or may take place between MS and MSC (mobile services centre), via BTS and BSC (base station controller), for instance when concerned with certain signalling.
The protocols contain elements which concern the release of a connection, more specifically a connection release which does not take place when communication is terminated but which occurs as a result of abortion due to poor connection quality or some other abnormal situation and which is monitored on the physical layer or on the data link layer, which is the layer directly above the physical layer as specified in the OSI model. Those layers in the GSM-system which are concerned with this problem are shown in FIG. 3 and have been referenced L1, L2A, L2B. These layers concern the transmission of the physical channel (protocol L1), and also the signalling used for example for establishing and handing over traffic channels (protocol L2A), and also for signalling and information transmission of short message services SMS (protocol L2B).
In the present system (GSM, January 1992), a failure on layer L1, L2A and L2B will cause the physical connection to be aborted. This takes place in the mobile by shutting down the transmitter, and in the base station, either by ordered release of the connection, which therewith guarantees that MS is also released, or by shutting down the transmitter. See FIG. 5. We assume that a traffic channel TCH has been established. The criterion for a failure existing on layer L1 is a fault indication from a leaky bucket counter, which is set to a given value and which counts down one step for each received faulty SACCH (slow access control channel) frame, and which counts up two steps for each correct received SACCH frame (see FIG. 5A). The criterion for a failure existing on layer L2A is missing acknowledgement for FACCH (fast access control channel) for a determined number of times, e.g. 34 times. The criterion for a failure to exist on layer L2B is the non-appearance of an acknowledgement on SACCH (slow access control channel) for SMS (short message service) for a given number of times, e.g. 5 times (see FIG. 5B). As before mentioned, a failure on any of the layers L1, L2A, L2B will thus result in an abortion of the physi
REFERENCES:
GSM Recommendation 04.08, v. 3.8.0, p. 55, section 3.5.2.
Bodin Stig R.
Nordstrand Ingrid V.
Marcelo Melvin
Telefonaktiebolaget LM Ericsson
Vu Huy D.
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