Multiplex communications – Special services – Conferencing
Reexamination Certificate
1997-11-04
2001-03-06
Ngo, Ricky (Department: 2731)
Multiplex communications
Special services
Conferencing
C379S202010, C379S207030
Reexamination Certificate
active
06198729
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a method and a device providing an explicit call transport service (ECT) or similar, in telecommunication.
STATE OF THE ART
According to conventional digital telecommunication system technology several speech channels share the same physical link. The sound in each channel is sampled and the channels are time-multiplexed by division of the time into a number of time slots. In each time slot a sample from one channel is then valid.
In a 32-channel telecommunication system 32 time slots are used in a frame in which the first sample from each channel are transmitted in sequence. The frame is repeated in time so that the second, third etc. sample from each channel can be transmitted. The time slots are usually denoted TS
0
to TS
31
.
One way of sending signalling over a telecommunication system is using a channel, e.g. sent in TS
16
, for common signalling for many channels. Such a signalling system is the Common Channel Signalling System Number 7 (CCS7), which comprises a Message Transfer Part (MTP) and user parts (UP). The user parts can, for instance, be Telephony User Part (TUP) or ISDN User Part (ISUP).
The ITU-report COM 11-R 141-E discusses the problem of loops in telecommunication networks. Loops are something which can arise when explicit call transfer (ECT) is executed. ECT means that a subscriber involved in two calls, which can be incoming or outgoing, disconnects himself while the two other subscribers are still connected. If several involved subscribers do this, a loop can arise which nobody can control.
This is solved in the report by using a special Loop Prevention message (LOP) sent by means of ISUP. When the local exchange belonging to the subscriber involved in two calls gets the request for ECT, it sends a Loop Prevention Request each to the two local exchanges belonging to the other two subscribers and starts a timer. If at least one of the local exchanges gives back a Loop Prevention Response: “No loop exists”, ECT is allowed and executed. If the Loop Prevention Request comes back unchanged or with “simultaneous transfer”, ECT is not executed. If the timer elapses without any response at all coming back or if Loop Prevention Response comes back with “insufficient information”, it is selectable if ECT is to be executed or not.
DESCRIPTION OF THE INVENTION
The problem with the previous solution is that it works only if modem ISUP-signalling is used everywhere in the telephone network. If older types of ISUP or any other type of signalling, such as Telephony User Part (TUP) or Channel Associated Signalling (CAS), are used somewhere, the LOP-message will disappear along the way.
The object of the present invention is to solve this problem by sending a short faint tone or a pattern of tones through one of the set up speech channels and starting a timer at the request of ECT instead of signalling over a signalling channel. If the tone returns in the other speech channel before the timer has elapsed, then there is a loop, and ECT will therefore not be executed. If the tone does not return, there is no loop and ECT will be executed as usual.
The advantage of the present invention is that it always works regardless of which signalling systems are used in the telephone network.
The invention will now be further described, using preferred embodiments and with reference to the annexed drawings.
REFERENCES:
patent: 4920565 (1990-04-01), Strawczynski et al.
patent: 4998243 (1991-03-01), Kao
patent: 5195086 (1993-03-01), Baumgartner et al.
patent: 5583925 (1996-12-01), Bernstein
patent: 5883947 (1999-03-01), Nakamura
patent: 0 428 448 (1991-05-01), None
Raneri, Giovanni, “ITU Report Com 11-4 141-E”, Telecom Italy, Jul. 17, 1995.
Patent Abstracts of Japan, Abstract of JP A 2-25147 (Fujitsu Ltd), Jan. 26, 1990.
Burns Doane Swecker & Mathis L.L.P.
Ngo Ricky
Telefonaktiebolaget LM Ericsson
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