Multiplex communications – Communication over free space – Having a plurality of contiguous regions served by...
Reexamination Certificate
1999-10-07
2001-08-14
Hsu, Alpus H. (Department: 2661)
Multiplex communications
Communication over free space
Having a plurality of contiguous regions served by...
C370S229000, C379S037000
Reexamination Certificate
active
06275481
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a procedure for setting up an emergency call in a wireless local loop.
2. Description of the Related Art
The invention concerns a wireless local loop system, in which a subscriber is connected over a wireless link via an access node (AN) to a wired network local exchange. The subscriber terminal devices are connected to the access node via a GSM/DCS 1800 interface (GSM, Global System for Mobile Communications; DCS, Digital Cellular System) . The access node is connected to the local exchange via a V5.2 interface consistent with the ETS 300 347 standard series. GSM is a European digital mobile communication system standardized by ETSI. DCS-1800 is a mobile communication system standardized by ETSI, which is based on the GSM specification and aims at a more effective use of microcells and which works in the frequency range of 1800 MHz. Between the terminal device and the access node there is a base station, through which call signals sent by the terminal device over a radio channel are transmitted via the access node to a public telephone network and vice versa. The access node can be connected to the telephone exchange using e.g. the V5.1 or V5.2 protocol.
Open interfaces (V5.1 and V5.2) between an access node and a telephone exchange are defined in the ETSI (European Telecommunications and Standards Institute) standards of the ETS 300 324 and ETS 300 347 series. V5 interfaces enable subscribers belonging to a physically separate access network, which may be either a wired or a wireless network, to be connected to a telephone exchange using a standard interface. A dynamic V5.2 concentrator interface consistent with the standards ETS 300 347-1 and 347-2 consists of one or more (1-16) PCM (Pulse Code Modulation) cables. One PCM cable comprises 32 channels, each of which with a transfer rate of 64 kbit/s, i.e. 2048 kbit/s in all. The V5.2 interface supports analogue telephones as used in the public telephone network, digital, such as ISDN (Integrated Services Digital Network) basic and system subscriptions as well as other analogue or digital terminal equipment based on semi-fixed connections.
A call initiated with an EMERGENCY_SETUP message as described in the GSM system specification may, if the resources prove to be insufficient, star a process of forced release of a call having a lower priority.
When a subscriber connected to the access node of a wireless local loop tries to make an emergency call to a public emergency number and if the call control system of the local exchange is unable to find a free time slot in the V5.2 interface within a predetermined period of time, then the call setup will fail. The subscriber will keep trying again until the call is successfully set up. The standard V5.2 interface contains no definition of forced call setdown or an emergency call as such. When the setup of an emergency call fails due to congestion, the WLL terminal will generate a busy tone for the subscriber. Consequently, the subscriber will try to call again. In practice, the entire signalling required for call setup is generated anew, starting from the allocation of a communication channel, resulting in unnecessary burdening of the wireless network resources.
BRIEF SUMMARY OF THE INVENTION
The object of the present invention is to eliminate the drawbacks described above.
The object of the invention is to disclose a procedure that makes it possible to increase the probability of successful setup of an emergency call and allows an emergency call to be set up over a congested V5.2 interface without repeated allocation of radio resources and without repeated call control signalling within the access node.
In accordance with the invention, there is provided 1. Procedure for setting up an emergency call in a wireless local loop, in which subscriber terminal units (TU) are connected over a wireless link via a base station (BS) to an access node (AN) and further from the access node to a local exchange (LE) via a standard V5.2 interface, in which, when the interface is congested and a subscriber (TU) connected to the access node (AN) is attempting to make an emergency call to a public emergency number, a call control system of the local exchange (LE) is unable to find a free time slot for the setup of the emergency call within a predetermined period of time t1, wherein call setup requests for other than emergency calls over the V5.2 interface are disabled during a predetermined period of time t2, and attempts to reserve a time slot in the V5.2 interface for the emergency call are repeated during the predetermined period of time t2.
In the procedure of the invention, an emergency call is set up in a wireless local loop in a congested situation. In the wireless local loop, WLL terminals are connected over a wireless link via a base station to the access node and further from the access node to a local exchange via a standard V5.2 interface. In a situation where the V5.2 interface is congested, a subscriber connected to the access node tries to make an emergency call to a public emergency number and the call control system of the local exchange is unable to find a free time slot, i.e. a channel for the setup of the emergency call in the V5.2 interface within a predetermined period of time t1.
According to the invention, new call setup requests for other than emergency calls over the V5.2 interface are disabled during a predetermined period of time t2 and attempts to allocate a time slot in the V5.2 interface for the emergency call are repeated during said predetermined period of time or until a channel is successfully allocated. However, it is also possible to implement the procedure of the invention by disabling only new outgoing non-emergency calls from the access node. In this case, new non-emergency calls addressed to subscribers connected to the access node could be enabled. A corresponding arrangement is feasible in all the embodiments described in the present application.
In an embodiment of the procedure, when a free time slot has been allocated in the V5.2 interface for the emergency call within a predetermined period of time t2 as mentioned above, call setup over the V5.2 interface is enabled.
In an embodiment of the procedure, when the subscriber who initiated the emergency call hangs up (subscriber on-hook) before a free time slot is found in the V5.2 interface, the disabled state of setup of new calls is cancelled and call setup is enabled.
In an embodiment of the procedure, when the attempts to allocate a time slot in the V5.2 interface fail during a predetermined period of time t2 as mentioned above, the emergency call is released, the disabled state of setup of new calls is cancelled and call setup is enabled.
In an embodiment of the procedure, a message indicating failure of an attempt to set up an emergency call is given by the V5.2 interface signalling program to the process responsible for the setup of the emergency call, and, via the process responsible for the setup of the emergency call, the higher-level process responsible for signalling is notified about the failed attempt to set up an emergency call. In a preferred embodiment, no such notification is given, but the V5 interface signalling program keeps sending standard establish messages until the attempt is cancelled e.g. when the subscriber hangs up (AN subscriber on-hook). In this case, the hanging up or the tripping of a timer t1 corresponds to a failure of call setup. A corresponding arrangement is also possible in other embodiments described in this application.
In an embodiment of the procedure, new call setup requests are disabled by a higher-level process and attempts to allocate a time slot in the V5.2 interface are continued by the lower-level process responsible for the emergency call.
In an embodiment of the procedure, the predetermined period of time t1 is defined using a first timer controlling normal call setup time, which is started at the beginning of call setup, and the predetermined period of time t2 is defined
Altera Law Group LLC
Hsu Alpus H.
Nguyen Brian
Nokia Networks Oy
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