WO1998008352A1

WO1998008352A1 - Procedure to improve the capacity of a v5 interface in a wireless local loop environment

Info

Publication number: WO1998008352A1
Application number: PCT/FI1997/000474
Authority: WO
Inventors: Jussi Sarpola; Pekka Multanen; Heimo PENTIKÄINEN; Simo Penttinen; Petri Saarela
Original assignee: Nokia Telecommunications Oy
Priority date: 1996-08-23
Filing date: 1997-08-12
Publication date: 1998-02-26
Also published as: FI963302A; BR9711636A; CA2263580A1; CN1228232A; AU3851997A; EP1016297A1; FI963302A0; FI103370B; FI103370B1; JP2001505722A; AU723323B2

Abstract

The present invention relates to a procedure for maximizing the available capacity of a V5 interface (1) in a wireless local loop environment, in which a terminal device (5) is connected via a radio link to a base station (4a, 4b, 4c) and further to an access node (2) and a telephone exchange (3). The procedure of the invention allows considerably more effective reservation and use of the time slots of the V5 interface than before because it achieves a significant reduction of abortive reservations of time slots.

Description

PROCEDURETOIMPROVETHECAPACITYOFA V5 INTERFACE INA WIRELESS LOCALLOOP ENVIRONMENT

The present invention relates to a procedure for maximizing the available capacity of V5 interface in a wireless local loop environment, in which a terminal device is connected via a radio link to a base station and further to an access node and a telephone exchange.

In a wireless local loop (WLL) , a terminal de- vice is connected via a radio link to an access node. Between the terminal device and the access node there is a base station, by means of which the call signals received via radiocommunication from the terminal device are further transmitted through the access node to the public telephone network and vice versa. The access node is connected to the telephone exchange using 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 local loop, which may be a wired or a wireless network, to be connected using the standard in- terface of a telephone exchange. A dynamic concentrator interface V5.2 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 a total of 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 subscriptions, such as ISDN (Integrated Services Digital Network) basic and system subscriptions as well as other analogue or digi- tal terminal equipment based on semi-fixed connections.

In a prior-art system, there is no way for the telephone exchange to determine whether the terminal de- vice is accessible or not. To set up a call addressed to a terminal device, the call control system of the telephone exchange reserves a time slot in the V5 interface and informs the access node about the call. The ac- cess node reserves resources for the call until the radio network control system announces that the terminal device is inaccessible. Based on this notice, the access node releases the resources it has reserved and informs the telephone exchange about the unsuccessful call se- tup, whereupon the telephone exchange releases the reserved V5 interface time slot, making it available for other users.

The problem with the procedure described above is that when call signals are transmitted from the te- lephone exchange via a concentrated access node to a closed terminal device, this involves unnecessary reservation of local loop capacity. Especially in the V5 interface between the telephone exchange and the access node, such call setup occupies a time slot or time slots to no purpose, because it is only in the access node that information about the inaccessibility of the terminal device is obtained.

The object of the present invention is to eliminate the problem described above. A specific object of the present invention is to produce a procedure that allows more effective utilization of the available capacity of a V5 interface.

As for the features characteristic of the invention, reference is made to the claims. In the procedure of the invention, to maximize the available capacity of a V5 interface in a wireless local loop environment, at least one of the time slots of the V5 interface is reserved for calls from the telephone exchange to the terminal device. Available capa- city refers to the maximum capacity of the V5 interface, which means a certain number of time slots. The local loop environment comprises an access node connected to a telephone exchange via a V5 interface, and a base station communicating with the access node and used to transmit call signals between the access node and the terminal device. In the procedure of the invention, the accessibility of the terminal device is monitored in the telephone exchange and the setup of a call addressed to an inaccessible terminal device is disabled in the telephone exchange. This makes it possible to avoid useless re- servation of time slots in a situation where the terminal device proves to be off and unable to receive calls. A terminal device is accessible when calls can be transmitted to it. The monitoring is based on sending to the telephone exchange access port status data, which is maintained in the access node and indicates the accessibility of the terminal device connected to the access port. The access port status data is preferably updated in the telephone exchange at the same time when the access port status data is updated in the access node. The maintenance and updating of the access port status data is implemented in accordance with the V5 recommendations by means of the control protocol. The access port status may be either OPERATIONAL or BLOCKED, i.e. accessible or inaccessible. Further, the access port status data is preferably updated to BLOCKED when the radio link between the base station and the terminal device is broken, i.e. when the terminal device is outside the coverage area of the base station or when the radio link is broken for other reasons. Thus, the call control system can immediately release the time slot which possibly had been reserved for the terminal device, i.e. if the terminal device was engaged in an active call when the radio link was broken.

In a preferred embodiment, the information re- lating to the accessibility of the terminal device is transmitted via IMSI attach and IMSI detach (IMSI, International Mobile Subscriber Identity) functions car- ried out by the terminal device, which functions are described e.g. in the standards of the ETS 300 530 series. When power is switched on m the terminal device, it starts the IMSI attach function, which in practice corresponds to a standard terminal device location update procedure. Data indicating that the terminal device is operational is generally stored in binary form in the access node. The IMSI detach function is performed when power is switched off from the terminal device. In this case, too, corresponding status data is stored in the access node. In the access node, the status of the terminal device is indicated by the access port status data.

As compared with prior art, the present inven- tion has the advantage that it makes it possible to reduce the load on the call control resources both in the local exchange and in the access node. Furthermore, the invention makes it possible to avoid unnecessary reservations of V5 interface time slots, thus making more ti- me slots available for other calls to be transmitted. A further advantage of the invention is that the terminal device status data can be better monitored using the IMSI attach and detach functions.

In the following, the invention is described in detail by the aid of an embodiment by referring to the attached drawing, which represents a wireless local loop environment according to the present invention.

The wireless local loop system presented in the drawing comprises an access node 2. The access node 2 functions as a concentrating element between a telephone exchange 3 and a terminal device 5, connecting the subscriber to the telephone exchange 3. The access node 2 is connected via a V5.2 interface 1, which comprises 1 - 16 PCM cables (2 Mbit/s) , to the exchange terminal (ET) (not shown) of the telephone exchange 3, the terminal exchange being provided with the functions required by the V5 interface. Moreover, the system illustrated by the drawing comprises a number of base stations 4a, 4b and 4c, each one of which has a given coverage area. In the system presented in the drawing, to set up a connection between a terminal device and the telephone exchan- ge, signals are transmitted via radiocommunication between the base station 4a and the terminal device 5 and further via wired connections from the base station to the access node 2 and via the V5 interface 1 from the access node to the telephone exchange. Further referring to the drawing, when the terminal device 5 is switched on, an IMSI attach function consistent with the above-mentioned recommendations is executed. Via this action, the terminal device 5 informs the network that it is operational, so calls addressed to the terminal device can be transmitted to it. In the access node 2, the status data for the access port corresponding to the terminal device 5 is updated to the value OPERATIONAL. At the same time, the access port status data is also updated in the telephone exchange 3 by means of the control protocol of the V5 interface 1 by updating the subscriber data stored in the telephone exchange for the V5 interface used by the access port.

When power is switched off from an operational terminal device 5, the terminal device carries out an IMSI detach function, for which the terminal device does not expect a confirmation from the base station. Via this action, the terminal device announces that it is not operational, in other words, that the terminal device is inaccessible, which means that no calls can be transmitted to the terminal device. The status data for the access port corresponding to the terminal device is now updated to the value BLOCKED. At the same time, the access port status data is also updated in the telephone exchange 3 by means of the control protocol of the V5 interface by updating the subscriber data for the V5 interface used by the access port, stored m the telephone exchange . Further, when a call is to be set up, a check can be carried out first in the telephone exchange to determine whether the called terminal device is operational or not, by reading the access port status data for the terminal device in question. In this way, abortive reservations of time slots in the V5 interface 1 between the access node 2 and the telephone exchange are avoided .

The invention is not restricted to the embodi- ment example presented above, but many variations are possible within the framework of the inventive idea defined by the claims.

Claims

1. Procedure for maximizing the available capacity of a V5 interface (1) in a wireless local loop en- vironment comprising an access node (2), which is connected to a telephone exchange (3) via the V5 interface, and a base station (4a, 4b, 4c) serving to transmit call signals between the access node and the terminal device (5) , in which procedure at least one time slot in the V5 interface is reserved for calls from the telephone exchange to the terminal device, characterized in that the accessibility of the terminal device is monitored in the telephone exchange; and a call to an inaccessible terminal device is inhibited in the telephone exchange.

2. Procedure as defined in claim 1, characterized in that access port status data indicating the accessibility of the terminal device (5) connected to an access port is transmitted to the telephone exchange (3) .

3. Procedure as defined in claim 2, characterized in that the access port status data is transmitted to the telephone exchange (3) when the access port status data is updated m the access node (2) .

4. Procedure as defined in any one of claims 1 - 3, characterized in that the access port status data is transmitted to the telephone exchange (3) by updating subscriber data for the V5 interface (1), which are stored in the telephone exchange.

5. Procedure as defined in any one of claims 1 - 4, characterized in that an IMSI attach function is carried out by the terminal device (5) when the terminal device is switched on; based on the IMSI attach function, the access port status data for the terminal device is updated to OPERATIONAL, indicating that the terminal device is accessible; and the access port status data is transmitted to the telephone exchange (3) .

6. Procedure as defined in any one of claims 1

- 4 , characterized in that an IMSI detach function is carried out by the terminal device (5) when the terminal device is switched off; based on the IMSI detach function, the access port status data for the terminal device is updated to BLOCKED, indicating that the terminal device is inaccessible; and the access port status data is transmitted to the telephone exchange (3).

7. Procedure as defined in any one of claims 1 - 6, characterized in that the access port status data is updated to BLOCKED when the radio link between the base station (4) and the terminal device (5) is broken.

8. Procedure as defined in any one of claims 1

- 7, characterized in that the access port status data is transmitted to the telephone exchange (3) via the

CONTROL protocol.

9. Procedure as defined m any one of claims 1

- 8, characterized in that the status of the terminal device (5) is monitored in the telephone exchange on the basis of the subscriber data of the V5 interface.