GB2390260A

GB2390260A - Route optimisation in telecommunications networks by determining whether a call has been tromboned

Info

Publication number: GB2390260A
Application number: GB0214615A
Authority: GB
Inventors: Giles Martin Wren-Hilton
Original assignee: Individual
Current assignee: Individual
Priority date: 2002-06-25
Filing date: 2002-06-25
Publication date: 2003-12-31
Anticipated expiration: 2022-06-25
Also published as: GB2390260B; GB0214615D0

Abstract

A telecommuncations switching device 200 performs route optimisation by transmitting an in-band signal on port 213, where inbound call 203 is being presented, and correlating the transmitted signal with the signals received on ports 211 and 212, where outbound calls 201 and 202 are in progress, to establish that device 300 has connected ports 311 and 313 to trombone transfer inbound call 201 to outbound call 203; subsequently device 200 creates a new internal connection 204 and disconnects telephone calls 201 and 203. (A call is 'tromboned' when a call is double routed over a network.) PSTN 100; Telecommunications devices 200, 300 and 400.

Description

( SYSTEM AND METHOD FOR RoUTE OPTIMISATION IN TELECOMMUNICATIONS NETWORKS

Background

In telecommuncations networks, there is a general need to manage network connections so that resources may be used efficiently. One aspect of such management is route optimisation. Route optimisation is the process of examining connections, either as the connection is being requested or after a connection has been established, to evaluate if a more efficient route may be established and subsequently creating a new route and removing the old route. Route optimisation, as described here, is also known as anti tromboning.

One well known example of a route optimisation method is the Call Path Replacement feature of the Q.SIG signalling protocol specified in ETS! standards ETS 300 258 and ETS 300 259. This method requires connected telecommunications devices to support and implement both the Q.SIG protocol and these features.

However there are a large number of telecommunications devices which do not explicitly support any route optimisation method, but for which the addition of route optimisation would be a very desirable feature. The present invention addresses this requirement by providing a system and method of optimising routes when used in connection with telecommunication devices that do not explicitly support route o ptimi sat ion.

The Invention The invention is a telecommunications device having the ability to optimise routes by emitting an in-band signal over a given circuit and then sampling the input from other circuits to establish if that same signal reappears; if the emitted in-band signal is detected, then a new route may be established and the current route may be removed.

A preferred example of such an in-band signal is a direct current (DC) bias, or digitally encoded equivalent. A DC bias has the advantage of being non audible - it is heard as silence - and is particularly suitable for use in route optimisation as a connection is being requested, given that the calling and called parties have not yet been connected so that the insertion of a short period of silence will not interfere with the call. In a digital telecommunications system with bit integrity there is a further advantage that as the DC bias is represented digitally it can be finely controlled and accurately measured according to the sample size of the audio encoding scheme used (e.g. 8-bit for A-law and u-law encoding).

Another example of such an in-band signal is a tone, which may be single frequency of multi-frequency, or digitally encoded equivalent.

The circuit to which the in-band signal is applied is preferably a circuit where an inbound call is being presented to the device. Detection of the emitted in-band signal is preferably achieved by sampling the input at all device ports where outbound calls have been placed. For efficiency, the ports sampled may be only those known by the

( routeptimising device to have outbound calls in place to the device or system from which the corresponding inbound call has come.

It is further desirable to sample the device ports for sufficient continuous duration or at intervals over a sufficient duration to decrease the likelihood of an incorrect signal being interpreted as the emitted signal.

The route-optimising telecommunications device may be a special purpose device or may be a general purpose device such as a voice switch, adapted to optimise routes according to the method described.

Example of Use

Diagram I shows a telecommunications network comprising three telecommunications devices: 200, 300 and 400. Device 200 is a specialpurpose voice switch adapted to provide an optimised route between the PSTN 100 and device 400 after the call has been routed to device 300.

The arrowheads in the diagram represent the direction of call setup, although the circuits 201, 202, 203 and 401 are full duplex.

Telephone call 101 originates from the PSTN 100 and is presented to routeoptimising device 200. Device 200 routes telephone call 101 to device 300 over circuit 201 between ports 21 1 on device 200 and 31 1 on device 300. The call signaling, including answer supervision, is passed from device 300 back to the PSTN 100 via device 200. At this stage, the calling party is connected via device 200 to device 300.

Device 300 subsequently initiates a trombone transfer to device 400 by making a call request over circuit 203 from port 313 to port 213. Device 200 detects the incoming call request and places an in-band signal, in this case a DC bias, on to port 213.

Device 200 then samples the input at all ports where outbound calls are in place (in this example, ports 211 and 212). Because device 300 has established a connection between ports 211 and 213 on device 200 the input on port 211 will be the same as the output on port 213, so the device 200 will detect this when it samples that port.

Device 200 initiates a call to device 400 over circuit 401. When device 400 answers the call (itself, or because a further attached device answers the call), answer supervision is sent back from device 200 to device 300 over circuit 203. Device 200 subsequently completes the route optimization by creating a new internal path 204, routing the call over that path and then removing the connections over circuits 201 and 203 by clearing the calls on those circuits.

In the event that device 400 presents a non-answer condition, such as number engaged or number unobtainable, then device 200 passes the condition back to device 300 over circuit 203. In this case, device 200 would not carry out the step of creating internal path 204 to optimise the route.

For clarification, circuits 201, 202 and 203 may be digital circuits carried over a single bearer using Time Division Multiplexing e.g. separate duplex DSO circuits on a duplex DS 1 bearer.

Claims

1. A system for optimsng routes m telecommunications systems composing a telecommunications switching device which performs the following functions: transmttmg an disband signal on one attached circuit sampling the input on one or more other attached circuits and correlating the transmitted signal and the received signals to establish if the connected telecommunications system has connected (tromboned) the circuit on which the signal is being transmitted to any of the circuits on which the signals are being received.

2. A system as claimed in Claim 1 in which the switching device is a special purpose

device. 3. A system as claimed In Claim l in which the switching device Is a general purpose switching device adapted to provide the transmission reception and correlation functions as described in Claim 1.

4. A system as claimed in Claims 1 to 3 in which the transmitted signal is a single frequency tone.

5. A system as claimed in Claims 1 to 3 in which the transmitted signal Is a multi frequency tone.

6. A system as claimed in Claims 1 to 3 in which the transmitted signal is a Direct Current bias signal.

7. system as claimed in Claims l to 6 in which the connected circuits are analogue circuits. 8. A system as claimed in Claims l to 6 in which the connected circuits are digital clrcults. 9. A system as claimed in any preceedng claim in which the correlation Is performed by comparing the outbound and Inbound signals over a given period of time. lo. A system as claimed in any proceeding claim which acts upon a correlation being detected by: optmismg the route by creating a new internal connection between the circuits which are connected to those circuits where the correlated signal was transmitted and received and disconnecting the circuits at the ports where the correlated signal was transmitted and received.

11. A system as claimed in any proceeding claim in which the functions of transmitting receiving and correlating are initiated when an inbound telephone call is received from the attached telecommumcations system.

12. A system as claimed in Claim 11 in which the route optimization occurs after answer supervision has been detected on an outbound call corresponding to the inbound call.

13. A system substantially according to any example hereinbefore described or illustrated in the accompanying drawings.