GB2286094A - Call migration in mobile telecommunications - Google Patents

Abstract

Where mobile services are provided by mobile switches connected to the public network in the same manner that Intelligent Network (IN) services are provided by Service Delivery Terminals connected to the public network and the IN Service Delivery Terminals (SDT) contain Mobile Switching Centres connecting to mobile subscribers, the IN-override facility for establishing a path through the public network from a SDT to a calling subscriber or other SDT is supplemented by a seamless-override facility for establishing a new path through the network when a mobile SDT receives a message from the IN message network indicating that a mobile subscriber needs to migrate to that SDT from another in mid-call. <IMAGE>

Description

CALL MIGRATION IN MOBILE TELECOMMUNICATIONS It is proposed that mobile services should be provided by mobile switches connected to the public network in the same manner that Intelligent Network (IN) services are provided by Service Delivery Terminals connected to the public network using the Alternative I.N. architecture described in Application No. GB 9321689.3 imported herein by reference. The proposition enables mobile services to be provided without the need for a separate mobile network and without the need to connect mobile switches in tandem as a call migrates from one switch to another. At all times a call would be routed through the public network over the most direct and economical path from source to destination.

At present the mobile network consists of base stations covering the whole country in a cellular manner. Cell size and the number of base stations within a cell being dependant upon topography and traffic density.

Base stations are star connected to a Base Station Controller (BSC) such that each BSC may have from 1 to 16 base stations. BSC's are in turn star-connected to Mobile Switching Centres (MSC) which provide the greater part of the control functions in the network; the BSC's and base stations having very much sub-ordinate roles.

The architecture proposed can be applied to the existing mobile network but is most effective when the MSC function is provided at BSC level - say at each major town, which may well be the evolutionary objective of the existing mobile network.

According to the present invention there is provided a telecommunications network including a public network with a plurality of switches connecting to fixed subscribers and an Intelligent Network (IN) with a plurality of IN Service Delivery Terminals (SDT) containing Mobile Switching Centres connecting to mobile subscribers, wherein the IN-override facility for establishing a path through the public network from a SDT to a calling subscriber or other SDT is supplemented by a seamless-override facility for establishing a new path through the network when a mobile SDT receives a message from the IN message network indicating that a mobile subscriber needs to migrate to that SDT from another in mid-call.

The term "seamless" is used to refer to the situation where a call is transferred between switches without the users being aware of or being involved in the process.

Figure 1 illustrates diagrammatically the procedure for initial establishment of a call from a fixed subscriber to a mobile subscriber; Figure 2 illustrates diagrammatically the procedure where preparations are made for a new call path to be established to hand-over from that in Figure 1 due to movement of the mobile subscriber; Figure 3 illustrates diagrammatically the procedure for completion of the handover shown in Figure 2; Figure 4 illustrates diagrammatically the procedure for initial establishment of a call from a mobile subscriber to a fixed subscriber; Figure 5 illustrates diagrammatically the procedure for establishment of a call between two mobile subscribers; Figure 6 illustrates diagrammatically the procedure where preparations are made for a new call-path to be established to hand-over from that illustrated in Figure 5 when the calling mobile subscriber moves;; Figure 7 illustrates diagrammatically the procedure where preparations are made for a new call-path to be established to hand-over from that illustrated in Figure 5 when the called mobile subscriber moves.

Referring to Figure 1, normal IN activity as described below, is triggered when a fixed network terminal dials the number of a mobile subscriber.

The local digital exchange sends a message to the IN Service Router containing the Calling Line Identity (CLI), a call-label and the called mobile subscriber's number.

The message includes a classification field indicating the need for special handling when necessary (e.g. coinbox, analogue exchange terminal).

The Service Router will re-address the message to the Mobile Location Service which will in turn re-address the message to the mobile switch currently in contact with the called subscriber.

The mobile switch, which may be connected to any convenient public exchange, will establish a connection through the public network to the calling subscriber using the CLI, the call-label and the IN-override facility in the normal Alternative-lN manner. The connection will be completed through the mobile switch to the called mobile subscriber and the call will progress as normal.

Referring to Figure 2, in the event that the called mobile subscriber migrates from one mobile switch to another while the call is in progress, the old mobile switch will send a message via the IN message network to the new mobile switch. The message will contain the information that was received from the originating exchange via the Mobile Location Service (CLI, label, mobile, number, classification), an indication that the call is migrating and any other relevant information. (This action is similar to that which is employed in the Alternative IN when a call is transferred from one IN service to another.) The new mobile switch will initiate a call through the public network to pick-up the caller using the CLI, call-label and the IN-override facility as before but, because the call is migrating, the IN-override signal will include the need for seamless hand-over as described below.

Upon receiving a request for the seamless handover of an existing call, the final digital exchange will instruct its digital switch to divert the call from the old junction (old mobile switch) to the new junction (new mobile switch) and will include the "seamless" requirement.

Initially, the digital switch will forward the speech samples from the local end to the new incoming junction (new mobile switch) in addition to the existing connection to the old mobile switch. The incoming speech samples from the new incoming junction will be connected only to a special terminal where the sample can be monitored.

Completing the diversion of the call connection from the old junction to the new junction will be delayed until the digital switch identifies that the speech channel from the new junction becomes active.

Referring to Figure 3, after passing the seamless hand-over instruction to the digital switch, the local exchange call processor will return the ADDRESS COMPLETE MESSAGE to the incoming junction (new mobile switch) without waiting for the digital switch to complete the operation.

The new mobile switch will complete the call connection to the newly allocated channel and will send a message via the IN message network to the old mobile switch indicating that the new call-path is ready.

The old mobile switch will instruct the mobile phone to change to the new channel and await the release of the connection.

When the mobile phone changes to the new channel, the speech samples reaching the distant digital exchange will become active and its digital speech will complete the seamless hand-over, informing its call-processor when the action is complete. The call processor will then commence the release of the disused connection.

Referring to Figure 4, when a mobile subscriber dials the number of a fixed subscriber, the mobile switch will establish an ordinary call through the public network to the called subscriber.

The INITIAL ADDRESS MESSAGE (IAM) will include a mark in the CALLING PARTY CATEGORY indicating that the call originates in an IN mobile switch terminal requiring the final digital exchange to return the called line identity, classification and call-label in the ADDRESS COMPLETE MESSAGE to the mobile switch.

The called line identity will be the called directory number in the case of lines terminating on a digital exchange. In the case of lines terminating on dependant analogue exchanges, the called line identity will be that directory number belonging to the final digital exchange which is reserved by the Alternative-I N to enable IN services to pick-up junctions instead of subscribers.

The originating mobile switch will then hold the same information as that held by the terminating mobile switch in Figure 1. If the calling mobile subscriber migrates to another area while the call is in progress, the hand-over will be as detailed in Figures 2and3.

Referring to Figure 5, when a mobile subscriber dials the number of another mobile subscriber or any Intelligent Network service, the originating mobile switch will send a message to the IN Service Router. The message will contain a CLI, call-label, called number and classification field as normal.

The CLI will not be the calling mobile subscriber's number. It will be the mobile switch identity (MSI), a directory number allocated to the mobile switch by the digital exchange to which the mobile switch is connected. Thus, each mobile switch will require a directory number in the same way that a PBX has a directory number.

The call-label will identify the actual call instance within the mobile switch; the called number will be the called mobile subscriber number or other IN service code; the classification will indicate that the call originates in a mobile switch.

The Service Router will re-address the message to the required service or via the Mobile Location Service to the appropriate mobile switch which will establish a call through the public network using the CLI(MSI), call-label and IN-override facility in the normal manner. Upon identifying that the called directory number is a mobile switch, the final digital exchange will perform a tandem function and extend the call to the mobile switch without terminating the C7 signalling (as though the mobile switch were a dependent local exchange).

Because the classification field indicates that the call is from a mobile subscriber, the IAM used by the called service or mobile switch to pick-up the caller will include additional fields containing the terminating CLI, classification and call-label. The CLI being the directory number (MSI) allocated to the called mobile switch or SDT group and the call-label identifying the call connection within that switch or SDT group. (Note that each SDT group requires the allocation of a discrete directory number as does each mobile switch.) Referring to Figure 6, if the calling mobile subscriber migrates to another mobile switch while the call is in progress, a message will be sent via the IN message network from the old mobile switch to the new mobile switch indicating that the call is migrating.

The message will contain the CLI, classification and call-label received from the distant end in the previous IAM.

The new mobile switch will use the CLI and call-label with seamless-override to pick-up the connection; the seamless override being performed by the terminating SDT.

Because the classification indicates that the distant end is a mobile switch or other in SDT, the IAM will include extra fields containing a new originating CLI(MSI), classification and call-label to be stored at the terminating end.

Referring to Figure 7, if the called mobile subscriber migrates to another mobile switch while the call is in progress, a message will be sent via the IN message network from the old mobile switch to the new mobile switch indicating that the call is migrating.

The message will contain the CLI, classification and call-label received from the IN message network when the call was established, or with the information modified by a subsequent IAM if the originating end has since migrated.

The new mobile switch will use the CLI and call-label with seamless-override to pick-up the connection. Because the classification indicates that the distant end is a mobile switch, the IAM will include extra fields containing a new terminating CLI, classification and call-label to be stored at the originating end.

The same procedure would apply if an ordinary IN SDT wished to transfer a call from a mobile subscriber to another SDT; with the exception that "seamless" override would not be required.

In an Alternative-lN environment, the only additions that would be required to existing public or Intelligent network equipment are as follows: (i) The addition of a facility to all public exchange and IN SDT digital switches enabling seamless hand-over as described when a call migrates from one mobile switch to another.

(ii) The allocation of a signal in an IAM, similar to the In-override signal, indicating when necessary, the need for seamless override.

(iiil) The allocation of a signal in the IAM used when a mobile subscriber makes a call to a fixed network subscriber. The signal solicits the return of call identifiers in the ADDRESS COMPLETE MESSAGE from the final digital exchange, enabling the originating mobile switch to transfer the call to another mobile switch if the mobile subscriber migrates.

(iv) The provision of a facility enabling a mobile switch to trigger and initiate IN activity when a mobile subscriber dials the number of another mobile subscriber or other IN service. Similarly, when a SDT requires to initiate an ordinary (non-override) call to a mobile subscriber or other IN service.

(v) The inclusion of call identifiers in the IAM used by a mobile switch or IN Service Delivery Terminal establishing a connection through the public network to pick-up another mobile switch or IN SDT. Thereby the mobile switch or SDT at either end of the connection is able to pass the call to another mobile switch or SDT if the mobile subscriber migrates or the IN service is transferred to another SDT.

(vi) The allocation of a directory number to each mobile switch or SDT group. Calls to this directory number will be passed to the mobile switch or SDT group without terminating the C7 signalling, as though the switch or SDT group were a dependant local exchange. Calls routed to the switch or SDT group in error will fail due to the absence of a relevant call-label etc..

Claims (4)

1. A telecommunications system including a public network with a plurality of switches connecting to fixed subscribers and an Intelligent Network (IN) with a plurality of IN Service Delivery Terminals (SDT) containing Mobile Switching Centres connecting to mobile subscribers, wherein the IN-override facility for establishing a path through the public network from a SDT to a calling subscriber of other SDT is supplemented by a seamless-override facility for establishing a new path through the network when a mobile SDT receives a message from the IN message network indicating that a mobile subscriber needs to migrate to that SDT from another in mid-call.

2. A telecommunications system as claimed in Claim 1, wherein the INITIAL ADDRESS MESSAGE used by a SDT making an ordinary non-override call to a subscriber includes a mark soliciting the return of references in the ADDRESS COMPLETE MESSAGE enabling the subsequent identification of that call connection within the final digital exchange.

3. A telecommunications system as claimed in Claim 1, wherein the INITIAL ADDRESS MESSAGE used by an SDT establishing a call to pick-up another SDT, includes references enabling the subsequent identification of that call connection within the originating SDT.

4. A telecommunications system substantially as hereinbefore described with reference to and as illustrated in the accompanying drawings.