A METHOD AND DEVICE FOR OPTIMAL ROUTING IN A TELECOMMUNICATIONS NETWORK. Field
The present invention relates to digital cellular telecommunications systems, such as GSM. In particular, the present invention relates to the routing of calls in a manner that facilitates the consideration of inter network roaming agreements and call charge sharing.
Background
The existing GSM architecture supports, as a primary technical requirement, a function known as optimal routing for mobile-to-mobile calls. A
Gateway Mobile services Switching Centre (GMSC) utilised by an originating caller in a Public Land Mobile Network (PLMN) can interrogate a Home Location
Register in a different PLMN of a called party to obtain routing information for a mobile terminated call. Figure 1 illustrates a particular problem with this optimal routing function.
By way of explanation, let us say that it is desired for a first mobile phone, A, to establish a communication path (set up a call) with a second mobile phone, B. In order for this to occur, the system architecture functions in a manner that the originating PLMN (IPLMN) interrogates the home PLMN of the second mobile phone's subscriber (HPLMN-B) in order ascertain the information necessary to enable optimal routing of the call to be set up. From this, the originating PLMN
(IPLMN) can determine how to route the call to be set up.
In the example illustrated in Figure 1 , the second mobile phone B is registered to its home PLMN in country Y, but is currently situated in country X. The first mobile phone A is also currently situated in country X. The call to be set up, in accordance with existing practice, is optimally routed directly to a visited
PLMN where B is registered (VPLMN-B).
Further still, in the situation where there is to be a diverted call for a roaming subscriber, such as the second mobile phone B, in a public land mobile network (PLMN), when optimal routing is applied, the call is dropped back from the visited PLMN (VPLMN-B) to the interrogating PLMN (IPLMN, subscriber's
home network or originating subscriber's visited network) and then routed directly from the interrogating PLMN (IPLMN) to the call diversion address C.
The problem stems from the fact that the call is dropped back from the visited PLMN (VPLMN-B) to the interrogating PLMN (IPLMN) and this results in a situation where the call is routed without transiting the visited PLMN current servicing the second mobile phone (VPLMN-B). Thus, dropping the call back from the visited PLMN (VPLMN-B) to the interrogation PLMN (IPLMN) results in a decrease of the income for the visited PLMN (VPLMN-B) because the effect of dropping the call back is that less chargeable traffic is routed through the visited PLMN (VPLMN-B). This results in a revenue deficiency.
In order to address the problem reduced chargeable traffic in the situation illustrated, some (but not all) telecommunication or network operators have sought to mutually agree with respect to charging arrangements in the case of optimal call routing. Because these agreements are not always in place creates a further problem in that there is the situation in existing telecommunication infrastructure, where for some mobile phone subscribers, mutual agreements should apply, whereas for other mobile phone subscribers, mutual agreements do not apply because agreements are not in place.
This problem has existed for some time because, at a technical level, networks are configured to operate to either divert all calls or none of them and the ability to selectively divert calls does not exist to date. This stems from the networks being configured to operate in accordance with optimal routing procedures as exemplified above, not necessarily mutual agreements.
There is, therefore, a need to provide a network configuration and / or method of optimal call routing which can support optimal routing and also support mutual agreements where applicable. In particular, it is desirable to have a method and/or configuration which will enable selective application of the charging of diverted calls.
The present invention seeks to address at least one problem of the prior art.
Summary of Invention
The present invention provides a telecommunications system adapted to initiate a communications path between a first mobile phone, registered with a first PLMN, and a second mobile phone, registered with a second visited PLMN, in accordance with a roaming capability, the communications path transiting an interrogated PLMN necessitating an optimal routing procedure to be put into effect, routing means adapted to put into effect, when applicable, optimal routing of calls, the improvement including control means adapted to control the optimal routing of calls in accordance with a first procedure or a second procedure.
The present invention also provides a method of initiating a communications path between a first mobile phone, registered with a first PLMN, and a second mobile phone, registered with a second visited PLMN, in accordance with a roaming capability, the communications path transiting an interrogated PLMN necessitating an optimal routing procedure to be put into effect, the method including the step of providing control of the optimal routing of calls in accordance with at least a first procedure or a second procedure.
Preferably, the first procedure enables normal optimal routing procedures to be used in the setting up of a communications path, and the second procedure enables the setting up of a communications path in accordance with a mutual agreement. The invention also preferably includes means to determine whether there exists a mutual agreement, which has application to the operation of the network. In essence, the present invention seeks to have a network or method, in establishing a communications path, consider whether routing procedures should be established in accordance with optimal routing procedures or in accordance with a mutual agreement.
In one form, the public land mobile network can define for each PLMN whether incoming calls from the interrogating PLMN are subject to optimal routing or some other agreement or procedure.
In one form, it is contemplated that if an MSC of the VPLMN-B, VMSCB detects that a call diversion condition is .unfilled, optimal routing may be applied to the call. In this situation, the optimal routing process is suspended and a check can be made of whether there exists mutual agreement(s) and / or whether conditon(s) in the agreements apply to the current condition and /or call, such as an agreement between PLMNs enabling optimal routing.
It is also contemplated that if the mutual agreement does not allow optimisation of the routing or no agreement exists, the VMSCB will not continue the optimal routing process and the diverted call is routed via the visited PLMN as if no optimal routing were supported in the network. Thus the diverted leg can also be charged by the visited PLMN as without optimal routing.
In one form, the step of checking whether agreements exist may be initiated by checking the GMSC address of the incoming message identifying the interrogating PLMN. If the GMSC address belongs to the PLMN with which the visited PLMN has a mutual agreement to allow optimal routing, the optimal routing handling will be resumed.
A preferred embodiment of the present invention will now be described with reference to the accompnying drawings, in which:
Figure 1 illustrates schematically the prior art arrangement, and Figure 2 illustrates one embodiment of the present invention.
Referring to Figure 2, A sets up a call to B. The originating PLMN (IPLMN) interrogates the HPLMN of the mobile subscriber B (HPLMN-B) in order to route the call. B is registered in the same country as A, and the call is optimally routed directly to VPLMN where B is registered (VPLMN-B). B has activated call diversion to destination C located in the same country as where B is registered. The normal optimal routing procedures lead to dropping the call leg from IPLMN to VPLMN-B and routing of the diverted call leg directly from IPLMN to C. The charging of the diverted call leg is performed in IPLMN. No charging information about the diverted leg will be collected in VPLMN-B. If the VPLMN-B applies the enhanced roaming agreement check before allowing the call to be dropped back to IPLMN, it can prohibit the dropping of the call, if so
required, and the call will be routed via the VPLMN-B to C. VPLMN-B will be thus able to charge for the diverted leg.