In modern telephony networks, particularly cellular networks, subscribers to the network generally either have a credit account or make use of prepaid airtime. In the first case, the cost of calls made by the subscriber is debited to the subscriber's account, which is paid from time to time, typically monthly, by the subscriber. In the case of prepaid accounts, the subscriber purchases a predetermined amount of airtime in advance, with the airtime balance being stored by the network and being reduced as the subscriber makes calls.

In the case of subscribers making use of prepaid airtime, it is not possible for the subscriber to make outgoing calls once the airtime balance reaches zero or a predetermined minimum balance, and the subscriber's airtime account must be replenished before further calls can be made.

It is an object of the invention to provide a method which permits replenishing of the accounts of subscribers of a communication network, particularly a telephony network.

SUMMARY OF THE INVENTION According to the invention there is provided a method of operating a communication network, the method comprising : establishing a transmission between a sender and a recipient, at least the recipient being a subscriber to the communication network ; and crediting an account of the recipient with a credit value related to the transmission.

Typically, the communication network will be a modern telephony network, and the transmission may comprise voice, a text message, or other data.

Thus, the sender will typically be a telephone caller and the recipient a call recipient, or a message/data sender and recipient, respectively.

The caller may be a subscriber to the same telephony network as the call recipient, or a different network.

The credit value may comprise a quantity of network airtime, a monetary amount, or a number of points or other value units, for example.

Typically, the credit value will comprise network airtime equivalent to conventional prepaid airtime.

The amount of airtime credited to the account of the call recipient may be a fixed amount.

Alternatively, the amount of airtime credited to the account of the call recipient may be related to the cost or duration of the call. For example, the amount may be equivalent to a percentage of the cost of the call.

The cost of the call may be the cost of the call as billed to the caller, or the interconnect cost of the call to the originating network where the caller is connected to a different network than the call recipient, for example.

In addition to crediting an account of the call recipient, the method may include crediting an account of the caller with additional credit or airtime related to the call.

In such a case, the accounts of the call recipient and the caller may be credited in a predetermined ratio.

The method may include monitoring the account status of the call recipient and crediting the account of the call recipient only if one or more predetermined conditions apply.

For example, the account of the call recipient may be credited only if the call recipient has no, or less than a predetermined amount of, remaining prepaid airtime.

The account of the call recipient may be credited a limited number of times, the account of the call recipient being eligible to be credited further only when at least a portion of an accrued credit value is used.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a simplified diagrammatic illustration of a telephony network operable to implement the method of the invention; and Figure 2 is a diagram illustrating the interconnect relationship between different networks.

DESCRIPTION OF EMBODIMENTS The drawing shows, in a highly simplified schematic form, the architecture of a part of a modern GSM mobile telephone network. The diagram does not purport to be comprehensive but merely illustrative. The network will typically embody intelligent network (IN) functionality, but this is not essential for implementation of the invention.

In the network illustrated in Figure 1, a mobile telephone 10 of a caller communicates with a first base station 12 which in turn communicates with a mobile switching center (MSC) 14. The base station 12 comprises a base station controller (BSC) and a base transceiver station (BTS) with associated antenna (not shown). Associated with the mobile switching center 14 is a visited location register (VLR) 16.

A call recipient has a mobile telephone 18 which communicates with a second base station 20. The base station 20 is connected to a further mobile switching center (MSC) 22 with its own associated visited location register 24. (In some cases, the two base stations could be connected to the same MSC. ) The respective mobile switching centers 14 and 22 and the respective visited location registers 16 and 24 are interconnected as shown. The visited location registers are also connected to a home location register (HLR) 26 and to a billing center 28. The MSC's 14 and 22 are also connected to the billing center. The HLR is a central database containing data relating to the account status and predetermined network settings of subscribers. The VLRs are decentralised databases which are updated with data from the HLR relating to a particular subscriber when that subscriber's telephone connects to the MSC in question.

The present invention is applicable to scenarios in which both the caller and call recipient are subscribers to the same network, and to scenarios where the caller is a subscriber to a different network from that of the call recipient. The call recipient will typically be a prepaid subscriber with a prepaid airtime account which is administered by the network, the airtime balance being reduced as calls are made. However, the call recipient could also be a subscriber with a credit account on the network. Thus, in the context of the present invention, the phrase"credit value"has a broad meaning which includes the concept of prepaid network airtime as generally understood in the art, but also includes a monetary credit in the case of a network subscriber with a credit account, or points (or other units of value) redeemable by the subscriber, for example.

When the caller dials the telephone number of the call recipient and a call is established between the caller and the call recipient, the caller is billed for the cost of the call. For example, where the caller and the call recipient are subscribers of the same network, the caller may be billed at R1. 80 per minute for the call.

According to the method of the invention, the balance in the account of the call recipient, whether it is a prepaid airtime account or a credit account, is increased when the call is established. In the simples version of the invention, a fixed, standard amount of airtime or monetary credit can be credited to the call recipient's account when the call is established.

Alternatively, utilising the billing information generated by the network, the balance in the call recipient's account can be increased by an amount related to the cost or duration of the call. This will typically be a percentage of the cost of the call, which can be set by the network operator.

In the above scenario, where the caller and call recipient are subscribers to the same network, the cost of the call is effectively the cost as billed to the caller. In the case of a caller who is a subscriber to a different network, establishing the call from the caller's network (the originating network) to the call recipient's network (the terminating network) incurs a termination fee, typically R1. 20 per minute in South Africa. In this case, where the amount of the credit placed in the call recipient's account is related to the cost of the call, the credit can be based on the interconnect cost.

Figure 2 illustrates the relationship between different networks, with network traffic and hence billing flowing between the networks along the triangular path illustrated.

It will be understood that merely by being a subscriber to a telephony network implementing the method of the invention, call recipients will benefit from the described method, in that the balances in their accounts (whether prepaid airtime accounts or credit accounts) will be increased whenever they are called. Where the caller is a subscriber to the same network as the call recipient, the network operator effectively passes on a portion of the charge levied on the caller to the call recipient (and, optionally, to the caller-so-called bi-directional crediting). Where the caller is a subscriber of a different network, the network operator effectively passes on a portion of the interconnect fee earned by the network from the call to the call recipient (uni-directional crediting).

In a variation of the invention, particularly applicable to the scenario which both the caller and call recipient are subscribers to the same network, both the caller's and call recipient's accounts can be credited in a predetermined ratio.

It will be appreciated that the worldwide emergent standard around interconnecting traffic has seen an extremely profitable source of revenue to operators who terminate traffic originating outside of their network, and the invention leverages this revenue stream in favour of smaller networks which can now incentivize their subscribers to be called (and hence generate interconnect in favour of their home network) rather than to call out of the home network (and incur interconnect fees in favour of the called network). It is envisaged that the described invention will increase network operator revenues, as each call made between subscribers utilising the method of the invention will result in the call recipient receiving further airtime which can be used to make further calls, even in the case of call recipients without airtime/credit of their own. It is expected that such a scheme will attract subscribers to a network offering it.

In order to prevent abuse of the described method, it may be necessary to implement velocity checks or the like. For example, without such checks, a user might be inclined to become addicted to the service and start calling his/her own network number repeatedly from an office telephone, thus loading airtime into his/her private account.

It is also possible to utilise so-called semaphores which essentially comprise rules regulating the operation of the method. For example, the system may only permit a certain number of airtime credits or"recharges" to accrue to a subscriber, then requiring the subscriber to use all or at least some of the accrued credits before being able to accrue further credits.

Similarly, the system may be set up to apply credits only to the accounts of subscribers who have no credit/airtime left, or less than a predetermined amount.

An example of a potentially beneficial scenario which could arise utilising the method of the invention is as follows. A parent may have one or more children, who are given mobile telephones and a certain, relatively small, amount of prepaid airtime per month. By accepting calls from his/her parent, the child's airtime balance is increased, thus encouraging communication between family members. If the child is a member of an approved reverse-charge caller group set up by the parent, as described in International patent application no. PCT/IB2004/001150, making a reverse charge call to the parent will result in billing being applied as if the parent were the caller and the child the call recipient, so that the additional airtime would accrue to the child. This would actively encourage children to call their parents, for example. In such a case, the crediting of airtime to the child who is a member of the approved reverse-charge caller group can be done at a preferential (that is, higher) rate than normal.

Although the invention has been described mainly with reference to the crediting of airtime or monetary value to call recipients, credit value in the form of redeemable points, vouchers, or other forms of credit could be distributed instead. It will also be appreciated that, although the invention has been described mainly with reference to a mobile telephony network, the principles of the invention are applicable to other communication networks.