GB2396524A

GB2396524A - Generating billing information in a packet switched communication system

Info

Publication number: GB2396524A
Application number: GB0229416A
Authority: GB
Inventors: Maya Benson; Howard Thomas
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2002-12-17
Filing date: 2002-12-17
Publication date: 2004-06-23
Anticipated expiration: 2022-12-17
Also published as: GB2396524B; GB0229416D0

Abstract

The invention relates to a system for generating billing information for a communication system comprising a packet control unit (215) that controls data packet communication over a wireless interface (211). The data packets are buffered in a buffer (217). A separate billing network element (219) collects billing information for the data packet communication. In accordance with the invention, the packet control unit (215) determines (307) that a packet data communication has terminated, for example due to a handover. In response, the packet control unit (215) generates (311) buffer information comprising information as to how much data is discarded in the buffer. The packet control unit communicates (311) the buffer information to the billing network element (219). When receiving the buffer information, the billing network element modifies (319) a billing record in response to the buffer information. Specifically, an indication of the amount of data communicated is reduced by the amount of discarded data. The invention is particularly applicable to a GPRS or UMTS communication system.

Description

METHOD AND APPARATUS FOR GENERATING BILLING

INFORMATION

5 Field of the invention

The invention relates to a method and apparatus for generating billing information and in particular to a method and apparatus for generating billing information in cellular communication system.

Background of the Invention

FIG. 1 illustrates the principle of a conventional cellular communication 15 system 100 in accordance with prior art. A geographical region is divided into

a number of cells 101, 103, 105, 107 each of which is served by base station 109, 111, 113, 115. The base stations are interconnected by a fixed network which can communicate data between the base stations 109, 111, 113, 115. A mobile station is served via a radio communication link by the base station of 20 the cell within which the mobile station is situated. In the example of FIG. 1, mobile station 117 is served by base station 109 over radio link 119, mobile station 121 is served by base station 111 over radio link 123 and so on.

As a mobile station moves, it may move from the coverage of one base station 25 to the coverage of another, i.e. from one cell to another. For example mobile station 125 is initially served by base station 113 over radio link 127. As it moves towards base station 115, it enters a region of overlapping coverage of the two base stations 115 and 113, and within this overlap region, it changes to be supported by base station 115 over radio link 129. As the mobile station 30 125 moves further into cell 107, it continues to be supported by base station 115. This is known as a handover or handoff of a mobile station between cells.

A typical cellular communication system extends coverage over typically an entire country and comprises hundreds or even thousands of cells supporting thousands or even millions of mobile stations. Communication from a mobile 5 station to a base station is known as uplink, and communication from a base station to a mobile station is known as downlink.

The fixed network interconnecting the base stations is operable to route data between any two base stations, thereby enabling a mobile station in a cell to 10 communicate with a mobile station in any other cell. In addition, the fixed network comprises gateway functions for interconnecting to external networks such as the Public Switched Telephone Network (PSTN), thereby allowing mobile stations to communicate with landline telephones and other communication terminals connected by a landline. Furthermore, the fixed 15 network comprises much of the functionality required for managing a conventional cellular communication network including functionality for routing data, admission control, resource allocation, subscriber billing, mobile station authentication etc. 20 Currently the most ubiquitous cellular communication system is the 2nd generation communication system known as the Global System for Mobile communication (GSM). GSM uses a technology known as Time Division Multiple Access (TDMA) wherein user separation is achieved by dividing frequency carriers into 8 discrete time slots, which individually can be 25 allocated to a user. A base station may be allocated a single carrier or a plurality of carriers. One carrier is used for a pilot signal that further contains broadcast information. This carrier is used by mobile stations for measuring the signal level of transmissions from different base stations, and the obtained information is used for determining a suitable serving cell during initial access 30 or handovers. Further description of the GSM TDMA communication system

can be found in 'The GSM System for Mobile Communications' by Michel

Mouly and Marie Bernadette Pautet, Bay Foreign Language Books, 1992, ISBN 2950719007.

To further enhance the services and performance of the GSM communication 5 system, a number of enhancements and additions have been introduced to the GSM communication system over the years.

One such enhancement is the General Packet Radio System (GPRS), which is a system developed for enabling packet data based communication in a GSM 10 communication system. Thus, the GPRS system is compatible with the GSM (voice) system and provides a number of additional services including provision of packet data communication, thereby augmenting and complementing the circuit switched communication of a traditional communication system. Furthermore, the packet based data communication 15 may also support packet based speech services. The GPRS system has been standardised as an add-on to an existing GSM communication system, and can be introduced to an existing GSM communication system by introducing new network elements. Specifically, a number of Serving GPRS Support Nodes (SGSNs) and Gateway GPRS Support Nodes (GGSNs) may be introduced to 20 provide a packet based fixed network communication.

Currently, 3rd generation systems are being rolled out to further enhance the communication services provided to mobile users. The most widely adopted 3rd generation communication systems are based on Code Division Multiple 25 Access (CDMA) wherein user separation is obtained by allocating different spreading and scrambling codes to different users on the same carrier frequency. An example of a communication system using this principle is the Universal Mobile Telecommunication System (UMTS), which is currently being deployed. UMTS has been designed for packet communication and with 30 a view to GSM compatibility. Specifically, UMTS has been designed to include SGSNs and GGSNs for packet data routing.

Further description of UMTS can be found in 'WCDMA for UMTS', Harri

Holma (editor), Antti Toskala (Editor), Wiley & Sons, 2001, ISBN 0471486876.

5 The emergence of packet data communication has required that new methods of billing or charging are developed. Traditional circuit switched cellular communication systems typically determine the duration of a call and derive a cost as proportional to the duration. However, in packet based communication systems an improved billing method is to determine the amount of data that 10 has been communicated and determine a cost from this. Specifically, the number of data packets communicated may be counted and used for determining the cost.

A problem typically encountered in packet communication networks is that 15 billing is performed in a different location than the communication element communicating with the end user. This requires that the billing processor is provided with information of the number of communicated data packets.

Frequently, this is done by counting the number of data packets that have been transmitted to the communication element communicating with the end 20 user. However, this may provide an erroneous cost determination as data packets may be lost before they reach the end user. Hence, the user may be charged for data that has not been received.

Specifically for a GPRS or UMTS communication system, data may frequently 25 be lost due to cell reselection (hangovers) or buffer overflows. In GPRS and UMTS, a Packet Communication Unit (PCU) controls packet data communication over the radio interface. The PCU is typically comprised in a Base Station Controller for a GSM radio access network and in a Radio Network Controller for a UMTS radio access network. However, the collection 30 of information for billing is performed in an SGSN and therefore data packets

which are lost after having been communicated from the SGSN to the PCU may be charged for.

According to the standards, GPRS mobile stations perform cell change 5 autonomously without involvement by the PCU. Following cell reselection, the PCU has no visibility of the mobile station's new location until it gets informed of this by the SGSN. If cell reselection is performed during packet transfer mode, the PCU has to buffer any data received from the SGSN for this mobile.

In conventional GPRS systems there are no provisions guaranteeing that the 10 remaining packets will be forwarded to a new PACKET CONTROL UNIT, and therefore the PCU may simply discard the buffered data packets. Since billing information is provided by the SGSN, the user will be billed for the packets that the PCU has discarded.

15 It has been proposed that the problem of lost packets may be resolved by implementing buffering in the SGSN, thereby enabling the SGSN to forward packets discarded by the old PCU to the new one. However, since SGSN buffering has to be performed for each individual mobile, this solution is complex, expensive and in particular has a very high memory requirement.

Hence, an improved system for generating billing information would be advantageous and in particular a system allowing for increased accuracy, reduced complexity, and/or reduced cost would be advantageous.

Summary of the Invention

Accordingly, the Invention seeks to mitigate, alleviate or eliminate one or more of the above mentioned disadvantages singly or in any combination.

According to a first aspect of the invention, there is provided a method of generating billing information for a communication system comprising a packet control unit operable to control data packet communication over a wireless interface, the packet control unit comprising buffering means for 5 buffering data packets, the communication system further comprising a billing network element operable to collect billing information associated with the data packet communication; the method comprising the steps of determining that a communication associated with the packet control unit has terminated; the packet control unit generating buffer information in response to buffered 10 data associated with the communication; communicating the buffer information to the billing network element; and the billing network element modifying a billing record in response to the buffer information The invention allows for a billing record to be modified in relation to a status 15 of the buffer means of the packet control unit when a communication through the packet control unit terminates. Specifically, the billing record may be modified to reflect loss of data associated with the termination of the communication. The communication may be continued over the wireless interface by another packet control unit. The billing record may be any means 20 for collecting or storing information related to billing. The communication system may for example be a cellular communication system or a Wireless Local Area Network (WLAN). The method does not rely on buffering in the billing network element and has low memory requirements. The invention enables improved accuracy of the billing information, is low complexity, easy 25 to implement and/or may be implemented at low cost.

According to a feature of the invention, the buffer information comprises an indication of a remaining buffer data quantity associated with the communication. This allows for the billing information to be corrected for any 30 remaining buffer data that is discarded thereby providing more accurate billing information.

According to another feature of the invention, the remaining buffer data quantity comprises an indication of a number of data packets of the communication that are present in the buffering means. This allows for a 5 simple implementation suitable for packet data communication systems.

According to another feature of the invention, the step of modifying comprises reducing a communicated data quantity parameter of the billing record in response to the buffer information. Preferably the billing record comprises 10 information related to the data quantity that has been communicated and this is reduced to reflect lost data. This allows for improved accuracy of the billing information. According to another feature of the invention, the communication comprises a 15 plurality of sub-communications. The communication may comprise several subcommunications such as different data services having different associated costs. For example, a GPRS communication system may provide a communication having sub-communications with different Packet Data Protocol (PDP) contexts. Hence, the invention allows for improved billing 20 information related to a plurality of sub-communications of a communication.

According to another feature of the invention, the sub-communications comprise sub communications having different quality parameters. Different quality parameters may be associated with different costs and the modification 25 of the billing record may compensate accordingly. Hence, improved accuracy of the billing information may be achieved for a communication comprising sub-

communications having different quality parameters and associated costs.

According to another feature of the invention, the sub-communications 30 comprise sub communications having different associated billing parameters.

The billing parameters may be associated with cost but may for example also

be associated with billing account, billing time or billing location. Hence, improved billing accuracy may be achieved for a communication comprising sub-communications having different billing parameters.

5 According to another feature of the invention, the sub-communications comprise sub communications having different sources of origin. The billing account, billing time, cost or billing location may depend on the source of origin. Hence, improved billing accuracy may be achieved for a communication comprising sub-communications having different sources of origin.

According to another feature of the invention, the method further comprises the step of the billing network element determining a distribution of the communication between the plurality of sub communications, and the step of modifying the billing record comprises modifying data of the billing record 15 associated with the plurality of sub-communications in response to the distribution. This allows for individual components of the billing record associated with different subcommunications to be modified appropriately even if the buffer information comprises no information related to which sub-

communications the information is related. As a specific example, the billing 20 network element may determine that a communication comprises 20% data packets for a first sub-communication and 80% data packets for a second sub-

communication. If the billing network element receives buffer information indicating that 10 data packets have been discarded, it may reduce a packet data count of the first sub-communication by 2 data packets and a packet data 25 count of the second sub-communication by 8 data packets According to another feature of the invention, the method further comprises the step of the billing network element determining a subcommunication parameter of the plurality of sub-communications associated with a previous 30 data packet, and the step of modifying the billing record comprises modifying data of the billing record associated with the sub-communication parameter.

This allows for individual components of the billing record associated with different sub-communications to be modified appropriately even if the buffer information comprises no information related to which subcommunications the information is related. For example, data packets may tend to come in 5 bursts of data packets related to one of the subcommunications. The billing network element store information of which sub-communication the last data packet related to. When receiving buffer information, it is assumed that any information related to discarded or lost data relates to the sub-communication of the last data packet.

According to another feature of the invention, the step of modifying the billing record comprises the step of associating the buffer information with data packets communicated to the packet control unit in response to a time indication of the data packets. This allows appropriate subcommunications to 15 be identified from a time indication. For example, the billing network element may store a time indication of all data packets sent to the packet control unit and when receiving buffer information may access the stored time indications to determine which subcommunications these relate to.

20 According to another feature of the invention, the communication system is a cellular communication system. Hence, a method is provided allowing for generation of billing information of improved accuracy in a cellular communication system.

25 According to another feature of the invention, the step of determining that the communication has terminated comprises determining that a handover of the communication has occurred. Hence, a method is provided allowing for generation of billing information of improved accuracy when a communication unit performs a handover in a cellular communication system.

According to another feature of the invention, the cellular communication system is a General Packet Radio Service (GPRS) communication system and the billing network element comprises a Serving GPRS Support Node (SGSN).

Hence, a method is provided allowing for generation of billing information of 5 improved accuracy in a GPRS communication system.

According to another feature of the invention, the cellular communication system is a Universal Mobile Telecommunication System (UMTS) and the billing network element comprises a Serving GPRS Support Node (SGSN).

10 Hence, a method is provided allowing for generation of billing information of improved accuracy in a UMTS communication system.

According to another feature of the invention, the packet control unit is part of a base station system. Hence, a method is provided allowing for generation of 15 billing information of improved accuracy for a system wherein the packet control unit is part of a base station system while allowing for the billing information to be generated outside of the base station system. For GSM based GPRS communication systems, the base station system comprises base stations and a Base Station Controller. For UMTS communication systems, 20 the base station system comprises Node Bs and a Radio Network Controller.

According to a second aspect of the invention, there is provided a communication system including a packet control unit operable to control data packet communication over a wireless interface, the packet control unit having 25 buffering means for buffering data packets, the communication system further including a billing network element operable to collect billing information associated with the data packet communication; the communication system comprising: means for determining that a communication associated with the packet control unit has terminated; means for generating buffer information in 30 response to buffered data associated with the communication; means for communicating the buffer information from the packet control unit to the

billing network element; and means for the billing network element modifying a billing record in response to the buffer information These and other aspects and advantages of the invention will be apparent from 5 and elucidated with reference to the embodiment(s) described hereinafter.

Brief Description of the Drawings

10 An embodiment of the invention will be described, by way of example only, with reference to the drawings, in which FIG. 1 is an illustration of a cellular communication system in accordance with the prior art;

FIG. 2 is an illustration of a GPRS cellular communication system 200 in accordance with an embodiment of the invention; and FIG. 3 is an illustration of a method of generating billing information in 20 accordance with an embodiment of the invention.

Detailed Description of a Preferred Embodiment of the Invention

25 The following description focuses on an embodiment of the invention

applicable to a cellular communication system and in particular to a GPRS cellular communication system. However, it will be appreciated that the invention is not limited to this application but may be applied to many other communication systems including for example Wireless Local Area Networks 30 (WLANs) and 3rd Generation cellular communication systems.

FIG. 2 is an illustration of a GPRS cellular communication system 200 in accordance with an embodiment of the invention.

The GPRS cellular communication system 201 is integrated with a 5 conventional GSM communication system. The communication system 200 comprises a number of base stations 201, 203, 205, 207which comprise functionality for communicating with communication units in accordance with the GPRS or GSM communication protocols depending on the nature of the communication unit and the service provided. For clarity and brevity, FIG.2 10 illustrates only a few functional elements associated with the described GPRS functionality. It will be appreciated that a practical GSM/GPRS communication system will comprise many additional functional elements as is well known in the art.

15 FIG. 2 illustrates a base station 203 supporting a GPRS communication unit 209 over a radio interface communication link 211. A communication unit may typically be a wireless user equipment, a subscriber unit, a mobile station, a communication terminal, a personal digital assistant, a laptop computer, an embedded communication processor or any communication element 20 communicating over the radio interface. The GPRS communication unit 209 communicates with the base station 203 in accordance with the GPRS standards. The base station 205 is coupled to a first Base Station Controller (BSC) 213 25 which is also coupled to another base station 201. The BSC 213 conveys information to and from the base stations 201, 205. In addition, much of the radio resource allocation is performed in the BSC 213. For example, the BSC 213 is responsible for controlling handovers of communication units between base stations.

In the shown embodiment, the BSC 213 is furthermore coupled to a packet control unit 215. The packet control unit 215 is responsible for allocation of packet data resources of the radio interface. In particular, the packet control unit 215 is responsible for scheduling GPRS data packets on the radio 5 interface. The BSC 213 receives data for communication over the radio interface. This is fed to the packet control unit 215 which schedules the data packets for the communication. The data packets are not received synchronously with the availability of the resource over the radio interface, and therefore the packet control unit 215 may need to temporarily store data 10 packets for later transmission. Therefore, the packet control unit 215 is connected to a buffer 217 which is capable of temporarily storing the packet data to be transmitted over the radio interface.

In the preferred embodiment, the packet control unit is part of a base station 15 system comprising a BSC 213 and associated BTSs 201, 203. Specifically, the packet control unit 215 and buffer 217 may be integrated with the BSC 213.

The BSC 213 is coupled to a first Serving GPRS Support Node (SGSN) 219, which is part of a packet based interconnecting network and comprises 20 functionality for routing the data from the GPRS communication units towards the desired destination. The SGSN 215 further provides mobility and session management functionality for the GPRS services.

The SGSN 215 is coupled to a number of other GPRS Serving Nodes of which 25 one is shown in FIG. 2. Hence, the SGSN 219 is shown to be coupled to a second SGSN 221, which is operable to serve the GPRS communication units in another given geographical area.

The second SGSN 221 is further coupled to a second BSC 223 which controls 30 two base stations 205, 207. The second BSC 223 is additionally coupled to a

second packet control unit 225, which is responsible for scheduling data packets over the associated radio interface communication links.

The GPRS communication unit 209 may initially be attached to a first base 5 station 203. Packet data communication will accordingly be controlled by the first packet control unit 215. Hence, the first SGSN 219 will forward data packets to the BSC 213 which then forwards it to the first packet control unit 215. The first packet control unit 215 temporarily stores the data packets in the buffer 217. The first packet control unit 215 then schedules packets for 10 communication by the base stations 201, 203 for a given time interval, and subsequently proceeds to communicate the appropriate data packets from the buffer 217 to the base stations 201, 203 through the BSC 213.

However, the GPRS communication unit 209 may perform a cell reselection 15 due to the prevailing propagation conditions or a change in location. As a specific example, the GPRS communication unit 209 may attach to a second base station 205 associated with the second SGSN 221. Accordingly, any further data packets communicated from the first base station 203 will be lost.

In connection with the cell reselection, the second SGSN 221 receives 20 information from the GPRS communication unit 209 that it has attached to the second base station 205. Accordingly, GPRS mobility management signalling is exchanged between the second SGSN 221 and the first SGSN 219.

Consequently, any further data packets to the GPRS communication unit 209 will be forwarded by the first SGSN 219 to the second SGSN 221 rather than 25 to the first BSC 213.

In the GPRS communication system of FIG. 2, the SGSNs 219, 221 collect billing information related to the packet data communication. Specifically, the first SGSN 219 counts all data packets communicated to the first BSC 213.

30 Following the cell reselection (or handover), the second SGSN 221 proceeds to count the number of data packets communicated to the GPRS communication

unit 209. The data packet counts are included in Call Detail Records (CDRs), which are communicated to a billing processor (not shown) wherein a cost associated with the packet data communication is determined.

5 In the example of FIG. 2, the first SGSN 219 determines the data packet count by counting how many data packets are sent to the first BSC 213. However, at the time of the GPRS communication unit 209 performing a cell reselection, the first buffer may comprise data packets for the GPRS communication unit 209. These data packets cannot be communicated to the GPRS communication 10 unit 209 but have already been counted by the first SGSN 219.

In the preferred embodiment, the BSC 213 determines that the communication with the GPRS communication unit 209 through the first BSC 213 has terminated. Preferably, this is determined from the first SGSN 219 15 communicating termination information to the first BSC 213. In response, the first BSC 213 triggers the first packet control unit 216 to generate buffer information related to the buffered data associated with the communication.

Specifically, the first packet control unit 215 determines how many data packets for the GPRS communication unit 209 remain in the buffer 217. This 20 information is subsequently communicated to the first SGSN 219, and the data packets are discarded from the buffer. In response, the first SGSN 219 compensates for the data packets remaining in the buffer 217. Specifically, the data packet count of a CDR is reduced by the number of packets remaining in the buffer 217. Accordingly, the CDR comprises a correct count of the number 25 of data packets communicated to the GPRS communication unit 209 through the first BSC 213. Hence, improved billing information is achieved.

In most communication systems, including TOP communication in GPRS communication systems, lost data packets are re-transmitted. Hence, any data 30 lost by discarding the data packets in the buffer will be compensated by re-

transmissions through the second SGSN 221. As the data packets

communicated through the second SGSN 221 are counted, the combined billing information will accurately reflect the number of data packets communicated to the GPRS communication unit 209 either through the first BSC 213 or the second BSC 223. FIG. 3 is an illustration of a method of generating billing information in

accordance with an embodiment of the invention. The method relates to generation of billing information for a communication comprising a plurality of sub-communications. The method of FIG. 3 will be described with reference to 10 the communication system of FIG. 2.

In step 301 data packets are communicated from the first SGSN 219 to the first BSC 213 for communication to the GPRS communication unit 209. In the specific embodiment, the communication to the GPRS communication unit 209 15 comprises a plurality of sub-communications. Specifically, a number of different services having different parameters have been set up. Specifically, the GPRS communication unit 209 may be provided with a plurality of services having different PDP contexts. These subcommunications may thus have different quality parameters. For example, different sub-communications 20 may have different requirements for data rate, error rate and delay.

It is within the contemplation of the invention, that the sub communications may have different associated billing parameters. Specifically, the different quality parameters may have different associated costs. Thus the cost for a 25 sub-communication having a high data rate, low error rate and low delay will tend to have a significantly higher associated cost than a sub-communication having a low data rate, high error rate and high delay. Hence, billing information should be derived not only for the communication as a whole but also for each individual sub-communication.

Each sub-communication may further be received from different sources of origin. Different billing parameters may be associated with different sources of origin. For example, some services may be provided from specific sources at an increased cost, or some services may be associated with a discount or a part 5 payment from the originating source. Accordingly, the billing information preferably comprises information related to each sub-communication and the therewith associated source of origin.

Hence, in the described embodiment, a communication to the GPRS 10 communication unit 209 comprises a plurality of sub-communications and the billing information is preferably determined for each sub- communication individually. Step 301 is followed by step 303. In step 303, a quantitative measure of the 15 data communicated to the GPRS communication unit 209 by each sub-

communication is determined. Specifically, each data packet for each of the sub-communications is counted and a packet data count for each sub-

communication is updated accordingly.

20 Step 303 is followed by step 305. In step 305, a distribution of the communication between the plurality of sub-communications is determined. In the specific embodiment, an average ratio for traffic for each sub-

communication is determined. For example, if two sub-communications are comprised in the communication and 20 data packets have been communicated 25 for the first sub-communication and 80 data packets have been communicated for the second sub-communication within a given evaluation time interval, the distribution is determined as 20% for the first subcommunication and 80% for the second sub-communication.

30 Step 305 is followed by step 307. In step 307, it is determined if the communication associated with the first packet control unit 215, and thus the

first BSC 213, has terminated. If not, the method continues in step 309 and otherwise the method continues in step 311.

In the preferred embodiment, the first SGSN 219 communicates a control 5 signal to the first packet control unit 215 through the first BSC 213 indicating that the communication has ended. This control signal may be instigated by the first SGSN 219 being informed of the GPRS communication unit 209 having performed a cell reselection. Alternatively or additionally, the packet control unit 215 may determine that no data has been communicated to the 10 GPRS communication unit 209 within a given time interval, and therefore that it is likely that the communication has terminated.

If the communication has not terminated, the packet control unit 215 schedules and buffers the data packets in step 309. Step 309 further comprises 15 sending these to the base station 203 and communicating them to the GPRS communication unit 209.

If the communication has terminated, the method proceeds in step 311 wherein the packet control unit 215 generates buffer information in response 20 to buffered data associated with the communication. The buffer information is preferably a remaining buffer data quantity associated with the communication, and specifically the remaining buffer data quantity comprises an indication of the number of data packets which still remain in the data buffer. This data is then discarded.

Preferably the buffer information comprises an indication of how many data packets of each sub-communication have been discarded. However, in some communication systems this information is not available to the packet control unit 215. Hence, in the described embodiment, the buffer information 30 comprises no indication of how the data packets relate to the individual sub

communications. Specifically, the buffer information may simply contain the amount of data packets that have been discarded.

Step 311 is followed by step 313. In step 313 the buffer information is 5 communicated to the first SGSN 219.

Step 313 is followed by step 315. In step 315, the first SGSN 219 extracts the remaining buffer data quantity from the buffer information. Specifically, the number of discarded data packets is extracted from a message comprising the 10 buffer information.

Step 315 is followed by step 317. In step 317, the remaining buffer data quantity is allocated to the different sub-communications. Specifically, it is assumed that the distribution of data packets between the sub 15 communications determined in step 305 is applicable to the discarded data packets. Hence, the remaining buffer data quantity, and specifically the number of discarded data packets, is allocated to each sub-communication in response to the distribution. As a specific example, if the buffer information indicates that 20 data packets have been lost, and if the distribution indicated 20 a 20% traffic ratio for the first subcommunication and an 80% traffic ratio for the second sub-communication, 4 discarded data packets will be allocated to the first sub-communication and 16 discarded data packets to the second sub-

communication. 25 Step 317 is followed by step 319. In step 319 the first SGSN 219 modifies a billing record in response to the buffer information, and specifically the data of the billing record associated with each of the plurality of sub-communications is modified in response to the remaining buffer data quantity as allocated to each of the subcommunications. More specifically, a billing record may 30 comprise a CDR for each sub-communication, and the CDR may comprise a data packet count for the corresponding sub-communication. The data packet

counts of the CDRs are reduced in accordance with the allocation of lost or discarded data packets to each sub communication. In the previous specific example, a data packet count of a CDR associated with the first sub communication will be reduced by four data packets and a data packet count of 5 a CDR associated with the second sub-communication will be reduced by 16 data packets.

Hence, this embodiment allows for accurate billing information to be generated for a plurality of sub-communications even if the buffer information 10 comprises no information related to the individual subcommunications.

In other embodiments, the first SGSN 219 may determine a sub-

communication parameter of the plurality of sub-communications associated with a previous data packet, such as for example the last communicated data 15 packet. The billing record may be modified in response to the sub-

communication parameter. For example, a sub-communication parameter may be determined as the sub-communication to which the last data packet belonged. The first SGSN 219 may consequently assume that any buffer information received relates to the same sub-communication and accordingly 20 reduce the packet data count associated with that sub- communication. As a specific example, if the buffer information indicates that 20 data packets have been discarded, and if the last data packet belonged to the first sub-

communication, the data packet count of the CDR of the first sub-

communication will be reduced by 20 data packets. This approach is 25 specifically suited for embodiments wherein data packets of different sub-

communications tend to be communicated apart from each other.

In another embodiment, a time indication may be associated with data packets. For example, the first SGSN 219 may store a time indication and an 30 associated sub-communication parameter for each data packet communicated to the first BSC 213. The first SGSN 219 may then modify the billing record by

associating the buffer information with the time indication of the communicated data packets. As a specific example, the first SGSN 219 may upon receiving information that 20 data packets have been discarded determine the associated sub-communications by looking up the stored sub 5 communication parameters of the last 20 data packets communicated to the first BSC 213. This provides very accurate billing information but requires additional memory in the first SGSN 219.

It will be appreciated that the SGSN is merely a specific example of a billing 10 network element suitable for the current invention, and that it is within the contemplation of the invention that any billing network element associated with billing information may be used.

The above description has focussed on an example wherein a communication

15 was terminated by a handover to a base station associated with a different packet control unit. However, it will be appreciated that any termination of a communication associated with a packet control unit is applicable. Specifically, a termination associated with a handover to another base station associated with the same packet control unit may be applicable. Hence, the termination 20 of the communication may in some cases be associated with a new communication being set up in the same packet control unit. This is particularly advantageous for packet control units not capable of forwarding data packets between different supported communications.

25 The invention can be implemented in any suitable form including hardware, software, firmware or any combination of these. However, preferably, the invention is implemented as software running on one or more data processors and/or digital signal processors. The elements and components of an embodiment of the invention may be physically, functionally and logically 30 implemented in any suitable way. Indeed the functionality may be implemented in a single unit, in a plurality of units or as part of other

functional units. As such, the invention may be implemented in a single unit or may be physically and functionally distributed between different units and processors. 5 Although the present invention has been described in connection with the preferred embodiment, it is not intended to be limited to the specific form set forth herein. Rather, the scope of the present invention is limited only by the accompanying claims. In the claims, the term comprising does not exclude the presence of other elements or steps. Furthermore, although individually listed, 10 a plurality of means, elements or method steps may be implemented by e.g. a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references 15 do not exclude a plurality. Thus references to "a", "an", "first", "second" etc do not preclude a plurality.

Claims

1. A method of generating billing information for a communication system comprising a packet control unit operable to control data packet 5 communication over a wireless interface, the packet control unit comprising buffering means for buffering data packets, the communication system further comprising a billing network element operable to collect billing information associated with the data packet communication; the method comprising the steps of 10 determining that a communication associated with the packet control unit has terminated; the packet control unit generating buffer information in response to buffered data associated with the communication; communicating the buffer information to the billing network element; 1 5 and the billing network element modifying a billing record in response to the buffer information.

2. A method of generating billing information as claimed in claim 1 20 wherein the buffer information comprises an indication of a remaining buffer data quantity associated with the communication.

3. A method of generating billing information as claimed in claim 2 wherein the remaining buffer data quantity comprises an indication of a 25 number of data packets of the communication that are present in the buffering means.

4. A method of generating billing information as claimed in any previous claim wherein the step of modifying comprises reducing a communicated data 30 quantity parameter of the billing record in response to the buffer information.

5. A method of generating billing information as claimed in any previous claim wherein the communication comprises a plurality of sub-

communications. 5

6. A method of generating billing information as claimed in claim 5 wherein the sub-communications comprise sub communications having different quality parameters.

7. A method of generating billing information as claimed in claim 5 or 6 10 wherein the sub-communications comprise sub communications having different associated billing parameters.

8. A method of generating billing information as claimed in any of the previous claims 5 to 7 wherein the sub communications comprise sub 15 communications having different sources of origin.

9. A method as claimed in claim 8 further comprising the step of the billing network element determining a distribution of the communication between the plurality of sub-communications, and the step of modifying the 20 billing record comprises modifying data of the billing record associated with the plurality of sub-communications in response to the distribution.

10. A method as claimed in claim 8 further comprising the step of the billing network element determining a sub-communication parameter of the 25 plurality of sub-communications associated with a previous data packet and the step of modifying the billing record comprises modifying data of the billing record associated with the sub-communication parameter.

11. A method as claimed in any previous claim wherein the step of 30 modifying the billing record comprises the step of associating the buffer

information with data packets communicated to the packet control unit in response to a time indication of the data packets.

12. A method as claimed in any previous claim wherein the communication 5 system is a cellular communication system.

13. A method as claimed in claim 12 wherein the step of determining that the communication has terminated comprises determining that a handover of the communication has occurred.

14. A method as claimed in any of the previous claims 12 or 13 wherein the cellular communication system is a General Packet Radio Service (GPRS) communication system and the billing network element comprises a Serving GPRS Support Node (SGSN).

15. A method as claimed in any of the previous claims 12 or 13 wherein the cellular communication system is a Universal Mobile Telecommunication System (UMTS) and the billing network element comprises a Serving GPRS Support Node (SGSN).

16. A method as claimed in any previous claim 12 to 15 wherein the packet control unit is part of a Base Station System (BSS).

17. A computer program enabling the carrying out of a method according to 25 claim 16.

18. A record carrier comprising a computer program as claimed in claim 17.

19. A communication system including a packet control unit operable to 30 control data packet communication over a wireless interface, the packet control unit having buffering means for buffering data packets, the

communication system further including a billing network element operable to collect billing information associated with the data packet communication; the communication system comprising: means for determining that a communication associated with the packet 5 control unit has terminated; means for generating buffer information in response to buffered data associated with the communication; means for communicating the buffer information from the packet control unit to the billing network element; and 10 means for the billing network element modifying a billing record in response to the buffer informati