Dynamic allocation of radio resources in a packet switched communications-system

0001DYNAMIC ALLOCATION OF RADIO RESOURCES IN A PACKET SWITCHED COMMUNICATIONS- SYSTEM

0002This invention relates to mobile communications, such as cellular

0003communications. The invention is particularly, but not exclusively, applicable

00045 to GSM-type mobile communications systems.

0005An example of a cellular communications system which provides

0006voice dispatch services is the Motorola (trademark) integrated digital

0007enhanced network, or iDEN (trademark), system. The system includes

0008Enhanced Base Transceiver Systems (EBTSs) at cell sites which link mobile

000910 terminals to the fixed network equipment via a TDMA radio interface, and

0010which are connected to controlling base station controllers (BSCs). The BSCs

0011provide a link with a mobile switching centre (MSC) which provides

0012conventional circuit switching with a public services telephone network

0013(PSTN), and a Metro Packet Switch (MPS) which provides switching for the

001415 dispatch services. A Dispatch Application Processor (DAP) coordinates and

0015controls dispatch communications, by registering the identifications and

0016locations of mobile terminals active in the system.

0017The iDEN system provides both voice dispatch services, circuit-

0018switched call services and other data communications services, such as a short

00190 message service.

0020US-A-5,416,770 describes a voice dispatch cellular communications

0021system, in which audio data packets are transported via frame relay links. Communication is established between a plurality of communication units by

0022replicating the transmitted data packets, and distributing the replicated packets

0023to identified target base stations.

0024US-A-5,448,620 describes a mobile terminal which is operable in both

0025a voice dispatch mode and a telephone interconnect mode.

0026A known GSM network, referred to as a public land mobile network

0027(PLMN), is schematically illustrated in Figure 1. A mobile switching centre

0028(MSC) 2 is connected via communication links to a number of base station

0029controller (BSCs) 4. The BSCs 4 are dispersed geographically across areas

0030served by the mobile switching centre 2. Each BSC 4 controls one or more base

0031transceiver stations (BTSs) 6 located remote from, and connected by further

0032communication links to, the BSC. Each BTS 6 transmits radio signals to, and

0033receives radio signals from, mobile stations 8 which are in an area served by that

0034BTS. That area is referred to as a "cell". A GSM network is provided with a

0035large number of such cells, which are ideally contiguous to provide continuous

0036coverage over the whole network territory.

0037A mobile switching centre 2 is connected via communications links to

0038other mobile switching centres in the remainder of the mobile communications

0039network 10, and to other networks such as a public service telephone network

0040(PSTN), which is not illustrated. The mobile switching centre 2 is provided

0041with a home location register (HLR) 12 which is a database storing subscriber

0042authentication data including the international mobile subscriber identity (IMSI)

0043which is unique to each mobile station 8. The IMSI is also stored in the mobile station in a subscriber identity module (SIM) along with other subscriber-

0044specific information.

0045The mobile switching centre is also provided with a visitor location

0046register (VLR) 14 which is a database temporarily storing subscriber

0047authentication data for mobile stations active in its area.

0048GSM was originally designed to support full duplex, circuit-switched

0049voice calls.

0050A new element of functionality is added in the GSM Phase 2+

0051Technical Specifications, which is referred to as the advanced speech call

0052items (ASCI). This provides for group calls which are broadcast to members

0053within a group. In order to establish a broadcast group call, an originating

0054mobile station sends a service request to the MSC, containing the requested

0055group identity. The MSC authenticates the subscriber using the VLR.

0056If the authentication check is successful, the MSC requests

0057identification data for the members of the group from a group call register.

0058With this information, the MSC sets up connections between the receiving

0059mobile stations and a group call dispatcher. Each of the cells in which

0060recipient mobile stations are located pages a notification, containing the

0061identity of the group being called and the description of the channel allocated

0062for the group call broadcast. The group call dispatcher transmits the group

0063call data to each of those cells, for broadcast on the allocated channels.

0064A further element of functionality which is added to GSM in the GSM

0065Phase 2+ Technical Specification is the general packet radio service (GPRS). GPRS provides a packet-mode service to transfer high-speed and low-

0066speed data and signalling efficiently over the GSM radio network. It is

0067designed to support a range of types of data transfer, from intermittent and

0068bursty data transfers to the occasional transfer of large volumes of data. It is

0069envisaged for use in Internet services, e-mail and other data services.

0070GPRS includes facilities for both point to point (PTP) and point to

0071multipoint (PTM) data packet transfer. In PTM data packet transfer, the data

0072packets are broadcast in all of the cells in a defined geographical area. In each

0073case, GPRS transmits the data packets transparently, insofar as other than

0074ensuring that the data packets are received correctly at their destination, there

0075is no knowledge of the contents of the data packets on the network side.

0076The GPRS radio interface is placed in a flexible number of TDMA

0077time slots of the GSM physical radio interface used for circuit-switched traffic

0078channels and signalling channels. The same GPRS radio resources are shared

0079by all mobile stations in a cell, the radio resources being reserved by or for

0080mobile stations only when there are data packets to be sent.

0081The packet-oriented network infrastructure includes a packet data

0082network having packet switches in the form of GPRS support nodes (GSNs)

0083interconnected by a GPRS backbone network, and including a gateway GPRS

0084support node (GGSN) for routing data packets to and from an external packet

0085data protocol (PDP) network, using a protocol such as TCP/IP, X.25 and the

0086like. In accordance with one aspect of the present invention there is

0087provided a method of controlling communication between user stations using

0088a mobile communications system having a radio interface, said method

0089comprising:

0090providing a data packet handler connected to a packet data network;

0091holding control data, indicating a state of a call between a first user

0092station and a second user station;

0093dynamically assigning radio resources for the transfer of data packets

0094carrying call data for said call over said radio interface, such that the amount

0095of radio resources assigned varies in accordance with the amount of call data

0096to be transferred at different points in said call; and

0097controlling the transfer of data packets between said first and second

0098user stations, using said data packet handler, in accordance with said control

0099data.

0100The state of a call may be held in a network-side store, to allow control

0101of the communication between the mobile stations. The functionality

0102provided by a packet data network, and the nature of radio resource allocation

0103and control, is such that data transfer is possible throughout a call, even when

0104the transfer of data is intermittent, without requiring an ongoing circuit-

0105switched connection between the user stations. The data transferred may be

0106voice call data, or video call data. In accordance with a further aspect of the invention there is provided a

0107method of handling the transfer of data in a GSM-type mobile

0108communications system, said method comprising:

0109receiving a first data packet from a first user station, said first data

0110packet containing a recipient ID;

0111mapping said recipient ID to a packet network protocol address

0112whereby routing to a second user station is identified by a gateway GPRS

0113support node; and

0114transmitting a second data packet to said gateway GPRS support node,

0115said second data packet containing said packet network protocol address.

0116This aspect provides functionality allowing the transfer of data packets

0117between user stations using GPRS, wherein a known recipient ID, rather than

0118a packet network protocol address (which may be only temporarily allocated),

0119may be used by the first user station to identify the second user station.

0120In accordance with a further aspect of the invention there is provided a

0121method of conducting communications between user stations using a mobile

0122communications system, each said user station comprising a camera for

0123picking up an image of the user and a display for displaying an image of a

0124remote party, said method comprising establishing a data transfer connection

0125between said user stations, and controlling said connection in a half-duplex

0126mode such that a user station may perform one of either only receiving or only

0127transmitting image data for a first period sufficient to receive or transmit

0128image data forming an image, and perform the other of only receiving or only transmitting video image data for a second period following said first period

0129and sufficient to transmit or receive image data forming an image.

0130In accordance with a still further aspect of the invention there is

0131provided a mobile station adapted to conduct video image communications,

0132said mobile terminal having a half-duplex communications mode controlled

0133by a data processor which in that mode prevents the transmission of video

0134image data during the reception of video image data and which allows the

0135transmission of video image data during a period selected by a user.

0136These aspects provide a method of conducting communications, and a

0137mobile station, which may be used for video conferencing in a novel and

0138advantageous fashion. By limiting the communications to a half-duplex

0139mode, the bandwidth and mobile station power requirements needed for the

0140call may be reduced.

0141In addition, operation in a dispatch communications mode, wherein

0142the video data is distributed amongst groups of recipients which may each

0143both transmit and receive data, is possible. One party may seize the call to

0144transmit video data which is received by the remaining participants. The call

0145may then be subsequently seized by different participants.

0146Further aspects of the invention are defined in the appended claims,

0147and features thereof will be apparent from the following description.

0148Embodiments of the invention will now be described, by way of

0149example only, with reference to the accompanying drawings, wherein: Figure 1 is a schematic block diagram of a known public land mobile

0150network;

0151Figure 2 is a schematic block diagram of a mobile station in

0152accordance with a first embodiment of the invention;

0153Figure 3 is a schematic block diagram of a mobile communications

0154network arranged in accordance with the present invention;

0155Figure 4 is a schematic illustration of a call group record used in

0156connection with embodiments of the present invention;

0157Figure 5 is a schematic illustration of a mobile subscriber record store

0158in connection with embodiments of the present invention;

0159Figures 6, 7 and 9 are flow diagrams illustrating procedures carried out

0160by mobile stations in accordance with embodiments of the present invention;

0161Figures 8, 10 and 11 are flow diagrams illustrating procedures carried

0162out by a data packet handler in accordance with embodiments of the

0163invention; and

0164Figure 12 is a schematic block diagram of a second embodiment of a

0165mobile station in accordance with the present invention.

0166Referring to Figure 2, a GSM-compliant mobile station 8 in accordance

0167with an embodiment of the present invention is a handset which comprises a

0168transmit/receive aerial 16, a radio frequency transceiver 18, a GPRS module 19

0169which includes a packetiser/depacketiser and buffer store, a speech

0170coder/decoder 20 connected to a loudspeaker 22 and a microphone 24, a

0171processor circuit 26 and its associated memory 28, an LCD display 30, a manual input port (keypad) 32 and a push-to-talk button 34. The mobile station is

0172connected to a removable subscriber identity module (SIM) not shown, via

0173electrical contacts.

0174Figure 3 is a schematic illustration of a GSM-type PLMN arranged in

0175accordance with an embodiment of the present invention. The PLMN

0176includes GPRS support nodes, including one or more serving GPRS support

0177nodes (SGSNs) 40, and a gateway GPRS support node (GGSN) 44. The

0178PLMN includes all of the components described in relation to Figure 1.

0179The mobile station 8 may conduct circuit-switched calls, via the MSC

01802, immediately after camping on to a serving cell, as in the prior art.

0181The GGSN 44 is the node provided to interface the PLMN with an

0182external packet data network 46, such as a TCP/IP network. It contains

0183routing information for active GPRS users in the PLMN, which is used to

0184transmit data packets, referred to as packet data protocol protocol data units

0185(PDP PDUs) to the current point of attachment of a mobile station in the

0186PLMN from the packet data network. The GGSN provides a mapping

0187function for mapping a packet data protocol (PDP) address, whereby a mobile

0188user is identified in the packet data network 46, to a mobile station identity,

0189whereby the mobile user is identified in the PLMN. The PDP address of a

0190mobile user conforms with the standard addressing scheme of the respective

0191network layer service used in the packet data network 46, for example an IP

0192version 4 address, an IP version 6 address or an X.121 address. A mobile user may be allocated a permanent, or '"static" PDP address,

0193which is stored in the mobile station 8 and the HLR 12, or may be allowed to

0194request a temporary, or "dynamic" PDP address, which is allocated by the

0195GGSN 44 on request.

0196The SGSNs 40, 42 are referred to as serving GPRS support nodes, in

0197that these nodes are those which serve mobile stations 8 in their routing areas.

0198On logon to the GPRS service of a mobile station, the SGSN establishes a

0199mobility management context containing information pertaining to mobility

0200and security for the mobile station. The SGSN also establishes a routing

0201context, referred to in GPRS as a "PDP context", with the GGSN 44 to be

0202used by the mobile station 8 to access the packet data network 46.

0203The SGSN and the GGSN functionalities may be combined in the

0204same physical node, or they may reside in different physical nodes.

0205The packet data network 46 may be the public Internet, an intranet

0206connection or a leased line. The packet data network 46 may also provide

0207connections with other elements, such as a GGSN 56 of other PLMNs or fixed

0208terminals 58.

0209Thus, with the additional functionality of the SGSNs 40 and the

0210GGSN 44 in the PLMN, and the GPRS module 19 in the mobile stations 8,

0211the mobile networks and users are GPRS enabled, whereby the mobile users

0212may transmit and receive packet mode data. For example, the mobile user

0213may use the mobile station 8 in order to access Web pages, using terminal

0214equipment attached to the mobile station 8, on the public Internet, via the gateway functionality provided by the GGSN 44 and the packet mode transfer

0215functionality provided in the remainder of the network including the SGSNs

021640, 42, the BSCs 4, the BTSs 6 and the GPRS radio interface.

0217The GPRS radio interface is described in GSM 03.64 Version 5.1.0,

0218entitled "Digital Cellular Communications System (Phase 2+)"; General

0219Packet Radio Service (GPRS); Overall Description of the GPRS Radio

0220Interface; Stage 2, published by European Telecommunications Standard

0221Institute, the contents of which are incorporated herein by reference.

0222The GPRS architecture and transmission mechanism, mobility

0223management functionality, network management functionality, radio resource

0224functionality, packet routing and transfer functionality, transmission and

0225information storage using GPRS are described in GSM 03.60 Version 5.2.0,

0226entitled "Digital Cellular Telecommunications System (Phase 2+)"; General

0227Packet Radio Service (GPRS); Service Description; Stage 2, published by the

0228European Telecommunications Standard Institute, the contents of which are

0229incorporated herein by reference.

0230In addition to the standard GPRS infrastructure, this embodiment of

0231mobile communications system of the present invention includes a dispatch

0232packet handler 48, a packet store 50, a packet user database (PUD) 52 and a

0233service management terminal 54.

0234The packet handler 48 is responsible for setting up virtual connections

0235between GPRS users in the PLMN, and for copying packets when data

0236packets are to be distributed to groups of users. The packet store 50 is responsible for storing data packets which are

0237intended for distribution to GPRS users within the PLMN who are

0238uncontactable via GPRS at the time of receipt of data packets for the

0239uncontactable user at the packet handler 48.

0240The packet user database 52 holds service data records used by the

0241packet handler 48 to set up and manage virtual connections between GPRS

0242users in the PLMN. The service management terminal 54 is used to update

0243the service data in the PUD 52.

0244The PUD 52 holds call group records for identifying the members of a

0245call group. Referring to Figure 4, which shows an exemplary call group

0246record, a field for a single call group is identified by a call group ID

0247containing fields 60, two or more mobile station IDs, MSID1, MSID2 ...

0248MSIDn are contained in fields 62, and each mobile station ID field 62 has an

0249associated call seize field 64 flagged to indicate that the associated mobile

0250station has currently seized the call group.

0251In addition to call group records, the packet user database 52 stores

0252identification records for each mobile subscriber in the PLMN who has a valid

0253subscription to the GPRS virtual connection service of the present invention.

0254Referring to Figure 5, each such subscriber has a mobile subscriber record

0255including a field 66 containing a permanent mobile station ID 66, a field 68

0256for containing an allocated PDP address, if current, and a field 70 for

0257containing a call group ID, if current, for the mobile subscriber in question. If

0258the PDP address field 68 is empty, this indicates that the mobile station is not currently attached to the GPRS service. If the current call group ID field 70 is

0259empty, this indicates that the subscriber is not currently participating in a

0260GPRS virtual connection call.

0261Figure 6 illustrates procedures carried out in the mobile station 8 in

0262order to participate in the GPRS virtual connection service of the present

0263invention.

0264In order to utilise the GPRS service, the user initiates a GPRS logon

0265procedure from the mobile station 8, step 100.

0266The GPRS logon signalling procedure is described in GSM 03.60

0267V.5.2.0, part 6.5 entitled "Attach Function", which part is incorporated herein

0268specifically by reference. This part also refers to part 9.2.2 entitled

0269"Activation Procedures" of the same document, which describes the PDP

0270context activation procedure at logon, which part is also incorporated herein

0271specifically by reference.

0272After having executed GPRS attach, the mobile station is in a "ready

0273state", in which packet transfer may occur via the GPRS radio interface

0274between the mobile station 8 and the PLMN, and mobility management

0275contexts are established in the mobile station and the SGSN 40. The mobile

0276station then activates its PDP context, by transmitting an 'Activate PDP

0277Context' request to the SGSN 40. If the mobile station is using a static PDP

0278address, it transmits its static PDP address in the 'Activate PDP Context'

0279request. The SGSN 40 queries the HLR 12, in which GPRS subscription

0280information is held for the subscriber, in order to check that the mobile station

02818 is allowed to activate the PDP address contained in the request. If allowed,

0282the SGSN transmits a 'Create PDP Context' request to the GGSN 44, which

0283creates a new entry in a PDP context table held in the HLR 12 on behalf of the

0284GGSN 44. This PDP context table includes the mobile station identity and

0285the PDP address allocated to the mobile station, allowing the GGSN 44 to

0286map between these two identifies and thereby route data packets between the

0287SGSN 40 and the packet data network 46.

0288If the mobile station 8 is not using a static PDP address, the 'Create

0289PDP Context' request sent by the SGSN 40 to the GGSN 44 results in the

0290GGSN allocating a dynamic PDP address, which is signalled, via the SGSN

029140, to the mobile station 8.

0292Whether the mobile station is using a static PDP address or a dynamic

0293PDP address, the mobile station 8 is provided in each case with a PDP address

0294whereby routing for packets arriving from the packet data network 46 is

0295identified. Routing within the PLMN is provided by the GPRS data packet

0296encapsulation procedure, which encapsulation is removed from the data

0297packets at the GGSN 44 and the mobile station 8. The encapsulation function

0298is described in part 9.6 of the document GSM 03.60 V.5.2.0, which part is

0299specifically incorporated herein by reference. GPRS transparently supports

0300the transfer of PDP PDUs between external networks and the mobile stations.

0301One encapsulation scheme (referred to herein as GSN-GSN encapsulation) is used for the GPRS backbone network between GSNs in the PLMN, and one

0302(referred to herein as SGSN-MS encapsulation) is used for the GPRS

0303connection between the SGSN 40 and the mobile station 8.

0304The GGSN 44 is arranged such that once the PDP context entry has

0305been made in the HLR 12 by the GGSN 44 for a newly logged-on GPRS user,

0306the GGSN 44 transmits a logon message to the packet handler, informing the

0307packet handler 48 of the mapping between the mobile station identity, held in

0308field 66 of the mobile station record held in the PUD 52, whereby the user is

0309permanently identified in the PLMN, and the allocated PDP address. On

0310receipt of the logon message, the packet handler 48 enters the allocated PDP

0311address in field 68 of the mobile subscriber record for the subscriber in

0312question.

0313Once logged-on to the GPRS service, the mobile station may transmit

0314data packets to, and receive data packets from, the packet handler 48.

0315Data packets originated in the mobile station 8 are transmitted over the

0316radio interface and via the BTS 6 and the BSC 4 to the SGSN 40. When the

0317SGSN 40 has received a packet completely and correctly, it GSN-GSN

0318encapsulates the packet into a GPRS backbone network packet which is sent

0319to the GGSN 44. The GGSN 44 decapsulates the packet and forwards the

0320data packet, using the PDP address allocated to the sender as the packet

0321originating address in a header portion of the data packet, to the packet

0322handler 48. Data packets originated in the packet handler 48 are transmitted to a

0323mobile station 8 by attaching the allocated PDP address, which is held in the

0324PUD 52 for the recipient, to the data packet as a destination address in a

0325header portion of the data packet. The data packet is transmitted, via the

0326packet data network 46, to the GGSN 44. In the GGSN 44, the PDP address

0327of the receiver is read, and the SGSN which is serving the mobile station is

0328identified from routing data held in the HLR 12. The data packet is then

0329GSN-GSN encapsulated and sent to the identified SGSN. The SGSN strips

0330the GPS backbone network encapsulation, and the original data packet is

0331SGSN-MS encapsulated and transmitted to the mobile station 8 via the BSC

03324, BTS 6 and GPRS radio interface.

0333When the mobile station 8 receives the packet, it removes the SGSN-

0334MS encapsulation and processes the data packet. If the data packet is a voice

0335data packet, a sequence of packets are reassembled and a voice signal is

0336generated in the mobile terminal.

0337The user may set up a call by selecting, via a man machine interface,

0338e.g. the keypad 32, of the mobile station 8, from a stored list of call groups of

0339which the mobile user is a member, a call group for which a virtual

0340connection is to be established. Such selection is part of the initiation of a call

0341set up-transmit procedure, step 102, which is to be described below in relation

0342to Figure 7.

0343Once logged-on to the GPRS service, the mobile station 8 is able to

0344receive call set up-receive requests from the packet handler 48, which initiates a procedure to be described below in relation to Figure 9. Once participating

0345in a call, the mobile station 8 is also able to start to receive call data packets,

0346step 106, and start to transmit call data packets, step 108, to be described

0347below in relation to Figures 7 and 8. In addition, a user has the facility to end

0348participation in a call, by interaction with a man machine interface, e.g. the

0349keypad 32, of the mobile station 8, step 110, which causes the mobile station

0350to transmit an end participation request to the packet handler 48, step 112, and

0351to delete the call group ID from its current call record, step 114.

0352The user may also logoff the GPRS service if desired, step 116, which

0353results in logoff procedures carried out by the mobile station 8, step 118,

0354including the deletion of the allocated PDP address for the subscriber in the

0355HLR records stored by the GGSN 44. The GGSN 44 is arranged such that, on

0356receiving a logoff message from the SGSN 40, the GGSN 44 also transmits a

0357logoff message to the packet handler 48, which results in the deletion of the

0358previously allocated PDP address from the PDP address field 68 in the mobile

0359subscriber record held for the subscriber in the PUD 52.

0360Referring to Figure 7, when a user first instructs the mobile station 8 to

0361set up a call for a particular call group, by the depression of the PTT button 34

0362after the selection of a call group from a list of call groups stored in the SIM

0363of the mobile station 8, the mobile station 8 transmits a set up request,

0364containing the selected call group ID, as one or more GPRS data packets to

0365the packet handler 48, step 200. The call handler conducts procedures to be

0366described below in relation to Figure 8, and, depending on the success of those call set up procedures, the packet handler 48 may transmit a set up

0367confirmation message to the mobile station within a time-out set within the

0368mobile station 8, or not. If the call set up confirmation is not received within

0369the time-out at the mobile station, step 202, the mobile station returns to the

0370general GPRS logged-on state, and the mobile station 8 may retry by

0371transmitting a further call set up request.

0372If the set up confirmation message is received from the packet handler

037348 within the time-out, the mobile station 8 provides an audio or visual

0374indication to the user that a virtual connection has been established, step 204.

0375In addition, the mobile station places the call group ID selected by the user in

0376a current call record, step 206.

0377At this point, the user may transmit voice data by speaking into the

0378microphone 24 as long as the PTT button 34 remains depressed. The speech

0379signals are coded by the codec 20 and passed on to the GPRS module 19, in

0380which the speech data is packetised and buffered, step 208, and SGSN-MS

0381encapsulated for transmission over the GPRS radio interface by the radio

0382frequency transceiver 18 and onward to the packet handler 48, step 210.

0383As soon as the PTT button 34 is released, step 212, the mobile station

03848 generates a transmit end message, in the form of a data packet, which is

0385transmitted to the packet handler 48, step 214.

0386Referring to Figure 8, on receipt of a call set up request, step 300, the

0387packet handler 48 retrieves, using the call group ID contained in the call set up

0388request, the recipient records from the PUD 52 which identify the recipients which are currently available for receipt of a call set up message, step 302.

0389Each mobile station in the call group record has an associated mobile station

0390record which is identified by the mobile station ID contained in the call group

0391record. For each mobile station record which contains a PDP address and no

0392current call group ID, a set up message is transmitted by the packet handler,

0393using the PDP address retrieved for the mobile station in question, step 304.

0394Mobile station records which contain either no allocated PDP address or

0395contain a current call group ID are placed in a call waiting list in the PUD 52,

0396and voice data packets subsequently received for the same call group are

0397forwarded to the packet store 50 for storage. In the case of a potential

0398recipient not yet logged-on to the GPRS service, on receipt of notification at

0399the packet handler 48 that the recipients have subsequently logged-on, a set up

0400message is then transmitted, to allow the previously unavailable recipient to

0401receive the data held in the packet store 50 if desired. Similarly, if a potential

0402recipient is unavailable because the recipient is engaged in a different call,

0403once the packet handler 48 receives an end participation message from the

0404potential recipient for the previous call, the packet handler responds by

0405transmitting a set up message to the previously unavailable recipient, to allow

0406the recipient to receive data previously held in the packet store 50 if desired.

0407If the packet handler receives no acknowledgements from the available

0408recipients to which set up messages have been sent within a time-out set in the

0409packet handler 48, step 306, the call set up has been unsuccessful and the packet handler ends the procedure without storing any references to the call

0410set up attempt either in the PUD 52 or in the packet store 50.

0411Otherwise, the packet handler 48 enters the call group ID into the

0412current call group field 70 for both the call set up request sender and the call

0413set up message recipients which have acknowledged call set up, step 308. As

0414further recipients acknowledge call set up, the current call group ID is entered

0415into the call group ID field 70 for each of the additional recipients.

0416In addition, the packet handler 48 sets the call seize flag in the field 64

0417of the call group record which corresponds to the mobile station ID of the call

0418set up request sender, and transmits a set up confirmation message to the

0419sender, step 310, indicating that the sender is now able to transmit voice data,

0420step 310.

0421Once the sender receives the set up confirmation message, as

0422described in relation to Figure 7, the sender presses the PTT button 34 and

0423begins the transmission of voice data packets, which are received at the packet

0424handler 48, step 312. If the number of recipients currently participating in the

0425call exceeds a single recipient, step 314, the packet handler 48 replicates the

0426contents of each packet for each recipient, step 316.

0427The receive packets are then transmitted to each participating

0428recipient, step 318, until such time as an end message is received from the

0429voice packet transmitting mobile station 8, step 320. Once the end message is

0430received from the sending mobile station 8, an end message is transmitted to

0431each recipient, step 322, and the call seize flag is removed from field 64 in the call group record corresponding to the sender mobile station ID, in the PUD

043252, step 324.

0433Referring to Figure 9, when a mobile station 8 receives the set up

0434message from the packet handler 48, step 400, the mobile station 8 displays

0435the identity of the sender, which is contained in a header portion of the data

0436packet, including the call group ID and the name of the individual subscriber,

0437step 402. In response, the recipient may accept the call by interaction with the

0438man machine interface of the mobile station, step 404. If the user does not

0439accept, the mobile station does not respond to the set up message. Otherwise,

0440the mobile station 8 transmits an acknowledgement to the packet handler 48

0441and places the call group ID in the current call record held in the mobile

0442station memory 28, steps 406 and 408.

0443As a result of the acknowledgement received at the packet handler 48,

0444any data packets subsequently transmitted by the voice data sender is then

0445transmitted, using the virtual connection provided by the packet handler 48, to

0446the recipient mobile station 8, step 410. At the recipient mobile station 8, the

0447data packets are converted into voice data and output as an audio signal, step

0448412, until such time as an end message is received from the packet handler 48,

0449step 414.

0450On receipt of the end message, the recipient mobile station provides

0451the user with an audio or visual indication of the end of receipt of the voice

0452data packets, step 416, to indicate that the call group may now be seized if

0453desired by the recipient. In order to seize the call group, following call set up, any participant

0454may push the PTT button 44 in a period of inactivity, that is to say, in the case

0455of a previously receiving mobile station, after receipt of a transmit end

0456message as in step 214 and preceding receipt of further voice data packets

0457from other parties, and in the case of a previously transmitting mobile station,

0458after the user releases the press to talk button and before receipt of voice data

0459packets from other parties.

0460Referring again to Figure 7, when the mobile station 8 detects pressing

0461of the PTT button in this inactive state, the mobile station 8 transmits a call

0462seize request to the packet handler 48, step 216. The call group ID held in the

0463current call group ID record in the mobile station 8 is included in the call seize

0464request message automatically by the mobile station. The user therefore does

0465not need to re-identify the call group of the call in which he is currently

0466participating.

0467If no call seize confirmation is received from the packet handler 48

0468within a time out period set within the mobile station 8, the mobile station 8

0469may retry to seize the call at a later stage, by the transmission of a further call

0470seize request.

0471If a call seize confirmation message is received from the packet

0472handler 48, step 218, an audio or visual indication is provided to the user to

0473indicate success, step 220, after which the user is able to transmit his voice to

0474all of the current call group participants by keeping the PTT button held down

0475and speaking into the microphone 24 of the mobile station 8. Referring to Figure 10, on receipt of a call seize request, step 500, the

0476packet handler 48 queries the PUD 52, step 502, in order to determine whether

0477another participant in the call has current seizure of the call group, as will be

0478indicated by a call seize flag held in a field 64 of the call group record. If no

0479call seize flag appears in the call group record, the packet handler 48 transmits

0480a call seize confirmation message to the sender of the call seize request, step

0481504, and adds a call seize flag to the field 64 corresponding to the sender in a

0482call group record held in the PUD, step 506.

0483Referring to Figure 11 , on receipt of an end participation request from

0484a mobile station of a user currently participating in a call, step 600, the packet

0485handler 48 deletes the call group ID from the current call group field 70 of the

0486record held in the PUD 52 for the sender of the end participation request, step

0487602.

0488If only one participant then remains in the call, step 604, the last

0489remaining participant is sent an end-of-call message, step 606, and the call

0490group ID is deleted from the current call group field in the last participant's

0491record held in the PUD 52, step 608. The unavailable recipient records are

0492also deleted from the call waiting list in the PUD, and the voice data packets

0493stored in the packet store 50 for the call group are deleted.

0494Figure 12 illustrates a further embodiment of mobile station 700 in

0495accordance with the present invention. The mobile station 700 includes

0496components described in relation to the embodiment of mobile station

0497illustrated in Figure 2. These components are referenced with the same reference numerals, and share functionality described in relation to the mobile

0498station 8.

0499The mobile station 700 is therefore capable of conducting GPRS

0500virtual connection voice calls as described in relation to Figures 2 to 11 , by

0501the user operating the keypad 32 and PTT button 34. In addition, the mobile

0502station 700 is operable in a video conferencing mode.

0503The mobile station 700 includes an LCD-type display 702, capable of

0504displaying still and video images, in place of the alphanumeric display 30 of

0505the mobile station 8. In addition, the mobile station 700 includes a CCD

0506camera 704, capable of picking up still and/or video images, and an image

0507data codec 706, capable of coding and decoding still and/or video images in

0508accordance with known still and/or video coding techniques, such as Jpeg

0509and/or Mpeg-4.

0510The image data codec 706 interfaces with the GPRS module 19, so as

0511to allow image data to be packetised and depacketised and transferred via the

0512GPRS radio interface.

0513The mobile station 700 interacts with the system described in relation

0514to Figure 2, and in particular the packet handler 48, in the same manner as

0515described in relation to each of Figures 6 to 11. Thus, the packet handler is

0516capable not only of forming virtual voice data connections for two-party calls

0517or group dispatch-type calls, but also capable of forming virtual image data

0518connections. The dynamic bandwidth allocation functionality provided by

0519GPRS allows the transmission of data at a sufficient rate to transmit video data captured by the video camera 704 and coded in the image data codec 706,

0520via the GPRS radio interface.

0521Referring to Figure 7, when using the mobile station 700 in a video

0522conferencing mode, the procedures previously described are conducted in

0523order for the mobile station to set up and seize a video call, and to transmit

0524video and audio data for receipt at one or more call group participants in the

0525PLMN. In this regard, step 208 previously described in relation to Figure 7

0526involves the reception of video data at the video camera 704 and its

0527conversion in the video codec 706, in addition the pickup of audio data at the

0528microphone 24 and its conversion in the audio codec 20. Step 210,

0529meanwhile, involves the transmission of both audio and video data, either in

0530separate data packets or in the same data packets, whilst the PTT button 34

0531remains actuated. In this regard, although referred to as a "PTT" button, this

0532is intended to include a "press to transmit audio and video" button.

0533In a further mode, the image data accompanying the audio data in step

0534210 is still image data picked up at the camera 704 and coded by the image

0535data codec 706.

0536In a yet further mode, the mobile station 700 is arranged to transmit

0537image data, being video or still image data, alone, in step 210.

0538The particular mode employed in the mobile station 700 is selectable

0539by the user of the mobile station via interactions with the man machine

0540interface, e.g. the keypad 32. Referring to Figure 8, the packet handler 48 is capable of performing

0541the procedures previously described to receive and respond to the call set up

0542request for an image and/or audio call. In this regard, in step 312, the packet

0543handler may receive image data packets and/or voice data packets during

0544seizure of a call by a recipient. The packet handler 48 handles the packets

0545transparently, without regard to the content of the data packets received.

0546Referring to Figure 9, the mobile station 700 is capable of receiving

0547call set up messages, and accepting same, for both image and audio calls. In

0548this regard, in step 410, the data packets received via the GPRS radio interface

0549include image and/or voice data packets, and step 412 involves the conversion

0550of those data packets in the image data codec and/or the voice codec, and the

0551output of images and/or audio signals on the display 702 and/or by the

0552loudspeakers 22.

0553Thus, this embodiment of the invention provides a method and

0554apparatus whereby half-duplex video conferencing calls may be conducted,

0555either between two parties, or in a dispatch mode between groups of call

0556participants. It is advantageous, in that video data, which requires relatively

0557high amounts of bandwidth, is transmitted only in one direction at a time, and

0558only intermittently when a user of the system wishes to transmit image data.

0559In addition, the power requirements for the mobile station may be relatively

0560low. This is to be contrasted with the conventional concept of a video

0561conferencing call, in which video data is transmitted continuously in full

0562duplex mode. It is to be understood that various modifications and equivalents may

0563be employed in relation to the embodiments described above, without

0564departing from the scope of the present invention.

0565The embodiments for mobile terminal 700 described are operable in

0566both a GPRS virtual connection mode and a conventional circuit-switched

0567mode. Other embodiments of the invention include mobile stations which are

0568operable only in the GPRS virtual connection mode of the present invention.

0569The GPRS virtual connection mode described above in relation to the

0570two embodiments of the invention is by nature half-duplex, insofar as only

0571one party to the call may transmit voice and/or image data at a time.

0572However, GPRS allows the simultaneous transmission and reception of data

0573packets via the radio interface, and therefore, in the case of two-party calls,

0574voice and/or image data transfers may occur at the same time, in order to

0575provide a full-duplex virtual connection. In this case, neither of the parties

0576"seizes" the call group, and neither party is prevented from transmitting voice

0577and/or image data when receiving such data.

0578In the above described embodiments, the GGSN 44 transmits logon

0579and logoff messages to the packet handler 48 when a subscriber attaches and

0580detaches to the GPRS service. Other signalling procedures are possible. For

0581example, the packet handler 48, when receiving a call set up request, may

0582query the HLR and/or the GGSN 44 in order to determine the current status of

0583a potential call participant. Logon/logoff messages may also be transmitted to

0584the packet handler 48 from the HLR 12, instead of from the GGSN 44. In the above described embodiments, control messages passed

0585between a mobile station and the packet handler 48 include a call group ID, to

0586be referenced against the call group records. In the case of a two-party call,

0587such a call group ID may be replaced by a single recipient ID, referenced to a

0588single recipient record in the PUD 52.

0589In the above, the packet data network 46 is referred to as an external

0590packet data network. The packet data network 46 is 'external' insofar as it is

0591beyond the GGSN 44, but it may be under the ownership and control of the

0592PLMN operator. Thus it may form part of an intranet, or suchlike. It may

0593also take the form of a single physical link between the GGSN 44 and the

0594packet handler 48. The functions of the packet handler 48 may be integrated

0595with those of the GGSN 44.

0596In the above description, virtual connections between mobile stations

0597operating in the same PLMN are controlled by the packet handler. As

0598illustrated in Figure 3, a GGSN 56 of another PLMN is also accessible, via the

0599packet data network 46 from the packet handler. Therefore, the packet

0600handler may also be used to set up virtual connections between mobile

0601stations operating within the PLMN illustrated, and mobile stations operating

0602in other PLMNs which include a GPRS infrastructure. In addition, the packet

0603handler 48 is also able to control virtual connections between a mobile station

0604operating in the PLMN illustrated and fixed terminals, such as the fixed

0605terminal 58 illustrated in Figure 3, connected to the packet data network 46. In the above described embodiments, the seizure of a call group, and

0606the period for which a mobile station transmits voice and/or image data is

0607defined by the manual depression of the PTT button 36. Other man machine

0608interface interactions may also be used to define a call seize operation and the

0609period for which the mobile terminal transmits voice or image data, for

0610example those operations and periods may be voice-activated.

0611In the above described embodiments, the packet store 50 holds data

0612packets received during a virtual call connection, for potential call

0613participants. In addition, the packet store may be used to hold voicemail

0614messages and data messages received via the GPRS service and to be

0615transmitted onwards via the GPRS service. In addition, the packet store 50

0616may hold information to be communicated to user stations via the GPRS

0617service on request, such as stock price information, news and weather, etc,

0618provided as textual information, still image information, audio information

0619and/or video information.

0620Embodiments of mobile terminal other than the handsets described are

0621envisaged. For example, the mobile terminal may be a car telephone,

0622consisting of a GPRS-enabled hardware unit installed in the vehicle and a

0623hand-held microphone/push-to-talk unit connected to the hardware unit via a

0624wire cord.

0625In the above, the transfer of audio and image data in half-duplex

0626communications modes has been described. The data packets transferred by

0627the packet handler 48 between user stations may also form textual messages (short messages) which may be transmitted within the context of a call, or in a

0628call-independent context. Preferably, the transfer of text messages is not

0629restricted by the packet handler 48, the packet handler serving only to identify

0630available recipients and recipient addresses from the PUD 52 for a text

0631message to be transferred, and to store messages in the packet store 50 for

0632unavailable recipients.

0633Herein, reference is made to GSM-type systems. Such systems

0634include ones which are at least partly based on the GSM system defined in the

0635GSM technical specifications published by the European Telecommunications

0636Standards Institute (ETSI), such as DCS 1800 systems, PCS 1900 systems and

0637third generation systems (such as UMTS) based at least partly on GSM.

0638It is envisaged that modifications and variations to the above-

0639described embodiments may be employed, without departing from the scope

0640of the invention, which is defined in the appended claims.