WO2002030137A1

WO2002030137A1 - Method and arrangement in a communication system for connecting a gprs radio access network to a umts core network

Info

Publication number: WO2002030137A1
Application number: PCT/SE2001/002014
Authority: WO
Inventors: Susanne Ahlstrand; Arnaud Vedrine; Mathias Cramby
Original assignee: Telefonaktiebolaget Lm Ericsson (Publ)
Priority date: 2000-10-06
Filing date: 2001-09-20
Publication date: 2002-04-11
Also published as: AU2001288194A1

Abstract

The present invention relates to a method and an arrangement in a communications system. The object of the present invention is to connect GPRS radio access network to UMTS core network for transmitting data packets to and from a mobile station and achieve a system where the performance of the current GPRS system is increased.The object is achieved by a method wherein the concept of Temporary Block Flow (TBF) and Radio Bearer (RB) is used. The method comprises the steps of establishing at least one RB; establishing at least one TBF, and associating at least one RB to each of the at least one TBF.

Description

METHOD AND ARRANGEMENT IN A COMMUNICATION SYSTEM FOR CONNECTING A GPRS RADIO ACCESS NETWORK TO A UMTS CORE NETWORK

FIELD OF THE INVENTION

The present invention relates to a method an arrangement in a communications system in accordance with the preambles of the independent claims. More specifically it relates to the connection of GPRS radio access network to UMTS core network.

BACKGROUND OF THE INVENTION

Figure 1 in the present application illustrates the basic configuration of a cellular mobile telecommunication system. Such a system comprises a number of cells, each cell comprising a base station for radio communication with a number of mobile stations, of which only one is shown in the figure. Basically the mobile station communicates with the base station of the cell in which it is presently moving. As the mobile moves from cell to cell, communication with the mobile station is handed over from the base station of one cell to the base station of another cell.

General packet radio service (GPRS) is a standard from the European Telecommunications Standards Institute (ETSI) on packet data in Global System for Mobile telephony (GSM) systems. GPRS has also been accepted by the Telecommunications Industry Association (TIA) as the packet-data standard for TDMA/IS-136 systems. By adding GPRS functionality to the public land mobile network (PLMN), operators can give their subscribers resource-efficient access to external Internet protocol-base (IP) networks.

GPRS offers radio-interface transfer rates up to 115 kbit/s subject to mobile terminal capabilities and carrier interference. Even higher transfer rates are provided by the use of so called EDGE technology, i.e. Enhanced Data Rates for Global Evolution. EDGE technology can increase end user data rates up to 384 kbit/s, and potentially higher in high quality radio environments. Moreover, GPRS allows several users to share the same radio-interface resources and enables operators to charge customers for wireless services based on the amount of transferred data instead of on connection time.

The present invention is in particular applicable in GSM/EDGE Radio Access Network (GERAN), wherein GPRS radio access network will be connected to Universal Mobile Telecommunications System (UMTS) core network.

For GERAN release 5, the RAB (Radio Access Bearer) and RB (Radio Bearer) concept from UMTS will be introduced.

Below are some important features of GPRS discussed in greater detail.

The GPRS radio interface, also called Um, is the logical link between the mobile station (MS) and the Base Station System (BSS). The BSS may comprise a Base Station Controller (BSC) or a Radio Network Server (RNS) and a Base Transceiver Station (BTS).

The RLC/MAC and the physical layers within the GPRS protocol stack, which are relevant for the invention, are described below.

RLC/MAC Radio Link Control (RLC) provides a radio-solution-dependent reliable link.

The Medium Access Control (MAC) function controls the access signalling (request and grant) procedures for the radio channel, and the mapping of data frames from higher layer onto the GSM physical channel (also referred to as GSM RF). The RLC/MAC layer is further described below. Logical Link Control Layer (LLC) frames received from the Serving GPRS Support Nodes (SGSN), see Figure 2, in a downlink transfer are cut up into smaller RLC/MAC blocks, which are coded into radio blocks in the physical layer. Each radio block is sent in four consecutive bursts on one time slot (TS). For example, if one MS is assigned time slots one to four, one radio block is sent in four bursts on time slot one, a second radio block is sent in four bursts on time slot two etc.

The transmission of packets to or from a certain MS is called a Temporary Block Flow (TBF). The correspondence to a circuit switched call setup is an assignment of an uplink or a downlink TBF for a packet transfer. An MS can have a TBF in one direction or one in each direction. Each TBF is addressed by a Temporary Flow Identity (TFI) assigned by the network. When a TBF is assigned, the MS is informed of which time slot(s) to use and its TFI address.

A number of MSs can be assigned resources on the same time slot(s). The header of every downlink traffic block contains a TFI that shows which MS the radio block is addressed to.

The header of every downlink traffic block also contains the Uplink State Flag (USF). The USF is used to notify the MSs having uplink TBFs on that time slot, which one of them that may send an uplink radio block in the next group of four bursts.

Some of the different parts of the system are further discussed below.

TBF in (E)GPRS

A TBF (Temporary Block Flow) is established when data is transferred over the radio interface in (E)GPRS. Each TBF over the RLC/MAC layer is assigned a Temporary Flow Identity (TFI) by the network. The mobile station shall assume that the TFI value is unique among concurrent TBFs in the same direction (uplink or downlink) on all Packet Data Traffic Channels (PDCHs) used for the TBF. The same TFI value may be used concurrently for TBFs on other PDCHs in the same direction and for TBFs in the opposite direction. Up to 32 TBFs can be established in each direction per PDCH.

An RLC/MAC block associated with a certain TBF shall comprise a TFI. TFI is used to unambiguously identify the mobile station during packet transfer mode in an uplink or downlink RLC/MAC control message.

TBF in GERAN

The TFI in GERAN release 5 identifies a TBF for shared channels, and dedicated channels if the MS has multiple flows on the same dedicated channel. The TFI is a temporary identifier and may exist as long as there is data to transfer on the shared channels, or the TFI may also be kept for a longer time. For dedicated channels, the data flow is identified by a TFI, which is permanent for at least as long as the dedicated channel is allocated, or the TBF may be composed of a frequency and a set of ti eslots provided that there is only one flow on the channel. The TFI is assigned as for GERAN release 99. The length of the TFI in GERAN release 99 is 5 bits.

Radio Access Bearer in UMTS

A Radio Access Bearer (RAB) connection in UMTS is realised by two concatenated segments, the lu bearer connection, between UMTS Terrestrial Radio Access Network

(UTRAN) and the core network, and the Radio Bearer (RB) connection, over the radio interface, referred to as Uu (comparable to Um in GPRS).

The RAB can be seen as the service provided to the MS. The RAB is defined by a set of Quality of Service (QoS) parameters e.g. traffic class and is set up at PDP context activation. Up to 256 RABs can be established per UE over the lu. An RAB can consist of several sub flows if unequal error protection is required. Each of those sub flows is then realised over the radio as a Radio Bearer.

RB Identifier for UTRAN/ GERAN The RB Identifier (RB Id) identifies a Radio Bearer over the Uu interface for UTRAN. A RB may carry signalling or user data and each RB is mapped onto one RLC entity. Over the radio interface, totally 32 RB/MS are supported in UTRAN. Since the same type of services are expected to be supported in GERAN as in UTRAN, it is likely that GERAN shall be able to support a maximum number of 32 RBs over the air.

SUMMARY OF THE INVENTION

The object of the present invention is to connect GPRS radio access network to UMTS core network for transmitting data packets to and from a mobile station and achieve a system where the performance of the current GPRS system is increased.

The above-mentioned object is achieved by a method and a system according to the characterising part of the independent claims.

The radio communications system provided by the present invention, comprising means for establishing at least one RB, means for establishing at least one TBF, and means for associating at least one RB to each of the at least one TBF, makes it possible to is to connect GPRS radio access network to UMTS core network for transmitting data packets to and from a mobile station and achieve a system where the performance of the current GPRS system is increased.

The method provided by the present invention comprising the steps of establishing at least one RB; establishing at least one TBF, and associating at least one RB to each of the at least one TBF, makes it possible to transmitting data packets to and from a mobile station when GPRS radio access network is connected to UMTS core network. An advantage with the present invention is that it makes it possible to-reuse parts of UMTS for GPRS and thereby get the co-ordination advantages of making the two systems more similar to each other.

Preferred embodiments are set force in the dependent claims.

According to a second embodiment of the present invention, several RBs are associated to one TBF. A reduced RB Identity is mapped to the real RB Identity. The reduced RB identity is included in a header of a RLC/MAC packet in order to inform a receiver from which RB the data belongs to.

An advantage with the second embodiment is that it signalling requirement decreases and thus the time delay.

Another advantage with the second embodiment is that the reduced RB identity saves space in the data packets.

BRIEF DESCRIPTION OF THE DRAWINGS

Figure 1 illustrates the basic configuration of a cellular mobile telecommunication system, Figure 2 illustrates an exemplary communication system in which the present invention may be implemented. Figure 3 is a diagram that shows the protocols influenced by the radio interface according to a first embodiment of the present invention. Figure 4 is a diagram that shows the protocols influenced by the radio interface according to a second embodiment of the present invention. Figure 5 is a diagram that shows the protocols influenced by the radio interface according to a second embodiment of the present invention. Figure 6 shows an uplink RLC/MAC data block header for MCS-1-4.

Figure 7 shows the downlink RLC data block header for MCS-1, MCS-2, MCS-3 and MCS-4. Figure 8 shows a flowchart of the method according to the present invention. Figure 9 shows a radio communications system according to the present invention.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENTS

Figure 2 illustrates an exemplaty communication system 2 in which the present invention may be implemented. In particular the system 2 depicted in Figure 2 conforms to the GSM specifications and supports GPRS and Enhanced GPRS (EGPRS) (e.g. GERAN) technology. The mobile telecommunications system 2 includes a circuit-switched network 4, a packet-switched network 6, and a radio network 8 that is shared by the circuit-switched and packet-switched networks 4 and 6. Generally, the circuit-switched network 4 is primarily used for voice applications, while the packet-switched network 6 is primarily used for data applications. In accordance with third generation mobile telecommunications standard, however, the circuit-switched network 4 can also support data communications, and the packet- switched network 6 can also support voice communications.

The circuit-switched network 4 includes a number of mobile services switching centre/visitor location registers (MSC/NLRs) 12. For purposes of simplifying the illustration, however, only one MSC/NLR 12 is shown. Each MSC/NLR 12 serves a particular geographic region and is used for controlling communications in the served region and for routing communications to other MSC/NLRs 12. The NLR portion of the MSC/NLR 12 stores subscriber information relating to mobile stations 10 that are currently located in the served region. The circuit-switched network 4 further includes at least one gateway mobile services switching centre (GMSC) 14 that serves to interconnect the circuit- switched network 4 with external networks, such as a public switched telephone network (PSTN) 16.

The packet-switched network 6 includes a number of Serving GPRS Support Nodes (SGSN) 18, which are used for routing and controlling packet data communications, and a backbone IP network 20. A gateway GPRS support node (GGSN) 22 interconnects the packet-switched network 6 with an external IP network 24 or other external data networks.

The radio network 8 includes a plurality of cells. Each cell in the mobile telecommunications system 2 is served by a base station 26 that communicates with mobile stations 10 in the cell via a radio interface 28. The radio network 8 comprises a plurality of base stations 26 and a base station controller (BSC) 27, alternatively referred to as a Radio Network Controller (RNC) or Radio Network Server (RNS), controlling said plurality of base stations 26. For circuit-switched communications, signals are routed from the MSC/NLR 12, to the base station controller 27 via an interface 34, to the base station 26 for the cell in which the target mobile station 10 is currently located, and over the radio interface 28 to the mobile station 10. For packet data transmissions, on the other hand, signals are routed from the SGSΝ 18, to the base station controller 27 via an interface 35, to the base station 26 for the cell in which the target mobile station 10 is currently located, and over the radio interface 28 to the mobile station 10.

Each mobile station 10 is associated with a home location register (HLR) 30. The HLR 30 stores subscriber data for the mobile station 10 that is used in connection with circuit-switched communications and can be accessed by the MSC/NLRs 12 to retrieve subscriber data relating to circuit-switched services. Each mobile station 10 is also associated with a GPRS register 32. The GPRS register 32 stores subscriber data for the mobile station 10 that is used in connection with packet-switched communications and can be accessed by the SGSNs 18 to retrieve subscriber data relating to packet-switched services.

How to map one RB onto one TBF

According to a first embodiment of the present invention, one RB is mapped onto one TBF.

In a first scenario, a mobile station (MS) has set up 2 RBs: RBI and RB2. Figure 3 shows the protocols influenced by the radio interface according to this first embodiment of the present invention. PHY stands for the Physical Layer.

On the uplink the following happens: a) The MS requires sending data for one first RB, i.e. RBI.

A TBF, i.e. TBF1, is set up for RBI: No data need to be sent for RB2 at the beginning. Here is TBF1, sent from the MS, associated to RBI. b) The MS then requires transmitting data for the second RB, i.e. RB2.

According to this first embodiment it is required to set up a new TBF for RB2. To do so, the MS must wait for the network to poll it, it must then send a "Packet Resource Request" message and receive an answer from the network. The answer is a "Packet Uplink Assignment" that assigns a new TBF, i.e. TBF2, associated to

RB2. Then, when the network polls the MS again, the MS can begin the transmission of data for RB2. This embodiment is one solution for reusing parts of UMTS for GPRS and thereby get the co-ordination advantages of making the two systems more similar to each other. Although, this will imply a delay (see below) before data can be transmitted for RB2. The solution for mapping RBs onto TBFs according to the second embodiment (see later on under "Mapping several RBs onto one TBF") does not have any delay. The delay before data can be transmitted for RB2 is 40 ms (20 ms for "Packet Resource Request" + 20 ms for "Packet Uplink Assignment") + the time the MS needs to wait before it is polled. Moreover, two signalling messages need to be sent. On the downlink the following happens: a) For the requirement of one TBF, TBF1 is associated to RBI. b) For the requirement of a second TBF, the network has to send a "Packet Downlink Assignment" to set up a new TBF, for the second RB before data can be sent for this RB, i.e. TBF2 is associated to RB2.

Mapping several RBs onto one TBF. There is a wish for sparing TBFs by using more than one RB per TBF simultaneously. Looking through the different layers, a RB is what comes on top of the Packet Data Convergence Protocol (PDCP) layer, while a TBF is what MAC offers to the physical layer. At each layer, multiplexing can occur so that several entities can be mapped onto one entity of the layer that comes under. In a second embodiment of the present invention multiplexing occurs at PDCP and MAC layers.

This second embodiment describes a solution for multiplexing of PDCP entities onto TBFs, which covers multiplexing at MAC levels. Several RBs are mapped onto one TBF, and a reduced RB Identity (RB Id) is included in the RLC/MAC header to differentiate between the different flows coming from the different RBs. The real RB identifier is reduced to become more space saving. An RB Id is suggested to 5 bits in UMTS and a reduced RB Id according to the present invention can be as short as 2 bits. The space in the header is limited and it is assumed here that the reduced RB Identity is 2 bits long but naturally it could be longer. The names of the field introduced in the MAC header ("Reduced RB Id") and of what has to be mapped to that ("RB Id") are used according to that assumption.

Two scenarios of this second embodiment will be described. Both are based on the assumption of 2 bits (x=2) reduced RB Id, which means that the number of different reduced RB Ids (n) are limited to four (00, 01, 10, 11). Therefore the method according to this second embodiment differs in the case where the required number of reduced RB Ids (n) are less than or equal to four and in the case where the required number of reduced RB Ids (n) exceeds four. An MS intend to set up a number of RBs: RBl,...,RBn. Figure 4 shows the protocols influenced by the radio interface according to the first scenario where n =< 4 and where the mapping of the reduced RB Id is implicit. Figure 5 shows the protocols influenced by the radio interface according to the second scenario where n>4 and where the mapping of the reduced RB Id is explicit.

On the uplink the following happens:

The MS requires sending data for RBI and a TBF i.e. TBFl, is to be established for RBI but it is preferable to assign further RBs for the TBFl when TBFl is established even if, for the time being, the MS requires to send data for less RBs. It is then not required any reconfiguring of the TBF if there is a requirement of sending further data for the rest of the assigned RBs later on. The MS only has to activate these RBs. To differentiate between the different RBs, a reduced RB Identity (RB Id) is included in the RLC/MAC header. As mentioned before, it is assumed here that the space within the header for the reduced RB Id is 2 bits long.

This means that if n =< 4, the mapping between the 2 bits reduced RB Id to the real RB Id can be implicit, i.e. for 2 bits there exists only four reduced RB Ids namely 00, 01, 10 and 11. According to the example of the first scenario shown in Figure 4, the MS requires sending data for RBI, but has established TBFl, which is assigned for four RBs i.e. RBI, RB2, RB3 and RB4. The lowest real RB Id is e.g. mapped onto the lowest reduced RB Id, for example for RBI a reduced RB Id would be 00, for RB2 e.g. 01, for RB3 e.g. 10 and for RB4 e.g. 11. If the MS later on wants to send data for RB2, the transmission of data can begin directly using TBFl and RB2, having the reduced RB Id 01. If n>4, i.e. the MS requires sending data for RBl but has established a TBFl assigned for e.g. RBl, RB2, RB3, RB4 and RB5 as shown in Figure 5, mapping between the 2 bit reduced RB Id to the real RB Id has to be done explicitly. The reduced RB Id is used to differentiate between the different flows coming from the different RBs, but the real RB Id has to be included in the payload in order to inform the receiver from which RB the data belongs to. If n>4, at least 2 TBFs have to be set up if we still assume that the length of the reduced RB id is two bits, since it is then only possible to differentiate between maximum four data flows on each TBF. In the example of the second scenario shown in Figure 5, TBFl is established which is assigned for RBl, RB2, RB3 and RB4. For RBl a reduced RB Id would be 00, for RB2, 01, for RB3, 10 and for RB4, 11. Further, TBF2 is established and assigned for RB5 and the reduced Id mapped to RB5 would e.g. be 00. The distribution of the RBs to the TBFs can be made in many ways, e.g. two RBs for TBFl and three RBs for TBF2 etc. The limit is that up to maximum four (2x) RBs can be assigned to one TBF if the space within the header for the reduced RB Id is 2 bits long (x=2). If the space within the header for the reduced RB Id is 3 bits long (x— 3), maximum eight RBs can be assigned to one TBF.

It should be noted that one bit in the payload may be used to indicate if the real RB Id is included in the payload or not, preferably the first bit.

If the RB uses an "acknowledged" RLC entity, and n>4, the real RB Id of RB2 needs only to be included into the payload of the first data block, since if the network does not receive it, the MS will retransmit anyway.

If the RB uses an "unacknowledged" RLC entity and n>4, the real RB2 has to be included in the header of all the data blocks transmitted with the new reduced RB Id (or maybe until the first acknowledge/non-acknowledge (ack/nack) report is received from the network, if the MS polls for ack/nack).

On the downlink a) A TBF, TBFl is setup between the network and the MS and Reduced RB Id" 00 is used for RBl. b) The transmission of data for RB2 can begin directly provided that RB2 is associated with TBFl at the assignment of TBFl, using another reduced RB Id.

The coupling between the real RB Id and the reduced one can be implicitly or explicitly transmitted depending of the number of established RB and assigned bits for the reduced RB ID.

The mapping of reduced RB Ids to RBs for n=<4 and n> 4 are provided in the same way as for the above mentioned uplink case.

Compared to the solution mapping one RB to one TBF, this solution does not have any delay before data can be transmitted on an extra RB, since no new TBF has to be set up.

Including the reduced RB Id in the RLC/MAC data block header.

The number of spare bits in the current EGPRS RLC/MAC data headers is very limited. Therefore, some fields have to be re-defined to be able to include a reduced RB Id in the headers: For the uplink

An RLC/MAC data block is encoded using any of the available channel coding schemes MCS-1, MCS-2, MCS-3, MCS-4, MCS-5, MCS-6, MCS-7, MCS-8, or MCS-9. Figure 6 shows an Uplink RLC/MAC data block header for MCS-1-4. For MCS-1-4, it is suggested to use the fields Spare and PI for a reduced RB Id with the length of two bits. It may also be possible to use the RSB and R bits if the number of bits of the reduced RB Id has to be increased in the future. For the current uplink RLC/MAC data header for MCS 5-9 there are enough spare bits which can be used for the reduced RB Id. For the downlink

Since the downlink RLC data headers do not contain any spare bits at all, we suggest to use the RRBP (Relative Reserved Block Period) field for a 2 bit RB Id. Figure 7 shows the Downlink RLC data block header for MCS-1, MCS-2, MCS-3 and MCS-4. The RRBP value may be signalled when the TBF is set-up and is fixed during the TBF. Different length could be used for the reduced RB Id fields on the up- and downlink, and some other fields could be reused instead or in addition to the ones named upon.

Mapping between the reduced RB Id and the real RB Id at the TBF set up

When a transmitter, whether it is the network or the mobile, has data to send for a certain RB, it needs first to establish a TBF for that data transfer.

On the downlink

On the downlink, a "Packet Downlink Assignment" message is sent from

GERAN to the MS. In this message, the identity of the RB(s) for which this TBF has been established shall be indicated, as well as the reduced RB Id(s) to which it is mapped. On the uplink

On the uplink, there could be two ways of establishing a TBF:

1) In the two phase access case, the MS sends a "Packet Channel Request" message to the network on the Random Access Channel (RACH) or the Packet Random Access Channel (PRACH). In this message, the MS indicates that it wants to be allocated one uplink block. Then, the network answers with a "Packet Uplink Assignment", allocating one uplink block to the MS. In that block, the MS sends a "Packet Resource Request" where it asks for an uplink TBF to be established. The identity of the RB(s) the TBF is requested for and the reduced RB Id(s) to which it (they) is (are) mapped may be indicated in this last message. The network responds with another "Packet uplink Assignment" where the mapping between the real RB Id and the reduced RB Id also may be sent.

2) An ARI based access could also be performed: in that case, the MS has previously been allocated one "ARI" (Access Request Identifier). In that case, the MS includes the ARI into the "Packet Channel Request" it sends onto the PRACH or the RACH. A "Packet Uplink Assignment" that allocates the TFI is then directly sent to the MS, since the MS is identified by the ARI. However, even though several ARIs could be allocated to the same user, it may be the case that an ARI does not identify the RB for which the access is performed. When the data transmission begins, a mechanism must be introduced for the network to understand which RB the data that are sent are meant for. For the coupling between the reduced RB Id that is used and the real identity of the RB the data are meant for, two methods are proposed:

I. If the ARI could be used for n<=4 RBs, the mapping could be implicit: if the MS uses for example reduced RB Id 00, it means that the data are meant for the RB with the lowest identity, and so on...

II. Another method that could be used more a;enerallv consists in introducing the real RB Id in the payload part of the blocks: one first bit of the payload, that is called Identity Indicator (II) bit, shall indicate whether the real RB Id has been included into the rest of the payload or not. When the data transmission begins after an ARI based access, the MS chooses a reduced RB Id to transmit the data for the RB it has data to send for. The real RB Id is included into the payload of the first blocks, and that is indicated by the II bit. If the RLC mode of the RB is "acknowledged", the real RB Id could just be included in the payload of the first block, since this block will be retransmitted until the network has succeeded to receive it. If the RLC mode of the RB is unacknowledged, then the RB Id shall be included into the payload until an Ack/Nack report is received by the MS that indicates that at least one block has been correctly received.

It shall be noted that the two methods are not exclusive, and can be used complementarity.

The following applies for both uplink and downlink: A timer could be used when a reduced RB Id shall be released, that could be the same for all RBs, or RB dependent (in which case it could be transmitted at RB setup). A control message could also be used for reduced RB Id reallocation i.e. the mapping between the reduced RB Id and the real RB Id is changed in order to avoid transmitting a Packet uplink (or downlink) assignment which are very big messages. The mapping between the reduced and real RB id is performed as described above.

Figure 8 shows a flowchart of a method in a packet switched radio communications system for transmission of packets over a radio interface to or from a Mobile Station (IVIS), wherein the system uses the Temporary Block Flow (TBF) and Radio Bearer (RB) concept, according to the invention in a general mode.

The method comprises the following steps: 801. At least one RB established. 802. At least one TBF is established.

803. At least one RB is associated to each of the at least one TBF.

804. A reduced RB Id is mapped to the real RB Id.

805. The reduced RB Id is included in a header of a RLC/MAC packet, in order to inform a receiver from which RB the data belongs to.

The method is implemented by means of a computer program product comprising the software code portions for performing the steps of the method. The computer program product is run on a computer stored in a base station system and in the mobile station, within the packet switched radio communications system. The computer program is loaded directly or from a computer usable medium, such as a floppy disc, a CD, the Internet etc.

Figure 9 shows a packet switched radio communications system according to the present invention wherein data packets can be transmitted over a radio interface 901 between a mobile station 900 and a base station system 903. The mobile station 900 and the base station system 903 are comprised in a radio access network such as e.g. Enhanced GPRS (EGPRS). The base station system 903 is connected to the UMTS core network 905 The system uses Temporary Block Flow (TBF) and Radio Bearer (RB) concept. The system comprises means 902 for establishing at least one RB; means 904 for establishing at least one TBF and means 906 for associating at least one RB to each of the at least one TBF. A real RB Identifier (RB Id) identifies a RB over the radio interface to differentiate between the different flows coming from the different RBs. The system comprises means 908 for mapping a reduced RB Id to the real RB Id to become more space-saving and for handling a plurality of RBs associated to one TBF. An RB Id is suggested to have the length of 5 bits as in UMTS and a reduced RB Id according to the present invention can be as short as 2 bits. The system comprises means 910 for including the reduced RB Id in a header of a Radio Link Control/Medium Access Control (RLC/MAC) packet in order to inform a receiver from which RB the data belongs to.

The system further comprises means for mapping the reduced RB Id to the real RB Id implicit, to handle the case where the number of established RBs is less than or equal to 2^X, and the reduced RB Id is x bits long. This means that, where the number of established RBs is less than or equal to 4, and the reduced RB Id is 2 bits long, the mapping can be implicit.

The system further comprising means for mapping the reduced RB Id to the real RB Id on the uplink to handle the case where the communications system comprises a GSM/EDGE Radio Access network (GERAN) and wherein an Access Request Identifier (ARI) based access is performed. The means for mapping of the reduced RB Id to the real RB Id can be performed explicit if the number of established RBs exceeds 2^X, and the reduced RB Id is x bits long. Which means if the number of established RBs exceeds 4, in the case where the reduced RB Id is 2 bits long. The explicit mapping can also be performed when the number of established RBs are less than or equal to 2^X. The explicit mapping is feasible by a system comprising means for including the real RB Id in the payload of said RLC/MAC packet.

The system further comprises means for using one bit in the payload to indicate whether the real RB Id is included in the payload or not. For handling cases where an acknowledged RLC entity is used by an established RB and the number of established RBs exceeds 2^X, e.g. four, the system further comprises means for including the full RB Id, only in a first data block of all data blocks transmitted with the mapped reduced RB Id. For handling cases where an unacknowledged RLC entity is used by an established RB and the number of established RBs exceeds 2^X, e.g. four, the system further comprises means for including the full RB Id in all data blocks transmitted with the mapped reduced RB Id, until a first acknowledge or non-acknowledge report is received. In one embodiment the system comprises a GSM/EDGE Radio Access network (GERAN). In that case the system might comprise means for indicating in a control message such as a "Packet Downlink Assignment" message, sent from GERAN to the MS, the real RB Id(s) for which a TBF has been established and the respective reduced RB Id(s) to which the real RB Id(s) is/are mapped. The system might further comprise means for indicating in a control message such as "Packet Resource Request" message, sent from MS to the GERAN, the real RB Id(s) for which a TBF has been established and the respective reduced RB Id(s) to which the real RB Id(s) is/are mapped.

The system might further comprise means for releasing a reduced RB Id by means of an indication of a timer and/or means for reallocating a reduced RB Id by transmitting a control message.

The present invention is not limited to the above-described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be taken as limiting the scope of the invention, which is defined by the appending claims.

Claims

1. Method in a packet switched radio communications system for transmission of packets over a radio interface to or from a Mobile Station (MS), the system using Temporary Block Flow (TBF) and Radio Bearer (RB) concept, characterised in that the method comprises the steps of: establishing (801) at least one RB; establishing (802) at least one TBF; associating (803) at least one RB to each of the at least one TBF.

2. Method according to the previous claim, wherein a plurality of RBs are associated to each of the at least one TBF.

3. Method according to the previous claim, wherein a real RB Identifier (RB Id) identifies an RB, the method comprises the further step of mapping a reduced RB Id to the real RB Id.

4. Method according to claim 3, comprising the further step of: including said reduced RB Id in a header of a Radio Link Control/Medium Access Control (RLC/MAC) packet in order to inform a receiver from which RB the data belongs to.

5. Method according to any of the previous claims 3-4, wherein the number of established RBs is less than or equal to 2^X, and the reduced RB Id is x bits long, said mapping of the reduced RB Id to the real RB Id is performed implicit.

6. Method according to claim 5, wherein x is equal to two.

7. Method according to any of the claims 3-6, wherein the communications system comprises a GSM/EDGE Radio Access network (GERAN) and wherein an Access Request Identifier (ARI) based access is performed and wherein said mapping of the reduced RB Id to the real RB Id is performed on the uplink.

8. Method according to claim 3, wherein the number of established RBs exceeds 2^X, and the reduced RB Id is x bits long, said mapping of the reduced RB Id to the real

RB Id is performed explicit.

9. Method according to the previous claim, wherein x is equal to 2.

10. Method according to the previous claim, wherein said explicit mapping is performed by: including the real RB Id in the payload of said RLC/MAC packet.

11. Method according to the previous claim, comprising the further step of using one bit in the payload to indicate whether the real RB Id is included in the payload or not.

12. Method according to any of the previous claims 8-11, wherein an established RB uses an acknowledged RLC entity and the number of established RBs exceeds 2^λ, the method comprising the further step of: including the full RB Id only in a first data block of all data blocks transmitted with the mapped reduced RB Id.

13. Method according to any of the previous claims 8-11, wherein an established RB uses an unacknowledged RLC entity and the number of established RBs exceeds

2^X, the method comprising the further step of: including the full RB Id in all data blocks transmitted with the mapped reduced RB Id, until a first acknowledge or non-acknowledge report is received.

14. Method according to any of the claims 3-13, wherein the communications system comprises a GSM/EDGE Radio Access network (GERAN),the method comprising the further step to be taken at the TBF setup on the downlink: indicating in a control message, sent from GERAN to the MS, the real RB Id(s) for which a TBF has been established and the respective reduced RB Id(s) to which the real RB Id(s) is /are mapped.

15. Method according to any of the claims 3-14, wherein the communications system comprises a GSM/EDGE Radio Access network (GERAN), the method comprising the further step to be taken at the TBF setup on the uplink: indicating in a control message, sent from MS to the GERAN, the real RB Id(s) for which a TBF has been established and the respective reduced RB Id(s) to which the real RB Id(s) is /are mapped.

16. Method according to any of the claims 3-15, comprising the further step of: releasing a reduced RB Id by means of an indication of a timer.

17. Method according to any of the claims 3-16 claims, comprising the further step of: reallocating a reduced RB Id by transmitting a control message.

18. A computer program product directly loadable into the internal memory of a computer within a mobile station or a base station system in a packet switched radio communications system, comprising the software code portions for performing the steps of any of the claims 1-17.

19. A computer program product stored on a computer usable medium, comprising readable program for causing a computer, within a mobile station or a base station system in a packet switched radio communications system, to control an execution of the steps of any of the claims 1-17.

20. Radio communications system for transmission of packets over an radio interface (901) to or from a Mobile Station (900), the system is packet switched and uses the Temporary Block Flow (TBF) and Radio Bearer (RB) concepts, characterised in that the system comprises: means (902) for establishing at least one RB; means (904) for establishing at least one TBF; and means (906) for associating at least one RB to each of the at least one TBF.

21. Radio communications system according to the previous claim, wherein a plurality of RBs are associated to each of the at least one TBF.

22. Radio communications system according to the previous claim, wherein a real RB Identifier (RB Id) identifies a RB, the system comprises means (908) for mapping a reduced RB Id to the real RB Id.

23. Radio communications system according to claim 22, wherein the system further comprises means (910) for including said reduced RB Id in a header of a Radio Link Control/Medium Access Control (RLC/MAC) packet in order to inform a receiver from which RB the data belongs to.

24. Radio communications system according to any of the previous claims 22-23, wherein the number of established RBs is less than or equal to 2^X, and the reduced RB Id is x bits long, the system further comprising means for mapping of the reduced RB Id to the real RB Id implicit.

25. Radio communications system according to claim 24, wherein x is equal to two.

26. Radio communications system according to any of the claims 22-25, wherein the communications system comprises a GSM/EDGE Radio Access network (GERAN) and wherein an Access Request Identifier (ARI) based access is performed, the system further comprising means for mapping of the reduced RB Id to the real RB Id on the uplink.

27. Radio communications system according to claim 22, wherein the number of established RBs exceeds 2^X, and the reduced RB Id is x bits long, said means for mapping of the reduced RB Id to the real RB Id is performed explicit.

28. Radio communications system according to claim 27, wherein x is equal to 2.

29. Radio communications system according to claim 28, wherein said explicit mapping is feasible by means for including the real RB Id in the payload of said RLC/MAC packet.

30. Radio communications system according to the claim 29, further comprising means for using one bit in the payload to indicate whether the real RB Id is included in the payload or not.

31. Radio communications system according to any of the previous claims 27-30, wherein an acknowledged RLC entity is usable by an established RB and the number of established RBs exceeds 2^X, the system further comprising means for including the full RB Id, only in the a first data block of all data blocks transmitted with the mapped reduced RB Id.

32. Radio communications system according to any of the previous claims 27-30, wherein an unacknowledged RLC entity is usable by an established RB the number of established RBs exceeds 2^X, the system further comprising means for including the full RB Id in all data blocks transmitted with the mapped reduced RB Id, until a first acknowledge or non-acknowledge report is received.

33. Radio communications system according to any of the claims 20-32, wherein the communications system comprises a GSM/EDGE Radio Access network (GERAN),the system further comprising means for indicating in a control message, sent from GERAN to the MS, the real RB Id(s) for which a TBF has been established and the respective reduced RB Id(s) to which the real RB Id(s) is/are mapped.

34. Radio communications system according to any of the claims 20-33, wherein the communications system comprises a GSM/EDGE Radio Access network (GERAN), the system further comprising means for indicating in a control message, sent from MS to the GERAN, the real RB Id(s) for which a TBF has been established and the respective reduced RB Id(s) to which the real RB Id(s) is/are mapped.

35. Radio communications system according to any of the claims 22-34, further comprising means for releasing a reduced RB Id by means of an indication of a timer.

36. Radio communications system according to any of the claims 22-35 claims, further comprising means for reallocating a reduced RB Id by transmitting a control message.