(12) United States Patent
`Leppisaari et al.
`
`USOO6532227B1
`US 6,532,227 B1
`Mar. 11, 2003
`
`(10) Patent No.:
`(45) Date of Patent:
`
`(54) GENERAL PACKET RADIO SERVICE
`(75) Inventors: Arto Leppisaari, Tampere (FI); Jari
`Hämäläinen, Kangasala (FI)
`(73) Assignee: Nokia Mobile Phones Limited, Espoo
`(FI)
`Subject to any disclaimer, the term of this
`patent is extended or adjusted under 35
`U.S.C. 154(b) by 0 days.
`
`(*) Notice:
`
`(21) Appl. No.: 09/063,167
`(22) Filed:
`Apr. 20, 1998
`(30)
`Foreign Application Priority Data
`Apr. 21, 1997
`(FI) ................................................. 971697
`(51) Int. Cl." ........................... H04B 71212; H04Q 7/20
`(52) U.S. Cl. ....................... 370/348; 370/322; 370/329;
`370/432; 370/342; 455/509; 455/450
`(58) Field of Search ................................. 370/321, 322,
`370/326, 329, 330, 332, 336,341, 343,
`347, 348, 349, 436, 437, 442, 443, 444,
`458, 468, 469, 431; 455/450, 451, 452,
`453, 455,464, 509, 512, 515, 516, 517
`
`(56)
`
`References Cited
`U.S. PATENT DOCUMENTS
`
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`5,396,539 A 3/1995 Slekys et al. ................. 379/59
`5,396,653 A 3/1995 Kivari et al. ................. 455/88
`5,430,740 A 7/1995 Kivari et al. .............. 371/37.1
`5,521,925 A * 5/1996 Merakos et al. ............ 370/337
`5.535,429 A * 7/1996 Bergenlid et al............ 370/329
`5,570,353 A 10/1996 Keskitalo et al. ............. 370/18
`5,577.024 A 11/1996 Malkamaki et al. .......... 370/18
`5,606,548 A 2/1997 Vayrynen et al. ........... 370/252
`5,640,395 A 6/1997 Hamalainen et al. ....... 370/322
`5,708,656 A
`1/1998 Noneman et al. ........... 370/320
`
`5,726,981 A 3/1998 Ylitervo et al. ............. 370/332
`5,729,534 A 3/1998 Jokinen et al. ............. 370/284
`5,729,541 A 3/1998 Hamalainen et al. ....... 370/337
`5,778,318 A * 7/1998 Talarmo et al. ............. 455/452
`5,784,362 A
`7/1998 Turina ........................ 370/321
`5,790,551 A
`8/1998 Chan .......................... 370/458
`6,009,331 A 12/1999 Ueda .......................... 455/450
`6,031827 A
`2/2000 Rikkinen et al. ........... 370/330
`6,031832 A
`2/2000 Turina ........................ 370/348
`FOREIGN PATENT DOCUMENTS
`
`EP
`EP
`WO
`WO
`
`O 168 927 A2
`O 755 164 A2
`WO95/16330
`WO 96/22665
`
`1/1986
`1/1997
`6/1995
`7/1996
`
`OTHER PUBLICATIONS
`Global System for Mobile Communications ETSI, GSM
`03.64, version 5.2.0.
`PCT International Search Report issued on PCT/FI98/
`OO214.
`* cited by examiner
`Primary Examiner Steven Nguyen
`(74) Attorney, Agent, or Firm-Perman & Green, LLP
`(57)
`ABSTRACT
`A method for quickly de-allocating physical channels
`(PDCH) assigned to packet switched calls in a GPRS
`Supporting GSM digital cellular telephone network. An
`PDCH de-allocation RLC/MAC control message is broad
`cast to listening mobile Stations from a base Station Sub
`system (BSS) and contains a temporary flow identity (TFI)
`which is recognised by the listening mobile stations (MS).
`The mobile Stations respond by terminating packet Switched
`data transmissions on the identified PDCHs. The RLC/MAC
`message also identifies the number of PDCH time slots
`which can be used before de-allocation must occur.
`
`12 Claims, 2 Drawing Sheets
`
`Application
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`IPI X.25
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`LLC Relay
`RLC
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`"I ATM
`FR
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`MS
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`Um
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`BS
`S
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`Gb
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`Ex.1012
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`

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`U.S. Patent
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`Mar. 11, 2003
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`Sheet 1 of 2
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`US 6,532,227 B1
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`U.S. Patent
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`Mar. 11, 2003.
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`Sheet 2 of 2
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`US 6,532,227 B1
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`1
`GENERAL PACKET RADIO SERVICE
`
`US 6,532,227 B1
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`2
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`1O
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`15
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`35
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`40
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`FIELD OF THE INVENTION
`The present invention relates to general packet radio
`service (GPRS) and more particularly to a method and
`apparatus for de-allocation of GPRS physical channels.
`BACKGROUND OF THE INVENTION
`Current digital cellular telephone systems such as GSM
`(Global System for Mobile communications) were designed
`with an emphasis on Voice communications. Data is nor
`mally transmitted between a mobile station (MS) and a base
`station Subsystem (BSS) over the air interface using the so
`called circuit Switched transmission mode where a physical
`channel, i.e. a Series of regularly Spaced time slots on one or
`more frequencies, is reserved for the duration of the call. For
`Voice communications, where the Stream of information to
`be transmitted is relatively continuous, the circuit Switched
`transmission mode is reasonably efficient. However, during
`data calls, e.g. facsimile transmissions, internet access, etc,
`the data Stream is bursty and the long term reservation of
`a physical channel in the circuit Switched mode represents
`an uneconomic use of the air interface.
`25
`Given that the demand for data services with digital
`cellular telephone Systems is increasing rapidly, a new GSM
`based service know as the General Packet Radio Service
`(GPRS) is currently being standardised by the European
`Telecommunications Standards Institute (ETSI). GPRS pro
`vides for the dynamic allocation of physical channels for
`data transmission. That is to say that a physical channel is
`allocated to a particular MS to BSS link only when there is
`data to be transmitted. The unnecessary reservation of
`physical channels when there is no data to be transmitted is
`avoided.
`GPRS is intended to operate in conjunction with conven
`tional GSM circuit Switched transmission to efficiently use
`the air interface for both data and Voice communications.
`GPRS will therefore use the basic channel structure defined
`for GSM. In GSM, a given frequency band is divided in the
`time domain into a Succession of frames, known as TDMA
`(Time Division Multiplexed Access) frames. The length of
`TDMA frame is 4.615 ms. Each TDMA frame is in turn
`divided into eight consecutive slots of equal duration. In the
`conventional circuit Switched transmission mode, when a
`call is initiated, a physical channel is defined for that call by
`reserving a given time slot (1 to 8) in each of a Succession
`of TDMA frames. A series of four consecutive time slots on
`a physical channel is known as a radio block and represents
`the shortest transmission unit for packet Switched data on a
`physical channel. Physical channels are similarly defined for
`conveying Signalling information. With the introduction of
`GPRS, physical channels will be dynamically assigned for
`either Switched circuit transmission mode or for packet
`Switched transmission mode. When the network requirement
`for Switched circuit transmission mode is high, a large
`number of physical channels may be reserved for that mode.
`On the other hand, when demand for GPRS transmission is
`high, a large number of physical channels may be reserved
`for that mode. In addition, a high Speed packet Switched
`transmission channel may be provided by assigning two or
`more slots in each of a Succession of TDMA frames to a
`single MS.
`There is illustrated in FIG. 1 the basic architecture of a
`GSM cellular network which supports GPRS. The terminol
`ogy used in FIG. 1 is defined, by convention, as follows:
`
`45
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`MS
`PC/PDA
`BSS
`BTS
`BSC
`GPRS
`HLR
`SGSN
`GGSN
`MSC
`SS7
`PSTN
`
`Mobile Station
`Personal Computer/Personal Data Assistant
`Base Station Subsystem
`Base Tranceiver Station
`Base Station Controller
`General Packet Radio Service
`Home Location Register
`Serving GPRS Support Node
`Gateway GPRS Support Node
`Mobile Switching Centre
`Signalling System number 7
`Public-Switched Telephone Network
`
`The full benefits promised by packet switched transmis
`Sion are only achieved if a data transmission can be set up
`very quickly, i.e. there is little point in providing for the
`transmission of Short duration packets if the time required to
`Set up each of those transmissions is relatively long. Rapid
`set-up is achieved in the proposed GPRS system by defining
`a 'virtual channel or “context between a MS and the SGSN
`when the MS first becomes active in the cellular network.
`This virtual channel is not an actual physical channel but
`involves creating and Storing parameterS Such as the MS
`identifier, encryption key, etc., at the SGSN and at the MS.
`When an actual data transmission is initiated between the
`MS and the SGSN using GPRS, there is no need to generate
`and/or transfer this information and the connection can be
`set up extremely quickly. The proposed GPRS air-interface
`protocols are set out in the GSM Technical Specification
`GSM 03.64 (ETSI).
`FIG. 2 shows schematically the radio link protocol stacks
`which are described in the GSM 03.64 specification. The
`terminology used in FIG. 2 is defined by convention as
`follows:
`
`IP
`SNDCP
`LLC
`RLC
`MAC
`GSMRF
`Um
`BSSGP
`ATM
`FR
`L1bis
`SGSN
`BSC
`Gb
`
`Internet Protocol
`Subnetwork Dependent Convergence Protocol
`Logical Link Control
`Radio Link Control
`Medium. Access Control
`GSM Radio Frequency
`GPRS/MS interface
`Base Station Subsystem GPRS Protocols
`Asynchronous Transfer Mode
`Frame Relay
`Layer 1 bis
`Serving GPRS Support Node
`Base Station Controller
`SGSNFBSC interface
`
`The assignment of physical channels at the radio interface
`for packet Switched transmission is carried out at the RLC/
`MAC layer by RLC/MAC layer control messages. For
`example, a MS may initiate a packet transfer by making a
`random access request using a RLC/MAC message. The
`number of time slots (or radio blocks) which the MS wishes
`may be conveyed using a further message. Similarly, the
`BSS may initiate a packet transfer to the MS using RLC/
`MAC messages. AS already described, when a virtual chan
`nel is created between a MS and a SGSN, a MS identifier is
`assigned to the MS. This identifier is known as a Temporary
`Logical Link Identifier (TLLI). When a data transmission is
`initiated between the MS and the BSS and one or more
`physical channels are allocated, a new RLC/MAC identifier
`known as a Temporary Flow Identifier (TFI) is assigned to
`the MS. During the data transmission, RLC/MAC messages
`will include the TFI in one of their fields to identify the
`receiving (or transmitting ) MS.
`
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`US 6,532,227 B1
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`3
`It is envisaged that, in a mixed circuit Switched/packet
`Switched network, priority will be given to the circuit
`Switched service. This means that if the amount of traffic in
`the network approaches the network capacity, and a request
`is made for a circuit Switched call, it is necessary to
`re-allocate physical channels from the packet Switched Ser
`Vice to the circuit Switched Service. Re-allocation may be
`achieved by waiting for ongoing packet Switched transmis
`Sions to be completed and, upon completion, assigning the
`released channels to the Switched circuit Service. However,
`it is considered more efficient to interrupt ongoing packet
`Switched transmissions on these channels and to immedi
`ately allocate the released channels, completing the inter
`rupted transmissions only when the demand for Switched
`circuit transmission has fallen Sufficiently (or other non
`interrupted packet Switched transmissions have been
`terminated). The existing GPRS proposals require that when
`capacity is required for Switched circuit transmission, RLC/
`MAC control messages are transmitted to the MSs instruct
`ing them to cease transmission on certain Specified physical
`channels and to request access to other physical channels
`from the BSS. More specifically, a new RLC/MAC control
`message is defined and which comprises a message identifier
`field defining the message as a resource reassignment mes
`sage and a TFI field specifying the MS to receive the
`message. It is of course necessary to transmit a resource
`reassignment message Separately for each mobile Station
`currently occupying a physical channel which must be
`de-allocated and the de-allocation process is therefore rela
`tively slow. It is noted that each packet Switched transmis
`Sion generally occupies an uplink and a downlink channel So
`that two separate RLC/MAC control messages must be sent
`for each MS.
`It is an object of the present invention to provide a
`physical channel de-allocation method and apparatus for
`GPRS which enables the interruption of a packet switched
`data transmission and the rapid de-allocation of a channel or
`channels occupied by that transmission.
`SUMMARY OF THE INVENTION
`According to a first aspect of the present invention there
`is provided a method of de-allocating one or more physical
`channels previously assigned for packet Switched transmis
`sion between a plurality of mobile stations (MS) and a base
`Station Subsystem (BSS), the method comprising broadcast
`ing from the BSS an RLC/MAC control message having a
`message-type field identifying the message as a channel
`de-allocation message, and a de-allocated channel field
`identifying the physical channel(s) to be de-allocated,
`wherein Said control message is received and acted on by
`said plurality of MSS using said physical channel(s).
`Preferably, said RLC/MAC control message comprises a
`field defining the number of time slots or radio blocks after
`which the identified physical channel(s) must be
`de-allocated. This number may be zero whereupon the
`physical channel(s) is (are) de-allocated immediately.
`Preferably, said RLC/MAC control message contains a
`field identifying a carrier (i.e. frequency) on which the or
`each said MS should transmit to the BSS a new packet
`channel request. More preferably, said RLC/MAC control
`message contains a PRACH (packet random access channel)
`allocation field for identifying the time slot(s) where said
`request should be made on the identified carrier.
`Preferably, said RLC/MAC control message is transmit
`ted on the same carrier frequency as was used for Said
`de-allocated physical channel(s). This identifies the message
`
`1O
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`4
`to the MSS as relating to channels on Said carrier. The
`de-allocated channel field therefore only needs to identify
`the de-allocated time slots. More preferably, said RLC/MAC
`control message contains a field defining the time slot(s) on
`the identified carrier where the BSS may transmit a down
`link resource reassignment message to the MSS and also a
`field defining the time slot(s) where the BSS may transmit an
`uplink resource reassignment message. These resource reas
`signment messages may include a TFI which was assigned
`to the MSs before deallocation.
`In one embodiment of the invention, said RLC/MAC
`control message contains a temporary flow identity field
`which conveys a temporary flow identity (TFI). This TFI is
`also stored in a memory of each of said MSs whereby each
`of the MSS can recognise the RLC/MAC control message as
`a broadcast message.
`In an alternative embodiment, the RLC/MAC control
`message does not require a TFI field. Rather, the message
`type field alerts each of the MSs to the fact that the message
`is a broadcast message to be acted upon by all MSS using the
`physical channel(s) identified in the de-allocated channel
`field.
`According to a Second aspect of the present invention
`there is provided apparatus for de-allocating one or more
`physical channels previously assigned for packet Switched
`transmission between a plurality of mobile stations (MS)
`and a base station Subsystem (BSS), the apparatus compris
`ing means for broadcasting from the BSS an RLC/MAC
`control message having a message-type field identifying the
`message as a channel de-allocation message, and a
`de-allocated channel field identifying the physical channel
`(s) to be de-allocated, wherein all of said MSs using said
`physical channel(s) are arranged to receive and act upon said
`control message.
`According to a third aspect of the present invention there
`is provided a cellular telephone System comprising a BSS
`incorporating the apparatus of the above Second aspect of
`the present invention and a plurality of MSS arranged to
`receive said broadcast RLC/MAC control message.
`
`BRIEF DESCRIPTION OF THE DRAWINGS
`FIG. 1 shows schematically the architecture of a GSM/
`GPRS digital cellular telephone network; and
`FIG. 2 illustrates the protocol layers of a GPRS radio link
`of the network of FIG. 1.
`
`DETAILED DESCRIPTION
`The architecture of a GSM network which supports GPRS
`has already been discussed with reference to FIGS. 1 and 2.
`The present invention relates to the transmission protocol
`used in transmissions between mobile stations (MS) and a
`base station subsystem (BSS), and more particularly to the
`transmission protocol at the RLC/MAC layer. The signalling
`process for allocating physical channels for packet Switched
`transmissions (packet data channels-PDCH) to individual
`MSs is described in detail in GSM technical specification
`GSM 03.64 and this will not be discussed further here.
`Rather, the present invention is concerned with the
`de-allocation of physical channels previously allocated by
`the BSS.
`When a BSS determines that physical channels previously
`allocated for packet Switched transmissions must be freed
`for other uses, and in particular for use in Switched circuit
`calls, MSS must be notified of this decision to avoid data
`being lost. More particularly, the MSS must be informed of
`
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`US 6,532,227 B1
`
`S
`the physical channels which are being re-allocated and when
`this re-allocation must occur. A new RLC/MAC control
`message is therefore defined.
`Each MS in a network is preprogrammed with a special
`temporary flow identity (TFI) code. This code is the same for
`all MSs and is used by the MSs to identify a broadcast
`de-allocation message. All active MSS Subsequently listen
`at the carrier frequency assigned for packet data transmis
`sion for RLC/MAC control messages transmitted in the
`downlink direction and containing the allocated TFI. The
`new RLC/MAC control message has the following structure
`where the letter 'M' indicates a mandatory field (in this
`embodiment) and the letter 'O' indicates an optional field:
`
`No.
`
`Field Name
`
`1.
`2
`3
`4
`5
`
`6
`7
`
`8
`
`M
`Message Type
`M
`Temporary Flow Identity (broadcast)
`M
`De-allocated PDCH
`Number of radio blocks before de-allocation M
`Channel Allocation for uplink
`O
`channel request
`PRACH allocation on defined channel
`Time slot to be used for uplink
`resource re-assignment
`Time slot to be used for downlink
`
`O
`O
`
`O
`
`resource re-assignment
`Sum of bits
`
`15
`
`25
`
`Bits
`
`8
`7
`8
`4
`4
`
`8
`8
`
`8
`
`55
`
`6
`de-allocation, it may be appropriate to send the RLC/MAC
`de-allocation message two or more times in case certain
`MSs are temporarily outside the area covered by the BSS.
`Embodiments of the invention may also involve the trans
`mission of the same RLC/MAC de-allocation message on
`two or more time slots. This may be necessary, for example,
`when MSs are using multiple time slots within a TDMA
`frame for a single packet Switched data transmission but are
`only listening for control messages on one of the time slots.
`With different MSs listening for control messages on dif
`ferent time slots, Such multiple transmission is required in
`order to notify all MSs using a physical channel of the
`de-allocation of that channel.
`The RLC/MAC de-allocation message may include some
`MS specific information which is identified by including a
`MS specific identifier in the message. This may be
`necessary, for example, to allocate different resource reas
`signment channels (uplink and downlink) to different MSs.
`What is claimed is:
`1. A method of de-allocating one or more physical chan
`nels previously assigned for packed Switched transmission
`between a plurality of mobile stations (MS) and a base
`Station Subsystem (BSS), the method comprising broadcast
`ing from the BSS an RLC/MAC control message having a
`message-type field identifying the message as a channel
`de-allocation message, and a de-allocated channel field
`identifying the physical channel(s) to be de-allocated,
`wherein Said control message is received and acted on by
`said plurality of MSS using said physical channels(s).
`2. A method according to claim 1, wherein Said RLC/
`MAC control message comprises a field defining the number
`of radio blocks after which the identified physical channel(s)
`must be de-allocated.
`3. A method according to claim 1, wherein said RLC/
`MAC control message contains a field identifying a carrier
`on which the MSS may transmit to the BSS a new packet
`channel request.
`4. A method according to claim 3, wherein said RLC/
`MAC control message contains a field identifying the time
`slots wherein a PRACH is allocated and where the MSs may
`transmit a random acceSS request for data on the identified
`carrier.
`5. A method according to claim 1, wherein said RLC/
`MAC control message is transmitted on the Same carrier
`frequency as was used for Said de-allocated physical channel
`(S), thereby identifying the message to the MSS as relating
`to physical channels on Said carrier.
`6. A method according to claim 5, wherein said RLC/
`MAC control message contains a field defining the time slot
`on said same carrier in which the BSS will transmit an
`uplink resource reassignment message to the MSS.
`7. A method according to claim 5, wherein said RLC/
`MAC control message contains a field defining the time slot
`on said same carrier in which the BSS will transmit a
`downlink resource reassignment message to the MSS.
`8. A method according to claim 1, wherein said RLC/
`MAC control message contains a temporary flow identity
`field which conveys a temporary flow identity (TFI).
`9. A method according to claim 8, wherein said TFI is
`stored in a memory of the MSS enabling the MSs to
`recognise the RLC/MAC control message as a broadcast
`meSSage.
`10. A method according to claim 1, wherein the message
`type field alerts each of the MSs to the fact that the message
`is a broadcast message to be acted upon by all MSS using the
`physical channel(s) identified in the de-allocated channel
`field.
`
`35
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`40
`
`The fields of the control message are explained below.
`Message Type
`This field identifies the control message to the listening
`MSS as a MAC packet resource de-allocation message.
`Temporary Flow Identity (Broadcast)
`This provides a TFI code and identifies the message as a
`broadcast message.
`De-allocated Time PDCH
`This field identifies one or more physical channels
`(PDCH) to be de-allocated. With an 8-bit field, it is possible
`to de-allocate PDCHS corresponding to all 8 time slots on
`the associated carrier frequency.
`Number of Radio Blocks Before De-allocation
`This field defines when the de-allocation must occur. If
`immediate de-allocation is required, then the number of
`radio blockS is defined as Zero.
`Channel Allocation for Unlink Channel Request
`This field identifies the carrier (i.e. frequency) on which
`the MSs should make a request for a new PDCH.
`PRACH Allocation on Defined Channel
`This field identifies the time slots on the allocated carrier
`where the PRACH is allocated.
`Time Slot to be Used for Uplink Resource Re-assignment
`If the BSS requires to initiate a new packet switched
`transmission with a MS, the BSS must transmit to the MS
`both an uplink and a downlink reassignment message on the
`55
`carrier frequency last used for packet Switched transmission
`between the BSS and that MS. This field identifies the time
`Slot on that carrier where the uplink reassignment message
`will be transmitted.
`Time Slot to be Used for Downlink Resource Re-assignment
`This field identifies the time slot where the downlink
`resource re-assignment message will be transmitted.
`It will be appreciated by the skilled person that modifi
`cations may be made to the above described embodiment
`without departing from the Scope of the present invention.
`For example, in order to ensure that all MSs using the
`PDCHS to be de-allocated are made aware of the
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`7
`11. Apparatus for de-allocating one or more physical
`channels previously assigned for packed Switched transmis
`sion between a plurality of mobile stations (MS) and a base
`Station Subsystem (BSS), the apparatus comprising means
`for broadcasting from the BSS an RLC/MAC control mes
`Sage having a message type field identifying the message as
`a channel de-allocating message, and a de-allocated channel
`field identifying the physical channel(s) to be de-allocated,
`
`8
`wherein all of Said MSS using said physical channel(s) are
`arranged to receive and act upon said control message.
`12. A cellular telephone System comprising a BSS incor
`porating the apparatus of claim 11 and a plurality of MSS
`arranged to receive said broadcast RLC/MAC control mes
`Sage.
`
`5
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