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3.5.3 利用CCCH的下行链路指配程序
从网络到MS的方向，利用CCCH的分组下行链路指配程序来建立临时块流，从而支持LCC PDUs的传输。
在分组空闲模式下，这个程序也可以用在指配PDCH上的一个单下行链路块上，来支持从网络到MS方向的RLC/MAC控制信息的传输。
3.5.3.1 进入分组传输模式：分组下行链路指配程序
网络利用分组下行链路支配程序可以发起下行链路临时块流的建立。这个程序由上层请求传输一个LCCPDU来触发，见GSM 04.07.上层的请求具体说明了选择的优先级，QoS文件（包括RLC模式请求，可选DRX参数，可选IMSI和可选的伴随于分组传输的MS无线接入能力）。
在上面的要求下，网络应该决定MS是应该处于分组空闲模式还是分组传输模式。利用CCCH的分组下行链路指配程序适用于当小区中不存在PCCCH时MS处于分组空闲模式的情况。
网络可能分配一个临时块流识别和分配一个分组下行链路资源来构成一个下行链路块流的PDCH。
3.5.3.1.2 分组下行链路指配程序的发起
网络通过发送一个"立即指配"消息，相应于属于MS CCCH组的CCCH时隙，以无证实方式发起分组下行链路指配程序。由IMSI来计算合适的CCCH组，见05.02.当RR实体不接收上层的IMSI时，网络的行为的实施依靠CCCH组来计算"立即指配"消息应该发送到哪。如果MS是非DRX模式或者RR实体不接收IMSI或者DRX参数是来自上层，那么对CCCH时隙的哪个部分来发送"立即指配"消息或第一个"立即指配"消息（在一个two-message指配情况下）没有限制。
"立即指配"消息包括：
- 分组信道描述；
- 初始定时提前；
- 分组下行链路指配的构建。
分组下行链路指配构建的内容来决定下一步采取的进一步行动。在下行链路临时块流建立时，分组下行链路指配构建应该包括：
- TLLI
- 临时块流识别；
- RLC模式；
- 功率控制参数；
- 轮寻比特；
- 初始定时提前有效标志；
- 可选，定时提前索引（见GSM 05.10）
- 可选，TBF起始时间。
如果应用跳频，那么网络可以利用在分组信道描述信息单元中的间接解码或者直接解码的频率结构。如果利用间接解码，那么MS利用在系统消息中接收的信息或者存储于前一个指配的信息来决定频率参数，见GSM 04.60。如果利用直接解码，那么MS利用小区分配的详细说明来解码移动分配。
如果利用间接解码，"立即指配"消息可能包含一个CHANGE_MARK_1域。如果CHANGE_MARK_1域存在，那么MS应该修改"立即指配"消息涉及的伴随GPRS移动分配的SI改变标志的合法性。如果CHANGE_MARK_1域和SI改变标志不匹配，那么消息并不满足PDCH的定义。
如果MS接收到一个"立即指配"消息，并且专用模式或TBF信息单元表明该消息是在一个two-message指配中的第一个消息，那么MS应该继续侦听所有CCCH。在两个复帧周期内，网络可能给MS发送紧接着第一个"立即指配"消息的第二个"立即指配"消息，详细说明分组信道面描述，如果需要的话，为了指配的一个一动分配。这两个在一个two-message 指配中的"立即指配"消息，其请求参考信息单元的内容应该相同。
当MS接收到一个two-message指配中的第一个消息时，如果MS操作在DRX模式，那么网络在第一个消息之后的两个块周期内不应该发送第二个"立即指配"消息。
在两个复帧周期内，如果MS没有接收到紧接着第一个"立即指配"消息的第二个"立即指配"消息，MS应该放弃接收到的第一个"立即指配"消息。在第一个消息的两个复帧周期后，MS可能回到DRX模式。
一接收到一个"立即指配"消息，或者在一个two-message指配的情况下，一对匹配的"立即指配"消息，那么MS停止监控下行链路CCCH并转向监控指配的PDCH，并且开始侦听下行链路RLC/MAC块，该块由指配的TFI识别；MS启动定时器T3190。
"立即指配"消息可能包含一个TBF起始时间。如果MS在TBF起始时间之前就接到了该消息，那么MS应该等到TBF起始时间指示的帧号再接入，启动定时器T3190并转向监控指配的PDCH。如果MS在TBF起始时间之后才接到该消息，那么MS应该忽略指示的TBF起始时间，立即启动定时器T3190，并转向监控指配的PDCH。
如果轮询比特设置为1，那么MS应该在指配的PDCH上发送一个"分组控制证实"消息(见04.60)，在上行链路块中，TBF开始时间详细说明了该消息。在这种情况下，TBF起始时间同时用于指示当指配的PDCH变为有效和详细说明上行链路块。如果TBF起始时间不存在或者逾时，那么MS应该忽略轮询请求。
一个"立即指配"消息可能在分组定时提前信息单元中指示一个定时提前索引（TAI）。接着MS应该利用连续更新定时提前机制，见GSM 05.10，用的是与指配PDCH时隙相同的PTCCH信道。
TA_VALID标志只是了定时提前信息单元是否有效。
如果网络在"立即指配"消息中没有一个有效的定时提前值给MS，那么网络应该在指配TBF上利用GSM 04.60规定的程序，或者如果给4个接入突发脉冲设置"分组控制证实"时利用以上章节的轮询机制，在新的指配信道上要求MS传输而不是接入突发脉冲之前，来获得定时提前值和更新初始指配定时提前值。
3.5.3.1.3 分组下行链路指配完成
在发送完分组下行链路指配之后，网络开始在指配的分组下行链路资源上发送下行链路RLC/MAC块，并且网络侧完成分组下行链路指配程序。
在MS侧，当MS接收到由指配临时块流识别识别的RLC/MAC块时，程序完成。MS停止定时器T3190。MS进入分组传输模式。
3.5.3.1.4 异常情况
如果在分组下行链路程序完成之前，MS侧发生失败（TBF建立失败），那么将释放临时块流；MS回到分组空闲模式：
- 如果在定时器T3190逾时之前，MS在指配的PDCH上没有接收到RLC/MAC块，那么将发生TBF建立失败。
- 如果在接收到一个"立即指配"消息或一个two-message指配的第二个"立即指配"消息之后，MS的信息不足以构成一个PDCH，那么将发生TBF建立失败。
- 如果在频率参数中的移动分配指示频率在多于一个频段上，那么将发生TBF建立失败。
如果一个"立即指配"消息指示PDCH在一个不支持的频段上，那么将发生TBF建立失败。
3.5.3.2 发送一个RLC/MAC控制消息：单块分组下行链路指配程序
在分组空闲模式下，给MS发送一个RLC/MAC控制消息可能由网络测RR实体利用分组下行链路指配程序发起。这个程序用于指配一个PDCH上的单下行链路块来传输RLC/MAC控制消息。
单下行链路块指配的完成是根据3.5.3.1.2规定的程序，下面的情况除外：
"立即指配"消息中的分组下行链路构建仅仅包括：
- TLLI和
- TBF起始时间。
如果MS在TBF起始时间之前接收到"立即指配"消息，那么MS需要等待到TBF其实时间指示的帧号时才能够接入。网络应该用TBF起始时间来指示属于指配给MS的单个块周期的第一个帧号。MS应该转向监控指配的PDCH并且尝试在指配的下行链路块中解码一个RLC/MAC控制消息。MS下一步采取的行动将依据网络发送RLC/MAC控制消息，见GSM 04.60。除非RLC/MAC控制消息指示，否则MS将保持在分组空闲模式。如果MS在分组空闲模式，那么MS将继续监控下行链路CCCH以防止TBF起始时间指示的块周期超时。
如果MS在指配的下行链路块中解码RLC/MAC控制消息失败，或者没收到RLC/MAC控制消息，那么MS将保持在分组空闲模式，并且MS将继续监控下行链路CCCH以防止TBF起始时间指示的块周期超时。
如果MS在TBF起始时间逾时之后才接收到"立即指配"消息，那么MS将忽略这个指配。
如果由于其他原因导致MS侧发生失败，那么MS应该忽略这个指配。
对应的英文协议
3.5.3 Packet downlink assignment procedure using CCCH
The packet downlink assignment procedure using CCCH may be used to establish a temporary block flow to support the transfer of LLC PDUs in the direction from the network to the mobile station.
This procedure may also be used to assign a single downlink block on a PDCH to support the transfer of an RLC/MAC control message from the network to a mobile station in packet idle mode, see clause 3.5.3.2.
3.5.3.1 Entering the packet transfer mode: packet downlink assignment procedure
The establishment of a downlink temporary block flow may be initiated by the RR entity on the network side using the packet downlink assignment procedure. The procedure is triggered by a request from upper layers to transfer a LLC PDU, see GSM 04.07. The request from upper layers specifies an optional Priority level, a QoS profile including the requested RLC mode, optional DRX parameters, an optional IMSI and an optional MS Radio Access Capability associated with the packet transfer.
Upon such a request, the network shall determine whether the mobile station is in packet idle mode or packet transfer mode. The packet downlink assignment procedure using CCCH is applicable when the mobile station is in packet idle mode and when there is no PCCCH present in the cell.
The network may allocate a temporary flow identity and assign a packet downlink resource comprising one PDCH for a downlink temporary block flow.
3.5.3.1.2 Initiation of the packet downlink assignment procedure
The network initiates the packet downlink assignment procedure by sending an IMMEDIATE ASSIGNMENT message in unacknowledged mode on the CCCH timeslot corresponding to CCCH group the mobile station belongs to. The appropriate CCCH group is calculated from the IMSI, see 05.02. The behaviour of the network when the RR entity does not receive the IMSI from the upper layers is implementation dependent for the calculation of the CCCH group where the IMMEDIATE ASSIGNMENT message has to be sent. If the mobile station is in non-DRX mode or if the RR entity does not receive the IMSI or the DRX parameters from the upper layers, there is no further restriction on what part of the downlink CCCH timeslot the IMMEDIATE ASSIGNMENT message, or the first part of the IMMEDIATE ASSIGNMENT message (in the case of a two-message assignment), can be sent. If the mobile station applies DRX, the IMMEDIATE ASSIGNMENT message, or the first part of the IMMEDIATE ASSIGNMENT message (in the case of a two-message assignment), shall be sent in a CCCH block corresponding to a paging group determined for the mobile station in packet idle mode, see GSM 05.02.
The IMMEDIATE ASSIGNMENT message contains:
- the packet channel description;
- the initial timing advance;
- the packet downlink assignment construction.
The contents of the packet downlink assignment construction determines the further action. At the establishment of a downlink temporary block flow, the packet downlink assignment construction shall contain:
- the TLLI;
- the temporary flow identity;
- the RLC mode;
- the power control parameters;
- the polling bit;
- the initial timing advance validity flag;
- optionally, the timing advance index (see GSM 05.10);
- optionally, the TBF starting time.
If frequency hopping is applied, the network may use the indirect encoding or the direct encoding of the frequency configuration in the Packet Channel Description information element. If the indirect encoding is used, the mobile station uses information received in system information or stored from a previous assignment to determine the frequency parameters, see GSM 04.60. If the direct encoding is used, the mobile station uses the cell allocation defined for the cell to decode the mobile allocation.
If the indirect encoding is used, the IMMEDIATE ASSIGNMENT message may contain a CHANGE_MARK_1 field. If that is present, the mobile station shall verify the validity of the SI change mark associated with the GPRS mobile allocation to which the message refers, see GSM 04.60. If the CHANGE_MARK_1 field and the SI change mark do not match,the message does not satisfactorily define a PDCH.
If the mobile station receives an IMMEDIATE ASSIGNMENT message and the Dedicated mode or TBF information element indicates that this is the first message in a two-message assignment, the mobile station shall start listen to the full CCCH. The network may send a second IMMEDIATE ASSIGNMENT message to the mobile station within two multiframe periods following the first IMMEDIATE ASSIGNMENT message, specifying the packet channel description and, if required, a mobile allocation for the assignment. The two IMMEDIATE ASSIGNMENT messages in a two-message assignment shall have the same contents of the Request Reference information elements.
If the mobile station was operating in DRX mode when it received the first message of a two-message assignment, the network shall not send the second IMMEDIATE ASSIGNMENT message within the two block periods immediately following the first message.
If the mobile station does not receive the second IMMEDIATE ASSIGNMENT messages in a two-message assignment within two multiframe periods following the first message, the mobile station shall discard the first IMMEDIATE ASSIGNMENT message received. After the two multiframe periods following the first message, the mobile station may resume to DRX mode.
On receipt of an IMMEDIATE ASSIGNMENT message or, in case of a two-message assignment, a matching pair of IMMEDIATE ASSIGNMENT messages, the mobile station stops monitoring downlink CCCH and switches to the assigned PDCH and starts listening for downlink RLC/MAC blocks identified by the assigned TFI; it starts timer T3190.
The IMMEDIATE ASSIGNMENT message may indicate a TBF starting time. If the mobile station receives the message before the TBF starting time has expired, it shall wait until the frame number indicated by the TBF starting time, start timer T3190 and switch to the assigned PDCH. If the mobile station receives the message after the TBF starting time has expired, it shall ignore the indicated TBF starting time, immediately start timer T3190 and switch to the assigned PDCH.
If the Polling bit is set to 1, MS shall send a PACKET CONTROL ACKNOWLEDGEMENT message (see 04.60) on the assigned PDCH, in the uplink block specified by the TBF Starting Time. In this case the TBF Starting Time is used both to indicate when the assigned PDCH becomes valid and to specify the uplink block. If the TBF Starting Time is not present or has expired, the MS shall ignore the polling request.
An IMMEDIATE ASSIGNMENT message may indicate a timing advance index (TAI) in the packet timing advance IE. The mobile station shall then use the continuous update timing advance mechanism, see GSM 05.10, using PTCCH in the same timeslot as the assigned PDCH. If there is no indication of a timing advance index, the continuous update timing advance mechanism shall not be used.
The TA_VALID flag indicates if the value of the Timing Advance IE is valid or not.
If the network does not have a valid timing advance value for the mobile station to include in the IMMEDIATE ASSIGNMENT message, the network shall use the procedures defined in GSM 04.60 on the assigned TBF, or the polling mechanism defined in the above paragraph if the PACKET CONTROL ACKNOWLEDGEMENT format is set to four access bursts, to obtain a timing advance value and to update the initially assigned timing advance value before the mobile station is required to transmit other than access burst on the newly assigned channel.
3.5.3.1.3 Packet downlink assignment completion
After having sent the packet downlink assignment, the network starts sending downlink RLC/MAC blocks on the assigned packet downlink resource and the packet downlink assignment procedure is completed at the network side.
On the mobile station side, the procedure is completed when the mobile station receives an RLC/MAC block identified by the assigned temporary flow identity. The mobile station stops timer T3190. The mobile station has entered packet transfer mode.
3.5.3.1.4 Abnormal cases
If a failure occurs on the mobile station side before the packet downlink assignment procedure is completed (TBF establishment failure), the temporary block flow is released; the mobile station returns to packet idle mode:
- If the mobile station does not receive a RLC/MAC block on the assigned PDCHs before timer T3190 expires, then a TBF establishment failure has occurred.
- If the information available in the mobile station, after the reception of an IMMEDIATE ASSIGNMENT message or the second IMMEDIATE ASSIGNMENT message of a two-message assignment, does not satisfactorily define a PDCH, then a TBF establishment failure has occurred.
- If the mobile allocation in the frequency parameters indexes frequencies in more than one frequency band, then a TBF establishment failure has occurred.
If an IMMEDIATE ASSIGNMENT message indicates a PDCH in a non-supported frequency band, then a TBF establishment failure has occurred.
3.5.3.2 Sending an RLC/MAC control message: single block packet downlink assignment procedure
The sending of an RLC/MAC control message to a mobile station in packet idle mode may be initiated by the RR entity on network side using the packet downlink assignment procedure. The procedure is used to assign a single downlink block on a PDCH for the transfer of the RLC/MAC control message.
The single downlink block assignment is done according to the procedure defined in 3.5.3.1.2, with the following exceptions:
The packet downlink assignment construction in the IMMEDIATE ASSIGNMENT message shall contain only:
- the TLLI; and
- the TBF starting time.
If the mobile station receives the IMMEDIATE ASSIGNMENT message before the TBF starting time has expired, it shall wait until the frame number indicated by the TBF starting time. The network shall use the TBF starting time to indicate the first frame number belonging to the single block period assigned to the mobile station. The mobile station shall switch to the assigned PDCH and attempt to decode an RLC/MAC control message in the assigned downlink block. Further action depends on the RLC/MAC control message sent by the network, see GSM 04.60. Unless otherwise indicated by the RLC/MAC control message, the mobile station remains in packet idle mode. If the mobile station remains in packet idle mode, it shall continue to monitor downlink CCCH once the block period indicated by the TBF starting time has passed.
If the mobile station fails to decode or does not receive an RLC/MAC control message in the assigned downlink block, it shall remain in packet idle mode and continue to monitor downlink CCCH once the block period indicated by the TBF starting time has passed.
If the mobile station receives the IMMEDIATE ASSIGNMENT message after the TBF starting time has expired, it shall ignore the assignment.
If a failure occurs on the mobile station side due to any other reason, the mobile station shall ignore the assignment. |
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发表于 2008-1-24 10:05:05
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