An MS in STANDBY state is paged by the SGSN before a downlink transfer to that MS. The paging procedure shall move the MM state to READY to allow the SGSN to forward downlink data to the radio resource. Therefore, any uplink data from the MS that moves the MM context at the SGSN to READY state is a valid response to paging.
The SGSN supervises the paging procedure with a timer. If the SGSN receives no response from the MS to the Paging Request message, it shall repeat the paging. The repetition strategy is implementation dependent.
The MS shall accept pages also in READY state if no radio resource is assigned. This supports recovery from inconsistent MM states in the MS and the SGSN.
The GPRS Paging procedure in A/Gb mode is illustrated in Figure 56.
一个STANDBY状态的MS在接收下行数据传递之前,首先要接收来自SGSN的寻呼。寻呼的流程应将MM状态迁移到READY,来允许SGSN来转发下行数据到这个空口的资源。因此,任何从MS来的上行数据都将做为一个有效的寻呼响应,并将在SGSN中MM上下文的状态变更为READY状态。
SGSN通过一个计时器来监管寻呼流程。如果SGSN没有在寻呼请求消息发送后从MS收到任何响应,它将重复进行寻呼。重复的策略和具体的实现有关。
如果没有分配任何空口资源的话,即使MS在READY状态也应接受这个寻呼。这将使得MS和SGSN的MM状态的不一致现象消除,并且同步。
GPRS A/Gb模式的寻呼流程在图例56中描述。
Figure 56: GPRS Paging Procedure (A/Gb mode) NOTE: The procedure describes the flow when there is an established user plane between SGSN and GGSN with Gn/Gp based SGSN, or between SGSN and S GW with S4 based SGSN. In case of an S4 based SGSN, when the S GW has no downlink user plane TEIDs, procedure steps (A) and (B) are defined in clause 8.1.4A.
注释:流程描述了当在SGSN和GGSN之间(这个SGSN是基于Gn/Gp的)或SGSN和SGW之间(这个SGSN是基于S4的)建立了用户平面的数据流。如果是基于S4 SGSN的case,当SGW没有下行用户数据的TEID,流程中的步骤(A)和(B)在章节8.1.4A中描述。 1) The SGSN receives a DL PDU for an MS in STANDBY state. Downlink signalling to a STANDBY state MS initiates paging as well.
2) The SGSN sends a BSSGP Paging Request (IMSI, P TMSI, Area, Channel Needed, QoS, DRX Parameters) message to the BSS serving the MS. IMSI is needed by the BSS in order to calculate the MS paging group. P TMSI is the identifier by which the MS is paged. Area indicates the routeing area in which the MS is paged. Channel Needed indicates GPRS paging. QoS is the negotiated QoS for the PDP context that initiates the paging procedure, and indicates the priority of this Paging Request relative to other Paging Request messages buffered in the BSS. DRX Parameters indicates whether the MS uses discontinuous reception or not. If the MS uses discontinuous reception, DRX Parameters in combination with the IMSI indicate when the MS is in a non-sleep mode able to receive paging requests.
1)SGSN收到了一个发给STANDBY状态MS的下行PDU。也可以是到MS的下行的信令消息。 2)SGSN发送一个BSSGP 寻呼请求(IMSI、P-TMSI、区域、需要的信道、QOS、DRX参数)消息给为MS服务的BSS。IMSI是需要包含的,因为BSS需要它来计算MS寻呼组。P-TMSI是在寻呼MS对MS的标识。区域则指明了MS寻呼的路由区。需要的信道指明了GPRS寻呼。QOS指的是发起寻呼流程为这个PDP上下文协商的QOS,并且指明了这个寻呼请求相对于那些缓存在BSS中的寻呼请求的优先级的对比。DRX参数指明了MS是否使用不连续接收。如果MS使用了不连续接收,DRX参数将和IMSI一起来指明当一个MS是在非睡眠模式能接收寻呼请求。 3) The BSS pages the MS with one Paging Request (P TMSI, Channel Needed) message in each cell belonging to the addressed routeing area. This is described in TS 43.064 [11].
4) Upon receipt of a GPRS Paging Request message, the MS shall respond with either any single valid LLC frame (e.g. a Receive Ready or Information frame) that implicitly is interpreted as a page response message by the SGSN. The MS shall not use the LLC NULL frame as a page response. When responding, the MS changes MM state to READY. The Packet Channel Request precedes the response and Packet Immediate Assignment procedures as described in TS 43.064 [11].
5) Upon reception of the LLC frame, the BSS adds the Cell Global Identity including the RAC and LAC of the cell and sends the LLC frame to the SGSN. The SGSN shall then consider the LLC frame to be an implicit paging response message and stop the paging response timer.
3)BSS带上寻呼请求(P-TMSI、需要的信道)在指明的路由区的每个小区来寻呼MS。这在TS43.064中描述。 4)一旦接收到一个GPRS寻呼请求消息,MS应响应任意类型的单一的有效LLC帧(例如一个Receive Ready或Information帧),这个帧将被隐含的做为寻呼响应消息发给SGSN。MS不应使用LLC NULL帧做为寻呼响应。当响应了的话,MS的状态切换为READY。Packet Channel Request处理响应,和Packet Immediate Assignment流程在TS43.064描述。 5)一旦接收到LLC帧,BSS加入CGI(小区全球标识符)以及小区的RAC和LAC然乎发送给SGSN。SGSN应认为这些帧是一个隐含的寻呼响应消息并且停止寻呼响应计时器。 8.1.4A Paging response for GPRS Downlink Transfer with no established user plane on S4 Figure 56a: Paging with no established user plane on S4 Figure 56b: Paging Response with no established user plane on S4 NOTE: Steps A, B and E are common for architecture variants with GTP based S5/S8 and PMIP-based S5/S8. For a PMIP-based S5/S8, procedure steps (C) are defined in TS 23.402 [90]. Steps C and D concern GTP based S5/S8.
注释:步骤A/B/E对于采用基于GTP还是PMIP的S5/S8架构来说都是公共的。对于基于PMIP的S5/S8,步骤C在TS23.402描述。步骤C和D和基于GTP的S5/S8架构相关。 A) When the S GW receives a downlink PDU and no downlink user plane exists for the UE at S4, the S GW buffers the downlink data packet and identifies which SGSN is serving that UE.
If that SGSN has requested the S-GW to throttle downlink low priority traffic and if the downlink data packet is received on a low priority bearer to be throttled (see clause 5.3.6.5), the SGW drops the downlink data packet. The steps below are not executed.
Otherwise the S-GW sends a Downlink Data Notification message to the SGSN.
Steps between A and B are described in clause 8.1.4.
A)当SGW收到一个下行PDU并且没有关于这个UE的下行用户平面在S4接口存在的时候,SGW将这些下行数据报文缓存起来,并识别出是哪个SGSN为这个UE提供服务。 如果那个SGSN请求SGW将低优先级的下行流量扼杀掉并且如果下行数据报文是在一个低优先级的将被扼杀的承载中收到的话(参考章节5.3.6.5),SGW丢弃下行数据报文。下面的步骤将不会执行。 除此以外,SGW将发送Downlink Data Notification消息给SGSN。步骤A和B在章节8.1.4描述。 B) Upon reception of the LLC frame in STANDBY state and if the user plane tunnel does not exist, the SGSN shall indicate the paging response from GERAN by sending a Modify Bearer Request (SGSN user plane address, RAT Type, TEID) to the Serving GW. The S GW is now able to transmit downlink data towards the UE.
C) If the RAT Type has changed compared to the last reported RAT Type, the S GW shall send the Modify Bearer Request message (RAT Type) to the PDN GW.
D) The PDN GW sends the Modify Bearer Response to the S GW.
E) The S GW sends a Modify Bearer Response to the SGSN.
B)一旦SGSN在STANDBY状态接收到LLC帧并且没有用户平面隧道存在,SGSN应发送一个Modify Bearer Reqeust(SGSN用户面地址、RAT类型、TEID)给SGW来指示从GERAN收到了寻呼响应。SGW现在能够将下行数据传递给UE了。 C)如果RAT类型和上次报告的RAT类型发生了变化,SGW应发送一个Modify Bearer Reqeust(RAT类型)消息给PGW。 D)PGW发送一个Modify Bearer Response给SGW。 E)SGW发送一个Modify Bearer Response给SGSN。
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