GPRS各接口信令分析

Request (Identity Type = IMSI). The MS shall respond with a GMM.Identity Response (IMSI) message.

3. Depending on PLMN parameter \GPRS Attach\(Authentication, see section (五)).

4.Depending on PLMN Parameter \attach\\六).

5.If the SGSN number has changed since the GPRS detach, or if it is the very first attach, then the SGSN informs the HLR and performs the Update Location procedure to HLR (see section (四): \to HLR\

6.The PAPU selects Radio Priority SMS, and sends an GMM.Attach Accept (P-TMSI, P-TMSI Signature, Radio Priority SMS, Periodic RA update timer, Force to Standby) message to the MS. Force to Standby (SGSN parameter: FTS) may indicate \to standby indicated\order to prevent the MS to perform cell updates. P-TMSI is included if the SGSN allocates a new P-TMSI. If P-TMSI was changed, the MS acknowledges the received P-TMSI with GMM.Attach Complete (P-TMSI).

A GPRS MS has now a MM context in PAPU serving the RA in which the MS in camped and the GPRS subscription data are downloaded from HLR and are stored in SMMU. If the Attach Request cannot be accepted, the PAPU returns a GMM. Attach Reject (IMSI, Cause) message to the MS.

MS makes Attach to network using IMSI

If MS has not a valid P-TMSI, the MS shall send the GMM.Attach request (IMSI, Attach Type) where Attach Type is \Step 3: Authentication procedure as mandatory (see section (五): \ Step 4: IMEI checking procedure (see section (六): \Identity

check

procedure\

Step 5: Update Location procedure to HLR (see section (四): \Update Location

procedure to HLR\

Step 6: The PAPU selects Radio Priority SMS, and sends a GMM.Attach Accept (P-TMSI, P-TMSI Signature, Radio Priority SMS) message to the MS. P-TMSI is included if the SGSN allocates a new P-TMSI. If P-TMSI was changed, the MS acknowledges the received P-TMSI with

GMM.Attach Complete (P-TMSI).

If the Attach Request cannot be accepted, the PAPU returns a GMM.Attach Reject (IMSI, Cause) message to the MS.

(二) GPRS Detach

The Detach function allows an MS to inform the network that it wants to make a GPRS and/or IMSI detach, and it allows the network to inform an MS that it has been GPRS-detached or IMSI-detached by the network. The different types of detach are: - IMSI detach; - GPRS detach; and

- combined GPRS / IMSI detach (MS-initiated only). The MS is detached from GPRS either explicitly or implicitly:

? Explicit detach: The network or the MS explicitly requests detach. ?

Implicit detach: The network detaches the MS, without notifying the MS, a

configuration-dependent time after the mobile reachable timer expired, or after an irrecoverable radio error causes disconnection of the logical link. In the explicit detach case, a Detach Request (Cause) is sent by the SGSN to the MS, or by the MS to the SGSN.

When network receive detach request from MS or send a detach request to MS, it aborts any data transfer for the subscriber.

The MS can make an IMSI detach in one of two ways depending on if it is GPRS-attached or not:

- A GPRS-attached MS sends a Detach Request message to the SGSN, indicating an IMSI detach. This can be made in combination with GPRS detach.

- An MS not attached to the GPRS makes the IMSI detach as already defined in GSM.

In the MO Detach Request message there is an indication to tell if the detach is due to switch off or not. The indication is needed to know whether a Detach Accept message should be returned or not.

In the network-originated Detach Request message there may be an indication to tell the MS that it is requested to initiate GPRS Attach and PDP Context Activation procedures for the previously activated PDP contexts.

After successful detach, the MS State shall change to IDLE and its MM context and PDP contexts in PAPU are removed. However, the subscribers IMSI-PTMSI association is not removed from PAPU. It is removed after the subscriber is removed from Visiting GPRS subscriber database in SMMU. The subscriber information in Visiting GPRS subscriber database (GSBASE) in SMMU may be deleted after a successful detach. Alternatively, the SMMU may keep the subscriber information and the authentication vectors of the detached MS, so that the contexts can be reused at a later GPRS attach without accessing the HLR. Subscriber information is removed from SMMU when the \subscriber storage time\timer expires (SGSN parameter: STT). When the SMMU deletes the subscriber data from its memory, it shall initiate the Purge procedure to inform HLR about deleting (see section 错误！未找到引用源。 \错误！未找到引用源。\

MS-initiated Detach Procedure

(1) 用户发送分离请求消息 带有Detach Type P-TMSI P-TMSI Signature Switch Off 给SGSN 从而发起分离流程 Detach Type指示将要进行何 种类型的分离流程 即GPRS分离 IMSI分离 联合分离 Switch Off指 示用户的分离是否是因为关机 分离请求消息带有用户的P-TMSI和 P-TMSI签名 签名是用来检查用户分离消息的合法性的 如果用户的签 名不合法或者没有带 SGSN应该发起鉴权

(2) 如果是GPRS分离 存在于GGSN中属于该用户的激活的PDP上下文的去 活 是通过SGSN向GGSN发送删除PDP上下文请求消息 带有TEID 来 实现的 GGSN以删除PDP上下文响应消息予以确认

(3) 如果是IMSI分离 SGSN应该发送IMSI分离指示消息给VLR

(4) 如果用户需要在GPRS分离同时保留IMSI附着 SGSN应该发送GPRS分离 指示消息给VLR VLR删除和SGSN的关联 并且不再通过SGSN发起寻 呼和Location Update

(5) 如用户不是因为关机发起分离 SGSN应该回应分离接受消息给用户 (6) 如果用户发起GPRS分离 SGSN释放PS域信令连接

MS requests detach from the GPRS network when it wants to stop using services of GPRS network. The procedure is described in Figure 2.

MSPAPUSMMUGGSN1. GMM.Detach Request2. GTP.Delete PDP context Request 2 GTP.Delete PDP context Response 3. DX200\Update MS record\ 4. GMM.Detach Accept

Figure 2. MS-initiated GPRS detach procedure

The MS detaches by sending GMM.Detach Request (Detach Type, Switch Off) to the PAPU serving the Routing Area where MS is camped. Switch Off indicates whether detach is due to a switch off situation or not. The Detach Type information element may indicate “GPRS detach with switching off”, “GPRS detach without switching off”.

In GPRS detach case, the MS could have one or more active PDP context. All the active PDP contexts in the GGSNs regarding this particular MS are deactivated by the PAPU sending GTP.Delete PDP Context Request (TEID) to the GGSNs. The GGSNs acknowledge with GTP.Delete PDP Context Response (TEID). Description of PDP context in module SGSN and Session Management.

As internal process of SGSN, PAPU removes MM context and PDP contexts of MS but it does not remove the IMSI-PTMSI association for that MS. In this way the MS can present itself to the network with PTMSI also during attach request. PAPU informs the SMMU with a DX200 message that MS is detached. SMMU may delete subscriber information in Visiting GPRS subscriber database (GSBASE) or may keep the information of MS updating the flag \detach\If Switch Off indicates that the detach is not due to a switch off situation, the PAPU sends a

GMM.Detach Accept (Force to Standby) to the MS. Force to Standby (SGSN parameter: FTS) may indicate \stop the Ready State timer in order to prevent the MS to perform cell updates.

Network-initiated Detach Procedure

The GPRS network may also initiate GPRS detach procedure. GPRS network may initiate detach procedure because of some error situation in network. Also if the subscriber's data is removed from HLR, the HLR initiates a detach procedure.

1) The SGSN informs the MS that it has been detached by sending Detach Request (Detach Type) to the MS. Detach Type indicates if the MS is requested to make a new attach and PDP context activation for the previously activated PDP contexts. If so, the attach procedure shall be initiated when the detach procedure is completed.

2) The active PDP contexts in the GGSNs regarding this particular MS are deactivated by the SGSN sending Delete PDP Context Request (TID) messages to the GGSNs. The GGSNs acknowledge with Delete PDP Context Response (TID) messages.

3) If the MS was both IMSI- and GPRS-attached, the SGSN sends a GPRS Detach Indication (IMSI) message to the VLR. The VLR removes the association with the SGSN and handles paging and location update without going via the SGSN.

4) The MS sends a Detach Accept message to the SGSN any time after step 1.

HLR-Initiated Detach Procedure

The HLR-Initiated Detach procedure is initiated by the HLR. The HLR uses this procedure for operator-determined purposes to request the removal of a subscriber's MM and PDP contexts at the SGSN.

1) If the HLR wants to request the immediate deletion of a subscriber's MM and PDP contexts from the SGSN, the HLR shall send a Cancel Location (IMSI, Cancellation Type) message to the SGSN with Cancellation Type set to Subscription Withdrawn.

2) The SGSN informs the MS that it has been detached by sending Detach Request (Detach Type) to the MS. Detach Type shall indicate that the MS is not requested to make a new attach and PDP context