发布时间 : 星期三 文章GPRS各接口信令分析更新完毕开始阅读93534e9e71fe910ef12df85d
activation.
3) 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.
4) 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.
5) The MS sends a Detach Accept message to the SGSN any time after step 2.
6) The SGSN shall confirm the deletion of the MM and PDP contexts with a Cancel Location Ack (IMSI) message.
(三) Purge
The Purge function allows an SGSN to inform the HLR that it has deleted the MM and PDP contexts of a detached MS.The SGSN may, as an implementation option, delete the MM and PDP contexts of an MS immediately after the implicit or explicit detach of the MS. Alternatively, the SGSN may keep for some time the MM and PDP contexts and the authentication triplets of the detached MS, so that the contexts can be reused at a later GPRS attach without accessing the HLR.
The Purge function allows an SGSN (SMMU) to inform the HLR that it has deleted the subscriber information of a detached MS stored in Visiting GPRS subscriber database (GSBASE). It shall initiate the Purge procedure as illustrated in Figure 3.
SMMUHLR1 MAP.Purge MS2 MAP.Purge MS Ack
Figure 3. Purge procedure
After deleting the subscriber information of a detached MS from Visiting GPRS subscriber database, the SMMU sends a MAP.Purge MS (IMSI, SGSN Number) message to the HLR. The HLR sets the MS Purged for GPRS flag and acknowledges with a MAP.Purge MS Ack message. In this way any request for routing
information for a mobile terminated short message will be treated as if the MS is not reachable.
(四) Update Location procedure to HLR
The Update Location procedure to HLR is performed during Attach procedure or Routing Area Update procedure if the current SGSN serving the MS is changed. The Update Location procedure is performed also when the MS is performing its first Attach to the network. The Update Location procedure is described in Figure 4.
new SMMUold SMMUHLR 1. MAP. Update Location 2. MAP. Cancel Location 2. MAP. Cancel Location Ack3. MAP. Insert subscriber3. MAP. Insert subscriber 4. MAP. Update Location
Figure 4. Update location procedure to HLR
The SGSN/SMMU sends a MAP.Update GPRS Location (IMSI, SGSN
Number, SGSN Address) to the HLR. SGSN Address is the IP address of SGSN (In Nokia 2G SGSN it represents the IP address of MCHU). In order to find the right HLR the SMMU has to perform IMSI analysis. 1.
If the mobile was previously registered in another SGSN the HLR sends MAP.Cancel Location (IMSI, Cancellation Type) to the old SGSN/SMMU with Cancellation Type set to Update Procedure. The old SGSN/SMMU acknowledges with MAP.Cancel Location Ack (IMSI). If there are any ongoing procedures for that MS, the old SGSN/SMMU shall wait until these procedures are finished before removing the MM and PDP contexts. HLR sends MAP.Insert Subscriber Data (IMSI, GPRS subscription data) to the new SGSN/SMMU that shall return a MAP.Insert Subscriber Data Ack (IMSI) message to the HLR. If subscription checking fails, the SGSN rejects the Attach Request/ Routing Area update request with an appropriate cause and SGSN/SMMU returns
2.
a MAP.Insert Subscriber Data Ack (IMSI, Cause) message to the HLR with appropriate error cause. 3.
The HLR acknowledges the Update Location message by sending a MAP.Update GPRS Location Ack to the SGSN/SMMU. If the Update Location is rejected by the HLR, the SGSN (PAPU) rejects the Attach Request/ Routing Area update request from the MS with an appropriate cause.
(五) Authentication
Authentication is executed from the PAPU. The authentication procedure performs also the selection of the ciphering algorithm and the synchronisation for the start of ciphering. Authentication vectors are stored in SMMU in the Visiting GPRS Subscriber Database (GSBASE). For each subscriber the SMMU can store 7 authentication vectors. The Authentication procedure is described in Figure 5.
MSBSSPAPUSMMUHLR/AuC1. DX200.Send Authentication Info 1 a. MAP.Send Authentication Info 1 b. MAP.Send Authent. Info Ack1. DX200.Send Authentication Info 2. GMM.Authentication Request2. GMM.Authentication Response
Figure 5. Authentication procedure
1．The PAPU sends a DX200 message DX200.Send Authentication Info
(IMSI) message to SMMU in order to receive authentication vectors.
a.If the SMMU does not have previously stored Authentication Vectors, it sends MAP.Send Authentication Info (IMSI) to the HLR/AuC. b.The HLR/AuC responds with MAP.Send Authentication Info Ack (Authentication Vectors)
With internal DX200.Send Authentication Info Ack (Authentication Vectors) message the SMMU sends the Authentication Vectors to
PAPU.
Note
Phase 1 is skipped if PAPU has already the Authentication Vectors. This happens in case of the inter-PAPU Routing Area Update or Attach procedure when different PAPUs are involved. In inter-PAPU Routing Area Update case the new PAPU receives Authentication Vectors from old PAPU in GTP.SGSN context response message while in Attach procedure case the new PAPU receives Authentication vectors from old PAPU with GTP.Identification Response message (see section (一) \GPRS Attach\
2.The PAPU sends GMM.Authentication and Ciphering Request (RAND, CKSN, Ciphering Algorithm for GPRS Authentication or RAND, AUTN for UMTS Authentication) to the MS. The MS responds with a
GMM.Authentication and Ciphering Response (SRES or XRES). The PAPU compares the SRES (or XRES) received by the MS with that contained in the vectors.
The MS starts ciphering after sending the GMM.Authentication and Ciphering Response message. The PAPU starts ciphering when a valid GMM.Authentication and Ciphering Response is received from the MS.
In the routing area update case, if ciphering was used before the routing area update, and if the Authentication procedure is omitted, then the PAPU shall resume ciphering with the same algorithm when a ciphered Routing Area Update Accept message is sent, and the MS shall resume ciphering when a ciphered Routing Area Update Accept message is received.
(六) Identity check procedure
MS identity check procedures already defined in GSM shall be used, with the distinction that the procedures are executed from the SGSN. The procedure is described in Figure 6.