第七章 GPRS 系統簡介 (GPRS System Overview) 習題解答 選擇題：1. (a)(b)(c)(d) 2. (c) 3. (a)(b) 4. (a)(b)(c)(d) 5. (a)(b)(c) 6. (a)(b) 7. (a)(b)(c) 8. (a)(d) 9. (a)(b)(c)(d) 10. (b)(c) 問答題： 1. 參閱 7.1.2 和 7.1.3 multiclass slot � 限制一個應用服務最多只能 6 個時槽，如果加上 cell load 考 2. 量，每個服務分配到的時槽會更少。 3. The SGSN-Initiated Detach procedure when initiated by the SGSN is illustrated in Figure 1. Each step is explained in the following list. MS BSS SGSN GGSN MSC/VLR 1. Detach Request 2. Delete PDP Context Request 2. Delete PDP Context Response 3. GPRS Detach Indication 4. Detach Accept Figure 1: SGSN-InitiatedGPRSDetach 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- andGPRS-attached, the SGSN sends aGPRSDetach 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. 6. The MS-Initiated Detach procedure when initiated by the MS is illustrated in Figure 2. Each step is explained in the following list.
MS BSS SGSN GGSN MSC/VLR 1. Detach Request 2. Delete PDP Context Request 2. Delete PDP Context Response 3. IMSI Detach Indication 4. GPRS Detach Indication 5. Detach Accept Figure 2: MS-Initiated CombinedGPRS/ IMSI Detach Procedure 1) The MS detaches by sending Detach Request (Detach Type, Switch Off) to the SGSN. Detach Type indicates which type of detach that is to be performed, i.e.,GPRSDetach only, IMSI Detach only or combinedGPRSand IMSI Detach. Switch Off indicates whether the detach is due to a switch off situation or not. 2) IfGPRSdetach, the active PDP contexts in the GGSNs regarding this particular MS are deactivated by the SGSN sending Delete PDP Context Request (TID) to the GGSNs. The GGSNs acknowledge with Delete PDP Context Response (TID). 3) If IMSI detach, the SGSN sends IMSI Detach Indication (IMSI) to the VLR. 4) If the MS wants to remain IMSI-attached and is doing aGPRSdetach, the SGSN sends aGPRSDetach 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) If Switch Off indicates that the detach is not due to a switch off situation, the SGSN sends a Detach Accept to the MS. 5. Figure 25 shows an example of message sequence for the (multislot) uplink data transfer with one resource reallocation and possible RLC Data Block re-transmissions.
MS Network Access and Assignment PDTCH Data Block PDTCH Data Block PDTCH Data Block (last in send window) PDTCH Packet Uplink Ack/Nack PACCH Data Block PDTCH Data Block PDTCH Data Block PDTCH Packet Uplink Assignment PACCH Packet Control Acknowledgement PACCH Data Block PDTCH Data Block (last) PDTCH Packet Uplink Ack/Nack (final) PACCH Figure 25: An example of dynamic allocation uplink data transfer 6. Figure 27 shows an example of message sequence for (multislot) downlink data transfer with one resource reallocation and possible RLC Data Block re-transmissions.
MS Network Packet Downlink Assignment PACCH, (P)CCCH Packet Control Acknowledgement (Optional) PACCH Data Block PDTCH Data Block PDTCH Data Block (polling) PDTCH Packet Downlink Ack/Nack PACCH Data Block PDTCH Data Block PDTCH Data Block PDTCH Packet Downlink Assignment (polling) PACCH Packet Control Acknowledgement PACCH Data Block PDTCH Data Block PDTCH Data Block (last, polling) PDTCH Packet Downlink Ack/Nack (final) PACCH Figure 27: An example of downlink data transfer 7. class A, B, C: Three GPRS MS modes of operation are supported: An MS in class-A mode of operation operates GPRS and other GSM services simultaneously. An MS in class-B mode of operation monitors control channels for GPRS and other GSM services simultaneously, but can only operate one set of services at one time. An MS in class-C mode of operation exclusively operates GPRS services.
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