GSM Network Protocols BY ENG Waleed Elsafoury GSM

GSM Network Protocols BY: ENG. Waleed Elsafoury

GSM Network Protocols Transmission function: MS, BTS and BSC are concerned with transmission HLR, VLR or EIR transmit their signaling needs.

GSM Network Protocols RR is a group of functions concerned with administration of channels at Um. Main RR procedures: Power control Channel quality monitoring Handover Frequency hopping Discontinuous transmission Timing advance.

GSM Network Protocols Enables power adaptation of MS and BTS. Main reasons for power control: Saving MS battery Power Improve CIR. Can be enabled or disabled. Performed separately for uplink and DL. Measurements on UL and DL are sent to BSC every 480 ms. Measurements in terms of: Signal strength in d. B. Signal quality in BER.

GSM Network Protocols MS Power (d. Bm) Max. transmit power Power increase step Distance Signal strength measured at BTS Upper threshold Lower threshold Power control increase command Distance

GSM Network Protocols Handover Control Automatic switching of a call from one TCH to another. Can be within the cell or between cells. Reasons for intra-cell handover 1. reduction of co-channel interference. 2. Maintenance activity 3. Equipment failure Handover occurs on TCH when call is in speech stage. Only started if power control is not helpful. Unique feature of mobile network.

GSM Network Protocols Handover types: Inter cell handover Involves change of carrier and BTS. Intra-cell handover Involves change of carrier in same cell.

GSM Network Protocols Handover types BSC MSC-B MSC-A BTS BTS BSC Intra-BSC HO BTS Inter-BSC HO Intra-MSC HO Intra-cell HO BTS Inter-MSC HO

GSM Network Protocols Requirements for Handover 1. Execution speed 2. Reliability • No excessive HO • No delayed HO • No early HO 3. Transparent to users (not aware) 4. Service-dependent (voice, data)

GSM Network Protocols Criteria for Handover BSC receives measurement data from BTS and MS. The MS measures downlink: Signal strength (d. Bm) Signal quality (BER) Signal strength of 6 neighboring BTSs downlink The BTS measures UL: Signal strength received from MS. Signal quality received from MS. Distance between BTS and MS.

GSM Network Protocols BSC MSC-A BTS

GSM Network Protocols Handling of Handover Reserved channel concept Some channels are reserved for HO 1 2 New calls Handover Nc N

GSM Network Protocols N-times retry v Multiple request for Handover queue v HO wait for a free channel. Sub-rating algorithm v Full rate TCH is split into 2 half rate TCHs.

GSM Network Protocols Intra-BSC (Inter-cell) HO 2 Old BTS 2 6 4 BSC 3 1 5 5 New BTS

GSM Network Protocols Inter-BSC (Intra-MSC) HO 4 Old BSC Old BTS 6 1 4 4 9 8 MSC 5 2 3 7 4 7 7 New BTS New BSC

GSM Network Protocols Inter-MSC HO GSM PLMN 5 Old BSC Old BTS 5 9 7 MSC-A 1 9 2 6 4 8 5 8 3 5 8 New BTS New BSC MSC-B PSTN

GSM Network Protocols Mobility Management (MM) o Main task of MM is to support mobility. o MM 1. 2. 3. 4. 5. 6. activities include: IMSI attach and detach. Location update Registration Update HLR/VLR TMSI re-allocation. Authentication of MS.

GSM Network Protocols Location Update in same MSC/VLR v If MS detects a change in LAI, it informs network v MSC/VLR check if it is a visitor 1 2 2 3 4 HLR 4 3 VLR BSC BTS MSC

GSM Network Protocols Location Update with New MSC/VLR v When MS enters into new LA, location update. v LA may belong to new MSC/VLR. 4 5 2 HLR 3 1 New VLR BSC BTS MSC 4 Old VLR

GSM Network Protocols Periodic Registration o o o o MS is forced to send registration periodically. If MS miss registration, the network marks it as detached. This occurs if MS is out of area. This avoids paging. Periodic registration has Ack. MS tries until it receives Ack.

GSM Network Protocols IMSI Attach o When MS is switched on, it performs attach. 1 4 MSC/VLR BSC BTS 2 3 4

GSM Network Protocols Mobile Originated Call GSM PLMN PSTN 1 Telephone 1 3 2 2 3 4 4 4 BSC BTS MSC/VLR 5 Exchange

GSM Network Protocols Mobile Terminated Call GSM PLMN 5 HLR GMSC 2 4 5 7 8 9 10 1 Local Exchange 1 6 MSC VLR 8 PSTN Telephone 11 BSC TRAU 8 11 BTS