tỔng quan vỀ gsm

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TNG QUAN V GSM 1.1 Gii thiu Cung cp cu trc tng quan v mng GSM, bao gm cc gii thch ngn gn v cc h thng con (subsystem) v m t chc nng ca cc thnh phn trong mi h thng con. Chng ny bao gm: Cu trc tng quan Mobile Station (MS) Subsystem v cc thnh phn Base Station Subsystem (BSS) v cc thnh phn Network Switching Subsystem (NSS) v cc thnh phn Gii thiu v cc giao din 1.2 Cc s nhn dng trong GSM 1.2.1 IMEI - International Mobile Equipment Identifier IMEI l thng s duy nht xc nh phn cng MS. N c ng k bi nh khai khc mng v (ty chn) c lu trong AuC cho cc mc ch xc nhn hp l. 1.2.2 IMSI - International Mobile Subcriber Identifier Khi mt thu bao ng k vi nh khai thc mng, thng s IMSI duy nht c to ra v lu tr trn SIM ca MS. Mt MS ch c th hot ng vi SIM hp l v IMEI hp l. 1.2.3 TMSI - Temporary Mobile Subcriber Identifier TMSI c s dng bo v s nhn dng thc (IMSI) ca mt thu bao. N c to ra v lu tr trong VLR khi qu trnh IMSI attach din ra hay cp nht Location Area (LA) din ra. Ti MS, n c lu trong SIM ca MS. TMSI ny ch hp l trong LA xc nh. 1.2.4 MSISDN Mobile Subscriber ISDN Number MSISDN l s thu bao di ng. N c gn cho thu bao bi nh khai thc mng khi ng k v c lu trong SIM. C th mt MS c nhiu MSISDN, mi MSISDN lin i vi mi dch v khc nhau. 1.2.5 MSRN Mobile Station Roaming Number MSRN l s ISDN tm, ph thuc vo v tr c to ra bi VLR cho tt c cc MS trong khu vc phc v ca n. N c lu tr trong VLR v HLR nhng khng lu trong MS. MSRN c s dng bi MSC/VLR cho mc ch nh tuyn cuc gi. 1.2.6 LAI Location Area Identity Mi LA trong PLMN c mt s nhn dng duy nht (LAI). LAI c qung b u n bi cc BTS trn knh BCCH (Broadcast Control Channel), 1.2.7 CI Cell Identifier CI l mt s nhn dng c gn cho mi cell trong mng. Tuy nhin, CI ch duy nht trong LA xc nh. Khi kt hp vi LAI trong LA tng ng, GCI (Global Cell Identity) c to ra v mang tnh duy nht. 1.2.8 BSIC Base Station Identity Code Mi BTS c mt s nhn dng duy nht l BSIC v n c s dng phn bit cc BTS ln cn (neighbour). 1.3 Cu trc tng quan

Hnh 1.1 Cu trc tng quan mng GSM Ch thch: MSC Mobile Switching Centre BSC Base Station Controller BTS Base Transceiver Station TRX Transceiver MS Mobile Station OMC Operation and Maintenance Centre PSTN Public Switched Telephone Network HLR Home Location Register VLR Visitor Location Register AuC Authentication Centre EIR Equipment Identity Register Mt mng GSM bao gm ba h thng con: Mobile Station (MS) Base Station Subsystem (BSS) bao gm BSC v cc BTS Network Switching Subsystem (NSS) bao gm MSC v cc thanh ghi tng ng Cc giao din c xc nh gia cc h thng con ny bao gm: Giao din A gia NSS v BSS Giao din Abis gia BSC v BTS (trong BSS) Giao din Um v tuyn gia BSS v MS

1.4 Mobile Station (MS) MS bao gm mt thit b vt l c s dng bi thu bao PLMN kt ni vi mng. N bao gm Mobile Equipment (ME) v Subcriber Identity Module (SIM). SIM lu tr IMSI, MSISDN, kha xc thc Ki v gii thut dng cho kim tra xc thc. ME c s xc nhn IMEI duy nht, c s dng bi EIR. 1.5 Base Station Subsystem (BSS) BSS bao gm cc thit b trm gc (transceivers, controllers) c nhn thy bi MSC thng qua giao din A. Thit b v tuyn ca mt BSS c th h tr mt hay nhiu cell. BSS c th bao gm mt hay nhiu trm gc, ti giao tip Abis c thc thi. BSS bao gm mt BSC v mt hay nhiu BTS. Chc nng ca BTS: Cung cp truy cp v tuyn cho cc MS Qun l cc mt v truy cp v tuyn ca h thng BTS bao gm: Thu pht v tuyn (TRX) Cc thit b x l v iu khin tn hiu Cc Antenna v cp feeder Chc nng BSC: Cp pht 1 knh cho sut mt cuc gi Duy tr cuc gi: o Gim st cht lng o iu khin cng sut truyn t BTS hay MS o Quyt nh handover sang mt cell khc khi cn thit Tm hnh ny c thu nh. Click vo y thy ton b tm hnh. Kch thc tht l 756x175.

Hnh 1.2 S u ni BSS Cc kiu u ni BSS: Mt xch Vng Sao 1.6 Network Switching Subsystem (NSS) 1.6.1 Tng quan v NSS

Cc thnh phn chnh ca NSS: MSC/VLR, HLR/AuC, EIR, GMSC. Cc thnh phn ny lin kt vi nhau s dng bo hiu s 7 (SS7).

Hnh 1.3 Tng quan v NSS 1.6.2 Mobile Switching Centre (MSC) Chc nng ca MSC: Chuyn mch cuc gi, iu khin cuc gi v ghi nht k cuc gi Giao tip vi PSTN, ISDN, PSPDN Qun l di ng (Mobility Management) thng qua mng v tuyn v cc mng khc Qun l ti nguyn v tuyn (Radio Resource Management) handover gia cc BSC Thng tin tnh cc 1.6.3 Visitor Location Register (VLR) VLR l mt c s d liu cha cc thng tin tm ca thu bao trong mt MSC area. Mi MSC trong mng c mt VLR lin i nhng mt VLR c th phc v nhiu MSC. Khi MS di chuyn vo LA mi, n s bt u qu trnh ng k. MSC c nhim v thng bo vic ng k ny v chuyn s xc nh LA cho VLR. Nu MS cha c ng k trc , VLR v HLR trao i thng tin cho php vic qun l cuc gi thch hp cho MS . VLR cng bao gm cc thng tin cn thit qun l vic thit lp hay nhn cuc gi bi cc MS ng k trong c s d liu ca n. Cc thnh phn ny bao gm: IMSI MSISDN

MSRN TMSI LMSI LA, ti MS tin hnh ng k 1.6.4 Home Location Register (HLR) HLR l mt c s d liu c trch nhim qun l cc thu bao di ng. PLMN c th c mt hay vi HLR ph thuc vo s lng thu bao, dung lng ca thit b ny v vic t chc trong mng. C 2 nhm thng tin c lu tr ti y: Thng tin thu bao Thng tin v tr cho php vic tnh cc v nh tuyn ti MSC vi MS c xc nh ti y (v d MSRN, a ch ca VLR, a ch ca MSC, LMSI) Hai kiu s nhn dng c attach cho mi thu bao di ng v c lu trong HLR: IMSI Mt hay nhiu s MSISDN IMSI hay MSISDN c th c dng nh l kha truy cp thng tin trong c s d liu cho mt thu bao di ng. 1.6.5 Authencation Centre (AuC) AuC c kt hp vi HLR, v lu tr kha xc nhn cho mi thu bao c ng k vi HLR. Kha ny dng to ra: D liu c s dng xc thc IMSI Mt kha c s dng bo mt thng tin qua knh v tuyn gia MS v mng 1.6.6 Gateway Mobile Switching Centre (GMSC) GMSC nh tuyn cc cuc gi ra ngoi mng v l mt im truy cp cho cc cuc gi vo mng t bn ngoi. 1.6.7 Equipment Identity Register (EIR) EIR l mt c s d liu lu tr s nhn dng IMEI cho ME. EIR iu khin truy cp vo mng bng cch tr v trng thi ca MS tr li cho IMEI query tng ng. Cc mc trng thi: White-listed: Thit b u cui c cho php kt ni vi mng Grey-listed: Thit b u cui ang c quan st bi mng bi cc vn c th xy ra Black-listed: Thit b u cui c bo mt hay khng phi l loi c ph chun cho mng GSM, do thit b u cui khng th kt ni vi mng Tm hnh ny c thu nh. Click vo y thy ton b tm hnh. Kch thc tht l 766x433.

Hnh 1.4 Cc giao din trong mng GSM 1.7 Cc giao din trong GSM 1.7.1 Giao din A (MSC-BSS) Giao din gia BSS-MSC c dng mang cc thng tin lin quan n: Qun l BSS Qun l cuc gi Qun l di ng 1.7.2 Giao din Abis (BSC-BTS) Giao din ny c s dng gia BSC v BTS h tr cc dch v cho ngi dng v thu bao GSM. Giao din ny cng cho php vic iu khin cc thit b v tuyn v tn s v tuyn cp pht cho BTS. 1.7.3 Giao din B (MSC-VLR) Bt c khi no MSC cn d liu lin quan ti mt MS ang trong khu vc ca n, n s hi VLR thng qua giao din ny. Th d khi m MS bt u th tc cp nht v tr vi mt MSC, MSC thng bo cho VLR ca n cc thng tin lin quan. 1.7.4 Giao din D (HLR-VLR) Giao din ny c s dng trao i d liu lin quan n v tr ca MS v vic qun l thu bao. Dch v chnh c cung cp cho thu bao di ng l kh nng thit lp hay nhn cc cuc gi trong ton b service area. h tr iu ny, cc thanh ghi v tr phi trao i d liu. Trao i d liu xy ra khi thu bao di ng i hi dch v c th, khi mun thay i d liu attach trong thng tin thu bao. 1.7.6 Giao din E (MSC-MSC) Khi MS di chuyn t MSC area sang MSC area khc trong sut cuc gi, th tc handover phi c tin hnh c th duy tr lin lc. Bi mc ch cc MSC phi trao i d liu bt u v thc hin vic ny

Sau khi handover hon tt, cc MSC s trao i thng tin truyn ti bo hiu giao din A nu cn thit. Khi m mt thng ip ngn c truyn gia MS v SMC (Short Message Service Centre), c 2 chiu, giao din ny c dng truyn thng ip gia MSC phc v MS v MSC c giao din vi SC. 1.7.7 Giao din F (MSC-EIR) Giao din ny dng cho trao i d liu gia MSC v EIR, mc ch EIR c th xc nhn trng thi khi nhn c IMEI t MS, 1.7.8 Giao din G (VLR-VLR) Khi MS di chuyn t VLR area ny sang VLR area khc, th tc ng k v tr s xy ra. Th tc ny c th bao gm vic ly IMSI v cc thng s xc thc trong VLR c. 1.7.9 Giao din H (HLR-AuC) Khi HLR nhn yu cu xc thc v m ha d liu cho MS, HLR yu cu d liu t AuC. Giao thc c s dng truyn d liu thng qua giao din ny khng c chun ha. 1.7.10 Giao din Um (MS-BTS) Giao din ny l giao din v tuyn.

1. Cu trc cc knh Logic ca h thng GSM. Trong h thng knh Logic ca GSM chia lm 2 loi nhm knh: Nhm knh bo hiu v nhm knh lu lng. *Nhm knh lu lng: ch yu dng phc v cho ch thoi ( khi bn v u bn kia ni chuyn thng sut vi nhau y), trong mt s ch d c bit khc th knh lu lng cng b chim dng phc v cho cc nhu cu khn cp khc nh HandOver (chuyn giao cell phc v) chng hn. Nhm knh ny gi chung l TCH (Traffic Channel). C 2 loi vi tc truyn khc nhau: -Knh lu lng ton tc ( Fullrate TCH or TCH/F): Mt knh TCH/F s chim trn mt TS ( Timeslot) ca khung TDMA. Tc truyn l 13kb/s cho thoi v 9.6 kb/s cho data. -Knh lu lng bn tc ( Halfrate TCH or TCH/H): 2 knh TCH/F s cng chim mt TS ca khung TDMA. Tc truyn b gim i mt na: 6.5kb/s cho thoi v 4.8kb/s cho data. Nu h thng kch hot ch HR ( halfrate) th cht lng thoi ca cuc gi s b gim, nhng b li s thu bao phc v c ca Cell s tng ln. Dng ng ph trong trng hp lu lng tng t bin v khng thng xuyn, khng tin hnh nng cp h thng kp. Khi lu lng gim xung ngi ta li b ch HR. Thng th HR c s dng km vi mt c ch na l AMR s ni sau). *Nhm knh bo hiu: Cc nhm knh ny ng nh t gi s m bo cho cc bo hiu ca h thng nh: ng b,qung b,cp knh ,thit lp cuc gi, ....c chia lm 3 nhm chnh sau: -Nhm knh qung b: Broadcast Channel ( BCH) y l knh mt chiu, theo ng xung, c n nh trn TS0 ca khung TDMA. Gm c cc knh: FCCH: Knh iu khin tn s gi ti MS (Mobile Station): gm mt cm ton bit 0, MS da vo hiu chnh tn s pht. SCH: Knh ng b cho MS kh nng ng b vi trm BTS( nhn bit cc thng s nhn dng trn h thng (BSIC)ca BTS), bit c s khung TDMA. BCCH:gi cc thng tin c th v mng, nh qun l ti nguyn v tuyn v cc bn tin iu khin, v d: m nhn din mng MNC, LAI,.

-Nhm knh iu khin chung: Common Control Channel (CCCH) Bao gm tt c cc knh ng xung im ti a im (BTS ti mt nhiu MS) v knh truy nhp ngu nhin ng ln: AGCH: c s dng n nh 1 knh dnh ring (SDCCH) ti MS. PCH: knh tm gi(pagging) gi tn hiu thng bo ti MS v 1 cuc gi n. CBCH: l 1 ty chn (c th c hoc ko) cho bn tin qung b SMS. NCH: l 1