7/30/2019 Phn bit a truy cp v ghp knh

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Phn bi t a truy cp v ghp knh.a truy cp v ghp knh l hai khi nim khc nhau. Tuy nhin, rt d nhm ln hainim ny. Nhn tin l bi bo co v cc phng php truy nhp, ti thy mt skhc nhau nh sau:

Mt s 2 phng php ghp knh c bn:TDM (stand for Time Division Multiplexing),FDM (stand for Frequency Division Multiplexing). V 3 phng php a truy nhpTDMA (stand for Time Division Multiple Access), FDMA, CDMA.Ly v d TDM v TDMA phn bit:

TDM l khi nim ghp knh, thuc phm vi truyn dn (transmission), trong khi TDl khi nim a truy nhp, thuc phm vi truy nhp mng (access network). Ghp knkhi nim v t chc truyn dn gia hai nt ca mt mng, trong khi a truy nhp

quan ti vic t chc kt ni t thu bao ti mng. TDM thng dng khi ni n ghp knh trn mt ng truyn point-to- point, hutuyn nh T1/E1-lung t BTS n BSC; cn TDMA th dng khi ni n cc h thngthng tin di ng, ng truyn v tuyn. TDM ch lin quan n1 transmitter v 1receiver (point-to- point) cnTDMA th c nhiu transmitters.

Mc du cng c im l chia khung thi gian thnh cc time slot (TS) cho nhiu ngchia s ti nguyn song c nhng im khc bit c bn gia TDM vTDMA sau y

+ TD M l s phn nh dung lng tng cng ca knh tng theo thi gian cho cc ngs dng khc nhau trn c s t u cui ti u cui v khng thay i TS dnh chongi s dng c nu khng config li ton b h thng. Ngha l mi mt ngdng s c n nh mt TS c nh truyn tin v d cho ngi s dng khng traffic (trng thi idle) truyn trn knh vt l (TS) dnh cho mnh th knh s rm ngi s dng khc khng th t ng chim knh truyn tin. Ngay c khc mun dng mt cch nht thi TS cho ngi s dng khc dng cng khngc.

Ly th d: Trong mt tuyn truyn dn quang t H Ni i Hi Phng gi d vi kdung lng l lung STM-4 c 3 lung STM-1 c nh (3TS dnh cho 3 lung STM-1)c dnh cho kt ni t H Ni i Hi Phng, cn mt lung STM-1 dnh cho kt nit H Ni n Hi Dng v t Hi Dng ti Hi Phng. Khi trn STM-1 lin lc H Ni- Hi Dng khng c traffic th h thng cng s khng t ng ly knh chtruyn t H Ni i Hi Phng c v on Hi Dng- Hi Phng li c th ang ctraffic (on HNI- HDG c th ang rng mt phn dung lng song an HDG- HPGli ang y).

7/30/2019 Phn bit a truy cp v ghp knh

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+ a truy nhp l phng thc m mng s dng phn bit cc thu bao khc nhaang truy nhp yu cu dch v vin thng. Vi mng in thoi c nh, tng phn bit cc thu bao (vo lc truy nhp th l ngi s dng/user) nh cc i dy tcc my l, gi l phng thc truy nhp bng cp.TDMA l phng thc m mngbit ngi s dng theo thi gian. Mng phn bit gia cc users khc nhau ang trunhp mng yu cu dch v thng qua TS c n nh tm thi cho cc users. Mkhi ngi s dng chm dt phin lin lc ca mnh th ti nguyn (TS) s c giphng tr li cho mng c th n nh cho ngi s dng khc (cho thu bao khcang c gng truy nhp mng yu cu dch v). Cng xin lu lun vi cc bn khc bit gia cc khi nim thu bao (subscriber) v khi nim ngi s dng (userTrong ghp knh khng c khi nim thu bao m ch c user (cn phn bit r khi nithu bao v khi nim ngi/t chc thu leased line).

Vi cc h thng thng tin di ng th a truy nhp l phn access t cc thu bao ti

mng m i din y l BTS (phn mng truy nhp- access network), cn t ntmng BTS ti cc nt khc trong mng (BSC hay MSC) th knh c t chc bng knh (phn mng/h thng truyn dn- transmission network/system). Th d, vi hthng GSM th TDMA thuc phn t MS ti BS cn TDM thuc phn t BS v mng(v MSC). Trn tuyn t cc BS v MSC trong h thng GSM, gi nh t chc truydn theo cu hnh chain, d lung E1 t BS ny v BSC c rng (do trong cell m BSqun l ang khng c mt MS no lin lc) th t mt BS xa hn v BSC ngang qBS cng khng th chim lung E1 truyn tin cho mnh nu khng config lthng truyn dn.