CC THUT NG VIT TTVit tt AMF API ATM DSL ETSI FR GII HLR IP ISDN ITU LAN LDP LGP MFS MGCP MGW MPLS NGN PBX PLMN PML POTS PSTN QoS RAS SCF SCP SCN SDH SG SIP SML Ting Anh Application Program Interface Asynchonous Tranfer Mode Ngha Giao din m ng dng Phng thc truyn khng ng

b Digital Subcriber Line ng thu bao s European Telecommunications Vin chun ho vin thng chu Standards Institute Frame Relay Global Infomation Infrastructure Home Location Register Internet Protocol Intergrated Service Network International u Chuyn tip khung Cu trc h tng thng tin ton

cu Thanh ghi nh v thng tr Giao thc lin mng Digital Mng s dch v tch hp

Telecommunication T chc vin thng quc t Mng ni vng Giao thc phn tn nhn Chc nng cng logic Din n chuyn mch a dch v Giao thc iu khin cng phng tin Cng phng tin Chuyn mch nhn a giao thc Mng th h mi Tng i nhnh cng cng

Union Local Area Network Label Distribution Protocol Logical Gateway Function MultiService Switching Forum Media Gateway Control Protocol Media Gateway Multi Protocol Label Switching Next Generation Network Public Branch Exchange

Network Management Layer Lp qun l mng Plain Old Telephony System H thng in thoi truyn thng Public Switched Telephone Mng in thoi chuyn mch Network Quality of Service Remote Access Server Service Control Function Service Control Point Switch circuit Network Synchronous Digital Hierachy Signalling Gateway Session Initiation Protocol Service Management Layer cng cng Cht lng dch v My ch truy nhp t xa Chc nng iu khin dch v im iu khin dch v Mng chuyn mch knh Phn cp s ng b Cng bo hiu Giao thc khi to phin Lp qun l dch v

SS7 TCP TDM TINA VDSL VoIP WDM WLAN WLL MIME

Signal System Number 7 Tranmission Control Protocol Time Division MultIPlex Telecommunication

H thng bo hiu s 7 Giao thc iu khin truyn dn Ghp knh phn chia theo thi

gian Information Cu trc mng thng tin vin thng Digital ng thu bao s tc rt cao Truyn thoi qua giao thc Internet Ghp knh phn chia theo bc sng Mng ni vng khng dy Lin kt ni vng khng dy Giao th c th in t

Network Achitecture Very Hight bit-rate

Subcriber Line Voice Over Internet Protocol Wavelength Division Multiplexing Wireless Local Areal Network Wireless Local Loop MultiPurpose Internet Protocol

LI NI UTrong mt vi nm gn y nhu cu v cc dch v vin thng tng mnh mang li nhiu li ch cho cc nh khai thc vin thng cng nh cc nh cung cp thit b vin thng, bn cnh s ra i ca nhiu cng ngh mi vi cc u im ni tri m ra c hi ln cho c ngi s dng ln nh cung cp. Mng th h mi ( The Next Generation Network ) ra i nhm em li mt cu trc mng mi vi chc nng p ng c hu ht cc nhu cu v ng thi s l nn tng kin to cho cc dch v vin thng tin tin trong tng lai. Xy dng mt mng NGN by gi l mc tiu v nhu cu ca nhiu quc gia trn th gii vi mc ch cng c v pht trin c s h tng thng tin ca quc gia . i vi Vit Nam, vic trin khai mng th h mi khng ch em li cho nh khai thc nhng li ch kinh t di do m cn l mt bc nhy vt gip cho chng ta tin gn hn n vi th gii. Vi nhng nhn nh trn em quyt nh chn phn mng th h mi (NGN) nghin cu, tm hiu v ng dng. Trong em tp trung ch yu vo ti Giao thc bo hiu trong mng th h sau ng vai tr quan trng trong hot ng ca mng NGN, trn c s l thuyt em tm hiu vic ng dng giao thc bo hiu NGN trong mng vin thng hin ti Vit Nam.

Em xin chn thnh cm n c gio Dng Thanh T, ging vin trng Hc Vin Cng Ngh Bu Chnh Vin Thng trc tip hng dn em thc hin ti. Em xin gi li cm n n phng k thut cng ty Vin Thng H Ni gip em thc hin ti ny.

CHNG 1: MNG VIN THNG TH H SAUGii thiu v mng NGNS hnh thnh khi nim v mng NGNTrong vi nm tr li y, rt nhiu nh khai thc vin thng ln k hoch nng cp mng tin ti mt m hnh mng c tn NGN (Next Generation Networks). Hu ht cc phn tch th trng u d on rng ton b mng PSTN s c thay th bi NGN trong vng 10 nm. Vy NGN l g v ti sao li c tm quan trng n nh vy? Khi nim mng th h sau NGN xut hin vo cui nhng nm 90 trc tc ng ca nhiu yu t: S ton cu ho v kinh doanh vin thng, nhu cu d liu tng mnh, nhng quan im mi v cng ngh, s pht trin ca thng tin di ng..v.v. c rt nhiu t chc quc t thc hin nghin cu v NGN c th a ra mt chun thng nht, cho n thi im hin ti cn tn to rt nhiu quan im khc nhau gia cc t chc quc t v gia h vi cc nh sn xut thit b vin thng. Tuy cn c nhiu vn vn cn phi nghin cu, tho lun v th nghim nhng cc nh nghin cu u c chung quan im cho rng: NGN c xem nh l mng tch hp IP hay mng da trn cng ngh chuyn mch gi, y s l nn tng hi t cc loi hnh dch v cng nh cng ngh mng. NGN khng ch mang y cc c tnh ca mng m cn c cc c tnh dch v nh cung cp cc c hi mi cho cc nh khai thc mng, cc nh cung cp dch v, cc nh sn xut thit b v ngi dng

Di y l nh ngha tham kho do ETSI (European Telecommunication Standards Institute) a ra trong khuyn ngh ca mnh, nh ngha ny c tc dng nh hng mi hnh ng do ETSI tin hnh trn lnh vc ny. NGN l mng c phn chia thnh cc lp v cc mt phng, s dng cc giao din m nhm a ra cho cc nh khai thc mng v cung cp mt nn tng thng tin kin to, trin khai v qun l cc dch v bao gm c cc dch v c v cc dch v trong tng lai. i vi ITU T (International Telecommunication Union), NGN c nh ngha l mt mng c nn tng chuyn mch gi c kh nng cung cp cc dch v bao gm cc dch v vin thng v c th tn dng ti a bng thng, cht lng dch v cho php truyn dn nhiu cng ngh v trn cc chc nng lin quan n dch v c lp vi cc cng ngh lin quan n truyn dn lp di. Nh vy c th c mt khi nim chung nht v mng vin thng th h sau cn y nhanh qu trnh chun ho cc giao thc v cng ngh c s dng trong NGN ng thi kt hp vi cc bi hc rt ra t vic trin khai mng NGN trn th gii.

c im mng NGNCho n thi im hin ti cc t chc nghin cu cng nh cc nh cung cp thit b mng vn cha thng nht v mt chun quc t duy nht v m hnh mng NGN, nhng cho d nghin cu hay trin khai mng NGN theo xu hng no th mc ch cui cng cng l c mt h thng mng vi mt s c im chnh nh sau:

Mng NGN l mng chuyn mch gi hay mng ton IP. C s phn tch cc dch v ng dng vi mng truyn dn. Mng NGN l mt h thng mng m. Mng NGN l mng di rng tch hp hay hi t. Mng NGN l mng rng khp. Mng NGN l mng c kh nng phn tn tim nng mng. Cc c im ny th hin mt cch r rt cc kh nng m NGN mang li cho con ngi c v pha cc nh cung cp dch v, cc nh pht trin cng ngh v v pha ngi s dng. Hu ht cc chuyn gia coi NGN nh mt mng a dch v da trn cng ngh IP (Internet Protocol). NGN, nh mt mng IP tch hp cho h thng thng tin v

tuyn cng nh hu tuyn, c th iu khin tt c cc loi lu lng hay dch v qua mng chuyn mch gi. Hn th na, nhiu nh nghin cu d on rng trong vi thp k ti NGN s thay th ton b mng PSTN (Public Switched T Telephone Network)ch khng ch tn ti song hnh cng PSTN. Nh c nhng t ph trong cng ngh gi v nhng u im to ln m cc mng chuyn mch gi thc t em li th NGN l mng chuyn mch gi, da trn mt giao thc thng nht s h tr cho vic tch hp cc mng trong mt mng IP thng nht, ngi ta gi l dung lng ba mng iu ny ng v mng vin thng, mng my tnh v mng truyn hnh cp. tng ni trn ngy cng tr thnh thc t khi m giao thc IP tr thnh giao thc vn nng v bt u c s dng lm nn tng cho cc mng a dch v, mc d vn cn nhng bt li so vi mng chuyn mch knh truyn thng trong vic h tr lu lng thoi v cung cp dch v m bo cho s liu nhng cc nh pht trin cng ngh tin rng vi tc pht trin ca cc tiu chun m s gip khc phc nhng thiu st ny. Trong cc mng hin nay, cc dch v c tch hp ti lp vn chuyn v mt phn ca mng c dnh cho mt dch v xc nh. Ni mt cch khc, NGN cung cp mt cu trc m cho php cc dch v v mng c chia s, theo cc dch v c th c pht trin mt cch c lp khng cn quan tm n nn tng mng ang dng. Nh vy, song song vi vic trin khai NGN vic cung cp cc cu trc m, s chun ho l v cng quan trng, iu ny gip cho vic giao tip gia cc dch v v cng ngh truyn thng vi cc dch v cng v cng ngh mi,v gip cho cc nh khai thc chn cc sn phm mi v cc dch v b sung cho s thiu ht ang tn ti trn mng PSTN hay IDSN. Hn th na s phn tch dch v c lp vi mng s gip cho cc nh cung cp dch v c th trin khai mt cch nhanh chng sn phm ca mnh cng nh cc nh pht trin cng ngh mng c th ng dng cc k thut mi h tr mt cch a dng cc loi hnh dch v. Thng thng mng phn tch c s dng cung cp cc dch v thoi, s liu v video, mi loi u yu cu cc thit b truy nhp ring r. NGN cho php nhiu loi dch v khc nhau chuyn thnh cc gi tin v truyn i mt cch ng thi. S kt hp gia NGN v cc mng ang tn ti nh PSTN, ISDN (Intergrated Services Digital Networ) v GSM c th thc hin thng qua cc Gateway.

NGN cho php ngi s dng truy cp vo tt c cc loi hnh dch v khc nhau, vi cht lng nh nhau ti bt k v tr a l no. V vi nhu cu s dng dch v cng nh kh nng cung cp dch v ngy cng tng th yu cu dung lng v kh nng thch ng ca mng cng phi tng theo, nh vy mng NGN vi kh nng thch ng rng ri s p ng nhu cu. Bng vic p dng cc cng ngh mi v ph hp nht cng nh thc hin phng n trin khai v qun l ti u vic pht trin dch v trn NGN tr nn thun li hn rt nhiu v nh vy cc khch hng c c hi tho mn cc nhu cu ca mnh. Mt c im quan trng ca mng NGN l cu trc phn lp theo chc nng v phn tn tim nng mng. iu ny gip mm ho mng qua c th s dng rng ri cc giao din m API (Apllicaion Programable Interface) kin to cc dch v m khng ph thuc vo cc nh cung cp thit b v khai thc mng.

1.1.3.

L do xy dng mng NGNVic xy dng v trin khai NGN l xu hng tt yu trong lnh vc vin

thng, tu vo iu kin ca mi ni m yu cu trin khai c th khc nhau nhng c th ni rng ba nguyn nhn sau l nhng l do chnh dn n vic pht trin NGN: S thay i c cu trong th trng vin thng. S thay i trong cc dch v cng nh nhu cu s dng. Cc t ph trong lnh vc cng ngh. Trc ht ta tm hiu v nhng thay i trong c cu th trng vin thng ta thy rng trong sut thp k qua th trng vin thng tri qua s thay i quan trng v c iu chnh v cu trc. l: S cnh tranh rt mnh c pha th trng PSTN truyn thng v ton b cc dch v khc nh cc dch v di ng cellular, t nhn ho cc nh khai thc vin thng v cc dch v mi xut hin. S pht trin ny l kt qu ca s gim st trong cc ngun li truyn thng ca th trng thoi. Mt hng mi cho cc nh khai thc PSTN l di chuyn cc li nhun v dung lng vin thng n cc nh cung cp dch v khc. Trong khi lu lng IP tng 85% hng nm. L do th hai thc y qu trnh trin khai NGN l s thay i v cc dch v v nhu cu ca ngi dng. Vi s ph bin cc dch v Internet bng rng, cc nh cung cp dch v mng xc nh s pht trin nhu cu ca khch hng i vi cc dch v a phng tin di rng phc tp hn, nh vy khng th ph hp bi

mng PSTN hin c. Cc vn i vi mng PSTN l s thiu ht dung lng tng h trong mt mi trng mng khng ng nht. Nh mt v d cho s cn thit ca cc dch v mng da trn nn IP trng cc khu vc thng mi, mt nghin cu gn y ca EGNS (Eropean Global Network Strategy) ch ra rng 90% s t chc sn xut (manufacturing organisations) hin gi c cc mng IP trung tm (IP-centric), v 74% cc nh sn xut c k hoch tch hp mng thoi v mng gi trong vng hai nm. S pht trin cn bn c tnh tng i trong cc dch v VOIP, t bo (cellular), khng dy v truyn hnh s to thm sc p cho cc nh khai thc vin thng do p ng nhu cu ngy cng tng ca cc khch hng cc nh khai thc nm ly cc hiu qu ca mng a dch v chuyn mch gi, hay NGNs. Cng vi Internet bng rng, s s sng rng ri VoiIP tc ng nh mt cht xc tc kch thch s pht trin ca NGNs. VoIP to ra s cnh tranh v mt gi c i vi cc nh cung cp thoi PSTN. Nm 2003 mt s lng ln cc nh cung cp trin khai VoIP v cc cng ty thoi truyn thng khc phi chu nhiu sc p t pha VoIP. Cui cng s pht trin cng ngh trong lnh vc IP bao gm IP v6, s ho, lm tng nng lc v b nh my tnh, v cng ngh quang cho php mt s kt hp lu lng thoi v a phng tin trn cc mng. Hn na cht lng dch v v k thut iu khin cng ngh cho IP nh SIP hay MPLS (Multi Protocol Label Switching) c nhng ci thin ng k. Nh vy chng ta c iu kin v cng ngh c th i n NGN.

Cc cng ngh s dng trong NGNCng ngh chuyn mchChuyn mch l thnh phn nm trong lp truyn ti ca cu trc NGN tuy nhin cng ngh chuyn mch s dng y c s thay i ln so vi cc thit b s dng cng ngh TDM (Time Division Multiplexing) trc y. Cc cng ngh chuyn mch truyn thng trc kia khng tho mn c a phng tin cng nh nhu cu a dch v bng rng trong tng lai trong khi vic ra i cc cng ngh chuyn mch mi nh IP, ATM (Asynchronous Tranfer Mode) hay chuyn mch quang ang v s to ln mt trin vng to ln trong cng ngh chuyn mch.

Cng ngh IP: TCP/IP l h giao thc cung cp cc phng tin lin kt cc mng nh vi nhau to ra mng ln hn gi l lin mng (Internetwork). Cu trc phn tng ca TCP/IP gm 4 tng: Lp lin kt d liu v vt l, lp IP, lp TCP/IP gm hai giao thc TCP (Tranmission Control Protocol) v UDP (User Datagram Protocol) trong TCP cung cp kh nng kt ni cn UDP cung cp kh nng phi kt ni, lp ng dng. ng dng v dch v So snh vi m TCP UDP IP Lin kt d liu v vt l hnh OSI ng dng Trnh din Phin Giao vn Mng Lin kt Vt l

Giao thc IP thc hin truyn thng tin di dng cc n v d liu gi l Datagram. C hai loi khun dng gi tin l IPv4 v IPv6, trong khi IPv4 ang tr ln li thi v bc l nhiu hn ch th s ra i ca IPv6 l mt bc pht trin tip theo trong cng ngh IP c th p ng cho cc yu cu mi. Cng ngh ATM: ATM l mt h thng truyn dn thng tin dng gi c bit s dng kiu ghp knh khng ng b. Cng ngh ATM xut hin vi mng din rng, a dch v bng rng, tc cao. ATM cng chp nhn loi dch v kt ni trong knh o c to ra truyn cc thng tin dch v. ID kt ni c ch nh khi thit lp knh v ID c gii phng khi kt thc kt ni. V c bn, ATM c xem nh kiu chuyn giao thng tin dng gi hay cn gi l t bo ATM. T bo ny lun c cu trc c nh l 53 byte trong c 5 bytes mo u v 48 bytes thng tin. Vic thit lp cc kt ni (gm cc ng o v knh o) i vi mng ATM cng ging nh mng chuyn mch theo khe thi gian. Khi nhn c yu cu ni, mng ATM cn phi xc nh rng n c th thit lp kt ni c khng v ngoi ra nhng kt ni no c chp nhn thit lp trn mng. Cng ngh ATM c mt u im ht sc ni tri l cht lng dch v, iu ny c th hin cc sn phm ng dng cng ngh ny mang li. Tng phn vi cc giao thc nh tuyn ca cng ngh IP giao thc nh tuyn ATM yu cu mt

cht lng dch v cao v n thng c s dng khi xy dng mt tuyn truyn dn. Cng ngh MPLS: MPLS l cng ngh mi trong lin lc IP, l s ci tin ca cng ngh IPoA (IP over ATM) truyn thng. MPLS s dng ch tch hp bi vy n c cc u im ca ATM nh tc cao, QoS (Quality of Service) m bo,iu khin lung mm do cng nh mm do kh nng m rng ca IP. MPLS khng nhng gii quyt c nhiu vn ca mng hin ti m cn h tr c nhiu chc nng mi, do c th ni rng MPLS l cng ngh mng IP xng sng l tng. Bng cch p dng nhn lp 2 vo khung IP v a n vo ra MPLS - phn mng nhn dng, nhn ny tng ng vi vic thit lp mt tuyn ng qua mng, MPLS to ra kh nng chuyn lu lng qua cc nh tuyn IP m trc y gp kh khn ti mi phn u ca IP trc khi chuyn sang chng khc. Bn cnh ti thi im nhn c a vo, cc tham s k thut v lu lng c xc nh trc c th c lp trnh vo phn cng nhm m bo cc mc ca bng thng lu lng, iu khin tc nghn. Cc cng ngh chuyn mch cho mng th h mi c th l IP, ATM, IP/ATM hay MPLS, iu ny tu thuc vo xu hng trin khai ca cc nh khai thc vin thng. Tuy nhin ni chung l da trn cng ngh chuyn mch gi, cho php thch ng vi nhiu tc v loi hnh dch v khc nhau. Song song vi cc cng ngh chuyn mch trn, chuyn mch quang ang trong giai on nghin cu v trong tng lai s c cc chuyn mch quang lm vic theo nguyn l sau: Chuyn mch quang phn chia theo khng gian, chuyn mch quang phn chia theo thi gian, chuyn mch quang phn chia theo bc sng.

Cng ngh truyn dnTrong mng th h mi (NGN) cng ngh truy nhp c s dng y l SDH (Synchronous Digital Hierachy) v WDM (Wavelength Division Multiplexing) nh cc u im nh kh nng hot ng mm do, linh hot, thun tin cho khai thc v iu hnh qun l ca chng. Cng ngh SDH v ang c s dng rt rng ri v cc tuyn truyn dn SDH vn ang c tip tc thit lp theo ng xu hng ca cu trc mng mi do vic s dng cc tuyn ny s gip cho vic trin khai NGN c nhiu thun li.

Cng ngh WDM cho php s dng rng bng tn rt ln ca si quang bng cch kt hp mt s tn hiu ghp knh theo thi gian vi di bc sng khc nhau.Nh kh nng truyn dn ca cc tuyn trn mng s c tng ln ng k, p ng y v mt dung lng cho mng. Nh vy cn pht trin cc h thng truyn dn cng ngh SDH v WDM, hn ch s dng cng ngh PDH. ng thi cn nghin cu pht trin cc phng tin truyn dn tin cy, c nh vy vic hi t cc mng trn nn cng ngh gi mi c th thc hin c. Cc phng tin truyn dn s dng trong NGN . Cp quang: S dng cng ngh truyn dn quang SDH cho php to nn ng truyn dn tc cao (n*155Mb/s). Cng ngh ny c s dng rng ri nhiu nc cng nh Vit Nam. Cng ngh WDM thc s tr thnh bc t ph trong cng ngh truyn dn trn mng quang vi kh nng tc ln ti 5Gb/s, 10Gb/s v 20Gb/s. V tuyn : Vi ba: trong h thng vi ba cng ngh SDH cng c pht trin tuy nhin do nhiu hn ch v mi trng truyn sng m tc khng c cao so vi cng ngh truyn dn quang. V tinh: Nh s pht trin ca thng tin v tinh trong nhng nm gn y m cc dch v trn rt pht trin vi a dng cc loi hnh: DTH tng tc, truy nhp Internet, cc dch v bng rngNgoi cc ng dng ph bin vi nhu cu thng tin qung b, vin thng nng thn, vi s kt hp s dng cng ngh CDMA gip tng s lng knh truyn, thng tin v tinh s c bit pht trin trong nhng nm ti trong lnh vc thng tin di ng, thng tin c nhn, nh v. Cp ng: y l phng tin truyn dn c bn trong mng truy nhp, do nhng hn ch ca mnh m cp ng ngy nay t c ch . Vi nhng cng ngh truy nhp mi ra i nh xDSL gip khc phc phn no v tc truyn dn nhng li hn ch v khong cch truyn dn do vy trong tng lai cp ng ch cn s dng trong nhng phm vi nh trong nhng vng mng truy nhp.

1.2.3. Cng ngh mng truy nhpVi nhu cu truy nhp cc dch v tin tin yu cu cht lng cao, thi gian p ng dch v ti u chi ph vn hnh kinh t th quan im truyn thng v ng dy thu bao c nhiu thay i. Bn cnh cc phng php truy nhp a knh nh TDM, FDMA, CDMA, SDMA ngi ta c th kt hp s dng thm cc k thut khc. Trong xu hng pht trin ca mnh, NGN s tch hp nhiu loi hnh mng truy nhp vo mt mi trng truyn dn chung. iu s to ra kh nng truy nhp hiu qu nh cc cng ngh tin tin: Mng truy nhp quang: Mng a truy nhp s dng k thut ghp bc sng

l mng s dng bc sng mt cch hiu qu bng cch truyn ng thi nhiu tn hiu quang cc bc sng khc nhau trn cng mt si quang. Mng a truy nhp s dng k thut ghp bc sng (WDMA) c chia lm hai loi chnh l: mng WDMA n bc (hay gi l mng ton quang) v WDM a bc. Trong khi cc mng a truy nhp phn chia theo sng mng ph (SCMA) c chia thnh hai loi l mng SCMA n knh v mng SCMA a knh. Mng truy nhp v tuyn: Nhng loi hnh thng tin v tuyn pht trin

mnh nht hin nay l thng tin v tuyn c nh (WLL Wireless Local Loop) v thng tin v tuyn c nh. Cc phng thc truy nhp cp ng xDSL (Digital Subcriber Line) in

hnh l HDSL, ADSL. Xu hng pht trin mng truy nhp bng rng: Trong mng truy nhp bng rng th mc tiu l cc dch v bng hp s c kt hp vo cng mt ng truy nhp cc dch v bng rng, nhng trong qu trnh pht trin cc dch v ny c th c truy nhp ring bit. Truy nhp ring bit cho bng rng: Theo phng php ny cc dch v bng

rng c a ti khch hng qua qua ng truy nhp ring bit ti tng i ni ht ATM. Nh vy s khng c s nh hng no n cc dch v mng hin ti H thng truy nhp kiu ghp knh: Phng php ny s dng mt lung

truy nhp bng rng n nht ti khch hng truyn ti ng thi cc dch

v bng hp v bng rng. Vi k thut ghp knh ATM tt c cc dch v c truyn trn knh o v mch o ATM sau khi ti thu bao th cc dch v bng hp c tch ra. Truy nhp mc tiu: Phng php ny gip cho khch hng s dng y nht thit b ATM ca mnh bng cch to kh nng truy nhp ATM y vo mt tng i ATM.

Cc thnh phn trong cu trc mng NGN

Hnh 1.1: Cc thnh phn chnh ca mng NGN.

Trong mng vin thng th h mi c rt nhiu thnh phn cn quan tm, nhng y ta ch xem xt nhng thnh phn chnh th hin r nt s tin tin ca NGN so vi mng vin thng truyn thng. chnh l:

Media Gateway (MC). Media Gateway Controller (MGC Call Agent - Softswitch). Signalling Gateway (SG). Media Server (MS).

Application Server (Feature Server).

GSM

Media GatewayMedia Gateway cung cp phng tin truyn ti thng tin thoi, d liu, fax v video gia mng gi IP v mng PSTN. Trong mng PSTN, d liu thoi c

mang trn knh DS0. truyn d liu ny vo mng gi, mu thoi cn c nn li v ng gi. c bit y ngi ta x dng mt b x l tn hiu s DSP (Digital Signal Processors) thc hin cc chc nng : Chuyn i AD (Analog to Digital), nn m thoi/audio, trit ting di, b khong lng, m ho, ti to tn hiu thoi, truyn cc tn hiu DTMF.

Hnh 1.2: Cu trc ca MG

Cc chc nng ca mt Media Gateway

Truyn d liu thoi s dng giao thc RTP.

Cung cp khe thi gian T1 hay ti nguyn x l tn hiu s (DSP) dui

Media Gate Un

s iu khin ca Media Gateway Controller (MG). ng thi qun l ti nguyn DSP cho cc dch v ny. H tr cc giao thc c nh loop-start, ground-start, E&M, CAS,

QSIG v ISDN qua T1. Cung cp kh nng thay nng cc Card T1 hay DSP. C phn mm Media Gateway d phng. Cho php kh nng m rng Media Gateway v : Cng (port), Card, cc nt m khng lm thay i cc thnh phn

c tnh h thng. Mt Media Gateway c cc c tnh sau:

L mt thit b vo ra c hiu (I/O).

Dung lng b nh phi lun m bo lu tr cc thng tin trng thi, thng tin cu hnh, cc bn tin MGCP, th vin DSP Dung lng a ch yu s dng cho qu trnh ng nhp (loggin). D phng y giao din Ethernet (vi mng IP), m rng mt vi

giao din T1/E1 vi mng TDM.

Mt khong 120 port (DSOs). S dng Bus H.110 m bo tnh linh ng cho h thng ni b.

Media Gateway ControllerMGC l n v chc nng chnh ca Softswitch. N a ra cc quy lut x l cuc gi, cn MG v SG s thc hin cc quy lut . N iu khin SG thit lp v kt thc cuc gi. Cc chc nng chnh ca MGC c th hin nh hnh trn.: MGC chnh l chic cu ni gia cc mng c c tnh khc nhau, nh PSTN, SS7, mng IP. N chu trch nhim qun l lu lng thoi v d liu qua cc mng khc nhau. N cn c gi l Call Agent do chc nng iu khin cc bn tin.

Hnh 1.3: Chc nng ca Media Gateway Controller Cc chc nng chnh ca Media Gateway Controller

M

MGCP

Hnh 1.4: Giao thc s dng gia cc thnh phn Cc chc nng ca MGC. iu khin cuc gi, duy tr trng thi ca mi cuc gi trn mt iu khin v h tr hot ng ca Media Gateway (Xc nh v Media Gateway.

cu hnh thi gian thc cho cc DSP, Phn b knh DS0, Truyn dn thoi), Signalling Gateway (Cc b x l thi gian, Cu hnh kt ni, M ca nt mng hay thng tin cu hnh).

Trao i cc bn tin c bn gia hai MG-F. X l bn tin SS7 (khi s dng SIGTRAN). X l bn tin lin quan n QoS. Pht hoc nhn bn tin bo hiu. nh tuyn (bao gm bng nh tuyn, phn tch s v dch s).

A F

Tng tc vi AS-F cung cp dch v hay c tnh cho ngi C th qun l cc ti nguyn mng (port, bng tn,). C th s dng cc giao thc bo hiu: - thit lp cuc gi: H.323, SIP. - iu khin MG: MGCP, Megaco/H.248. - iu khin SG: SIGTRAN ( SS7 ). - truyn thng tin: RTP, RTCP.

s dng.

c tnh h thng

L mt CPU c hiu yu cu l h thng a x l, c kh Cn b nh ln lu tr d liu. iu ny cng rt cn Ch yu lm vic vi lu lng IP, do yu cu cc kt H tr nhiu loi giao thc. sn sng cao.

nng m rng theo chiu ngang. thit cho cc qu trnh a x l.

ni tc cao.

Signalling GatewaySignalling Gateway to ra mt chic cu gia mng bo hiu SS7 vi mng IP di s iu khin ca MGC. SG lm cho Softswitch ging nh mt nt SS7 trong mng bo hiu SS7. Nhim v ca SG l x l thng tin bo hiu. Cc chc nng ca Signalling Gateway Cung cp mt kt ni vt l n mng bo hiu.

Truyn thng tin bo hiu gia Media Gateway Controller Cung cp ng dn truyn dn cho thoi, d liu v cc

v Signalling Gateway thng qua mng IP.

dng d liu khc. (Thc hin truyn d liu l nhim v ca Media Gateway) Cung cp cc hot ng SS7 c s sn sng cao cho cc dch v vin thng.

c tnh h thng L mt thit b vo ra I/O. Dung lng b nh phi lun m bo lu tr cc thng Dung lng a ch yu s dng cho qu trnh ng nhp D phng y giao din Ethernet (vi mng IP). tng hiu xut v tnh linh ng ngi ta s dng busYu cu sn sng cao: nhiu SG, nhiu lin kt bo hiu

tin trng thi, thng tin cu hnh, cc l trnh

(logging), do khng yu cu dung lng ln.

H.110 hoc H.100.

1.3.4.

Media Server Media Server l thnh phn la chn ca Softswich, c s dng x l cc

thng tin c bit. Mt Media Server phi h tr phn cng DSP vi hiu xut cao nht. Cc chc nng ca mt Media Server. Chc nng Voicemail c bn. Hp th Fax tch hp hay cc thng bo c th s dng e-mail hay cc bn tin ghi m trc. Kh nng nhn dng ting ni (nu c). Kh nng hi ngh truyn hnh (video conference). Kh nng chuyn thoi sang vn bn. (Speech to text).

c tnh h thng L mt CPU, c kh nng qun l l lng bn tin MGCP. Lu tr cc phng php thc hin lin kt vi DSP ni b hay ln cn. Cn dung lng b nh ln lu tr cc c s d liu, b nh m, th vin,.. Dung lng a tng i nh. Qun l hu ht cc lu lng IP nu tt c ti nguyn IP c s dng

x l thoi. S dng Bus H110 tng thch vi card DSP v MG. sn sng cao.

1.3.5.

Application Server/ Feature ServerServer c tnh l mt server mc ng dng cha mt lot cc dch v ca

doanh nghip. Chnh v vy m ta cn gi l Server ng dng thng mi. V hu ht cc Server ny u qun l cc dch v v truyn thng qua mng nn chng khng rng buc nhiu vi Softswitch v vic phn chia hay nhm cc thnh phn ng dng.

Hnh 1.5: Cu trc Server ng dng Cc dch v cng thm c th thuc Call Agent, hoc cng c th thc hin mt cch c lp. Nhng ng dng ny giao tip vi Call Agent thng qua cc giao thc nh SIP, H.323 Chng thng c lp vi phn cng nhng li yu cu truy nhp c s d liu c trng.Chc nng ca Feature Server

Xc nh tnh hp l v h tr cc thng s dch v thng thng cho h thng a chuyn mch.Mt s v d v cc dch v c tnh H thng tnh cc: Call Agent s dng cc b CDR (Call Detail

Record). Chng trnh CDR c rt nhiu c tnh, chng hn kh nng ng dng tc da trn loi ng truyn, thi im trong ngyDch v ny cho php cc khch hng truy nhp vo bn tin tnh cc ca h thng qua cuc gi thoi hay yu cu trang Web.

Primary

H.323 Gatekeeper - Dch v ny h tr nh tuyn thng qua cc min

khc nhau (cc mng khc nhau). Mi min c th ng k mt s in thoi v s truy nhp trung k vi Gatekeeper thng qua giao thc H.323. Gatekeeper s cung cp dch v nh tuyn cuc gi (v chuyn dch sang dng s) cho mi u cui H.323. Gatekeeper cn c th cung cp iu khin tnh cc v qun l bng thng cho Softswitch. VPN - Dch v ny s thit lp mng ring o cho khch hng vi cc c

tnh: Bng thng xc nh (thng qua mng thu ring tc cao), m bo QoS, Nhiu tnh nng ring theo chun, K hoch quay s ring, Bo mt cc m thoi c truyn dn..c tnh h thng

Do tnh c bit nn n yu cu mt CPU tin ch cao. iu ny cng cn ph thuc vo cc ng dng c bit khc nhau. Cn b nh ln vi tr thp. CPU c kh nng m rng p ng cho vic nng cp dch v v lu lng. t mt vi c s d liu trong Server. Dung lng a ln, tu thuc vo c tnh ca tng ng dng. V d nh dung lng 100GB-1T cho ngn hng Voicemail. Giao din Ethernet (vi mng IP) c thc hin vi y kh nng d

phng.

CHNG 2: CC GIAO THC BO HIU TRONG MNG NGN

2.1. Giao thc bo hiu cuc gi2.1.1. H323Khi cp n in thoi IP, tiu chun quc t thng c cp n l H.323. c ban hnh ln u tin vo nm 1996 v gn y nht l vo 02/1998, khuyn ngh ny hin ang l mt bn ch tiu k thut c bn v cc sn phm thoi qua IP. Tuy nhin khuyn ngh H.323 rt chung chung nn t c coi l tiu chun c th. Trong thc t, hon ton c th thit k mt h thng hon ton thoi tun th

H.323 m khng cn n IP. Khuyn ngh ny ch a ra yu cu v giao din mng gi ti thit b u cui. C mt cht c bit l H.323 d nh ginh cho X.25, sau l ATM, nhng gi y li l Internet v TCP/IP. Theo tiu ca ITU-T cho H.323: H thng truyn thng a phng tin da trn cng ngh gi, H.323 thc t m t cch thc ca h thng kt ni l nhng h thng c nhiu kh nng hn ngoi kh nng truyn v nhn tn hiu audio thoi. Ngi ta hi vng rng cc h thng truyn thng a phng tin ny c th h tr cho ngnh vin thng v c th h tr cho cc ng dng video nh Teleconferencing v Data-conferencing hoc truyn file. Mc d H.323 c nhiu cng dng hn nhng trng tm chnh ca th trng i vi khuyn ngh ny l kh nng audio thc hin thoi IP.

2.1.1.1. Cu trc ca H.323V VoIP ch s dng mt phn cu trc H.323 nn s rt tt nu ta xem xt cu trc H.323 mt cch hon chnh trc khi khai thc mt phn ca H.323 c s dng trong mng VoIP. Cu trc H.323 c th c s dng LAN hoc mng gi din rng. Bt k mt mng gi khng tin cy (khng c m bo v cht lng dch v), hoc c tr cao u c th s dng H.323.

Hnh 2.1: Mng H.323 H323 nh ngha 4 thnh phn chnh trong h thng giao tip. Terminal H tr truyn thng hai chiu vi cc thc th H.323 Terminal khc. Gateway To tnh tng thch gia cc loi mng khc nhau. Gatekeeper Qun tr min. chuyn i i ch, iu khin bng thng MCU H tr hi thoi t ba thnh phn tr ln Terminal (u cui). L cc im u cui trong mng LAN. Terminal n thun l my tnh c nhn hoc mt thit b c lp no h tr giao tip hai chiu thi gian thc vi cc my trm khc qua thoi v d liu. Mi Termial phi m bo tnh tng thch vi cc loi mng khc nhau. Cc u cui H.323 phi h tr cc giao thc sau: H.245 cho vic chuyn i dung lng ca u cui v cho vic to lp mt knh truyn thng. H.225 cho vic bo hiu v thit lp cuc gi.

RAS cho vic khai bo v cc iu khin cho php khc vi mt Gatekeeper. RTP RTCP cho vic sp xp thnh dy cc gi tin thoi v hnh nh. Cc u cui H.323 cng phi h tr G.711 v kt ni c bn ti thiu ca H.323 l thoi. Cc thnh phn ty ch trong mt u cui H.323 l cc Codec cho hnh nh, giao thc T-120 cho hi ngh d liu v MCU cho kh nng hi ngh a im. Gateway (cng truyn thng). Mt Gateway cung cp kh nng kt ni gia mt mng H.323 vi cc mng khc. V d nh: Mt gateway c th kt ni lin lc gia mt u cui H.323 vi cc mng SCN (SCN gm cc mng chuyn mch thoi nh kiu PSTN). Kh nng kt ni cc mng khc nhau ny c thc hin bi vic phin dch giao thc cho vic thit lp v gii phng cuc gi bng vic chuyn i cc nh dng truyn thng gia cc mng khc nhau v bng vic trao i thng tin gia cc mng m kt ni bi Gateway. Tuy nhin vic kt ni gia cc u cui H.323 s khng i hi s c mt ca mt Gateway . Gatekeeper (gim st cng truyn thng). Mt min H.323 (zone) trn c s mng IP l tp hp ca tt c cc u cui. Trong , mi u cui c gn vi mt b danh. Mi min c qun tr bi mt Gatekeeper duy nht, l trung tm u no, ng vai tr gim st mi hot ng trong min . y l thnh phn tu chn trong h thng VoIP theo chun H.323. Tuy nhin nu c mt GateKeeper trong mng th cc u cui H.323 v cc Gateway phi hot ng theo cc dch v ca Gatekeeper . Mi thng tin trao i ca Gatekeeper u c nh ngha trong RAS. Mi ngi dng ti u cui c Gatekeeper gn cho mt mc u tin duy nht. Mc u tin ny rt cn thit cho c ch bo hiu cuc gi m cng mt lc nhiu ngi s dng. H.323 nh ngha c nhng tnh cht bt buc ti thiu phi c cho Gatekeeper v cc c tnh ty chn.

Cc chc nng bt buc ti thiu ca mt Gatekeeper gm: Phin dch a Cc chc nng ty chn ca gatekeeper gm c: Bo hiu iu khin cuc

ch, iu khin cho php truy nhp, iu khin di thng, qun l (vng)

gi, cp php cho cuc gi, qun l cuc gi. Gatekeeper hot ng hai ch :

Ch trc tip: Gatekeeper ch c nhim v cung cp a ch ch m khng tham gia vo cc hot ng kt ni khc. Ch chn ng: Gatekeeper l thnh phn trung gian, chuyn tip mi thng tin trao i gia cc bn. MCU (n v iu khin a im-MultIPoint Control Unit ). Cung cp chc nng hi thoi vi s bn tham gia ln hn 3. N phi hp cc phng thc giao tip ca cc bn tham gia b cung cp cc c trng thuc m thanh v hnh nh (nu cn) cho cc Terminal. MCU bao gm hai thnh phn: B iu khin a im (MultIPoint Controller- MC) c nhim v thit lp v

qun l hi thoi nhiu bn qua H.245. MC c th c t trong Gatekeeper, Gateway, Terminal hoc MCU. B x l a im (MultIPoint Processor-MP): ng vai tr tn hiu, phn

knh v lu chuyn dng bit qu trnh giao tip gia cc bn tham gia hi thoi. i vi MCU tp trung th c y MC v MP. i vi MCU phn quyn th ch cn cc chc nng ca MC. S khc bit l ch trong hi thoi phn quyn cc bn trao i trc tip vi nhau m khng cn thng qua MCU. Ngoi ra, ngi ta c th kt hp gia hai loi ny to thnh MCU lai ghp.

2.1.1.2. Thit lp v hy cuc gi H.323.Bo hiu trong H.323 l mt qu trnh thc s phc tp. Tng tc gia cc phn t trong mng bo hiu H.323 trong qu trnh bo hiu c m t nh sau:

Hnh 2.2: Bo hiu thit lp cuc gi gia mng chuyn mch gi v mng PSTN

Nu xem xt mt cch chi tit th cuc gi gia hai u cui H.323 c thit lp nh sau:

Trc ht c hai phi c dng k ti Gatekeeper. u cui A gi yu cu ti Gatekeeper ngh thit lp cuc gi. Gatekeeper gi cho u cui A thng ti cn thit v u cui B. u cui A gi bn tin SETUP ti u cui B. u cui B tr li bng bn tin Call Proceeding v ng thi lin lc vi Gatekeeper xc nhn quyn thit lp cuc gi. u cui B gi bn tin Alerting v Connect. Hai u cui trao i mt s bn tin H.245 xc nh ch t, kh nng x l ca u cui v thit lp kt ni RTP.

y l trng hp cuc gi im - im n gin nht, khi m bo hiu cuc gi khng c nh tuyn ti Gatekeeper. H.323 cn h tr nhiu kch bn thit lp cuc gi phc tp khc.

2.1.2. SiPITU-T khng phi l t chc tiu chun duy nht a ra k hoch thit lp kt ni thoi IP v ng gi audio. Hn hn bt k mt t chc qun l cc chun mc Internet, IETF cng c nhng yu cu ca mnh i vi h thng VoIP v gi l Giao thc iu khin phin SIP (Session Initiation Protocol). Nhng ngi xut SIP cho rng H.323, giao thc ang xut hin trong bo hiu ATM v ISDN, l khng thch hp cho iu khin h thng VoIP ni chung v trong thoi Internet ni ring. H cho rng H.323 vn d rt phc tp, h tr hu ht cc chc nng khng cn thit cho cho thoi IP do i hi chi ph cao m li khng hiu qu. Trong khi nhng ngi ng h SIP cho rng H.323 khng c kh nng m rng yu cu i vi giao thc bo hiu cho cng ngh chng hn nh VoIP, l nhng cng ngh chc chn s pht trin v h tr cc dch v v c tnh mi. SIP trn tng v cu trc ca HTTP (Hypertext Tranfer Protocol), giao thc trao i thng tin ca World Wide Web. N c nh ngha nh mt giao thc Client-Server, trong cc yu cu c bn gi (Client) a ra v bn b gi (Server) tr li. SIP s dng mt s kiu bn tin v mt s trng mo u va HTTP, xc nh ni dung lung thng tin kiu mo u thc th v cho php xc nhn cc phng

php s dng ging nhau c s dng trn Web. SIP nh ngha cc bn tin INVITE v ACK ging nh bn tin Setup v Connect trong H.225, trong c hai u nh ngha qu trnh m mt knh ng tin cy m thng qua cuc gi c th i qua. Tuy nhin khc vi H.225, tin cy ca knh ny khng ph thuc vo TCP. Cc nh xut SIP kin ngh rng vic tch hp tin cy vo lp ng dng ny cho php kt hp mt cch cht ch cc gi tr iu chnh ng dng, c th ti u ho VoIP hn l ph thuc vo nhng gi tr chung chung ca TCP. Cui cng SIP da vo giao thc m t phin SDP, mt tiu chun khc ca IETF, thc hin s sp xp tng t nh c cu chuyn i dung lng ca H.245. SDP c dng nhn dng m tng i hay s dng chuyn cc phn t thng tin ca cc giao thc bo hiu thi gian thc RTSP sp xp cc tham s hi ngh a im v nh ngha khun dng chung cho nhiu loi thng tin khi c chuyn trong SIP. Theo nh ngha ca IETF (Internet Engineering Task Force), SIP l giao thc bo hiu lp ng dng m t vic khi to thay i v hu cc phin kt ni tng tc a phng tin gia nhng ngi s dng . SIP c th s dng cho rt nhiu dch v khc nhau trong mng IP nh dch v thng ip, thoi, hi ngh truyn thoi, e-mail, gio dc t xa, qung b (MPEG, MP3..) truy nhp HTM, XML, hi ngh video.. 2.1.2.1. Cu trc SIP.

Hnh 2.3: Cu trc SIP Trong hnh trn User Agent l thit b u cui trong mng SIP, c th l mt my in thoi SIP, c th l my tnh chy phn mm u cui SIP.

Proxy Server l phn mm trung gian hot ng c nh Server v Client thc hin cc yu cu thay mt cc u cui khc. Tt c cc yu cu c x l ti ch bi Proxy Server nu c th, hoc c chuyn cho cc my ch khc. Trong cc trng hp Proxy Server khng trc tip p ng cc yu cu ny th Proxy Server s thc hin khu chuyn i hoc dch sang cc khun dng thch hp trc khi chuyn i. Location Server l phn mm nh v thu bao, cung cp cc thng tin v nhng v tr c th ca pha b gi cho cc phn mm Proxy Server v Redirect Server, Redirect Server l phn mm nhn yu cu SIP v chuyn i a ch IP sang mt s a ch khc v gi li cho u cui. Khng ging nh Proxy Server, Redirect Server khng bao gi hot ng nh mt u cui, tc l khng gi i bt k mt yu cu no. Redirect Server cng khng nhn hoc hu cuc gi Registrar Server l phn mm nhn cc yu cu ng k REGISTER. Trong nhiu trng hp Registrar Server c ci t cng vi Proxy hoc Redirect Server hoc cung cp dch v nh v thu bao. Mi ln u cui c bt ln (th d nh l my T hoc phn mm SIP) th u cui li ng k vi Server. Nu u cui cn thng bo cho Server v a im ca mnh th bn tin REGISTER cng c gi i. Ni chung cc u cui u thc hin vic ng k li mt cch nh k. Cc tnh nng SiP Giao thc SIP c thit k vi nhng tiu ch sau:

Tch hp vi cc giao thc c ca IETF. n gin v c kh nng m rng. H tr ti a s di ng ca u cui. D dng to tnh nng mi cho dch v v cc dch v mi Tch hp vi cc giao thc c ca IETF. RSVP (Resource Reservation Protocol) giao thc lu tr ti nguyn mng. RTP (Realtime Tranfer Protocol) giao thc giao vn d liu thi gian

thc. RTSP (Real Time Streaming Protocol) giao thc kim sot lung d liu. SAP (Session Advantisement Protocol) giao thc qung co trong phin kt ni.

SDP (Session DescrIPtion Protocol) Giao thc m t phin kt ni a phng tin. MIME (MultIPurpose Internet Protocol) giao thc th in t. HTTP (Hypertext Transfer Protocol) giao thc truyn ti siu vn bn. n gin v c kh nng m rng. SIP c rt t bn tin, khng c cc chc nng tha nhng SIP c th s

dng thit lp nhng phin kt ni phc tp nh hi ngh.. n gin, gn nh, da trn khun dng text, SIP l giao thc ra i sau v khc phc c im yu ca nhiu giao thc trc y. Cc phn mm Proxy Server, Registr Server, Redirect Server, Location Serverc th chy trn cc my ch khc nhau v vic ci t thm my ch hon ton khng nh hng n cc my ch c. Chnh v th h thng chuyn mch SIP c th d dng nng cp. H tr ti a s di ng ca u cui. Do c Proxy Server, Registrar Server, Redirect Server h thng lun nm c a im chnh xc ca cc thu bao. Th d nh thu bao vi a chdtvt@hut.edu.vn c th nhn c cuc gi hay thng ip bt c a

im no qua bt c u cui no nh my tnh bn, my tnh xch tay, in thoi SIPVi SIP rt nhiu dch v di ng mi c h tr nh presence ( bit trng thi ca u cui ) v call forking. D dng to tnh nng mi cho dch v v dch v mi L giao thc khi to phin trong mng chuyn mch gi, SIP cho php to ra nhng tnh nng mi hay dch v mi mt cch nhanh chng. Call Processing Language (CPL) v Common Gateway Interface (CGI) l mt s cng c thc hin iu ny. SIP h tr cc dch v thoi nh waiting, call forwarding, call blocking, h tr thng ip thng nht

2.1.2.2. Thit lp v hu cuc gi SIPCc bn tin SIP, mo u v nh s.

INVITE - Bt u thit lp cuc gi bng cch gi bn tin mi u cui khc tham gia. ACK - Bn tin ny khng nh Client nhn c bn tin tr li bn tin INVITE.

BYE - Bt u kt thc cuc gi. CANCEL - Hu yu cu ang nm trong hng i. REGISTER - u cui SIP s dng bn tin ny ng k vi Registar Server. OPTION - S dng xc nh nng lc ca Server. INFO - S dng ti cc thng tin nh tone DTMF. Giao thc SIP c nhiu c im trng hp vi giao thc HTTP. Cc bn tin tr li cc bn tin SIP nu trn gm c: 1xx Cc bn tin chung. 2xx Thnh cng. 3xx - Chuyn a ch. 4xx Yu cu khng c p ng. 5xx - S c ca Server. 6xx - S c ton mng. Cc bn tin SIP u c khun dng text, tng t nh HTTP. Mo u ca bn tin SIP cng tng t nh HTTP v SIP cng h tr MIME (mt s chun v e-mail). Sau y l th d v mo u ca bn tin SIP:---------------------------------------------------SIP Header ---------------------------------------------------INVITE sIP:5120@192.168.36.180 SIP/2.0 Via: SIP/2.0/UDP 192.168.6.21:5060 From: sIP:5121@192.168.6.21 To: Call-ID: c2943000-e0563-2a1ce-2e323931@192.168.6.21 CSeq: 100 INVITE Expires: 180 User-Agent: Cisco IP Phone/ Rev. 1/ SIP enabled Accept: application/sdp Contact: sIP:5121@192.168.6.21:5060 Content-Type: application/sdp

Cc u cui SIP c nh s ging nh a ch e-mail, th d

dtvt@hut.edu.vnThit lp v hu cuc gi SIP.

Trong mng SIP qu trnh thit lp v hu cuc gi SIP gm c 6 bc nh sau: ng k, khi to v nh v u cui. Xc nh Media ca cuc gi, tc l m t phin m u cui c mi tham d. Xc nhn mong mun ca u cui b gi, tr li hay khng. Pha b gi phi gi bn tin xc nhn chp thun cuc gi hoc t chi. Thit lp cuc gi. Thay i hay iu khin cuc gi (th d nh chuyn cuc gi). Hu cuc gi.

2.2. Giao thc bo hiu gia MGC - MGMGCP 2.2.1.1. Gii thiuPhn ny s gii thiu giao thc MGCP (Media Gateway Control Protocol) s dng trong cc thit b ca Siemens. Cc sn phm ny chnh l b hiS signaling Gateway/Media Gateway Controller ca Siemens s dng cung cp cc dch v VoIP v RAS. Giao thc MGCP c s dng iu khin cc Gateway thoi t thit b iu khin cuc gi bn ngoi c gi l Media Gateway Controller hay Call Agent. Gateway thoi l phn t mng thc hin s chuyn i tn hiu audio trong cc knh thoi thnh cc gi d liu (thng l cc gi IP trong mng IP) Trunking Gateway l giao din gia mng thoi thng thng v mng VoIP. Loi Gateway ny c kh nng kt ni vi mt s lng ln cc knh thoi.MGCP l giao thc trong s thng minh trong vic iu khin cuc gi nm bn ngoi cc Gateway, n l giao thc kiu master/slave trong cc Gateway phi c trch nhim thc thi cc lnh t Call Agent.

2.2.1.2. Thit lp v hy cuc gi trong MGCP.Hnh v sau m t vic thit lp v gii ta cuc gi MGCP thng thng gia 2 thu bao PSTN kt ni vi cc tng i s dng CCS7 bo hiu. Thu bao PSTN bn A (ch gi) nhc my, quay s ri gi cc ch s a ch thu bao b gi ny ti tng i (bn ch gi bn A).

Tng i bn A sau khi nhn song a ch thu bao b gi (bn B), to ra bn

tin ISUP IAM (Initial address message) gi cho Signaling Media Gateway Controller /Media Gateway Controller (MGC) chnh thc t vn kt ni vi thu bao b gi (1) MGC gi cho Media Gateway (MG) bn A bn tin MGCP CRCX -

Createconnection (2) MG bn A tr li bng bn Resp - Response (3) MGC gi cho tng i bn B (b gi) bn tin ISUP IAM (4) MGC gi tip bn tin MGCP CRCX cho MG bn B (5) MG bn B tr li bng bn tin Resp (6) MGC gi cho MG bn A bn tin MGCP MDCX - Modifyconnection (7) MG bn A tr li bng bn Resp (8) MGC gi cho MG bn B bn tin ISUP COT (Continuity message) bo

co kt qu kim tra tnh lin tc (c yu cu trong bn tin IAM) trn mt mch (knh B c chn) (9) Tng i bn B gi cho MGC bn tin ISUP ACM (hon tt vic nhn a

ch) ng thi rung chung cho thu bao B (10) MGC chuyn cho tng i bn A bn tin ISUP ACM ny (11) Sau khi thu bao B nhc my, tng i bn B gi cho MGC bn tin ISUP

ANM (Answer message) thng bo vic nhc ny ny (12) Bn tin ANM ny li c MGC chuyn cho tng i bn A v hai bn thu

bao A v B c th bt u m thoi (13) Di y l th tc gii ta cuc ni MGCP gia 2 thu bao A v B khi mt

trong hai bn gi s bn B t my Tng i bn B gi bn tin ISUP REL cho MGC yu cu gii ta cuc ni

(1) MGC sau gi bn tin REL ny cho tng i bn A (2) MGC gi bn tin MGCP DLCX Deleteconnectioncho MG bn B thng

bo yu cu MG gii ta cuc ni (3). MG bn B gi tr li bn tin MGCP Resp (4) MGC cng ng thi gi bn tin MGCP DLCX cho MG bn A thng bo

yu cu MG gii ta cuc ni (5).

MG bn A cng gi tr li bn tin MGCP Resp (6) Tng i bn A gi cho MGC bn tin ISUP RLC thng bo hon tt vic gii

ta cuc ni (7) MGC sau cng gi cho tng i bn B bn tin ISUP RLC thng bo hon

tt vic gii ta cuc ni. Cuc ni kt thc (8)

Hnh 2.4: Thit lp v gii phng cuc gi MGCP (virtual trunking) Trng hp trn l khi mi vic din ra bnh thng. C mt s trng hp khng bnh thng chng ta s cp sau. MGCP a ra khi nim cuc ni (connection) v thit b u cui (endpoint). Endpoint l ngun ca d liu v c th l thit b vt l hay l o. Endpoint vt l l giao din ca mt gateway ni vi tng i TDM qua trung k. Mt gateway kt ni vi trung k c gi l trunking gateway. Connection c th c thit lp trn c s vic truyn cc gi thoi s dng RTP v UDP qua mng IP. i vi cuc ni im-ti-im, cc endpoint ca mt cuc ni c th thuc cc Media Gateway tch bit nhau hay trn cng mt Gateway.

Tran

Cc bn tin MGCP c truyn trn UDP. Cc lnh c gi ti 1 trong cc a ch IP c xc nh trong DNS cho mt endpoint nht nh. Bn tin tr li (Resp) c gi li a ch ngun ca lnh. Khi khng c cng c th dnh ring cho endpoint, cc lnh c th c gi nh sau: Bi call agent, ti cng MGCP mc nh cho Gateway: 2427. Bi Gateway, ti cng MGCP mc nh cho call agent: 2727. Chc nng giao tip thc hin vic iu khin kt ni v endpoint. C hai u s dng cng mt quy c v vic t tn . Cu trc lnh ca MGCPGiao thc MGCP gm hai tp lnh sau: Lnh MGC

EndpointConfiguration NotificationRequest CreateConnection ModifyConnection DeleteConnection AuditEndpoint AuditConnection DeleteConnection RestartInProgress Lnh Gateway DeleteConnection RestartInProgress

2.2.2. MEGACO/H248Khi cu trc phn tn MG/MGC c chp nhn rng ri, th nhiu chun giao thc gia MG v MGC c a ra. Trn c s MGCP mt s giao thc mi c pht trin dng iu khin Media Gateway. MGCP ra i khi IETF hp nht hai giao thc SGCP v IPDC. Trong khi ITU-T cng nghin cu v pht trin v a ra mt giao l MDCP ( Media Device Control Protocol ). Hai giao thc ny c bn l hon ton ging nhau, nn thng 6

1999 hai t chc ny hp nht hai giao thc thnh mt duy nht l MEGACO/H.248. MEGACO l tn do IETF t tn hoc H.248 l tn gi ca ITU-T i vi giao thc ny do ti liu v MEGACO v khuyn ngh v H.248 l hon ton ging nhau. MEGACO l trng tm ca vic thc hin gii php thoi qua gi VoIP. N c th tch hp tr thnh sn phm nh tng i trung tm, my ch truy nhp mng, modem cp, PBX, in thoi IPHin nay, tiu chun MEGACO ang c tin hnh xy dng phin bn 2. Giao thc MEGACO cung cp mt gii php ton din cho vic iu khin cc MG. Cng nh vi cc th h gii php iu khin cng iu khin cng truyn thng trc , MEGACO cng hot ng da trn nguyn tc l ton b s thng minh trong qu trnh x l cuc gi u thuc v MGC. MG s khng nh c cc thng tin ca trng thi cuc gi, n ch cung cp kh nng kt ni cho cc loi dng media khc nhau di s iu khin ca MGC, v kh nng tch sng ri truyn ti cc loi tn hiu khc nhau m kt hp mt cch tng ng vi cc dng media . MEGACO xem cc nh mt tp hp cc u cui m mi ci i din cho mt dng media xc nh. Mt u cui c th l mt thc th vt l c nh chng hn nh mt ng Analog hay mt khe thi gian trong mt giao din TDM, hoc c th l mt thc th logic nh mt dng lu lng gi VoIP. Cc u cui logic c th c thit lp hoc c gii phng bi cc lnh ca MEGACO. Cc kt ni cho trong phm vi MG c to ra bi cc lnh ca MEGACO m i hi t nht l hai u cui c t trong cng mt phm vi. Nu cc dng media kt hp vi cc u cui nm trong cng phm vi l nhng loi media khc nhau ( v d nh mt u l khe thi gian mt u l dng lu lng gi VoIP ) th MG c iu khin thc hin chuyn i gia cc loi media . h tr cho chc nng ny, cc u cui c y cho cc c tnh ca cc loi media khc nhau v d nh c tnh ca cc m thoi s c s dng. Cc u cui c nhiu c tnh khc nhau v d nh mt danh sch cc s kin ca tn hiu ang c ch i khai bo n MGC v mt danh sch cc tn hiu c kh nng truyn ti theo yu cu ca MGC. V d mt u cui s dng ng Analog s c kh nng khai bo vi MGC khi n nhn ra s xut hin tn hiu tr li ca ngi thu bao hoc tn hiu bo dng my

MEGACO c thit k tr thnh mt giao thc c th m rng. Kh nng m rng ny khc phc c nhc im chnh ca cc giao thc ca cc cng truyn thng trc y nh MGCP, v n gii quyt c nhng i hi ca cc giao thoi gi khc ngoi VoIP, v bi v n cung cp phng thc thc hin c nhng dch v in thoi Analog a dng ph thuc vo tng nc khc nhau. ` MEGACO l mt giao thc truyn ti khng ph thuc vo cc giao thc khc, mc d c tnh k thut cha mt vi ph lc m t vic s dng c TCP/IP v UDP nh nhng tu chn chuyn ti nhng phn ln cc hot ng ca chuyn mch mm u hp vi vic s dng truyn ti da trn c s IP ca MEGACO.

2.3. SIGTRAN Gii php truyn ti bo hiu SS7 qua mng IP2.3.1. Tng quan v SIGTRANNhim v chnh ca giao thc SIGTRAN l dng truyn thng tin bo hiu ca mng PSTN qua mng IP. y l mt giao thc truyn ti mi (transport protocol) c xy dng thay th TCP (Transmission Control Protocol) trong vic truyn tn hiu SS7. L do vic ra i ca SIGTRAN l do mt s hn ch sau ca TCP: - Cc c ch truyn m bo s tin cy: TCP l giao thc cung cp vic truyn d liu tin cy. Vic ny c thc hin thng qua c ch xc nhn (acknowledgments mechanism) v c ch tun t (sequencing mechanism). Mt s ng dng cn s truyn tin cy nhng khng cn s h tr ca 2 c ch trn nn vic s dng TCP trong nhng trng hp ny s gy ra tr. - Yu cu thi gian thc: Vi vic gy ra tr khng cn thit do s dng cc c ch trn lm cho TCP khng thch hp vi cc ng dng thi gian thc. - C ch socket ca TCP: C ch ny lm phc tp vic cung cp kh nng truyn tin cy ca multi-homed host. - Vn an ton: TCP d b s c vi cc tn cng t chi dch v (denial-of-service attack). Sau y l m hnh chc nng ca SIGTRAN.

M hnh chc nng

Hnh 2.5: M hnh chc nng ca SIGTRAN M hnh chc nng ca SIGTRAN bao gm 3 thnh phn c th hin trn hnh. Theo thut ng ca Softswitch, m hnh ny th hin chc nng chnh ca SIGTRAN l truyn bn tin bo hiu s 7 gia Signaling Gateway v Media Gateway Controller qua mng IP. Lu : c nhiu giao thc thch ng (Adaptation protocol) c nh ngha nhng ti 1 thi im ch c duy nht 1 giao thc c s dng.

2.3.2. SCTP (Stream Control Transport Protocol)SCTP l giao thc hng kt ni cng cp vi TCP c chc nng cung cp vic truyn cc bn tin mt cch tin cy gia cc ngi s dng SCTP ngang cp. Chc nng ca SCTP c th hin hnh sau:

Hnh 2.6: Chc nng ca SCTP Trong : Association startup & teardown: Association trong thut ng SCTP c hiu l mt kt ni c thit lp gia 2 im cui trc khi thc hin vic truyn d liu ngi dng (do SCTP l giao thc hng kt ni). Mi im cui SCTP c xc nh bi 1 a ch IP v s th t cng. Chc nng ny c kch hot to ra mt kt ni khi c yu cu t ngi s dng SCTP. Sequenced delivery within streams: c s dng xc nh ti thi im khi to tng s dng v s th t dng d liu (data stream) ca ngi dng trn mt kt ni. Mi dng l mt knh logic mt chiu. User data fragmentation: Nhim v ca chc nng ny l phn on v tp hp bn tin ngi dng . Acknowledgement & congestion avoidance: Mi bn tin ngi dng ( c phn on hay cha) u c SCTP gn mt s th t truyn TSN

(Transmissionsequence number). Ni nhn s xc nhn tt c TSN nhn c k c khi s th nhn khng lin tc. Chunk bundling: Mt gi SCTP bao gm mt header chung v mt hay Packet validation: Dng kim tra gi SCTP thng qua trng xc nhn Path management: Dng chn a ch truyn ch cho mi gi SCTP nhiu chunk. Cc loi chunk bao gm ti d liu, khi to, kt thc, v32-bit checksum. SCTP: truyn i da trn lnh ca SCTP user v trng thi ca ch n. Cu trc ca gi

Hnh 2.7: Cu trc ca gi SCTP

Hnh 2.8: nh dng ca header chung ca gi SCTP Vi: Source/Destination port number: 16 bits ny dng xc nh cng ca ngi gi v ngi nhn SCTP. Verification tag: bn nhn gi ny s dng trng ny kim tra s hp l ca ngi gi. Checksum: 32 bits ny dng cha kt qu checksum ca gi SCTP.

2.3.3. Cc giao thc thch ng M2PA (Message Transfer Part 2 Peer-to-Peer Adaptation) M2PA h tr vic truyn bn tin bo hiu s 7 lp MTP3 qua mng IP. Signaling Gateway s dng giao thc thch ng ny ng vai tr nh mt nt trong mng SS7. M2PA c chc nng tng t nh MTP2. M2UA (MTP2 User Adaptation) M2UA cng c s dng truyn bn tin lp MTP3 nhng Signaling Gateway s dng n khng phi l mt nt mng SS7. M3UA (MTP3 User Adaptation) M3UA dng truyn bn tin ca ngi dng lp MTP3 (nh bn tin ISUP, SCCP). Lp ny cung cp cho ISUP v SCCP cc dch v ca MTP3 ti Signaling Gateway xa. SUA (SCCP User Adaptation) SUA nh ngha giao thc truyn bn tin bo hiu ca ngi dng lp SCCP (TCAP, RANAP). SUA cung cp cho TCAP cc dch v ca lp SCCP ti Signaling Gateway xa. hiu r hn cc giao thc thch nghi trn, xin xem thm phn so snh M2PA vi M2UA, M3UA vi SUA trong phn ph lc.

CHNG 3. BO HIU CUC GI H.3233.1. Tng quan v H.323H.32x l h giao thc ca ITU-T nh ngha cc dch v a phng tin qua cc mng khc nhau v H.323 l mt phn trong h ny. H.323 l giao thc xc nh cc thnh phn, cc giao thc cng nh cc bc thc hin cung cp dch v a phng tin qua mng gi.

Cc dch v a phng tin y c th l truyn tn hiu ting, tn hiu hnh thi gian thc v d liu. Mng gi c th l Internet, EN (Enterprise Network), LAN (Local Area Network), MAN (Metropolitan Area Network), WAN (Wide Area Network). H.323 c th cung cp 1 trong 3 dch v sau ting, hnh hay d liu cng nh t hp cc dch v trn nn n c th c ng dng nhiu ni nh ng dng ti nh khch hng, doanh nghip hay cng nghip gii tr. Ngoi ra n c th c s dng cung cp dch v a phng tin a im (multipoint multimedia communications)

3.2. Cc thnh phn ca H.323M hnh mng H.323 c th hin trong hnh sau:

Hnh 3.1: M hnh mng H323 n gin Giao thc H.323 nh ngha 4 thnh phn sau: u cui (terminal c k hiu l T), cng (gateway - GW), b gi cng (gatekeeper - GK), v n v iu khin a im (multipoint control unit - MCU). Ring vi GK th y l thnh phn la chn, c th c hoc khng c trong mng. V GW v MCU thng c coi l cc im cui (endpoint). Cc thnh phn ny c th c tp trung trong mt h thng n hay c lp t nhiu h thng khc nhau ti nhng v tr a l cng nh vt l khc nhau.

Hnh 3.2: Mng H 323

Hnh 3.3: Cc giao thc thuc H 323 Phn trnh by cc giao thc cng nh hot ng ca cc giao thc trong mng H.323 s c xem xt trong phn sau.

3.2.1. TerminalL thnh phn dng trong truyn thng 2 chiu a phng tin thi gian thc c dng trong vic kt ni cc cuc gi. u cui H.323 c th l mt my tnh, mt in thoi, in thoi truyn hnh, h thng voicemail, thit b IVR (Interactive Voice Response) hay l 1 thit b c lp c cc ng dng a phng tin H.323. Ngoi ra n cn tng thch vi u cui H.324 ca mng chuyn mch knh v mng di ng, u cui H.310 ca B-ISDN, u cui H.320 ca ISDN, v.v. Mt u cui H.323 phi h tr cc c tnh sau: H.245 cho vic trao i kh nng ca u cui v to cc knh thng tin. H.225 cho qu trnh bo hiu v thit lp cuc gi. RAS cho vic ng k v iu khin cc hot ng qun l khc vi GK.

RTP/RTCP c s dng cho vic truyn cc gi thng tin thoi v hnh. G.711 cho qu trnh m ha v gii m ting ni, T.120 cho hi tho d liu v h tr kh nng tng t ca MCU. Hnh sau minh ha cc giao thc m mt u cui H.323 phi h tr:

Hnh 3.4: Chng giao thc ti u cui H.323

3.2.2. GatewayGW l thnh phn dng kt ni 2 mng khc loi nhau. Mt cng H.323 dng lin kt mng H.323 vi mng khng phi l mng chun H.323. Vic kt ni gia 2 mng khc loi nhau thc hin c nh vic dch cc giao thc (protocol translation) khc nhau cho qu trnh thit lp v gii ta cuc gi, vic chuyn i dng thng tin gia cc mng khc nhau v vic truyn thng tin gia cc mng kt ni vi GW. Tuy nhin mt GW s khng cn thit cho vic lin lc gia cc u cui thuc cng mng H.323. Cu to ca mt gateway bao gm mt Media Gateway Controller (MGC), Media Gateway (MG) v Signaling Gateway (SG) c minh ha trong hnh v sau:

Hnh 3.5: Cu to ca gateway Chc nng ca MGC, MG, SG c trnh by trong chng 1, phn Cu trc vt l ca mng NGN. Cc giao thc m mt GW phi h tr c minh ha trong hnh

Hnh 3.6: Chng giao thc ca mt Gateway Cc c tnh c bn ca mt gateway: Mt GW phi h tr cc giao thc hot ng trong mng H.323 v mng s dng chuyn mch knh (SCN Switched Circuit Network). V pha H.323, GW phi h tr bo hiu iu khin H.245 cho qu trnh trao i kh nng hot ng ca terminal cng nh ca GW, bo hiu cuc gi H.225, bo hiu RAS. V pha SCN, GW phi h tr cc giao thc hot ng trong mng chuyn mch knh (nh SS7 s dng trong PSTN).

3.2.3. GatekeeperMt GK c xem l b no ca mng H.323, n chnh l im trung tm cho mi cuc gi trong mng H.323. Mc d l thnh phn ty chn nhng GK cung cp cc dch v quan trng nh vic dch a ch, s ban quyn v nhn thc cho u cui terminal v GW, qun l bng thng, thu thp s liu v tnh cc. Ngoi ra n cng cung cp dch v nh tuyn cuc gi. y l mt chc nng c rt nhiu u im v qu trnh gim st cuc gi cng nh nh tuyn qua GK s cung cp hot ng mng tt hn.

iu ny l do vic GK a ra quyt nh nh tuyn da trn rt nhiu yu t, v d nh yu t cn bng ti gia cc GW.

Hnh 3.7: Chc nng ca mt Gatekeeper Cc chc nng cn thit ca mt GK: Chc nng ch a ch nh ngha Ngi gi thng khng bit a ch IP ti u cui ca ngi nghe m ch bit b danh ca ngi . thit kp iu quyn nhp. (Admission cuc gi th Gatekeeper phi dch b danh ny sang a ch IP. khin Vi mt ti nguyn mng c th, ngi qun tr mng t ra truy mt ngng ch s hi thoi cng mt lc cho php trn mng . Gatekeeper c nhim v t chi kt ni mi mi khi t ti ngng. N iu khin quyn truy nhp mng ca

Control) ngi dng theo mc u tin gn trc. iu khin di Gim st v iu khin vic iu khin gii thng mng, ng thng (Bandwidth thi Gatekeeper cng phi m bo lu lng thng tin truyn thng khng vt qu ti ca mng do nh qun tr

Control) mng t ra. iu khin bo Ty chn Gatkeeper cung cp a ch ch cho ngi gi theo hiu cuc gi Control) hai ch trc tip v chn ng. Ti ch trc tip sau ng bt tay gia cc bn.Ti ch chn ng, a ch ch l a ch ca Gatekeeper nn n ng vai tr trung gian chuyn tip mi thng tin trao i trong qu trnh bt tay gia cc bn. Gatekeeper x l cc thng tin bo hiu Q.931 trao (Call Signalling khi cung cp a ch ch Gatekeeper ngng tham gia hot

i gia cc bn. Qun thng (Bandwidth Management) Dch v qun l Ty chn Gatekeeper lu tr mt danh sch cc cuc gi hin cuc gi (Call Management Service) Dch v xc Gatekeeper loi b cuc gi khi qu trnh xc nhn l sai ngay c khi cha ti ngng. (Call Authorilization Service) Dch v (Directory Service) Cc chc nng ty chn ca GK: Bo hiu iu khin cuc gi (Call Control Signaling). Chp nhn cuc gi (Call Authorization): GK c quyn quyt nh cho mt im cui (endpoint) c th thc hin mt cuc gi hay khng. Qun l cuc gi (Call Management): chc nng ny cho php GK lu tr tt c cc thng tin v cc cuc gi m n x l (cc cuc gi xut pht t vng hot ng ca n). Mt min H.323 (zone) trn c s mng IP l tp hp ca tt c cc u cui. Trong , mi u cui c gn vi mt b danh. Mi min c qun tr bi mt Gatekeeper duy nht, l trung tm u no, ng vai tr gim st mi hot ng trong min . y l thnh phn tu chn trong h thng VoIP theo chun H.323. Tuy nhin nu c mt GateKeeper trong mng th cc u cui H.323 v cc Gateway phi hot ng theo cc dch v ca Gatekeeper . Mi thng tin trao i ca Gatekeeper (ch C s d liu ca Gatekeeper cha thg tin v ngi s dng phc v qu trnh tm kim ngi dng. thi cung cp thng tin cho vic qun l gii thng v xc nh u cui no ang bn. l gii Ty chn Gatekeeper gii hn s cuc gi cng mt lc trong min ca n trong phin Q.931.

nhn cuc gi

dn) nin gim

u c nh ngha trong RAS. Mi ngi dng ti u cui c Gatekeeper gn cho mt mc u tin duy nht. Mc u tin ny rt cn thit cho c ch bo hiu cuc gi m cng mt lc nhiu ngi s dng. H.323 nh ngha c nhng tnh cht bt buc ti thiu phi c cho Gatekeeper v cc c tnh ty chn. Cc chc nng bt buc ti thiu ca mt Gatekeeper gm: Phin dch a ch, iu khin cho php truy nhp, iu khin di thng, qun l vng Cc chc nng ty chn ca gatekeeper gm c: Bo hiu iu khin cuc gi, cp php cho cuc gi, qun l cuc gi. Gatekeeper hot ng hai ch : Ch trc tip: Gatekeeper ch c nhim v cung cp a ch ch m khng tham gia vo cc hot ng kt ni khc. Ch chn ng: Gatekeeper l thnh phn trung gian, chuyn tip mi thng tin trao i gia cc bn.Vng hot ng

Mt vng hot ng H.323 l tp hp tt c cc u cui, cc GW v cc MCU chu s qun l duy nht ca mt GK. Vng hot ng ny c lp vi topo ca mng thc t v c th bao gm nhiu on mng (segment) ni vi nhau qua router hay cc thit b khc. M hnh v mt vng hot ng n gin c minh ha trong hnh sau:

Hnh 3.8: Mt vng hot ng

3.2.4. Multipoint Control UnitMultipoint Control Unit (MCU) l thnh phn h tr trong dch v hi ngh a im c s tham gia ca t 2 terminal H.323 tr ln.

Mi terminal tham gia vo hi ngh u phi thit lp mt kt ni vi MCU. V MCU qun l ti nguyn phc v cho hi ngh, thng lng gia cc terminal xc nh loi codec (Coder/Decoder) no cho ting v hnh c s dng ng thi x l dng thng tin truyn. Mt MCU bao gm 2 thnh phn con: b iu khin a im (Multipoint Controller MC) v thnh phn ty chn b x l a im (Multipoint Processor MP).

Hnh 3.9: Cu to ca Multipoint Control Unit MC c chc nng qun l bo hiu cuc gi. Trong lc , MP x l vic trn v chuyn mch cc dng thng tin cng nh cc qu trnh x l thng tin khc.

3.3. Cc giao thc thuc H.323Cc giao thc thuc H.323 bao gm

Giao thc m ha v gii m cho thoi gm c: G.711 (64kbps), G.722 (64, 56 v 48kbps), G.723.1 (5.3 v 6.3kbps) v G.729 (8kbps). Giao thc m ha v gii m cho tn hiu hnh bao gm: h.261 v H.263. Giao thc bo hiu RAS, giao thc bo hiu cuc gi H.245.

3.3.1. Giao thc bo hiu RAS (H.225.0)Giao thc RAS (Registration, Admission and Status) l giao thc c s dng thc hin vic ng k, qun l vic tham gia ca cc im cui, thay i bng thng, trao i trng thi v loi b ng k gia cc im cui vi GK. Cc bn tin RAS s c trao i qua knh bo hiu RAS v knh bo hiu ny s c thit lp u tin trc khi cc knh khc c thit lp. Ngoi ra, cc bn tin RAS c truyn qua giao thc UDP khng tin cy nn vic trao i cc bn tin ny c th b timeout v dn n vic chng s

c pht li. Cc bn tin RAS truyn qua UDP nh cc cng 1718 (cho multicast) v 1719 (cho unicast c ngha l ch truyn n 1 ni nhn). Ghi ch: cc endpoint y c th l GW hay terminal. Phn ln cc bn tin RAS c 3 loi: yu cu (request, thng c vit tt xRQ), xc nhn (confirm, vit ngn gn l xCF) v t chi (reject, vit gn l xRJ). Mt s trng hp c bit s c cp sau. Bo hiu RAS c cc chc nng c bn nh sau: Khm ph GK hay xc nh GK (Gatekeeper discovery): cho php mt endpoint xc nh GK iu khin n. Qu trnh ny c th c thc hin ng hay tnh. i vi qu trnh xc nh tnh th im cui bit trc a ch truyn ti (transport address) hay a ch mng ca GK qun l n. i vi qu trnh xc nh ng th im cui s pht i bn tin multicast GRQ (Gatekeeper discovery Request) tm GK iu khin mnh. Cc GK s phn hi bng bn tin GCF (confirm) tr li cho bn tin trn nu n chnh l GK iu khin ca im cui . Ngc li n s p ng bng bn tin GRJ (reject). C th c 1 hay nhiu GK l GK iu khin ca im cui a ra yu cu. ng k im cui (Endpoint Registration): qu trnh ng k c cc im cui s dng tham gia vo mt vng hot ng ng thi n thng bo cho GK qun l n a ch truyn ti cng nh b danh (alias) ca mnh. im cui mun ng k n 1 GK no s gi bn tin RRQ (Registration Request). Nu GK ng cho im cui tham gia vo mng s p ng cho im cui bng bn tin RCF (confirm). Nu khng th im cui s nhn c phn hi RRJ (reject) v n s khng c GK cung cp bt c mt dch v no. Xc nh v tr ca im cui (Endpoint Location): y l qu trnh xc nh a ch truyn ti ca mt endpoint trong trng hp ch bit b danh ca n. C GK hay im cui c th thc hin chc nng ny. Bn c yu cu xc nh im cui s pht bn tin LRQ (Location Request). Ni nhn yu cu c p ng c hay khng th hin qua bn tin phn hi LCF (confirm) hay LRJ (reject). iu khin vic tham gia (Admission control): y l qu trnh xem xt s cho php tham gia ca mt endpoint no vo mt phin lm vic. u tin, endpoint mun tham

gia vo phin lm vic th n s gi yu cu n GK qun l n bng mt bn tin ARQ (Admission Request). Nu GK chp nhn th n s p ng bng bn tin ACF (confirm), ngc li th bn tin ARJ (reject) s c tr v. Thot khi kt ni (Disengage): khi c 1 im cui mun thot khi mt kt ni th n s gi n GK bn tin DRQ (Disengage Request). Nu yu cu trn c ng n s nhn c p ng DCF (confirm), ngc li s nhn c DRJ (reject). S thay i bng thng (Bandwidth change): y l chc nng yu cu thay i bng thng cho mt kt ni no , c th c yu cu bi endpoint tham gia kt ni hay GK. Bn mun thay i bng thng s pht ra bn tin BRQ (Bandwidth Request). Bn nhn yu cu ny nu chp nhn s phn hi bng bn tin BCF (confirm), ngc li s p ng bng bn tin BRJ (reject). Trao i thng tin trng thi (Status hay cn gi l Information): l qu trnh c s dng bi GK v endpoint EP thng bo cho GK cc thng tin trng thi ca mt kt ni no . Khi GK mun bit thng tin trng thi v cuc gi no n s gi bn tin IRQ (Information Request). Endpoint gi tr cc thng tin chi tit v cuc gi yu cu bng bn tin phn hi l IRR (Information Response). Ngoi ra trong bo hiu RAS cn c mt s chc nng sau: qu trnh loi b ng k ca mt im cui ra khi vng hot ng v s qun l ca 1 GK (Unregistration). Qu trnh ny l qu trnh ngc li vi qu trnh ng k, v cc bn tin c th c trao i khi thc hin chc nng ny l URQ (Unregistration Request), UCF (confirm), URJ (reject). Ngoi ra im cui c th bit kh dng ca ti nguyn (xem ti nguyn n s dng n gii hn cho php hay cha) bng cch gi bn tin RAI (Resource Availability Indicate). GK s phn hi bng bn tin RAC (Resource Availability Confirm). Mt chc nng khc na l kch hot mt s loi dch v c bit bng bn tin SCI (Service Control Indication). Bn tin phn hi l SCR (Service Control Response). Chc nng ny c s dng bi c cc im cui v GK. Mt s bn tin chc nng khc c s dng trong cc trng hp c bit l Unknown Message Response v Non-standard Message.

3.3.2. Giao thc bo hiu cuc gi H.225y l giao thc h trc cc chc nng bo hiu cho mt cuc gi, c s dng thit lp knh kt ni gia cc endpoint. Qu trnh trao i cc bn tin bo hiu cuc gi H.225 c thc hin qua knh bo hiu cuc gi, l knh truyn tin cy

s dng giao thc TCP. Cc bn tin H.225 c trao i trc tip gia cc endpoint nu khng c GK trong mng H.323. Nu trong mng c GK, cc bn tin ny c th c truyn trc tip gia cc endpoint hay c truyn thng qua GK ti cc endpoint. Cch thc truyn s c xc nh trong qu trnh thc hin bo hiu RAS, qua bn tin tham gia cuc gi. Cc bn tin c bn bao gm: Bn tin SETUP: c s dng khi mt im cui mun thc hin mt kt ni vi mt im cui khc. Nu n s dng cch thc truyn thng qua GK th mun pht bn tin ny i trc ht n phi nhn c bn tin ACF ca GK. Bn tin CALL PROCEEDING: bn tin ny cho bit bn tin SETUP c nhn v th tc thit lp cuc gi ang c tin hnh. Bn tin ALERTING: im cui b gi s pht bn tin ny cho bit n ang c cnh bo c 1 cuc gi n n. Bn tin CONNECT: c pht i bi im cui b gi, nhm thng bo n chp nhn cuc gi. Bn tin RELEASE COMPLETE: bn tin ny dng kt thc cuc gi. Ngoi ra cn c cc bn tin sau: bn tin PROGRESS, bn tin FACILITY, bn tin STATUS, bn tin STATUS INQUIRY, bn tin SETUP ACKNOWLEDGE v bn tin NOTIFY. Hnh sau minh ha mt bo hiu cuc gi c bn s dng giao thc bo hiu H.225:

Hnh 3.10: Qu trnh bo hiu cuc gi c bn s dng H.225

3.3.3. Giao thc bo hiu iu khin H.245Bo hiu iu khin H.245 ging bo hiu iu khin Q.931 nhng khng phi tt c cc bn tin c trong Q.931 u c s dng trong H.245 m c nhng khc bit nht nh. Bo hiu iu khin H.245 dng trao i cc bn tin iu khin H.245 t u cui n u cui (end-to-end, khng phi l terminal) gia cc im cui H.323 (endpoint). Cc bn tin H.245 c truyn trn knh iu khin H.245. Knh ny l knh lun l s 0 v lun lun c m (m thng trc). Cc bn tin H.245 dng trao i v kh nng ca cc terminal v dng yu cu m hay ng cc knh lun l. Lu cc knh lun l y l cc knh mt chiu. C 4 loi bn tin H.245 l bn tin yu cu (Request), bn tin p ng (Response), bn tin lnh (Command) v bn tin ch nh (Indication). Mt bn tin yu cu cn phi c i km theo sau l mt bn tin p ng, trong khi bn tin lnh th khng nht thit cn c bn tin p ng. Cc chc nng chnh ca H.245 l Trao i kh nng (Terminal Capability Exchange) Bo hiu knh lun l (Logical Channel Signaling) Xc nh Master/ Slave (Master/ Slave Determination) iu khin hi ngh (Conference Control) y ch trnh by 2 chc nng u tin nhm minh ha cho qu trnh thc hin cuc gi c trnh by phn sau, ngh cc bn SV t tm hiu thm 2 chc nng cn li ca bo hiu H.245 hiu r hn cc hot ng ca bo hiu ny.2 chc nng cn li c ng dng ch yu trong dch v hi ngh a im (Multipoint Conference). * Trao i kh nng Qu trnh trao i kh nng s dng cc bn tin ca cc terminal ang lin lc vi nhau cung cp cho im cui ngang cp vi n thng tin v kh nng truyn v nhn ca mnh. Kh nng truyn l kh nng ca cc terminal truyn cc dng thng tin, trong khi kh nng nhn bao hm c vic nhn v x l dng thng tin n ca terminal.

Vic trao i kh nng gia 2 im cui l cn thit c 2 c th c cng phng thc CODEC trong qu trnh tham gia mt kt ni. Cc kh nng s c nh s trong mt bng gi l bng kh nng (Capabiltity Table). Mi kh nng s c km theo cc thuc tnh ca mnh v chng cng c lu tr trong bng trn Bao gm cc bn tin c bn sau: TerminalCapabilitySet: l bn tin dng request c im cui ch gi gi cho im cui b gi nhm thng bo cho bn b gi bit kh nng ca mnh. TerminalCapabilitySetAck: khi im cui b gi nhn c bn tin TerminalCapabilitySet v nhn bit c kh nng ca bn gi th n s tr p ng bng bn tin ny. TerminalCapabilitySetReject: l bn tin t chi ca bn tin TerminalCapabilitySet. TerminalCapabilitySetRelease: l bn tin loi ch nh nhm thng bo n (bn ch gi) pht i bn tin TerminalCapabilitySet nhng cha nhn c p ng trong mt thi gian cho trc no . * Bo hiu knh lun l Mt im cui c th yu cu thit lp mt knh lun l bng cch gi bn tin openLogicalChannel. im cui nhn yu cu ny c th chp nhn hoc t chi. Nu ng , n s p ng bng bn tin openLogicalChannelAck, ngc li n s gi bn tin phn hi openLogicalChannelReject. Qu trnh ng knh lun l cng din ra tng t nh trn vi cc bn tin closeLogicalChannel, closeLogicalChannelAck. c th ng 1 knh bo hiu iu khin H.245 th im cui trc ht phi ng tt c cc knh lun l v ch tt c bn tin p ng cho yu cu ng cc knh lun l . Sau n s gi mt lnh (command) endSession cho im cui b gi v i n lc nhn c p ng endSession t pha bn kia th n mi c th ng knh bo hiu iu khin H.245.

3.4. Cc th tc bo hiu cuc giQu trnh thc hin 1 cuc gi tiu biu trong H.323 bao gm cc giai on sau: Khm ph GK v ng k: s dng bo hiu RAS.

Thit lp cuc gi: ln lt s dng bo hiu RAS (c th trong giai on ny xy ra qu trnh xc nh im cui thng qua b danh alias) v H.225. Qu trnh thng tho cc thng s cuc gi v xc nh kh nng ca im cui: s dng bo hiu H.245. Qu trnh trao i thng tin: s dng giao thc RTP/ RTCP. Kt thc cuc gi: ln lt s dng bo hiu H.245, H.225 v RAS. Cc hnh sau s minh ha cc giai on bo hiu ca qu trnh thc hin 1 cuc gi trong mng H.323. y khng xt n qu trnh pht hin Gatekeeper cng nh qu trnh ng k (gi s cc qu trnh ny c thc hin trong giai on u mi thit lp mng). Trong cc minh ha sau ta s xt n qu trnh bo hiu gia 2 terminal c thng qua GK. Lc ny cc terminal nhn bit c GK qun l mnh v gi s khng xy ra qu trnh xc nh im cui.

3.4.1. Pha A Thit lp cuc giKhi thu bao c nhu cu trao i thng tin, thu bao s yu cu mng thit lp mt cuc gi. Ty thuc vo cu hnh c th trong vng mng ca thu bao ch gi v b gi m qu trnh thit lp cuc g c th khch nhau. Nhng ni chung, trc ht u cui ch gi phi ng nhp mng, thit lp mt knh bo hiu cuc gi trao i cc bn tin thit lp cuc gi H.225.0. Mc tiu ca qu trnh ny l phi thit lp nn mt knh iu khin cuc gi gia cc thch th tham gia cuc gi trao i cc bn tin iu khin H.245 trong pha thit lp cuc gi. Trong th tc thit lp cuc gi khng c s ng b ha v phn bit r rng gia hai im u cui. iu ny c ngha im u cui A c th gi mt bn tin thit lp cuc gi ti im u cui A. iu ny c ng dng xc nh c phi ch c mt yu cu hay khng v a ra hnh ng ph hp. i vi im u cui, hnh ng ny c th ch ra rng n bn nu bt c lc no cng c bn tin thit lp cuc gi ng i. Nu im u cui h tr nhiu cuc gi cng mt lc th n ch ra rng n bn khi nhn c cc bn tinthit lp t cng mt im u cui. im u cui c kh nng gi bn tin cnh bo (Alerting). Cnh bo c ngi l pha b gi c thng bo v cuc gi n. Thng bo ny ch im u cui c gi cui cng v ch sau khi thng bo ti ngi dng. Trong trng hp lm vic thng qua Gateway. Gateway s gi thng bo khi nhn c ch th chung t SCN. Nu

im u cui p ng li bn tin kt ni, tip tc cuc gi, hon thnh gii phng trong 4s th n khng yu cu gi bn tin Alerting. im u cui gi bn tin thit lp c th nhn c bn tin hoc l thng bo, tip tc cuc gi hoc hon thnh gii phng trong vng 4s sau khi truyn dn thnh cng.

3.4.1.1. Thit lp cuc gi c bn khng qua GatekeeperTrong trng hp ny, c bn ch gi v b gi u khng c ng k vi gatekeeper. Do chng khng phi tin hnh cc th tc ng nhp mng m chng s thc hin trao i bo hiu trc tip vi nhau. im u cui (ch gi) s gi mt bn tin Setup(1) ti nhn dng TSAP knh bo hiu cuc gi ca im u cui 2 (b gi) nh bit c a ch ny. im u cui 2 s p ng vi cc bn tin Call Proceeding (2), Alerting (3) ng thi to ra mt knh iu khin H.245. Cui cng, n p ng bng mt bn tin Connect (4) mang a ch truyn ti knh iu khin H.245 thng bo cho bn ch giEndpoint 1 Setup (1) Endpoint 2

Call proceeding (2)

Alerting (3)

Connect (4)

Bn tin bo hiu cuc gi

Hnh 3.11: Thit lp cuc gi c bn khng c Gatekeeper

3.4.1.2. Hai im u cui c ng k ti cng mt gatekeeperTrong trng hp ny, trc ht bn ch gi phi tin hnh ng nhp mng qua knh RAS. Gatekeeper s quyt nh cho php ng nhp hay khng. Nu

gateeeper cho php, n s quyt nh c tham gia vo qa trnh bo hiu thit lp cuc gi hay khng v s gi cho bn ch gi mt a ch truyn ti knh bo hiu cuc gi tng ng.Endpoint 1ARQ (1) ACF (2) Setup (3) Call proceeding (5) Setup (4) Call proceeding (5) ARQ (6) ACF/ARJ (7)

Gatekeeper

Endpoint 2

Alerting (8)

Alerting (8) Connect (9) Connect (10)

HBn tin RAS Bn tin bo hiu cuc gi

nh 3.12: Hai im cui ng k Gatekeeper nh tuyn bo hiuTrong trng hp gatekeeper quyt nh tham gia vo qu trnh bo hiu cuc gi, a ch truyn ti knh bo hiu cuc gi ca gatekeeper s c gi ti bn ch gi. Khi , bn tin Setup ss c nh tuyn thng qua gatekeeper gi n bn b gi. u cui b gi cng phi xin php gatekeeper dng nhp mng trc khi c th p ng cho bn ch gi. Cc bn tin p ng ny cng c nh tuyn tr li thng qua gatekeeper. im u cui 1 khi to trao i ARQ(1)/AFC(2) vi gatekeeper. Gatekeeper s gi li a ch truyn dn knh bo hiu cuc gi ca chnh n trong ACF. Sau

im u cui 1 gi bn tin thit lp (3) bng cch dng a ch truyn dn trn. Tip theo, Gatekeeper gi bn tin thit lp (4) ti im u cui 2. Nu im u cui 2 chp nhn cuc gi n khi to trao i ARQ(6)/ACF(7) vi Gatekeeper.Endpoint 1ARQ (1) ACF/ARJ (2) Setup (3)

Gatekeeper

Endpoint 2

Call proceeding (4) ARQ (5) ACF/ARJ (6)

Alerting (7) Connect (8)

Bn tin RAS Bn tin bo hiu cuc gi

Hnh 3.13 Hai im cui ng k vi Gatekeeper Bo hiu cuc gi trc tipTrong trng hp im u cui 2 nhn c ARJ n gi bn tin hon thnh

gii phng ti Gatekeeper. im u cui 2 p ng vi bn tin kt ni (9) vi a ch truyn dn knh iu khin H.245 dng trong bo hiu H.245. Gatekeeper gi bn tin kt ni (10) ti im u cui 1 vi a ch truyn dn knh iu khin H.245 ca Gatekeeper, trn c s Gatekeeper c chn phng thc nh tuyn knh iu khin H.245 hay khng.

Trong trng hp gatekeeper quyt nh bo hiu trc tip, th n s gi ti u cui ch gi a ch truyn ti knh bo hiu cuc gi ca thu bao b gi. a ch ny c c nh dch v bin dch a ch ca gatekeeper. Sau , cc bn tin bo hiu s c trao i trc tip gia hai im u cui da vo a ch ny. Khi nhn c bn tin Setup, bn b gi s phi yu cu ng nhp mng trc khi c th tr li cho bn b gi. Sau , cc bn tin thit lp cuc gi s c hai bn trao i trc tip vi nhau.

3.4.1.3. Ch ch gi ng kTrong trng hp ny trc ht u cui ch gi phi tin hnh trao i cc bn tin ARQ/ACF vi gatekeeper qun l n, sau khi c chp nhn ng nhp nu gatekeeper c th quyt nh tham gia hoc khng tham gia vo qu trnh bo hiu gia hai u cui. Trong trng hp gatekeeper quyt nh tham gia vo qu trnh bo hiu, a ch m u cui ch gi nhn c l a ch truyn ti knh bo hiu cuc gi ca gatekeeper v cc bn tin bo hiu H.225.0 s c trao i gia hai u cui thng qua gatekeeper. im u cui 1 khi to trao i ARQ(1)/ACF(2) vi gatekeeper. Gatekeeper gi li a ch truyn dn knh bao hiu cuc gi ca chnh n trong ACF(2). Sau im u cui 1 gi bn tin thit lp bng cch dng a ch truyn dn trn. Tip theo Gatekeeper gi bn tin thit lp (4) ti a ch truyn dn knh bo hiu cuc gi chung (well-known) ca im u cui 2. Nu im u cui 2 chp nhn cuc gi n p ng bng bn tin kt ni (7) vi a ch truyn dn knh bo hiu H.245 dng cho bo hiu H.245. Gatekeeper gi bn tin kt ni (8) ti im u cui 1 vi a ch truyn dn knh iu khin H.245 ca im u cui 2 hoc a ch truyn dn knh iu khin H.245 ca Gatekeeper, trn c s Gatekeeper c chn nh tuyn knh iu khin H.245 hay khng.

Endpoint 1ARQ (1) ACF/ARJ (2)

Gatekeeper

Endpoint 2

Setup (3) Call proceeding (4)

Setup (4) Call proceeding (5)

Alerting (6) Alerting (6) Connect (7) Connect (7)

Bn tin RAS Bn bo hiu cuc gi

Hnh 3.14: Ch gi ng k vi Gatekeeper nh tuyn bo hiu cuc gi

Endpoint 1

Gatekeeper

Endpoint 2ARQ (1) ACF/ARJ (2) Setup (3)

Call proceeding (4) Alerting (5) Connect (6)

HBn tin RAS Bn tin bo hiu cuc gi

nh 3.15: Ch gi ng k vi Gatekeeper bo hiu cuc gi trc tipTrong trng hp gatekeeper quyt nh bo hiu trc tip. Ban u, im u cui 1 khi to trao i ARQ(!)/ACF(2) vi Gatekeeper. Sau im u cui 1 gi bn tin thit lp (3) ti im u cui 2 bng cch dng a ch truyn dn kiu bo hiu cuc gi qung b (wellknown). Nu im u cui 2 chp nhn cuc gi n p ng bng bn tin kt ni (6) vi a ch truyn dn knh iu khin H.245 dng cho bo hiu H.245.

3.4.1.4. Ch c b gi ng k gatekeeperTrong trng hp ny, ch c bn b gi c ng k vi gatekeeper. Nu nh Gatekeeper chn bo hiu cuc gi trc tip, im u cui 1 gi bn tin thit lp (1) ti im cui 2 bng cch dng a ch truyn dn knh bo hiu cuc gi qung b

(well-known). Nu im cui 2 chp nhn cuc gi n khi to trao i ARQ(3)/ACF(4) vi Gatekeeper. Nu im cui 2 chp nhn cuc gi n khi to trao i ARQ(3)/ACF(4) vi Gatekeeper. Nu im cui 2 nhn c ARQ(4) th n gi hon thnh gii phng ti im cui 1. im cui 2 p ng bng bn tin kt ni (6) vi a ch truyn dn knh iu khin H.245 dng bo hiu H.245.Endpoint 1 Gatekeeper Endpoint 2

Setup (1)

Call proceeding (2) ARQ (3) ACF/ARJ (4) Alerting (5)

Connect (6)

Bn tin RAS Bn tin bo hiu cuc gi

Hnh 3.16: im u cui b gi ng k bo hiu cuc gi trc tipTrong trng hp Gatekeeper tham gia nh tuyn bo hiu cuc gi. im u cui 1 gi bn tin thit lp (1) ti a ch truyn dn knh bo hiu cuc gi qung b

(well-known) ca im cui 2.

Gatekeeper

Endpoint 2

Endpoint 1

Setup (1)

Call proceeding (2) ARQ (3) ACF/ARJ (4) Facility (5) Release Complete (6) Setup (7) Call proceeding (8) Call proceeding (8) ARQ (9) ACF/ARJ (10) Alerting (11) Connect (12) Alerting (11) Connect (12) Setup (7)

Bn tin RAS Bn tin bo hiu cuc gi

Hnh 3.17: im u cui b gi ng k nh tuyn bo hiu cuc giNu im cui 2 chp nhn cuc gi n khi to trao i ARQ(3)/ACF(4) vi gatekeeper. Nu chp nhn gatekeeper s gi a ch truyn dn knh bo hiu cuc

gi ca chnh n trong ARJ(4) vi m ca routCallToGatekeeper. im cui 2 p li im cui 1 bn tin Facility(5) gm c a ch truyn dn knh bo hiu cuc gi ca Gatekeeper ca n. Sau im cui 1 gi bn tin hon thnh gii phng (6)ti im cui 2. im u cui 1 gi bn tin thit lp (7) ti a ch truyn dn knh bao hiu cuc gi ca Gatekeeper. Gatekeeper gi bn tin thit lp (8) ti im cui 2. im cui 2 p li bng bn tin kt ni (12) vi a ch truyn dn knh bo hiu H.245 ca n dng cho bo hiu bn tin kt ni (12) vi a ch truyn dn knh bo hiu H.245 ca n dng cho bo hiu H.245. Gatekeeper s di bn tin kt ni (13) ti im cui 1 vi a ch truyn dn knh iu khin H.245 ca Gatekeeper, trn c s Gatekeeper c chn knh iu khin H.245 hay khng.

3.4.1.5. Hai im u cui c ng k ti hai gatekeeper khc nhauEndpoint 1ARQ (1) ACF/ARJ (2)

Gatekeeper 1

Gatekeeper 2

Endpoint 2

Setup (3)

Call proceeding (4) ARQ (5) ACF/ARJ (6) Alerting (7)

Connect (8)

Bn tin RAS Bn tin bo hiu cuc gi

Hnh 3.18: Hai im cui ng k bo hiu cuc gi trc tip

y cng l mt trng hp rt hay xy ra trong thc t. C hai im u cui u c ng k nhng ti hai vng ng vi hai gatekeeper khch nhau v cc Gatekeeper u chn bo hiu cuc gi trc tip, khi im u cui 1 khi to trao i ARQ(1)/ACF(2) vi Gatekeeper 1. Gatekeeper 1 gi li a ch truyn dn knh bo hiu cuc gi ca im u cui 2 trong bn tin ACF, nu Gatekeeper 1 c mt phng thc truyn thng vi Gatekeeper 2. Sau im u cui 1 gi bn tin thit lp (3) ti a ch truyn dn m Gatekeeper gi n hoc a ch truyn dn knh bo hiu cuc gi qung b ca im cui 2. Nu im cui 2 chp nhn cuc gi n khi to trao i ARQ(5)/ACF(6) vi Gatekeeper 2. C th im cui 2 nhn c ARJ(6), trong trng hp ny n gi ban tin hon thnh gi phng ti im cui 1. im cui 2 p li bng bn tin kt ni vi a ch truyn dn knh iu khin H.245. i vi trng hp hai im cui ng k vi cc Gatekeeper khc nhau v Gatekeeper ca im cui gi chn bo hiu cuc gi trc tip, Gatekeeper ca im cui b goi chn nh tuyn bo hiu cuc gi th khi , im cui 1 khi to trao i ARQ(1) /ACF(2) vi Gatekeeper 1. Gatekeeper 1 gi tr a ch truyn dn knh bo hiu cuc gi ca im cui 2 trong ACF(2) nu Gatekeeper 1 c phng thc truyn thng vi Gatekeeper 2. Sau im cui 1 gi bn tin thit lp (3) ti a ch truyn dn do Gatekeeper 1 gi li hoc a ch truyn dn knh bo hiu cuc gi ca im cui 2. Nu im cui 2 chp nhn cuc gi n khi to trao i ARQ(5)/ACF(6) vi gatekeeper 2. Nu chp nhn Gatekeeper 2 s gi li a ch truyn dn knh bo hiu cuc gi ca chnh n trong ARJ vi m ca routCallToGatekeeper. im cui 2 p ng li im cui 1 bng bn tin Facility(7) vi a ch truyn dn bo hiu cuc goi ca Gatekeeper 2. Sau im cui 1 gi bn tin hon thnh gii phng (8) ti im u cui 2. im cui 1 s gi ARQ(9) yi Gatekeeper 1. Gatekeeper 1 p li bng DCF(10). Sau im cui 1 khi to ARQ(11)/ACF(12) mi vi Gatekeeper 1.

Gatekeeper +

Gatekeeper

Endpoint 2

Endpoint 1ARQ (1) ACF (2)

Setup (3)

Call proceeding (4) ARQ (5) Facility (7) Release complete (8) DRQ (9) DCF (10) ARQ (11) ACF (12) Call proceeding (4) Setup (13) ACF/ARJ (6)

Setup (14) Call proceeding (4) ARQ (15) ACF/ARJ (16)

Alerting (17)

Alerting (17) Connect (18)

Alerting (19)

Endpoint 1ARQ (1) ACF (2)

Setup (3)

Call proceeding (4) ARQ (5) Facility (7) Release complete (8) DRQ (9) DCF (10) ARQ (11) ACF (12) Call proceeding (4) Setup (13) ACF/ARJ (6)

Setup (14) Call proceeding (4) ARQ (15) ACF/ARJ (16)

Alerting (17)

Alerting (17) Connect (18)

Alerting (19)

Bn tin RAS

Bn tin bo hiu cuc gi

Hnh 3.19: Hai im u cui ng k - bo hiu trc tip /nh tuynim cui 1 gi bn tin thit lp (13) ti a ch truyn dn knh bao hiu cuc gi ca Gatekeeper. Gatekeeper 2 gi bn tin thit lp (14) ti im cui 2. im cui 2 khi to trao i ARQ(15)/ACF(16) vi Gatekeeper 2. im cui 2 p ng bng bn tin kt ni (18) vi a ch truyn dn knh iu khin H.245 ca n dng cho bo hiu H.245. Gatekeeper 2 gi bn tin kt ni (19) ti im cui 1 vi a ch truyn dn kn iu khin H.245 ca im cui 2 hoc a ch truyn dn knh iu

khin H.245 ca Gatekeeper 2 trn c s Gatekeeper c chn nh tuyn knh iu khin H.245 hay khng.Enpoint 1ARQ (1) ACF (2) Setup (3) Call proceeding (5)

Gatekeeper 1

Gatekeeper 2

Enpoint 2

Setup (4) Call proceeding (5) ARQ (6) ACF/ARJ (7)

Alerting (8)

Alerting (8)

Conennect (10)

Conennect (9)

Bn tin RAS Bn tin bo hiu cuc gi

Hnh 3.20: Hai im u cui ng k bo hiu nh tuyn/trctipTrong trng hp Gatekeeper 1 ca im cui 1 ch nh tuyn bo hiu cuc gi, Gatekeeper 2 bo hiu cuc gi trc tip. im cui 1 khi to trao i ARQ(1)/ACF(2) vi Gatekeeper 1. Gatekeeper 1 gi tr a ch truyn dn knh bo hiu cuc gi ca im cui 2 trong ACF(2). Sau im cui 1 gi bn tin thit lp (3) ti a ch truyn dn do Gatekeeper 1 gi li. Sau Gatekeeper 1 gi bn tin thit lp (4) vi a ch truyn dn knh bo hiu cuc gi ca n ti a ch truyn dn quqngr b knh bo hiu cuc gica im cui 2. Nu im cui 2 chp nhn cuc gi n khi to trao i ARQ(6)/ACF(7) vi Gatekeeper 2. C th im cui 2 nhn c ARJ, trong trng hp ny, n gi bn tin hon thnh gi phng ti im cui 1. im cui 2 p ng Gatekeeper 1 bng bn tin kt ni (9) vi a ch truyn dn knh iu khin H.245 ca n dng cho bo hiu H.245 ca im cui 2 hoc a ch truyn

dn knh iu khin H.245 ca im cui 2 hoc a ch truyn dn knh iu khin H.245 ca Gatekeeper, trn c s Gatekeeper c chn iu khin H.245 hay khng.

Enpoint 1ARQ (1) ACF (2)

Gatekeeper 1

Gatekeeper 2

Enpoint 2

Setup (3) Call proceeding (5)

Setup (4) Call proceeding (5) ARQ (6) ACF/ARJ (7) Facility (8) Release Complete (9)

Bn tin RAS Setup (10) Bn tin bo hiu cuc gi

Setup (11)Call proceeding (5)

ARQ (12) ACF/ARJ (13) Alerting (14) Alerting (14) Alerting (14) Conennecting (16) Connect (17) Conennecting (15)

Hnh 3.21: Hai im u cui ng k c hai inh tuyn cui giCn i vi trng hp hai im cui ng k vi cc Gatekeeper khc nhau v c hai Gatekeeper chn nh tuyn bo hiu cuc gi th im cui 1 khi to trao i ARQ(1)/ACF(2) vi Gatekeeper 1, Gatekeeper 1 gi li a ch truyn dn knh bo hiu cuc gi ca n trong ACF(2). Sau im cui 1 gi bn tin thit lp (3) dng a ch truyn dn trn. Tip theo Gatekeeper 1 gi bn tin thit lp (4) ti a ch qung b knh bo hiu cuc gi ca im cui 2. Nu im cui 2 chp nhn cuc gi, n khi to trao i ARQ(6)/ACF(7) vi Gatekeeper 2. Nu chp nhn Gatekeeper 2 s gi li a ch truyn dn knh bo hiu cuc gi trong ARJ(7) vi m ca routeCallToGatekeeper. im cui 2 tr li Gatekeeper 1 vi bn tin Faclity(8) cha a ch truyn dn knh bo hiu cuc gi ca Gatekeeper 2. Sau Gatekeeper 1 gi bn tin hon thnh gi phng (9) ti im cui 2. Sau Gatekeeper 1 gi bn tin thit lp (10) ti a ch truyn dn knh bohiu cuc gi ca Gatekeeper 2. im cui 2 khi to trao i ARQ(12)/ACF(13) vi Gatekeeper 2. Sau im cui 2 p ng Gatekeeper 2 bng bn tin kt ni (15) cha a ch truyn dn knh iu khin H.245 . Sau im cui 2 p ng Gatekeeper 2 bng bn tin kt ni (15) cha a ch truyn dn knh iu khin H.245 dng cho bo hiu H.245. Gatekeeper 2 gi bn tin kt ni (16) ti Gatekeeper 1 cha a ch truyn dn knh iu khin H.245 hoc a ch truyn dn knh iu khin H.245 ca Gatekeeper 2 trn c s Gatekeeper 2 c chn nh tuyn knh iu khin H.245 hay khng. Gatekeeper 1 gi bn tin kt ni (17) ti im cui 1 cha a ch truyn dn knh iu khin H.245 c gi ti Gatekeeper 2 hoc a ch truyn dn knh iu khin H.245 trn c s Gatekeeper 1c chn nh tuyn knh iu khin H.245 hay khng.

3.4.1.6. Cuc gi c thit lp qua Gatewayy l mt cuc gi c thc hin gia mt u cui trong h thng H.232 vi mt u cui khc mt h thng phi H.232. Trong trng hp mt u cui bn ngoi thc hin mt cuc gi ti mt im u cui ca mng H.232 thng qua mt Gateway, vic thit lp cuc gi gia

Gateway v im u cui mng s c x l ging nh trong trng hp hai im u cui ca mng thit lp cuc gi vi nhau. Trong trng hp mt im u cui trong mng H.323 cn thit lp cuc gi ti mt u cui bn ngoi mng thng tin qua mt gateway. Qu trnh thit lp cuc gi gia hai im u cui trong mng H.323. Gateway s nhn c a ch ch ( E.164 hoc privateNumber) trong bn tin Setup. Sau , n s s dng a ch ny thit lp cuc gi bn ngoi mng H.323. Gateway c th tr li cc bn tin Call Proceeding cho im u cui trong mng trong khi n ang thit lp cuc gi bn ngoi.

3.4.2. Pha B: Khi to knh iu khin v trao i kh nngSau khi hai bn b gi v ch gi trao i cc bn tin thit lp cuc gi t pha A chng s thit lp knh iu khin H.245. Nhim v ca knh ny l nh tuyn cc bn tin ITU T Rec.H.245 trao i kh nng gia cc im cui v m cc knh phng tin. Knh iu khin H.245 c th c thit lp bi bn b gi sau khi nhn c bn tin Setup hoc bn ch gi sau khi nhn c Alerting hay Call Proceeding. Trong trng hp khng nhn c bn tin Connect hay mt im cui gi i bn tin Release Complete, knh H.245 s b ng li. Cc kh nng ca im u cui s c trao i bng cch truyn i bn tin H.245 terminalCapabilitySet. Bn tin ny s l bn tin H.245 u tin c gi tr khi im u cui ch th rng n hiu trng parallelH245Control. Nu trc khi hon thnh vic trao i kh nng ca u cui m c bt k mt th tc no b li th im cui khi to knh s to ra mt bn tin hon tt v kh nng u cui trc khi c gng bt k mt th tc no khc. Mt im cui nu nhn c mt bn tin terminalCapabilitySet t im cui pha bn kia khi to trao i kh nng s p ng v to ra mt bn tin hon tt v trao i kh nng vi pha bn kia khi to bt k mt th tc no khc. im cui s h tr th tc xc nh ch - khch (master slaver). Trong trng hp hai im cui trong cuc u c kh nng MC, vic xc nh ch khch c dng xc nh MC no l MC hot ng trong hi ngh. Sau MC hot ng s gi bn tin meLocationIndication. Th tc cng cung cp kh nng xc nh ch khch m knh hai hng i vi d liu. Vic xc nh ch khch t c trong bn tin H.245 u tin sau khi trao i kh nng u cui c khi to.

Nu trao i kh nng khi to hoc th tc xc nh ch khch tht bi chng s c th li thm t nht hai ln trc khi im cui b kt ni v thc hin tip pha C. Khi hon thnh cc yu cu ca pha B im cui chuyn sang pha C.

3.4.3. Pha C: Thit lp knh truyn thngTip theo qu trnh trao i kh nng v xc nh ch khch, th tc H.245 s c s dng m knh logic cho nhng lung thng tin khc nhau. Trong , cc knh logic thit lp cho cc dng audio v video s c truyn ti qua nhn dng TSAP ng v s dng giao thc khng tin cy UDP cn cc knh logic thit lp cho cc dng d liu s s dng mt giao thc tin cy TCP. Khi c nhu cu m mt knh logic, mt bn tin yu cu openlogicalChannel s c gi i. p ng cho bn tin ny, hoc bn tin openLogicalChannelAck hay reverseLogicalChannelIParameters s c tr li. Trong bn tin tr li ny c cha a ch truyn ti m bn im cui nhn bn tin yu cu gn cho knh logic. T , a ch truyn ti ny s c s dng gi cc dng thng tin thuc knh logic tng ng.Sau khi cc knh logic c m, mt bn tin h2250MaximumSkewIndication s c gi i bi bn pht trong mi cp truyn thng lin quan xc nhn cc thng s ca knh truyn. Thay i mode

Trong mt phin lm vic th tc thay i cu trc knh, kh nng kiu nhn, s c thc hin trong khuyn ngh v H.245.

3.4.3.1. Trao i video bng tha hip tng hCh th videoIndicateReadyToActive c nh ngha trong khuyn ngh H.245 ca IUT-T. y l mt ty chn. Khi th tc ny c chn n hot ngt heo cc bc sau. im u cui 1 c thit lp sao cho video khng c truyn dn cho n khi im u cui 2 ch th sn sng tuyn dn video. im u cui 1 s gi ch th videoIndicateReadyToActive khi trao i kh nng khi to hon thnh, nhng s khng truyn tn hiu video n khi n nhn hoc l videoIndicateReadyToactive hoc l tn hiu video n t im u cui 2. im u cui khng c thit lp ty chn ny khng bt buc phi i cho n khi nhn videoIndicateReadyToActive hoc trc khi truynd video ca n.

3.4.3.2. Phn b a ch lung phng tinTrong phng thc hot ng n im, im cui s m knh logic ti MCU hoch im cui khc. a ch c truyn trong bn tin openLogicalChannelACK Trong phng thc hot ng da im MC gn a ch a im v phn phi ti im cui trong bn tin communicationModeCommand. Trch nhim ca MC l nh v v gn a ch a im duy nht. im cui gi bn tin openLogiclChannel ti MC bng a ch a im c gn. MC s tip tc gi bn tin openLogicalChannel ti didm cui nhn. Trong trng hp lung phng tin t mt im cui a im trong hi ngh c truyn dn trong mt phin lm vic n (V d l a ch a im n) th MC s m mt knh logic ti mi im u cui nhn lung phng tin t mt im cui trong hi ngh. Trong trng hp im cui tham gia vo hi ngh sau khi bn tin khi to CommunicationModeCommand c truyn MC c trch nhim gi communicationModeCommand cp nht n im u cui mi v m mt knh logic ph hp cho lung phng tin t im cui mi. Trong trng hp im cui ri im hi ngh sau khi communicationModeCommand khi to c truyn, MC c trch nhim ng knh logic ph hp ca im u cui . Trong phng thc nhiu n im (multiunicast), im cui phi m knh logic ti mi im cui khc, openLogicalChannel c gi ti MC vi s u cui ca im cui cho knh tham d. im cui xt s trng hp openLogicalChannelACK bng forwardLogicalchannelNumber. 3.4.3.3. Phi hp nhng lung a phng tin trong hi ngh a im Phng php di y s c s dng lin kt knh logic vi lung RTP trong hi gnhi a im. im cui ngun ca lung phng tin gi openLogicalChannel ti MC. Trong trng hp ngun mun ch ra ch cho openLogicalChannel, n t terminalLabel ca im cui ch trong trng ch h.245.0LogicalChannelPrameters. im cui ngun cng t terminalLabel ca n trong trng sourcecah.225.0LogicalChannelParameter. Ch trong phng thc a im, s vng mt ca ch ch ra rng lung c th ng dng cho tt c im cui. Nu MC gn terminal cho im cui ngun th dim cui s dng SSRC gm nhng byte thp nht ca terminalLabel nh l nhng byte SSRC thp nht ca n. im cui ch c th kt hp s knh logic vi lung RTP ngun bng cch so snh

trng openLogicalChannel.h225.0LogicalParamenter.source vi byte thp nht ca SSRC trong header ca RTP. C th xy ra xung t gia SSRC khi u cui H.323 trong hi ngh. im cui pht hin ra s xung t s theo th tc trong RTP gii quyt xung t SSRC.

3.4.3.4. Cc th tc yu cu phng thc truyn thngMC H.323 gi H.245 communicationModeCommand xc nh phng thc truyn thng cho mi kiu phng tin n im hoc a im. Cc lnh ny c th gy ra hot ng chuyn mch gia hi ngh tp trung v phn tn v do c th lin quan ti ng v thot knh logic, m mt knh logic mi. CommunicationModeCommand xc nh tt c phin lm vic trong hi ngh. i vi mi phin d liu c xc nh theo: b nh dng RTP, ID phin RTP c lin kt nu c p dng, nhn u cui, m t phin, kiu d liu ca phin (v d G.711), a ch n im v a im cho phng tin v knh iu khin phng tin vi cu hnh v kiu hi ngh. CommunicationModeCommand vn chuyn mode truyn dn m im cui hi ngh dng. Yu cu khng vn chuyn mode nhn v chng c xc nh bi openLogicalChannel c gi i t MC ti im cui. C th cho rng communicationModeCommand ang nh ngha phng thc hot ng ca hi ngh v bi vy c gi i sau ch th multipointConference thng bo vi im cui rng n phi tun theo lnh ca MC. im cui s i communicationModeCommand trc khi m knh logic khi chng nhn ch th multipointConference. im cui nhn communicationModeCommand s dng terminalLabel ca mi mc trong bng xc nh mc ny c c p dng cho qu trnh x l ca n hay khng. Nhng mc khng c terminalLabel l ch th xc nh im cui trng terminalLabel trong hi ngh. V d: khi nhng lung audio t tt c im cui c t vo mt a ch a im (mt phin), mc ca bng i vi mode audio, a ch phng tin v a ch iu khin phng tin s khng c terminalLabel. Khi mc ca bng ny lnh cho im cui gi video ca n ti mt a ch a im, MC s thm v terminalLabel ca im cui. CommunicationModeCommand c th c s dng ch dn im cui trong hi ngh thay i mode bng cch ch ra mode mi cho knh phng tin ang

dng. N cng c th c s dng ni cho im cui truyn dn cho mt a ch mi bng cch ch ra mode ang s dng hin ti nhng vi knh phng tin mi. Tng t im cui nhn CommunicationModeCommand c th ch ra mode hin ti ang s dng v khng c knh phng tin s ng knh thch hp v th m li bng cch dng th t trong openLogicalChannel openLogicalChannelACK, openLogicalChannelACK c a ch im cui phng tin.

3.4.4. Pha D: Cc dch v cuc giTrong qu trnh din ra cuc gi, cc thc th tham gia c th yu cu mt s dch v nh thay i rng bng tn, gim st trng thi hay m rng hi ngh, .

3.4.4.1. Thay i rng bng tn rng bng tn ca cuc gi c thit lp v c cung cp bi Gatekeeper trong giai on trao i chp nhn cuc gi. im cui gi phi m bo rng tng tt c knh audio v video truyn dn v nhn bao gm c header RTP, header ti trng v nhng mo u khc ph hp vi rng bng tn ny. Knh d liu v iu khin khng nm trong gii hn ny. Ti bt k thi im no trong hi ngh, im cui hoc Gatekeeper c th yu cu tng hoc gim rng bng tn cuc gi. im cui c th thay i tc bit ca knh logic m khng yu cu rhay i rng bng tn t Gatekeeper nu tng tc bit ca tt c knh truyn v nhn khng vt qu rng bng tn hin ti. Nu s thay i ny n n tng tc bt tng ln qu rng bng tn hin ti th im cui yu cu thay i rng bng tn cuc gi t Gatekeeper ca n v i c