cong nghe dien thoai ip

8/9/2019 Cong Nghe Dien Thoai Ip

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SVTH: THAI QUANG TUNG 1

http://www.ebooks.vdcmedia.com

MUC LUC

Li noi u ....................................................................................... 3

Chng 1: Dch vu in thoai IP ................................................. 51. in thoai IP........................................................................... 5

1.1 Gii thiu............................................................................ 5

1.2 Cac ng dung cua in thoai IP....................................... 7

1.3 Li ch cua in thoai IP................................................... 9

1.4 u im va nhc im cua in thoai IP.................... 10

2. Phat trin dch vu in thoai IP.......................................... 11

2.1 Kha nng trin khai dch vu in thoai IP................... 11

2.1 Cac yu cu khi phat trin in thoai IP...................... 12

2.3 Nhng kho khn khi trin khai dch vu ....................... 13

2.4 Xu hng phat trin........................................................14

3. H323 - tiu chun ap dung cho in thoai IP .................... 14

3.1 Gii thiu.......................................................................... 14

3.2 Cu hnh mang theo chun H323.................................. 15

3.3 Cac giao thc H323 tham chiu n.............................. 20

C

hng 2: X ly cuc goi ............................................................ 28

1. Cac thu tuc thc hin trn knh H225 RAS ...................... 28

1.1 Tm gatekeeper ................................................................ 28

1.2 Thu tuc ng k vi gatekeeper ..................................... 29

1.3 nh v im cui............................................................. 31


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1.4 Cac thu tuc khac..............................................................31

2. Cuc goi gia hai im cui trong mang H323.................. 32

2.1 nh tuyn knh iu khin va bao hiu...................... 32

2.2 Cac thu tuc bao hiu va x l cuc goi...........................35

Chng 3: Xy dng gateway gia mang PSTN va mang IP. 711. Khai quat chung.................................................................... 71

1.1 Muc tiu............................................................................ 71

1.2 Mi trng phat trin ..................................................... 73

1.3 Cu hnh th nghim...................................................... 74

2. Xac nh giai phap phn cng. ............................................ 74

2.1Xem xet mt s giai phap phn cng. .......................... 742.2 Cu truc phn cng......................................................... 77

2.3 Gii thiu kin truc Dm3 cua Card Dm3/IP Link........78

1.3 Cu truc chng trnh..................................................... 86

Chng 4: Xy dng phn mm x l cuc goi cho gateway..... 891. La chon m hnh lp trnh............................................. 89

2. Th vin AFC cho card Dm3/IP Link.............................. 94

3. Xy dng may trang thai.................................................. 97

4. Xy dng chng trnh ................................................... 102

Kt lun va khuyn ngh............................................................ 105

Thut ng va t vit tt ............................................................. 108

Tai liu tham khao...................................................................... 111


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LI NOI U

Trn thgii, cng ngh in thoai IP a c thng mai hoat nm 1995, vi li thgia cc thp, cht lng dch vu co th chpnhn a lam nhiu nha kinh doanh vin thng quan tm. Tai VitNam, dch vu nay cung va mi c a vao s dung nhng con

mang tnh cht th nghim. Qua mt thi gian s dung, nh gia ccre hn hn so vi dch vu thoai truyn thng, dch vu nay thc s amang lai nhng li ch to ln cho ngi s dung.

Nhn thy kha nng phat trin cua dch vu nay trong tnglai, Vin khoa hoc va ky thut bu in a trin khai, nghin cunhiu tai khoa hoc v cng ngh thoai IP, tin hanh xy dng thnghim san phm Gateway PSTN - IP va a thanh cng vi gatewaydung lng 4 knh thoai tng t. Hin tai, vic phat trin gateway

vi dung lng lung E1 ang c Phong nghin cu dch vu miva t ng hoa trin khai xy dng co th ap dung tai cac buin tnh.

Trong thi gian thc tp tai Phong nghin cu dch vu mi vat ng hoa, em a c tham gia vao nhom nghin cu phat trinsan phm gateway. V vy, em a la chon tai X l cuc goi


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dch vu in thoai IP va ng dung trong Gateway PSTN-IP lam an tt nghip.

an c chia lam 4 chng nh sau:

+ Chng 1: Gii thiu dch vu in thoai IP, a ra nhngng dung, li ch cua dch vu nay, xem xet cac u im, nhc imcua cng ngh thoai IP, kha nng phat trin dch vu, nghin cu tiuchun c ap dung.

+ Chng 2: i su vao vn x l cuc goi, trc tin lacuc goi gia hai im cui trong cung mang IP vi cac trng hpkhac nhau, sau o la cuc goi co s tham gia cua mang chuyn machknh.

+ Chng 3: Gii thiu d an phat trin san phm GatewayPSTN - IP vi giao tip mang thoai la lung E1. Trong chng naya ra muc tiu cn at c, cac giai phap phn cng, gii thiukin truc phn cng, phn chia cu truc phn mm.

+Chng 4: ng dung c s l thuyt trong chng 2 xydng thit kphn mm x l cuc goi cho gateway.

Em xin chn thanh cam n s hng dn tn tnh cua PGSPTS H Anh Tuy, Ths inh Vn Dung a giup em hoan thanh annay.

Sinh vin thc hin

Thai Quang Tung


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CHNG 1: DCH VU IN THOAI IP

1. in thoai IP

1.1 Gii thiu

Trong in thoai thng thng, tn hiu thoai co tn snmtrong khoang 0.4 - 3.3 KHz c ly mu vi tn s8KHz theoNyquyst. Sau o cac mu se c lng t hoa vi 8bit/mu va ctruyn vi tc 64KHz n mang chuyn mach sau o c truyn

ti ch. bn nhn, dong s64 Kbps nay c giai ma cho ra tnhiu thoai tng t.

Thc cht thoai qua mang IP (Voice over IP - VoIP) cung khnghoan toan khac hn in thoai thng thng. u tin tn hiu thoaicung c shoa, nhng sau o thay v truyn trn mang PSTN quacac trng chuyn mach, chung se c nen xung tc thp, ong

Ly

mu 8KHz

Lng t hoa

8bit/mu110001.

64 Kbps

Chuynmach

thng


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goi va chuyn ln mang IP. Tai bn nhn, cac goi tin nay c giainen thanh cac lung PCM 64 Kb truyn n thu bao b goi. S khacnhau chnh la mang truyn dn va khun dang thng tin dung truyn dn. Trn hnh 1.2 a ra v du v mt cuc goi VoIP:

Gia s thu bao A mun goi n thu bao B. Thu bao Aquay sin thoai cua thu bao B. Mang PSTN co nhim vu phntch a ch va kt ni n gateway1. Tai y a ch cua B lai cphn tch va gateway 1 xac nh c thu bao B c kim soat bigateway2. No se thit lp mt phin lin kt vi gateway2. Cac thngtin bao hiu ma gateway1 nhn c t PSTN se c chuyn ithch hp sang dang goi va truyn n gateway2.

Tai gateway2, cac goi tin lai c chuyn i ngc lai va

truyn sang mang PSTN. Mang PSTN co nhim vu nh tuyn cucgoi n thu bao B. Cac thng tin tra li se c chuyn i ngc laiqua gateway2 n gateway1.

Sau khi cuc goi c thit lp, cac gateway co nhim vuchuyn i gia cac goi tin thoai trn mang IP va cac lung PCMtruyn trn mang PSTN .

Gateway IIGateway IP S T N

Internet/


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Ngoai cu hnh phone to phone trn, dch vu thoai IP concho phep cac PC ( Personal Computer ) co trang b in thoai trongcac mang LAN co th trao i thoai vi nhau (cu hnh PC to PC) va

vi cac thu bao in thoai trong mang PSTN (cu hnh PC to phonehay phone to PC) nh trong hnh 1.2.

1.2 Cac ng dung cua in thoai IP

Giao tip thoai se vn la dang giao tip c ban cua con ngi.Mang in thoai cng cng khng th b n gian thay th, thm chthay i trong thi gian ti. Muc ch tc thi cua cac nha cung cpdch vu in thoai IP la tai tao lai kha nng cua in thoai vi mt

chi ph vn hanh thp hn nhiu va a ra cac giai phap ky thut bsung cho mang PSTN.

in thoai co th c ap dung cho gn nh moi yu cu cuagiao tip thoai, t mt cuc am thoai n gian cho n mt cuc goihi ngh nhiu ngi phc tap. Cht lng m thanh c truyncung co th bin i tuy theo ng dung. Ngoai ra, vi kha nng cuaInternet, dch vu in thoai IP se cung cp thm nhiu tnh nngmi.

Ta co th xem xet mt vai ng dung trc mt cua in thoai:Thoai thng minh

H thng in thoai ngay cang tr nn hu hiu: re, ph bin,d s dung, c ng. Nhng no hoan toan ng ngn. No ch co mtsphm iu khin . Trong nhng nm gn y, ngi ta a cgng tao ra thoai thng minh, u tin la cac thoai ban, sau lan cac server. Nhng moi cgng u tht bai do s tn tai cua cach thng co sn.

Intrnet se thay i iu nay. K t khi Internet phu khp toancu, no a c s dung tng thm tnh thng minh cho mangin thoai toan cu. Gia mang may tnh va mang in thoai tn taimt mi lin h. Internet cung cp cach giam sat va iu khin caccuc thoai mt cach tin li hn. Chung ta co th thy c kha


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nng kim soat va iu khin cac cuc thoai thng qua mangInternet.

Dch vu in thoai Web

"World Wide Web" a lam cuc cach mang trong cach giao dchvi khach hang cua cac doanh nghip. in thoai Web hay " bm s"(click to dial) cho phep cac nha doanh nghip co th a thm cacphm bm ln trang web kt ni ti h thng in thoai cua ho.Dch vu bm sla cach d nht va an toan nht a thm cacknh trc tip t trang Web cua ban vao h thng in thoai.

Truy cp cac trung tm tra li in thoai

Truy nhp n cac trung tm phuc vu khach hanh qua mang

Internet se thuc y manh me thng mai in t. Dch vu nay secho phep mt khach hanh co cu hoi v mt san phm c chaohang qua Internet oc cac nhn vin cua cng ty tra li trc tuyn.

Dch vu fax qua IP

Nu ban gi nhiu fax t PC, c bit la gi ra nc ngoai thvic s dung dch vu Internet faxing se giup ban tit kim c tinva ca knh thoai. Dch vu nay se chuyn trc tip t PC cua ban quakt ni Internet. Hang nm, thgii tn hn 30 ty USD cho vic gifax ng dai. Nhng ngay nay Internet fax a lam thay i iunay.Vic s dung Internet khng nhng c m rng cho thoai macon cho ca dch vu fax.

Khi s dung dch vu thoai va fax qua Internet, co hai vn cban:

Nhng ngi s dung dch vu thoai qua Internet cn co chngtrnh phn mm chng han Quicknet's Internet PhoneJACK. Cu

hnh nay cung cp cho ngi s dung kha nng s dung thoai quaInternet thay cho s dung in thoai ban truyn thng.

Kt ni mt gateway thoai qua Internet vi h thng in thoaihin hanh. Cu hnh nay cung cp dch vu thoai qua Internet gingnh vic m rng h thng in thoai hin hanh cua ban.


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1.3 Li ch cua in thoai IP

Cng ngh VoIP se em lai nhng li ch chu yu sau:

Giam chi ph:

Mt gia cc chung se thc hin c vi mang Internet va doo tit kim ang k cac dch vu thoai va fax. Ngi ta c tnh cokhoang 70% cac cuc goi n Chu A la gi fax, phn ln trong so co th c thay thbi FoIP (Fax over IP). S chia se chi phthit b va thao tac gia nhng ngi s dung thoai va d liu cungtng cng hiu qua s dung mang bi le d tha bng tn trnmang cua ngi nay co th c s dung bi mt ngi khac.

n gian hoa:

Mt c s ha tng tch hp h tr tt ca cac hnh thc thng tincho phep chun hoa tt hn va giam tng sthit b. C s ha tngkt hp nay co th h tr vic ti u hoa bng tn ng.

Thng nht:

V con ngi la nhn tquan trong nhng cung d sai lm nhttrong mt mang vin thng, moi c hi hp nht cac thao tac, loaibo cac im sai sot va thng nht cac im thanh toan se rt co ch.

Trong cac t chc kinh doanh, s quan l trn c s SNMP (SimpleNetwork Management Protocol) co th c cung cp cho ca dch vuthoai va d liu s dung VoIP. Vic s dung thng nht giao thc IPcho tt ca cac ng dung ha hen giam bt phc tap va tng cngtnh mm deo. Cac ng dung lin quan nh dch vu danh ba va dchvu an ninh mang co th c chia se d dang hn.

Nng cao ng dung:

Thoai va fax ch la cac ng dung khi u cho VoIP, cac li ch

trong thi gian dai hn c mong i t cac ng dung a phngtin (multimedia) va a dch vu. Chng han cac giai phap thngmai Internet co th kt hp truy cp Web vi vic truy nhp trc tipn mt nhn vin h tr khach hang...


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1.4 u im va nhc im cua in thoai IP

V mt ky thut in thoai IP co nhng u im va nhc imsau:

u im:- Thng tin thoai trc khi a ln mang IP se c nen xung

dung lng thp (tuy theo ky thut nen), v vy se lam giam c lulng mang.

- Trong trng hp cuc goi mang chuyn mach knh mtknh vt l se c thit lp va duy tr gia hai bn cho n khi mttrong hai bn huy bo lin kt. Nh vy, trong khoang thi giankhng co ting noi, tn hiu thoai vn c ly mu, lng t hoa va

truyn i. V vy, hiu sut ng truyn se khng cao. i vi inthoai Internet co cac c ch phat hin khoang lng (khoang thigian khng co ting noi) nn se lam tng hiu sut mang.

Nhc im:

- Nhc im chnh cua in thoai qua mang IP chnh la chtlng dch vu. Cac mang sliu vn d khng phai xy dng vi mucch truyn thoai thi gian thc, v vy khi truyn thoai qua mang sliu cho cht lng cuc goi thp va khng th xac nh trc c.S d nh vy la v goi tin truyn trong mang co tr thay i trongpham vi ln, kha nng mt mat thng tin trong mang hoan toan coth xy ra. Mt yu tlam giam cht lng thoai na la ky thut nen tit kim ng truyn. Nu nen xung dung lng cang thp thky thut nen cang phc tap, cho cht lng khng cao va c bit lathi gian x l se lu, gy tr.

- Mt nhc im khac cua in thoai IP la vn ting vong.Nu nh trong mang thoai, do tr t nn ting vong khng anh hng

nhiu th trong mang IP, do tr ln nn ting vong anh hng nhiun cht lng thoai. V vy, ting vong la mt vn cn phai giaiquyt trong in thoai IP.


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2. Phat trin dch vu in thoai IP

2.1 Kha nng trin khai dch vu in thoai IP

Thoai qua IP hin a nh hnh thanh mt dch vu, nhng iu

khin no tr thanh mt phn chnh yu cua th thng thoai tch hphay vn ch la mt dch vu thiu sphu thuc nhiu vao s phattrin cua mang Internet noi chung. Thi im chuyn t mangchuyn mach knh sang mang chuyn mach goi la mt yu tquytnh s thanh bai cua nha cung cp dch vu va vai tro cua VoIP trongtng lai. Kha nng ph bin dich vu VoIP nm gia hai phng an:

Phng an 1 - cht lng dch vu cua mang Internet tip tuckhng n nh, cc in thoai giam manh (loai bo kha nng ha giathoai Internet), va VoIP vn ch la mt dch vu chim thiu s

Phng an 2 -hiu qua va tng trng cua cac dch vu va mangtch hp khin khach hang chuyn sang dung mang Internet lam chohiu qua kinh ttng cung vi tng trng cua lu lng.

Thiu tai nguyn trn

Giao thc interrnet mi

Cht lng Vol IPvn thp

Khng con li thgia ca

Dch vu Vol IP vn la thius

Hnh 1.3: Dch vu in thoaiIP vn chim thiu s


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2.1 Cac yu cu khi phat trin in thoai IP

Muc ch cua nha phat trin la thm cac tnh nng goi inthoai (ca truyn thoai va bao hiu) vao cac mang IP, kt ni chungvi mang in thoai cng cng, cac mang in thoai ca nhn sao choduy tr cht lng thoai hin tai va cac tnh cht ma ngi dungmong mun in thoai. Co nhng yu cu chnh khi phat trin

VoIP nh sau:

Cht lng thoai phai so sanh c vi cht lng thoai cuamang PSTN va vi cac mang co cht lng phuc vu khac nhau.

Mang IP c ban phai ap ng c nhng tiu ch hoat ngkht khe gm giam thiu vic khng chp nhn cuc goi, mt mat goiva mt lin lac. iu nay oi hoi ngay ca trong trng hp mang bnghen hoc khi nhiu ngi s dung chung nng lc cua mang cungmt luc.

Tn hiu iu khin goi (bao hiu) khng anh hng n hoatng cua mang sao cho ngi s dung khng bit ho ang c cungcp dch vu da trn cng ngh g ?.

Lin kt cac dch vu PSTN/VoIP bao gm cac Gateway gia cacmi trng mang thoai va mang d liu.

u tai nguyn trn manginerternet

Dch vu trn IP phat

Gia cung cp VoIPthay i

Li thgia ca tr nnkhng cn thit

Mang IP tai phn ln lu

Cac nha cung cp dch vu mi va ISP co ch

Hnh 1.4: in thoai IP c s sung rng


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ra E1. Tuy nhin dung lng cua thit b hin nay con cach xa so vicac san phm cua vin thng.

2.4 Xu hng phat trin

Hin tai manh t ha hen cho VoIP hin nay la cac mangdoanh nghip Intranet va mang Extranet thng mai. C s ha tngda trn IP cho phep iu khin quan l vic s dung cac dch vu, chophep hay khng cho phep truy nhp cac dch vu. Cac san phm inthoai trn mang Internet cha th ap ng cac yu cu cht lngdch vu nh in thoai thng thng. Bi vy, phat trin VoIP trnIntranet, Extranet la hng phat trin trc mt.

Mt xu hng phat trin khac cung nhiu ha hen la xy dng

cac cng ni gia mang IP va mang thoai (cac VoIP Gateway). NhngGateway nay xy dng t nn tang PC tr thanh cac h thng manhco kha nng iu khin hang trm cuc goi ng thi. Bi vy cacdoanh nghip se phat trin mt lng ln cac Gateway trong n lcgiam cac chi ph lin quan n lu lng thoai, fax va video hi ngh.

3. H323 - tiu chun ap dung cho in thoai IP

3.1 Gii thiu

H323 la mt chun quc tv hi thoai trn mang c a rabi hip hi vin thng quc t ITU (InternationalTelecommunication Union). Chun H323 cua ITU xac nh cac thanhphn, cac giao thc, cac thu tuc cho phep cung cp dch vu truyn dliu a phng tin (multimedia) audio, video, data thi gian thcqua mang chuyn mach goi (bao gm ca mang IP) ma khng quantm n cht lng dch vu. H323 nm trong b cac khuyn nghH32x cung cp cac dch vu truyn d liu a phng tin qua cac loaimang khac nhau. Mt trong cac ng dung cua H323 chnh la dch vu

in thoai IP.n nay, H323 a phat trin thng qua hai phin ban. Phin

ban th nht c thng qua vao nm 1996 va phin ban th haic thng qua vao nm 1998. ng dung vao chun nay rt rng baogm ca cac thit b hoat ng c lp cung nh ng dung truynthng nhung trong mi trng may tnh ca nhn, co th ap dung cho


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am thoai im - im cung nh cho truyn thng hi ngh. H323con bao gm ca chc nng iu khin cuc goi, quan l thng tin aphng tin va quan l bng thng va ng thi con cung cp giaodin gia mang LAN va cac mang khac.

3.2 Cu hnh mang theo chun H323.

Mang H323 da trn c s mang IP cung cp cac dch vu truynd liu a phng tin thi gian thc (trong o co dch vu thoai IP),hoat ng theo chun H323. Cu hnh cua mang H323 co th baogm cac thanh phn c ban nh trn hnh 1.5.

Thit b u cui

H323 Terminal la mt thit b u cui trong mang LAN co kha

nng truyn thng hai chiu. No co th la mt may PC hoc mtthit b c lp. Tt ca cac u cui H323 u phai c h tr khanng truyn d liu audio va video hai chiu va phai h tr chunH245 c dung iu tit cac knh truyn d liu. Ngoai ra nophai c h tr cac thanh phn sau:

Hnh 1.5: Cac thanh phn trong mang H323


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- Giao thc bao hiu H225 phuc vu trong qua trnh thit lp vahuy bo cuc goi.

- Giao thc H225 RAS (Registration/Admision/Status) thchin cac chc nng ng k, thu nhn... vi gatekeeper.

- Giao thc RTP/RCTP truyn va kt hp cac goi tin audio,video...

Mt u cui H323 cung co th c trang b thm cac tnhnng nh:

- Ma hoa va giai ma cac tn hiu audio, video.

- H tr giao thc T120 phuc vu cho vic trao i thng tin s

liu (data).- Tng thch vi MCU h tr cac lin kt a im

Chc nng iu khin h thng

H245 Control

RAS Control

Call Control

Video CODEC

Audio CODEC(G.711, G.722,

G.723, G.728,...

Receive

Path

Delay

L

n

idliuMedia

Camera,DisplaySpeaker

ng dung sliu

Giao diniu khin

h thng chongi s

dng

Cac chc nng H323

Hnh 1.6: Cc thit b u cui H323

Giaodinvim

nL

AN


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Gatekeeper

Gatekeeper la mt thanh phn quan trong trong mang H323,no c xem nh b nao cua mang. Gatekeeper hoat ng nh mtb chuyn mach ao. Gatkeeper co cac chc nng nh anh a ch;

cho phep va xac nhn cac u cui H323, cac gateway; quan l giaithng; tnh cc cuc goi; ngoai ra no con co th cung cp kha nngnh tuyn cuc goi. gatekeeper quan l giai thng nh kha nng chophep hay khng cho phep cac cuc goi xay ra. Khi scuc goi a vtqua mt ngng nao o th no se t chi tt ca cac cuc goi khac.Ngoai ra gatekeeper con co th cung cp kha nng nh tuyn baohiu.

Mc du vy, gatekeeper la thanh phn tuy chon trong mang

H323. Tuy nhin nu trong mang co gatekeeper th cac thit b ucui va cac Gateway phai s dung cac thu tuc cua gatekeeper. Cacchc nng cua mt gatekeeper c phn bit lam 2 loai la cac chcnng bt buc va cac chc nng khng bt buc.

Cac chc nng bt buc cua gatekeeper

- Chc nng dch a ch: - gatekeeper se thc hin vic chuyni t mt a ch hnh thc (dang tn goi) cua cac thit b u cuiva gateway sang a ch truyn dn thc trong mang (a ch IP).Chuyn i nay da trn bang i chiu a ch c cp nhtthng xuyn bng ban tin ng ky dch vu cua cac u cui.

- iu khin truy nhp - gatekeeper se chp nhn mt truynhp mang LAN bng cach s dung cac ban tin H.225.0 la

ARQ/ACF/ARJ . Vic iu khin nay da trn rng bng tn vang ky dch vu hoc cac thng skhac do nha san xut qui nh.y cung co th la mt thu tuc rng co ngha la chp nhn moi yucu truy nhp cua cac thit b u cui.

- iu khin rng bng tn - gatekeeper h tr vic trao icac ban tin H.225.0 la BRQ/BCF/BRJ iu khin rng bng tncua mt cuc goi. y cung co th la mt thu tuc rng co ngha la nochp nhn moi yu cu v s thay i rng bng tn.


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- iu khin min - Mt min la mt nhom cac u cui H323,cac gateway, MCU c quan l bi 1 gatekeeper. Trong mt min coti tiu mt u cui H323, mi min ch co duy nht mtgatekeeper. Mt min hoan toan co th c lp vi cu truc mang,

bao gm nhiu mang c kt ni vi nhau. Thng qua cac chc nng trn: dch a ch, iu khin truy nhp, iu khin rng bngtn, gatekeeper cung cp kha nng quan l min.

Cac chc nng khng bt buc cua Gatekeeper

- iu khin bao hiu cuc goi - gatekeeper co th la chon giahai phng thc iu khin bao hiu cuc goi la: no kt hp vi knhbao hiu trc tip gia cac u cui hoan thanh bao hiu cuc goihoc ch s dung cac knh bao hiu cua no x ly bao hiu cuc goi.

Khi chon phng thc nh tuyn bao hiu cuc goi trc tip gia cacu cui, th gatekeeper se khng phai giam sat bao hiu trn knhH.225.0.

- Han chtruy nhp - Gatekeeper co th s dung bao hiu trnknh H.225.0 t chi mt cuc goi cua mt thit b u cui khinhn thy co li trong vic ng ky. Nhng nguyn nhn t chi baogm: mt Gateway hoc u cui ng ky han chgoi i ma lai cgng thc hin mt cuc goi i va ngc lai hoc mt u cui ng

ky han chtruy nhp trong nhng gi nht nh.- Giam sat rng bng tn - Gatekeeper co th han chmt

lng nht nh cac u cui H.232 cung mt luc s dung mang. Noco th thng qua knh bao hiu H.225.0 t chi mt cuc goi dokhng co u bng tn thc hin cuc goi. Vic t chi nay cung coth xay ra khi mt u cui ang hoat ng yu cu thm rngbng. y co th la mt thu tuc rng ngha la tt ca moi yu cu truynhp u c ng y.

- Giam sat cuc goi - Mt v du cu th v chc nng nay cuaGatekeeper la no lu danh sach tt ca cac cuc goi H.323 hng iang thc hin ch th cac thu bao b goi nao ang bn va cungcp thng tin cho chc nng quan ly rng bng tn.

MCU (Multipoint Control Unit)


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MCU la mt im cui (Endpoint) trong mang, no cung cp khanng nhiu thit b u cui, gateway cung tham gia vao mt lin kta im (multipoint conference). No bao gm mt MC (MultipoimtController) bt buc phai co va mt MP (Multipoint Process) co th co

hoc khng. Nhim vu cua MC la iu tit kha nng audio, video,data gia cac thit b u cui theo giao thc H245. No cung iukhin cac tai nguyn cua hi thoai bng vic xac nh dong audio,video, data nao cn c gi n cac u cui. Tuy nhin, MC khngthao tac trc tip trn cac dong d liu ma nhim vu nay c giaocho MP. MP se thc hin vic kt hp, chuyn i, x l cac bt dliu.

GatewayNhim vu cua gateway la thc hin vic kt ni ga 2 mang

khac nhau. H323 gateway cung cp kha nng kt ni gia 1 mangH323 va mt mang khac (khng phai H323). V du nh mt gatewayco th kt ni va cung cp kha nng truyn tin gia mt u cuiH323 va mang chuyn mach knh (bao gm tt ca cac loai mangchuyn mach in thoai chng han PSTN). Vic kt ni nay cthc hin nh chc nng chuyn i giao thc trong qua trnh thitlp, giai phong cuc goi va chc nng bin i khun dang d liugia hai mang khac nhau cua gateway. Nh vy i vi kt ni giahai thit b u cui H323 th khng cn thit phai co gateway,nhng i vi cuc goi co s tham gia cua mang chuyn mach knhth gateway la bt buc phai co.


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Lan

Gateway khi hoat ng se co c im cua mt thit b u cuiH.323 hoc mt MCU trong mang LAN va co c im cua mt thitb u cui trong SCN hoc mt MCU trong SCN. V vy ta co 4 cuhnh c s cua gateway c th hin trn hnh 1.7. Mi gateway coth co t hp cua cac cu hnh c s hoc co th gm ca 4 cu hnh

nay.3.3 Cac giao thc H323 tham chiu n

Khuyn ngh H323 a ra mt tp cac giao thc phuc vu choqua trnh truyn d liu media thi gian thc trn mang chuynmach goi. Kin truc phn tng giao thc c m ta trn hnh 1.8 :

Data iu khin va bao hiu Audio/Video ng k

Chc nng

u cuiH323

Chc nng

chuyn i

Chc nng

u cuiSCN

Chc nngu cui

H323

Chc nng

chuyn i

Chc nngMCU

Chc nngMCU

Chc nng

chuyn i

Chc nngu cui

SCN

Chc nngMCU

Chc nng

chuyn i

Chc nngMCU

Hnh 1.7: Cc cu hnh c s ca Gateway


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T120

H225 Callsignalling

H245

RTP/RTCP H225RAS

TCP UDP

Tng mang

Tng lin kt d liu

Tng vt l

Hnh 1.8 Kin truc phn tng giao thc H323.

Giao thc H225 RAS ( Registration/Admission/Status )

Cac ban tin H225 RAS c dung trao i gia cac im cui(cac u cui , cac gateway ) va gatekeeper cho cac chc nng nhtm gatekeeper, ng k, quan l giai thng...

- Tm gatekeeper: La qua trnh im cui tm mt gatekeeper no co th ng k.

- ng k: tham gia vao mt min do gatekeeper quan l, cacim cui phai ng k vi gatekeeper va thng bao a ch giao vnva cac a ch hnh thc cua no. (Trong h thng co gatekeeper tha ch hnh thc chnh la sc quay) .

- nh v cac im cui: La tin trnh tm a ch giao vn chomt im cui khi bit a ch hnh thc cua no (thng quagatekeeper). Mi khi co cuc goi, gatekeeper nhn c a ch hnhthc cua pha b goi, no phai thc hin thu tuc nay xac nh c

a ch dung truyn tin cua b goi.- Cac iu khin khac: Giao thc RAS con c dung trong cac

c chiu khin khac nh iu khin thu nhn han chsimcui tham gia vao min, iu khin giai thng, iu khin giai phongkhoi gatekeeper.


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Cac ban tin H225 RAS c truyn trn knh RAS khng tincy v vy chung c tai i trong goi tin UDP.

Giao thc bao hiu cuc goi H225.

Giao thc H225 dung thit lp lin kt gia cac im cuiH323 (cac u cui, cac Gateway), qua lin kt o cac d liu thigian thc se c truyn i. Bao hiu cuc goi mang H323 la traoi cac ban tin cua giao thc H225 qua mt knh bao hiu tin cy. Doyu cu tin cy cua bao hiu nn cac thng bao cua H225 se ctruyn i trong goi tin TCP.

Qua trnh bao hiu cua cuc goi c bt u bi ban tinSETUP c gi i trn knh bao hiu tin cy H.225.0. Theo sau ban

tin nay se la chui cac ban tin phuc vu cho qua trnh thit lp cucgoi vi trnh t da trn khuyn ngh H225 ma u tin la ban tinyu cu giam sat bt buc. Yu cu nay cung vi nhng ban tin sauo lin quan n qua trnh khai bao/tm kim gia u cui vaGatekeeper se c truyn i trn knh khng tin cy RAS (knhtruyn thng tin v khai bao, giam sat va trang thai). Qua trnh naykt thuc khi thit b u cui nhn c trong ban tin CONNECTa ch chuyn tai an toan ma trn o se gi i cac ban tin iu khinH.245. Ban tin bao hiu H.225.0 se khng b phn oan khi i qua

cac PDU (Protocol Datagram Unit), con nhng ban tin c truyn itrn knh RAS la nhng ban tin khng chun hoa.

Khi khng co gatekeeper trong mang th cac ban tin H225 sec trao i trc tip gia cac im cui. Nu co gatekeeper trongmang th gatekeeper se quyt nh vic trao i cac ban tin H225gia cac im cui la trc tip hay phai thng qua gatekeeper.

Trong chng sau khi nghin cu v x l cuc goi se noi ro hnv giao thc bao hiu cuc goi H225.

Giao thc iu khin cuc goi H245.

Giao thc iu khin H245 dung thc hin vic giam sat cachoat ng cua cac thc th H323 bao gm: trao i kha nng cacim cui; ong m knh logic; iu khin lung; quyt nh chu t;va cac lnh va ch th khac.


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Knh H245 c thit lp gia hai im cui, mt im cui viMC, hoc mt im cui vi gatekeeper. Cac im cui ch thit lpmt knh H245 duy nht cho mi cuc goi ma no tham gia.

- Trao i kha nng: Trc khi tin hanh cuc goi a phng

tin, mi u cui phai bit c kha nng nhn va giai ma tn hiucua u cui kia. Bit c kha nng nhn cua u cui nhn, ucui truyn se gii han ni dung cua thng tin ma no truyn i,ngc lai, thng bao kha nng truyn no se cho phep u cui nhnla chon ch thu phu hp. Tp hp cac kha nng cua u cui chonhiu lung thng tin co th c truyn i ng thi va u cui coth khai bao lai tp hp cac kha nng cua no bt ky luc nao. Tp hpcac kha nng cua mi u cui c cung cp trong ban tin H245TerminalCapabilitySet.

- Bao hiu knh logic:Mt knh logic la mt knh mang thngtin t im cui nay ti im cui khac (trong trng hp hi thoaiim - im) hoc n nhiu im cui khac (trong trng hp hithoai im - a im). H245 cung cp cac ban tin ong m cacknh logic. Sau khi knh logic c m thng tin media mi ctruyn i trn cac knh nay.

- Xac nh chu t:Thu tuc nay nhm giai quyt vn xung t

gia hai im cui u co kha nng MC khi cung tham gia vao mtcuc goi hi ngh, hoc gia hai im cui khi mun m mt knhthng tin mt chiu.

Giao thc RTP ( Real-time Transport Protocol )

Giao thc truyn thi gian thc (RTP) la mt thu tuc da trnky thut IP tao ra cac h tr truyn tai cac d liu yu cu thigian thc, v du nh cac dong d liu hnh anh va m thanh. Cacdch vu cung cp bi RTP bao gm cac c chkhi phuc thi gian,

phat hin cac li, bao an va xac nh ni dung. RTP c thit kchuyu cho vic truyn a i tng nhng no vn co th c s dung truyn cho mt i tng. RTP co th truyn tai mt chiu nhdch vu video theo yu cu cung nh cac dch vu trao i qua lai nhin thoai Internet.


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Hoat ng cua RTP c h tr bi mt thu tuc khac la RCTP nhn cac thng tin phan hi v cht lng truyn dn va cacthng tin v thanh phn tham d cac phin hin thi.

Hoat ng cua giao thc.

Cac goi tin truyn trn mang Internet co tr va jitter khng doan c. Nhng cac ng dung a phng tin yu cu mt thigian thch hp khi truyn cac d liu va phat lai. RTP cung cp cacc chbao am thi gian, sth t va cac c chkhac lin quan nthi gian. Bng cac c chnay RTP cung cp s truyn tai d liuthi gian thc gia cac u cui qua mang.

Tem thi gian (time-stamping) la thanh phn thng tin quan

trong nht trong cac ng dung thi gian thc. Ngi gi thit lp cactem thi gian ngay thi im octet u tin cua goi c ly mu.Tem thi gian tng dn theo thi gian i vi moi goi. Sau khinhn c goi d liu, bn thu s dung cac tem thi gian nay nhmkhi phuc thi gian gc chay cac d liu nay vi tc thch hp.Ngoai ra, no con c s dung ng b cac dong d liu khac nhau( chng han nh gia hnh va ting). Tuy nhin RTP khng thc hinng b ma cac mc ng dung pha trn se thc hin s ng b nay.

B phn nhn dang tai xac nh kiu nh dang cua tai tincung nh cac phng cach ma hoa va nen. T cac b phn nh dangnay, cac ng dung pha thu bit cach phn tch va chay cac dong dliu tai tin. Tai mt thi im bt ky trong qua trnh truyn tin, cacb phat RTP ch co th gi mt dang cua tai tin cho du dang cua taitin co th thay i trong thi gian truyn (thay i thch ng vis tc nghen cua mang).

Mt chc nng khac ma RTP co la xac nh ngun . No chophep cac ng dung thu bit c d liu n t u. V du thoai hi

ngh, t thng tin nhn dang ngun mt ngi s dung co th bitc ai ang noi.

IP header UDP header RTP header RTP payload

Hnh 1.9: Ma hoa goi tin RTP trong goi IP


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Cac c chtrn c thc hin thng qua mao u cua RTP.Cach ma hoa goi tin RTP trong goi tin IP c m ta trn hnh ve.

RTP nm pha trn UDP, s dung cac chc nng ghep knhva kim tra cua UDP. UDP va TCP la hai giao thc c s dungchu yu trn Internet. TCP cung cp cac kt ni nh hng va cacdong thng tin vi tin cy cao trong khi UDP cung cp cac dch vukhng lin kt va co tin cy thp gia hai tram chu. S d UDPc s dung lam thu tuc truyn tai cho RTP la bi v 2 l do:

- Th nht, RTP c thit kchu yu cho vic truyn tin ai tng, cac kt ni co nh hng, co bao nhn khng ap ng tt

iu nay.- Th hai, i vi d liu thi gian thc, tin cy khng quan

trong bng truyn ung theo thi gian. Hn na, s tin cy trongTCP la do c chbao phat lai, khng thch hp cho RTP. V du khimang b tc nghen mt sgoi co th mt, cht lng dch vu du thpnhng vn co th chp nhn c. Nu thc hin vic phat lai th segy nn tr rt ln cho cht lng thp va gy ra s tc nghen cuamang.

Thc tRTP c thc hin chu yu trong cac ng dung ma taicac mc ng dung nay co cac c chkhi phuc lai goi b mt, iukhin tc nghen.

Giao thc RTCP (Real-time Transport Control Protocol).

RTCP (Real-time Transport Control Protocol) la giao thc htr cho RTP cung cp cac thng tin phan hi v cht lng truyn dliu. Cac dch vu ma RTCP cung cp la:

- Giam sat cht lng va iu khin tc nghen:y la chcnng c ban cua RTCP. Nocung cp thng tin phan hi ti mt ngdung v cht lng phn phi d liu. Thng tin iu khin nay rthu ch cho cac b phat, b thu va giam sat. B phat co th iuchnh cach thc truyn d liu da trn cac thng bao phan hi cuab thu. B thu co th xac nh c tc nghen la cuc b, tng phn


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hay toan b. Ngi quan l mang co th anh gia c hiu sutmang.

- Xac nh ngun:Trong cac goi RTP, cac ngun c xac nhbi cac sngu nhin co dai 32 bt. Cac snay khng thun tin

i vi ngi s dung RTCP cung cp thng tin nhn dang ngun cuth hn dang vn ban. No co th bao gm tn ngi s dung, sin thoai, a ch e-mail va cac thng tin khac.

- ng b mi trng:Cac thng bao cua b phat RTCP chathng tin xac nh thi gian va nhan thi gian RTP tng ng.Chung co th c s dung ng b gia m thanh vi hnh anh.

- iu chnh thng tin iu khin:Cac goi RTCP c gi theo

chu ky gia nhng ngi tham d. Khi slng ngi tham d tngln, cn phai cn bng gia vic nhn thng tin iu khin mi nhtva han chlu lng iu khin. h tr mt nhom ngi s dungln, RTCP phai cm lu lng iu khin rt ln n t cac tainguyn khac cua mang. RTP ch cho phep ti a 5% lu lng choiu khin toan b lu lng cua phin lam vic. iu nay c thchin bng cach iu chnh tc phat cua RTCP theo slng ngitham d.

Ma hoa/giai ma (CODEC) tn hiu Audio

bn phat, tn hiu Audio t microphone trc khi ctruyn tip phai c ma hoa. Con bn nhn, chung phai c giaima trc khi a n speaker. CODEC la dch vu ti thiu ma ucui H323 nao cung phai co. V vy mt thit b u cui H323 phaic h tr ti thiu la mt chun CODEC. Hin nay ang tn taimt schun ma hoa nh sau: G.711 (ma hoa tc 64kbps); G.722(64,56,48 kbps); G.723.1 (5.3 va 6.3 kbps); G.728 (16 kbps); G.729 (8kbps).

Voice CODEC Tc phc tap Cht lng tr

G.711 PCM 64 Thp Rt tt Cc thp


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G.726 ADPCM 40/32/24 ThpTt (40K)

Ti (16K)Rt thp

G.729 CS-ACELP 8 Cao Tt Thp

G.729 A CA-ACELP 8 Va phai Kha tt Thp

G.723 MP-MLQ 6,4/5,3Cao va phai Tt (6,4 K)

Ti (5,3 K)Cao

G.723.1 MP-MLQ 6,4/5,3 nt nt nt

G.728 LD-CELP 16 Rt cao Tt Thp

Hnh 1.10: Bang so sanh cac chun CODEC

Vic la chon thut toan CODEC la mt trong nhng yu tcban nng cao cht lng thoai Internet.

Ma hoa/giai ma (CODEC) tn hiu Video

Video CODEC ma hoa tn hiu hnh anh t camera truyn

dn va giai ma cac tn hiu video nhn c (a c ma hoa) hin th hnh anh. Trong H323, truyn hnh anh co th co hockhng, v vy vic h tr video CODEC la tuy chon. Tuy nhin cacu cui cung cp kha nng lin lac hnh anh phai c h tr giaothc ma hoa, giai ma tn hiu video. Cac giao thc h tr la H261,H263...


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CHNG 2: X LY CUC GOI

Trong chng nay, trc tin chung ta nghin cu cac thu tucbao hiu x l cuc goi gia hai im cui (u cui hoc gateway)trong mang H323 vi cac trng hp khac nhau. Cac thu tuc naytun theo cac khuyn ngh H323, H225, H245 cua ITU-T. Sau o,chung ta se chuyn sang cuc goi co s tham gia cua thit b u cuimang SCN. Trong trng hp nay se co s tham gia cua gateway ktni mang H323 va mang SCN. Cac thu tuc nay tun theo tiu chunTS 101 322 va TS 101 471 cua ESTI. Trong qua trnh nghin cuthu tuc x l cuc goi, chung ta se khng i su vao cu truc, cacthanh phn thng tin cua cac goi tin ma ta ch xem xet hoat ng cuacac thu tuc nay nh thnao.

1. Cac thu tuc thc hin trn knh H225 RAS

Knh H225 RAS la mt knh logic khng tin cy c dung

truyn tai cac ban tin gia gatekeeper va cac phn t khac trongmang thc hin cac thu tuc nh: Tm gatekeeper, ng k...

Bi v cac ban tin RAS c truyn trn knh khng tin cynn cac ban tin nay phai c t mt khoang thi gian timeout vasln phat lai khi khng nhn c hi m. Mt im cui hocgatekeeper khng th ap ng lai mt yu cu trong thi giantimeout th no phai tra li bng ban tin RIP (Request In Progress) cho bit no ang x l yu cu. Khi nhn c ban tin RIP, chungphai khi ng lai timeout va sln phat lai.

1.1 Tm gatekeeper

Thu tuc nay c thc hin khi mt im cui mun tm cho nomt gatekeeper ng k. Thu tuc nay phai c thc hin ngaykhi im cui o hoat ng. Co hai phng thc tm gatekeeper:


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+ Trong cu hnh cua im cui co a ch cua gatekeeper (coth t trong tp khi ng).

+ im cui gi ban tin GRQ theo a ch multicast n tt cacac gatekeeper (a ch nay c

quy nh trong khuyn ngh H225).Nu gatekeeper nao o co th quanl c im cui nay th co th trali bng ban tin GCF co cha ach cua knh RAS (xem hnh 2.1).

Vi muc ch d tr, gatekeeper ch nh cac gatekeeper thaythtrong trng hp xay ra li. Danh sach cac gatekeeper thay thnay c lu trng

AlternateGatekeeper trong cac ban tinGCF va RCF (xem muc sau).Nu mt im cui nhn thy s ng k cua no khng hp l,

no phai thc hin lai thu tuc tm gatekeeper. ng k la khng hp lkhi im cui nhn c ban tin RRJ tra li cho ban tin RRQ hockhng nhn c tra li cho ban tin RRQ trong thi gian timeout.

1.2 Thu tuc ng k vi gatekeeper

tham gia vao mt min do gatekeepet quan l, cac im cui

phai thc hin thu tuc ng k. y la qua trnh im cui thng baocho gatekeeper bit a ch giao vn cung nh a ch hnh thc (aliasaddress) cua no. Thu tuc ng k phai c thc hin trc khi co caccuc goi xay ra va sau khi a thc hin thu tuc tm gatekeeper.

im cui gi ban tin RRQ (Registration Request) ngatekeeper trn knh H225RAS. Knh H225 RAS cxac nh trong thu tuc tm

gatekeeper. Gatekeeper co thtra li bng ban tin RCF(Request Confirm) hoc RRJ(Request Reject) (Hnh 2.2). Mt im cui ch ng k vi 1gatekeeper.

Endpoint GatekeeperGRQ (a ch muticast )

GCF/GRJ

Hnh 2.1: T ng tm gatekeeper

Endpoint GatekeeperRRQ

RCF hoc RRJ

Hnh 2.2: Th tc ng k vi gatekeeper


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im cui co th ng k thi han s dung bi yu cutimeToLive (tnh bng giy) trong ban tin RRQ. Gatekeeper tra libng ban tin RCF vi cung gia tr timeToLive hoc be hn. Saukhoang thi gian nay, s ng k nay ht hiu lc. Trc khi ht thi

gian ng k ht, im cui co th thit lp lai timeToLive keo daithi han ng k bng cach gi i ban tin RRQ vi bit keepAlive cthit lp (ban tin RRQ nay ch co mt t thng tin c ch ro trongkhuyn ngh H225.0). Sau khi ht thi han, cac im cui phai ngk lai vi gatekeeper vi ban tin RRQ y u.

Gatekeeper phai am bao mi a ch hnh thc c chuyni thanh mt a ch giao vn. Tuy nhin, im cui co th ch nhmt a ch giao vn d tr hay thay th nh cu trucalternateEndpoint trong ban tin RAS cho phep im cui co mt giaodin mang th cp. Gatekeeper se t chi ng k nu xet thy sng k o la mp m, khng u thng tin.

Nu im cui khng xac nh mt a ch hnh thc trong bantin RRQ th gatekeeper se cp phat cho no mt a ch hnh thc vathng bao cho no trong ban tin xac nhn RCF.

im cui co th huy bo s ng k bng cach gi ban tin URQ(Unregistration Request) n gatekeeper. Gatekeeper xac nhn bng

ban tin UCF (Unregistration Confirm). iu nay cho phep im cuithay i a ch hnh thc lit kt vi a ch giao vn hoc ngclai. Nu nhn thy im cui cha ng k, gatekeeper tra li bngban tin URJ (Unregistration Reject).

Gatekeeper cung co th yu cu huy bo ng k cua im cui(dung ban tin URQ), luc o im cui phai tra li bng ban tin UCF.Sau khi huy bo ng k, im cui phai ng k lai (co th vi mtgatekeeper khac).

Endpoint GatekeeperURQ

UCF hoc URJ

Gatekeeper EndpointURQ

UCF

Hnh 2.3: Th tc ng k vi gatekeeper


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Mt im cui nu khng ng k se khng chu s quan l cuagatekeeper.

1.3 nh v im cuiMt im cui hoc gatekeeper co a ch hnh thc cua mt

im cui khac va mun bit thng tin lin lac cua im cui nay, nose s dung ban tin LRQ (Location Request). Ban tin nay co th cgi n mt gatekeeper nao o (co a ch ro rang) hoc gi theo ach multicast n nhiu gatekeeper. Gatekeeper quan l im cui coa ch hnh thc trong ban tin LRQ se tra li lai bng ban tin LCFcha cac thng tin lin lac cua im cui o. Thng tin lin lac bao

gm a ch knh bao hiu, a ch knh RAS va mt sthng tinkhac.

Nu mt gatekeepr nao o nhn c ban tin LRQ trn knhRAS cua no th phai tra li lai. Nu gatekeeper nhn c trn knhRAS multicast th no se khng tra li (trong trng hp no khngquan l im cui).

1.4 Cac thu tuc khac

Ngoai cac thu tuc trn, knh RAS con dung truyn tai cacban tin iu khin truy nhp, thay i bng thng, giam sat trangthai va giai phong. Chi tit v cac thu tuc nay c trnh bay phnsau.

Trong ban tin ARQ ( Admission Request) yu cu truy nhp,im cui xac nh mt gia tr bng thng truyn va nhn thngtin. Gia tr nay la gii han trn cua tc lung tng hp audio,video truyn va nhn (khng k cac header cac lp giao thc).Gatekeeper co th giam gia tr nay xung trong ban tin xac nhn

ACF. Cac im cui ch c phep truyn thng tin vi tc nmtrong gii han nay.


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2. Cuc goi gia hai im cui trong mang H323

im cui trong mang H323 co th la mt thit b u cui hocmt gateway. Cac thu tuc x l cuc goi gia hai im cui trongmang H323 tun theo cac thu tuc trong khuyn ngh H323, H225.0

va H245. u tin, knh bao hiu c thit lp (bn goi phai bita ch tng mang (IP) va a ch tng giao vn (TCP) cua bn b goi), sau o a ch cua knh iu khin c xac nh trong qua trnhtrao i cac ban tin bao hiu. Sau khi xac nh c a ch, knhiu khin c thit lp va a ch cua knh thng tin se c xacnh qua cac ban tin trn knh Iu khin. Cui cung, knh thngtin c thit lp cho phep hai im cui co th trao i thng tin.Ngoai ra, H323 con h tr thu tuc kt ni nhanh (khng cn m knhH245).

2.1 nh tuyn knh iu khin va bao hiu

Bao hiu x l cuc goi gia hai im cui trong mang H323lin quan n ba knh bao hiu tn tai c lp vi nhau la: knh iukhin H.245, knh bao hiu cuc goi va knh bao hiu RAS.

Trong mang khng co gatekeeper, cac ban tin bao hiu cuc goic truyn trc tip gia hai im cui chu goi va b goi bng cachtruyn bao hiu a ch trc tip. Trong cu hnh mang nay th phachu goi phai bit a ch bao hiu cua pha b goi trong mang va vvy co th giao tip mt cach trc tip.

Nu trong mang co gatekeeper, trao i bao hiu gia chu goiva gatekeeper c thit lp bng cach s dung knh RAS cua

Hnh 2.4: Cc knh logic trong mt cuc gi

Knh bo hiu

Knh iukhin

im cui 1 im cui 2

Trao i a chknh iukhin

Trao i a chRTP, RTCP

Cc bn tin

Cc bn tin H245

Knh thng tin mediaRTP - RTCP


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gatekeeper truyn a ch. Sau khi trao i ban tin bao hiu ac thit lp, khi o gatekeeper mi xac nh truyn cac ban tintrc tip gia hai im cui hay nh tuyn chung qua gatekeeper.

nh tuyn knh bao hiu cuc goi

Cac ban tin bao hiu cuc goi co th c truyn theo mt tronghai phng thc va vic la chon gia cac phng thc nay dogatekeeper quyt nh:

+ Th nht la cac ban tin bao hiu cua cuc goi c truyn tim cui no ti im cui kia thng qua gatekeeper gia hai imcui (hnh 2.5).

+ Th hai la cac ban tin bao hiu cua cuc goi c truyn trc

tip gia hai im cui (hnh 2.6).Ca hai phng thc nay u s dung cac kt ni ging nhau vi

cung muc ch, dang ban tin c s dung cung ging nhau, cac bantin thit lp bao hiu c trao i trn knh RAS cua gatekeeper,sau o ti trao i ban tin bao hiu cuc goi trn knh bao hiu cucgoi. Sau o mi ti thit lp knh iu khin H.245.

Trong phng thc gatekeeper nh tuyn cac ban tin th no coth ong knh bao hiu cuc goi khi vic thit lp cuc goi hoanthanh hoc vn duy tr knh nay h tr cac dch vu b xung. Chco gatekeeper mi co th ong knh bao hiu cuc goi, nhng khiGateway tham gia vao cuc goi th cac knh nay khng c phepong.


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nh tuyn knh iu khin

Khi cac ban tin bao hiu cuc goi c gatekeeper nh tuynth sau o knh iu khin H.245 se c nh tuyn theo 2 cach thhin trn hnh 2.7 va 2.8:

Knh bo hiu RAS

Knh bo hiu cuc gi

1. ARQ2. ACF/ARJ

3. Setup4. Setup5. ARQ

6. ACF/ARJ7. Connect8. Connect

Endpoint 1 Endpoint 2

Hnh 2.6: Bn tin bo hiu c truyn trc trc tip gia cc im cui

1. ARQ2. ACF/ARJ

3. Setup4. ARQ

5. ACF/ARJ6. Connect

Knh bo hiu RAS

Knh bo hiu cuc gi

Gatekeeper

Endpoint 1 Endpoint 2


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+ Giai oan 4: dch vu (xem muc 2.2.2.5)

+ Giai oan 5: kt thuc cuc goi (xem muc 2.2.2.6).

Bc 1 - Thit lp cuc goi

Trong giai oan nay cac phn t trao i vi nhau cac ban tinc nh ngha trong khuyn ngh H.225.0 theo mt trong cac thutuc c trnh bay sau y.

Cuc goi c ban - Ca hai im cuiu khng ng ky

Khi ca hai im cui u khng ng

ky vi gatekeeper, th chung se trao i trctip cac ban tin vi nhau nh hnh 2.9. Khio chu goi se gi ban tin thit lp cuc goitrn knh bao hiu a bit trc a ch cuab goi.

Ca hai im cui u ng kyti mt gatekeeper

Tnh hung nay co 2 trng hp xay ra:+ Ca hai im cui u ng ky ti mt gatekeeper va

gatekeeper chon phng thc truyn bao hiu trc tip gia 2 imcui (hnh 2.10). u tin pha chu goi trao i vi gatekeeper cpban tin ARQ (1)/ACF (2) thit lp bao hiu. Trong ban tin ACF dogatekeeper tra li cho pha chu goi co cha a ch knh bao hiu cuapha b goi. Sau o pha chu goi se cn c vao a ch nay gi bantin Setup (3) ti pha b goi. Nu pha b goi chp nhn yu cu, no se

trao i cp ban tin ARQ (5)/ ACF (6) vi gatekeeper. Nu pha b goinhn c ARJ (6) th no se gi ban tin Release Complete ti phachu goi.

Knh bo hiu cuc gi

Hnh 2.9: Cuc gi c bn

khng c gatekeeper

Endpoint 1 Endpoint 2Setup (1)

Connect (4)

Call proceeding (2)Alerting (3)


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gatekeeper. Nu nhn c ARJ (7) th pha b goi se gi ban tinRelease Complete ti gatekeeper.

Ch co pha chu goi co ng ky vi gatekeeper

Trong trng hp ch co pha chu goi co ng ky vi gatekeeperva bao hiu cuc goi c truyn trc tip gia hai im cui, thu tucbao hiu cua no c th hin trn hnh 2.12. Sau khi nhn c

ACF (2), pha chu goi se gi ban tin Setup (3) ti pha b goi. Nu

pha b goi chp nhn cuc goi no se tra li bng ban tin Connect tipha chu goi.

Hnh 2.13: Ch c pha ch gi ng k - gatekeepernh tuyn bo hiu

Setup (4)

Knh bo hiu RAS

Knh bo hiu cuc gi

Endpoint 1 Endpoint 2GatekeeperARQ (1)

ACF/ARJ (2)Setup (3)

Call proceeding (5)Alerting (6)

Connect (7)

Call proceeding (5)

Connect (8)Alerting (6)

Hnh 2.12: Ch c pha ch gi ng k - bo hiu trc tip

Knh bo hiu RASKnh bo hiu cuc gi

Endpoint 1 Endpoint 2GatekeeperARQ (1)

ACF/ARJ (2)

Setup (3)

Call proceeding (4)

Alerting (5)

Connect (6)


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Khi cac ban tin bao hiu cuc goi do gatekeeper nh tuyn, ththu tuc thit lp cuc goi c th hin trn hnh 2.13. Trong trnghp nay cac th t ban tin cua thu tuc ging ht trng hp trn, chkhac duy nht mt im o la tt ca cac ban tin bao hiu gi t thu

bao nay ti thu bao kia u thng qua phn t trung gian lagatekeeper 1.

Ch copha b goi cong kyvi gatekeeper

Trong trng hp ch co pha b goi ng ky vi gatekeeper vacac ban tin bao hiu truyn trc tip th thu tuc bao hiu cua no se codang nh hnh 2.14.

u tin pha chu goi gi ban tin Setup (1) trn knh bao hiu

a bit a ch ti pha b goi. Nu pha b goi chp nhn no se traoi cp ban tin ARQ (3)/ACF (4) vi gatekeeper 2. Pha b goi cung coth nhn c ARJ (4), khi o no se gi ban tin Release Complete tipha chu goi. Trong trng hp chp nhn pha b goi se tra li bngban tin Connect (6) co cha a ch knh iu khin H.245 cho phachu goi.

Trng hp bao hiu do gatekeeper nh tuyn, thu tuc baohiu c th hin trn hnh 2.15. u tin pha chu goi se gi bantin Setup (1) trn knh bao hiu a bit trc a ch ti pha b goi ,nu pha b goi chp nhn cuc goi no se trao i ban tin ARQ(3)/ARJ (4) vi gatekeeper. Trong ban tin ARJ ma gatekeeper tra licho pha b goi cha ma yu cu nh tuyn cuc goi qua gatekeeper(routeCallTogatekeeper). Khi o pha b goi se gi ban tin Facility (5)co cha a ch knh bao hiu cua gatekeeper ti pha chu goi. Sau opha chu goi gi ban tin Release Complete (6) ti pha chu goi va cnc vao a ch knh bao hiu pha chu goi se gi ban tin Setup (7) tigatekeeper, gatekeeper gi ban tin Setup (8) ti pha b goi. Sau opha b goi se trao i ban tin ARQ (9)/ACF (10) vi gatekeeper, phab goi gi ban tin Connect (12) co cha a ch knh iu khin H.245ti gatekeeper. gatekeeper se gi ban tin Connect (13) co cha a chknh iu khin H.245 cua pha b goi.


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Hai thu bao ng kyvi hai gatekeeper khac nhau

Tnh hung nay co 4 trng hp xay ra:

+ Ca hai gatekeeper u chon cach nh tuyn bao hiu trctip gia hai thu bao, khi o thu tuc bao hiu c th hin trn

Hnh 2.14: Ch c pha b gi ng k - Bo hiu truyn trc tip

Knh bo hiu RAS

Knh bo hiu cuc gi

Endpoint 1 Endpoint 2GatekeeperSetup (1)

Call proceeding (2)ARQ (3)

ACF/ARJ (4)Alerting (5)Connect (6)

Call proceeding (2)

Hnh 2.15: Ch c pha b gi ng k gatekeeper nh tuyn bo hiu

Knh bo hiu RAS

Knh bo hiu cuc gi

Endpoint 1 Endpoint 2GatekeeperSetup (1)


ACF/ARJ (4)

Alerting (11)

Connect (12)

Release completeSetu

Setup

Call proceedingARQ (9)

ACF/ARJ (10)

Alerting (11)

Connect (13)


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hnh 2.16. u tin pha chu goi trao i cac ban tin ARQ (1)/ACF (2)vi gatekeeper 1, trong ban tin ACF se cha a ch knh bao hiucua pha b goi. Cn c vao a ch nay pha chu goi gi ban tin Setup(3) ti thu bao b goi. Nu pha b goi chp nhn th no se trao i

ARQ (5)/ACF (6) vi gatekeeper 2, nu pha b goi nhn c ARJ (6)th no se gi ban tin Release Complete ti pha chu goi. pha b goi.Khi nhn c ACF pha b goi se gi bao tin Connect (8) co cha ach knh iu khin H.245 ti pha chu goi.

Trng hp th hai la gatekeeper 1 pha chu goi truyn baohiu theo phng thc trc tip con gatekeeper 2 pha b goi nhtuyn bao hiu cuc goi qua no. Thu tuc bao hiu trong trng hpnay c th hin trn hnh 2.17. u tin pha chu goi trao i ARQ(1)/ACF (2) vi gatekeeper 1, sau o pha chu goi se gi ban tin Setup(3) ti pha b goi. Nu pha b goi chp nhn, no se trao i ARQ(5)/ARJ (6) vi gatekeeper 2, trong ban tin ARJ (6) co cha a chknh bao hiu cua no va cha ma ch th bao hiu nh tuyn tigatekeeper 2 (routeCallTogatekeeper). Sau o pha b goi se tra lipha chu goi bng ban tin Facility (7) co cha a ch knh bao hiucua gatekeeper 2. Tip theo pha chu goi se gi ban tin ReleaseComplete ti pha b goi va trao i cp ban tin DRQ (9)/DCF (10) vi

Hnh 2.16: Hai thu bao u ng k vi hai gatekeeper - C

hai gatekeeper u truyn bo hiu trc tip gia hai thu bao

ARQ (1)

ACF/ARJ (2)

Setup (3)

Call proceeding (4)

Alerting (7)

Connect (8)

ARQ (5)ACF/ARJ (6)

Endpoint 1 Endpoint 2Gatekeeper 1 Gatekeeper 2

Knh bo hiu RAS

Knh bo hiu cuc gi


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gatekeeper 1. Khi nhn c DCF pha chu goi se lai bt u trao iban tin ARQ (11)/ACF (12) vi gatekeeper 1. Tip theo pha chu

Goi se gi ban tin Setup (13) ti a ch knh bao hiu cuagatekeeper 2, sau o gatekeeper 2 se gi ban tin Setup (13) ti phab goi. Pha b goi se bt u trao i ARQ (15)/ACF (16) vigatekeeper 2, sau o pha b goi se gi ban tin Connect (18) co chaa ch knh iu khin H.245 cua no ti gatekeeper 2. gatekeeper 2se gi ban tin Connect (19) ti pha chu goi.

Hnh 2.17: Hai thu bao ng k vi 2 gatekeeper - Pha ch gi truyn trctip cn pha b gi th nh tuyn bo hiu qua gatekeeper 2

Connect (19)Connect (18)

Knh bo hiu RAS

Knh bo hiu cuc gi


ARQ (1)

ARQ (11)

Setup (3)

Call proceeding (4)

Facility (7)

Release complete (8)

ARQ (5)

ACF/ARJ (6)

ACF/ARJ (2)

ACF (12)

DRQ (9)DCF (10)

Setup (13)

Call proceeding (4)

ARQ (15)

ACF/ARJ (16)

Setup (14)

Call proceeding (4)

Alerting (17)Alerting (17)


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+ Trng hp th 3 la gatekeeper 1 pha chu goi nh tuyn baohiu qua no con gatekeeper 2 pha b goi chon phng thc truynbao hiu trc tip. Thu tuc bao hiu cua trng hp nay c thhin trn hnh 2.18.

u tin pha chu goi trao i ban tin ARQ (1)/ACF (2) vigatekeeper 1, khi nhn c ACF co cha a ch knh bao hiu cuagatekeeper 1 th TB chu goi se gi ban tin Setup (3) ti gatekeeper 1.gatekeeper 1 se gi ban tin Setup (4) co cha a ch knh bao hiucua no ti TB b goi. Nu TB b goi chp nhn, no se trao i ARQ(6)/ACF (7) vi gatekeeper 2, nu nhn c ARJ (7) th no se giban tin Release Complete ti pha chu goi. Nu nhn c ACF (7)th TB b goi se gi ban tin Connect (9) co cha a ch knh iukhin H.245 cua no ti gatekeeper 1. gatekeeper 1 se gi ban tin

Connect (10) co cha a ch knh iu khin H.245 cua TB b goi tiTB chu goi.

+ Trng hp th 4 la hai im cui ng ky vi 2 gatekeeperva ca hai gatekeeper nay u chon phng thc nh tuyn bao hiucuc goi qua chung. Thu tuc bao hiu cua trng hp nay c thhin trn hnh 2.19.

Connect (10)

Connect (9)

Hnh 2.18: Hai thu bao ng k vi 2 gatekeeper - gatekeeper 1 phach gi nh tuyn bo hiu cn pha b gi th truyn trc tip

Knh bo hiu RAS

Knh bo hiu cuc gi

Endpoint 1 Endpoint 2Gatekeeper 1 Gatekeeper 2ARQ (1)

Setup (4)


ACF/ARJ (7)

ACF/ARJ (2)

Setup (3)

Call proceeding (5)

Alerting (8) Alerting (8)


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u tin TB chu goi trao i ARQ (1)/ACF (2) vi gatekeeper 1,trong ban tin ACF co cha a ch knh bao hiu cua gatekeeper 1.Tip theo TB chu goi cn c vao a ch nay gi ban tin Setup (3) tigatekeeper 1.. Qua trnh trao i ban tin co trnh t gn ging cac

trng hp trc nhng ch khac mt im o la cac TB ch trao iban tin bao hiu vi cac gatekeeper quan ly no va cac gatekeeper cotrao i ban tin bao hiu cuc goi vi nhau.

Bao hiu kiu Overlap

Cac thanh phn trong mang H323 co th c h tr kha nngbao hiu kiu Overlap. Nu trong mang co gatekeeper th thu tuc baohiu kiu Overlap se c dung, cac im cui gi n gatekeeper

Hnh 2.19: Hai thu bao u ng k - nh tuyn qua hai gatekeeper


Knh bo hiu RAS

Knh bo hiu cuc gi

ARQ (1)

Setup (3)

Call proceeding (5)

ACF/ARJ (2)

Facility (8)

Release complete (9)

ARQ (6)

ACF/ARJ (7)

Setup (10)

Call proceeding (5)

ARQ (12)ACF/ARJ (13)

Setup (11)Call proceeding (5)

Alerting (14)Connect (15)

Alerting (14)

Connect (16)Alerting (14)

Connect (17)

Setup (4)Call proceeding (5)


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ban tin ARQ mi khi co thm thng tin v a ch goi. a ch nayc lu trong trng destinationInfo cua ban tin ARQ. Nu a chnay la cha y u (gatekeeper khng th xac nh c ch) thgatekeeper se tra li bng ban tin ARJ vi thanh phn thng tin

AddmissionRejectReason co gia tr la incompleteAddress (nu co giatr khac th cuc goi coi nh b huy bo). V vy, im cui phai gitip cac ban tin ARQ cho n khi a ch ma gatekeeper nhn c lay u. Nu a nhn u a ch, gatekeeper tra li bng ban tin

ACF.

Khi im cui nhn c a ch knh bao hiu chdestCallSignalAddress (co th la cua gatekeeper hoc cua ch tuytheo phng phap nh tuyn bao hiu) t gatekeeper, no gi n ach nay goi tin Setup vi trng canOverlapSend

ch nh liu

phng phap bao hiu Overlap co c ap dung hay khng. Nu phanhn nhn c ban tin Setup vi a ch cha y u va thanhphn thng tin canOverlapSend co gia tr la TRUE th no se khing thu tuc bao hiu kiu Overlap bng cach tra li bng ban tinSetup Acknowledge. Cac thng tin thm v a ch se c pha chugoi gi trong ban tin Information. Nu a ch nhn c la khngy u va trng canOverlapSend co gia tr FALSE th pha nhntra li bng ban tin ReleaseComplete huy bo cuc goi.

Thu tuc kt ni nhanh

Sau khi trao i cac ban tin bao hiu, knh iu khin cthit lp, sau o knh thng tin mi c m. Tuy nhin, co th boqua giai oan thit lp knh iu khin bng cach dung thu tuc ktni nhanh trn knh bao hiu.

Pha chu goi khi ng thu tuc kt ni nhanh khi gi ban tinSetup co kem theo thanh phn thng tin fastStart n ph b goi.Thanh phn thng tin fastSatrt nay cha mt chui cu trucOpenLogicalChanel m ta y u cac thng tin v knh thng tin mano ngh thit lp.

Pha b goi co th t chi thu tuc kt ni nhanh bng cachkhng gi thanh phn thng tin fastStart trong bt c goi tin tra linao. Luc o, knh iu khin H245 phai c thit lp. Ngc lai,


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nu pha b goi chp nhn, trong goi tin tra li se co cha thanh phnthng tin fastStart la chon mt cu truc Open LogicalChanel trongscac cu truc ma bn goi ngh. Qua o, knh thng tin c thitlp ging nh thu tuc ong m knh logic cua knh H245.

Pha b goi co th bt u truyn thng tin (media) ngay saukhi nhn c goi tin bao hiu t pha chu goi co cha thanh phnthng tin fastStart. Do o pha chu goi phai chun b sn sang nhn bt c mt knh thng tin nao ma no a a ra trong ban tinSetup. Khi nhn c ban tin tra li co cha thanh phn thng tinfastStart , pha chu goi co th ngng chun b nhn thng tin trncac knh khng c chp nhn. Pha chu goi co th yu cu pha bgoi cha gi thng tin trc khi tra li bng ban tin Connect. Nunh trong ban tin Setup, thanh phn thng tinmediaWaitForConnect c thit lp la TRUE th pha b goi khngc phep gi dong thng tin media cho n khi a gi i ban tinConnect.

Pha chu goi co th bt u truyn thng tin media ngay khinhn c ban tin tra li co thanh phn thng tin fastStart.V vy,bn b goi phai sn sang nhn thng tin media trn knh ma no achp nhn.

Chuyn sang knh H245Sau khi thit lp cuc goi s dung thu tuc kt ni nhanh, mt

trong hai bn co nhu cu s dung cac thu tuc ch co knh H245.Mt trong hai bn co th khi ng thu tuc thit lp knh H245trong bt k thi im nao cua cuc goi, s dung phng thc ma hoagoi tin H245 trong goi tin H225 (xem phn sau) hoc s dung kt niknh H245 ring. Khi s dung thu tuc kt ni nhanh, knh bao hiuphai c m cho n khi cuc goi kt thuc hoc knh H245 cthit lp.

Khi s dung knh H245 ring, tt ca cac thu tuc bt buc cuaH245 phai c thc hin trc khi khi ng cac thu tuc khac.Knh thng tin a c thit lp trong thu tuc kt ni nhanh se ctha kva c xem nh chung a c m bi thu tuc m knhthng tin cua H245.


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Giai phong cuc go

Nu knh thng tin c thit lp bng thu tuc kt ni nhanhva khng chuyn sang knh H245, cuc goi c giai phong khi mttrong hai bn gi i goi tin bao hiu ReleaseComplete.

Thit lp knh iu khin

Sau khi trao i csac ban tin thit lp cuc goi, cac im cui sethit lp knh iu khin H.245 vi a ch c xac nh trong bc1. Knh iu khin nay co th do pha b goi thit lp sau khi nonhn c ban tin Setup hoc do pha chu goi thit lp khi no nhnc ban tin Alerting hoc Call Proceeding. Trong trng hp khngnhn c ban tin Connect hoc mt im cui gi Release

Complete, th knh iu khin H.245 se b ong.u tin cac im cui trao i cac ban tin trao i kha nng

thu phat lung thng tin media. Sau o chung se thc hin thu tuc xac nh chu - t (master - slave). Trong trng hp ca hai imcui u co kha nng cua MC, thu tuc nay se xac nh im cui naola active MC (active MC se la chu trong cuc goi hi ngh).

Sau khi thc hin xong cac thu tuc nay, cuc goi chuyn sangbc th 3 thit lp knh thng tin.

Ma hoaban tin H245 trong ban tin bao hiu H225.0

Vi muc ch duy tr tai nguyn, ng b hoa gia bao hiu vaiu khin cuc goi, giam thi gian thit lp cuc goi, cac ban tinH245 se c ma hoa trong ban tin bao hiu H225 truyn trn knhbao hiu thay v thit lp mt knh iu khin H245 ring.

im cui mun s dung phng thc nay se thit lp thanhphn thng tin h245Tunneling ln gia tr TRUE trong ban tin Setup

va cac ban tin bao hiu sau o trong thi gian phng thc nay vnc s dung. Nu chp nhn phng thc nay, bn nhn se thitlp thanh phn thng tin h245Tunneling ln gia tr TRUE trong bantin tra li cho ban tin Setup va trong cac ban tin tip theo trong thigian phng thc nay vn c s dung.


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Bi v co th trong thi gian khi tao knh H245, cac ban tinbao hiu co ma hoa ban tin H245 vn co th c truyn i, nn cacim cui phai co kha nng x l cac ban tin nay cho n khi nhnc ban tin bao hiu co thanh phn thng tin h245Tunneling la

FALSE. Tra li cho cac ban tin nay se c truyn trn knh iukhin a c thit lp. Sau khi knh H245 c thit lp th khngth quay tr lai s dung phng thc ma hoa ban tin H245 trong bantin bao hiu na.

Thit lp knh truyn thng

Sau khi trao i kha nng (tc nhn ti a, phng thc mahoa..) va xac nh master-slave trong giao tip trong giai oan 2, thutuc iu khin knh H.245 se thc hin vic m knh logic truyn

thng tin. Sau khi m knh logic truyn tn hiu la m thanh vahnh anh th mi im cui truyn tn hiu se truyn i mt ban tinh2250MaximumSkewIndication xac nh thng struyn.

Thay i ch hoat ng

Trong giai oan nay cac im cui co th thc hin thu tucthay i cu truc knh, thay i kha nng va ch truyn cung nhnhn.

Trao i cac lung tn hiu videoVic s dung ch th videoIndicateReadyToActive c nh

ngha trong khuyn ngh H.245 la khng bt buc, nhng khi sdung th thu tuc cua no nh sau.

u tin pha chu goi se khng c phep truyn video cho nkhi pha b goi ch th sn sang truyn video. Pha chu goi setruyn ban tin videoIndicateReadyToActive sau khi kt thuc quatrnh trao i kha nng, nhng no se khng truyun tn hiu video

cho n khi nhn c ban tin videoIndicateReadyToActive hocnhn c lung tn hiu video n t pha pha b goi.


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Phn phi cac a ch lung d liu

Trong ch mt a ch, mt im cui se m mt knh logic

ti MCU hoc mt im cui khac. a ch cua cac knh cha trongban tin openLogicalChannel va openLogicalChannelAck.

Trong ch a ch nhom, a ch nhom se c xac nh biMC va c truyn ti cac im cui trong ban tincommunicationModeCommand. Mt im cui se bao cho MC vicm mt knh logic vi a ch nhom thng qua ban tinopenLogicalChannel va MC se truyn ban tin o ti tt ca cac imcui trong nhom.

Dch vu

Luc nay, cuc goi a c thit lp, hai bn co th trao ithng tin media. Cac dch vu giam sat cht lng hoat ng, thay i rng bng tn, cac dch vu b tr khac cung c tin hanh.

Thay i rng bng tn

rng bng tn cua mt cuc goi c gatekeeper thit lptrong khoang thi gian thit lp trao i. Mt im cui phai chc

chn rng tng tt ca lung truyn, nhn m thanh va hnh anh uphai nm trong rng bng tn a thit lp.

Tai moi thi im trong khi hi thoai, im cui hocgatekeeper u co th yu cu tng hoc giam rng bng tn. Mtim cui co th thay i tc truyn trn mt knh logic ma khngyu cu gatekeeper thay i rng bng tn nu nh tng tc truyn va nhn khng vt qua rng bng tn hin tai. Trongtrng hp ngc lai th im cui phai yu cu gatekeeper ma no

ng ky thay i rng bng tn.Thu tuc thay i rng bng tn - thay i thng struyn

c th hin trn hnh 2.20. Khi im cui 1 mun tng tc truyn trn knh logic trc ht no phai xac nh xem co th vtqua rng bng tn cua cuc goi hin tai khng. Nu co th th nose gi ban tin BRQ (1) ti gatekeeper 1. Khi nhn c ban tin BCF


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(2) co ngha la co u rng bng tn cho yu cu, im cui 1 se giban tin closeLogicalChannel (3) ong knh logic. Sau o no se mlai knh logic bng cach gi ban tin openLogicalChannel (4) co chagia tr tc mi ti im cui 2. Trc ht no phai xac nh xem gia

tr o co vt qua rng bng tn cua knh hay khng, nu chpnhn gia tr nay th no se trao i ban tin yu cu thay i rngbng tn BRQ (5)/BCF (6) vi gatekeeper 2. Nu rng bng tn ucho yu cu thay i th im cui 2 se tra li im cui 1 bng bantin openLogicChannelAck (7), trong trng hp ngc lai no se tchi bng ban tin openLogicChannelReject.

Thu tuc thay i rng bng tn - Thay i thng snhnc th hin trn hnh 2.21. Khi im cui 1 mun tng tc nhntrn knh logic cua mnh, trc ht no phai xac nh xem co th vtqua rng bng tn cua cuc goi hin tai khng. Nu co th th nose gi BRQ (1) ti gatekeeper 1, khi nhn c BCF (2) th no se giban tin flowControlCommand (3) co cha gii han tc mi cuaknh ti im cui 2. Trc ht im cui 2 phai xac nh xem bngtn mi co vt qua kha nng cua knh khng, nu chp nhn c

th no se gi ban tin yu cu thay i rng bng tn BRQ (4) tigatekeeper 2. Khi nhn c BCF (5) th im cui 2 se gi ban tincloseLogiclChannel (6) ong knh logic sau o m lai knh logicbng ban tin openLogicalChannel (7) co cha tc bit mi ti imcui 1. u cui 1 se xac nh tc mi va tra li im cui 2 bngban tin openLogicalChannelAck (6).

Knh RAS

Knh H245

Ch : Gatekeeper 1 v gatekeeper 2 cth l mt.

CloseLogicalChannel

OpenLogicalChannel

OpenLogicalCh Ack

BRQ (5)

BCF/BRJ (6)

BRQ (1)BCF/BRJ (2)

Endpoint 1 GatekeeperGatekeeper Endpoint 2

Hnh 2.20: Yu cu thay i rng bng tn - thay i thng s truyn


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Giam sat trang thai

giam sat trang thai hoat ng cua im cui, gatekeeperlin tuc trao i cp ban tin IRQ/IRR vi cac im cui do no kimsoat . Khoang thi gian u n gia cac ln trao i cac ban tin co

th ln hn 10 giy va gia tr cua no do nha san xut quyt nh.Gatekeeper co th yu cu mt im cui gi cho no ban tin

IRR mt cach u n nh gia tr cua trng irrFrequency trong bantin ACF gi cho im cui o xac nh tc truyn ban tin IRR.Khi xac nh c gia tr cua trng irrFrequency, im cui se giban tin IRR vi tc o trong sut khoang thi gian cua cuc goi.Trong khi o gatekeeper co th vn gi IRQ ti im cui va yu cutra li theo c chnh a trnh bay trn.

Trong khoang thi gian din ra cuc goi, mt im cui hocgatekeeper co th u n hoi trang thai t im cui bn kia bngcach s dung ban tin Status Enquiry. im cui nhn c ban tinStatus Enquiry se tra li bng ban tin ch th trang thai hin thi.Thu tuc hoi ap nay co th c gatekeeper s dung kim tra mtcach u n xem cuc goi co con ang hoat ng khng. Co mt lu

Hnh 2.21: Yu cu thay i rng bng tn - thay i thng s nhn

Knh RAS

Knh H245

Ch : Gatekeeper 1 v gatekeeper 2 c

th l mt.

Endpoint GatekeeperGatekeeper 1 Endpoint 2

BRQ (4)BCF/BRJ

BRQ (1)

BCF/BRJ

CloseLogicalChannel

O enLo icalChannel

OpenLogicalCh Ack

FlowControlCommand


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y la cac ban tin nay la ban tin H.225.0 c truyn trn knh baohiu cuc goi khng anh hng n cac ban tin IRR c truyn trnknh RAS.

Kt thuc cuc goi

Mt im cui co th kt thuc cuc goi theo cac bc cua thutuc sau:

Dng truyn lung tn hiu video khi kt thuc truyn mt anh,sau o ong tt ca cac knh logic phuc vu truyn video.

Dng truyn d liu va ong tt ca cac knh logic dung truyn d liu.

Dng truyn audio sau o ong tt ca cac knh logic dung truyn audio.

Truyn ban tin H.245 endSessionCommand trn knh iukhin H.245 bao cho thu bao u kia bit no mun kt thuc cucgoi. Sau o no dng truyn cac ban tin H.245 va ong knh iukhin H.245.

No se ch nhn ban tin endSessionCommand t bn kia va seong knh iu khin H.245

Nu knh bao hiu cuc goi ang m, th no se truyn i bantin Release Complete sau o ong knh bao hiu.

No cung co th kt thuc cuc goi theo cac thu tuc sau y:

+ Mt im cui nhn ban tin endSessionCommand ma trco no khng truyn i ban tin nay, th no se ln lt thc hin cacbc t 1 n 6 trn y ch bo qua bc 5.

Chu y: Kt thuc mt cuc goi khng co ngha la kt thuc mt

hi ngh (cuc goi conhiuim cui tham gia), mt hi ngh se chcchn kt thuc khi s dung ban tin H.245 dropConference. Khi o cacim cui se ch MC kt thuc cuc goi theo thu tuc trn.

Trong mt cuc goi khng co s tham gia cua gatekeeper th chcn thc hin cac bc t 1 n 6.


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Nhng trong cuc goi co s tham gia cua gatekeeper th cn cohoat ng giai phong bng tn, thu tuc nay c th hin trn hnh2.22. V vy sau khi thc hin cac bc t 1 n 6, mi im cui setruyn i ban tin DRQ (3) ti gatekeeper yu cu giai phong khoigatekeeper. Sau o gatekeeper se tra li bng ban tin DCF (4). Saukhi gi DRQ, th im cui se khng gi ban tin IRR ti gatekeeperna va khi o cuc goi kt thuc.

Trn y la thu tuc kt thuc cuc goi co s tham gia cuagatekeeper do im cui thc hin. Thu tuc kt thuc cuc goi dogatekeeper thc hin c th hin trn hnh 2.23. u tingatekeeper gi ban tin DRQ ti im cui, khi nhn c ban tin nayim cui se ln lt thc hin cac bc t 1 n 6 sau o tra ligatekeeper bng ban tin DCF. Thu bao u kia khi nhn c bantin endSessionCommand se thc hin thu tuc giai phong ging

Hnh 2.22: im cui kt thc cuc gi c s tham gia caatekee er

Knh RAS

Knh bohiu

KnhH245

Ch : Hai gatekeeper c th l mt

Endpoint 1 Gatekeeper 2Gatekeeper 1 Endpoint 2

DRQ (3)DRQ (3)

EndSessionCommand(1)

EndSessionCommand(1)

Release Complete(2)

DCF (4)DCF (4)


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trng hp im cui chu ng kt thuc cuc goi (hnh 2.23). Nucuc goi la mt hi ngh th gatekeeper se gi DRQ ti tt ca cacim cui tham gia hi ngh

Cuc goi co s tham gia cua u cui trong mang SCN

i vi cuc goi co s tham gia cua mang SCN co th xay ra cactrng hp sau:

Cuc goi t u cui H323 n u cui SCN.Cuc goi t u cui SCN n u cui H323.

Cuc goi gia hai u cui SCN qua mang IP (H323).

Khi co s tham gia cua u cui trong mang SCN th bt bucphai co gateway chuyn i giao thc gia mang SCN va mangH323. Bao hiu gia gateway vi u cui hoc mt gateway khactun theo khuyn ngh H323 cua ITU. Tuy nhin khng phai tt cacac thu tuc, ban tin cua H323 u c ap dung cho VoIP, tiu chunky thut TS 101 322 va TS 101 471 cua ESTI se gii han cac thu tuccua H323 ap dung trong VoIP. Bao hiu gia u cui SCN vagateway tun theo giao thc cua mang SCN (co th la bao hiu R2,bao hiu s7...). Trong phn nay, ta se khng ch ro giao thc baohiu c ap dung gia mang SCN va gateway.

Hnh 2.23: Kt thc cuc gi bt u t gatekeeper

Knh RAS

Knh bo hiu

Knh H245

Ch : Gatekeeper 1 v gatekeeper 2c th l mt

Endpoint 1 GatekeeperGatekeeper Endpoint 2

EndSessionCommandRelease Complete (2)

DCF (4)

DRQ

DCF


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Cuc goi c chia lam 3 phn : thit lp cuc goi, x l cuc goiva giai phong cuc goi.

Thit lp cuc goi

iu kin ban u: cuc goi ch c thit lp sau khi cac thutuc ng k vi gatkeeper c hoan thanh.

Cuc goi t u cui H323 n u cui SCN

Thit lp cuc goi c ban

Cuc goi co th c thit lp theo thu tuc c nh nghatrong khuyn ngh H.323 (xem muc 2.2) theo cac iu kin sau:

Theo khuyn ngh nay th mt cuc goi se ch c s dung mt

knh kt ni vi mang SCN. Cac cuc goi yu cu s dung nhiuknh khng c h tr.

Gatekeeper va gateway do no quan ly phai h tr ca hai kiubao hiu en-bloc va Overlap.

Thu tuc bao hiu kiu en-bloc

Thu tuc bao hiu en-bloc co th c ch nh bi u cuiH323. Ngoai ra, no cung c thc hin khi gatekeeper nhn thy

a ch cua pha b goi nm trong thanh phn thng tinCalledPartyNumber cua ban tin SETUP la y u.

Thng tin CalledPartyNumber coi nh y u theo cac iukin sau:

+ Gatekeeper bit y u thng tin v phng phap anh sthu bao b goi va xac nh snhn c la y u.

+ Trong ban tin SETUP co cha thanh phn thng tin Sending

complete.+ Thng scandOverlapSend (Xem bao hiu kiu Overlap phn

2.2.2.1) khng co mt hoc nhn gia tr la FALSE.

+ CalledPartyNumber co ch scui cung la #.


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Khi u cui H.323 nhn c tra li bng ban tin CALLPROC, th thanh phn thng tin "Sending complete" se c chenvao ban tin SETUP hoc ban tin INFORMATION va truyn ti cacphn t mang tip theo (v du nh gatekeeper hoc gateway tip

theo).Thu tuc bao hiu kiu Overlap

Khi nhn c ban tin SETUP co cha sb goi ma gatekeeperkhng xac nh c th no se khi ng b nh thi T302 (gia trcua b nh thi T302 c ch ra trong khuyn ngh Q.931 cua ITU-T) sau o no gi tr lai ban tin SETUPACK.

Gatekeeper se khi ng lai b nh thi T302 khi nhn c

tt ca cac ban tin INFORMATION khng cha ch th "Sendingcomplete" va co cha thanh phn thng tin spha b goi vi t nhtmt ky t co ngha.

Hnh 2.24 th hin mt thu tuc bao hiu kiu Overlap cho cucgoi t mt u cui H.323 ti mt thu bao trong mang SCN

Hnh 2.24: Thit lp cuc gi kiu Overlap - s dng thtc kt ni nhanh

Knh media m t gateway n u cui H323

u cui H323 Gatekeeper Gateway SCNSetup

Infomation

Setup

Infomation Infomation Infomation

Call Proc Call Proc Call Proc

Alertin AlertingAlertin

ConnectConnectConnect

Knh media m c hai chiu


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NOTE 1: Ngay khi gatekeeper nhn c u ch sco ngha nh tuyn cuc goi th no se gi ban tin SETUP n cho gateway.

NOTE 2+3: Ban tin INFORMATION co th c gi i khingi s dung mun cung cp thm thng tin.

NOTE 4: Khi mang SCN nhn u sco ngha hoan thanhvic phn tch sth no se gi i ban tin CALL PROCEEDING sec gi i thay v ban tin SETUP ACK khi tra li ban tin SETUPva cac ban tin INFORMATION se bi loai bo.

NOTE 5: Gia s rng vic ng ky cua u cui H.323 cthc hin trc khi bt u gi va nhn tun t cac ban tin.

Chuy: Spha b goi c coi nh la y u trong mt siukin sau:

Nu gatekeeper co cha toan b danh ba va no xac nh cpha b goi hoan thanh kt ni.

Nu ban tin SETUP co cha thanh phn thng tin "Sendingcomplete".

Nu khng co thng scanOverlapSend hoc b t vao trangthai FALSE.

Nu spha b goi co cha ky t cui cung la '#'.

Nu spha b goi c nhn dang la tun theo nh dangE.164 va co cha thng sdestinationInfo.

Thit lp cac knh thng tin

Thu tuc kt ni nhanh

Thu tuc kt ni nhanh s dung trong mang VoIP c trnhbay trong muc 2.2.2.2.

Chuy1: thu tuc nay cho phep trao i thit lp knh thngtin theo khuyn ngh H.245hoc quay tr lai thu tuc bao hiu H.245tai moi thi im cua cuc goi.


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Chu y 2: Thu tuc na y cho phe p trao i cac thng tin trongbng tn (in-band) khi thit lpcuc goi.

Ma hoaban tin H.245 trong ban tin H.225.0

Mang VoIP cho phep ma hoa ban tin H.245 trong ban tinH.225.0 nh c trnh bay trong muc 2.2.2.3.

Chu y: trong VoIP vic ma hoa ban tin H.245 trong ban tinH.225.0 c u tin s dunghn thit lp knh H245 ring bi vno mang lai hiu qua cao hn.

Cac thng tin bao hiu trong bng

Trong giai oan thit lp cuc goi

Nu gateway kt ni vi mang SCN nhn c ban tinPROGRESS (trc khi nhn c ban tin ALERTING) hoc ban tinCALL PROCEEDING co cha thng tin ch th Progress t phamang SCN, th gateway se gi ban tin PROGRESS ti gatekeeper.Ban tin nay cha thng tin ch th Progress a nhn c.

Nu nhn c ban tin CALL PROCEEDING t pha mangSCN trong khi cha gi ban tin CALL PROCEEDING, th gatewayse gi ban tin CALL PROCEEDING. Ban tin nay co cha thng tin

ch th Progress.Khi gatekeeper nhn c ban tin CALL PROCEEDING co

cha thng tin ch th Progress th gatekeeper (trc khi truyn bantin CALL PROCEEDING) se dng moi b nh thi giam sat cuc goiang chay va khi ng b nh thi T301.

Khi gatekeeper nhn c ban tin PROGRESS (trc khi nhnc ban tin ALERTING) co cha thng tin ch th Progress (nhngkhng cha thng tin ch th Cause) th gatekeeper (trc khi truyn

ban tin PROGRESS) se dng moi b nh thi giam sat cuc goi angchay va khi ng b nh thi T301.

Khi u cui H.323 nhn c ban tin CALL PROCEEDING cocha thng tin ch th Progress, th no se dng moi b nh thi giamsat cuc goi ang chay va khi ng b nh thi T301.


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Khi u cui H.323 nhn c ban tin PROGRESS (trc khinhn c ban tin ALERTING) co cha thng tin ch th Progress(nhng khng thng tin ch th Cause), u cui H.323 se dng moib nh thi giam sat cuc goi ang chay va khi ng b nh thi

T301.Trong giai oan giai phong cuc goi

Nu gateway kt ni vi mang SCN nhn c phn t thngtin ch th Progress trong ban tin DISCONNECT t pha mang SCNth gateway se gi ban tin PROGRESS ti gatekeeper. Ban tin nayse co cha ca thng tin ch th Progress va ch th Cause nhn c.

Chu y:Nu gateway nhn c ban tin PROGRESS co cha

thng tin ch th Cause va Progress th ban nay se c gi nguynva gi n gatekeeper.

Khi gatekeeper nhn c ban tin PROGRESS co cha thngtin ch th Progress va Cause th gatekeeper (trc khi gi i ban tinPROGRESS) se dng moi b nh thi giam sat cuc goi ang chayva khi ng b nh thi T301.

Khi u cui H.323 hoc gateway nhn c ban tinPROGRESS co cha thng tin ch th Progress va Cause th

gatekeeper se dng moi b nh thi giam sat cuc goi ang chay vakhi ng b nh thi T301.

Gatekeeper dch a ch sb goi

Ban tin ARQ gi t im cui H.323 n gatekeeper co cha spha b goi trong trng destinationInfo va destExtraCallInfo. Cnc vao o gatekeeper se dch spha b goi nhn c t u cuiH.323 thanh a ch tng ng va cac thng tin b sung.

Trong trng hp cuc goi c nh tuyn trc tip (khngqua gatekeeper) cac thng tin a dch nay se c gi tr lai u cuiH.323 trong ban tin ACF s dung cac trng destinationInfo,destExtraCallInfo va remoteExtensionAddress. Cn c vao cac thngtin nhn c u cui H.323 se gi ban tin SETUP ti u cuich. u cui H.323 co th che cac thng tin nay tranh khachhang khac s dung truy nhp. Nu khng tm thy cac thng tin


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nay th u cui H.323 se s dung cac cac sgi trong ban tin ARQ gi trong ban tin SETUP. Nu tm thy cac trng thng tin naynhng khng co ni dung th u cui H.323 se khng gi thng tinv thu bao ch trong ban tin SETUP. Trong trng hp o

gatekeeper se cung cp thng tin nh tuyn trong cac Token chei cac thng tin nay t u cui.

Nu mang mun bao v cac thng tin nh tuyn khoi cac ketruy nhp trm t u cui H.323, th no se s dung m hnhgatekeeper nh tuyn cuc goi bng trng thng tin preGrantedtrong ban tin ARQ.

Cuc goi t u cui SCN ti u cui H.323

Thit lp cuc goi c banCuc goi co th c thit lp theo thu tuc c nh ngha

trong khuyn ngh H.323 cua ITU-T theo cac iu kin sau:

Theo khuyn ngh nay th mt cuc goi ch c s dung mtknh kt ni vi mang SCN. Cac cuc goi yu cu s dung nhiuknh khng c h tr;


Hnh 2.25 th hin mt thu tuc bao hiu kiu Overlap cho cucgoi t mt thu bao trong mang SCN ti u cui H.323.


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NOTE 1: Gatekeeper cha nhn u thng tin nh tuyncuc goi.

NOTE 2: Gatekeeper a nhn u thng tin cn thit nh

tuyn cuc goi.NOTE 3: Khng phu thuc vao vic s dung thu tuc kt ni

nhanh, vic kch hoat knh truyn thng b tr lai cho dn khigatekeeper nhn c ban tin CONNECT. Hoat ng nay ng vivic gatekeeper s dung thng s mediaWaitForConnect thay vthng sfastStart.

nh v pha b goi H.323

Nu gateway nhn c mt yu cu cuc goi t mang SCN thno se cgng nh v pha b goi H.323.

Cach thc gatekeeper nh v c trnh bay trong muc 2.1.3.

Bao hiu kiu Overlap

Call Proc

Hnh 2.25: Thit lp cuc gi t u cui SCN n u cuiH323

Gatewa Gatekeeper u cui H323Setup

Setup

Infomation

SetupCall Proc

Alerting AlertingAlertin

ConnectConnectConnect

Call Proc


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Gateway phai h tr truyn tn hiu bao hiu kiu Overlaptrong giao din vi mang SCN. Nu u cui H.323 cung h trphng thc truyn bao hiu nay th gatekeeper cung se s dungkiu bao hiu Overlap vi u cui.

Chuy:Nu mang SCN s dung kiu truyn bao hiu Overlapth gateway hoc gatekeeper quan ly no phai lu cac sa ch anhn c cho n khi tm thy u cui H.323 ch.

Bao hiu kiu En-bloc

Sau khi u cui H.323 c gatekeeper nh v th thu tuc baohiu En-bloc se c s dung. Khi o gateway (trong trng hp cucgoi nh tuyn trc tip ) hoc gatekeeper (trong trng hp cuc goi

do gatekeeper nh tuyn) se gi phn t thng tin "Sendingcomplete" ti u cui H.323.

Thit lp knh thng tin

Thu tuc kt ni nhanh

Mang VoIP co th s dung thu tuc kt ni nhanh c trnhbay trong muc 2.2.2.1.

Chuy1:Thu tuc nay cho phep trao i thit lp knh thng

tin theo khuyn ngh H.245 hoc quay tr lai thu tuc bao hiu H.245tai moi thi im cua cuc goi.

Chu y 2: Thu tuc nay cho phep trao i cac thng tin trongbng (in-band) trong giai oan thit lp cuc goi.

Ma hoaban tin H.245 trong ban tin H.225.0

Mang VoIP cho phep ma hoa ban tin H.245 trong ban tinH.225.0 nh c trnh bay trong muc 2.2.2.2.

Chuy:Vic ma hoa ban tin H.245 trong ban tin H.225.0 cu tin hn s dung knh H245 ring bi v no mang lai hiu qua caohn.


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iu khin hi m chung

Khi u cui H.323 ap ng bng ban tin ALERTING thgatekeeper quan ly u cui H.323 b goi se phat hi m chung vpha pha chu goi. Sau khi phat hi m chung, gatekeeper se chen

phn t thng tin ch th vi PI c thit lp gia tr la 8 co ngha lacho phep trao i thng tin bao hiu trong bng.

Nu gateway nhn c ban tin ALERTING khng co chaphn t thng tin ch th Progress vi PI co gia tr la 8 th gateway sebt u phat hi m chung.

Khi gateway nhn c ban tin ALERTING trong khi nhnc cuc goi t SCN th gateway se chen phn t thng tin ch th

Progress vi PI c thit lp la 8 co ngha la cho phep trao ithng tin bao hiu trong bng nu nh thng tin nay cha c thitlp.

Cuc goi gia hai u cui SCN qua mang IP

Thit lp cuc goi c ban

Cuc goi co th c thit lp theo thu tuc c nh nghatrong khuyn ngh H.323 cua ITU-T theo cac iu kin sau:

Theo khuyn ngh nay th mt cuc goi se ch c s dung mtknh kt ni vi mang SCN. Cac cuc goi yu cu s dung nhiuknh khng c h tr.


Thu tuc bao hiu kiu en-bloc

Thu tuc bao hiu en-bloc co th c ch nh bi u cui SCN

chu goi. Nu thu bao chu goi s dung bao hiu kiu en-loc, va cacthng tin la y u co th nh tuyn n egress gateway(gateway cua thu bao b goi) th thit lp cuc goi ti u cui b goise c khi ng.

Thu tuc bao hiu kiu Overlap


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Gateway phai h tr thu tuc bao hiu kiu Overlap trong giaodin vi mang SCN.

Chuy:Nu u cui chu goi s dung thu tuc bao hiu Overlapth ingress gateway (gateway cua thu bao chu goi) va gatekeeper

phai lu cac snhn c cho n khi tm ra c egress gatewayKhi gatekeeper nhn c ban tin SETUP ma trng thng tin

sb goi khng th xac nh c egress gateway th no se khi ngb nh thi T302 va gi tra lai ban tin SETUP ACKNOWLEDGE.

Mi khi nhn c ban tin INFORMATION khng cha ch thSending complete va co trng thng tin v sb goi co cha ntnht mt ch s, th no se khi ng lai b nh thi T302.

Hnh 2.26 th hin giai oan thit lp cuc goi gia hai ucui SCN qua mang IP.

SCNch gi

IngressGateway

EgressGatewayGatekeepe

Call Proc Call ProcCall ProcCall Proc

Alerting AlertingAlertingAlerting

Connect ConnectConnectConnect

Setup Setup

Setup SetupSetup

Knh thng tin m t gateway b gi n ch gi

Knh thng tin mt chiu t thu bao b gi n thu bao ch gi

Knh thng tin m c hai

(note 1)

(

(note 2)

(note 3)

Hnh 2.26: Cuc gi gia hai u cui SCN qua mngIP, bo hiu kiu Overlap S dng th tc kt ni nhanh


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Khai nim chung

i vi cuc goi ti mt thu bao trong mang SCN, giai oanthc hin cuc goi c tnh t khi pha b goi tra li va gatewaynhn c ban Connect. i vi cuc goi t mang SCN th giai oan

thc hin cuc goi c tnh t khi gateway truyn ch th tra li chomang SCN.

Khi phat hin co li cua cuc goi trong mang IP th li nay sec thng bao cho khi chc nng ghi cc.

Chuy1: phat hin li cuc goi trong mang IP cho muc chquan ly va tnh cc, gatekeeper phai xac nh chu ky kim tra knhtruyn th hin bng gia tr cua trng irrFrequency trong ban tin

AdmissionConfirm (ACF).Cac trng hp ngoai l trong giai oan thc hin cuc goi

+ Nu gatekeeper nhn thy co li, no se thc hin giai phongcuc goi.

+ Nu gateway nhn thy co li, no se giai phong cuc goi vpha mang SCN sau o giai phong cuc goi pha mang IP.

+ Nu u cui H.323 nhn thy co li no se kch hoat vic kt

thuc cuc goi.Giai phong cuc goi

Cuc goi co th c giai phong bi mt trong cac: u cuiH.323, gateway (khi u cui trong mang SCN kch hoat giai phongcuc goi) hoc gatekeeper. Nguyn nhn giai phong cuc goi co th lado kt thuc cuc goi mt cach bnh thng hoc phat hin co li trongkhi thc hin cuc goi. Cac thu tuc giai phong cuc goi tun theokhuyn ngh H323 nh a trnh bay phn 2.2.2.6.

Hin tng xung t ban tin c khc phuc bi mt trong cac:u cui H.323, gatekeeper, gateway.

Chuy:Hin tng xung t ban tin xay ra khi ca u cui lngateway giai phong cucgoi vao cung mt thi im.

Mt svn khac

cong nghe dien thoai ip

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