46701406 tong dai asterisk va voip nguyenthiquynhtrang04dt1

TRNG I HC BCH KHOA

KHOA IN T - VIN THNG

N TT NGHIP

ti:

TNG I ASTERISK

V CNG NGH VoIP

NGI THC HIN : NGUYN TH QUNH TRANG

LP : 04DT1

NGI HNG DN : GVC.TS.NGUYN VN CNG

NNG, 06/2009

Cng ho x hi ch ngha Vit Nam

c lp - T do - Hnh Phc

*****

LI CAM OAN

Em tn l: Nguyn Th Qunh Trang

Sinh vin lp: 04T1

Em xin cam oan ni dung n ny khng ging hon ton vi bt c n hoc

cng trnh c t trc. Nu khng ng, em xin chu hon ton trch nhim.

Mc lc

MC LC

MC LC M U DANH MC HNH V DANH MC BNG BIU CC T VIT TT

CHNG 1 TNG QUAN V VOIP ................................................................. 1

1.1 Gii thiu chng ................................................................................... 1

1.2 Khi qut v mng VoIP ........................................................................ 1 1.2.1 Gii thiu .............................................................................................. 1 1.2.2 Khi nim .............................................................................................. 1 1.2.3 c im ca in thoi IP ................................................................... 2 1.2.4 Cc hnh thc truyn thoi qua IP ........................................................ 4 1.2.5 Mt s ng dng VoIP ......................................................................... 6 1.2.6 c tnh ca mng VoIP ....................................................................... 7 1.2.7 Yu cu cht lng i vi VoIP ......................................................... 9

1.3 Kin trc v cc thnh phn mng VoIP ........................................... 10 1.3.1 Kin trc tng qut mng VoIP .......................................................... 10 1.3.2 M hnh phn lp chc nng .............................................................. 11 1.3.3 Cc thnh phn trong mng VoIP ....................................................... 13

1.4 Kt lun chng ................................................................................... 14

CHNG 2 CC GIAO THC BO HIU TRONG MNG VOIP ........... 15

2.1 Gii thiu chng ................................................................................. 15

2.2 Cc giao thc bo hiu trong mng VoIP .......................................... 15 2.2.1 H.323................................................................................................... 15 2.2.2 SIP ....................................................................................................... 23 2.2.3 Giao thc SGCP (Simple Gateway Control Protocol) ....................... 31 2.2.4 Giao thc MGCP (Media Gateway Control Protocol) ....................... 31 2.2.5 Kt lun chng .................................................................................. 32

CHNG 3 TNG I ASTERISK ................................................................ 33

3.1 Gii thiu chng ................................................................................. 33

3.2 Tng i IP-PBX .................................................................................. 33 3.2.1 Mt s m hnh cuc gi s dng tng i IP-PBX ........................... 36

Mc lc

3.3 Tng i Asterisk .................................................................................. 37 3.3.1 Kin trc h thng Asterisk ................................................................ 39 3.3.2 Mt s tnh nng c bn ..................................................................... 40 3.3.3 Ng cnh ng dng ............................................................................. 42

3.4 Asterisk vi VoIP .................................................................................. 44 3.4.1 Cc thit b dng trong VoIP .............................................................. 44 3.4.2 Cc giao thc VoIP c Asterisk h tr ........................................... 46 3.4.3 Cc chun nn v nh dng file ......................................................... 47 3.4.4 File cu hnh ....................................................................................... 50 3.4.5 Dialplan trong Asterisk ....................................................................... 53

3.5 Kt lun chng ................................................................................... 56

CHNG 4 TRIN KHAI H THNG ASTERISK ..................................... 57

4.1 Gii thiu chong ................................................................................. 57

4.2 Kt ni phn cng ................................................................................ 57

4.3 Ci t phn mm ................................................................................ 58

4.4 Cu hnh h thng Aterisk ................................................................... 59

4.5 Thc hin cuc gi ................................................................................ 62

4.6 Kt lun chng ................................................................................... 64

KT LUN V HNG PHT TRIN TI

PH LC

Li m u

M U

Nhng nm gn y, s lng ngi s dng Internet trn th gii ngy mt tng.

Mng Internet pht trin thnh mt mng s liu ton cu cho php nhiu loi hnh

thng tin truyn i trn . Ra i sau mng chuyn mch knh, s pht trin ca Internet

lin quan nhiu n cc k thut ca mng PSTN. Rt nhiu ngi truy nhp vo Internet

bng modem thng qua ng dy in thoi v mng in thoi c th tr thnh mi

trng truyn i nhng thng tin s liu. Cc dch v multimedia trn mng Internet

ang ngy cng pht trin, thng tin truyn trn Internet khng ch cn l s liu na m

bao gm c ting ni v hnh nh. Mng Internet v mng PSTN ang c xu hng hi

nhp li vi nhau. Mt biu hin ca s hi nhp gia mng Internet v mng PSTN l

dch v truyn thoi qua mng IP.

Dch v truyn thoi qua mng IP trong vi nm gn y ang pht trin rt mnh. N

ha hn em li nhiu li ch bao gm gim chi ph cc cuc gi ng di v tch hp

thoi v s liu vo mt mng duy nht da trn cng ngh chuyn mch gi. V vy, vic

nghin cu v nm bt cng ngh VoIP ang c nhiu i tng quan tm.

Trong qu trnh tm hiu em chn ti : Tng i ASTERISK v cng ngh

VoIP. Ni dung ti gm 4 chng:

Chng 1 Tng quan v VoIP

Trong chng ny s tm hiu cc khi nim VoIP, ng dng ca VoIP, trnh by

cc u, nhc im cng nh yu cu cht lng i vi VoIP v tm hiu v kin

trc mng v cc thnh phn ca mng VoIP.

Chng 2 Cc giao thc trong mng VoIP

Chng ny s trnh by cc khi nim, chc nng ca giao thc bo hiu trong

mng VoIP

Chng 3 Tng i Asterisk

Gii thiu v tng i Asterisk, trnh by kin trc , tnh nng v ng cnh ng

dng ca tng i Asterisk, gii thiu cc giao thc ca VoIP ca tng i.

Chng 4 Trin khai h thng Asterisk

Thc hin th nghim hnh thc truyn thoi qua mi trng IP thy c cc

tnh nng m h thng Asterisk em li.

Li m u

Trong qu trnh lm n, em c gng rt nhiu song do kin thc hn ch nn

khng th trnh khi nhng thiu st. Em rt mong nhn c s gp , hng dn v s

gip ca Thy C, bn b.

Sut qu trnh hc tp, Thy C truyn t cho em nhiu kin thc qu bu to c

s cho em hon thnh n ny. Em xin chn thnh gi li cm n n cc Thy C

trong khoa in T-Vin Thng. c bit l Thy Nguyn Vn Cng ng gp

nhiu kin qu bu v c v, ng vin em trong thi gian qua.

Em xin chn thnh cm n!

Nng, thng 6 nm 2009

Sinh vin thc hin

Nguyn Th Qunh Trang

Danh mc hnh v

DANH MC HNH V

Hnh 1.1 M hnh PC to PC ......................................................................................... 5

Hnh 1.2 M hnh PC to Phone ................................................................................... 5

Hnh 1.3 M hnh Phone to Phone .............................................................................. 6

Hnh 1.4 M hnh kin trc tng quan ca mng VoIP ............................................. 10 Hnh 1.5 M hnh phn cp chc nng ...................................................................... 11 Hnh 1.6 Cu hnh mng VoIP trong xu hng mng th h mi NGN ................... 13 Hnh 2.1 Cc giao thc s dng trong H.323 ............................................................ 15 Hnh 2.2 Cc thnh phn ca H.323 .......................................................................... 16 Hnh 2.3 Tp giao thc H.323 ................................................................................... 18 Hnh 2.4 Qu trnh thit lp cuc gi H.323 ............................................................. 22 Hnh 2.5 Cc thnh phn ca SIP .............................................................................. 23 Hnh 2.6 Hot ng ca Proxy server........................................................................ 25 Hnh 2.7 Hot ng ca Redirect Server ................................................................... 26 Hnh 2.8 Thit lp v hy cuc gi SIP ..................................................................... 27 Hnh 3.1 M hnh IP-PBX hay PBX mm ............................................................. 33 Hnh 3.2 M hnh cuc gi ni b ............................................................................. 36 Hnh 3.3 M hnh cuc gi t my IP ra mng PSTN .............................................. 36 Hnh 3.4 M hnh cuc gi t PSTN vo my IP-PBX ............................................ 37 Hnh 3.5 M hnh cuc gi s dng dch v SIP cng cng ..................................... 37 Hnh 3.6 S giao tip tng qut. ........................................................................... 38 Hnh 3.7 S khi ca Asterisk .............................................................................. 39 Hnh 3.8 IP BPX ........................................................................................................ 42

Hnh 3.9 Kt ni IP PBX vi PBX ............................................................................. 42 Hnh 3.10 Kt ni gia cc server asterisk ................................................................. 43 Hnh 3.11 Trin khai server IVR, VoiceMail, Conference Call ................................... 43 Hnh 3.12 Phn phi cuc gi vi hng i ................................................................ 44 Hnh 3.13 Cc chun nn ........................................................................................... 48 Hnh 3.14 Cc nh dng file ..................................................................................... 48 Hnh 4.1 M hnh trin khai h thng Asterisk trong mng LAN ............................ 57 Hnh 4.2 Giao din Fedora Core 8 ............................................................................. 58 Hnh 4.3 Giao din softphone X-lite 3.0 ................................................................... 59 Hnh 4.4 Cu hnh softphone ..................................................................................... 60 Hnh 4.5 Softphone X-Lite ng k thnh cng ti khon 200 ................................. 61 Hnh 4.6 Cc user c xc nhn ca h thng Asterisk PBX ............................. 61 Hnh 4.7 User 200 rung chung 201.......................................................................... 62

Hnh 4.8 Cuc gi c thit lp gia user 200 v 201 ............................................ 62 Hnh 4.9 Li nhn c gi n voicemail box ca user 200 ................................... 63 Hnh 4.10 Truy nhp vo voicemail ca user 200 bng cch bm gi 500 ................ 63 Hnh 4.11 Cuc gi gia user 200 vi skype-username ............................................. 64

Danh mc bng biu

DANH MC BNG BIU

Bng 3.1 So snh gia PBX truyn thng v IP-PBX ................................................ 34 Bng 3.2 H thng qun l file trong Asterisk ........................................................... 50

Cc t vit tt

CC T VIT TT

A

AA Automated Attendant

ACD Automatic Call Distribution

Phn phi cuc gi t ng

ATM Asynchronous Transfer Mode

Ch truyn khng ng b

ATA Advanced Technology Attachment

Chun truyn d liu cho cc thit b lu tr.

ADSL Asymmetric Digital Subcriber Line

ng truyn thu bao s bt ng b

API Application Program Interface

Giao din ng dng

ARP Address Resolution Protocol

Giao thc phn gii a ch ARP

C

CRC cyclic redundancy check

Kim tra vng d

CPL Call Processing Language

Ngn ng x l cuc gi

COPS Common Open Policy Service

Dch v chnh sch m chung

D

DTMF Dual Tone Multi Frequency

a tn kp

Cc t vit tt

H

HTTP Hypertext Transfer Protocol

Giao thc truyn siu vn bn

I

IAX Inter-Asterisk eXchange

IP Internet Protocol

Giao thc Internet

IPDC Internet Protocol Device Control

Giao thc iu khin thit b

IVR Interactive Voice Response

Tng tc thoi

M

MAC Media Access Control

Kh nng kt ni tng vt l

MCU Multipoint Control Unit

Khi iu khin a im

MGCP Media Gateway Control Protocol

Giao thc iu khin Media Gateway

MGW Media GateWay

Cng truyn thng

MGWC Media GateWay Controller

iu khin cng truyn thng

MIME Multipurpose Internet Mail Extension

M rng th tn Internet a mc ch: Giao thc th in t

Cc t vit tt

N

NIC Network Information Center

Trung tm thng tin mng

O

OSP Open Settlement Protocol

Giao thc tha thun m

P

PSTN Public Switch Telephone Network

Mng in thoi cng cng

PPP Point-to-Point Protocol

Giao thc im ti im

PBX Private branch exchange

Tng i c nhn

PCI Peripheral Component Interconnect

Cc thnh phn cu hnh nn cng giao tip ngoi vi theo chun

ni tip

Q

QoS Quality of Service

Cht lng dch v

R

RTP Real-time Transport Protocol

Giao thc truyn thi gian thc

RTCP Real Time Control Protocol

Giao thc iu khin thi gian thc

RAS Register Admission Status

Bo hiu ng k, cp php, thng tin trng thi

RTSP Real Time Streaming Protocol

Giao thc to lung thi gian thc

RSVP Resource Reservation Protocol

Giao thc ginh trc ti nguyn mng

Cc t vit tt

S

SIP Session Initiation Protocol

Giao thc khi to phin

SGCP Simple Gateway Control Protocol

Giao thc iu khin cng mng n gin

SAP Session Advertisement Protocol

Giao thc thng bo trong phin kt ni

SDP Session Description Protocol

Giao thc m t phin

SS7 Signaling System 7

H thng bo hiu s 7

SGW Signalling Gateway

Gateway bo hiu

Cc t vit tt

T

TCP Transport Control Protocol

Giao thc iu khin truyn TCP

TDM Time Division Multiplex

Ghp knh phn chia thi gian

TLS Transmission layer security

Giao thc bo mt lp truyn ti

TTL Time to live

Thi gian tn ti gi tin

U

UDP User Datagram Protocol

Giao thc gi ngi s dng

V

VoIP Voice over IP

Cng ngh truyn thoi trn mng IP

Chng 1: Tng quan v VoIP

1

CHNG 1

TNG QUAN V VoIP

1.1 Gii thiu chng

VoIP- in thoi internet hay thng gi l dch v in thoi di rng (Broadband

Telephony) ang lm thay i ngnh in thoi th gii. Trong mi trng doanh nghip

ang dn dn thay th kiu in thoi truyn thng tn dng cc li ch v c im m

in thoi internet mang li. Do bit r hn v VoIP, trong chng ny ta ln lt

tm hiu khi qut v VoIP, trnh by cc khi nim VoIP, m hnh truyn thoi qua mng

IP, ng dng ca VoIP, trnh by cc u, nhc im cng nh yu cu cht lng i

vi VoIP.Tm hiu v kin trc mng v cc thnh phn ca mng VoIP.

1.2 Khi qut v mng VoIP 1

1.2.1 Gii thiu

u nm 1995 cng ty VOCALTEC a ra th trng sn phm phn mm thc hin

cuc thoi qua Internet u tin trn th gii. Sau c nhiu cng ty tham gia vo

lnh vc ny. Thng 3 nm 1996, VOLCALTEC kt hp vi DIALOGIC tung ra th

trng sn phm kt ni mng PSTN v Internet. Hip hi cc nh sn xut thoi qua

mng my tnh sm ra i v thc hin chun ho dch v thoi qua mng Internet.

Vic truyn thoi qua internet gy c ch ln trong nhng nm qua v dn

c ng dng rng ri trong thc t.

1.2.2 Khi nim

C th nh ngha: Voice over Internet Protocol (VoIP) l mt cng ngh cho php

truyn thoi s dng giao thc mng IP, trn c s h tng sn c ca mng Internet.

VoIP l mt trong nhng cng ngh vin thng ang c quan tm nht hin nay khng

ch i vi cc nh khai thc, cc nh sn xut m cn c vi ngi s dng dch v.

VoIP c th va thc hin cuc gi thoi nh trn mng in thoi knh truyn thng

(PSTN) ng thi truyn d liu trn c s mng truyn d liu. Nh vy, n tn dng


2

c sc mnh v s pht trin vt bc ca mng IP vn ch c s dng truyn d

liu thng thng.

1.2.3 c im ca in thoi IP

in thoi IP ra i nhm khai thc tnh hiu qu ca cc mng truyn s liu, khai

thc tnh linh hot trong pht trin cc ng dng mi ca giao thc IP v n c p dng

trn mt mng ton cu l mng Internet. Cc tin b ca cng ngh mang n cho in

thoi IP nhng u im sau:

+ Gim chi ph cuc gi: u im ni bt nht ca in thoi IP so vi dch v

in thoi hin ti l kh nng cung cp nhng cuc gi ng di gi r vi cht lng

chp nhn c. Nu dch v in thoi IP c trin khai, chi ph cho mt cuc gi

ng di s ch tng ng vi chi ph truy nhp internet. Nguyn nhn dn n chi

ph thp nh vy l do tn hiu thoi c truyn ti trong mng IP c kh nng s dng

knh hiu qu cao. ng thi, k thut nn thoi tin tin gim tc bt t 64 Kbps

xung thp ti 8 Kbps (theo tiu chun nn thoi G.729A ca ITU-T) kt hp vi tc

x l nhanh ca cc b vi x l ngy nay cho php vic truyn ting ni theo thi gian

thc l c th thc hin c vi lng ti nguyn bng thng thp hn nhiu so vi k

thut c.

So snh mt cuc gi trong mng PSTN vi mt cuc gi qua mng IP, ta thy:

Chi ph phi tr cho cuc gi trong mng PSTN l chi ph phi b ra duy tr cho mt

knh 64kbps sut t u cui ny ti u cui kia thng qua mt h thng cc tng i.

Chi ph ny i vi cc cuc gi ng di (lin tnh, quc t) l kh ln.

Trong trng hp cuc gi qua mng IP, ngi s dng t mng PSTN ch phi

duy tr knh 64kbps n Gateway ca nh cung cp dch v ti a phng. Nh cung cp

dch v in thoi IP s m nhn nhim v nn, ng gi tn hiu thoi v gi chng i

qua mng IP mt cch c hiu qu nht ti c Gateway ni ti mt mng in thoi

khc c ngi lin lc u kia. Vic kt ni nh vy lm gim ng k chi ph cuc gi

do phn ln knh truyn 64Kbps c thay th bng vic truyn thng tin qua mng

d liu hiu qu cao.


3

+ Tch hp mng thoi, mng s liu v mng bo hiu: Trong in thoi IP, tn

hiu thoi, s liu v ngay c bo hiu u c th cng i trn cng mt mng IP. iu

ny s tit kim c chi ph u t xy dng nhng mng ring r.

+ Kh nng m rng (Scalability): Nu nh cc h tng i thng l nhng h

thng kn, rt kh thm vo nhng tnh nng th cc thit b trong mng internet

thng c kh nng thm vo nhng tnh nng mi. Chnh tnh mm do mang li cho

dch v in thoi IP kh nng m rng d dng hn so vi in thoi truyn thng.

+ Khng cn thng tin iu khin thit lp knh truyn vt l: Gi thng tin

trong mng IP truyn n ch m khng cn mt s thit lp knh no. Gi ch cn mang

a ch ca ni nhn cui cng l thng tin c th n c ch. Do vy, vic iu

khin cuc gi trong mng IP ch cn tp trung vo chc nng cuc gi m khng phi

tp trung vo chc nng thit lp knh.

+ Qun l bng thng: Trong in thoi chuyn mch knh, ti nguyn bng

thng cung cp cho mt cuc lin lc l c nh (mt knh 64Kbps) nhng trong in

thoi IP vic phn chia ti nguyn cho cc cuc thoi linh hot hn nhiu. Khi mt cuc

lin lc din ra, nu lu lng ca mng thp, bng thng dnh cho lin lc s cho cht

lng thoi tt nht c th; nhng khi lu lng ca mng cao, mng s hn ch bng

thng ca tng cuc gi mc duy tr cht lng thoi chp nhn c nhm phc v

cng lc c nhiu ngi nht. im ny cng l mt yu t lm tng hiu qu s dng

ca in thoi IP. Vic qun l bng thng mt cch tit kim nh vy cho php ngi ta

ngh ti nhng dch v cao cp hn nh truyn hnh hi ngh, iu m vi cng ngh

chuyn mch c ngi ta khng thc hin v chi ph qu cao.

+ Nhiu tnh nng dch v: Tnh linh hot ca mng IP cho php to ra nhiu tnh

nng mi trong dch v thoi. V d cho bit thng tin v ngi gi ti hay mt thu bao

in thoi IP c th c nhiu s lin lc m ch cn mt thit b u cui duy nht (V d

nh mt thit b IP Phone c th c mt s in thoi dnh cho cng vic, mt cho cc

cuc gi ring t).

+ Kh nng multimedia: Trong mt cuc gi ngi s dng c th va ni

chuyn va s dng cc dch v khc nh truyn file, chia s d liu, hay xem hnh nh

ca ngi ni chuyn bn kia.


4

in thoi IP cng c nhng hn ch:

+ K thut phc tp: Truyn tn hiu theo thi gian thc trn mng chuyn mch

gi l rt kh thc hin do mt gi trong mng l khng th trnh c v tr khng c

nh ca cc gi thng tin khi truyn trn mng. c c mt dch v thoi chp nhn

c, cn thit phi c mt k thut nn tn hiu t c nhng yu cu kht khe: t s

nn ln ( gim c tc bit xung), c kh nng suy on v to li thng tin ca

cc gi b tht lc...Tc x l ca cc b Codec (Coder and Decoder- B m ha v

gii m) phi nhanh khng lm cuc m thoi b gin on. ng thi c s h

tng ca mng cng cn c nng cp ln cc cng ngh mi nh Frame Relay,

ATM,... c tc cao hn v phi c mt c ch thc hin chc nng QoS (Quality of

Service- Cht lng dch v). Tt c cc iu ny lm cho k thut thc hin in thoi IP

tr nn phc tp v khng th thc hin c trong nhng nm trc y.

+ Vn bo mt (security): Mng Internet l mt mng c tnh rng khp v

hn hp (hetorogenous network). Trong c rt nhiu loi my tnh khc nhau cng cc

dch v khc nhau cng s dng chung mt c s h tng. Do vy khng c g m bo

rng thng tin lin quan n c nhn cng nh s lin lc truy nhp s dng dch v ca

ngi dng c gi b mt.

Nh vy, in thoi IP chng t n l mt loi hnh dch v mi rt c tim nng.

Trong tng lai, in thoi IP s cung cp cc dch v hin c ca in thoi trong mng

PSTN v cc dch v mi ca ring n nhm em li li ch cho ng o ngi dng.

Tuy nhin, in thoi IP vi t cch l mt dch v s khng tr nn hp dn hn PSTN

ch v n chy trn mng IP. Khch hng ch chp nhn loi dch v ny nu nh n a

ra c mt chi ph thp v nhng tnh nng vt tri hn so vi dch v in thoi hin

ti.

1.2.4 Cc hnh thc truyn thoi qua IP

1.2.4.1 M hnh PC to PC

Trong m hnh ny, mi my tnh cn c trang b mt sound card, mt microphone,

mt speaker v c kt ni trc tip vi mng Internet thng qua modem hoc card

mng. Mi my tnh c cung cp mt a ch IP v hai my tnh c th trao i cc

tn hiu thoi vi nhau thng qua mng Internet. Tt c cc thao tc nh ly mu tn hiu


5

m thanh, m ho v gii m, nn v gii nn tn hiu u c my tnh thc hin. Trong

m hnh ny ch c nhng my tnh ni vi cng mt mng mi c kh nng trao i

thng tin vi nhau.

` `

Internet

PC PC

Hnh 1.1 M hnh PC to PC

1.2.4.2 M hnh PC to Phone

M hnh PC to Phone l mt m hnh c ci tin hn so vi m hnh PC to PC. M

hnh ny cho php ngi s dng my tnh c th thc hin cuc gi n mng PSTN

thng thng v ngc li. Trong m hnh ny mng Internet v mng PSTN c th giao

tip vi nhau nh mt thit b c bit l Gateway. y l m hnh c s dn ti

vic kt hp gia mng Internet v mng PSTN cng nh cc mng GSM hay a dch v

khc.

PSTNInternet`

PC Phone

Hnh 1.2 M hnh PC to Phone

1.2.4.3 M hnh Phone to Phone

y l m hnh m rng ca m hnh PC to Phone s dng Internet lm phng tin lin

lac gia cc mng PSTN. Tt c cc mng PSTN u kt ni vi mng Internet thng qua

cc gateway. Khi tin hnh cuc gi mng PSTN s kt ni n gateway gn nht. Ti

gateway a ch s c chuyn i t a ch PSTN sang a ch IP c th nh tuyn

cc gi tin n c mng ch. ng thi gateway ngun c nhim v chuyn i tn

hiu thoi tng t thnh dng s sau m ho, nn, ng gi v gi qua mng. Mng


6

ch cng c kt ni vi gateway v ti gateway ch, a ch li c chuyn i tr

li thnh a ch PSTN v tn hiu c gii nn, gii m chuyn i ngc li thnh tn

hiu tng t gi vo mng PSTN n ch.

Hnh 1.3 M hnh Phone to Phone

1.2.5 Mt s ng dng VoIP

Giao tip thoi s vn l dng giao tip c bn ca con ngi.Mng in thoi cng

cng khng th b n gin thay th, thm ch thay i trong thi gian ti. Mc ch tc

thi ca cc nh cung cp dch v in thoi IP l ti to li kh nng ca in thoi vi

mt chi ph vn hnh thp hn nhiu v a ra cc gii php k thut b sung cho mng

PSTN.

in thoi c th c p dng cho gn nh mi yu cu ca giao tip thoi, t mt

cuc m thoi c bn cho n mt cuc gi hi ngh nhiu ngi phc tp. Cht lng

m thanh c truyn cng c th bin i tu theo ng dng. Ngoi ra, vi kh nng ca

Internet, dch v in thoi IP s cung cp thm nhiu tnh nng mi.

Ta c th xem xt mt vi ng dng ca in thoi :

Thoi thng minh

H thng in thoi ngy cng tr nn hu hiu: r, ph bin, d s dng, c

ng. N ch c mt s phm iu khin. Trong nhng nm gn y, ngi ta c

gng to ra thoi thng minh, u tin l cc thoi bn, sau l n cc server. Nhng

mi c gng u tht bi do s tn ti ca cc h thng c sn.

Internet s thay i iu ny. K t khi Internet ph khp ton cu, n c s

dng tng thm tnh thng minh cho mng in thoi ton cu. Gia mng my tnh v

mng in thoi tn ti mt mi lin h. Internet cung cp cch gim st v iu khin cc


7

cuc thoi VoIP mt cch tin li hn. Chng ta c th thy c kh nng kim sot v

iu khin cc cuc gi thng qua mng Internet.

Dch v in thoi Web

World Wide Web lm cuc cch mng trong cch giao dch vi khch hng ca

cc doanh nghip. in thoi Web hay bm s (click to dial) cho php cc doanh

nghip c th a thm cc phm bm ln trang web kt ni ti h thng in thoi

ca h.

Truy cp cc trung tm tr li in thoi

Truy cp n cc trung tm phc v khch hng qua mng Internet s thc y

mnh m thng mi in t. Dch v s cho php mt khch hng c cu hi v mt sn

phm c cho hng qua Internet c cc nhn vin ca cng ty tr li trc tip.

Dch v fax qua IP

Vic s dng Internet khng nhng c m rng cho thoi m cn cho c dch v

fax. Nu bn gi nhiu fax t PC, c bit l gi ra nc ngoi th vic s dng dch

v Internet faxing s gip bn tit kim c tin v c knh thoi. Dch v ny s

chuyn trc tip t PC ca bn qua kt ni Internet.

1.2.6 c tnh ca mng VoIP

1.2.6.1 u im

Gim chi ph: y l u im ni bt ca VoIP so vi in thoi ng di thng

thng. Chi ph cuc gi ng di ch bng chi ph cho truy nhp Internet. Mt gi cc

chung s thc hin c vi mng Internet v do tit kim ng k cc dch v thoi

v fax. S chia s chi ph thit b v thao tc gia nhng ngi s dng thoi v d liu

cng tng cng hiu qu s dng mng. ng thi k thut nn thoi tin tin lm gim

tc bit t 64Kbps xung di 8Kbps, tc l mt knh 64Kbps lc ny c th phc v

ng thi 8 knh thoi c lp. Nh vy, l d ln nht gip cho chi ph thc hin cuc

gi VoIP thp chnh l vic s dng ti u bng thng.

Tnh thng nht : H thng VoIP c th tch hp c mng thoi , mng s liu v

mng bo hiu. Cc tn hiu thoi, d liu, bo hiu c th cng i trn mt mng IP. Vic

ny s gim ng k chi ph u t.


8

Vn qun l bng thng: Trong PSTN, bng thng cung cp cho mt cuc gi

l c nh. Trong VoIP, bng thng c cung cp mt cch linh hot v mm do hn

nhiu. Cht lng ca VoIP ph thuc vo nhiu yu t, quan trng nht l bng thng.

Do khng c s bt buc no v mt thng lng gia cc thit b u cui m ch c

cc chun tu vo bng thng c th ca mnh, bn thn cc u cui c th t iu chnh

h s nn v do iu chnh c cht lng cuc gi.

Nng cao ng dng v kh nng m rng: Thoi v fax ch l cc ng dng khi

u cho VoIP, cc li ch trong thi gian di hn c mong i t cc ng dng a

phng tin (multimedia) v a dch v. Tnh linh hot ca mng IP cho php to ra nhiu

tinh nng mi trong dch v thoi. ng thi tnh mm do cn to kh nng m rng

mng v cc dch v.

Tnh bo mt cao: VoIP c xy dng trn nn tng Internet vn khng an ton,

do s dn n kh nng cc thng tin c th b nh cp khi cc gi tin b thu lm

hoc nh tuyn sai a ch mt cch c khi chng truyn trn mng. Cc giao thc SIP

(Session ineitiation Protocol giao thc khi u phin) c th thnh mt m v xc nhn

cc thng ip bo hiu u cui. RTP (Real Time Protocol) h tr m thnh mt m ca

phng thc truyn thng trn ton tuyn c m ho thnh mt m m bo truyn

thng an ton.

1.2.6.2 Nhc im

Cht lng dch v cha cao: Cc mng s liu vn d khng phi xy dng vi

mc ch truyn thoi thi gian thc, v vy khi truyn thoi qua mng s liu cho cht

lng cuc gi khng c m bo trong trng hp mng xy ra tc nghn hoc c

tr ln. Tnh thi gian thc ca tn hiu thoi i hi cht lng truyn d liu cao v n

nh. Mt yu t lm gim cht lng thoi na l k thut nn tit kim ng

truyn. Nu nn xung dung lng cng thp th k thut nn cng phc tp, cho cht

lng khng cao v c bit l thi gian x l s lu, gy tr.

Vn ting vng: Nu nh trong mng thoi, tr thp nn ting vng khng

nh hng nhiu th trong mng IP, do tr ln nn ting vng nh hng nhiu n cht

lng thoi.


9

K thut phc tp: Truyn tn hiu theo thi gian thc trn mng chuyn mch

gi l rt kh thc hin do mt gi trong mng l khng th trnh c v tr khng c

nh ca cc gi thng tin khi truyn trn mng. c c mt dch v thoi chp nhn

c, cn thit phi c mt k thut nn tn hiu t c nhng yu cu kht khe: t s

nn ln ( gim c tc bit xung), c kh nng suy on v to li thng tin ca

cc gi b tht lc... Tc x l ca cc b Codec (Coder and Decoder) phi nhanh

khng lm cuc m thoi b gin on. ng thi c s h tng ca mng cng cn

c nng cp ln cc cng ngh mi nh Frame Relay, ATM,... c tc cao hn

hoc phi c mt c ch thc hin chc nng QoS (Quality of Service). Tt c cc iu

ny lm cho k thut thc hin in thoi IP tr nn phc tp v khng th thc hin

c trong nhng nm trc y

Ngoi ra c th k n tnh phc tp ca k thut v vn bo mt thng tin (do

Internet ni ring v mng IP ni chung vn c tnh rng khp v hn hp, khng c g

bo m rng thng tin c nhn c gi b mt).

1.2.7 Yu cu cht lng i vi VoIP

T nhng nhc im chnh ca mng chuyn mch gi t ra nhng yu cu

cho VoIP nh sau:

Cht lng thoi phi n nh, tr chp nhn c.

Mng IP c bn phi p ng c nhng tiu ch hot ng kht khe gm gim

thiu vic khng chp nhn cuc gi, mt mt gi v mt lin lc. iu ny i hi ngay

c trong trng hp mng b nghn hoc khi nhiu ngi s dng chung ti nguyn ca

mng cng mt lc.

Vic bo hiu c th tng tc c vi bo hiu ca mng PSTN.

Qun l h thng an ton, a ch ho v thanh ton phi c cung cp, tt nht l

c hp nht vi cc h thng h tr hot ng PSTN.


10

1.3 Kin trc v cc thnh phn mng VoIP

1.3.1 Kin trc tng qut mng VoIP

Hnh 1.4 M hnh kin trc tng quan ca mng VoIP

Trong m hnh ny l s c mt ca ba thnh phn chnh trong mng VoIP l:


11

IP Phone (hay cn gi l SoftPhone): l thit b giao din u cui pha ngi dng

vi mng VoIP. Cu to chnh ca mt IP Phone gm hai thnh phn chnh:Thnh phn

bo hiu mng VoIP: bo hiu c th l H.323 s dng giao thc TCP hay SIP s dng

UDP hoc TCP lm giao thc truyn ti ca mnh. Thnh phn truyn ti media: s dng

RTP truyn lung media vi cht lng thi gian thc v c iu khin theo giao

thc RTCP.

VoIP Server: chc nng chnh ca Server trong mng VoIP ty thuc vo giao thc

bo hiu c s dng. Nhng v m hnh chung th VoIP Server thc hin cc chc

nng sau:

nh tuyn bn tin bo hiu trong mng VoIP

ng k, xc thc ngi s dng

Dch a ch trong mng

Ni chung, VoIP Server trong mng nh l u no ch huy mi hot ng ca mng.

Server c th tch hp tt c cc chc nng (SoftSwitch) hoc nm tch bit trn cc

Server chc nng khc nhau ( Location Server, Registrar Server, Proxy Server,).

1.3.2 M hnh phn lp chc nng

V mt chc nng, cng ngh VoIP c th c chi lm ba lp nh sau:

Lp ng dng dch v

Lp iu khin cuc gi

Lp c s h tng mng gi

Giao din m v tun theo chun

Giao din m v tun theo chun

Hnh 1.5 M hnh phn cp chc nng

Lp c s h tng mng gi thc hin chc nng truyn ti lu lng thoi. Trong

VoIP, c s h tng l cc mng IP. Giao thc truyn ti thi gian thc RTP (Realtime

Transport Protocol) kt hp vi UDP v IP gip truyn ti thng tin thoi qua mng IP.

RTP chy trn UDP, cn UDP hot ng trn IP hnh thnh ln c ch truyn

RTP/UDP/IP trong VoIP.


12

Trong cc mng IP, hin tng cc gi IP tht lc hoc n khng theo th t

thng xuyn xy ra. C ch truyn TCP/IP khc phc vic mt gi bng c ch truyn

li khng ph hp vi cc ng dng thi gian thc vn rt nhy cm vi tr. RTP vi

trng tem thi gian (timestamp) c dng bn thu nhn bit v x l cc vn nh

tr, s thay tr(jitter) v s mt gi.

Lp iu khin cuc gi thc hin chc nng bo hiu, nh hng cuc gi trong

VoIP. S phn tch gia mt phng bo hiu v truyn ti c thc hin PSTN vi

bo hiu knh chung SS7, nhng y nhn mnh mt thc t c nhiu chun bo hiu

cho VoIP cng tn ti nh H323, SIP hay SGCP/MGCP (Simple Gateway Control

Protocol/ Media Gateway Control Protocol). Cc giao thc bo hiu ny c th hot ng

cng nhau, c ng dng ph hp vi nhng nhu cu c th ca mng. Ngoi ra lp

ny cn cung cp chc nng truy nhp ti dch v bn trn cng nh cc giao din lp

trnh m pht trin ng dng.

Lp ng dng dch v m nhim chc nng cung cp dch v trong mng vi c

dch v c tong t nh trong PSTN v dch v mi thm vo. Cc giao din m cho

php cc nh cung cp phn mm c lp pht trin ra nhiu ng dng mi. c bit l

cc ng dng da trn Web, cc ng dng kt hp gia thoi v d liu, cc ng dng

lin quan ti thng mi in t. S phn tch lp dch v lm cho cc dch v mi c

trin khai nhanh chng. Ngoi ra, cc chc nng nh qun l, nhn thc cuc gi v

chuyn i a ch cng c thc hin lp ny.

Do cc giao din gia cc lp l m v tun theo chun, to ra nhiu s la chn

khi xy dng thit k mng. V d, ng vi lp c s h tng mng ta c th dng cc

router v switch ca hng Cisco, iu khin cuc gi thc hin bng cc gatekeeper ca

VocalTec v cc dch v c cung cp bi server dch v ca Netspeak. Do m hnh

trn khng ch c gi tr v mt l thuyt.


13

1.3.3 Cc thnh phn trong mng VoIP

Hnh 1.6 Cu hnh mng VoIP trong xu hng mng th h mi NGN

Mng VoIP phi c kh nng thc hin cc chc nng m mng in thoi cng

cng thc hin, ngoi ra phi thc hin chc nng ca mt gateway gia mng IP v

mng in thoi cng cng. Thnh phn ca mng in thoi IP c th gm cc phn t

sau y:

+ Thit b u cui kt ni vi mng IP: L mt nt cui cng trong mng in

thoi IP, mt thit b u cui c th cho php mt thu bao trong mng IP thc hin

cuc gi. Cuc gi s c gatekeeper m u cui hoc thu bao ng k gim st.

+ Mng truy nhp IP: L cc loi mng d liu s dng chng giao thc TCP/IP

trong s dng giao thc IP cho lp mng (lp 3) cn lp truy nhp mng (lp 2) c

th l giao thc ca mng LAN, x25, Frame Relay, PPP....

+ Gateway: L thit b c chc nng kt ni hai mng khng ging nhau, hu ht

cc trng hp l mng IP v mng PSTN. C 3 loi gateway l: Gateway truyn ti

knh thoi, Gateway iu khin truyn ti knh thoi v Gateway bo hiu.

- Gateway bo hiu (SGW- Signalling Gateway): chc nng trung chuyn gia bo

hiu trong mng chuyn mch knh (nh l SS7 hay R2) v bo hiu trong mng IP

(H.323), phi hp hot ng vi Gateway truyn ti v h thng qun l mng. Gateway

bo hiu c th ng c lp hoc c th kt hp vi Gateway truyn ti thoi thnh mt

Gateway duy nht.


14

- Gateway truyn ti knh thoi( MGW- Media Gateway): Chc nng chuyn i

khun dng thng tin t thng tin ghp knh theo thi gian (TDM) trong mng chuyn

mch gi thnh cc gi tin IP v ngc li, nn tn hiu thoi (voice compression), nn

khong lng (silent comppression) trit ting vng (echo cancellation). Ngoi ra cn cung

cp cc giao din vt cho cc kt ni ca cc mng (nh E1/T1 vi mng chuyn mch

knh, ethernet/frame relay vi mng IP).

- Gateway iu khin truyn ti knh thoi (MGWC-Media Gateway Controller): Vai

tr nh l phn t kt ni gia Gateway bo hiu v gatekeeper. N nhn thng tin bo

hiu t mng chuyn mch knh thng qua gateway bo hiu, t mng IP thng qua

gatekeeper thc hin vic iu khin gateway truyn ti knh thoi.

+ Gatekeeper: C th xem gatekeeper nh l b no ca h thng mng in thoi

IP. N cung cp chc nng qun l cuc gi mt cch tp trung v mt s cc dch v

quan trng khc nh l: nhn dng cc u cui v gateway, qun l bng thng, chuyn

i a ch (t a ch IP sang a ch E.164 v ngc li), ng k hay tnh cc...Mi

gatekeeper s qun l mt vng bao gm cc u cui ng k, nhng cng c th

nhiu gatekeeper cng qun l mt vng trong trng hp mt vng c nhiu gatekeeper.

1.4 Kt lun chng

S pht trin nhy vt ca mng chuyn mch gi IP hin nay khng ch em li cho

chng ta nhng dch v mi a dng m cn l c hi ci thin cc dch v vin thng

trc kia vi cht lng tt hn v gi thnh r hn. Trn c s , mng VoIP ra i v

ngy cng p ng tt hn cc yu cu t ra nh cht lng dch v, gi thnh, s lng

tch hp cc dch v thoi ln phi thoi.Chng 1 ta tm hiu khi nim kin trc mng

VoIP, nhng u, nhc im ca mng VoIP, nhng yu cu v cht lng ca VoIP

m bo cht lng cuc gi. Chng 2 ta s tm hiu v cc giao thc truyn ti v bo

hiu trao i gia cc thit b u cui trong kt ni VoIP.

Chng 2 Cc giao thc bo hiu trong mng VoIP

15

CHNG 2

CC GIAO THC BO HIU TRONG MNG VoIP

2.1 Gii thiu chng

Cng ngh VoIP l cng ngh truyn tn hiu thoi trn nn IP, chnh v th m h

thng VoIP phi c h tr cc giao thc c s dng trn mng Internet v phi c

kin trc thch ng vi kin trc mng IP. Chng 2 trnh by cc khi nim, chc nng

ca giao thc bo hiu trong mng VoIP.

2.2 Cc giao thc bo hiu trong mng VoIP

2.2.1 H.323

Giao thc H.323 l chun do ITU-T pht trin cho php truyn thng a phng tin qua

cc h thng da trn mng chuyn mch gi, v d nh Internet. Tiu chun H.323 bao

gm bo hiu v iu khin cuc gi, truyn v iu khin a phng tin v iu khin

bng thng cho hi ngh im - im v a im.

2.2.1.1 Tiu chun H.323 bao gm cc giao thc

Tnh nng Giao thc

Call Signalling H.225

Media Control H.245

Audio Codecs G.711, G.722, G.723, G.728, G.729

Video Codecs H261, H263

Data Sharing T.120

Media Transport RTP/RTCP

Hnh 2.1 Cc giao thc s dng trong H.323


16

2.2.1.2 Cc thnh phn ca H.323:

Hnh 2.2 Cc thnh phn ca H.323

H323 Terminal: Thc hin cc chc nng u cui : thc hin gi hoc nhn cuc

gi.

Gm c:

- System Control Unit.

- Media Transmission.

- Audio Codec.

- Network Interface.

- Video Codec.

- Data channel Support Application.

Gateway:

Gateway l phn t khng nht thit phi c trong mt giao tip ca cc phn t

H.323, n ng vai tr lm phn t cu ni v ch tham gia vo mt cuc gi khi c s

chuyn tip t mng H.323 (v d nh mng LAN hoc Internet) sang mng phi H.323

( nh PSTN). Gateway thc hin mt s chc nng nh :

Chuyn i gia cc dng khung truyn dn.

Chuyn i gia cc th tc giao tip.

Chuyn i gia cc dng m ho khc nhau ca cc lung tn hiu hnh nh cng

nh m thanh.


17

Thc hin vic thit lp v xo cuc gi c pha mng LAN cng nh pha mng

chuyn mch knh.

Gatekeeper:

Gatekeeper l phn t khng nht thit phi tn ti trong mt h thng H.323, n

thc hin vic iu khin cc dch v gi ca cc u cui H.323. Cc chc nng ca mt

Gatekeeper c phn bit lm hai loi l cc chc nng bt buc v cc chc nng

khng bt buc.

Cc chc nng ca Gatekeeper :

Dch a ch (Address Translation): Dch a ch Address Translation: Gatekeeper

s thc hin vic chuyn i t mt a ch hnh thc (dng tn gi) ca cc thit b u

cui v Gateway sang a ch truyn dn thc trong mng (a ch IP).

iu khin quyn truy nhp (Admission Control):Vi mi ti nguyn mng c th,

ngi qun tr mng t ra mt ngng ch s hi thoi cng 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 ngi dng theo mc u tin gn trc.

iu khin gii thng (Bandwidth Control):Gim st v iu khin vic s dng

gii thng mng. ng thi Gatekeeper cng phi bo m lu lng thng tin truyn

khng c vt qu ti ca mng do nh qun tr mng t ra.

iu khin vng (Zone Management): y ch vng c trng cho tp hp tt

c cc phn t H.323 gm thit b u cui, Gateway, MCU c ng k hot ng vi

Gatekeeper.

iu khin bo hiu cuc gi (Call Control Signaling): Ty chn. Gatekeeper cung

cp a ch ch cho ngi gi theo hai ch trc tip v chn ng. Ti ch trc

tip, sau khi cung cp a ch ch th Gatekeeper ngng tham gia hot 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 i gia cc bn.

Qun l gii thng (Bandwidth Management): Ty chn. Gatekeeper gii hn

s cuc gi cng lc trong min ca n trong phin Q.931.


18

Dch v qun l cuc gi (Call Management Service): Ty chn. Gatekeeper lu

tr mt danh sch cc cuc gi hin thi cung cp thng tin cho vic qun l gii

thng v xc nh Terminal no ang bn.

Dch v xc nhn cuc gi (Call Authorization Service): Ty chn. Gatekeeper

loi b cuc gi khi qu trnh xc nhn l sai ngay c khi cha ti ngng.

Ngoi ra Gatekeeper cn thng xuyn c cp nht thm cc dch v ph nh

FORWARD, TRANSFER,...

MCU (Multipoint Control Unit)

Cung cp chc nng hi thoi vi s bn tham gia nhiu hn hai. N phi hp cc

phng thc giao tip ca cc bn tham gia v cung cp cc c trng trn m thanh v

hnh nh (nu cn) cho cc Terminal.

MCU bao gm hai thnh phn :

B iu khin a im (Multipoint Controller- MC) : thit lp v qun l hi thoi

nhiu bn qua H.245. MC c th c t trong Gatekeeper, Gateway, Terminal, MCU.

B x l a im ( Multipoint Processor- MP): ng vai tr trn 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 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 phi thng qua MCU. Ngoi ra, ngi ta c th kt

hp gia hai loi ny, to thnh MCU lai ghp.

2.2.1.3 Tp giao thc H.323

Hnh 2.3 Tp giao thc H.323


19

2.2.1.3.1 Bo hiu RAS

Cung cp cc th tc iu khin tin cuc gi trong mng H.323 c GK. Knh bo

hiu RAS c thit lp gia cc u cui v cc GK trc cc knh khc. N c lp vi

knh bo hiu cuc gi v knh iu khin H.245. Cc bn tin RAS c truyn qua

mng thng qua kt ni UDP, thc hin vic ng k, cho php, thay i bng thng,

trng thi v cc th tc hu b cuc gi. Bo hiu RAS gm nhng qu trnh sau:

- Tm GateKeeper.

- ng k : ng k l mt qu trnh cho php GW, cc u cui v MCU

tham gia vo mt vng v bo cho GK bit a ch truyn vn v a ch b danh ca n.

- nh v u cui

- Cho php, thay i bng thng, trng thi v hu quan h

2.2.1.3.2 Bo hiu iu khin cuc gi H.225

Trong mng H.323, th tc bo hiu cuc gi c da trn khuyn ngh H.225 ca

ITU. Khuyn ngh ny ch r cch s dng v tr gip ca cc bn tin bo hiu Q.931.

Sau khi khi to thit lp cuc gi. Cc bn tin iu khin cuc gi v cc bn tin gi cho

knh bo hiu cuc gi tn ti (keepalive) c chuyn ti cc cng.

Cc bn tin Q.931 thng c s dng trong mng H.323:

Setup: c gi t thc th ch gi thit lp kt ni ti thc th H.323 b gi

Call Proceeding: ch th rng th tc thit lp cuc gi c khi to.

Alerting: ch th rng chung bn ch bt u rung.

Connect: thng bo rng bn b gi tr li cuc gi.

Release Complete: ch th rng cuc gi ang b gii phng.

Facility: y l mt bn tin Q.932 dng yu cu hoc phc p cc dch v b

sung. N cng c dng cnh bo rng mt cuc gi s c nh tuyn trc tip hay

thng qua GK.

2.2.1.4 Cc th tc bo hiu

2.2.1.4.1 Bo hiu v x l cuc gi

Cc bc bo hiu khi thc hin cuc gi qua Internet c trnh by trong khuyn

co H.323 ca UTU-T. C 3 knh bo hiu tn ti c lp nhau lin quan n bo hiu v

x l cuc gi: knh iu khin H.245, knh bo hiu cuc gi v knh bo hiu RAS.


20

Trong mng khng c Gatekeeper, cc bn tin bo hiu cuc gi c truyn trc tip

gia thu bao ch gi v b gi bng cch truyn bo hiu a ch trc tip, v vy c th

giao tip mt cch trc tip.

Nu trong mng c Gatekeeper, trao i bo hiu thu bao ch gi v Gatekeeper

c thit lp bng cch s dng knh RAS ca Gatekeeper truyn a ch, sau khi trao

i bn tin trc tip gia hai u cui hay nh tuyn chng qua Gatekeeper.

2.2.1.4.2 Thit lp cuc gi H.323

Mt cuc gi tri qua cc bc nh sau:

- Thit lp cuc gi.

- Khi to truyn thng v trao i kh nng.

- Thit lp knh truyn thng nghe nhn.

- Dch v cuc gi.

- Kt thc cuc gi.

Giai on 1 - Thit lp cuc gi

Trong giai on ny cc phn t trao i vi nhau cc bn tin c nh ngha trong

khuyn co H.225.0 theo mt trong cc th tc c trnh by sau y.

- C hai thit b u cui u khng ng k vi Gatekeeper: Hai thit b u cui

trao i trc tip vi nhau.

- C hai thu bao u ng k ti mt Gatekeeper: C 2 tnh hung xy ra l

Gatekeeper chn phng thc truyn bo hiu trc tip gia 2 thu bao hoc bo hiu

cuc gi c nh tuyn qua Gatekeeper.

- Ch c mt trong 2 thu bao c ng k vi Gatekeeper: Bo hiu cuc gi c

truyn trc tip gia hai thu bao.

Khi cuc gi c s chuyn tip t mng PSTN sang mng LAN hoc ngc li th

phi thng qua Gateway. V c bn c th phn bit cuc gi qua Gateway thnh 2 loi:

cuc gi t mt thu bao in thoi vo mng LAN v cuc gi t mt thu bao trong

mng LAN ra mt thu bao trong mng thoi PSTN.

Giai on 2 - Thit lp knh iu khin

Trong giai on 1, sau khi trao i tn hiu thit lp cuc gi, cc u cui s thit lp

knh iu khin H.245. Knh iu khin ny c th do thu bao b gi hoc thu bao gi


21

thit lp. Trong trng hp khng nhn c tn hiu kt ni hoc mt u cui gi tn

hiu kt thc th knh iu khin H.245 s b ng.

Giai on 3 - Thit lp knh truyn thng o

Sau khi trao i kh nng (tc nhn ti a, phng thc m ha) v xc nh

master-slaver trong giao tip trong giai on 2, th tc iu khin knh H.245 s thc

hin vic m knh logic (H.225) truyn thng tin. Sau khi m knh logic th mi u

cui truyn tn hiu xc nh thng s truyn.

Giai on 4 - Dch v

- rng bng tn: rng bng tng ca mt cuc gi c Gatekeeper thit

lp trong thi gian thit lp trao i. Mt u cui phi chc chn rng tng tt c lung

truyn/nhn m thanh v hnh nh u phi nm trong rng bng tn thit lp.

- Trng thi: gim st trng thi hot ng ca u cui, Gatekeeper lin tc

trao i tn hiu vi cc u cui do n kim sot. Khong thi gian u n gia cc ln

trao i ln hn 10 giy v gi tr ny do nh sn xut quyt nh.

Trong khong thi gian din ra cuc gi, mt u cui hoc Gatekeeper c th u

n hi trng thi t u cui bn kia bng cch gi tn hiu yu cu. u cui nhn c

tn hiu s p tr trng thi hin thi.

Giai on 5 - Kt thc cuc gi

Mt thit b u cui c th kt thc cuc gi theo cc bc ca th tc sau:

Dng truyn lung tn hiu video khi kt thc truyn mt nh, sau ng tt

c cc knh logic phc v truyn video.

Dng truyn d liu v ng tt c cc knh logic dng truyn d liu.

Dng truyn audio sau ng tt c cc knh logic dng truyn audio.

Truyn tn hiu trn knh iu khin H.245 bo cho thu bao u kia bit n

mun kt thc cuc gi. Sau n dng truyn cc bn tin H.245 v ng knh iu

khin H.245.

N s ch nhn tn hiu kt thc t thu bao u kia v s ng knh iu khin

H.245.

Nu knh bo hiu cuc gi ang m, th n s truyn i tn hiu ngt sau

ng knh bo hiu.


22

N cng c th kt thc cuc gi theo cc th tc sau: Mt u cui nhn tn

hiu kt thc m trc n khng truyn i tn hiu yu cu, n s ln lt thc hin

cc bc t 1 n 6 trn ch b qua bc 5. Trong mt cuc gi khng c s tham gia

ca Gatekeeper th ch cn thc hin cc bc t 1 n 6. Nhng trong cuc gi c s

tham gia ca Gatekeeper th cn c hot ng gii phng bng tn. V vy sau khi thc

hin cc bc t 1 n 6, mi u cui s truyn tn hiu ti Gatekeeper. Sau

Gatekeeper s c tn hiu p tr. Sau u cui s khng gi tn hiu ti Gatekeeper

na v khi cuc gi kt thc.

Hnh v di y m t qu trnh thc hin kt ni gia 2 im u cui H323:

Hnh 2.4 Qu trnh thit lp cuc gi H.323

Trc ht c hai phi c ng k ti thit b iu khin cng kt ni

u cui A gi yu cu ti thit b iu khin cng kt ni ngh thit lp

cuc gi.

Thit b iu khin cng ni gi cho u A thng tin 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 thit

b iu khin cng ni xc nhn quyn thit lp cuc gi.

u cui B gi bn tin cnh bo v kt ni.

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.


23

y l trng hp cuc gi im im n gin nht, khi m bo hiu cuc gi khng

c nh tuyn ti thit b iu khin cng ni. H.323 h tr nhiu kch bn thit lp

cuc gi khc

H.323 l h thng ghp lai c xy dng t cc thit b tp trung thng minh nh :

thit b iu khin cng ni, MCU, cng kt ni v im cui. Mc d chun H.323 trong

phin bn gn y nht c phn ton din hn song vn vn ny sinh, nh thi gian

thit lp cuc gi di, qu nhiu chc nng thit b iu khin cng ni phi thc hin v

kh nng m rng khi s dng kiu bo hiu cuc gi

nh tuyn qua thit b iu khin cng ni (GKRCS)

Khi cn s dng cng kt ni dung lng ln kt ni mng PSTN, ngi ta s s

dng giao thc cng n gin (SGCP : Simple Gateway Control Protocol) v giao thc

iu khin cng phng tin (MGCP: Media Gateway Control Protocol) thay th giao

thc cho cng kt ni H.323. Cc h thng iu khin cuc gi ny c v hiu qu hn,

p ng nhu cu ca cc nh cung cp c ln.

2.2.2 SIP

SIP l giao thc iu khin bo hiu thuc lp ng dng, c pht trin nh l mt

chun m RFC 2543 ca IEFT. Khc vi H.323, n da trn ngun gc Web (HTTP) v

c thit k kiu modul, n gin v d dng m rng vi cc ng dng thoi SIP. SIP l

mt giao thc bo hiu thit lp, duy tr v kt thc cc phin a phng tin nh :

thoi IP, hi ngh v cc ng dng tng t khc lin quan n vic truyn thng tin a

phng tin.

2.2.2.1 Cc thnh phn ca SIP

Hnh 2.5 Cc thnh phn ca SIP


24

User Agent: L 1 ng dng khi to, nhn v kt thc cuc gi.

User Agent Clients (UAC) Khi to cuc gi.

User Agent Server (UAS) Nhn cuc gi.

C UAC v UAS u c th kt thc cuc gi.

Proxy Server: L 1 chng trnh tc thi hot ng va l client va l server.

Chng trnh ny c s dng to ra cc yu cu (requests) thay cho cc client. Mt

proxy server m bo chc nng nh tuyn v thc hin cc quy tc (policy) (v d nh

m bo ngi dng c c php gi hay khng). Proxy Server c th bin dch khi cn

thit, sa i 1 phn ca bn tin yu cu trc khi chuyn i.

Location Server: c s dng bi SIP redirect hoc proxy server ly thng

tin v a im ca ngi c gi.

Redirect Server: L server nhn cc yu cu SIP, sp xp cc a ch v tr a ch

v pha client. Khc vi Proxy Server, Redirect server khng t khi to ra cc yu cu

SIP ca ring n. ng thi n cng khng chp nhn hay hu cuc gi ging nh User

Agent Server.

Registrar Server: L server chp nhn cc yu cu REGISTER, server ny c th

h tr them tnh nng xc thc, ng thi hot ng vi proxy hoc redirect server a

ra cc dch v khc.

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 in thoi SIP, c th l my tnh chy phn mm u cui

SIP.

2.2.2.2 Cc bn tin SIP, mo u v nh s

Di y l cc bn tin ca SIP :

INVITE : bt u thit lp cuc gi bng cch gi bn tin mi u cui khc

tham gia

ACK : bn tin ny khng nh my trm nhn c bn tin tr li bn tin

INVITE

BYE : bt u kt thc cuc gi

CANCEL : hy yu cu nm trong hng i


25

REGISTER : u cui SIP s dng bn tin ny ng k vi my ch ng

k

OPTION : s dng xc nh nng lc ca my ch

INFO : s dng ti cc thng tin nh m bo DTMF

Giao thc SIP c nhiu im trng hp vi giao thc HTTP. Cc bn tin tr li cc

bn tin SIP nu trn gm c :

- 1xx (PROVISIONAL) cc bn tin chung

- 2xx (SUCCESS) thnh cng

- 3xx (REDIRECTION) - chuyn a ch

- 4xx (CLIENT ERORR) yu cu khng c p ng

- 5xx (SERVER ERORR) - s c ca my ch

- 6xx (GLOBAL FAILURE)- s c ton mng

Cc bn tin SIP 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 email)

2.2.2.3 Cc bc thit lp, duy tr v hu cuc gi

Thit lp v hy cuc gi SIP

Trc tin ta tm hiu hot ng ca my ch y quyn v my ch chuyn i

Hot ng ca my ch y quyn (Proxy Server)

Hnh 2.6 Hot ng ca Proxy server

Hot ng ca Proxy server c trnh by nh trong hnh 2.6

Client SIP [email protected] gi bn tin INVITE cho [email protected]

mi tham gia cuc gi.


26

Cc bc nh sau:

+ Bc 1: [email protected] gi bn tin INVITE cho UserB min hotmail.com,

bn tin ny n proxy server SIP ca min hotmail.com (Bn tin INVITE c th i t

Proxy server SIP ca min yahoo.com v c Proxy ny chuyn n Proxy server ca

min hotmail.com).

+ Bc 2: Proxy server ca min hotmail.com s tham kho server nh v

(Location server) quyt nh v tr hin ti ca UserB.

+ Bc 3: Server nh v tr li v tr hin ti ca UserB (gi s l

[email protected]).

+ Bc 4: Proxy server gi bn tin INVITE ti [email protected]. Proxy server

thm a ch ca n trong mt trng ca bn tin INVITE.

+ Bc 5: UAS ca UserB p ng cho server Proxy vi bn tin 200 OK.

+ Bc 6: Proxy server gi p ng 200 OK tr v [email protected].

+ Bc 7: [email protected] gi bn tin ACK cho UserB thng qua proxy server.

+ Bc 8: Proxy server chuyn bn tin ACK cho [email protected]

+ Bc 9: Sau khi c hai bn ng tham d cuc gi, mt knh RTP/RTCP c

gia hai im cui truyn tn hiu thoi.

+ Bc 10: Sau khi qu trnh truyn dn hon tt, phin lm vic b xa bng cch

s dng bn tin BYE v ACK gia hai im cui.

Hot ng ca my ch chuyn i a ch (Redirect Server)

Hnh 2.7 Hot ng ca Redirect Server

Hot ng ca Redirect Server c trnh by nh hnh 2.7.


27

Cc bc nh sau:

+ Bc 1: Redirect server nhn c yu cu INVITE t ngi gi (Yu cu ny c th i

t mt proxy server khc).

+ Bc 2: Redirect server truy vn server nh v a ch ca B.

+ Bc 3: Server nh v tr li a ch ca B cho Redirect server.

+ Bc 4: Redirect server tr li a ch ca B n ngi gi A. N khng pht yu cu

INVITE nh proxy server.

+ Bc 5: User Agent bn A gi li bn tin ACK n Redirect server xc nhn s trao

i thnh cng.

+ Bc 6: Ngi gi A gi yu cu INVITE trc tip n a ch c tr li bi Redirect

server (n B). Ngi b gi B p ng vi ch th thnh cng (200 OK), v ngi gi p

tr bn tin ACK xc nhn. Cuc gi c thit lp.

Ngoi ra SIP cn c cc m hnh hot ng lin mng vi SS7 (n PSTN) hoc l lin

mng vi chng giao thc H.323.

Tng qut li trong mng SIP qu trnh thit lp v hy mt phin kt ni:

Hnh 2.8 Thit lp v hy cuc gi SIP


28

ng k, khi to v xc nh v tr ngi s dng.

Xc nh bng thong cn thit c s dng.

Xc nh s sn sng ca pha c gi, pha c gi phi gi 1 bn tin phn hi

th hin s sn sng thc hin cuc gi: chp nhn hay t chi.

Cuc gi c thit lp.

Chnh sa cuc gi (v d nh chuyn cuc gi) v duy tr.

Kt thc cuc gi.

2.2.2.4 Tnh nng ca SIP

Giao thc SIP c thit k vi nhng ch tiu 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

2.2.2.4.1 Tch hp vi cc giao thc c ca IETF

Cc giao thc khc ca IETF c th xy dng xy dng nhng ng dng SIP. SIP

c th hot ng cng vi nhu giao thc nh :

- RSVP(Resource Reservation Protocol): Giao thc ginh trc ti nguyn mng.

- RTP (Real-time transport Protocol): Giao thc truyn ti thi gian thc

- RTSP (Real Time Streaming Protocol): Giao thc to lung thi gian thc

- SAP(Session Advertisement Protocol):Giao thc thng bo trong phin kt ni

- SDP (Session Description Protocol): Giao thc m t phin kt ni a phng tin

- MIME (Multipurpose Internet Mail Extension - M rng th tn Internet a mc

ch) : Giao thc th in t

- HTTP (Hypertext Transfer Protocol): Giao thc truyn siu vn bn

- COPS (Common Open Policy Service): Dch v chnh sch m chung

- OSP (Open Settlement Protocol): Giao thc tha thun m

2.2.2.4.2 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


29

vn bn, SIP l giao thc ra i sau v khc phc c im yu ca nhiu giao thc

trc y.

Cc phn mm ca my ch y quyn, my ch ng k, my ch chuyn i a ch,

my ch nh v c 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.

2.2.2.4.3 H tr ti a s di ng ca u cui

Do c my ch y quyn, my ch ng k v my ch chuyn i a ch h thng

lun nm c a im chnh xc ca thu bao. Th d thu bao vi a ch

[email protected] c th nhn c cuc gi thoi hay thng ip bt c a im no

qua bt c u cui no nh my tnh bn, my xch tay, in thoi SIP Vi SIP rt

nhiu dch v di ng mi c h tr.

2.2.2.4.4 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. Ngn ng x l cuc gi (Call

Processing Language) v Giao din cng kt ni chung (Common Gateway Interface) l

mt s cng c thc hin iu ny. SIP h tr cc dch v thoi nh ch cuc gi,

chuyn tip cuc gi, kha cuc gi (call waiting, call forwarding, call blocking), h

tr thng ip thng nht

2.2.2.5 So snh gia giao thc SIP v H.323

Gia H.323 v SIP c nhiu im tng ng. C hai u cho php iu khin, thit

lp v hu cuc gi. C H.323 v SIP u h tr tt c cc dch v cn thit, tuy nhin c

mt s im khc bit gia hai chun ny.

H.323 h tr hi ngh a phng tin rt phc tp. Hi ngh H.323 v nguyn tc

c th cho php cc thnh vin s dng nhng dch v nh bng thng bo, trao

i d liu, hoc hi ngh video.

SIP h tr SIP-CGI (SIP-Common Gateway Interface) v CPL (Call Processing

Language).

SIP h tr iu khin cuc gi t mt u cui th 3. Hin nay H.323 ang c

nng cp h tr chc nng ny.


30

SIP H.323

Ngun gc IETF ITU-T

Quan h mng Ngang cp Ngang cp

Khi im K tha cu trc HTTP. K tha Q.931, Q.SIG

u cui SIP H.323

Server

Proxy Server

Redirect Server

Location Server

Registrar Servers.

H.323 Gatekeeper

Khun dng Text, UTF-8 Nh phn

Tr thit lp cuc gi

1.5 RTT 6-7 RTT hoc hn

Gim st trng thi cuc gi

C 2 la chn:

- trong thi gian thit

lp cuc gi

- sut thi gian cuc gi

Phin bn 1 v 2: my ch phi gim st trong sut thi gian cuc gi v phi gi trng thi kt ni TCP. iu ny hn ch kh nng m rng v gim tin cy

Bo hiu qung b

C h tr Khng

Cht lng dch v

S dng cc giao thc khc nh RSVP, OPS, OSP m bo cht lng dch v

Gatekeeper iu khin bng thng. H.323 khuyn ngh dng RSVP lu d ti nguyn mng.

Bo mt ng k ti Registrar server, c xc nhn u cui v m ho

Ch ng k khi trong mng c Gatekeeper, xc nhn v m ho theo chun H.235.

nh v u cui v nh tuyn cuc gi

Dng SIP URL nh a ch. nh tuyn nh s dng Redirect v Location server

nh v u cui s dng E.164 hoc tn o H.323 v phng php nh x a ch nu trong mng c Gatekeeper. Chc nng nh tuyn do Gatekeeper m nhim.

Tnh nng thoi H tr cc tnh nng ca cuc gi c bn

c thit k nhm h tr rt nhiu tnh nng hi ngh, k c thoi, hnh nh v d liu, qun l tp trung nn c th gy tc nghn Gatekeeper

Kh nng m rng

D dng Hn ch


31

2.2.3 Giao thc SGCP (Simple Gateway Control Protocol)

Giao thc ny cho php cc thnh phn iu khin cuc gi c th iu khin kt ni

gia trung k, cc thit b u cui vi cc gateway. Cc thnh phn iu khin c gi

l Call Agent. SGCP c s dng thit lp, duy tr v gii phng cc cuc gi qua

mng IP. Call Agent thc hin cc chc nng bo hiu cuc gi v gateway thc hin

chc nng truyn tn hiu m thanh. SGCP cung cp nm lnh iu khin chnh nh sau:

Notification Request: yu cu gateway pht cc tn hiu nhc t my v cc tn

hiu quay s DTMF.

Notify: gateway s dng lnh ny thng bo vi Call Agent v cc tn hiu

c pht hin trn.

Create Connection: Call Agent yu cu khi to kt ni gia cc u lin lc trong

gateway.

Modify Connection: Call Agent dng lnh ny thay i cc thng s v kt ni

thit lp. Lnh ny cng c th dng iu khin lung cho cc gi tin RTP i

t gateway ny sang gateway khc.

Delete Connection: Call Agent s dng lnh ny gii phng cc kt ni thit

lp.

Nm lnh trn y iu khin gateway v thng bo cho call agent v cc s kin xy ra.

Mi lnh hay yu cu bao gm cc thng s c th cn thit thc thi cc phin lm

vic.

2.2.4 Giao thc MGCP (Media Gateway Control Protocol)

Giao thc MGCP cho php iu khin cc gateway thng qua cc thnh phn iu

khin nm bn ngoi mng. MGCP s dng m hnh kt ni tng t nh SGCP da trn

cc kt ni c bn gia thit b u cui v gateway. Cc kt ni c th l kt ni im-

im hoc kt ni a im. Ngoi chc nng iu khin nh SGCP, MGCP cn cung cp

thm cc chc nng sau:

Endpoint Configuration: Call Agent dng lnh ny yu cu gateway xc nh

kiu m ho ph ng dy kt ni n thit b u cui.

AuditEndpoint v AuditConnection: Call Agent dng lnh ny kim tra trng

thi v s kt ni mt thit b u cui.


32

RestartIn-Progress: Gateway dng lnh ny thng bo vi Call Agent khi no

cc thit b u cui ngng s dng dch v v khi no quay li s dng dch v.

2.2.5 Kt lun chng

Qua chng 2 ta tm hiu v cc giao thc bo hiu trong mng VoIP. V mt cc

giao thc bo hiu ta thy 2 giao thc bo hiu chnh l H.323 v SIP, ty vo yu cu c

th ca mng m ta la chn giao thc bo hiu cho thch hp. Chng 3 tip theo s gii

thiu tng qut v tng i Asterisk vi cc giao thc VoIP c Asterisk h tr.

Chng 3 Tng i ASTERISK

33

CHNG 3

TNG I ASTERISK

3.1 Gii thiu chng

Asterisk l h thng chuyn mch mm, l phn mm ngun m c vit bng ngn

ng C chy trn h iu hnh linux thc hin tt c cc tnh nng ca tng i PBX v

hn th na.Chng 3 trnh trnh by v khi nim v tng i IP-PBX, so snh IP-PBX

vi PBX truyn thng, gii thiu v tng i Asterisk, trnh by kin trc , tnh nng v

ng cnh ng dng ca tng i Asterisk, gii thiu cc giao thc ca VoIP ca tng i.

3.2 Tng i IP-PBX

Khi qut v tng i IP-PBX

ng dng ph bin nht v sm nht ca VoIP, nn tng to ra IP-PBX, l vic

thit lp gateway VoIP bn pha trung k ca PBX. Gateway ny ng gi lung thoi v

nh tuyn n qua mng VoIP. Gii php ny tn dng cc c tnh hin c ca tng i

PBX, nh thoi hi ngh, chuyn tip cuc gi,

Cui cng, cc nh pht trin phn mm pht trin ln PBX mm, hay IP-PBX. IP-

PBX cung cp kh nng chuyn mch, thc hin cc dch v gia tng qua mng d liu.

Cc cuc gi trong mt tng i v cc cuc gi gia cc tng i c nh tuyn qua

mng IP, i vng qua ton b mng PSTN. IP-PBX c th giao tip vi mng PSTN

thng qua Gateway.

Hnh 3.1 M hnh IP-PBX hay PBX mm


34

Cc u im so vi tng i PBX truyn thng:

Cc u im ca IP-PBX xut pht t nhng u im ca mng chuyn mch gi IP

so vi mng chuyn mch knh, nh:

- Qun l v bo dng d dng hn

- Kh nng kt ni t xa, kh nng di ng

- Kt hp thoi/d liu to ra ng dng mi

- D dng pht trin cc dch v mi do cu trc m v cc giao din chun

- D s dng do c h tr nhiu bi phn mm v giao din ho GUI

- Thng tin hp nht ...

So snh gia IP-PBX v PBX truyn thng:

Bng 3.1 So snh gia PBX truyn thng v IP-PBX

PBX truyn thng IP-PBX

PBX khng thc hin c mt s

chc nng ca IP-PBX: Web,

Instant message, E-mail

IP-PBX c y cc chc nng ca

mt PBX truyn thng (CTI,

VoiceMail, ACA v kt ni ISDN ra

PSTN).

PBX i hi phi c mt h

thng mng in thoi ni b.

Cho php thc hin lin lc ni b

qua mng LAN ngay c khi cha c h

thng PBX.

PBX truyn tn hiu thoi trn

h thng ng in thoi ni b.

Nu mun truyn d liu, bt buc

phi c thm h thng mng LAN.

IP-PBX truyn d liu v thoi trn

cng mt ng dy.

H tr duy nht mt loi u cui

l in thoi tng t.

IP-PBX c kh nng h tr nhiu u

cui thoi khc nhau: in thoi tng

t, in thoi IP, my tnh c nhn...

Kh nng pht trin cc loi hnh

dch v gi tr gia tng km.

C thm nhiu dch v gi tr gia tng

khc; telephone, e-mail, fax, web

call back, web chat, instant messaging

Mi ng dy thoi ch c th Tn hiu trc khi chuyn n ng


35

thc hin c mt cuc gi ti

mt thi im, do khng tit

kim bng thng.

truyn c thng qua cc b nn

v gii nn, bng thng cho mi cuc

gi c th c nn xung cn

5,3 Kbits/s (chun nn thoiG.723.1),

thay v 64 Kbits/s ca thoi thng.

Do tnh cht tit kim bng thng nh

vy nn vi mt ng dy thoi

(CO line) c th thc hin c nhiu

cuc gi hn.

Kh m rng, nng cp v

bo dng

D dng m rng, nng cp v bo

dng.

Kh nng p dng trong cc doanh nghip va v nh

C th n gin ho qu trnh trin khai tng i IP-PBX cho mt doanh nghip nh

sau:

Xy dng mng LAN

Thit lp h thng my ch v ci t phn mm iu khin IP-PBX

Thit lp cc Gateway ra mng PSTN hoc Internet

Thit lp cc u cui VoIP

Bc th nht l phc tp nht v i hi u t ln nht nhng thc ra li n gin

nht v a s cc doanh nghip c sn mng LAN. Bc th 2 quan trong nht, nhng

thc ra cng ch n gin l ci t phn mm ln mt my ch. My ch ny c th l

ginh ring cho IP-PBX hoc cng c th c chia x vi cc ng dng khc ca doanh

nghip. Bc th 3 i hi phi mua thit b chuyn dng kt ni vi mng PSTN.

Gateway kt ni IP/PSTN thng l card PCI cm trong my ch cng vi phn mm

iu khin chuyn dng.

Cc u cui VoIP trong bc 4 c th l phn mm chy ngay trn my PC (nh

Windows Messenger) hay l mt thit b chy c lp (nh IPPhone ca Cisco).


36

3.2.1 Mt s m hnh cuc gi s dng tng i IP-PBX

Cuc gi ni b

Cuc gi gia hai u cui SIP do IP-PBX qun l

Hnh 3.2 M hnh cuc gi ni b

Cuc gi t my thuc IP-PBX ra mng PSTN

u tin u cui SIP s bm s chim trung k ra PSTN, ri bm s thu bao ca

PSTN

Hnh 3.3 M hnh cuc gi t my IP ra mng PSTN

Cuc gi t PSTN vo my IP- PBX

Thu bao PSTN gi vo mt trung k ca IP-PBX , ri bm s my l tng ng vi

u cui SIP


37

Hnh 3.4 M hnh cuc gi t PSTN vo my IP-PBX

Cuc gi t ngoi mng Internet s dng dch v SIP cng cng

Hnh 3.5 M hnh cuc gi s dng dch v SIP cng cng

3.3 Tng i Asterisk

Asterisk l phn mm ngun m, c vit bng ngn ng C, ra i nm 1999 bi

Mark Spencer, u tin c thit k v trin khai trn GNU/Linux nn x86 (ca Intel).

Nhng hin nay Asterisk c th chy trn cc h iu hnh khc nh: Mac OS X,

FreeBSD, OpenBSD v Microsoft Windowns.

Asterisk c xem nh l mt tng i PBX (Private Branch eXchange) v c thm

nhiu tnh nng mi. Ngoi nhng tnh nng ca mt tng i PBX thng thng,

Asterisk cn c tch hp c chuyn mch TDM v chuyn mch VoIP, c kh nng m


38

rng p ng nhu cu cho tng ng dung nh m rng giao tip vi mng PSTN (Public

Switched Telephone Network).

Vi mt my tnh r tin ci h iu hnh (mt trong cc h iu hnh ni trn,

y ta thin v h iu hnh Microsoft Windowns) v c thm phn mm Asterisk cu

hnh, khi my tnh ny s c y tnh nng ca mt tng i in thoi v c th

hn th.

Asterisk l mt phn mm ngun m, min ph, c tin cy cao nn c xem l

phn mm mang tnh cch mng.

Bi nhng tin ch: h thng v gi cc r, d s dng, y cc tnh nng ca mt

tng i v con hn th nn c nhiu h thng Asterisk c ci t thnh cng trn

th gii. Hin nay h thng Asterisk ang c pht trin mnh, nhiu doanh nghip,

cng ty v ang trin khai h thng to lin lc bn trong v ra c mng ngoi thng

qua mng my tnh, gi in thoi.

Hnh 3.6 S giao tip tng qut.

T hnh 3.6 ta thy Asterisk khng ch giao tip, kt ni gia cc in thoi vi nhau

m cn c th m rng kt ni n cc tng i khc, vi IP Phone v nhiu dch v nh:

Softswitch, Media Gateway, Voicemail Services, Conference Server, Music on hold


39

3.3.1 Kin trc h thng Asterisk

Hnh 3.7 S khi ca Asterisk

V c bn kin trc ca Asterisk l s kt hp gia nn tng cng ngh in thoi v

ng dng in thoi cho VOIP nh SIP, H323, IAX, MGCP... cc cng ngh in thoi

cho h thng chuyn mch mch TDM nh T1, E1, ISDN v cc giao tip ng truyn

thoi Analog.

- Khi khi ng h thng Asterisk th chc nng Dynamic Module Loader thc hin

np driver ca thit b, np cc knh giao tip, cc format, codec v cc ng dng lin

quan, ng thi cc hm API cng c lin kt np vo h thng.

- Sau h thng PBX Switching Core ca Asterisk chuyn sang trng thi sn sng

hot ng chuyn mch cuc gi, cc cuc gi c chuyn mch tu vo k hoch quay

s (Dialplan) c thc hin cu hnh trong file extension.conf.

- Application Launchar rung chung thu bao, quay s, nh hng cuc gi, kt

ni vi hp th thoi

- Scheduler and I/O Manager m nhim cc ng dng nng cao.

- Codec Translator xc nhn cc knh nn d liu ng vi cc chun khc nhau c th

kt hp lin lc c vi nhau.

H thng cng bao gm 4 chc nng API chnh:

Codec translator API: cc hm thc thi, gii nn cc chun nh G711, G729

Asterisk Channel API : Giao tip vi cc knh lin lc khc nhau.


40

Asterisk file format API : x l cc loi file c nh dng nh Mp3, wav, gsm

Asterisk Aplication API : Bao gm tt c cc ng dng c thc thi trong h

thng Asterisk nh voicemail, callerID

3.3.2 Mt s tnh nng c bn

3.3.2.1 Voicemail

Hp th thoi vi tnh nng cho php h thng nhn cc thng ip tin nhn thoi, mi

my in thoi c khai bo trong h thng Asterisk cho php khai bo thm chc nng

hp th thoi. Khi s in thoi b gi bn hay ngoi vng ph sng th h thng asterisk

nh hng trc tip cuc gi n hp th thoi tng ng khai bo trc.

Voicemail cung cp cho ngi s dng nhiu tnh nng nh: xc nhn password khi

truy cp vo hp th thoi, gi mail bo khi c thng ip mi.

3.3.2.2 Call Forwarding

Call Forwarding: chuyn hng cuc gi.

y l tnh nng thng c s dng trong h thng Asterisk. Chc nng cho php

chuyn mt cuc gi n mt hay nhiu s my in thoi c nh trc.

Mt s trng hp cn chuyn cuc gi nh : Chuyn cuc gi khi bn, chuyn

cuc gi khi khng tr li, chuyn cuc gi tc thi, chuyn cuc gi vi thi gian nh

trc.

3.3.2.3 Caller ID

Caller ID: cuc gi c hin th s.

Vi chc nng ny th s in thoi ca ngi gi n my in thoi ca bn s c

hin th, nhm gip bn c th bit c ai ang gi ti.

Ngoi ra Caller ID cng cho php chng ta xc nhn s thu bao gi n c ngha l

da vo caller ID chng ta c tip nhn hay khng tip nhn cuc gi t pha h thng

Asterisk. Ngn mt s cuc gi ngoi mun.

3.3.2.4 Interactive Voice Response

Interactive Voice Response (IVR) hay Automated Attendant (AA): u c dng

ch chc nng tng tc thoi (tng i tr li t ng).

Chc nng tng tc thoi c rt nhiu ng dng trong thc t, khi gi in thoi n

mt c quan hay x nghip thu bao thng c nghe thng ip nh:Xin cho

mng bn gi n cng ty chng XXX hy nhn phm 1 gp phng kinh doanh,


41

phm 2 gp phng k thut, phm 3 gp phng h tr khch hng sau tu vo s

tng tc ca thu bao gi n, h thng Asteisk s nh hng cuc gi theo mong mun.

Dch v xem im thi, tin cc in thoi ca thu bao, t gi t in t hin nay nh

th no, hay kt qu s s, bn tin d bo thi tit tt cc nhng mong mun trn u

c th thc hin qua chc nng tng tc thoi.

3.3.2.5 Time and Date

Nhm ch nh cc khong thi gian c th cuc gi s nh hng n mt s in

thoi hay mt chc nng c th khc, v d trong cng ty gim c mun ch cho php

nhn vin s dng my in thoi trong gi hnh chnh cn ngoi gi th s hn ch hay

khng cho php gi ra bn ngoi.

3.3.2.6 Call Parking

Chc nng Call Parking cng thc hin vic chuyn cuc gi nhng c qun l. C mt s

in thoi trung gian v hai thu bao c th gp nhau khi thu bao c gi nhn vo s

in thoi m thu bao ch gi ang ch trn v t y c th gp nhau v m thoi.

3.3.2.7 Remote call pickupe

Vi tnh nng ny s cho php chng ta t my in thoi ny c th nhn cuc gi t

my in thoi khc ang rung chung.

3.3.2.8 Privacy Manager

Khi mt ngi ch doanh nghip trin khai Asterisk cho h thng in thoi ca cng

ty mnh nhng li khng mun nhn vin trong cng ty gi i ra ngoi tr chuyn vi bn

b, khi Asterisk cung cp mt tnh nng tin dng l ch cho php s in thoi c

lp trnh c php gi n nhng s my c nh no thi, cn nhng s khng c

trong danh sch nh sn s khng thc hin cuc gi c.

3.3.2.9 Backlist

Backlist cng ging nh Privacy Manager nhng c mt s khc bit l nhng my in

thoi nm trong danh sch s khng gi c n my ca mnh (s dng trong tnh trng

hay b quy ri in thoi).

V cn rt nhiu tnh nng na m h thng asterisk c th cung cp cho ngi s dng,

trn y ch l mt s tnh nng thng c s dng.


42

3.3.3 Ng cnh ng dng

Asterisk thc hin rt nhiu ng cnh ng dng khc nhau tu vo nhu cu s dng,

di dy s g i i th iu m t s ng cnh ng dng thng c s dng trong thc

t v c trin khai trn h thng asterisk.

3.3.3.1 Tng i VoIP IP PBX

Hnh 3.8 IP BPX

y l h thng chuyn mch VoIP c xy dng phc v cc cng ty c nhu cu thc

hin trn nn tng mng ni b trin khai. Thay v lp t mt h thng PBX cho nhu

cu lin lc ni b th nn lp t h thng VoIP, v m hnh ny chi ph phi tr s c

gim ng k. H thng lin lc vi mng PSTN qua giao tip TDM.

3.3.3.2 Kt ni IP PBX vi PBX

Hnh 3.9 Kt ni IP PBX vi PBX

Ng cnh t ra l hin ti Cng ty trang b h thng PBX by gi cn trang b

thm p ng nhu cu lin lc trong cng ty sao cho vi chi ph thp nht, gii php


43

thc hin l trang b h thng Asterisk v kt ni vi h thng PBX ang tn ti qua

lung E1. Ngoi ra tng kh nng lin lc vi mng PSTN v VoIP khc, Cng Ty s

ng k kt ni dch v vi nh cung cp dch v VoIP.

3.3.3.3 Kt ni gia cc server Asterisk

Hnh 3.10 Kt ni gia cc server asterisk

Phng php trn ng dng rt hiu qu cho cc cng ty nm ri rc cc v tr a l

khc nhau nhm gim chi ph ng di. V d Cng ty M c tr s t ti nc M v

c cc Chi nhnh t ti Vit Nam vi hai a im l H Ni v thnh ph H Ch Minh.

Thng qua mng WAN ca Cng Ty cc cuc gi ni b gia cc v tr khc nhau s lm

gim chi ph ng k.

3.3.3.4 Cc ng dng IVR, VoiceMail, Conference Call

Hnh 3.11 Trin khai server IVR, VoiceMail, Conference Call

ng dng thc hin cc server kt ni vi h thng PSTN hay tng i PBX trin

khai cc ng dng nh tng tc thoi IVR. Mt v d cho ng dng tng tc thoi l


44

cho bit kt qu s s, kim tra cc cuc, dch v gii tr tra cu thng tin thng qua

s 19001260. ng dng VoiceMail thu nhn nhng tin nhn thoi t pha thu bao

ging nh chc nng hp th thoi ca Bu in trin khai.

Chc nng cuc gi hi ngh c thit lp cho nhiu my in thoi cng ni

chuyn vi nhau.

3.3.3.5 Chc nng phn phi cuc gi t ng ACD

Hnh 3.12 Phn phi cuc gi vi hng i

ACD (Automatic Call Distribution): Phn phi cuc gi t ng.

Chc nng c ng dng cho nhu cu chm sc khch hng hay nhn phn hi t

pha khch hng.

Gi s mt Cng ty h thng in thoi c kh nng tip nhn cng mt lc 10 cuc

gi, nh th nu c thm cuc gi th 11 gi n th h thng gii quyt nh th no?

Bnh thng th s nghe tn hiu bn nhng vi chc nng phn phi cuc gi s a

thu bao vo hng i ch tr li, trong khi ch tr li cuc gi thu bao c th

nghe nhng bi ht hay do asterisk cung cp v khi no mt trong mi s in thoi ang

gi tr v trng thi ri th cuc gi ang ch s c tr li. Ging nh chc nng ca

dch v: dch v h tr thng tin 1080, dch v hn gi 116 ca Bu in, dch v h

tr khch hng ca cc tng i in thoi.

3.4 Asterisk vi VoIP

3.4.1 Cc thit b dng trong VoIP

3.4.1.1 VoIP phone

L thit b phn cng kt ni vi VoIP ging nh my in thoi c nh thng

thng. Tuy nhin s dng cho VoIP cn phi cu hnh trc khi s dng.


45

Mt s tnh nng khi thc hin mua thit b in thoi VoIP:

+ Low Bandwidth: h tr cho loi Codec no, thng hin nay ngi ta s dng G729.

+ Web Interface: phi c giao tip thit lp cu hnh thn thin d s dng.

+ Audio Interface: c speaker phone hay khng.

3.4.1.2 Softphone

L mt phn mm c ci trn my tnh, thc hin tt c cc chc nng ging nh

thit b in thoi VoIP. Khi s dng softphone, giao tip my tnh phi c card m

thanh, headphone v firewall khng b kha.

i vi h thng Asterisk, nn dng softphone vi cng ngh giao thc mi dnh cho

Asterisk l IAX.

3.4.1.3 Card giao tip vi PSTN

Mun cho php cc my in thoi ni b trong h thng Asterisk kt ni v thc hin

cuc gi vi mng PSTN, chng ta cn phi c thit b phn cng tng thch. Thit b


46

phn cng s dng cho h thng Asterisk do chnh tc gi lp cng ty Digium phn phi,

xut pht t tng phn phi phn mm Asterisk v h thng ngun m min ph.

Thit b phn cng thng k hiu bt u bng cm t TDMxyB trong x l s

lng port FXS, y l s lng port FXO. Gi tr ti a ca c x v y l 4.

Hnh Card TDM22B gm 4 port 2 FXS v 2 FXO

3.4.1.4 ATA (Analog Telephone Adaptors)

ATA l thit b kt ni vi in thoi Analog thng thng n mng VoIP, mt thit

b ATA gm c hai loi port: RJ-11 kt ni vi my analog thng thng v RJ-45

kt ni vi mng VoIP.

ATA l thit b FXS chuyn i tn hiu Analog sang tn hiu s s dng cho mng

VoIP tn dng thit b Analog cho kt ni VoIP.

Thit b ATA s dng vi giao thc IAX c Digium phn phi l thit b ATA c

s dng rng ri vi Asterisk c tn gi l IAXy.

3.4.2 Cc giao thc VoIP c Asterisk h tr

Asterisk h tr hai giao thc chun v mt giao thc dnh ring cho Asterisk.


47

3.4.2.1 IAX ( Inter-Asterisk eXchange)

IAX l giao thc chun dnh ring cho Asterisk. N cung cp hot ng lin kt trong

sut vi tng la NAT v PAT. N h tr vic thit lp, nhn, chuyn cuc gi v ng

k cuc gi. Vi IAX, cc in thoi hon ton c ng. Ch cn kt ni in thoi vi

Asterisk server bt c u trn mng Internet, chng s ng k vi PBX ch v c

nh tuyn cuc gi ngay tc th.

IAX c on mo u rt nh. Vi bn byte ca mo u, so snh vi 12 byte mo

u ca SIP hay H.323, bn tin IAX c th ni l nh hn rt nhiu.

IAX h tr xc thc i vi cc cuc gi n v i. Asterisk cung cp nm phng thc

iu khin truy nhp. Ta c th gii hn truy cp vo tng phn ca dial plan.

3.4.2.2 SIP (Session Initiation Protocol)

SIP l chun ca IETF dnh cho VoIP. Giao thc ny c m t chi tit phn

trn. Cu trc iu khin ca SIP bao gm c SMTP, HTTP, FTP v cc chun khc ca

IETF. SIP chy trn nn TCP/IP v iu khin cc phin RTP (Real Time Protocol). RTP

truyn d liu vi mi phin ca VoIP. SIP l mt chun thit yu ca VoIP bi v tnh

n gin ca n khi so snh vi cc giao thc khc nh H.323. Giao thc SIP trong

Asterisk h tr tt vic giao tip gia cc thit b ca cc nh cung cp khc nhau, trong

c c SNOM v Cisco.

3.4.2.3 H.323

H.323 l chun ITU dnh cho VoIP. Trong khi H.323 vn c s dng trong Asterisk

th ngy nay n cng ngy cng t c s dng. N ang dn c thay th bng cc

chun hin i hn nh SIP v IAX.

3.4.3 Cc chun nn v nh dng file

Mt b nn v gii nn (codec: compressor/decompressor) c s dng nn tn

hiu thoi tng t thnh lung d liu s hay gii nn d liu thnh tn hiu tng t.

Asterisk c th hot ng vi nhiu nh dng file v chun nn khc nhau. Bi v n l

mt phn mm vi cu trc m nn n d dng hot ng vi cc nh dng file v codec

thm vo.

C hai chun nn PCM 64kbps ph bin, lut A v lut u. C hai iu s dng nn

logarit t c 12 n 13 bit cho vic nn tuyn tnh 8 bit. Nn logarit lm gim cc

tn s cao hay m lng ln. Lut A tt hn trong vic nn tn hiu mc thp v c t s


48

nn tn hiu trn nhiu tt hn. Lut u thng c s dng Bc M, cn lut A thng

c s dng chu u.

Asterisk cung cp vic chuyn i hon ho gia cc chun nn vi nhau.

Cc chun nn gm c:

Chun nn Tc

16 bit tuyn tnh 128 kbps

G.711u (lut u) 64 kbps

G.711a (lut A) 64 kbps

IMA-ADPCM 32 kbps

GSM 6.10 12 kbps

MP3 bin i

LPC-10 2.4 kbps

Hnh 3.13 Cc chun nn

Thm vo , cc chun nn khc nh G.723.1 v G.729 c th i qua mt cch trong

sut. Thng thng, ngi ta s dng b nn v gii nn lut A, lut u hay tuyn tnh cho

bng DTMF. Hu ht cc chun nn c mt mt d liu tng i ln khi truyn fax.

Cc nh dng file

Asterisk s dng nhiu file khc nhau lu tr d liu m thanh bao gm voicemail

v music on hold. Asterisk h tr nhiu nh dng file v file m thanh khc nhau.

Cc nh dng c h tr bao gm:

nh dng M t

Raw d liu 16 bit tuyn tnh

Pcm d liu 8 bit lut u

Vox d liu 4 bit IMA-ADPCM

Wav file WAV tuyn tnh 16 bit 8 KHz

WAV file WAV nn GSM 8 KHz

Gsm d liu nn GSM

g723 nh dng g723 n gin vi nhn thi gian

Hnh 3.14 Cc nh dng file


49

H thng qun l file ca Asterisk

Th mc M t

/etc/asterisk Tt c cc file cu hnh tr /etc/zaptel.conf

/usr/sbin Cc on m v file thc thi ca Asterisk bao

gm asterisk, astman, astgenkey v safe_asterisk

/usr/lib/asterisk Cc i tng nh phn ring ca cu trc Asterisk

/usr/lib/asterisk Cc module thi gian thc cho cc ng dng,

iu khin knh, b nn v gii nn, nh dng file,...

/usr/include/asterisk Cc file mo u cn thit cho xy dng cc ng

dng ca Asterisk, iu khin knh v cc

module hot ng.

/var/lib/asterisk Cha bin c s dng bi Asterisk trong

sut hot ng bnh thng

/var/lib/asterisk/agi-bin Cc on m AGI dng bi ng dng dial plan AGI

/var/lib/asterisk/astdb C s d liu ca Asterisk, lu tr cc thng tin

cu hnh. File ny khng bao gi thay i bi

ngi s dng c, m ch c th thay i bng

cu lnh c s d liu ca Asterisk: thm vo v

chnh sa file ny

/var/lib/asterisk/images Cc hnh c tham chiu bi cc ng dng hay

bi dial plan

/var/lib/asterisk/keys Cc kho chung hoc ring c s dng

trong Asterisk cho xc thc RSA. IAX s dng

nhng cha kho c lu tr y.

/var/lib/asterisk/mohmp3 Cc file MP3 c s dng cho chc nng music

on hold. Cu hnh cho music on hold c cha

trong th mc ny.

/var/lib/asterisk/sounds Cha cc file m thanh, cnh bo,... c s dng


50

bi cc ng dng ca Asterisk. Mt vi ng dng c

th lu tr cc file ring ca mnh trong cc th

mc con

/var/run Cc file PID v tn chng trnh chy thi gian thc

/var/run/asterisk.pid Primary Process Identifier (PID) ca cc ng

dng Asterisk ang thc thi

/var/run/asterisk/ctl H thng tn c s dng bi Asterisk cho

php iu khin t xa.

/var/spool/asterisk Cc file chy thi gian thc cho voicemail, cc

cuc gi ra ngoi,...

/var/spool/asterisk/outgoing Asterisk iu khin th mc ny cho cc cuc gi ra

ngoi. Mt cuc gi ra ngoi s lu kt qu vo

mt file trong th mc ny. Asterisk phn tch

file c to ra v thit lp cuc gi.Nu nh cuc

gi c tr li, n s chuyn ti Asterisk PBX.

/usr/spool/asterisk/qcall c s dng phn khng ng dng qcall.

Khng c s dng.

/var/spool/asterisk/vm Hp th thoi, thng bo v cc th mc

Bng 3.2 H thng qun l file trong Asterisk

3.4.4 File cu hnh

3.4.4.1 Gii thiu

S linh ng ca Asterisk c iu khin thng qua cc file cu hnh c cha trong

th mc /etc/asterisk ngai tr file zaptel.conf cu hnh cho phn cng TDM nm ti th

mc /etc. nh dng ca cc file cu hnh trong Asterisk tng t vi dng file .ini (trong

Window). File ny nh dng theo m ASCII c chia ra thnh nhiu phn (sections).

Cc ni dung sau du chm phy l ch thch trong file cu hnh. Cc dng trng,

khong trng khng c ngha trong file cu hnh. Cc php gn c s dng: = dng

gn cc bin, => gn cc i tng


51

; The first non-comment line in a config file

; must be a section title

;

[section1]

keyword = value ; Variable assignment

[section2]

keyword = value

object => value ; Object declaration

3.4.4.2 Cc kiu ca file cu hnh

Mc d cc file cu hnh ca Asterisk c nh dng ging nhau, nhng chng c

phn ra lm 3 kiu c bn thng c s dng.

3.4.4.2.1 Simple Group

Simple Group l dng n gin nht c s dng bi cc file cu hnh m mi i

tng ch c ngha trn dng .

V d:

[mysection]

object1 => option1a,option2a,option3a

object2=> option1b,option2b,option3b

Tng ng vi object1 l cc i tng option1a, option2a, option3a. Cn object2

c gn cho cc i tng option1b, option2b, option3a.

Cu hnh ny thng c s dng trong cc file: extensions.conf, meetme.conf,

voicemail.conf

3.4.4.2.2 Inherited option object:

Kiu cu hnh ny thng c s dng bi cc file: zapata.conf, phone.conf,

mgcp.conf . Trong kiu cu hnh ny, cc dng pha di tha k cc thng s ca cc

dng trn n.


52

V d:

[mysection]

option1 = foo

option2 = bar

object => 1

option1 = baz

object => 2

Hai dng u tin gn hai gi tr foo, bar cho option1, option2. i tng 1 c to

ra bi hai thng s l option1=foo v option2=bar. Khi option1 c thay i thnh baz

th i tng 2 c to thnh t hai thng s l option1=baz v option2=bar.

Nh vy thay i gi tr option1 sau khi i tng 1 c gn ch nh hng n

i tng 2 m khng nh hng n i tng 1.

3.4.4.2.3 Complex entity object:

Kiu cu hnh ny s dng bi cc file: iax.conf, sip.conf, c t chc thnh nhiu

thc th (entity), ng vi mi entity c nhiu thng s c khai bo, mi entity l cc

section khai bo.

V d:

[myentity1]

option1=value1

option2=value2

[myentity2]

option1=value3

option2=value4

Entity myentity1 c cc gi tr value1, value2 cho cc thng s option1, option2. Trong

khi entity myentity2 cng c cc thng s l option1, option2 nhng vi cc gi tr l

value3, value4.


53

3.4.4.3 Channel interfaces:

Phn ny gii thiu cc file cu hnh cho cc Asterisk channel drivers.

Asterick c th c cu hnh vi nhiu mc ch khc nhau, nhng m hnh thng

thng nht l Client/Server. M hnh ny cho php cc client hay cn gi l UAC

user agent client kt ni vo server l Asterisk hay cn gi l UAS User Agent Server.

Cc UAC l ni sinh ra cc session trong khi UAS th x l th ng cc session nhn

c da trn tp hp rule c sn. Phn IV s i r hn v cc dng ng dng ny.

Ta c th cu hnh Asterisk trong console mode, hoc c mt cch tin li hn l edit

trc tip cc file cu hnh trong /etc/asterisk. Mi ng dng ring ca Asterisk nh

voicemail, zaptel, music-on-hold, meetme, conference, iax u c configuration ring

ca mnh, tuy nhin c 2 file cu hnh quan trng nht l sip.conf v extension.conf:

- Sip.conf : file cu hnh v cc thng tin ca cc UAC nh username, password, IP,

type, security, codec, l thnh phn cn bn nht lu gi thng tin trong Asterisk.

- Extension.conf: file cu hnh v cc lut nh tuyn cuc gi, lut quay s, cc

extension trong ngoi v nhng tnh nng c bit khc. Extensions.conf l file quan

trng nht

46701406 tong dai asterisk va voip nguyenthiquynhtrang04dt1

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