Ebook Công nghệ VoIP và các giải pháp nâng cao chất lượng dịch vụ: Phần 2

ChiTdng IV
C A C G IA O TH lTC D IE U K H IE N

4.1. GlCrt THIEU
So vai thoai truyen thong, thoai IP hoat dong trong mot moi
trudng mdi, hien da co mot sd cac giao thuc lap ung dung phat
trien cho thoai Internet. Mot diem quan trong de co mot ha tang
ca sd goi dua tren tieu chuan la kha nang co cac tieu chuan md
cho cac lap dieu khien cuoc goi. N hung chuan m a nay duac
cung cap bdi cac giao thuc nhu H.323, MGCP. SIP va cac giao
dien m d dugc phat trien rong khap qua c a sd ha tang dong goi.
Mot trong cac cong viec cua giao thuc dieu khien cuoc goi la chi
cho cac dong RTP bat dau d dau va ket thuc d dau. Giao thuc
dieu khien cuoc goi hoan tat nhiem vu nay bang viec bien dich
giua cac dia chi IP va cac sd dien thoai.
Hien nay chung ta chua the thay the hoan toan mang dien
thoai chuyen mach cong cong (PSTN) bang cong nghe VoIP bai
con nhieu dieu phirc tap ben trong cac giao thirc mdi chay tren
nen tang ciia IP. Tuy nhien, gan day cac giao thirc cho bao hieu
cuoc goi va dieu khien thiet bi dang dugc chuan hoa. chung ta
dang gdn dat den mot mdi trudng co tinh lien ket hoat dong cao.
Giao thirc dieu khien truyen thong (M GCP) hien nay da trd
thanh tieu chuan chinh thirc, trong khi do cac cai tien dugc thira


Chut m g IV: Cac giao Ihire dieu khien

139

nhan gan day trong phien han 4 cua H.323 da tao dieu kien thuan
lgi khi ket hgp voi cac giao thirc khac de tao ra cac giai phap cho

lie thong truyen thoai hoan chinh va dac tinh ket noi ngang cap
cho cac mang goi. Giao thirc khai tao phic’n (SIP) dang dirge
xem nhu giao thirc bao hieu chinh trong he thong chuyen mach
mem (softsvvitch). Hinh 4.1 dudi day la mo ta chong giao thirc
sir dung cho VoIP.

Hinh 4 .1: Chong giao (hire VoIP
Giao thirc H.323 phien ban 1 va 2 ho trg H.245 tren nen
TCP, Q.93 1 tren nen TCP va RAS tren nen UDP. Cac phien ban
3 va 4 cua H.323 ho trg them H.245 va Q.931 tren nen UDP.
Giao thirc SIP ho trg ca TCP va UDP. Trong mang NGN cac
cuoc goi thoai deu la cac cuoc goi VoIP. Chinh vi the phan tilp
theo se d<3 cap den cac giao thirc bao hieu trong mang VoIP mot
cach chi tiet han.


Cong nghe VoIP vd cdc giai phap

140

4.2. BO GIAO TH tfC H.323
11.323 la chuan m d dugc ITU-T phat trien cho viec dieu
khien cuoc goi ngang hang, dua tren co sd cua H.320 va ISDN
Q .9 3 1. 11.323 la mot cau true chat che. phuc tap va phu hgp vdi
vice thuc thi cac dac tinh thoai truyen thong. Tieu chuan H.323
thiet ke cho truyen audio, video va du lieu qua mang IP bao gom
Internet. Tieu chuan H.323 bao gom bao hieu va dieu khien cuoc
goi. truyen va dieu khien da phuong tien va dieu khien bang
thong cho hoi nghi diem - diem va da diem. Tieu chuan H.323
bao gom cac giao thirc dugc liet ke trong bang 4.1.

Bang 4.1. Bo giao thuc 11.323
Dac di&m
Bao hi£u
Dieu

gpi (Cail Signalling)

H.225

phuang

H.245

cuqc

khien

Giao thi>c

tien

(Media

Control)
Bo codec am thanh (Audio Codecs)

G 711, G.722, G.723.1. G 728. G 729

Bo codec vi-de-o (Video Codecs)

H.261,H 263

Chia se du li$u (Data Sharing)

T 120

T ruyln

tai

phuang

tien

(Media

RTP/RTCP

Transport)

Cac thanh phan co ban ciia he thong mang H.323 dugc nio
ta trong hinh 4.2 dudi day. Bao gom cac dau cuoi, cong ket ndi.
thiet bi dieu khien cong ndi (gatekeeper) va khoi dieu khien da
diem (MCU).


Chuang IV: Cdc giao Ihue dieu khien

141

Dien thoai

Hinh 4.2: Cdc thanh phan mang H.323
4.2.1. Thiet bi dau cuoi
Dau cuoi cung cap thong tin diem - diem va da diem vai
cac ddu cuoi khac. Dau cuoi H.323 gom cac khoi nhu dieu khien
he thdng, khdi truyen tai p h u an g tien. ma hoa audio va giao dien
voi mang IP. Phan thiet bi tuy chon co the la ma hoa video va
thiet bi truyen du lieu.

4.2.2. Cong ket noi
Cong ket ndi cung cap giao dien giua hai mang khac nhau.
Cdng k it ndi H.323 ket noi mang H.323 voi mang khong phai
H.323

nhu PSTN.

Cong ket noi chuyen ddi giua audio

(am thanh). video va cac dinh dang truyen du lieu cung nhu cac
giao thuc va he thong thong tin. Cong ket ndi chi can thiet khi


Cong nghe VoIP vd cdc giai phap

142

phai ket noi vai mang phi 11.323, do do khong can thiet khi ket
noi giua hai thiet hi dau cuoi H.323.

4.2.3. Thiet bj dieu khien cong noi
Thiet bi dieu khien cong noi la tuy chon, co the sir dung
hoac khong. Thiet bi dieu khien cong noi cung cap cac djch vu
truac khi dien ra cuoc goi va dich vu dieu khien cuoc goi cho
cac diem cuoi H.323. Tuy nhien, neu thiet bi dieu khien cong noi
co mat trong mang no se co nhiem vu: bien dich dja chi, dieu
khien chap nhan, dieu khien bang thong va quan ly viing.
Cac chirc nang tuy chon ciia thiet bi dieu khien cong noi bao
gom: bao hieu dieu khien cuoc goi, xac thuc cuoc goi, quan ly
bang thong, quan ly cuoc goi.

4.2.4. Khoi dieu khien da diem (MCU)
Khoi dieu khien da diem la diem cuoi (endpoint) ho trg hoi
nghi giua 3 thanh vien hoac nhieu han. MCU dien hinh bao gom
bo dieu khien da diem (MC) va mot hoac nhieu bo xir ly da diem
(MP). MC xir ly dieu khien va bao hieu de ho trg hoi nghj trong
khi MP nhan d u lieu audio, video va luong du lieu, xir ly va
/

r

*

r

phan bo chung den cac diem cuoi thanh vien trong hoi nghi
da diem.
Bo giao thuc H.323 bao gom nhieu giao thirc. Bo giao thuc
ho trg chap nhan cuoc goi, thiet lap, trang thai, giai phong. luong
p h uang tien va cac ban tin trong he thong H.323. Cac giao thirc

dugc ho trg ca c a che truyen dua ra goi tin cay va khong tin cay
qua mang IP nhu minh hoa trong hinh 4.3.


143

Chuang IV Cdc giao thuc dieu khien
Truyen tai TCP tin c$y

Truyen tai UDP khong tin cay
Du lieu audio/video

H 225
Dieu
khien
cuoc goi

H 245

RAS

RTP

RTCP

UDP

TCP

IP

Lap vat ly va lien ket du lieu

Hinh 4.3: Cdc lap ciia bo giao thuc H.323
Bo giao thirc H.323 bao gom ba viing dieu khien:
- Bao hieu dang ky, thira nhan va trang thai (RAS): Bao
hieu RAS cung cap dieu khien truac cuoc goi trong mang thiet
bi dieu khien cong noi H.323.
- Bao hieu dieu khien cuoc goi (H.225): dua tren khuyen
nghi H.225 ciia ITU-T ma no chi ra viec sir dung cac ban tin ban
hieu Q.931. Kenh dieu khien cuoc goi tin cay TCP dugc tao ra
tren mang IP vai ma cong la 1720.
- Dieu kh iln va truyen tai thong tin Media (H.245 va
RTP/RTCP): H.245 xir ly cac ban tin dieu khien tir dau den cuoi
giua cac diem cuoi H.323. Thu tuc giao thirc H.245 thiet lap
kenh cho truyen audio, video dir lieu va thong tin kenh dieu
khiln. T ru y ln da p h uan g tien trong H.323 dugc cung cap bai
RTP va RTCP.

4.2.5. Trinh tu thiet lap cuoc goi
N£u xem xet mot cach chi tiet thi cuoc goi giua hai dau cuoi
H.323 dugc thilt lap nhu hinh 4.4 duai day.


Cong nglw VoIP va cdc giai phap..

144

□
[L IT !
Dau cuoi A

Thiet bi dieu khien cong noi

O^u cuoi B

1. A R Q ---------2. ACF ---------■3 S ETUP4. Call Proceeding
5 ARQ
6. ACF
7 Alerting

I

8. Connect
H.245 Messages

I

RTP Media Path
-RAS messages
•Call Signaling Messages

Hinh 4.4: Thiet lap cuoc goi H.323
- Trudc het ca 2 phai da dugc dang ky tai thiet hi dieu khien
cong noi
- Dau cuoi A gui yeu cau tdi thiet bi dieu khien cong ndi de
nghi thiet lap cuoc goi
- Thiet bi dieu khien cong ndi gui cho dau cuoi A thong tin
can thiet ve dau cuoi B

Chuang IV Cdc giao Ihire dieu khien

145

- Dau cuoi A giri ban tin SETUP tai dau cuoi B
- Dau cuoi B tra ldi bang ban tin Call Proceeding va dong
thdi lien lac vdi thiet bi dieu khien cong noi de xac nhan quyen
thiet lap cuoc goi

f

*

* j .

* r

v

•

&

/

i

- Dau cuoi B giri ban tin canh bao va ket ndi (Alerting and
Connect)
- Hai dau cuoi trao ddi mot sd ban tin H.245 de xac dinh

chii/td, kha nang xir ly ciia dau cuoi va thiet lap ke ndi RTP.
Day la trudng hop cuoc goi diem-diem don gian nhat, khi
ma bao hieu cuoc goi khong duoc dinh tuyen tdi thiet bi dieu
khien cong ndi. H.323 hd tro nhieu kich ban thiet lap cuoc goi
phirc tap khac.
H.323 la he thong ghep lai duoc xay dung tir cac thiet bi tap
trung thong minh nhu: thiet bi dieu khien cong ndi. MCU, cong
ket ndi va diem cuoi. Mac dii chuan H.323 trong phien ban gan
day nhat co phdn hoan thien hon song van de van nay sinh. nhu
thdi gian thidt lap cuoc goi dai, qua nhieu chirc nang thiet bj dieu
khidn cdng ndi phai thuc hien va kha nang m d rong khi sir dung
ki£u bao hieu cuoc goi djnh tuyen qua thiet bi dieu khien cdng
ndi (GKRCS).
Khi cdn sir dung cdng ket ndi dung luong ldn de ket ndi
mang PSTN, ngudi ta se sir dung giao thirc dieu khien cdng don
gian (SGCP: Simple Gateway Control Protocol) va Giao thuc
didu khidn cdng p h u a n g tien (MGCP: Media Gateway Control
Protocol) dd thay thd giao thirc cho cdng ket ndi H.323. Cac he
thdng didu khien cuoc goi nay co ve hieu qua hon. dap img nhu
cau cua cac nha cung cap cd ldn.


Cdng nghe VoIP vd cdc giai phap..

146

Cung vay, giao thuc khoi tao phien SIP (Session Initiation
Protocol) co the giai quyet mot so ton tai cua H.323 va no kha
nang sc thay the H.323.

4.3. GIAO THU’C KHOI TAO PHIEN (SIP)
SIP la giao thuc dieu khien bao hieu thuoc lap ung dung,
duoc phat trien nhu la mot chuan m a RFC 2543 cua ILTF. Khac
voi H.323, no dua tren nguon goc Web (HTTP) va co thiet ke kieu
mo-dun, dem gian va de dang m a rong vai cac ung dung thoai SIP.
SIP la mot giao thuc bao hieu de thiet lap, duy tri va ket thuc cac
phien da phuang tien nhu: thoai IP, hoi nghi va cac ung dung
tuang tu khac lien quan den viec truyen thong tin da phuang tiyn.
Uu diem chinh cua SIP so vai cac giao thuc bao hieu khac
la cung cap mot su mem deo. No dirge thiet ke nhanh va dan
gian. Giao thuc SIP cung cap cac chuc n in g sau:
- Djnh vi nguai dung thong qua dia chi tuang tu nhu email.
- Nang luc nguai dung: cac tham so phien co the thuang
lugng giua hai phia.
- Lgi l'ch ngucri dung: Xac dinh dua tren kieu ben bi gpi
muon tien hanh truyen thong.
Giao thuc SIP bao gom hai thanh phan: dai ly tram cua
ngudi su dung (user agent) va may chii mang (network server).
User agent la mot ling dung ket cuoi he thong ma no bao gom ca
user agent client (UAC) khdi tao cuoc gQi va user agent server
(UAS) no se tra ldi cuoc goi. Kien true cua SIP cho phep thong
tin ngang cap sir dung giao thuc may khach/may chii.
Network servers bao gom bon kieu la: Proxy server (may
chu liy quyen). Location server (may chu cuc bo;. Redirect


Chuang IV: Cdc giao thuc dieu khien

147

server (may chu ch uy ln tidp) va Register server (may chu
dang ky).
ITU-T khong phai la to chuc tieu chuan duy nhat dua ra ke
hoach thiet lap ket noi thoai IP va dong goi audio. Hem han hat
ky mot to chuc quan ly cac chuan muc Internet, IETF cung co
nhung yeu cau cua rieng minh doi voi nhung he thong VoIP va
dugc goi la "Giao thuc dieu khien phien" - SIP.
Nhung nguai de xuat SIP cho rang H.323 dang xuat hien
trong bao hieu ATM va ISDN, la khong thich hgp cho dieu
khien he thong VoIP noi chung va trong thoai Internet noi rieng.
Yeu cau nay khang dinh la H.323 von di rat phuc tap. ho trg cac
chuc nang phan 1cm la khong can thiet cho thoai IP do do doi hoi
chi phi cao va khong hieu qua. Vi du H.323 xac djnh 3 phucmg
phap khac nhau dc phoi hgp hoat dong giua H.225 va H.245, vai
cac ket noi khac nhau, H.245 ngang qua ket noi H.225 va tien
hanh phuang phap "ket noi nhanh" cua 2 giao thuc tich hgp.
Mac du hau het cac kha nang thuc hien chi ho trg cho cac ket noi
nhanh, tinh tuang thich H.323 lien quan den yeu cau ho trg cua
ca 3 phuang phap.
Ddng thai, nhung ng uai ung ho SIP cung cho rang H.323
khong co kha nang m d rong yeu cau ddi vdi giao thirc bao hieu
cho cdng nghe chang han nhu VoIP, la nhung cdng nghe chac
chin se phat triln va hd trg cac dich vu va dac tinh mdi. Kinh
nghiem trong sir dung cac giao thirc Internet mail (SMTP) da
cung cap rdt nhieu triet ly phat trien SIP, trong do tap trung vao
kha nang thich img ciia bao hieu trong tuang lai.


Cdng nghe VoIP vd cac giai phap

148

SIP dua tren y tucrng va cau true cua HTTP ( Hypertext
Transfer Protocol), giao thuc trao doi thong tin cua World Wide
Web. No dugc dinh nghTa nhu mot giao thuc Client-Server,
trong do cac yeu cau dugc ben goi (client) dua ra va ben bi gpi
(server) tra ldi. SIP su dung mot so kieu ban tin va cac trudng
mao dau cua HTTP, xac dinh noi dung luong thong tin theo mao
dau thuc the (md ta noi dung - kieu loai) va cho phep xac nhan
cac phuang phap su dung giong nhau dugc sir dung tren Web.
*

«

SIP dinh nghTa cac ban tin INVITE va ACK giong nhu ban
tin Setup va Connect trong H.225, trong do ca hai deu dinh nghTa
qua trinh m d 1 kenh dang tin cay ma thong qua do cuoc gpi co
the di qua. Tuy nhien khac vdi H.225, do tin cay cua kenh nay
khong phu thuoc vao TCP. Cac nha de xuat SIP kien nghi rang
viec tich hgp do tin cay vao lap ung dung nay cho phep ket hop
mot cach chat che cac gia tri dieu chinh de ung dung, co the tdi
uu hoa VoIP han la phu thuoc vao nhung gia tri "muc dich
chung chung" cua TCP.
Cuoi cung, SIP dua vao giao thuc mo ta phien (SDP). mot
tieu chuan khac cua IETF, de thuc hien su sap xep tuang tu theo
r

t

t

*

c a cau chuyen ddi dung lugng cua H.245. SDP dugc dung de
nhan dang m a tong dai trong nhung cuoc gpi sir dung mot mo ta
nguyen ban dan. SDP cung duac sir dung de chuyen cac phan tir
thong tin ciia giao thirc bao hieu thdi gian thuc RTSP de sap xep
cac tham so hoi nghi da diem va djnh nghTa khuon dang chung
cho nhieu loai thong tin khi dupe chuyen trong SIP.
Cuoc tranh luan lieu chuan H.323/H.225 hay SIP phii hop
cho thoai Internet hay khong thi chi mang tinh chat hoc thuat. Ca
hai cach deu co nhung thuan lgi va bat lgi. Trong khi H.323 co
thuan lgi r k ldn trong thj trudng (da xuat hien trudc SIP) thi SIP


( huang IV Cue giao thirc dieu khien

149

co lgi the ciia IETF la mot trong so cac to chirc tieu chuan hoat
dong tich cuc. Voi muc dich nghien ciru cac giao thirc va giai
phap cho van de VoIP, tot nhat la luu y den ca FI.323 va SIP.
Theo dinh nghTa ciia IETF, SIP la “giao thirc bao hieu lop
img dung mo ta viec khai tao, thay doi va huy cac phien ket noi
tuang tac da phuang tien giua nhung ngudi sir dung”. SIP co the
sir dung cho rat nhieu djch vu khac nhau trong mang IP nhu dich
vu thoai, hoi nghj thoai, email, day hoc tu xa, quang ba (MPEG,
MP3...), truy nhap HTML, XML, hoi nghi truyen hinh...
' A
a

4.3.1. Phan mem chuyen mach cuoc gpi SIP
Phan mem chuyen cuoc goi SIP co cau true nhu sau:
Cac thanh phan cua SIP

May chu
uy quyen

May chu
uy quyer

Hinh 4.5: Cau trite SIP


Cong nghe VoIP vd cdc gidi phap .

150

Trong hinh tren, dai ly ngudi dung (User Agent) la thiet bi
dSu cuoi trong mang SIP, co the la mot may dien thoai SIP, c6
th i la may tinh chay phan mem dau cuoi SIP.
May chu uy quyen (Proxy Server) la phan mem trung gian
hoat dong vira nhu may chu va vira nhu may tram de thuc hien
cac yeu cau thay mat cac dau cuoi khac. Tat ca cac veu cau dirge
xir ly tai cho boi may chu uy quyen neu co the, hoac dugc
chuyen cho cac may chu khac. Trong trudng hop may chu uy
quyen khong true tiep dap ung cac yeu cau nay thi may chu uy
quyen se thuc hien khau chuyen doi hoac dich sang khuon dang
thich hop truac khi chuyen di.
May chu dinh vi (Location Server) la phan mem dinh vi thue
bao, cung cap thong tin ve nhung vj tri co the cua phia bj goi cho

cac phan mem may chu uy quyen va may chu chuyen doi dja chi.
May chu chuyen doi dja chi (Redirect Server) la phan mem
nhan yeu cau SIP va chuyen doi dja chi SIP sang mot so dja chi
\

f

r

khac va gui lai cho dau cuoi. Khong giong nhu may chu uy
quyen, may chu chuyen doi dja chi khong bao g ia hoat dong nhu
mot dau cuoi, tuc la khong gui di bat cu yeu cau nao. May chu
chuyen doi dja chi (Redirect Server) cung khong nhan hoac huy
cuoc gpi.
M ay chu dang ky (Registrar Server) la phan mem nhan cac
yeu cau dang ky. Trong nhieu trudng hap may chu dang ky dam
nhiem luon mot sd chuc nang rn ninh nhu xac nhan ngudi sir
dung. Thong thudng may chu dang ky dupe cai dat cung vai
may chii uy quyen va may chu hay dja chi hoac cung cap djch
vu djnh vj thue bao. Mdi lan d£u cuoi dupe bat len (thi du may


Chu
151

dien thoai hoac phan mcm SIP) thi dau cudi lai dang ky voi may
chu. Neu dau cuoi can thong bao cho may chu ve dja diem cua
minh thi ban tin REGISTER cung duoc gui di. Noi chung cac
dau cuoi deu thuc hien viec dang ky lai mot cach djnh ky.

4.3.2. Cac ban tin SIP, mao dau va danh so
D uai day la cac ban tin cua SIP:
- INVITE: Bat dau thiet lap cuoc goi bang cach giri ban tin
mdi dau cuoi khac tham gia.
- ACK: Ban tin nay khang djnh may tram da nhan dugc ban
tin tra ldi ban tin INVITE.
- BYE: Bat dau ket thuc cuoc goi
- CANCEL: Huy yeu cau dang nam trong hang dgi
- REGISTER: Dau cuoi SIP sir dung ban tin nay de dang ky
vdi may chu dang ky.
- OPTIONS: Sir dung de xac djnh nang luc cua may chii.
- INFO: Sir dung de tai cac thong tin nhu am bao DTMF.
Giao thirc SIP co nh ilu diem trung hgp vdi giao thirc HTTP.
Cac ban tin tra ldi cac ban tin SIP neu tren gom co:
- lxx - Cac ban tin chung
- 2xx - Thanh cdng
- 3xx - Chuyen dja chi
- 4xx - Yeu cSu khong dugc dap ung
- 5xx - Su co ciia may chii
- 6xx - Su co toan mang.


Cong nghe VoIP vd cdc g iai phap..

152

Cac ban tin SIP deu co khuon dang text, tuang tu nhu
HTTP. Mao dau cua ban tin SIP cung tuang tu nhu HTTP va
SIP cung ho trg MIM E (mot so chuan ve email). Sau day la thi

du ve mao dau cua ban tin SIP:

SIP Header

INVITE sip:512 0 @ 1 9 2 .168.36.180 SIP/2.0
Via: SIP/2.0/UDP 192.168.6.21:5060
From: sip :5 121 @ 192.168.6.21
To: <sip:5120@ 192.168.36.180>
Call-ID: c2943000-e0563-2alce-2e323931@ 192.168.6.21
CSeq: 100 INVITE
Expires: 180
User-Agent: Cisco IP Phone/ Rev. 1/ SIP enabled
Accept: application/sdp
Contact: sip :5 121@ 192.168.6.21:5060
Content-Type: application/sdp
Cac dau cuoi SIP dugc danh so tuang tu nhu dia chi email,
thi du nhu ptit@ vnpt.com .vn.

4.3.3. Thiet lap va huy cuoc goi SIP
Trong mang SIP qua trinh thiet lap va huy mot phien ket noi
th uang gom co 6 budc nhu sau:


153

C h u a n g I V C u e g ia o thirc dieu khien

ap
E
Dai ly ngi/di

suf dung

May chu
uy quyen

INVITE

May chu
dinh vj/dSng ky

May chu
uy quyen

Oai ly
ngudi stf
dung

INVITE

Thiet lap
cuoc goi

302
(Dich chuyen
tarn thdi)
-

ACK

----INVITE

INVITE
302
(Dich chuyen
tarn thdi)
— ACK ----— INVITE

180 (rung
chuong)

180 (rung chuong)

- 200 (OK) •

----- 200 (O K )--------

-ACK-

Dudng
phUdng
tien

I

-ACK-

180 (rung
chuong)
•200 (OK) —
-ACK-

RTP MEDIA PATH
— BYE —

Huy
— 200 (OK)
cuoc goi

I

------------ BY E --------200 (OK)

•BYE200 (OK)

Hinh 4.6: Thiet lap va huy cuoc gpi SIP
1. Dang ky, khdi tao va dinh vj dau cuoi
2. Xac dinh phuong tien cua cuoc goi. tuc la mo ta phien ma
dau cuoi dugc mdi tham du
3. Xac dinh mong muon cua dau cuoi bi goi, tra ldi hay
khong. Phia bj goi phai giri ban tin xac nhan chap thuan cuoc goi
hoac tir choi


154

Cong nghe VoIP va cdc g iai phap

4. Thiet lap cuoc goi
5. Thay doi hay dieu khien cuoc gpi (thi du nhu chuyen
cuoc gpi)
6. Huy cuoc gpi.

Qua trinh thiet lap va huy cuoc gpi SIP co ban dupe mo ta
troim hinh 4.6 sau.

4.3.4. Tinh nang cua SIP
Giao thuc SIP dupe thiet k<3 vdi nhung tieu chi sau:
- l ich hop vdi cac giao thuc da co cua IETF
- Don gian va co kha nang m d rong
- Hd tro tdi da su di dong cua dau cuoi
- De dang tao tinh nang mdi cho djch vu.

a) Tich hap vai cdc giao thirc c1d co ciia IETF
Cac giao thirc khac ciia IETF co the sir dung de xay dimg
nhung irng dung SIP. SIP co the hoat dong ciing vdi nhieu giao
thirc nhu:
- RSVP (Resource Reservation Protocol): Giao thirc danh
trudc tai nguyen mang
- RTP (Real-time transport Protocol): Giao thirc truyen tai
thdi gian thuc
- RTSP (Real Time Streaming Protocol): G iao thuc tao
luong thdi gian thuc
- SAP (Session Advertisement Protocol): Giao thuc thong
bao trong phien ket ndi


( huang IV; Cdc giao Ihire dieu khien

155

- SDP (Session Description Protocol): Giao tlu'rc mo ta
phien ket noi da phuang tien

- M IM E (Multipurpose Internet Mail Extension - M d rong
thir tin Internet da muc dich): Giao thirc thu dien tu
- HTTP (Hypertext Transfer Protocol): Giao thuc truyen
sieu van ban
- COPS (Common Open Policy Service): Dich vu chinh
sach m d chung.
- OSP (Open Settlement Protocol): Giao thirc thoa thuan md

h) Dan gian vd co kha ndng m a rong
SIP co rat it ban tin, khong co cac chirc nang thira nhung
SIP co the sir dung dc thiet lap nhung phien ket noi phirc tap nhu
hoi nghi... Don gian, gon nhe, dua tren khuon dang van ban. SIP
la giao thirc ra ddi sau va da khac phuc dugc diem yeu cua nhieu
giao thirc trudc day.
Cac phan mem ciia may chii uy quyen, may chu dang ky.
may chii chuyen ddi dia chi. may chu dinh vi... co the chay tren
cac may chii khac nhau va viec cai dat them may chu hoan toan
khong anh hudng den cac may chu da co. Chinh vi the he thong
chuyln mach SIP co the de dang nang cap.

c) Ho tra loi da su di dong cua ddu cuoi
Do cd may chii uy quyen. may chii dang ky va may chii
chuyln ddi dja chi he thong luon nam dugc dja diem chinh xac
ciia thue bao. Thi du thue bao vdi dja chi cd thd


156

Cdng nghe VoIP vii ciic g iai phap..

nhan dugc cuoc ggi thoai hay thong diep a bat cu dia diem nao
qua bat cu dau cuoi nao nhu may tinh de ban, may xach tay, ditjn
thoai SIP... Vcri SIP rat nhieu djch vu di dong inoi dugc ho trg.

d) De dang tao tinh ndng mdi cho dich vu vd dich vu mdi
La giao thuc khoi tao phien trong mang chuyen mach goi
SIP cho phep tao ra nhung tinh nang moi hay djch vu mai mot
cach nhanh chong. Ngon ngu xir ly cuoc ggi (Call Processing
Language) va Giao dien cong ket noi chung (Common Gateway
Interface) la mot so cong cu de thuc hien dieu nay. SIP ho tra
cac djch vu thoai nhu c h a cuoc goi, chuyen tiep cuoc goi, khoa
cuoc goi... (call waiting, call forwarding, call blocking...), ho trg
thong diep thong nhat...

4.3.5. So sanh H.323 va SIP
Giua H.323 va SIP co nhieu diem tuang dong. Ca hai deu
cho phep dieu khien, thiet lap va huy cuoc goi. Ca H.323 va SIP
deu ho trg tat ca cac djch vu can thiet, tuy nhien co mot so diem
khac biet giua hai chuan nay. Do la:
- H.323 ho trg hoi nghi da phuang tien rat phirc tap. Hoi
'

r

nghj H.323 ve nguyen tac co the cho phep cac thanh vien sir
dung nhung djch vu nhu bang thong bao, trao doi d u lieu, hoac
hoi nghj video.
- SIP ho trg SIP-CGI (SIP - Common Gateway Interface).
- SIP ho trg dieu khien cuoc goi tir mot dau cuoi thu 3. Hien
nay H.323 dang dugc nang cap de ho trg chirc nang nay.

157

C huang IV : Cdc giao thuc dieu khien

Bang 4.2: So sanh H.323 vd SIP
H .3 2 3

S IP

To chicc

IETF

ITU

Quan he k it noi

Ngang cap

Ngang cap

Khoi diem

Dya tren mang Internet
va Web. Cu phap va
ban tin tuong tu1 nhu
HTTP

Co so la mang thoai.
Giao thuc bao hieu
tuan theo chuan ISDN
Q.SIG

Dau cuoi

Dau cuoi thong minh
SIP

Dau cuoi thong minh
H.323

Cac may chu loi

May chu uy quyen SIP,
may chu chuyen doi
dia chi, may chu djnh vj
va may chu dang ky.

Dieu khien cong noi
H.323

Tinh hinh hien nay

Giai doan thi> nghiem
kha n3ng cung hoat
dong cua thiet bi cua
c^c nha cung cap khac
nhau da k it thuc. SIP

nhanh chong tro nen
pho b iin

Da duoc su dung rong
rai

Khuon dang ban tin

Text, UTF-8

Nhj phan ASN 1 PER

T r i th iit lap cuoc
goi

1,5 RTT (round-trip
time, tire chu ky gui
ban tin va nhan ban tin
tra loi hay xac nhan)

6-7 RTT hoac hon

Giam sat trang thai
cuoc goi

Co 2 lua chon: chi
trong thai gian thiet lap
cu6c goi hoac suot thai
gian cuoc goi

Phien ban 1 va 2: may
chu phai giam sat trong
suot thoi gian cuoc goi
va phai giu trang thai
k it noi TCP -> han c h i
kha nang md rang va
giam do tin cay

Bao hi§u quang ba
(cho ca nh6m. .)

C6 h6 tro

Khong


Cong nghe VoIP va cuc g iai phap..

158
Ch£t luong dich vy

St> dyng cac giao thirc
khac nhir RSVP, OPS,
OSP de dam bao chat
luong dich vu

Thidt bi dieu
c6ng noi dieu
bang thdng
khuyen

nghj
RSVP d4 li/u
nguyen mang.

khi4n
khi£n
H 323
dung
trO tai

Bao mat

D3ng ky tai may chu
d3ng ky, c6 xac nhan
dau cuoi va ma hoa

Chi dang ky khi trong
mang co thi£t b| di&u
khien cong noi, xac
nhan va ma h6a theo
chu£n H.235

Dinh vi dau cuoi va
dinh tuyen cuoc goi

Diing SIP URL de
danh dia chi. Djnh
tuyen nho sir dung
may chu thay dia chi
va may chu dinh vi.

Dinh vi dau cudi si>
dung E 164 hoac t6n ao
H.323 va phi/cmg phap
anh xa dia chi neu trong
mang co thi£t bj di£u
khien cong n6i Chirc
nang dinh tuy§n do thiSt
bi dieu khi£n cong noi
dam nhiem

Tinh nang thoai

Ho tro cac tinh nang
cua cuoc goi co ban

Ho tro cac tinh nang
cua cuoc gpi co ban

Hoi nghi

Hoi nghi co so, quan ly
phan tan

Duoc thi6t k6 nham ho
tro rat nhi^u tinh nang
h6i nghi, ke c i thoai
video va dur Ii6u. quan
ly tap trung nen MC c6
the tac nghen

Tao tinh nang va
dich vu moi

De dang, sir dung SIPCGI va CPL

H 450 1

Kha nang m d rong

D6 dang

Han ch£

Tich hop vdi web

Rat tot hd tro nhan
chudt de quay s6
(click-to-dial)

K6m
II


159

Chuong IV : Cue giao I hue dieu khien

4.4. GIAO THtTC MGCP
Giao thirc dieu khien cong noi phuang tien (M GCP) la giao

thirc dung dc dieu khien cac cong noi thoai tir cac thiet bj dieu
khien cuoc goi. Giao thirc nay la chirc nang ciia bo dieu khien
cong noi p h u an g tien (MGC) hoac dai ly cuoc goi (CA).

MGCP

Cong noi
phirong tien (MG)

MGCP

Cong noi
phUdng tien (MG)

Hinh -I. 7; Cong ket ndi phuang tien va bo dieu khien cdng ndi
phirong tien
Quan he giua MG va MGC (hay CA) dugc mo ta tren
hinh 4.7. MGC thuc hien bao hieu cuoc goi, dieu khien MG.
MGC va MG trao d6i lenh vai nhau thong qua MGCP.

4.4.1. Thiet lap cuoc gpi
Hinh 4.8 mo ta viec thiet lap va giai phong cuoc goi MGCP
thonc thu ang giua 2 thue bao PSTN ket noi vai cac tong dai sir
dung C C S 7 de bao hieu.


160

Cong nghe VoIP vd cdc gidi phap

Hinh 4.8: Thiet lap vd gidi phong cuoc goi MGCP
- Thue bao PSTN ben A (chu goi) nhac may, quay so roi giri
cac chir so dia chi thue bao bi goi nay toi tong dai (ben chii gpi ben A).
- Tong dai ben A sau khi nhan xong dja chi thue bao bi goi
(ben B), tao ra ban tin ISUP IAM (Initial Address M essage) de


Chuang IV : Cac giao thuc dieu khien

161

giri bao hieu cho cong noi phuang tien/thiet bj dieu khien cong
noi p h uang ti$n (M G /M GC) de chinh thuc dat van de ket noi voi
thue bao bj goi (1)
- M GC gui cho M G ben A ban tin M GCP CRCX “CreateconnectionM(2)
- MG ben A tra lai bSng ban Resp - “Response” (3)
- MGC gui cho tong dai ben B (bi goi) ban tin I SUP IAM (4)
- MGC gui tiep ban tin M GCP CRCX cho M G ben B (5)
- MG ben B tra lai bang ban tin Resp (6)
- MGC giri cho MG ben A ban tin M GCP MDCX (7)
- MG ben A tra lai bang ban Resp (8)
- MGC giri cho MG ben B ban tin ISUP COT (Continuity
message) de bao cao ket qua kiem tra tinh lien tuc (dugc yeu cau
trong ban tin 1AM) tren mot mach (kenh B dugc chon) (9)
- Tong dai ben B giri cho MGC ban tin ISUP ACM (hoan
tat viec nhan dia chi) dong thai rung chuong cho thue bao B (10)
- MGC chuyen cho tong dai ben A ban tin ISUP ACM nay (11)
- Sau khi thue bao B nhac may, tong dai ben B giri cho
MGC ban tin ISUP ANM (ANswer Message) thong bao viec
nhac may nay (12)

- Ban tin ANM nay lai dugc MGC chuyen cho tong dai ben
A va hai ben thue bao A va B co the bat dau dam thoai (13).
D uai day la thu tuc giai phong ket noi M GCP giua 2 thue
bao A va B khi mot trong hai ben gia sir ben B dat may
- Tcing dai ben B giri ban tin ISUP REL cho MGC yeu cku
giai phong ket noi (1)
- MGC sau do giri ban tin ISUP REL nay cho tong dai ben A (2)


Cdng nghe VoIP va cdc gidi phup

162

- M GC giri ban tin M GCP DLCX “Deleteconnection”cho
MG ben B de thong bao yeu cau MG giai phong ket noi (3)
- MG ben B giri tra lai ban tin M GCP Resp (4)
- MGC cung dong thai giri ban tin M GCP DLCX cho MG
ben A de thong bao yeu cau MG giai phong ket noi (5)
- MG ben A cung giri tra lai ban tin MGCP R esp (6)
- Tong dai ben A giri cho MGC ban tin ISUP RLC thong
bao hoan tat viec giai phong ket noi (7)
- MGC sau do cung giri cho tong dai ben B ban tin ISUP RLC
thong bao hoan tat viec giai phong ket noi. Ket noi ket thuc (8).

4.4.2. Cac lenh MGCP
Giao thirc M GCP co 2 nhom lenh nhu sau:

a) Lenh MGC
- EndpointConfiguration
- NotificationRequest

- CreateConnection
- M odifyConnection
- DeleteConnection
- AuditEndpoint
- AuditConnection
- DeleteConnection
- RestartlnProgress

b) Lenh cdng ndi
- DeleteConnection
- RestartlnProgress