giao thuc_voip

7/31/2019 Giao thuc_voip

1/98

I HC QUC GIA H NI

TRNG I HC CNG NGH

o Ngc Anh

NGHIN CU GIAO THC TRONG MNG VOIP

KHO LUN TT NGHIP I HC H CHNH QUY

Ngnh: in t - Vin thng

H NI - 2008


2/98

I HC QUC GIA H NI

TRNG I HC CNG NGH

o Ngc Anh

NGHIN CU GIAO THC TRONG MNG VOIP

KHO LUN TT NGHIP I HC H CHNH QUY

Ngnh: in t - Vin thng

Cn b hng dn: Th.S Nguyn Quc Tun

H NI - 2008


3/98

LI CM N

Trc ht em xin gi ti thy gio Nguyn Quc Tun nguyn Ch nhim B

mn H thng Vin thng , li cm n chn thnh v su sc trc tip hng dn ,

ch bo tn tnh trong sut qu trnh em lm lun vn.

Em cng xin chn thnh cm n cc thy c gio trong Trng i hc Cng

Ngh - i hc Quc Gia H Ni ht lng dy bo, gip em trong nhng nm hc

i Hc, gip em c nhng kin thc v kinh nghim qu bu trong chuyn mn v

cuc sng. Nhng hnh trang l mt ti sn v gi nng bc cho em ti c vi

nhng thnh cng trong tng lai.Cui cng, em xin cm n nhng ngi thn trong gia nh v bn b gip ,

ng vin em hon thnh lun vn ny.

H ni, thng 05 nm 2008

Sinh vin


4/98

TM TT NI DUNG

Vi 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. t lu, mng chuyn

mch knh ghp phn knh theo thi gian PSTN c mt vai tr v cng quan trng

vi s pht trin ca x hi. Bn cnh nhng u im v cht lng dch v tt, vng

dch v rng ln trn khp mi lnh th, th mng PSTN cng bc l nhiu hn ch

nh s lng cc dch v hn ch, s dng ti nguyn ng truyn khng ti u, gi

thnh cao.

Trn c s , mng VoIP ra i v ngy cng p ng tt hn cc yu cu t ranh cht lng dch v, gi thnh, s lng tch hp cc dch v thoi ln phi thoi.

Cng nh cc cng ngh ra i trong thi gian gn y, th vn Giao thc l c bit

quan trng. Vic nm chc Giao thc l cha kha thnh cng ca vic trin khai mi

mt cng ngh mi vo thc t. Chnh v vy, trong ni dung ca bi Lun vn tt

nghip ny, em xin c gii thiu v Giao thc s dng trong mng VoIP. Bi lun

vn s gm cc ni dung chnh nh sau:

Chng 1: Tng quan v mng VoIP.Chng 2: Cc giao thc truyn ti trong VoIP.

Chng 3: Giao thc bo hiu VoIP.

Mt vn c bit quan trong khi mi cng ngh, mt giao thc mi c sinh

ra l vn tng thch vi cc cng ngh v giao thc trc . cng l mt trong

nguyn nhn quyt nh s sng cn ca mng VoIP c cp ti ti:

Chng 4: Kt ni mng VoIP v PSTN.

V phn cui cng trong bi Lun vn tt nghip:

Chng 5: Kho st giao thc cuc gi VoIP SIP PSTN trn thc t.

y l mt minh chng r nt v vic trin khai cc giao thc VoIP nghin cu

trong ton b ni dung bi Lun vn tt nghip vo bi ton vin thng thc t.


5/98

MC LC

Chng 1. Tng quan v mng VoIP ...............................................................................2

1.1. Tng quan v mng VoIP .......................................................................................2

1.2. c tnh ca mng VoIP .........................................................................................4

1.2.1. u im ...........................................................................................................4

1.2.2. Nhc im .....................................................................................................5

1.3. Yu cu cht lng i vi VoIP ...........................................................................6

Chng 2. Cc giao thc truyn ti trong VoIP ...............................................................8

2.1. Giao thc IP ............................................................................................................8

2.1.1. Giao thc IP phin bn 4 (IPv4) ......................................................................8

2.1.2. Giao thc IP phin bn 6 (IPv6) ....................................................................12

2.2. Giao thc TCP/IP .................................................................................................13

2.3. Giao thc UDP .....................................................................................................19

2.4. Giao thc SCTP .................................................................................................... 192.5. Giao thc RTP ......................................................................................................24

2.6. Giao thc RTCP ...................................................................................................30

Chng 3. Giao thc bo hiu VoIP ..............................................................................33

3.1. Giao thc bo hiu H.323 .....................................................................................33

3.1.1. Cc thnh phn trong mng ...........................................................................33

3.1.2. Giao thc H.323 ............................................................................................. 373.1.3. Thit lp cuc gi VoIP s dng giao thc H.323 ........................................42

3.2. Giao thc SIP ........................................................................................................ 46

3.2.1. Cc thnh phn trong mng SIP ....................................................................47

3.2.2. Bn tin SIP ..................................................................................................... 49

3.2.3. M t cuc gi SIP .......................................................................................54

3.3. So snh gia giao thc H.323 v SIP ...................................................................56


6/98

Chng 4. Kt ni gia mng VoIP v PSTN ..............................................................58

4.1. Mng bo hiu SS7 ............................................................................................... 58

4.1.1. Cc thnh phn trong mng bo hiu SS7 .....................................................58

4.1.2. Lin kt trong mng SS7 ...............................................................................59

4.1.3. nh tuyn trong mng SS7 ........................................................................... 60

4.1.4. Giao thc trong mng SS7 .............................................................................61

4.1.5. Cc bc thit lp cuc gi trong mng SS7 .................................................66

4.2. Giao thc Sigtran .................................................................................................. 67

4.2.1. M2UA/ M2PA ...............................................................................................68

4.2.2. M3UA ............................................................................................................ 69

4.2.3. SUA ...............................................................................................................70

4.2.4. Kt ni mng VoIP vi mng PSTN ............................................................71

Chng 5. Kho st giao thc cuc gi VoIP SIP PSTN trn thc t ........................76

5.1. Gii thiu kin trc mng VoIP c nghin cu ................................................76

5.2. Gii thiu chng trnh Wireshark .......................................................................77

5.3. Kho st giao thc cuc gi VoIP SIP PSTN trn thc t .................................78


7/98

DANH MC CC T VIT TT

K hiu

vit tt Vit y ngha

VoIP Voice over IP Cng ngh truyn thoi trn mng IP

PSTNPublic Switch

Telephone NetworkMng in thoi cng cng

PCMPulse-Code

ModulationB m ha m xung

SNMPSimple Network

Management ProtocolGiao thc qun tr mng n gin

SIPSession Initiation

ProtocolGiao thc thit lp phin

RTP Real Time Protocol Giap thc thi gian thc

RTCP

Real Time Control

Protocol Giap thc iu khin thi gian thc

ATMAsynchronous

Transfer ModeCh truyn khng ng b

QoS Quality of Service Cht lng dch v

ToS Type of Service Kiu dch v

IP Internet Protocol Giao thc Internet

IPv4 IP version 4 Giao thc Internet phin bn 4

IPv6 IP version 6 Giao thc Internet phin bn 6

TCPTransmission Control

ProtocolGiao thc iu khin truyn thng tin

UDPUser Datagram

ProtocolGiao thc Datagram ngi dng


8/98

SCTPStream Control

Transmission ProtocolGiao thc truyn iu khin lung

ITU-T

International

TelecommunicationUnion-

Telecommunication

Standardization Sector

Hip hi vin thng quc t

- B phn chun vin thng

RASRegister Admission

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

SAP

Session

Announcement

Protocol

Giao thc thng bo phin

SDPSession Description

ProtocolGiao thc m t phin

SS7 Signaling System No.7 H thng bo hiu s 7

SSP Switch Service Point im dch v chuyn mch

SCP Signal Control Point im iu khin bo hiu

STP Signal Tranfer Point im truyn bo hiu

MTP Message Tranfer Part Phn truyn bn tin

TCAP

Transaction

Capabilities

Application Part

Phn ng dng cung cp giao dch

TUP Telephone User Part Phn ngi dng in thoi

ISUP ISDN User Part Phn ngi dng ISDN

ISDNIntegrated Services

Digital NetworkMng tch hp dch v s

SCCPSignaling Connection

Control PartPhn iu khin kt ni bo hiu

M2UA MTP2 User Adapter B chuyn i ngi dng MTP2


9/98

M2PAMTP L2 Peer-to-Peer

AdapterB chuyn i bn tin lp 2 ngang hng

M3UA MTP3 User Adapter B chuyn i ngi dng MTP3

IUA ISDN User Adapter B chuyn i ngi dng ISDN

SUA SCCP User Adapter B chuyn i ngi dng SCCP


10/98

M U

Mng VoIP ra i nh l mt cuc cc mng ca h thng vin thng v x hi.

Vi nhng u im vt tri, mng VoIP chng t c sc sng v tnh thc tin

cao ca n. S pht trin qu nhanh ca mng VoIP cng t ra mt vn nan gii

l vic chun ha gia cc giao thc VoIP ca nhiu nh pht trin khc nhau. M trong

c hai giao thc c nhc ti nhiu nht l H.323 ca ITU-T v SIP ca IETF.

Nh mt tt yu khch quan, mng VoIP s c chia thnh nhiu min giao thc khc

nhau. Nn vn quan trng c th trin khai c mng VoIP vo thc t l phi

hiu c bn cht ca cc giao thc VoIP v quan trng nht l cc giao thc bo

hiu s dng trong VoIP. Tuy vyh mi l iu kin cn cho s ra i cn vn thencht cho s tn ti v pht trin ca mng VoIP li l vn kt ni vi h thng vin

thng vn c. V c th l vn kt ni gia mng VoIP v mng PSTN. V y cng

l hai ni dung chnh ca bi Lun vn tt nghip ny.

Trn c s nhn thc r s quan trng cng nh cch thc hot ng ca giao thc

trong mng VoIP, th phng php nghin cu ca em trong ni dung Lun vn ch yu

i su nghin cu thng qua ti liu quy chun v Giao thc VoIP (RFC ca IETF, cc

ti liu chun ca ITU-T); ng thi tham chiu n cc ti liu chuyn mn su v

VoIP lm r cc vn cn gii quyt.

T nhng hiu bit nghin cu l thuyt kh su v chuyn mn, em s tham chiu

vi m hnh thc t. T lm r cc vn vng mc m khi nghin cu l thuyt

cha th gii quyt v lm r c.

1


11/98

Chng 1. Tng quan v mng VoIP

1.1. Tng quan v mng VoIP

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.

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

truyn d liu thng thng.

c th hiu c nhng u im ca VoIP mang li, trc ht chng ta i vonghin cu s khc bit gia mng knh PSTN hin c vi mng chuyn mch gi ni

chung v mng VoIP ni ring.

K thut chuyn mch knh (Circuit Switching): Mt c trng ni bt ca k

thut ny l hai trm mun trao i thng tin vi nhau th gia chng s c thit lp

mt knh (circuit) c nh, knh kt ni ny c duy tr v dnh ring cho hai trm

cho ti khi cuc truyn tin kt thc. Thng tin cuc gi l trong sut. Qu trnh thit lp

cuc gi tin hnh gm 3 giai on:

Giai on thit lp kt ni:Thc cht qu trnh ny l lin kt cc tuyn gia cc

trm trn mng thnh mt tuyn (knh) duy nht dnh ring cho cuc gi. Knh

ny i vi PSTN l 64kb/s (do b m ha PCM c tc ly mu ting ni

8kb/s v c m ha 8 bit).

Giai on truyn tin: Thng tin cuc gi l trong sut. S trong sut th hin qua

hai yu t: thng tin khng b thay i khi truyn qua mng v tr nh.

2


12/98

Giai on gii phng (hu b) kt ni: Sau khi cuc gi kt thc, knh s c

gii phng phc v cho cc cuc gi khc.

Qua , ta nhn thy mng chuyn mch knh c nhng u im ni bt nh cht

lng ng truyn tt, n nh, c tr nh. Cc thit b mng ca chuyn mchknh n gin, c tnh n nh cao, chng nhiu tt. Nhng ta cng khng th khng

nhc ti nhng hn ch ca phng thc truyn d liu ny nh:

S dng bng thng khng hiu qu: Tnh khng hiu qu ny th hin qua hai

yu t. Th nht, rng bng thng c nh 64k/s. Th hai l knh l dnh

ring cho mt cuc gi nht nh. Nh vy, ngay c khi tn hiu thoi l lng

(khng c d liu) th knh vn khng c chia s cho cuc gi khc.

Tnh an ton: Do tn hiu thoi c gi nguyn bn trn ng truyn nn rtd b nghe trm. Ngoi ra, ng dy thu bao hon ton c th b li dng an

trm cc vin thng.

Kh nng m rng ca mng knh km: Th nht l do c s h tng kh nng

cp v tng thch vi cc thit b c. Th hai, l hn ch ca h thng bo

hiu vn c s dng t trc khng c kh nng ty bin cao.

K thut chuyn mch gi (Packet Switching): Trong chuyn mch gi mi

bn tin c chia thnh cc gi tin (packet), c khun dng c quy nh trc. Trongmi gi cng c cha thng tin iu khin: a ch trm ngun, a ch trm ch v s

th t ca gi tin, Cc thng tin iu khin c ti thiu, cha cc thng tin m

mng yu cu c th nh tuyn c cho cc gi tin qua mng v a n ti ch.

Ti mi node trn tuyn gi tin c nhn, nh v sau th chuyn tip cho ti chm

ch. V k thut chuyn mch gi trong qu trnh truyn tin c th c nh tuyn

ng truyn tin. iu kh khn nht i vi chuyn mch gi l vic tp hp cc gi

tin to bn tin bn u c bit l khi m cc gi tin c truyn theo nhiu con

ng khc nhau ti trm ch. Chnh v l do trn m cc gi tin cn phi c nhdu s th t, iu ny c tc dng, chng lp, sa sai v c th truyn li khi hin

tng mt gi xy ra.

Cc u im ca chuyn mch gi:

Mm do v hiu sut truyn tin cao:Hiu sut s dng ng truyn rt cao v

trong chuyn mch gi khng c khi nim knh c nh v dnh ring, mi

ng truyn gia cc node c th c cc trm cng chia s cho truyn tin,

cc gi tin sp hng v truyn theo tc rt nhanh trn ng truyn.

3


13/98

Kh nng tryn u tin: Chuyn mch gi cn c th sp th t cho cc gi c

th truyn i theo mc u tin. Trong chuyn mch gi s cuc gi b t chi

t hn nhng phi chp nhn mt nhc im vi thi gian tr s tng ln.

Kh nng cung cp nhiu dch v thoi v phi thoi.

Thch nghi tt nu nh c li xy ra: c tnh ny c c l nh kh nng nh

tuyn ng ca mng.

Bn cnh nhng u im th mng chuyn mch gi cng b l nhng nhc im

nh:

Tr ng truyn ln: Do i qua mi trm, d liu c lu tr, x l trc khi

c truyn i.

tin cy ca mng gi khng cao, d xy ra tc nghn, li mt bn tin

Tnh a ng c th gy l lp bn tin, loop lm tng lu lng mng khng

cn thit.

Tnh bo mt trn ng truyn chung l khng cao.

1.2. c tnh ca mng VoIP

1.2.1. 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 Inter-

net. 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 di8Kbps, 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.

Tch hp dch v nhiu dch v: Do vic thit k c s h tng tch hp nn c

kh nng h tr tt c cc hnh thc thng tin cho php chun ho tt hn v

gim thiu s thit b. Cc tn hiu bo hiu, thoi v c s liu u chia s cng

4


14/98

mng IP. Tch hp a dch v s tit kim chi ph u t nhn lc, chi ph xy

dng cc mng ring r.

Thng nht: V con ngi l nhn t quan trng nhng cng d sai lm nht

trong mt mng vin thng, mi c hi hp nht cc thao tc, loi b ccim sai st v thng nht cc im thanh ton s rt c ch. Trong cc t chc

kinh doanh, s qun l trn c s SNMP (Simple Network Management Proto-

col) c th c cung cp cho c dch v thoi v d liu s dng VoIP. Vic s

dng thng nht giao thc IP cho tt c cc ng dng ha hn gim bt phc tp

v tng cng tnh mm do. Cc ng dng lin quan nh dch v danh b v

dch v an ninh mng c th c chia s d dng hn.

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 ngdng 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 uphin) 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.

1.2.2. 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

5


15/98

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.

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 dchv 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).

1.3. 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.

6


16/98

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.

7


17/98

Chng 2. Cc giao thc truyn ti trong VoIP

2.1. Giao thc IP

Giao thc mng IP c thit k lin kt cc mng my tnh s dng phng

php truyn thng v nhn d liu di dng gi. Giao thc IP cho php truyn cc gi

d liu t im ngun ti im ch c a ch c nh. n v d liu c trao i l

cc gi d liu. Cc chc nng c thc hin IP l:

nh a ch: tt c cc host trong mng v trong lin mng u c cung cp

mt a ch IP duy nht. Theo giao thc IP version 4, mi a ch IP gm 32bit v

c chia lm 5 lp A,B,C,D,E. Cc lp A,B,C c s dng nh danh cc

host trn cc mng. Lp c s dng cho qu trnh truyn a im cn lp E

d phng.

nh tuyn: gip xc nh ng i (tuyn)cho gi tin khi c truyn trn

mng. N gip la chn ng i ti u cho cc gi d liu. Nu hai host cn

lin lc khng nm trn mt subnet th bng nh tuyn s c s dng quyt

nh vic chuyn d liu v cc b nh tuyn thng xuyn trao i v cp nht

thng tin trong bng nh tuyn ty thuc vo phng php nh tuyn c s

dng.

Truyn a im:

Hin nay c ba cch truyn cc gi IP l:

o Truyn mt im ch (unicast): cc gi tin c truyn t host ngun

n host ch duy nht.

o Truyn qung b: gi tin c truyn n tt c cc host trong mng.

o Truyn a im: gi tin c gi n mt s cc host nht nh trongmng

Ngoi ra, giao thc IP cn cung cp kh nng phn mnh d liu ln thnh cc gi

c kch thc nh hn truyn qua mng.

2.1.1. Giao thc IP phin bn 4 (IPv4)

Cu trc ca header IPv4 nh sau:

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18/98

Hnh 1. Cu trc gi IP phin bn 4

ngha cc trng nh sau:

Version: rng 4 bit m t phin bn IP

IP Header Length(IHL): c rng 4 bit, xc nh rng ca phn tiu ca gi tin IP

Type of Service: c rng 8 bit, xc nh cc tham s ch dch v s dng

khi truyn gi tin qua mng. Rt nhiu mng cung cp cc dch v v u

tin lu thng, c bit khi mng b qu ti. Vic la chn ny m bo

ng truyn t ba tiu chun l thi gian tr, tin cy, b thng sut ca

gi tin. c m t c th nh sau:

o Quyn u tin (3 bit)

o tr D (1 bit)

D=0: tr bnh thng

D=1: tr cao

o Thng lng T (1bit)

T=0: thng lng bnh thng

T=1: thng lng cao

o tin cy (1bit):

R=0: tin cy bnh thng

R=1: tin cy cao

9


19/98

Total Length (16bit): xc nh di ca gi tin k c phn tiu . C gi tr

ti a l 65535 byte. Thng thng cc host ch c th x l gi tin c di

l 576 byte gm 512 byte d liu v 64 byte tiu . Cc host ch c th gi

cc gi tin c di ln hn 576 byte khi bit trc l host ch c kh nng

x l gi ny.

Indentification: cng vi trng a ch ngun, ch dng nh danh duy

nht cho mt gi tin trong khong thi gian n tn ti.

Flag : c rng 3 bit, ch phn on ca gi tin

o Bit 0: lun bng 0

o Bit 1 (DF):

DF=0: c phn on

DF=1: khng phn on

o Bit 2 (MF):

MF=0: mnh cui cng

MF=1: khng phi mnh cui cng

Fragment Offset: rng 13 bit, ch r v tr ca phn mnh trong gi tin tnh

theo n v 64bit.

Time to Live: rng 8 bit, quy nh thi gian tn ti ca gi tin.

Protocol: rng 8 bit, xc nh giao thc tng giao vn. V d

o Protocol = 6: giao thc TCP

o Protocol=17: giao thc UDP

Header Checksum: rng 16 bit, m kim tra CRC-16 ca phn tiu cho

pht hinli

Source Address: rng 32 bit, xc nh a ch ngun.

Destination Address: rng 32 bit, xc nh a ch ch

10


20/98

Option: c di thay i lu thng tin ty bin ca ngi dng

Padding: c di thay i, m bo di ca header lun l bi 32 bit

Data: c di ti a l 65535 byte cha d liu lp cao hn.nh a ch trong IPv4

H thng a ch ny c thit k mm do qua mt s phn lp, c 5 lp a ch

IP l: A, B, C, D, E. S khc nhau c bn gia cc lp a ch ny l kh nng t chc

cc cu trc con ca n.

Lp Nhn dng a ch u a ch cui Mt n mng

A 0xxx 0.0.0.0 127.255.255.255 255.0.0.0

B 10xx 128.0.0.0 191.255.255.255 255.255.0.0

C 110x 192.0.0.0 223.255.255.255 255.255.255.0

D 1110 224.0.0.0 239.255.255.255

E 1111 240.0.0.0 255.255.255.255

a ch lp A:Lp A s dng byte u tin ca 4 byte nh a ch mng. Nh

hnh trn, n c nhn ra bi bit u tin trong byte u tin ca a ch c tr gi 0. Ba

byte cn li c s dng nh a ch my trong mng. C 126 a ch lp A vi s

my tnh trong mng l 2563 2 = 16.777.214 my cho mi a ch lp A. a ch lp

A thng c cp cho nhng t chc c s lng my tnh ln. Nguyn nhn ch c

126 network trong khi dng 8 bit v bit u tin mang gi tr 0 dng nh ngha lp

A. Do vy cn li 7 bit nh t 0 127, tuy nhin ngi ta khng s dng mt a ch

cha ton cc con s 1 hoc 0 nn ch cn li 126 mng lp A c s dng. Gi trbyte u tin ca lp A s lun nm trong khong t 1 ti 126, mi mt byte trong 3

byte cn li s c gi tr trong khong 1 n 254.

a ch lp B:Mt a ch lp B c nhn ra bi 2 bit u tin ca byte th

nht mang gi tr 10. Lp B s dng 2 byte u tin ca 4 byte nh a ch mng v

2 byte cui nh a ch my trong mng. C 64*256 2 = 16.128 a ch mng lp B

vi 65.534 my cho mi a ch lp B.

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21/98

a ch lp C:Mt s t chc c quy m nh c th xin cp pht a ch lp C.

Mt a ch lp C c nhn ra vi 3 bit u mng gi tr 110. Mng lp C s dng 3

byte u nh a ch mng v 1 byte cui nh a ch my trong mng. C

2.097.150 a ch lp C, mi a ch lp C c 254 my.

T cc lp mng c bn trn, ta c th thc hin chia subnet cho mng to

thnh cc mng con (subnet) ty theo yu cu c th. Phn dng nh mng con

c ly nh subnet c ly t phn dnh nh a ch host.

Hnh 2. Quy cc a ch IP khi chia subnet

Khi , xc nh a ch mng ca trm, ta cn phi bit mt n mng tng

ng vi IP c chia. Vic tnh ton ra a ch mng ca IP c tnh nh sau:

Dng thp phn Dng nh phn

a ch IP ca trm 192.168.5.130 11000000.10101000.00000101.10000010

Mt n mng 255.255.255.192 11111111.11111111.11111111.11000000a ch mng 192.168.5.128 11000000.10101000.00000101.10000000

2.1.2. Giao thc IP phin bn 6 (IPv6)

Trong IPv4 trng a ch ngun v ch c di 32 bit nn khng th p ng

nhu cu nh a ch ca mng. Ngoi ra, do s pht trin ca Internet, bng nh

tuyn ca router khng ngng ln ln v kh nng nh tuyn bc l hn ch. Yu

cu nng cao cht lng dch v v bo mt c t ra. IPv6 l giao thc Internet mi

c k tha c im chnh ca IPv4 v c nhiu ci tin khc phc nhng hn ch:

Tng kch thc a ch t 32 bit ln 128 bit

Phm vi nh tuyn a im: giao thc ny h tr phng thc truyn mi

anycasting. Phng thc ny s dng gi cc gi tin n mt nhm xc

nh.

12


22/98

Phn tiu ca IPv6 c n gin ha hn IPv4. iu cho php x l

gi tin nhanh hn. Ngoi ra, IPv6 cn cung cp mt s tiu ph cho php

giao thc IPv6 c th s dng mt cch mm do hn hn so vi IPv4.

Cu trc gi tin IPv6 nh sau:

Hnh 3. Cu trc gi tin IP phin bn 6


Version: c gi tr bng 6 vi IPv6

Traffic Class: di 8 bit, xc nh u tin

Flow Label: di 20bit, xc nh cc gi d liu c u tin trn ng

truyn nu c xy ra tranh chp, thng c s dng cho cc dch v i

hi cht lng dch v cao hay thi gian thc.

Payload Length: di 16 bit, xc nh di phn d liu khng tnh phntiu .

Hop Limit: di 8 bit, ging nh trng Time to Live ca IPv4

Source Address v Destination Address ging nh IPv4 nhng c di

128bit.

Data: c di ti a l 65535 byte.

2.2. Giao thc TCP/IP

Giao thc TCP l giao thc iu khin truyn thng hng kt ni v c tin cy

cao. TCP cung cp l giao thc c xy dng phc tp hn UDP rt nhiu, ngoi cc

dch v nh UDP, TCP cn cung cp cc dch v khc cho ng dng. Dch v quan

trng nht l truyn d liu c tin cy cao, cc c ch iu khin lu lng v kim

sot tc nghn, nh s th t v s th t bn nhn, b nh thi,....C th TCP cung

cp cc dch v sau:

13


23/98

Thit lp lin kt: TCP l giao thc hng kt ni, trc khi gi d liu cn thit

lp trc ng truyn (chnh l 1 lin kt lgic gia hai thc th TCP), th tc

ny gi l th tc bt tay. Lin kt c thit lp phi m bo tnh chnh xc

v tin cy, mt lin kt khi khng cn tin cy th s b hu b v thit

lp li. Khi qu trnh truyn tin hon thnh th kt ni c gii phng .

Cung cp ng truyn hai chiu (song cng - full duplex).

m bo tin cy:Giao thc TCP cung cp cc tham s kim tra cng vi s

th t (Sequence number), xc nhn (ACKnowledge ) v kim tra li tng

(Checksum). Cc segment c nh s tun t, cch lm ny nhm mc ch

loi b cc segment b trng lp hay khng ng yu cu. Ti bn thu, khi nhn

c cc segment thc hin vic kim tra nh trng checksum. Nu segment

nhn c khng li hay lp, tn hiu ACK s c gi tr li bn pht khng

nh d liu nhn tt. Ngc li nu segment nhn c b li hay b trng lp

th segment ny s c loi b v bn thu s gi mt tin hiu yu cu bn pht

pht li segment b li , bng c ch ny s m bo tnh chnh xc v tin

cy cho d liu.

Cung cp cc dch v (chc nng) kim tra ng truyn, cho php iu khin

lung v iu khin tc nghn.

Trong ng dng VoIP, giao thc TCP c s dng lm giao thc truyn bo hiu

ch khng phc v vic truyn tn hiu thoi. L do l v phn mo u ca TCP ln

Hnh 4. Cu trc n v d liu TCP


Source Port: di 16 bit, xc nh s hiu cng ca trm ngun

Destination Port: di 16 bit, xc nh s hiu cng ca trm ch

14


24/98

Sequence Number: di 32 bit. S hiu ca byte u tin ca segment t

khi bit SYN c thit lp. Nu bit SYN c thit lp th Sequence Number

l s hiu tun t khi u (ISN) v byte d liu u tin l ISN+1

ACK Number: di 32 bit, xc nh s hiu ca segment tip theo m trmngun ang ch c xc nhn

Data Offset: di 4 bit, xc nh v tr bt u ca khi d liu lp trn

trong n v d liu TCP.

Control bit:

o URG: vng Urgent Pointer c hiu lc

o ACK: vng ACK c hiu lc

o PSH: chc nng Push

o RST: khi ng li lin kt

o SYN: ng b ha cc s hiu tun t

o FIN: khng cn s liu t trm cui

Window: cp pht th bi kim sot lung d liu theo c ch ca s. y

chnh l s lng cc byte d liu bt u t byte c ch ra trong vng

ACK m trm ngun sn sng nhn.

Checksum: m CRC-16

Urgent Pointer: con tr tre ti s hiu tun t ca byte i sau d liu khn,

cho bn nhn bit c di ca d liu khn. Vng ny c hiu lc khi bit

URG c thit lp.

Option: c di thay i, khai bo cc la chn ca TCP trong c di

ti a ca vng d liu trong mt n v d liu segment.

Padding: m bo phn tiu ca TCP lun l bi 32 bit.

TCP data: cha d liu lp trn c gi tr ti a l 536 byte. Gi tr ny c th

thay i nh khai bo trong Option

15


25/98

Thit lp v hy kt ni TCP

hiu c chc nng ca hm connect, accept, close v gip debug cc ng

dng TCP bng chng trnh netstat, chng ta cn hiu lm th no thit lp v hy

mt kt ni TCP, cng nh trng thi ca TCP.

Hnh 5. Bt tay 3 bc trong thit lp kt ni TCPGin trn y din ra khi mt kt ni TCP c thit lp:

1) Server sn sng accept mt kt ni ti. Cng vic ny c thc hin bng

vic gi hm socket, bind, listen. V c gi l passive open (m trng thi

b ng)

2) Client thit lp mt active open bng cch gi hm connect. Khi , pha client

s gi SYN bo cho server bit s th t ca d liu client s gi trong kt

ni. Thng thng, SYN khng cha d liu, ch cha tiu IP, TCP v c th

l cc ty chn TCP.

3) Server xc nhn SYN ca server. N s SYN vi s th t cho d liu ca n.

Server gi SYN v ACK cho SYN ca client trong cng mt segment.

4) Client xc nhn SYN ca server.

S gi ti thiu c truyn l ba nn c gi l there-way handshake (bt tay 3

bc).

Hy kt ni TCP

Trong khi ch cn ba segment thit lp mt kt ni TCP th cn bn segment

hy kt ni.

1) Mt ng dng gi hm close trc, chng ta gi u cui ny thc hin active-

close. u cui ny s gi FIN segment k thc vic gi d liu

16


26/98

2) u cui khc nhn FIN thc hin passive close. FIN nhn c gi xc nhn

bi TCP. FIN nhn c cng c truyn ln lp ng dng nh l end-of-

file(sau khi cc d liu khc c nhn ). Khi nhn c FIN ngha l ng

dng khng nhn thm d liu na.

3) ng dng sau khi nhn c end-of-file s close (ng) socket li. TCP ca n

s gi FIN.

4) TCP ca pha yu cu hy kt ni nhn bn tin FIN cui cng, xc nhn FIN.

Hnh 6. Hy kt ni TCP

Hot ng ca TCP trong thit lp v hy cuc gi c m t bng lc trng

thi. C 11 trng thi khc nhau cho mt kt ni v lut cho php chuyn t trng thi

ny sang trng thi khc da trn c s trng thi c. V d: nu mt ng dng thit

lp mt active open trng thi CLOSED, TCP gi SYN v trng thi mi l

SYN_SENT. Nu TCP sau nhn c SYN vi ACK, n s gi ACK v mt trng

thi mi ESTABLISH. Trng thi cui khi m vic truyn d liu din ra. Hai ng

mi tn ch t trng thi ESTABLISHED ti trng thi ngt kt ni. Nu ng dng gi

close trc khi nhn FIN, th trng thi l FIN_WAIT1. Nhng nu ng dng nhn FIN

trong khi ang ESTABLISHED, trng thi s l CLOSE_WAIT.

Mt l do cn thit phi hiu c lc trng thi l hiu c 11 trng thiTCP vi tn ca n. Trng thi ny c hin bi netstat, l mt cng c hu hiu trong

vic debug ng client/server.

17


27/98

Hnh 7. S thay i trng thi thit lp TCP

Truyn cc gi

Hnh 8. Truyn d liu vi TCP

Hnh trn biu din vic truyn gi thc din ra cho mt TCP hon chnh: thit lp kt

ni, truyn d liu, hy kt ni. Client trong v d ny thng bo MSS=536(xc nh

kch thc buffer ca n) v server c kch thc buffer l 1460. Vi mi kt ni c

thit lp, client to mt yu cu v gi n ti server. Yu cu ny c gn trn trong

ch mt TCP segment. Server x l yu cu v gi tr li (kch thc nh hn 536). Hai

gi d liu c biu din bng ng mi tn m. Ch rng ACK ca yu cu ca

18


28/98

client c gi km vi tr li ca server. Cch thc ny c gi l piggybacking v

thng c thc hin khi thi gian server x l v tr li nh hn 200ms. Nu lu hn,

th ACK s c gi trc khi gi tr li. Mt iu quan trng trong m hnh ny l:

Nu ch gi mt segment yu cu i v nhn mt segment tr li th cn tm segment

khc. Nu UDP c s dng, ch c hai segment c truyn: yu cu, tr li. Nhng

chuyn t TCP sang UDP th chng ta khng cn tnh tin cy m TCP cung cp cho ng

dng na, vic m bo truyn tin s do chng trnh UDP thc hin. Mt yu t quan

trng na ca TCP l iu khin tc nghn m UDP khng c. Cc ng dng

thng s dng UDP vi cc d liu nh cn tc truyn cao( tr nh).

2.3. Giao thc UDP

UDP l giao thc lp Giao vn n gin nht, c m t trong RFC 768. ng

dng gi bn tin ti socket UDP, sau c ng gi thnh mt UDP paragram v

c truyn xung lp IP gi ti ch. Gi tin UDP c truyn m khng m bo

rng n c th ti ch, gi ng th t v n ch mt ln. Vn ca ngi lp trnh

mng vi UDP l m bo tnh tin cy. Nu datagram ti ch nhng trng kim tra

tng (checksum) c li hay gi tin b drop trn mng th n s c truyn li. Nu

mun xc nh c rng gi tin ti ch th cn rt nhiu tnh nng trong ng dng:

ACK t u cui khc, iu khin vic truyn li,.. Mi mt UDP datagram c chiu di

v c truyn ln cng vi d liu cho lp ng dng. iu ny khc vi TCP l giaothc lung byte (byte-stream protocol). Chng ta cng c th ni: UDP cung cp dch

v khng hng kt ni. V d, client UDP c th to mt socket v gi datagram ti

server ny v sau gi mt datagram khc cng ti server khc. Cng ging nh

server UDP c th nhn nhiu datagram trn mt socket UDP t cc client khc nhau.

Hnh 9. Cu trc n v d liu UDP

2.4. Giao thc SCTP

Nm 1998, nhm lm vic ca IETF c tp hp thit k mt c ch giao vn

tin cy truyn bo hiu iu khin cuc gi trn mng Internet. Kt qu l Sigtran

c ra i cho php truyn cc bn tin SS7 trn mng IP. Vn chnh m Sigtran cn

gii quyt chnh m TCP cha p ng c l:

19


29/98

Head of line blocking: Vn xy ra khi gi cc bn tin c lp trn kt ni

TCP c thit lp th cc bn tin c nhn sau b lm tr v lu trong b

m ca tng giao vn ca pha nhn ti khi cc bn tin trc b mt c

truyn li v ti ch. M , cc bn tin sau thng thit lp cc cuc gi c

lp. Nh vy, tr cc bn tin sau l nguyn nhn sinh ra timeout trong iu

khin cuc gi gy ra li khng mong mun trong qu trnh iu khin cuc gi.

Multihoming: Khi mt trm vi nhiu ng truy cp Internet vi mc ch d

phng, khng mun i nh tuyn trong khi mng b tc nghn truyn tin

vi trm ngang hng vi n. Vi bo hiu cuc gi, tr ny l khng th chp

nhn c khi c nhiu ng c. Do TCP ch gn mt ng kt ni gia

hai u cui nn s khng th gii quyt c vn ny.

Cn nhc nhng vn ny, Sigtran c thit k nh l mt giao thc tng giao

vn mi cho php mang bo hiu cuc gi trn mng IP. ng thi, IETF m rng

phm vi ca nhm thit k t mt nhm nh n mt nhm chuyn trch thit k mt

giao thc giao vn c th phc v nhiu mc ch v hot ng tt vi nhiu ng dng.

V khi SCTP ra i vi cc c tnh sau:

Multistreaming: SCTP h tr a lung (stream) bn tin c lp vi nhau

trn mt lin kt SCTP. Mi bn tin c gi trn c gn cho mt

lung ring. Tt c d liu trong mt lung c nhn theo th t vi d liukhc trong lung. D liu trong cc lung khc nhau th khng c c tnh

ny. Do vy, SCTP cung cp c ch cho php vic nhn d liu c th t mt

cch cc b. Nh vy l n gii quyt c vn head-of-line blocking.

ng dng ca a lung (multistreaming) c th h tr cc ng dng lin quan

ti hp knh d liu nh thoi, vn bn, video trn mt ng truyn gia hai

u cui thay v m nhiu kt ni TCP cho mi lung.

Multihoming: gia hai u cui trong qu trnh thit lp lin kt c th xcnh lin kt a im. Vic c nhiu giao din cho php d liu c t ng

gi theo nhiu a ch khc nhau khi c li xy ra. iu ny l hon ton

khng th thc hin c TCP v n gn kt mt u cui vi mt giao

din nht nh. Nu nh c li xy ra, tt c cc kt ni c gn vi giao

din vn c thi gian timeout v c hy b. V sau , ng dng l phi

thit lp li cc kt ni khc.

20


30/98

Message Orientation: Trong TCP, d liu c gi gia hai u cui l

lung cc byte. Nu cn thit, ng dng phi lm chc nng nh dng khung

(frame) cho bn tin. SCTP, bn tin c gi nguyn nh dng. Tc l nu

tng ng dng pha pht gi bn tin 100 byte i th pha thu cng nhn c

ng 100 byte. UDP cng cung cp dch v hng bn tin nhng khng c

tin cy cao nh SCTP.

Un-ordered Service: i vi TCP, tt c cc bn tin c nhn tin cy ng

theo th t c gi. Cn vi SCTP, giao thc ny cung cp c ch nhn tin

khng c th t (gia cc lung song song vi nhau). UDP cng cp dch

v ny nhng khng c tin cy nh SCTP.

Extensibility: Gi TCP b gii hn bi 40 byte trng Option. Tri li, giSCTP c m rng thng qua vic s dng trng TLV (Tag-Length-Val-

ue).

Heartbeat/Keep-alive : SCTP c mt ty chn cho php xc nh thi gian

sng ca bn tin. N cho php ng dng truyn tin xc nh khong thi gian

m bn tin cn c ch. Nu thi gian ny ht hn trc khi c truyn tin

cy ti pha nhn, th thc th SCTP gi c th dng vic c gi bn tin hay

hy b bn tin. Kiu tin cy ny gi l tin cy cc b. iu ny rt hu chnh trong truyn tin di ng hay cc game online. Vic ny s gip tit

kim bng thng ng truyn chng tc nghn.

Syn cookie: SCTP s dng bt tay bn bc bi vic s dng cookie c du

hiu nh trc. Pha nhn ca bn tin thit lpk lin kt SCTP mi duy tr

trng thi no-state (khng c cp ti nguyn) cho ti khi pha khi to

chng thc c l IP ca i tng yu cu kt ni. C ch ny cho php

chng li tn cng t chi dch v bng cch SYN flooding.

Stronger checksum: SCTP cung cp 32 bit kim tra tng vi kh nng pht

hin li tt hn 16 bit TCP hay UDP.

Advanced TCP services: cc dch v mi ca TCP nh SACK (RFC 2018),

Appropriate Byte Counting Byte Counting (RFC 3465) v Explicit Conges-

tion Notificaion (RFC3168) c tch hp sn trong SCTP.

Services/Features SCTP TCP UDP

21


31/98

Hng lin kt C C Khng

Song cng C C C

Tin cy C C Khng

Tin cy cc b optional Khng Khng

Nhn d liu c th t C C Khng

Nhn d liu khng c th t C no C

iu khin lung C C Khng

iu khin tc nghn C C Khng

C ch ECN C C Khng

Selective ACKs C Ty chn Khng

Hng bn tin C no C

Tm li ng MTU C C Khng

Phn mnh PDU tng ng dng C C Khng

Bc cc PDU tng ng dng C C Khnga lung C Khng Khng

Multihoming C Khng Khng

Chng tn cng trn SYN C Khng Khng

Kt ni half-closed Khng C Khng

Kim tra d liu ti ch C C Khng

Gi tiu cho checksumKhng

(s dng vtags)C C

Trng thi i vtags 4-tuple Khng

SCTP l giao thc hng kt ni ging nh TCP v cng c vic bt tay thit

lp v hy kt ni. Tuy vy, vic bt tay ca SCTP khc so vi TCP.

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32/98

Hnh 10. Thit lp kt ni SCTP

1) Server sn sng chp nhn mt association n. Vic ny c thc hin thng

qua li gi hm socket, bind, listen v c gi l passive open.

2) Client thit lp mt active open bng cch gi hm connect hay gi mt bn tin

yu cu m mt association. Khi , SCTP client s gi bn tin INIT thng bo

vi server danh sch a ch IP ca n, s hiu th t, tag thit lp xc nh tt

c cc gi l trong mt association, s lung m client yu cu, s lung vo m

n h tr.

3) Server xc nhn bn tin INIT ca client vi bn tin INIT-ACK cha danh sch

a ch IP, s th t thit lp, tag thit lp, s lung m n h tr v mt cookie

trng thi. Cookie trng thi cha tt c cc trng thi m server xc nhn associ-

ation l hp l v c gn s cho vic xc thc ny.

4) Client gi li cookie trng thi ca server vi bn tin COOKIE-ECHO. Bn tin

ny cha d liu ngi dng gn km.

5) Server xc nhn rng cookie l hp l v association c thit lp vi bn tin

COOKIE-ACK. Bn tin ny cng cha d liu ngi dng.

Hy association

Khng ging nh TCP, SCTP khng cho php half-closed association. Khi mt

u cui ngng th u cui kia cng phi dng gi d liu mi. Pha nhn yu cu hy

kt ni gi nt d liu c xp hng trc khi hy kt ni. SCTP khng c trng

thi TIME_WAIT nh TCP m s dng tag lm vic ny. Tt c cc chunk c tag

ha vi tag gi trong chunk INIT, mt chunk t mt kt ni c s c nhn vi tag sai.

Nh vy, SCTP s dng vic xc nhn gi tr tag trong TIME_WAIT.

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33/98

Hnh 11. Hy kt ni SCTP

Cc trng thi trong kt ni SCTP c biu din bng lc sau:

Hnh 12. S trng thi thit lp SCTP

2.5. Giao thc RTP

RTP l mt giao thc da trn giao thc IP to ra cc h tr truyn ti cc d

liu yu cu thi gian thc vi cc yu cu: Lin tc: Cc gi tin phi c sp xp theo ng th t khi chng n bn nhn,

cc gi n c th khng theo th t v nu gi tin b mt th bn nhn phi d

tm hay b li s mt cc gi tin ny.

S ng b trong cc phng thc truyn thng: Cc khong lng trong ting ni

c trit v nn li gim thiu bng thng cn thit, tuy nhin khi n bn

nhn, thi gian gia cc khong lng ny phi c khi phc mt cch chnh

xc.

24


34/98

S ng b gia cc phng thc truyn thng: C th tn hiu thoi s dng

mt phng thc truyn thng trong khi tn hiu video li s dng mt phng

thc truyn thng khc, cc tn hiu ting v hnh phi c ng b mt cch

chnh xc, gi l s ng b ting - hnh.

S nhn din phng thc truyn ti: Trong Internet, thng thng cn thay i

s m ho cho phng thc truyn ti (payload) trn hnh trnh truyn hiu

chnh thay i rng bng thng sn sng hoc kh nng cho ngi dng

mi kt ni vo nhm. Mt vi c ch cn c s dng nhn din s m ho

cho mi gi n.

Cc dch v cung cp bi RTP bao gm:

a pht p thn thin: (multicast friendly): RTP v RTCP l k thut cho apht p, cung cp kh nng m rng cuc hi thoi nhiu bn. Trn thc t,

chng c thit k c th hot ng trong c cc nhm a pht p nh, ph

hp cho cc cuc in m ba bn. i vi cc nhm ln, chng s dng a pht

p qung b (broadcasting).

c lp thit b: RTP cung cp cc dch v cn thit chung cho phng thc

truyn thng thi gian thc ni chung nh thoi, video hay bt k mt b m ho,

gii m c th no c s nh ngha cc phng thc m ho v gii m ring

bng cc thng tin tiu v nh ngha.

Cc b trn v chuyn i: Cc b trn l thit b nm gi phng thc truyn

thng t mt vi ngi s dng ring l, trn hoc ni chng vo cc dng

phng thc truyn thng chung, chuyn i chng vo khun dng khc v gi

n ra. Cc b chuyn i c ch cho s thu nh bng thng yu cu ca dng s

liu t dng s liu chung trc khi gi vo tng kt ni bng thng hp hn m

khng yu cu ngun pht RTP thu nh tc bit ca n. iu ny cho php cc

bn nhn kt ni theo mt lin kt nhanh vn nhn c truyn thng chtlng cao. RTP h tr c cc b trn v c cc b chuyn i.

M ho thnh mt m:Cc dng phng thc truyn thng RTP c th m ho

thnh mt m dng cc kho, vic m ho m bo cho vic thng tin trn mng

c an ton hn.

Cc gi tin truyn trn mng Internet c tr v jitter khng d on c. Nhng

cc ng dng a phng tin yu cu mt thi gian thch hp khi truyn cc d liu v

pht li. RTP cung cp cc c ch bo m thi gian, s th t v cc c ch khc lin

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quan n thi gian. Bng cc c ch ny RTP cung cp s truyn ti d liu thi gian

thc gia cc u cui qua mng.

Bn thn RTP khng cung cp mt c ch no cho vic bo m phn phi kp

thi cc d liu ti cc trm m n da trn cc dch v ca tng thp hn thc hiniu ny. RTP cng khng m bo vic truyn cc gi theo ng th t. Tuy nhin, s

th t trong RTP header cho php bn thu xy dng li ng th t cc gi ca bn

pht.

Hot ng ca RTP c h tr bi mt giao thc khc l RTCP nhn cc

thng tin phn hi v cht lng truyn dn v cc thng tin v thnh phn tham d cc

phin hin thi. Khng ging nh cc giao thc khc l s dng cc trng trong header

thc hin cc chc nng iu khin, RTP s dng mt c ch iu khin c lp

trong nh dng ca gi tin RTCP thc hin cc chc nng ny.

Khun dng bn tin RTP:

RTP header bao gm mt phn c nh c mi gi RTP v mt phn m rng

phc v cho cc mc ch nht nh.

Phn c nh:

Hnh 13. Phn c nh ca n v d liu RTP

Version (2 bits): Ch ra version ca RTP, hin nay l version 2.

Padding (1 bit): Nu bit ny c t, s c thm mt vi octets thm vo cui

gi d liu. Cc octets ny khng phi l thng tin, chng c thm vo

nhm mc ch:

o Phc v cho mt vi thut ton m ho thng tin cn kch thc ca gi

c nh.

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o Dng cch ly cc gi RTP trong trng hp c nhiu gi thng tin

c mang trong cng mt n v d liu ca giao thc tng di.

Extension (1 bit): nu bit ny c t, th theo sau phn header c nh s l mt

header m rng. Contributing Sources Count (4 bits): s lng cc thnh phn nhn dng ngun

CSRC nm trong phn header gi tin. S ny ln hn 1 nu cc gi tin RTP n

t nhiu ngun.

Marker (1 bit): mang ngha khc nhau, tu theo tng trng hp c th, c

ch ra trong profile i km.

Payload Type (7 bits): ch ra loi ti trng mang trong gi. Cc m s dng trong

trng ny ng vi cc loi ti trng c quy nh trong mt profile i km.

Sequence Number (16 bits): mang s th t ca gi RTP. S ny c tng thm

1 sau mi gi RTP c gi i. C th c s dng pht hin c s mt

gi v khi phc mt gi ti u thu. Gi tr khi u ca trng ny l ngu

nhin.

Time stamp (tem thi gian, 32 bits): Phn nh thi im ly mu ca octet u

tin trong gi RTP. Thi im ny c ly t mt ng h tng u n v

tuyn tnh theo thi gian cho php vic ng b v tnh ton jitter. Tn s

ng h ny khng c nh, tu thuc vo loi ti trng. Gi tr khi u c

chn ngu nhin. Mt vi gi RTP c th mang cng mt gi tr Tem thi gian

nu nh chng c pht i cng lc v mt logic. Nu gi d liu c pht ra

u n th tem thi gian c tng mt cch u n. Trong trng hp khc

th gi tr tem thi gian tng khng u.

Tem thi gian l thnh phn thng tin quan trng nht trong cc ng

dng thi gian thc. Ngi gi thit lp cc tem thi gian ngay thi im octetu tin ca gi c ly mu. Tem thi gian tng dn theo thi gian i vi

mi gi. Sau khi nhn c gi d liu, bn thu s dng cc tem thi gian ny

nhm khi phc thi gian gc chy cc d liu ny vi tc thch hp.

Ngoi ra, n cn c s dng ng b cc dng d liu khc nhau (chng

hn nh gia hnh v ting). Tuy nhin RTP khng thc hin ng b m cc

ng dng pha trn s thc hin s ng b ny.

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Synchronization Source Identifier (SSRC, 32 bits): ch ra ngun ng b ca

gi RTP, s ny c chn ngu nhin. Trong 1 phin RTP c th c nhiu hn

mt ngun ng b. Mi mt ngun pht ra mt lung RTP. Bn thu nhm cc

gi ca cng mt ngun ng b li vi nhau pht li tn hiu thi gian thc.

Contributing Source Identifier (CSRC, t 0-15 mc, mi mc 32 bits): ch ra

nhng ngun ng gp thng tin vo phn ti trng ca gi. Gip bn thu nhn

bit c gi tin ny mang thng tin ca nhng ngun no.

Hnh 14. V d v Cu trc gi RTP

Phn m rng: c di thay i. S tn ti ph thuc vo bit Extension ca

phn c nh.

Hnh 15. Phn m rng cu trc d liu RTP

16 bit u tin c s dng vi mc ch ring cho tng ng dng c nhngha bi profile. Thng c dng phn bit cc loi header m rng.

Length (16 bits): gi tr chiu di phn header m rng tnh theo n v 32 bit,

khng bao gm 32 bit u tin ca phn header m rng.

C ch m rng ca RTP cho php cc ng dng ring l ca giao thc RTP thc

hin c vi nhng chc nng mi i hi nhng thng tin thm vo phn header ca

gi. C ch ny c thit k mt vi ng dng c th b qua phn header m rng

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ny (m vn khng nh hng ti hot ng) trong khi mt s ng dng khc li c th

s dng c phn .

B phn nhn dng ti xc nh kiu nh dng ca ti tin cng nh cch m ho

v nn. T cc b phn nh dng ny, cc ng dng pha thu bit cch phn tch vchy cc dng d liu ti tin. Ti mt thi im bt k trong qu trnh truyn tin, cc b

pht RTP ch c th gi mt dng ca ti tin cho d dng ca ti tin c th thay i

trong thi gian truyn (thay i thch ng vi s tc nghn ca mng).

Mt chc nng khc ca RTP l xc nh ngun: cho php pha thu bit c d

liu n t u. V d trong thoi hi ngh, t thng tin nhn dng ngun mt ngi s

dng c th bit c ai ang ni.

RTP c c tnh cho khng hon thin. N ch cung cp cc dch v phthng nht cho hu ht cc ng dng truyn thng hi ngh a phng tin. Mi mt

ng dng c th u c th them vo RTP cc dch v mi sao cho ph hp vi cc yu

cu ca n. Cc kh nng m rng ny c m t trong mt profile i km. Profile ny

cn ch ra cc m tng ng s dng trong trng PT (Payload Type) ca phn tiu

RTP ng vi cc loi ti trng mang trong gi.

RTP nm pha trn UDP, s dng cc chc nng ghp knh v kim tra ca

UDP. S d UDP c s dng lm th tc truyn ti cho RTP l bi v 2 l do:

Th nht, RTP c thit k ch yu cho vic truyn tin a i tng, cc kt

ni c nh hng, c bo nhn khng p ng tt iu ny.

Th hai, i vi d liu thi gian thc, tin cy khng quan trng bng truyn

ng theo thi gian. Hn na, s tin cy trong TCP l do c ch bo pht li,

khng thch hp cho RTP. V d khi mng b tc nghn mt s gi c th mt,

cht lng dch v d thp nhng vn c th chp nhn c. Nu thc hin vic

pht li th s gy nn tr rt ln cho cht lng thp v gy ra s tc nghn

ca mng.

Thc t RTP c thc hin ch yu trong cc ng dng m ti cc mc ng dng

ny c cc c ch khi phc li gi b mt, iu khin tc nghn.

Mng Internet hin nay vn cha th p ng c y cc yu cu ca cc dch v

thi gian thc. Cc dch v RTP yu cu bng thng cao c th lm gim cht lng cc

dch v khc trong mng n mc nghim trng. Trong qu trnh trin khai phi ch

n gii hn bng thng s dng ca cc ng dng trong mng.

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2.6. Giao thc RTCP

RTCP (Real-time Transport Control Protocol) l giao thc h tr cho RTP cung

cp cc thng tin phn hi v cht lng truyn d liu. Cc dch v m RTCP cung cp

l: Gim st cht lng v iu khin tc nghn: y l chc nng c bn ca

RTCP. N cung cp thng tin phn hi ti mt ng dng v cht lng phn

phi d liu. Thng tin iu khin ny rt hu ch cho cc b pht, b thu v

gim st. B pht c th iu chnh cch thc truyn d liu da trn cc thng

bo phn hi ca b thu. B thu c th xc nh c tc nghn l cc b, tng

phn hay ton b. Ngi qun l mng c th nh gi c hiu sut mng.

Xc nh ngun: Trong cc gi RTP, cc ngun c xc nh bi cc s ngunhin c di 32 bt, cc s ny khng thun tin i vi ngi s dng. RTCP

cung cp thng tin nhn dng ngun c th hn dng vn bn. N c th bao

gm tn ngi s dng, s in thoi, a ch e-mail v cc thng tin khc.

ng b mi trng: Cc thng bo ca b pht RTCP cha thng tin xc

nh thi gian v nhn thi gian RTP tng ng. Chng c th c s dng

ng b gia m thanh vi hnh nh.

iu chnh thng tin iu khin: Cc gi RTCP c gi theo chu k gia nhng

ngi tham d. Khi s lng ngi tham d tng ln, cn phi cn bng gia

vic nhn thng tin iu khin mi nht v hn ch lu lng iu khin. h

tr mt nhm ngi s dng ln, RTCP phi cm lu lng iu khin rt ln

n t cc ti nguyn khc ca mng. RTP ch cho php ti a 5% lu lng cho

iu khin ton b lu lng ca phin lm vic. iu ny c thc hin bng

cch iu chnh tc pht ca RTCP theo s lng ngi tham d. Mi ngi

tham gia mt phin truyn RTP phi gi nh k cc gi RTCP n tt c nhngngi khc cng tham gia phin truyn. Nh vy m c th theo di c s

ngi tham gia.

Gi RTCP gp phn lm tng nghn mng. Bng thng yu cu bi RTCP l 5%

tng s bng thng phn b cho phin. Khong thi gian trung bnh gia cc gi RTCP

c t ti thiu l 5s.

Cc loi thng bo iu khin chnh c RTCP cung cp l:

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SR (Sender Report): cha cc thng tin thng k lin quan ti kt qu

truyn nh t l tn hao, s gi d liu b mt, khong tr. Cc thng bo

ny pht ra t pha pht trong 1 phin truyn thng.

RR (Receiver Report): Cha cc thng tin thng k lin quan ti kt qunhn, c pht t pha thu trong 1 phin truyn thng.

SDES (Source Description): thng s m t ngun (tn, v tr)

APP (Application): cho php truyn cc d liu ng dng

BYE: ch th s kt thc tham gia vo phin truyn.

Gi tr ca trng PT (Packet Type) ng vi mi loi gi c lit k trong bng

sau.

Mi gi thng tin RTCP bt u bng 1 phn tiu c nh ging nh gi RTP

thng tin. Theo sau l cc cu trc c chiu di thay i theo loi gi nhng lun

bng s nguyn ln 32 bit. Cc gi thng tin RTCP c th gp li vi nhau thnh cchp gi (compound packet) truyn xung lp di m khng phi chn thm cc bit

cch ly. S lng gi trong hp gi tu thuc vo chiu di n v d liu lp di.

Mi gi RTCP u phi c truyn, ngay c khi ch c mt gi duy nht. Khun

dng hp gi c xut nh sau:

Encription Prefix (32 bit): c dnh khi hp gi cn m ho. Gi tr trong

trng ny cn trnh trng vi 32 bit u tin trong gi RTP

Gi u tin trong hp gi lun l SR hoc RR. Nu khng thu nhn thng tin,

hoc hp gi ch c mt gi BYE th mt gi RR rng c dn u trong hp

gi.

Nu s lng cc ngun ln hn 31 (khng va trong mt gi SR hoc RR) th

cc gi RR thm vo s theo sau gi thng k u tin. Vic bao gm gi thng

k (RR hoc SR) trong mi hp gi nhm thng tin thng xuyn v cht lng

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thu ca nhng ngi tham gia. Vic gi hp gi i c tin hnh mt cch u

n v thng xuyn theo kh nng cho php ca bng thng.

Trong hp gi c gi SDES nhm thng bo v ngun pht.

Cc gi APP nm v tr bt k trong hp gi.

Gi BYE nm v tr cui cng.

Hnh 16. V d Cu trc gi RTCP

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Chng 3. Giao thc bo hiu VoIP

3.1. Giao thc bo hiu H.323

Khi cp n thoi IP, tiu chun quc t thng c cp n l 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. N c ITU_T

ban hnh ln u tin vo nm 1996 v gn y nht l nm 1998. H.323 l chun ring

cho cc thnh phn mng, cc giao thc v cc th tc cung cp cc dch v thng tin

multimedia nh : audio thi gian thc, video v thng tin d liu qua cc mng chuyn

mch gi, bao gm cc mng da trn giao thc IP.

3.1.1. Cc thnh phn trong mng

3.1.1.1. Thit b u cui H.323 (H.323 Endpoint)

Cc thit b nm ngoi phm vi khuyn ngh H.323

Thit b vo ra Video.

Thit b vo ra Audio.

Thit b vo ra s liu.

Giao din mng LAN. Giao din ngi s dng.

Cc phn t nm trong phm vi khuyn ngh H.323

B m ho v gii m Video.

B m ho v gii m Audio.

B m nhn d liu.

Khi iu khin h thng.

Khi iu khin theo chun H.245

S dng knh iu khin H.245 mang cc bn tin iu khin im - im iu

khin hot ng ca thc th H.323 bao gm : kh nng trao i, m v ng cc

knh logic, cc yu cu ch hot ng thch hp, iu khin lung bn tin, pht cc

lnh v cc ch th.

iu khin bo hiu cuc gi

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S dng bo hiu cuc gi theo khuyn ngh H.225 thit lp mt kt ni gia

hai u cui H.323. Knh bo hiu cuc gi c lp vi knh RAS v knh iu khin

H.245. Trong h thng khng c Gatekeeper th knh bo hiu cuc gi c thit lp

gia hai u cui H.323 tham gia cuc gi. Cn trong h thng c Gatekeeper th knh

bo hiu cuc gi c thit lp gia cc u cui v Gatekeeper hoc gia hai u cui

vi nhau, vic la chn phng n thit lp knh bo hiu cuc gi nh th no l do

Gatekeeper quyt nh.

Chc nng bo hiu RAS

S dng cc bn tin H.225 thc hin : ng k, cho php dch v, thay i bng

thng, trng thi, cc th tc tch ri gia cc u cui v Gatekeeper.

Hnh 17. S khi thit b u cui H.323

3.1.1.2. Gatekeeper

Mt min H.323 trn c s mng IP l tp hp tt c cc u cui c gn vi

mt b danh. Mi min c qun tr bi mt Gatekeeper duy nht, l trung tm uno, ng vai tr gim st mi hot ng trong min . y l thnh phn tu chn

trong h thng VoIP theo chun H.323. Tuy nhin nu c mt Gatekeeper trong mng

th cc u cui H.323 v cc Gateway phi hot ng theo cc dch v ca Gatekeeper

. Mi thng tin trao i ca Gatekeeper u c nh ngha trong RAS. Mi ngi

dng ti u cui c Gatekeeper gn cho mt mc u tin duy nht. Mc u tin ny

rt cn thit cho c ch bo hiu cuc gi m cng mt lc mhiu ngi s dng. H.323

nh ngha c nhng tnh cht bt buc ti thiu phi c cho Gatekeeper v nhng c

tnh tu chn:

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Cc chc nng bt buc ti thiu ca mt Gatekeeper gm : Phin dch a

ch, iu khin cho php truy nhp, iu khin di thng, qun l min dch

v.

Cc chc nng tu chn ca Gatekeeper gm c : Bo hiu iu khin cucgi, cp php cho cuc gi, qun l cuc gi.

Gatekeeper hot ng hai ch :

Ch trc tip: Gatekeeper ch c nhim v cung cp a ch ch m khng

tham gia vo cc vic nh tuyn cc bn tin bo hiu.

Hnh 18. Phng thc nh tuyn trc tip

Ch nh tuyn qua Gatekeeper : Gatekeeper l thnh phn trung gian,

nh tuyn mi bn tin bo hiu trong mng H.323.

Hnh 19. Phng thc nh tuyn qua Gatekeeper

Cc chc nng c th ca Gatekeeper c m t nh sau:

Chc nng dch a ch: Gatekeeper s thc hin chuyn i a ch URI (dng tn

gi hay a ch hp th ) ca mt u cui hay Gateway sang a ch truyn dn (a ch

IP). Vic chuyn i c thc hin bng cch s dng bn i chiu a ch c cp

nht thng xuyn bi cc bn tin ng k. Cng c th l vic chuyn i t quy cch

nh s E.164 sang dng URI.

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iu khin truy cp: Gatekeeper cho php mt truy cp mng LAN bng cch s

dng cc bn tin H.225 l ARQ/ACF/ARJ. Vic iu khin ny da trn s cho php

cuc gi, bng thng, hoc mt vi thng s khc do nh sn xut quy nh. N c th l

chc nng rng c ngha l chp nhn mi yu cu truy nhp ca u cui.

iu khin rng bng thng: Gatekeeper h tr cc bn tin BRQ/BRJ/BCF cho

vic qun l bng thng. N c th l chc nng rng ngha l chp nhn mi yu cu

thay i bng thng. Gatekeeper c th hn ch mt s cc u cui H.323 cng mt lc

s dng mng. Thng qua vic s dng knh bo hiu H.225, Gatekeeper c th loi b

cc cc cuc gi t mt u cui do s hn ch bng thng. iu c th xy ra nu

Gatekeeper thy rng khng bng thng sn c trn mng tr gip cho cuc gi.

Vic t chi cng c th xy ra khi mt u ang tham gia mt cuc gi yu cu thm

bng thng. N c th l mt chc nng rng ngha l mi yu cu truy nhp u cng .

Qun l min dch v: y min dch v (domain) ngha l tp hp tt c cc

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

Gatekeeper thc hin lin lc gia cc phn t trong min dch v hay t dch v ny

sang dch v khc.

iu khin bo hiu cuc gi: Gatekeeper c th la chn hai phng thc iu

khin bo hiu cuc gi l: hon thnh bo hiu cuc gi vi cc u cui v x l bohiu cuc gi chnh bn thn n, hoc Gatekeeper c th ra lnh cho cc u cui kt

ni mt knh bo hiu cuc gi hng ti nhau. Theo phng thc ny th Gatekeeper

khng phi gim st bo hiu trn knh H.225.

Qun l cuc gi: Mt v d c th v chc nng ny l Gatekeeper c th lp mt

danh sch tt c cc cuc gi H.323 hng i ang thc hin ch th rng mt u

cui b gi ang bn v cung cp thng tin cho chc nng qun l bng thng.

3.1.1.3. Khi iu khin a im

Khi iu khin a im (MCU) c s dng khi mt cuc gi hay hi ngh cn

gi nhiu kt ni hot ng. Do c mt s hu hn cc kt ni ng thi, nn cc MCU

gim st s tho thun gia cc u cui v s kim tra mi u cui v tnh nng m

chng c th cung cp cho hi ngh hoc cuc gi. Cc MCU gm hai phn: B iu

khin a im (MC) v B x l a im (MP).

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B iu khin a im c trch nhim trong vic tho thun v quyt nh kh

nng ca cc u cui. Trong khi b x l a im c s dng x l

multimedia, cc lung trong sut qu trnh ca mt hi ngh hoc mt cuc gi a im.

3.1.2. Giao thc H.323

Hnh 20. Giao thc bo hiu H.323

Giao thc H.323c chia lm 3 phn chnh:

Bo hiu H.225 RAS (Registration, Admissions, and Status): bo hiu gia

thit b u cui vi H.323 gatekeeper trc khi thit lp cuc gi.

Bo hiu H.225 Q.931 s dng kt ni, duy tr v hy kt ni gia hai u

cui.

Bo hiu H.245 s dng thit lp phin truyn media s dng giao thc

RTP.

3.1.2.1. Bo hiu RAS

Bo hiu RAS cung cp iu khin tin cuc gi trong mng H.323 c tn ti

gatekeeper v mt vng dch v(do gatekeeper qun l). Knh RAS c thit lp

gia cc thit b u cui v gatekeeper qua mng IP. Knh RAS c m trc khi cc

knh khc c thit lp v c lp vi cc knh iu khin cuc gi v media khc.Bo hiu ny c truyn trn UDP cho php ng k, chp nhn, thay i bng thng,

trng thi v hy.

Bo hiu RAS chia lm cc loi sau:

Tm kim Gatekeeper: vic ny c th c thc hin th cng hoc t ng cho

php xc nh gatekeeper m thit b u cui ng k ( c th s dng dch v

sau ny); bao gm:

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Gatekeeper Request (GRQ): bn tin multicast gi bi thit b u cui

tm gatekeeper.

Gatekeeper Confirm (GCF): bn tin thng bo a ch knh RAS ca

gatekeeper cho thit b u cui. Gatekeeper Reject (GRJ): bo cho thit b u cui bit rng

gatekeeper t chi.

ng k: cho php gateway, thit b u cui v MCU tham gia vo mt vng

dch v do gatekeeper qun l v thng bo cho gatekeeper v a ch v b danh

ca n; bao gm:

Registration Request (RRQ): c gi t thit b u cui ti a ch knh

RAS ca gatekeeper.

Registration Confirm (RCF): c gi bi gatekeeper xc nhn cho

php vic ng k bi bn tin RRQ.

Registration Reject (RRJ): khng chp nhn ng k ca thit b

Unregister Request (URQ): c gi bi thit b u cui hy ng k

vi gatekeeper trc v c tr li bng Unregister Confirm (UCF)

v Unregister Reject (URJ) (tng t nh trn). Xc nh v tr thit b u cui: Thit b u cui v gatekeeper s dng bn tin

ny ly thm thng tin khi ch c thng tin v danh c ch ra. Bn tin ny

c gi thng qua a ch knh RAS ca gatekeeper hoc multicast. Loi bn

tin ny bao gm:

Location Request (LRQ): c gi yu cu thng tin v thit b u

cui, gatekeeper, hay a ch E.164.

Location Confirm (LCF): c gi bi gatekeeper chc cc knh bo hiucuc gi hay a ch knh RAS ca n hay thit b u cui yu cu.

Location Reject (LRJ): c gi bi gatekeeper thng bo LRQ trc

khng hp l.

Admissions: bn tin gia cc thit b u cui v gatekeeper cung cp c s cho

vic thit lp cuc gi v iu khin bng thng sau ny. Bn tin ny bao gm c

cc yu cu v bng thng(c th c thay i bi gatekeeper). Loi bn tin ny

gm:

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Admission Request (ARQ): Gi bi thit b u cui thit lp cuc gi

Admission Confirm (ACF): Cho php thit lp cuc gi. Bn tin ny c

chc a ch IP ca thit b c gi hay gatekeeper v cho php gateway

ngun thit lp cuc gi. Admission Reject (ARJ): khng cho php thit b u cui thit lp cuc

gi.

Thng tin trng thi: dng ly thng tin trng thi ca mt thit b u cui.

Ta c th s dng bn tin ny theo di trng thi online hay offline ca thit b

u cui trong tnh trng mng b li. Thng thng bn tin ny s c gi 10

giy mt ln. Trong qu trnh cuc gi, gatekeeper c th yu cu thit b u

cui gi theo chu k cc bn tin trng thi. Loi bn tin ny bao gm:

Information Request (IRQ): gi t gatekeeper ti thit b u cui yu cu

thng tin trng thi.

Information Request Response (IRR): c gi t thit b u cui ti

gatekeeper tr li cho bn tin IRQ. Bn tin ny cng c gi t thit b

u cui ti gatekeeper theo chu k.

Status Enquiry Sent : Thit b u cui hay gatekeeper c th gi bn tin

ny ti thit b u cui khc xc thc v trng thi cuc gi.

iu khin bng thng: Dng thay i bng thng cho cuc gi vi cc bn

tin nh sau:

Bandwidth Request (BRQ): gi bi thit b u cui yu cu tng hoc

gim bng thng cuc gi

Bandwidth Confirm (BCF): chp nhn thay i yu cu bi thit b u

cui. Bandwidth Reject (BRJ): khng chp nhn thay i yu cu bi thit b

u cui.

Hy kt ni: Khi mun kt thc cuc gi th trc ht thit b u cui dng ht

mi kt ni v ng ht cc knh logic li. Sau , ne s ngt phin H.245 v

gi tn hiu RLC trn knh bo hiu cuc gi. bc ny, nu khng c

gatekeeper th cuc gi s c hy cn nu khng th cc bn tin sau s c

gi trn knh RAS kt thc cuc gi:

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Disengage Request (DRQ): Gi bi thit b u cui hay gatekeeper

kt thc cuc gi.

Disengage Confirm (DCF): Gi bi thit b u cui hay gatekeeper

chp nhn bn tin DRQ trc . Disengage Reject (DRJ): c gi bi thit b u cui hoc gatekeeper

thng bo khng chp nhn yu cu DRQ.

3.1.2.2. Bo hiu iu khin cuc gi H.225

Trong mng H.323, chc nng iu khin cuc gi da trn c s giao thc H.323

vi vic s dng bn tin bo hiu Q.931. Mt knh iu khin cuc gi c to ra da

trn giao thc TCP/IP vi cng 1720. Tng ny thit lp cc bn tin iu khin cuc gi

gia hai thit b u cui vi mc ch thit lp, duy tr v kt thc cuc gi. H.225

cng s dng bn tin Q.932 cho cc dch v b sung. Cc bn tin Q.931 v Q.932

thng c s dng trong mng H.323:

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

th H.323 b gi qua cng 1720 TCP.

Call Proceeding: thc th b gi gi bn tin ny ti thc th ch gi ch th

rng th tc thit lp cuc gi c khi to.

Alerting: c gi t thc th b gi ti thc th ch gi ch th rng chung

bn ch bt u rung.

Connect: c gi t thc th b gi thng bo rng bn b gi tr li cuc

gi. Bn tin Connnect c th mang a ch truyn vn UDP/IP.

Release Complete: c gi bi mt u cui khi to ngt kt ni, n ch th

rng cuc gi ang b gii phng. Bn tin ny ch c th c gi i nu knh

bo hiu cuc gi c m hoc ang hot ng.

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.

Cc bn tin trong qu trnh thit lp cuc gi nh sau:

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Hnh 21. Q.931 trong thit lp cuc gi

1. Thit b u cui H.323 gi bn tin Setup yu cu thit lp cuc gi. Gi s

y bn tin c gi ti Gatekeeper (thit lp cuc gi thng qua

Gatekeeper).

2. Gatekeeper s gi tr li bn tin Call Proceeding nhm thng bo cho pha

gi rng: Thit b ny ang thc hin thit lp cuc gi.

3. Khi u cui b gi rung chung, Gatekeeper s gi bn tin Alerting v u

cui gi thng bo v trng thi ny.

4. Khi ngi c gi nhc my, bn tin Connect s c gi ti u cui gi

thng bo cuc gi c thit lp.

5. Cuc gi c thc hin

3.1.2.3. Giao thc H.245

Chc nng H.245 l thit lp cc knh logic truyn audio, video, data v cc

thng tin knh iu khin. Gia hai thit b u cui c thit lp mt knh H.245 chomt cuc gi. Knh iu khin ny c to da trn TCP gn ng port. Chc nng

iu khin ca knh H.245 l thng lng v mt s thng s sau:

B m ha ting ni s c s dng hai pha. Ly v d, chun m ha ting

ni v tc bit tng ng nh sau: G.729 - 8 kbps, G.728 - 16 kbps, G.711 - 64

kbps, G.723 - 5.3 hay 6.3 kbps, G.722 - 48, 56, v 64 kbps

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Thng lng v Ch/t gia hai thit b u cui: xc lp vai tr ca cc thit

b trong khi thc hin cuc gi trnh hin tng xung t.

Round-Trip Delay: xc nh tr gia pha pht v pha thu. Da vo thng s

ny xc nh kt ni vn hot ng. Bo hiu trn knh logic thc hin vic m v ng cc knh logic. Cc knh

ny c thit lp trc khi thng tin c truyn n . Bo hiu ny c th

thit lp knh n hng hoc song hng. Sau khi knh logic c thit lp,

cng UDP cho knh media RTP c truyn t pha nhn ti pha pht. Khi s

dng mt hnh nh tuyn qua Gatekeeper th Gatekeeper s chuyn hng lung

RTP bng cch cung cp a ch UDP/IP thc ca thit b u cui. Lung RTP

s truyn trc tip gia hai thit b u cui vi nhau.

Mi knh media s dng RTP truyn thi gian thc - s c mt knh phn

hi v cht lng dch v QoS theo chiu ngc li gip pha pht kim sot c

lung media truyn i v c nhng iu chnh ph hp.

Hnh 22. Cu trc lung media gia cc u cui

3.1.3. Thit lp cuc gi VoIP s dng giao thc H.323

3.1.3.1. Bo hiu trc tip gia cc thit b u cui

Trong m hnh ny, c ch l cc thit b u cui (Endpoint) ch xin phpGatekeeper thc hin cuc gi thng qua bo hiu RAS cn cc bc bo hiu gia cc

thit b ny c thc hin trc tip khng thng qua Gatekeeper.

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Hnh 23. Thit lp bo hiu H.323 trc tip gia cc u cui

Bc 1: Endpoint O ng k vi Gatekeeper yu cu cho php thc hin mt cuc

gi ti Endpoint T. Cc bc thc hin xc thc thu bao gi s c thc hin bc

ny. Gatekeeper tr li cho php Endpoint O thc hin cuc gi v a ch ca chnh xc

ca Endpoint T. Trong trng hp ny, hai Endpoint thc hin cuc gi trc tip vinhau.

Bc 2: Endpoint O v Endpoint T thit lp mt kt ni TCP cho bo hiu H.225

truyn cc bn tin Q.931 cho php thit lp cuc gi. Endpoint O gi bn tin Setup

ti Endpoint T yu cu thit lp cuc gi. Endpoint T tr li bng bn tin Call

Proceeding thng bo cuc gi ang c thc hin.

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Bc 3: Endpoint T xin php Gatekeeper cho php thc hin cuc gi vi

Endpoint O. Gatekeeper tr li ng cho Endpoint T chp nhn cuc gi. Endpoint T

thc hin rung chung v bo cho Endpoint O bit l ang rung chung ngi b gi.

Bc 4: Ngi b gi nhc ng nghe. Endpoint T gi bn tin Conect ti EndpointO thng bo knh cuc gi c thit lp. Lc ny, gia hai Endpoint m mt kt

ni TCP na cho knh bo hiu H.245 thng lng, thit lp v duy tr knh media.

Bc 5: Khi thng lng xong (cc thng s c m t trong phn bo hiu

H.245), mi Endpoint yu cu m mt kt ni audio truyn thoi. Nh vy s tn ti

hai knh cho php thc hin cuc gi hai chiu gia hai thu bao. Qu trnh thoi c

thc hin hin da trn giao thc RTP vi s kim sot ca RTCP.

3.1.3.2. Bo hiu c nh tuyn thng qua GatekeeperTrong hnh thc bo hiu ny th mi bn tin bo hiu c gi qua

Gatekeeper. Gatekeeper s x l v chuyn tip bo tin ti pha b gi. Khi , pha gi

khng nht thit phi bit chnh xc a ch ca pha b gi nhng qu trnh ny s b tr

nhiu hn.

Cc bn tin bo hiu trong m hnh ny gn nh ging vi trng hp bo hiu

trc tip gia hai thit b u cui nhng c mt s ch nh sau:

Gatekeeper y s gm c hai giao din: giao din vi Endpoint O v EndpointT. Vic phn bit nh vy s gip chng ta r rng hn trong vic gi nhn cc

bn tin v hai giao din ny hot ng c s c lp nht nh vi nhau.

Knh bo hiu H.225 c thit lp gia cc Endpoint v Gatekeeper

Khi nhn c bn tin Setup t Endpoint O gi ti, Gatekeeper s gi

bn tin ny ti Endpoint T v gi ngay bn tin Call Proceeding v cho

Endpoint O bo rng cuc gi ang trong qu trnh thit lp.

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Sau khi nhn c bn tin Connect t Endpoint T, Endpoint O v Endpoint T s

thc hin bo hiu trc tip vi nhau m knh truyn media.

Hnh 24. Thit lp bo hiu H.323 nh tuyn qua Gatekeeper

3.1.3.3. Thit lp cuc gi gia hai thit b u cui hai vng dch v

Trong m hnh ny l vic thc hin cuc gi gia hai thit b u cui hai vng

dch v khc nhau cho nhau. y l m hnh bo hiu da trn vic nh tuyn ca cc

Gatekeeper.

Sau khi nhn c yu cu ca Endpoint O mun thit lp cuc gi vi Endpoint

T, Gatekeeper 1 gi ti Endpoint T yu cu thit lp cuc gi. V Endpoint T nm trong

vng dch v do Gatekeeper 2 qun l nn n phi xin s cho php c th thc hin

cuc gi (ging nh cc trng hp trc). trong trng hp ny, Gatekeeper 2 cng

gi tr li bn tin ARQ ca Endpoint T bng bn tin ACF cho php thit lp cuc gi

nhng phi thng qua n (khng cho thc hin cuc gi trc tip ti Endpoint T). Dovy, Endpoint T gi bn tin Facility ti Gatekeeper 1 thng bo l cuc gi c chp

nhn nhng phi c nh tuyn li thng qua Gatekeeper 2. Chnh v vy, knh bo

hiu H.245 c c hy v thay bng cc knh bo hiu biu din nh trong hnh v.

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Hnh 25. Thit lp kt ni gia hai vng dch v3.2. Giao thc SIP

SIP (Session Initiation Protcol ) l giao thc bo hiu iu khin lp ng dng

c dng thit lp, duy tr, kt thc cc phin truyn thng a phng tin

(multimedia). Cc phin multimedia bao gm thoi Internet, hi ngh, v cc ng dng

tng t c lin quan n cc phng tin truyn t (media) nh m thanh, hnh nh,

v d liu. SIP s dng cc bn tin mi (INVITE) thit lp cc phin v mang cc

thng tin m t phin truyn dn. SIP h tr cc phin n b (unicast) v qung b(multicast) tng ng cc cuc gi im ti im v cuc gi a im. C th s dng

nm chc nng ca SIP thit lp v kt thc truyn dn l nh v thu bao, kh nng

thu bao, sn sng ca thu bao, thit lp cuc gi v x l cuc gi. SIP c IETF

a ra trong RFC 2543. N l mt giao thc da trn tng v cu trc ca HTTP

(HyperText Transfer Protocol) giao thc trao i thng tin ca World Wide Web v l

mt phn trong kin trc multimedia ca IETF. Cc giao thc c lin quan n SIP bao

gm giao thc t trc ti nguyn RSVP (Resource Reservation Protocol), giao thc

truyn vn thi gian thc (Realtime Transport Protocol), giao thc cnh bo phin SAP

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(Session Announcement Protocol), giao thc miu t phin SDP (Session Description

Protocol). Cc chc nng ca SIP c lp, nn chng khng ph thuc vo bt k giao

thc no thuc cc giao thc trn.

Mt khc, SIP c th hot ng kt hp vi cc giao thc bo hiu khc nhH.323. SIP l mt giao thc theo thit k m do n c th c m rng pht

trin thm cc chc nng mi. S linh hot ca cc bn tin SIP cng cho php p ng

cc dch v thoi tin tin bao gm c cc dch v di ng.

3.2.1. Cc thnh phn trong mng SIP

3.2.1.1. Gii thiu chung v cc thnh phn trong mng SIP

SIP Client: l thit b h tr giao thc SIP nh SIP phone, chng trnh chat,y chnh l giao din v dch v ca mng SIP cho ngi dng.

SIP Server: l thit b trong mng x l cc bn tin SIP vi cc chc nng c thnh sau:

1) Proxy Server: l thc th trong mng SIP lm nhim v chuyn tip ccSIP request ti thc th khc trong mng. Nh vy, chc nng chnh can trong mng l nh tuyn cho cc bn tin n ch. Proxy server cngcung cp cc chc nng xc thc trc khi cho khai thc dch v. Mt

proxy c th lu (stateful) hoc khng lu trng thi (stateless) ca bn tintrc . Thng thng, proxy c lu trng thi, chng duy tr trng thitrong sut transaction (khong 32 giy).

2) Redirect Server: tr v bn tin lp 300 thng bo thit b l chuynhng bn tin ti a ch khc t lin lc thng qua a ch tr v.

3) Registrar server: l server nhn bn tin SIP REGISTER yu cu v cpnht thng tin t bn tin request vo location database nm trong Loca-tion Server.

4) Location Server: lu thng tin trng thi hin ti ca ngi dng trongmng SIP.

3.2.1.2. Mi lin h gia cc thnh phn trong mng SIP

Trong v d th nht, cho ta c mt ci nhn khi qut v chc nng ca Proxy

Server, Redirect Server, SIP Phone trong mng. Gi s thu bao c tn user1 trong min

dch v do here.com mun thc hin mt cuc gi thoi ti thu bao c th l user2

( thuc there.com)

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Hnh 26. Chc nng ca Proxy, Redirect Server trong mng SIP

1. Khi User 1 mun gi ti User 2, trc ht n s gi bn tin INVITE 1 nProxy Server 1. Proxy Server 1 chuyn tip bn tin ti Redirect Server.

2. Redirect Server ny x l v tr v m 3xx thng bo cho Proxy Server tthc hin kt ni.

3. Proxy Server 1 gi bn tin INVITE 2 ti ch tr v bi Redirect Server( chnh l Stateless Proxy Server 1). V y l Stateful Proxy nn thc cht

bn tin INVITE c gi bi Stateful Proxy l khc so vi bn tin nhn

c t User1(ban u).

4. Stateless Proxy Server chuyn tip bn tin INVITE ti SIP Statefull Proxy2. Do l Stateless Proxy nn cng vic ca n n gin l chuyn tip bntin.

5. SIP Statefull Proxy 2 chuyn tip bn tin INVITE ti user2.

6. Khi user2 nhc my th n s gi bn tin 200 OK theo chiu ngc li.

7. Sau khi nhn c bn tin 200 OK, user1 s gi xc nhn ACK ti user2.

8. Lung RTP trc tip gia hai thu bao c thit lp. V cuc gi cthc hin.

Trong v d th hai s m t qu trnh mt SIP Phone ng k vi vi Registrar

Server qun l n,hot ng ca Location Server, Proxy Server.

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Hnh 27. Chc nng ca Location, Registrar Server trong mng SIP

Khi mt SIP Phone c kt ni vi mng. N lin tc gi bn tin REGISTER ti

Registrar Server thng bo v tr hin ti ca n. Gi s trong min dch v c tn

chicago.com th qu trnh REGISTER (ng k) c tin hnh nh sau:

1. Thu bao c tn Carol gi bn tin REGISTER ti Registrar Server. Serverny tin hnh xc thc. Nu hp l th cc thng tin c lu trong Lo-cation Server.

2. Khi mt thu bao khc (c tn l Bob) gi bn tin INVITE ti Proxy Serv-er xin kt ni ti thu bao Carol. Proxy Server s truy vn cc thng tinv thu bao b gi thng qua Location Server.

3. Proxy Server gi bn tin INVITE ti thu bao Carol thit lp cuc gi.

3.2.2. Bn tin SIP

3.2.2.1. Cc loi bn tin SIP

Bn tin yu cu (Request): c gi t client ti server. RFC 3261 nh ngha 6

kiu bn tin request cho php UA v proxy c th xc nh ngi dng, khi to,

s i, hy mt phin.

Bn tin INVITE: yu cu thit lp mt phin hoc thay i cc c

tnh ca phin trc .Trong bn tin ny c s dng SDP nh ngha

v cc thng s media ca phin. Mt response thnh cng c gi tr 200

c tr li cc thng s m ngi c gi chp nhn trong phin media.

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Bn tin ACK xc nhn rng client nhn c response cui cng ca

bn tin INVITE. ACK ch c s dng km vi bn tin INVITE. ACK

c gi t u cui n u cui cho response 200 OK. ACK cng c

th cha phn thn bn tin vi m t phin cui cng nu bn tin INVITE

khng cha.

Bn tin OPTIONS: UA s dng request ny truy vn ti server v kh

nng ca n.

Bn tin BYE: UA s dng bn tin ny yu cu hy mt phin c

thit lp trc .

Bn tin CANCEL: cho php client v server hy mt request, v d nh

INVITE. N khng nh hng ti request hon thnh trc mserver gi response.

Bn tin REGISTER: Mt client s sng REGISTER yu cu ang k v

tr ca n ti AOR (address of record) ca ngi dng vi SIP server.

Bn tin p ng (Response): server gi bn tin SIP p ng (SIP response) ti

client bo v trng thi ca SIP request m client gi trc . Cc SIP

response c nh s t 100 n 699, c chia thnh cc lp ngha khc nhau

Cc lp Response M tr v M t

Thng tin 100 ang thc hin kt ni

180 ang chung

181 Cuc gi ang c chuyn tip

182 c t vo hng i

183 Phin ang c x l

Thnh cng 200 Thnh cng

Chuyn hng 300 Nhiu la chn

301 Chuyn vnh vin

302 Chuyn tm thi

305 S dng proxy

380 Dch v khc

Li Client 400 Yu cu khng hp l

401 Khng nhn dng c

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402 Yu cu thnh ton

403 B cm

404 Khng tm thy405 Phng thc khng c php

406 Khng chp nhn

407 Yu cu xc thc Proxy

408 Request timeout

410 di i

413 Yu cu qu di

414 URL c yu cu qu ln415 Khng h tr kiu media

416 Khng h tr URI

420 Phn m rng li

421 Yu cu phn m rng

423 Khong thi gian gia hai s kin qu ngn

480 Tm thi cha sn sng

481 Transaction khng tn ti482 Pht hin thy loop (chu trnh)

483 Qu nhiu hop

484 a ch khng

485 Mt m khng r rng

486 ang bn

487 Yu cu b hy

488 Khng th chp nhn ti y491 Yu cu cha c gii quyt

493 Khng gii m c

Li Server 500 Li ni ti trong server

501 Cha c thc hin u

502 Gateway li

503 Dch v khng tn ti

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504 Server timeout

505 Phin bn SIP khng c h tr

513 Bn tin qu lnLi ton cc 600 Bn khp mi ni

603 Suy sp

604 Khng tn ti

606 Khng th chp nhn

3.2.2.2. Cu trc bn tin SIP

Bn tin Request:

INVITE sip:[email protected] SIP/2.0

Via: SIP/2.0/UDP ph1.company.com:5060;branch=z9hG4bK83749.1

From: Alice ;tag=1234567

To: Bob

Call-ID: [email protected]

CSeq: 1 INVITE

Contact:

Content-Type: application/sdp

Content-Length: ...

v=0

o=alice 2890844526 28908445456 IN IP4 172.18.193.102

s=Session SDPc=IN IP4 172.18.193.102

t=0 0

m=audio 49170 RTP/AVP 0

a=rtpmap:0 PCMU/8000

Bn tin Response:

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SIP/2.0 200 OK

Via: SIP/2.0/UDPph1.company.com:5060;branch=z9hG4bK83749.1

From: Alice ;tag=1234567To: Bob ;tag=9345678

Call-ID: [email protected]

CSeq: 1 INVITE

Content-Length: ...

v=0

o=bob 3800844316 3760844696 IN IP4 172.18.193.109

s=Session SDP

c=IN IP4 172.18.193.109

t=0 0

m=audio 48140 RTP/AVP 0

a=rtpmap:0 PCMU/8000

ngha ca cc trng trong bn tin:

Tiu SIP M t

From Thng l AOR(Address of Record) ca ngi gi. N bao gm SIP hocSIPS URI v vi ty chn tn c hin th.

To M t ngi nhn ca bn tin SIP, AOR ca ngi nhn. Vi chc nngforward hay redirect thi anh khng phi l a ch ngi nhn. Trng nyging trng From.

Call-ID nh ngha series ca bn tin SIP. Call-ID phi c xc nh trong mibn tin SIP c gi bi tt c cc UA trong mt dialog.

Cseq Cha mt gi tr nguyn v tn phng thc. Trng ny dng xc nh,spx xp, nh du chui SIP request trong mt dialog. Cseq c th khcnhau gia bn tin c truyn li v truyn mi.

Via Xc nh ng i c ch ra request v cc response s c gi.

Contact Cha SIP hoc SIPS URI ca UA mun nhn c SIP request mi.

Allow Lit k tp cc phng thc SIP c h tr bi UA.

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Tiu SIP M t

Supported Lit k tp cc phn m rng ca SIP h tr bi UA.

Require Trng ny rt ging nh trng Supported nhng l ca cc UA xa cnthit cho mt transaction c x l.

Content-Type

Kiu ca phn thn ca bn tin SIP (nu c phn thn)

Content-Length

Kch thc ca phn thn bn tin SIP. Trng ny l bt buc khi bn tinSIP c truyn trn TCP.

3.2.3. M t cuc gi SIP

3.2.3.1. Cuc gi c nh tuyn qua Proxy Server

Hnh 28. Thit lp cuc gi SIP vi Proxy Server

1. Proxy server nhn c bn tin INVITE t client.

2. Proxy server lin lc vi Location server xc nh a ch ca ngi b gi.

3. Location server xc nh v tr ca ngi c gi v cung cp a ch server

ch.

4. Bn tin INVITE c chuyn tip ti a ch m Location server tr v.Proxy server s thm tiu Record-Route vo bn tin INVITE chc rng

tt c cc bn tin tun t sau c nh tuyn qua proxy. iu ny cn

thit cho qu trnh tnh cc hoc cc ng dng khc cn thit kim sot

cc bn tin cho dialog ny.

5. Pha c gi rung chung. Ngi c gi nhc my.

6. Pha c gi gi bn tin 200 OK thng bo cuc gi bt u.

7. Bn tin 200 OK c chuyn tip qua proxy server ti pha gi.

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8. Pha gi tr li bn tin 200 OK nhn c bng bn tin ACK ti proxy-server

( khi proxy chn tiu Record-Route vo trong bn tin INVITE) hoc gi

trc tip ti pha ngi c gi.

9. Proxy chuyn tip ACK ti ngi c gi.10. Cuc gi thoi c thit lp.

3.2.3.2. Bo hiu trc tip gia cc thit b u cui

Hnh 29. Thit lp cuc gi vi Redirect Server

1. Redirect server nhn c bn tin INVITE t pha UA gi.

2. Redirect server lin lc vi Location server ly thng tin a ch ca UA

c gi.

3. Location server tr li a ch ca UA c gi.

4. Redirect server tr a ch trc tip v UA gi vi bn tin 3xx vi trng

Contact c cp nht. Khng ging nh Proxy server, Redirect serverkhng chuyn tip bn tin INVITE.

5. UA gi gi bn tin ACK ti Redirect server xc nhn v bn tin 3xx.

6. UAC gi gi trc tip bn tin INVITE vi trng Contact: l a ch tr v

bi Redirect server ti UA c gi.

7. UA c gi rung chung v ngi dng nhc my. UA c gi gi bn tin

200 OK ti UA gi.

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8. UAC gi gi bn tin ACK xc nhn.

3.3. So snh gia giao thc H.323 v SIP

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, tuynhin 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 thngbo, 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.

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.SIGu 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 gi1.5 RTT 6-7 RTT hoc hn

Gim st trng

thi cuc gi

C 2 la chn:

trong thi gian thit lp

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

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sut thi gian cuc gi m rng v gim tin cy

Bo hiu

qung bC 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.164hoc 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 thoiH 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

To tnh nng

v dch v mi

D dng, s dng SIP-CGI

v CPLH.450.1

Kh nng

m rngD dng Hn ch

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Chng 4. Kt ni gia mng VoIP v PSTN

4.1. Mng bo hiu SS7

4.1.1. Cc thnh phn trong mng bo hiu SS7

4.1.1.1. SSP (Service Switch Point)

SSP lun gn lin vi chc nng chuyn mch. Do chuyn mch c phn cp

(s phn cp ca h thng vin thng) nn cc SSP cng c phn cp. Mt chuyn

mch vi chc nng SS7 s c 2 giao din:

giao din kt ni chc nng thoi

giao din kt ni cho d liu SS7

C th ni cc chuyn mch ng ngha vi SSP. Bi l, cc SSP chuyn bo hiu

cho cuc gi thnh cc bn tin bo hiu SS7. Chc nng chnh ca SSP l x l cuc

gi, qun l cuc gi v gip nh tuyn cuc gi ti ch.

4.1.1.2. SCP (Service Control Point)

SCP cung cp cc dch v truy cp c s d liu (CSDL) ti mng in thoi. V

d dch v ca SCP l dch v chuyn i s 1-800 (toll-free) hay dch v Local numberPortability (LNP) M. SCP hot ng nh l mt giao din ti my tnh c lu CSDL.

4.1.1.3. STP (Service Tranfer Point)

STP c xem nh l cc router trong mng SS7. Chc nn

giao thuc_voip

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