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GVHD: Nguyn Minh Hi SVTH: Mai Thanh Sn
0 THIT LP TNG I VOIP
TRNG I HC CNG NGHIP TP.HCM
KHOA CNG NGH THNG TIN
----------
N CHUYN NGHNH
THIT LP TNG I VOIP
Gio vin hng dn: Sinh vin thc hin:
Nguyn Minh Hi Mai Thanh Sn - 10071091
TPHCM, Ngy 2 Thng 7 Nm 2014
GVHD: Nguyn Minh Hi SVTH: Mai Thanh Sn
1 THIT LP TNG I VOIP
NHN XT CA GIO VIN HNG DN
(TPHCM, NgyThngNm 2014)
K tn
GVHD: Nguyn Minh Hi SVTH: Mai Thanh Sn
2 THIT LP TNG I VOIP
NHN XT CA GIO VIN PHN BIN
(TPHCM, NgyThngNm 2014)
K tn
GVHD: Nguyn Minh Hi SVTH: Mai Thanh Sn
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MC LC
CHNG I. TNG QUAN V VOIP ..6
I. TNG QUAN V VOIP ............................................................................................................ 6
1. GII THIU CHUNG V VOIP ....................................................................................................... 6
1.1. u im .................................................................................................................................. 6
1.2. Nhc im. ........................................................................................................................... 7
2. CC KIU KT NI .......................................................................................................................... 8
2.1. Computer to Computer .......................................................................................................... 8
2.2. Computer to Phone ................................................................................................................ 9
2.3. Phone to Phone ................................................................................................................ .10
3. CC THNH PHN TRONG MNG VOIP...11
II. CCH THC HOT NG CA VOIP ............................................................................................ 12
1. VOIP HOT NG NH TH NO?........................................................................................... 12
1.1. Qu trnh ly mu (Sampling) ............................................................................................... 14
1.2. Qu trnh lng t ha (Quantization) ................................................................................ 14
1.3. M ha (Encoding) ................................................................................................................ 14
1.4. Nn ging ni (Voice Compression).......14
2. CC NHN T NH HNG15
2.1. Tr (Delay)...15
2.2. S bin thin tr (Jitter ).15
2.3. Mt gi...15
III. CC GIAO THC TRONG VOIP16
1. GIAO THC H.323..16
1.1. Gii thiu.............................................................................................................................. 16
1.2. Cc giao thc ca H.323 ....................................................................................................... 16
1.3. Cc thnh phn c bn ca H.323 ....................................................................................... 16
1.4. Phng thc hot ng ca H.323 ...................................................................................... 17
2. GIAO THC SIP .......................................................................................................................... 21
2.1. Gii thiu .............................................................................................................................. 21
2.2. Cc thnh phn trong SIP...................................................................................................... 21
2.3. Cc bn tin trong SIP ............................................................................................................. 23
2.4. Phng thc hot ng........................................................................................................ 24
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2.5. Tnh nng ca SIP .................................................................................................................. 27
2.6. Cc giao thc ca SIP......27
IV. TNH BO MT V HNG KHC PHC...28
1. TNH BO MT TRONG VOIP .............................................................................................. .28
2. HNG KHC PHC V BIN PHP GII QUYT ..................................................................... 29
CHNG II.....ASTERISK30
I. GII THIU V ASTERISK....30
II. CI T ASTERISKNOW 3.0 V CU HNH CC TNH NNG CN BN...31
1. CI T31
2. CU HNH..37
2.1. To s in thoi (user).38
2.2. ng k s dng v thc hin cuc gi..40
2.3. Chc nng nhc ch....44
2.4. Thit lp tng i IVR.....47
2.5. Kt ni hai tng i.....49
CHNG IIITNG KT.66
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LI M U
Ra i t cch y rt lu nhng in thoi vn l phng tin lin lc hu
hiu trong mi lnh vc - t qun s, an ninh quc phng cho n sinh hot i sng
sinh hot hng ngy ca chng ta.
Ngy nay, vi s pht trin mnh m ca Internet, ra i nhiu loi hnh dch
v phc v cho vic lin lc ca con ngi. Trong VoIP l cng ngh mang tnh
cch mng lm thay i th gii in thoi vi cht lng dch v kh cao.
hiu r c bn cht v ng dng ca VoIP, chng ta cng tm hiu c th
qua tng phn ca cng ngh ny.
Ni dung ti gm 2 chng ln:
Chng 1: Tng quan v VoIP
Tm hiu v VoIP, cch thc hot ng, cc giao thc s
dng trong h thng VoIP.
Chng 2: Asterisk
Dng Asterisk ci t, cu hnh cc chc nng c bn
xy dng mt tng i VoIP n gin.
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CHNG I: TNG QUAN V VOIP
I. TNG QUAN V VOIP
1. GII THIU CHUNG V VOIP
VoIP (Voice over Internet Protocol) 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 nh khai thc, cc nh sn xut m cn c vi ngi s dng dch v.
VoIP cho php to cuc gi dng kt ni bng thng rng thay v dng ng
dy in thoi tng t (analog). Nhiu dch v VoIP c th ch cho php bn gi
ngi khc dng cng loi dch v, tuy nhin cng c nhng dch v cho php gi
nhng ngi khc dng s in thoi nh s ni b, ng di, di ng, quc t.
Trong khi cng c nhng dch v ch lm vic qua my tnh, cng c vi dch v dng
in thoi truyn thng qua mt b iu hp (adaptor).
Nguyn tc hot ng ca VoIP bao gm vic s ho tn hiu ting ni, thc
hin vic nn tn hiu s, chia nh cc gi nu cn v truyn gi tin ny qua mng, ti
ni nhn cc gi tin ny c rp li theo ng th t ca bn tin, gii m tn hiu
tng t phc hi li ting ni ban u.
1.1. u im
Mt u im u tin l gi min ph nu s dng cng dch v, cng
thit b VoIP hoc cng tng i IP ( hay cn gi l gi ni mng). Hoc
nu khng th gi thnh cng r ng k so vi s dng cch gi truyn
thng PSTN (Public Switched Telephone Network)
Gii php VoIP cng lm gim ng k chi ph cho vic qun l bo tr
h thng mng thoi v d liu.
Tch hp mng thoi, mng s liu v mng bo hiu: trong in thoi
IP, tn hiu thoi, s liu v ngay c bo hiu u c cng i trn mt
mng IP. iu ny s gip tit kim chi ph khi u t nhiu mng ring
l.
Kh nng m rng: Cc tng i in thoi thng l nhng h thng
kn, rt kh thm vo nhng tnh nng th cc thit b trong mng
internet thng c kh nng thm vo nhng tnh nng mi.
Trong mt cuc gi ngi s dng c th va ni chuyn va s dng
cc dch v khc nh truyn file, chia s d liu hay xem hnh nh ca
ngi ni chuyn bn kia.
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Mt li ch na l, vic s dng ng thi c in thoi bn thng
thng v in thoi IP (c dy hoc khng dy) qua h thng mng
LAN (Local Area Network) s m bo thng tin lin lc ca doanh
nghip khng b gin on khi xy ra s c.
1.2 . Nhc im
K thut phc tp: c c mt dch v thoi chp nhn c, cn
thit phi c mt k thut nn tn hiu phi t c cc yu cu nh: t
s nn ln, 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
Vn bo mt (Security): Mng internet l mt mng c tnh rng
khp v hn hp. Trong c rt nhiu loi my tnh khc nhau v cc
dch v khc nhau cng s dng chung mt c s h tng. Do vy khng
c g m bo rng nhng thng tin ca ngi s dng c bo mt an
ton.
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2. CC KIU KT NI
2.1. Computer to Computer
Vi 1 knh truyn Internet c sn, l 1 dch v min ph c s dng
rng ri khp ni trn th gii. Ch cn ngi gi (caller) v ngi nhn
(receiver) s dng chung 1 VoIP service (Skype, Yahoo Messenger,),
2 headphone + microphone, sound card . Cuc hi thoi l khng gii
hn.
M hnh ny p dng cho cc cng ty, t chc, c nhn p ng nhu cu lin lc m khng cn tng i ni b
Hnh 1: Computer to conputer
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2.2. Computer to Phone
L 1 dch v c ph. Bn phi tr tin c mt account v mt software
(VDC, Evoiz, Netnam,). Vi dch v ny mt my PC c kt ni ti
mt my in thoi thng thng bt c u ( tu thuc phm vi cho
php trong danh sch cc quc gia m nh cung cp cho php). Ngi
gi s b tnh ph trn lu lng cuc gi v khu tr vo ti khon hin
c.
Hnh 2: Computer to phone
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2.3. Phone to Phone
L mt dch v c ph. Bn khng cn kt ni Internet m ch cn mt
VoIP adapter kt ni vi my in thoi. Lc ny my in thoi tr
thnh mt IP phone.
Hnh 3: Phone to phone
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3. CC THNH PHN TRONG MNG VOIP
Cc thnh phn ct li ca 1 mng VoIP bao gm: Gateway, VoIP Server, IP
network, End User Equipments
Hnh 4: Cc thnh phn trong VoIP
Gateway: l thnh phn gip chuyn i tn hiu analog sang tn hiu s
(v ngc li).
VoIP gateway : l cc gateway c chc nng lm cu ni gia mng
in thoi thng ( PSTN ) v mng VoIP.
VoIP GSM Gateway: l cc gateway c chc nng lm cu ni cho cc
mng IP, GSM v c mng analog.
VoIP server : l cc my ch trung tm c chc nng nh tuyn v bo
mt cho cc cuc gi VoIP. Trong mng H.323 chng c gi l
gatekeeper. Trong mng SIP cc server c gi l SIP server.
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Thit b u cui (End user equipments ): Softphone v my tnh c
nhn (PC): bao gm mt headphone, mt phn mm v mt kt ni
Internet. Cc phn mm min ph ph bin nh Skype, Ekiga,...
in thoi truyn thng vi IP adapter: s dng dch v VoIP th my
in thoi thng dng phi gn vi mt IP adapter c th kt ni vi
VoIP server. Adapter l mt thit b c t nht mt cng RJ11 ( gn
vi in thoi) , RJ45 ( gn vi ng truyn Internet hay PSTN) v
mt cng cm ngun.
IP phone : l cc in thoi dng ring cho mng VoIP. Cc IP phone
khng cn VoIP Adapter bi chng c tch hp sn bn trong
c th kt ni trc tipvi cc VoIP server
II. CCH THC HOT NG CA VOIP
1. VOIP HOT NG NH TH NO?
Trong VoIP khi ni vo ng nghe hay microphone, ging ni s to ra tn hiu
in t, l nhng tn hiu analog. Tn hiu analog c chuyn sang tn hiu s
dng thut ton c bit chuyn i. Nhng thit b khc nhau c cch chuyn
i khc nhau nh VoIP phone hay softphone, nu dng in thoi analog thng
thng th cn mt Telephony Adapter (TA). Sau ging ni c s ha s
c ng vo gi tin v gi trn mng IP.
Cc bc c bn thc hin mt cuc gi trong VoIP:
Xc nh a im cn gi n (m quc gia, m tnh,) v bm s cn
gi n.
Cc kt ni gia ngi gi v ngi nhn s c thit lp.
Khi ni vo ng nghe hay microphone, ging ni s to ra tn hiu in
t, l nhng tn hiu analog. Tn hiu analog c chuyn sang tn
hiu s dng thut ton c bit chuyn i. Sau ging ni c
s ha s c ng thnh gi tin v gi trn mng IP. Trong sut tin
trnh mt giao thc nh SIP hay H323 s c dng iu khin
(control) cuc gi nh l thit lp, quay s, ngt kt ni, v RTP th
c dng cho tnh nng m bo tin cy v duy tr cht lng dch
v trong qu trnh truyn.
D liu s c truyn ti qua kt ni c thit lp lc u.
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D liu cha m thanh m bn ni s c chuyn ha tr li thnh m
thanh m ngi nghe hiu c.
Cui cng m thanh bn ni ra s c pht ra bn pha ngi nhn.
Qu trnh s ha tn hiu analog:
Biu din tn hiu analog thnh dng s (digital) l cng vic kh khn.
V bn thn dng m thanh nh ging ni con ngi dng analog do phi
cn mt s lng ln cc gi tr digital biu din bin (amplitude), tn s,
v pha (phase), chuyn i nhng gi tr thnh dng s nh phn (0 & 1) l
rt kh khn. V vy, thc hin s chuyn i ny chng ta cn phi dng
n thit b c gi l codec (coder-decoder) hay l thit b m ha v gii
m. Tn hiu analog c t vo u vo ca thit b ny v c chuyn
thnh cc chui s nh phn u ra. Sau qu trnh ny thc hin tr li
bng cch chuyn i chui s nh phn thnh dng analog u cui.
C 4 bc lin quan n qu trnh s ha mt tn hiu analog:
Ly mu (Sampling)
Lng t ha (Quantization)
M ha (Encoding)
Nn ging ni (Voice Compression)
Cc k thut s dng trong qu trnh s ha: Multiplexing: Ghp knh l qui trnh chuyn mt s tn hiu ng thi qua mt
phng tin truyn dn. TDM (Time Division Multiplexing): Ghp knh phn chia theo thi gian:Phn
phi khong thi gian xc nh vo mi knh, mi knh chim ng truyn cao tc trong sut mt khong thi gian theo nh k.
FDM (Frequency Division Multiplexing): Ghp knh phn chia theo tn s: Mi knh c phn phi theo mt bng tn xc nh, thng thng c b rng 4Khz cho dch v thoi.
PCM (Pulse Code Modulation): iu ch theo m: l phng php thng dng nht chuyn i cc tn hiu analog sang dng digital ( v ngc li) c th vn chuyn qua mt h thng truyn dn s hay cc qu trnh x l s.
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1.1. Ly mu (Sampling)
Simpling l t l ly mu th - s mu mi giy dng m ha m thanh.
Tn hiu m thanh trn mng in thoi c ph nng lng t n 10KHz. Tuy
nhin, hu ht nng lng u tp trung phn thp hn trong di ny.
Trong VoIP, t l ly mu thng l 8 KHz, tn s khong 16 KHz. C th s
dng trong cc tnh hung khi m yu cu cht lng m thanh cao (bng thng
cao). Vic la chn tn s ly mu cho tng loi m thanh khng phi ngu nhin,
m c mt quy tc ring l: tn s ly mu phi ln hn hoc bng hai ln so vi
lu lng bng thng.
1.2. Lng t ha (Quantization)
Lng t ha l s bit c s dng biu th cho tng mu m thanh. Trong
thc t, mun lm vic vi ton b byte chng ta phi xem xt 8 bit hoc 16 bit.
Mu 8 bit, mi mu c th biu th cho 256 gi tr khc nhau, v vy chng ta
c th lm vic vi cc dy s trong dy t -128 n +127. V ton b l s nn
khng th trnh khi cc ting n ln vo trong tn hiu cng nh chuyn i n
thnh mu s. Ch vi 256 gi tr, vic chuyn i analog sang tn hiu s s to
qu nhiu ting n. ci thin chng ta chuyn qua cc mu 16 bit, n s cung
cp cho chng ta 65536 gi tr i din khc nhau (t -32768 n +32767).
1.3. M ha (Encoding)
Mi mc lng t c ch nh mt gi tr s 8 bit, kt hp 8 bit c 256 mc
hay gi tr. Quy c bit u tin dng nh du gi tr m hoc dng cho mu.,
by bt cn li biu din cho ln.
1.4. Nn ging ni (Voice Compression)
Phng php ny thc hin m ha ting ni vi tc nh hn tc ca
PCM, nh tn dng c kh nng ca h thng truyn dn s. Chc hn, cc
m ha tc thp ny s b hn ch v cht lng, t bit l nhiu v lch tn s.
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2. CC NHN T NH HNG
Cht lng ca m thanh c khi phc qua mng in thoi l mc tiu c bn
ca dch v. C 3 nhn t c th nh hng n cht lng dch v thoi:
2.1. Tr (Delay)
Hai vn gy ra bi s tr u cui trong mt mng thoi l ting vang v
chng ting. y l mt vn cht lng ng k, nn cc h thng VoIP phi
kim sot v cung cp cc phng tin loi b ting vang. Hin tng chng ting
l ging ngi ny gi ln ging ngi kia.
2.2. S bin thin tr (Jitter)
Jitter l s bin thin thi gian tr gy nn bi s tr ng truyn khc nhau
trn mng. Loi b jitter i hi thu thp cc gi v gi chng lu ghp cc
gi chm nht n pht li ng th t, lm cho s tr tng ln.
2.3. Mt gi
Mng IP khng th cung cp mt s bo m rng cc gi tin s c chuyn
ti ch ht. Cc gi s b loi b khi qu ti v trong thi gian tc nghn. Truyn
thoi rt nhy cm vi vic mt gi. Tuy nhin, vic truyn li gi ca TCP thng
khng ph hp. Cc cch tip cn c s dng b li cc gi mt l thm vo
cuc ni chuyn bng cch pht (play) li gi cui cng, v gi i thng tin d.
Tuy th, s tn tht gi trn 10% ni chung l khng chp nhn c.
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III. CC GIAO THC TRONG VOIP
1. GIAO THC H.323
1.1. Gii thiu
H thng giao tip da trn gi a phng tin, hay cn gi l H.323. L
mt chun quc t ca VoIP c pht trin bi Lin Minh Vin Thng Quc
T (ITU International Telecommunicatinons Union). y l cu trc cht
ch, phc tp v ph hp vi vic thc thi cc c tnh thoi truyn thng.
H.323 thit k cho vic truyn audio, video v data qua mng IP.
1.2. Cc giao thc ca H.323
Khi lm vic vi H.323, c th nhn ra rng n khng phi l mt giao thc
n m l tp hp ca mt nhm giao thc. Cc giao thc ring c s dng
trong mng H.323 bao gm:
H.255 - bo hiu cuc gi.
H.245 - iu khin a phng tin (thng s knh m thanh v
video).
H.235 - bo mt v chng thc.
Q.391 - s dng cho tn hiu cuc gi.
T.120 - chia s d liu.
RTP - truyn ti a phng tin (truyn dng m thnh v video).
1.3. Cc thnh phn c bn ca H.323
Cc thnh phn c bn trong h thng mng H.323 c quy nh nh sau:
cc u cui, cng kt ni, thit b iu khin cng kt ni (gatekeeper) v khi
iu khin a im MCU (Mutipoint Conference Unit).
Terminal th thng l phn mm hoc phn cng in thoi VoIP. Mt s
chng trnh c th xem nh cc thit b terminal trong vic trao i giao thc.
Gateway l mt thit b cho php mt thng tin giao tip hai chiu vi cc
thit b trong mng vin thng khc. Cc mng vin thng khc thng l
PSTN.
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MCU l mt thit b c dng cho cuc hi thoi nhiu ngi. L ni chu
trch nhim cho vic trn cc knh m thanh video trong cc cuc hi thoi.
Terminal, gateway, cc MCU c gi chung l cc thit b u cui. Ngoi
cc thit b u cui trn, mng H.323 c thm mt thnh phn th 4 l
gatekeeper. Thit b gatekeeper ng vai tr nh mt b iu khin trung tm
trong mng. Nhim v chnh ca gatekeeper l ng k thit b u cui gi
vo. Tp hp cc thit b u cui c qun l cng mt gatekeeper gi l mt
khu (Zone).
Hnh 5: Cc thnh phn ca H.323
1.4. Phng thc hot ng ca H.323
Phn trn chng ta tm hiu v H.323, by gi chng ta s tm hiu v
phng thc hot ng ca H.323, xem H.323 hot ng nh th no?
Gi s, mt mng s dng gatekeeper v cc dng dch chuyn tn hiu i
thng qua gatekeeper (m hnh c nh tuyn). Chng ta c hai thit b
u cui (in thoi IP) v mt gatekeeper, cc s in thoi c gn cho cc
thit b tng ng l 100 v 200. Mt ngi vi s in thoi l 100 quay s
200. Nhng vic c din ra nh sau:
Thit b u cui m thit lp cuc gi bit c s gi l 200 nhng
n khng bit a ch IP lin quan n s . Cng thi im, t khi
n c ng k vi gatekeeper, n phi yu cu gatekeeper cp
quyn t cuc gi bng cch gi thng ip ARQ (Admission
Request - thng ip yu cu cp IP) cho gatekeeper. ARQ s ch s
Internet
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c gi (200) bo co cho gatekeeper rng thit b u cui cn c
s c phn gii thnh a ch IP.
Gatekeeper s kim tra d liu ca cc thit b u cui ng k
d n cha s 200. Vy th gatekeeper s kim tra nu 100 c gi
n 200 th gatekeeper s gi li mt cu tr li thng ip ACF
(Admiss Confirm thng ip chng thc) cha a ch IP ca 200
v gi ACF n thit b cui ang gi.
Hnh 6: M t hai bc u
Thit b u cui 100 by gi s m mt knh tn hiu cuc gi
(knh TCP) n a ch c cung cp bi gatekeeper trong thng
ip ACF. Thng ip tn hiu cuc gi c gi qua TCP vi giao
thc H.255, c nhng vo Q.931 (k hiu l Q.931/H.255).
Thit b u cui s m mt knh TCP ti gatekeeper v gi thng
ip Setup (ci t) Q.931/H.255, gatekeeper s m mt knh TCP
th hai n thit b u cui 200 v chuyn tip thng ip ci t.
Hnh 7: Gi thng ip Setup
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Thit b u cui 200 u tin s tr li Q.931/H.255 bng thng
ip Call Proceeding (cch tin hnh gi) cho bit n bt u
lm vic trn thit lp cuc gi v gatekeeper s chuyn tip thng
ip n thit b u cui ang gi (100). Sau 200 s yu cu
gatekeeper quyn gi (ARQ) v gatekeeper s tr li bng thng ip
ACF.
Hnh 8: Gi thng ip call proceeding
Cc in thoi c gi (200) bt u chung v gi li tn hiu
cho bn kia vi thng ip cnh bo (Alerting).
Bn c gi (200) bt my v thit b u cui c th bo hiu cuc
gi c chp nhn. Vic ny kt thc bng cch gi thng ip
Connect. Ti thi im ny, cc bn s phi iu chnh gi tr cho
cc knh m thanh v ty chn video. Giao thc H.245, s c s
dng cho vic iu chnh ny.
Hnh 9: Gi thng ip Alerting v Connect
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Thit b u cui gi i m mt knh TCP ti a ch H.245 nhn
c trong thng ip Connect v gatekeeper s to mt na knh
bo hiu H.245 th hai.
Cui cng, hai thit b u cui c th bt u gi cc dng RTP v
hai bn s nghe ln nhau.
Hnh 10: Trao i thng ip ca H.245
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2. GIAO THC SIP
Trc y khi cp n VoIP, tiu chun quc t thng cp n l H.323.
Nhng nhng nm gn y th giao thc SIP li chim u th v dn s thay th
hn H.323, v VoIP l mt trong nhng dch v s rt pht trin trong tng lai.
By gi chng ta s i tm hiu c th v giao thc ny:
2.1. Gii thiu
SIP (Session Initiation Protocol) 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 mang phin truyn dn. SIP h tr cc phin n b (unicast) v
qung b (mutilcast) tng ng cc cuc gi im ti im v cc cuc gi a
im.
SIP l mt giao thc dng vn bn, rt cng khai v linh hot. c thit k
tng thch tng thch vi cc giao thc khc nh TCP, UDP, IP,. cung cp
mt lnh vc rng hn cho dch v VoIP.
2.2. Cc thnh phn trong SIP
SIP gm hai thnh phn ln l SIP client (l thit b h tr giao thc SIP) v
SIP server (l thit b trong mng x l cc bn tin SIP). Trong SIP c 5 thnh
phn quan trng l:
User Agents (UA): l cc u cui trong mng SIP, n i din cho
pha ngi s dng khi to mt yu cu ti SIP server hoc User
Agent server.
Proxy server: lm nhim v chuyn tip cc SIP request ti cc ni
khc trong mng. Chc nng chnh ca n l nh tuyn cho cc bn
tin n ch.
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Hnh 11: Proxy server
Redirect server: l user agent server nhn cc bn tin request t cc
user agent client v tr v bn tin return thng bo thit b l
chuyn hng bn tin ti a ch khc t lin lc thng qua a ch
tr v.
Hnh 12: Redirect Server
Registrar server: l server nhn bn tin SIP Register yu cu cp nht
thng tin m user agent cung cp t bn tin Register.
Location Server: lu lng thng tin, trng thi hin ti ca ngi
dng trong mng SIP.
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2.3. Cc bn tin trong SIP
INVITE: bt u thit lp cuc gi bng cch gi bn tin mi u
cui khc tham gia
ACK: bn tin ny khng nh my trm nhn c cc bn tin tr
li bn tin INVITE
BYE: bt u kt thc cui gi
CANCEL: hy yu cu nm trong hng i
REGISTER: thit b u cui ca SIP s dng bn tin ny ng
k vi my ch ng k
OPTION: s dng xc nh nng lc ca my ch
INFO: s dng ti cc thng tin nh m bo
REQUEST: cho php user agent v proxy c th xc nh ngi
dng, khi to, sa i, hy mt phin.
RETURN: c gi bi user agent server hoc SIP server tr li
cho mt bn tin request trc .
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2.4. Phng thc hot ng
Hot ng ca my ch y quyn (Proxy Server)
Hnh 13: M hnh hot ng ca Proxy server
Hot ng ca Proxy server c trnh by nh trong hnh: SIP Client
[email protected] gi bn tin INVITE cho [email protected] mi
tham gia cuc gi.
Cc bc c thc hin nh sau:
Bc 1: [email protected] gi bn tin INVITE cho user B
min hotmail.com, bn tin ny n Proxy server SIP ca min
hotmail.com (bn tin INVITE c th i t Proxy server SIP
ca min yahoo.com v c Proxy ny chuyn n Proxy
server ca min hotmail.com)
Bc 2: Proxy ca min hotmail.com s tham kho server
nh v (Location server) quyt nh v tr hin ti ca user
B. T Proxy server ca min hotmail n s n Location
server nh v tr hin ti ca user B.
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Bc 3: Server nh v tr li v tr hin ti ca user B (gi s
l [email protected] ).
Bc 4: Proxy server gi bn tin INVITE ti
[email protected]. Proxy server thm a ch ca n trong
mt trng ca bn tin INVITE.
Bc 5: User B p ng cho server Proxy vi bn tin 200 OK.
Bc 6: Proxy server gi p ng 200 OK tr v
Bc 7: [email protected] gi bn tin ACK cho user B
thng qua Proxy server.
Bc 8: Proxy server chuyn bn tin ACK cho
Bc 9: sau khi c hai bn ng tham d cuc gi, mt
knh RTP/RTCP c m gia hai im cui truyn tn
hiu thoi.
Bc 10: Sau khi qu trnh truyn dn hon tt, phin lm
vic b xa bng cch s dng bn tin BYE v ACK gia hai
im cui.
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Hot ng ca my ch chuyn i a ch (Redirect Server)
Hnh 14: M hnh hot ng ca Redirect server
Hot ng ca Redirect Server c trnh by nh trong hnh:
Cc bc c thc hin nh sau:
Bc 1: Redirect server nhn c yu cu INTIVE t user A
(Yu cu ny c th i t mt Proxy server khc).
Bc 2: Redirect server truy vn server nh v a ch ca user
B.
Bc 3: Server nh v tr li a ch ca user B cho Redirect
server.
Bc 4: Redirect server tr li a ch ca user B cho user A. N
khng pht yu cu INTIVE nh Proxy server.
Bc 5: User Agent bn user A gi li bn tin ACK n Redirect
server xc nhn s trao i thnh cng.
Bc 6: user A gi yu cu INVITE trc tip n a ch c
tr li bi Redirect server. User B p ng vi ch th thnh cng
(200 - OK), v user A p tr bn tin ACK xc nhn. Cuc gi
c thit lp.
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2.5. Tnh nng ca SIP
Thit lp mt phin: SIP s dng bn tin INVITE yu cu thit
lp mt phin truyn thng.
n gin v c kh nng m rng: SIP c rt t bn tin, khng c
chc nng tha nhng SIP c th s dng thit lp nhng phin
kt ni phc tp nh hi ngh Cc phn mm ca my ch y
quyn, my ch ng k, my ch chuyn i a ch,c th chy
trn cc my ch khc nhau v vic ci t thm my ch hon ton
khng nh hng n my ch c.
H tr ti a s di ng ca u cui: do my ch y quyn, my
ch ng k v my ch chuyn i a ch h thng lun nm c
a im chnh xc ca thu bao. V d thu bao vi a ch
[email protected] c th nhn c cuc gi thoi hay thng ip
bt c a im no qua bt c u cui no nh my tnh bn,
my xch tay, in thoi SIP Vi SIP rt nhiu dch v di ng
mi c h tr.
nh v ngi s dng: nhng ngi s dng u cui s lun di
ng v a ch IP ca h l khng c nh, cc u cui c th ng
k vi mt SIP server thng qua bn tin REGISTER, SIP server s
lu li a ch IP ca u cui ng k. Khi c mt yu cu thit lp
cuc gi ti SIP server, SIP server s tm a ch ca ngi c gi
v forward bn tin INVITE ti ngi c gi.
2.6. Cc giao thc ca SIP
UDP (User Datagram Protocol): l giao thc tng vn chuyn khng
c iu khin tc nghn. N c dng vn chuyn bn tin SIP v
n gin v thch hp vi cc ng dng thi gian thc.
TCP (Transmission Control Protocol): l giao thc tng vn
chuyn do c iu khin tc nghn, hn na c th vn chuyn nhiu
gi tin c kch thc bt k.
SDP (Session Description Protocol): c s dng m t cc
thng s media cho mt cuc gi, cc thng s ny l cc thng tin
v bng thng, cc chun ha audio, video v mt s thng tin khc.
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IV. TNH BO MT V HNG KHC PHC
1. TNH BO MT TRONG VOIP
Chnh v VoIP da trn kt ni Internet nn n c th c im yu i vi bt
k mi e da v cc vn m my tnh phi i mt. VoIP c th cng b tn
cng bi virus v m nguy him khc. Nhng k tn cng c th chn vic truyn
thng, nghe trm v thc hin cc tn cng gi mo bng vic thao tng ID m
lm hng dch c ca bn.
Gy gin on v quy ri dch v: k tn cng c gng ph dch v
VoIP cc mc: h thng qun tr, h thng d phng, h thng truy
nhp v iu khin. Phng thc tn cng c th t xa, thng qua vic
li dng cc l hng ca giao thc dng trong VoIP.
S gin on dch v: c th l do tn cong t chi dch v Dos. Tn
cng Dos c hai loi chnh l Dos thng thng v DDos DDos phn
tn, khi b tn cng ny th rt t h thng c kh nng chng c.
Cc tn cng lin quan n dch v thoi: m bo thng sut trong
h thng VoIP th cc h thng in thoi kt ni vo phi hot ng
mt cch thng sut. Cc dch v lin quan ny gm c:
Voicemail
Caller ID (thng tin c nhn)
Location
Call waiting
V d: Voicemail tn cng mt cch n gin c th l on mt khu nu
mt khu khng mnh. Chng s xa tin nhn, i thng tin c nhn,
Nghe trm: y l hnh thc tn cng t ra hiu qu khi d liu trn ng truyn khng c m ha. Ngi tn cng c th da vo cc
li bt cc gi tin ti cc im trung gian nh gateway, proxy,
Gi mo: v nguyn l phng php tn cng ny rt n gin l gi mo ci gi l thc. Phng thc ny xut pht t chnh i sng x hi.
Truy cp tri php: l kh nng xm nhp vo dch v, h thng chc nng, thnh phn mng mt cch khng chnh thng. Ngi tn cng c
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th xm nhp qua cc l hng nh trn b m, cu hnh mc nh, mc
bo v km c th b b gy.
2. HNG KHC PHC
Trc khi i vo tm hiu nhng cng ngh m bo cho mng VoIP. u
tin cn phi hiu nhng vn v nhu cu bo mt tiu biu.
IP Sec: l giao thc bo mt c chng t v trin khai rng ri, n
s gip cho dch v trnh b nghe ln.
Ch k s: s dng nh trong th gii thc xc nhn mt thng ip
hay mt d liu no .
Share key (kha dng chung): trong mt h thng, ngi gi v ngi
nhn chia s vi nhau mt mt khu m bn th ba khng th bit c.
Ngi gi s dng mt khu dng chung m ha ni dung thng ip
v truyn d liu m ha ti ngi nhn. Ngi nhn m ha vi mt
khu dng chung v ta li vn bn gc.
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CHNG II: ASTERISK
I. GII THIU V ASTERISK
Asterisk l phn mm m ngun m, c vit bng ngn ng C v ban u c
to ra bi Mark Spencer (nay l Gim c cng ngh ca Digium - cng ty ti tr cho
hu ht cc pht trin ca Asterisk).
Asterisk c th c ci t trn bt k phn phi Linux, v vy chng ta c th s
dng Debian, Ubuntu, Mint, CentOS, RedHat, OpenSuse,. N cng c th c ci
t trong FreeBSD, h iu hnh MacOS v c mt s cng cho Windows, nhng
Linux l ni h tr y thc hin.
Asterisk em n cho ngi s dng cc tnh nng v ng dng ca h thng tng
i PBX v cung cp nhiu tnh nng m tng i PBX khng c, nh s kt hp
chuyn mch VoIP v chuyn mch TDM, l kh nng m rng p ng nhu cu
cho tng ng dng.
V mun cu hnh c asterick ta phi da trn tng i FreePBX. FreePBX l
phn mm m ngun m vit trn Web, nh chng ta bit asterisk khng cung cp cho
ngi s dng cu hnh h thng qua giao din ha, mun cu hnh asterisk khng
cch no khc l thc hin cc dialplan qua cc tp tin cu hnh do asterisk cung cp
ti th mc etc/asterisk. V d: mun cuc gi i theo lung iu khin nht nh no
th phi khai bo cc cu lnh bn trong tp tin extensions.conf. Ni chung vic cu
hnh asterisk v cng kh khn vi nhng ngi khng chuyn su v asterisk.
FreePBX ra i nh l mt cng c h tr cu hnh cho asterisk, FreeBBX c
thit k thn thin vi ngi s dng, cu hnh asterisk mt cch d dng qua giao
din ha trn nn web mt cch trc quan d hiu. Ngi s dng khng chuyn
cng c th cu hnh c asterisk.
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II. CI T ASTERISKNOW 3.0 V CU HNH CC
TNH NNG CN BN
1. CI T
c c mt my o asterick, u tin cn chun b file ISO ca
AsteriskNOW 3.0, chng ta c th ti v a ch:
http://www.asterisk.org/downloads/asterisknow
y chng ta s xy dng mt i bng my o trn VMWare nn ch cn
mt my o RAM t nht l 1GB, a o mount file ISO vo, cng khong
15GB. Nu ci trc tip trn my tht th cn chp file ISO vo a DVD hoc
USB ci t, cc bc tin hnh ging nh ci trn my o.
Tin hnh ci t:
Sau khi khi ng my o c gn file ISO, my s chy vo mn hnh
la chn cch thc ci. Chn phm 1 ci asterisk v FreePBX, phm 2
ci asterisk v khng c FreePBX. y chng ta xy dng mt tng
i asterisk da trn FreePBX nn ta chn phm 1 ci asterisk v
FreePBX.
Hnh 1: Giao din ci FreePBX
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Chn v tr ni gn nht ca bn:
Hnh 2: Chn v tr
Lp mt khu cho my ch: ti khon y l s dng ti khon qun
tr cho h thng Linux ROOT, mt khu l: 123456
Hnh 3: To mt khu cho my ch
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Chn cng: do l cng mi nn ta s chn Use All Space dng
ht cng.
Hnh 4: Chn cng cho my
Qu trnh ci t bt u
Hnh 5: Qu trnh ci t
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Su khi ci t hon tt, chon Reboot khi ng li my
Hnh 6: Reboot my o
Sau khi Reboot li h thng, n s cp cho chng ta mt a ch IP
Hnh 7: Mn hnh chnh ca Asterisk
Ta s dng a ch IP c cp trn truy cp vo asterisk thng qua
giao din Web. Chn FreePBX Administration bt u cu hnh cho
tng i
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Hnh 8: Mn hnh tng i FreePBX
Nhp user name v password mc nh l admin/admin ng nhp:
Hnh 9: ng nhp vo FreePBX
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Mn hnh chnh sau khi ng nhp: v y cng l giao din chng ta s
lm vic, cu hnh trn giao din FreePBX
Hnh 10: Giao din chnh ca FreePBX
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2. CU HNH
Hnh 11: M hnh tng i VoIP
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2.1. To s in thoi (user)
to s in thoi, ta vo mc Extensions:
Hnh 12: Ca s Extensions
Trong qun l s (extensions), do tng i mi ci t nn cha c s.
to s, ta chn loi thit b ti mc Device - y chn thit b SIP, sau
chn Submit
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Hnh 13: Device
Cn bn to mt s in thoi ta ch cn in thng tin nh sau: User 1
s in thoi l 1001, Display Name l 1001 (tn hin th) v mt khu l
abc123, sau chon Submit
Hnh 14: To user
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2.2. ng k s dng v thc hin cuc gi
Ta s dng mt phn mm SIP phone ng k s dng s in thoi
c ng k trn tng i. dy chng ta dng phn mm Express Talk
cu hnh ng k user 1 vi s in thoi l 1001: Vo mc Option Line
(phn mm ny h tr 6 Line), ta s chn Default Line Settings ng k
mu cho cc Line khc. Display Name l tn hin th cho ti khon, phn
server y ta s nhp a ch IP ca tng i PreePBX cung cp cho
chng ta, SIP number l s in thoi mun ng k, Password ta nhp mt
m ca s in thoi khi chng ta ng k trong phn Extensions:
Hnh 15: ng k cho Line 1
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Giao din chnh ca phn mm vi ti khon c ng k l 1001, n
hin th hp thoi cui cng:
Hnh 16: ng k thnh cng cho cc user
Ngoi ra, chng ta cn to thm cc s in thoi khc nh: 1002, 1003,
1004, ng k cng ging nh user 1.
Ta s ly user 4 c s in thoi l 1004 v ng k trn Express Talk
tin hnh gi 2 user (gi ni b). Dng my tnh th 2 ci t Express
Talk v tin hnh ng k Line nh my 1:
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Hnh 17: ng k user cho my 2
Kt qu cuc gi :
User 1 gi user 4:
Hnh 18: user 1 gi user 4
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User 4 gi tr li user 1:
Hnh 19: user 4 gi user 1
l phn chng ta gi ni b trong mt tng i, v mun gi ra mng
in thoi thng thng PSTN, ta cn phi mua mt ti khon gi l ti
khon Trunk, th chng ta mi c th gi c ra mng ngoi. V t mng
ngoi gi tr li vo trong l cng vic rt kh v khi chng ta mua mt ti
khon Trunk nh cung cp cho chng ta mt u s gi ra ngoi, v u
s khng c c nh nn chng ta khng th thc hin c cng vic
gi li vo trong tng i.
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2.3. Chc nng nhc ch
s dng chc nng nhc ch, ta vo mc Music On Hold:
Hnh 20: Music onHold
To mt th mc cha nhc ch, ta chn Add Music Category v nhp tn
th mc sau bm Submit Changes:
Hnh 21: To th mc nhc ch
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Ti ca s Music On Hold, vo th mc Nhacchodienthoai va to:
Hnh 22: On Hold Music
Chn tp tin (nh dang WAV) ri bm upload a bn nhc ch vo h
thng, sau khi upload xong bm Apply Config thao tc c hiu lc:
Hnh 23: Upload file m thanh
xa mt bi nhc ch upload ln, ta chn du tr (-) sau mi bi ht.
Mc nh nhc ch s pht bi ht u tin trong danh sch, ta chn Enable
Random Play nhc ch c pht ngu nhin. Tip theo, chon sang Tab
Applycations vo mc Fllow Me gn nhc ch cho cc user ty .
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Tip theo ta chn Flow Me gn nhc ch cho cc user:
Hnh 24: Flow Me
Trong Flow Me ta chn user cn gn nhc ch, y ta dng user 2 (1002)
gn cc bn nhc ch ti ln:
Hnh 25: Gn nhc ch cho user
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2.4. Thit lp tng i IVR
u tin ta v phn System Recordings a file m thanh c pht khi
gi vo tng i:
Hnh 26: System Recordings
Sau khi upload file nhc chng ta s save li, ta vo phn IVR v chn Add
New IVR, ti trang ny ta nhp tn IVR vo IVR Name, mc
Announment chn file m thanh va upload ln. Phn IVR Entries ta s cu
hnh cho cc phm khi gi vo tng i:
Phm 1: Nghe gii thiu v n
Phm 2: Gi n user 2 (s in thoi l: 1002)
Phm 3: Gi n user 3 (s in thoi l: 1003)
Phm 4: thc hin chc nng gi nhm (Ring Group)
Phm 0: Tt my
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Hnh 27: Cu hnh IVR
Tip theo , tao vo phn Extensions v to s my l 1900, s my ny s
khng ng k nh cc user to trn nn ta s ty chnh ti phn Optional
Destinations Not Reachable v chn IVR l IVR s c pht khi gi
vo s 1900, y ta chn tongdaiIVR va to, sau chon Submit
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Hnh 28: To s tng i
2.5. Kt ni hai tng i (Trunk)
Khi chng ta c sn mt tng i v chng ta mun st nhp thm mt
tng i khc vo. Mt tng i khc cng c c s h tng, th chng
ta khng th xa b ht c, lm nh vy s mt rt nhiu thi gian. Thay
vo chng ta s thc hin mt phng l Trunk 2 tng i vi nhau
bng SIP Trunk.
Trunk l mt ng mng o, gip kt ni cc h thng tng i vi nhau
cng nh cc dch v vin thng khc.
y mun kt ni hai tng i vi nhau, ta phi dng hai my o Asterisk
ring bit, hai my l:
Server 1: a ch IP l 192.168.43.206
Hnh 29: Server 1
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Server 2: a ch IP l 192.168.43.2
Hnh 30: Server 2
trn hai server chng ta to khong 3 user (Extensions), dng kt ni
v gi cho nhau. (cch to user xem phn to s in thoi).
Sau trn mi Server chng ta chn 1 user dng Trunk sang tng
i bn kia, user ny c gi l mt user ni b (hay cn gi l user lm
mu) dng lin lc vi tt c cc user khc c trong tng i. V khi to
mt user chng ta cng nn t chng mt cch nht thng v khng c
t ba bi, lm vy s rt kh qun l v sau.
server 1 , a ch IP l 192.168.43.206, cc user c t theo th t
l 1001, 1002, 1003 (1xxx).
Hnh 31: Extensions ca server 1
server 2 , a ch IP l 192.168.43.2, cc user c t theo th t l
101, 102, 103 (1xx).
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Hnh 32: Extensions ca server 2
By g chng ta s bt u cu hnh trn Server 1:
y mnh chn user 1 (1001) lm user ni b
Hnh 33: Tab Trunk
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Sau chn Add SIP Trunk:
Hnh 34: Add SIP Trunk
phn ny chng ta s cu hnh Trunk sang Server 2 (192.168.43.2), tab Trunk Name
ta s t tn l trunk-sv2:
Hnh 35: trunk server2
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Outgoing Settings l phn cu hnh rt quan trng chng ta Trunk sang Server 2
Hnh 36: Cu hnh Trunk Outgoing server 1
phn cu hnh trn chng ta thy c rt nhiu phn, nhng chng ta ch cn
cu hnh cc phn : host, user name, v secret (mt khu ca user). y chnh l phn
cu hnh chng ta gi sang server 2.
Ci a ch host chnh l a ch IP ca server 2 192.168.43.2. V chng ta
cng chn mt user bn server 2 lm user ni b, y chng ta chn user 101 lm
user ni b cho server 2. User 101 vi s in thoi l 101 v mt khu l abc123.
l phn Outgoing, khi m c cuc gi t server 1 (192.168.43.206) theo lut
i ra, th n s tm trong ci Trunk m chng ta to trn (trunk-sv2) sau n s
tm n ci a ch m chng ta cu hnh Trunk sang server 2 theo a ch host l
192.168.43.2 v trong ci host n s ly ci user 101 ca server 2 kt ni.
Khi m server 1 c user bn server 2 gi vo chng ta s cu hnh trong phn
Incoming Settings:
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Hnh 37: Cu hnh Incoming Settings server 1
Chng ta s ly user 1001 lm user ni b, th phn USER Context chnh l
ci user dng lm user ni b cho server1, mt khu l abc123. Cui cng ta chn
Submit Changes hon thnh cng vic cu hnh.
phn trn chng ta cu hnh cho server 1, bn server 2 chng ta cng
s cu hnh tng t nh server 1:
Chng ta cng to cc user cho server 2, sau chng ta cng to mt
ng Trunk nh server 1, nhng cch t tn th chng ta t l trunk-
sv1:
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Hnh 38: Add SIP Trunk
phn Outgoing Settings, chng ta s cu hnh Trunk sang server 1. a ch IP
ca server 1 l 192.168.43.206, bn server 1 chng ta chn trn, user 1001 l user
ni b, nn phn username chng ta s chon l 1001 vi mt khu l abc123.
Hnh 39: Cu hnh Trunk Outgoing server 2
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phn Incoming Settings, l phn gi vo cho server 2. Chng ta chon user
101 lm user ni b cho server 2, nn phn USER Context s l user 101, mt khu
ca 101 l abc123
Hnh 40: Cu hnh Incoming Settings server
V cui cng chng ta chn Submit hon thnh cu hnh cho server 2.
Nh vy l chng ta cu hnh xong cng vic l Trunk 2 tng i vi
nhau, nhng chng ta vn cha th gi 2 tng i vi nhau c v n ang
cn thit mt ci lut gi. By gi chng ta s to mt ci lut gi cho 2
tng i, vo phn Outbound Routes:
Hnh 41: Outboand Routes
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Sau chn phn Add Route
Hnh 42: Add Route
server 1 chng ta t tn l goi-sv2:
Hnh 43: Route Settings
Trong phn Dial Patterns that will use this Route l ci phn cu hnh gi sang
server 2, do server 2 chng ta t cc user l 101, 102, 103 nn chng ta s g l cc
k t sao cho n gn gng cc s in thoi trong user, y chng ta g 1xx.
Trong phn Trunk Sequence for Matched Routes chng ta tr n trunk-sv2
cu hnh trunk m chng ta va to trn. Cui cng chon Submit Changes hon
tt cng vc
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Hnh 44: Thao tc lut gi
bn server 2, chng ta lm tng t nh trn, ch cch t tn l khc vi bn
server1, phn Route Name chng ta t tn l trunk-sv1
Hnh 45: Route Settings server 2
Trong phn Dial Patterns that will use this Route ta g l 1xxx v bn server 1
cch t cc user l 1001, 1002, 1003.
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Hnh 46: Thao tc lut gi server 2
Trong phn Trunk Sequence for Matched Routes chng ta tr n trunk-sv1
cu hnh trunk m chng ta va to server 2. Cui cng chn Submit Changes
hon thnh.
Nh vy l chng ta hon thnh cng vic cu hnh Trunk hai tng i
vi nhau. V by gi chng ta s tin hnh thc hin cuc gi cho hai tng
i. y chng ta cng dng phn mm Express Talk ng k s in
thoi ca hai server gi vi nhau.
server 1 cc user l 1001, 1002, 1003. Chng ta c th ng k 1 hoc
nhiu user. Nhng khi tng i bn kia gi sang, ch c mt user hin th
l user dng lm user ni b: server 1 l 1001
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ng k cho 1001
Hnh 47: ng k cho 1001
ng k cho 1002:
Hnh 48: ng k cho 1002
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ng k cho 1003:
Hnh 49: ng k cho 1003
Cc user c ng k:
Hnh 50: ng k hon tt
bn server 2 chng ta lm tng t vi 3 user 101, 102, 103
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ng k cho 101:
Hnh 51: ng k cho 101
ng k cho 102:
Hnh 52: ng k cho 102
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ng k cho 103:
Hnh 53: ng k cho 103
Cc user c ng k cho server2:
Hnh 54: ng k hon tt
By gi chng ta s tin hnh gi hai tng i
Bn server 2 chng ta chn mt user bt k ca server 1 gi sang server 1:
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y ta chn user 1002
Kt qu: do user 1001 l user ni b nn khi gi tt c cc user trong server 1 th user
1001 s hin th trong cuc gi:
Hnh 55: Server 2 gi server 1
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Server 1 gi server 2: ta chn 102
Kt qu: bn server 2 101 l user ni b
Hnh 56: Server 1 gi server 2
Nh vy l chng ta hon thnh cc tnh nng quan trng trong Asterisk.
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CHNG III: TNG KT
Qua vic nghin c v VoIP, ti nhn thy c c hi v hng pht trin ca
n trong tng lai. VoIP gip cho cch doanh nghip gim chi ph cuc gi, gp phn
pht trin nn kinh t, to iu kin Vit Nam c nhng sn phm c ch nu c
u t v pht trin ng hng.
AsteriskNow l mt h thng gip chng ta xy dng mt tng i rt tt. Vic
cu hnh Asterisk cng kh n gin do s dng giao din Web FreePBX gip cho
ngi s dng c th d dng thit lp nhng kt ni in thoi analog bnh thng
vi in thoi IP. Asterisk l gii php hp l cho cc cng ty, doanh nghip mun
xy dng mt h thng in thoi ni b cng nh gim chi ph gi in ng di.
i vi bn thn, lm mt n chuyn nghnh ny em cng tm hiu rt
nhiu v cng ngh VoIP ny, do kin thc v kinh nghim nghin cu cn t nn em
cha th tm hiu su sc tt c c cc tnh nng cao cp khc ca VoIP cng nh cc
tng i h tr cho VoIP (FreePBX, Asterisk, Trixbox, Elastix,.). Vi vn kin thc
tm hiu c em ch dng li vic xy dng mt m hnh VoIP nh vi cc tnh
nng cn bn nh: gi ni b, gi ra mng ngoi (PSTN), thit lp tng i tr li t
ng, nhc ch,.
Nu c thi gian, cng vi nim am m v c s vt cht, hy vng trong thoi
gian ti em c th xy dng mt m hnh tng i VoIP ln hn v chuyn su hn
ca cng ngh ang rt pht trin hin nay.
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Bng k hiu cc t ting anh trong n
K HIU TN Y
VOIP Voice over Internet Protocol
UAC User Agent Client
UAS User Agent Server
SIP Session Initiation Protocol
IVR Interactive Voice Response
UDP User Datagram Protocol
PSTN Public Swiched Telephone Network
RTP Real Time Protocol
RTCP Real Time Control Protocol
TDM Time Division Multiplexing
FDU Frequency Division Multiplexing
PCM Pulse Code Modulation
TCP Transmission Control Protocol
SDP Session Description Protocol
MCU Mutilpoint Conference Unit
PBX Private Branch Exchange
UA User Agent
ARQ Admission Request
ACF Admission Confirm