I Doan hang doiC)
Dd an tdt nghi¢n
42
Phtpn Van Ng(JC /Op: H07VTTD
mnh2. 6 Cac hang il(J'i cho cdc goi ilti.nh dilU va khong iltinh dilll
Vi cac g6i bi danh dftu co de) uu tien thftp nen khi thuc hien phai Iva chon d€ dam
bao dQ uu tien bang each ftn djnh J?p lich bang thong cho cac hang doi cua cac goi bi
danh dftu va khong bi danh dau. Hau qua la cac goi bi danh dftu den tnroc cac g6i khong bi danh dftu co th€ tim thfty be) l?p lich cua no d€ truyen dfin truce cac goi
khong bi danh dftu .. Cac goi bi danh dftu tao thanh tftt ca cac duong khac toi di~m cu6i
va ben nhan co th€ nhan duce cac g6i khong hQ'p l~. M~c du IP khong th\i:c hi~n ngan
ngfra cac goi s~p xep i?i tren m?ng, nhung di~u nay co th€ b6 qua vi h~u het cac giao
thi'.rc xuyen su6t khOng th€ thµc hi~n b~ng tay trong tmang hgp nay m<)t each hi~u qua
. Trong m?ng vi~c danh dftu duQ'c mong d9·i la se lam tang them cac goi co th€ bi tach
khoi hang, giai phap nay cung rftt kho khan. Cac router Joi ban d~u khong ct€ y den
chinh sach XU ly g6i khi phan lo?i cac g6i vao cac hang dQ'i, dam bao tftt ca cac goi trong lop Juu Jugng d~u dUQ'C d~t vao m<)t hang dQ'i belt chftp ca quy~n U'U tien tach goi. Ngu6'ng tach g6i cua m6i hang dQ'i dUQ'C xac dinh tren CO' so goi bj danh dftu ho~c khong. Thu?t toan tach g6i cua cac router Joi vi the ho?t d<)ng linh ho?t d6i voi cac goi
bj danh dftu, danh du9·c quy~n xu ly t~i m(rc bien.
Lenh di
Danh d.iu 11 Ko danh d.iu Ko danh d.iu 11 Danh d.iu
Lenh den
0 C6ngM C6ngM Hang dqi(bi danh dau)
Schedule Hang doifko danh d~u) I
~--~D 0 0
Phan loai C6ngN
them nguong bung n6 kep (mot nguong cao va mot nguong thap), neu mot goi bung
n6 vuot qua ngtrong thftp, cac goi den sau bi danh dftu va duce truyen di, neu bung n6
tiep tuc va vuot qua nguong bung n6 cao cac goi se bi tach khoi hang doi. Chinh sach 41i cac node phai b6 sung cac mire cua t6c de) goi den trung binh "cho phep't-toc de)
nay thftp hon t6c dQ cua cac goi da dUQ'C xac dinh la khong bi danh dftu Va cao hon
nguong ma cac goi co th€ bi tach.
Nhieu thuat toan co th€ duoc dua ra d€ cung cftp cac mire diroc danh dftu va tinh toan gia tri nguong. Du sao nguoi thiet ke mang d~t ra ke hoach sir dung luu luong bi
danh dftu a bien ciing dn d.n than khi hra chon cac router Joi. M6i quan tam chinh la kha nang s~p xep lai cac g6i bi danh dftu va khong bi danh dftu trong lop luu hrong .
Giai phap nay co th€ xay ra neu router loi su dung hai hang doi rieng biet cho cac goi
bi danh dftu va cac goi khong bi danh dau. Di~u nay duce mo ta nhu trong hinh ve :
Chmrng 2:KiRn trllc COS
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Phf1,tn Van Ng(JC /Op: H07VTTD
Hinh 2. 7 Router nguJn cho mfi-ng IP Best Effort
Khi giao <lien dau vao chip nhan cac g6i nr cac router khac, va (dua tren dia chi IP
cua m6i g6i) khoi dinh huong chuyen cac g6i toi giao dien dau vao phu hop. Sau d6
m6i giao dien sl'.r dung cac ca du k€t n6i d~c tnrng d~ truyen d§n g6i theo duong
truyen d§n toi router ti€p theo (hcac host). Khi router tin chac rfmg vung t~c nghen
tang them mot each khong thich hop, cac g6i co th~ bi tach hoac bi danh dau. Be'.) xir ly
cac g6i tren cua khoi dinh huong (lua chon giao <lien dfiu vao Va d6i ph6 voi viec t~C
nghen) duce di~u khien boi khoi quan ly.
Trong hinh ve tren, m6i router co mot khoi xu' ly trung tam CPU d~ xu ly tit ca cac
chirc nang dinh huong goi va quan ly. Trong cac router xuong s6ng co de'.) thuc thi cao,
kh6i dinh huong duce phan phoi thanh cac the k€t n6i nho mot ca du chuyen rnach
t6c de'.) cao hoac mot ban n6i da nang, Tuy nhien tit ca cac router co rn<'.)t chu6i cac
bu6c tna cac g6i phai qua khi da du9·c Xlr [y.
put lnpu
Out
put
Cap nhat ban tin T~p hop ban tin
nr cac router khac I-- Khfii quan Iy - tu cac router khac ..... t ~ (i Inpu . : put :. !
·.· Khfii djnh hunng : ..... ' Out
{\ r~ Inpu t : ~ put ~ ! ·.· ·.· Out Inpu Out
2. 4. Cac irng dung cua ki~n true CQS
D€ dinh huong cac g6i qua cac hop tiep theo mot each thich h<.YP cac router phai b6
sung them be'.) phan loai, hang doi va l~p lich. Ki€n true CQS cung dp cac d~c di€m
dinh huong khac biet d6. Them vao do, cac k€t n6i dn co phan du doan QoS cua minh
phu hop voi viec cung dp cua cac router thuc t€. Trong phan 3. 1 nay se gioi thieu v~
mot router co QoS va kien true CQS (router nay duce goi la router nguon), viec xay
dung cac dich vu end-to-end vf d1,1 nhu DiffServ va JntServ.
2. 4. 1. Router nguf>n
Mot router nguon chi co mot vai khdi clnrc nang ca ban sau:
• Cac giao <lien
• Kh6i dinh huong
• Kh6i quan ly
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Phtpn Van Ng(JC /Op: H07VTTD
Ngay nay QoS da la mot vAn de rAt quan trong, vi the khi cac router giri cac g6i thi kh6i xir ly dinh huong dn phai tinh toan cac gia tri dn thiet. Nhin chung mdt g6i khi truyen di phai qua ba giai dean chinh sau:
• Phan loai va truy tim FBI (tao dinh dang g6i tai giao dien dfiu vao ). FBI (Forwarding Information Base) la mot bang truy tim thong tin quyet dinh su dinh huong cua mot router (dt\ giri cac g6i). V6'i m6i dia chi IP, viec tim mot tien t6 dai nhAt phu hop duce thuc hien qua FIB. Neu mot gia tri phu hop duce tim thay, dfiu vao tuong ung se cho biet khdi dinh hirong ma giao dien dfiu ra co tht\ nhan cac g6i; neu cac gia tri phu hop khong duce tim thAy, g6i d6 se bi tach. Noi dung cua FBI phan anh trang thai hien tai cua cac topo IP vay quanh cac router nhir viec xac dinh boi cac giao tlurc dinh tuyen IP vi du OSPF (Open Shortest Path First)-giao thirc tim duong dfin dfiu tien ngan nhAt hoac BGP4 (Border Gateway Protocol version 4)-giao thirc cong bien version 4 dang chay tren khoi quan ly.
• Chinh sach va danh dAu (tac dong nguoc lai n€u g6i khong den duce khung thoi gian thich hop)
• Quan ly hang doi va l?p lich (dt\ dinh huong cac g6i theo cac qui tic dinh hinh tuyen hoac dinh hinh luu luong hoac tach g6i theo cac qui tic dieu khien tic nghen)
Giai dean phan loai cac g6i tao thanh mot kh6i cho viec xir ly cac goi den sau cua cac router. Mac du, hfiu h~t cac khoi duoc sir dung dt\ tao thoi gian xu' ly rieng biet (chinh sach, danh dau, quan ly hang doi va l?p lich), mot vai kh6i them vao co tht\ duce sir dung d€ sira d6i quy€t dinh dinh huong. Vi du, mot router tien ti€n phai duy tri duce cac FIB (mo ta cac cay co duong di ngan nhat tren co so cac ma tran khac nhau) va lua chon chung nho viec sir dung thong tin khac trong phan tieu de g6i (vi du dia chi nguon cua g6i). Hay it nhfrt ding la dong m<)t quan h~ thuang t6n t?i gifra m<)t khf>i Clla g6i (duqc tbiet l?p qua bQ phan lo?i) Va "lop" CUa no (nhu da thiy tren CO' SO end-to-end). Hinh ve sau phiin anh don gian dng tic nghen se chic chin chi xay ra t?i giao di~n dfiu vao. Kien tn'.1c CQS duqc yeu du t?i tit ca cac dit\m tic nghen, trong m(H m?ng ho~c trong m<)t router. Kien tn'.1c cl'.ia m<)t router ciing c6 tht\ c6 6 hen trong cac dit\m tic nghen (vi d\l t?i dfiu vao CUa khf>i chuyt\n ill?Ch ho~c t?i bang nf>i da nang) va cling cung dp cac hang dqi va cac be) l?p lich khac nhau cho tit ca cac dit\m
tic nghen d6.
Cac d?i ly router cung dp cac san phftm khac nhau cl'.ia h9 tren co s6 c?nh tranh gia
ca. Cac router Best Effort dfiu tien se tim thong tin tren FIB da gay ra hi~n tuqng nghen
c6 chai. Du sao, trong nhfrng nam g§n day, cac thu?t toan cho vi~c tra cl'.ru thong tin tren FIB da pbat trit\n qua nhanh v6'i hang tri~u thong tin tra cl'.1·u trong m<)t giay.
Chmrng 2:KiRn trllc COS
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Ph{ltn Van Ng(JC !Op: H07VTTD
ffinh 2.8 Phan lofli, quiin ly hang il(/i va l~p ljch cho Per-hop
lP payload IP header ~ I I I I I Ph~l~ig~ ~j j _ FIB FIB Quan ly hitngdqi, l~p l[ch Kh6i chuy~n lTI\!Ch Chinh sach vii
danh d~u Cacbang
djnh lm&ng
2. 4. 2. Cac dich V\l ti'ng dung
a. Djch V\l Best Effort
Day la kieu rnang hien hanh dang duce str dung, Hfru h€t cac ung dung dtr lieu d~u
duoc v~ hanh theo each nay. Chung doi dli' lieu d€n va Xlr ly chung cang sorn cang t6t
ngay khi nhan duoc. Lap dich vu nay se h6 tro them cho lap hru luong thoi gian thuc.
Cac (mg d\111g co th€ lira chon str dung mot trong cac lap dich V\1 do, va khi chung thay
khong th€ ch§p nhan duce do tr~ do thi co th€ sir dung mot trong cac lap dich Vl,1 khac.
Lap dich vu best effort thi khong co TSpec hoac RSpec, khong co dam bao m mang va
mang khong thuc hien b§t kl di~u khi~n dp phep nao. Cac mang ki~u nay khong cung
dp b§t kl mot tinh nang d~c biet nao d~ khoi phuc lai cac goi bi mAt hoac bi hong. Cac
dich cu duoc cung dp boi cac M thong dfru cudi.
Trong chcng giao thirc TCP/IP thi TCP cung dp cac dich vu dam bao trong khi IP
cung dp kieu truyen Best effort (khong c6 dam bao ), n6 se c6 gang truyen cac g6i d~n
dich nhung khong co clnrc nang khoi phuc lai cac g6i bi m§t hay truyen sai. Bo giao tlnrc Internet truce day chi bao gom giao tlnrc TCP/IP. Trong qua trinh phat trien thi cac nha thi~t k~ da nhan ra tfrm quan trong cua thoi gian truyen hon la do tin cay truyen. N6i each khac la quan tam toi t6c do hon la viec khoi phuc cac g6i. Trong kieu
truyen voice, video thoi gian thuc thi mot s6 goi bi mat CO th€ bo qua dU'Q'C boi viec
khoi phuc lai c6 th~ tao ra phfrn tieu d~ qua 16'n lam giam hieu nang cua mang. D~
cung cap loai hru hrong thi TCP da duoc t6 chuc lai trong TCP, IP, UDP. Cac dich vu
chuyen g6i va danh dia chi co ban trong lap mang duce thuc hien bo: IP. TCP, UDP
n~m 6 16'p truyen tai, phia tren cua IP. TAt ca d~u sir dung dich V\1 cua IP, UDP la mot
phien ban cua TCP chap nhan cac dich vu Best effort cua IP. Cac img dung c6 th~ sfr
FIB out put ill put Chmrng 2:KiRn trllc COS Dd an tdt nghi¢n
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Pham Viin Ngoc lop: H07VTTD
* Khdi nifm
Cau hoi d?t ra la tai sao ta dn phai phat trien ki~u mang moi cho de ung dung dich
vu moi phat trien tren mang. Mang kieu best effort khong con phu hop voi cac kieu dich vu moi nhu: thoai, video yeu du d(l tr~ nho. Thong thuong d6i voi de ung dung
Hink 2. 9 Chuc ruing cua cdc tJng trong me.mg Best Effort
Trong 16p v~t ly hoac 16p mang cac Frame co th~ bi loai bo, trong 16p mang cac
router bi t~c nghen c6 th~ loai bo cac g6i.
TCP la mot dich vu truyen dli" lieu tin c~y duce cac h~ thong d~u cu6i st'.r dung d~
khoi phuc lai de g6i da bi loai bo trong mang trong tnrong hQ"P c6 t~c nghen xay ra, hay bi loai bo boi chinh n6 khi b9 dem bi d~y. Trong mang cac g6i ciiug co th~ bi loai bo nham muc dich bao hieu t~c nghen cho phia nguoi giri biet, Khi co g6i bi mat trong
mang thi phia thu se giri ban tin thong bao khong nhan duce g6i d6 cho phia giri biet
d~ gui lai g6i. Ca ch~ nay goi la ca che di~u khien t~c nghen, ca ch~ di~u khien luong.
b. Djch V\l tich hop lntServ (Integrated Service)
Dung tnroc nhu du ngay cang tang trong viec cung dp cac dich ~1 tho i gian thuc
(thoai, video) va dich vu bang rong (da phuong tien) djch vu tich hop IntServ da ra
doi, Day la sir phat trien cua mang IP nham d6ng thoi cung dp dich ~1 truyen thong
116 Ive t6i da va cac dich vu thoi gian thuc.
Appllcatian Application ~tation Ple:lentati.o:n Session <ActivedWogtotnckdala~ Sessian 'll'amport '&ansport
Network Network ~I~~ Network Network Data link Data link Datagram Dat.alink Data link
could be
Physical Phy5iall lost or Phyaiall Physical delayed
Router Router
FJ 11111111 tj r , r , -
dung UDP khi khong dn cac dich vu cua TCP. D6i voi de dich vu Best effort viec loai bo de g6i c6 th~ chap nhan duce do viec khoi phuc duce xir ly boi cac dich vu
khac.
Chmrng 2:KiRn trllc COS
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Phtpn Van Ng(JC /Op: H07VTTD
thoai thi de) tr~ <150 ms la thoa man, do d6 voi cac g6i duoc truyen di lau hon 150 ms
thi se bi loai bo. Di~u nay khac biet so voi cac irng dung truyen thong. Cac img dung
da phuong tien co cac tham s6 va cac yeu du khac biet hon so voi irng dung truyen
thong, Cac irng dung thoi gian thuc moi nay it dan h6i va pham vi chiu anh hirong cua thay d6i de) tr~ it hon. Khi kibt n6i xay ra t~c nghen thi viec gift duoc chat hrong thoai va video la r~t kh6, d6ng thoi chung khong th€ thfch nghi duce voi t~c nghen, di~u nay d~n dibn viec gioi han bang thong tham chi khong th€ truyen duoc g6i.
Muc dich cua b~t ki mang nao la t6i da hoa hieu nang cua cac ung dung hay noi each
khac la phai thoa man duce cac yeu du dich vu. D€ co th€ h6 tro duce cac ung dung
moi nhu voice, video thi mang phai h6 tro duoc cac irng dung da phuong tien moi bang viec dam Mo duce cac yeu du cua dich vu. Nibu mang chi cung dp duoc mot 16-p dich
vu best effort thl that kho d€ dap irng duoc cac yeu du cua cac dich vu, do do mang
phai cung dp duce da 16-p dich vu thi rnoi h6 tro duce cac dich vu nay t6t duce. Viec tron giita cac 16-p dich vu voi cac irng dung phai dua tren yeu du cua dich vu.
Nibu mang hoan toan hra chon mc)t 16-p dich vu d€ phu thuoc ung dung thi ta chi dn
h6 tro mot 16-p dich vu gioi han, De\ co cac ung dung yeu du dich vu ma no thuc hien
mot each ro rang thi mang phai co lira ch911 duce 16-p dich vu, Ngoai ra viec quyet dinh xem trong mang co h6 tro di~u khien dp phep hay khong cling la mot cau hoi kh6. Nibu khong c6 chi dinh dp phep thi chung khong th€ phan djnh ro du9·c cac djch Vl,l va m?ng khOng th€ chi ro duqc cac yeu d.u U'ng dl,lng duqc cung dp. Di~u khi~n dp phep dtr()'C yeu du hi~u nang Cua CaC dich Vl,l th(yj gian thl,l"C phai duqc Slr dl,lng tfJi da bftng vi~c lo?i b6 di cac yeu du cu cua Iu6ng lm1 luqng m6i Do d6 cac dich Vl,l
Internet ma rc)ng phai plwc vi,1 duqc cac i'.rng dl,lng nlwy v6'i de) tr~ biing vi~c cung dp da 16-p dich Vl,l va vi~c dam bao cac tham s6 bai di~u khit\n dp phep.
Cach Xlr ly vi~c nay la phat tri€n them cac ki~u m?ng cho yeu du cua cac djch Vl,l m6'i. M?ng tfch hqp duqc dua ra cling vi ml,lc dich d6 .
*Ctic yeu c&u cua djch V![ IntServ
• Tai nguyen phai duqc quan ly ro rang d€ thoa man cac yeu du cua djch vi,1
• Dich Vl,l dam bao cho dich Vl,l thai gian thl,l"C khong th€ th\t'C hi~n duqc ma khong c6 sv d~t tnr6'c.
• M~c du c6 cac U'ng d\mg c6 th€ thfch nghi dc)ng v6i sv thay d6i cua m?ng thl
v~n phai thiibt l~p bien cho de) tr~ d§u cu6i.
• Vi~c chia xe tai nguyen th6ng ke gili'a luu lu9·ng c6 tinh thai gian thvc v6'i luu luqng phi thai gian thvc cung duqc thi,rc hi~n thong qua ca so lwn t§ng cua m?ng thai gian thi,rc. N6i each khac thi m:;mg Internet duqc sl'.r di,mg nhu
CO' SO h? t§ng cbo cbo vi~c trny~n d~n ca cac dich Vl,l CO tinh thai gian thl,l"C
lfrn phi thai gian thi,rc.