d ng ng P2P
Chia s file ngang hng
V d
A ch y m t ng d ng chia
s file trn my tnh
k t n i vo Internet
tm ki m bi ht Hello
ng d ng hi n th cc my
(peer) c ch a m t copy
c a bi ht .
A ch n m t my trong s
, B.
File c truy n t my B
n my A: HTTP
khi A ang load file, cc
my khc c th copy t
A
A v a l client, v a l
server.
T t c cc my c th l
server = Tnh m r ng
cao!
P2P: Th m c t p trung
Phin b n g c thi t k ki u
Napster
My ch ch a
th m c t p trung
1) Khi m t my k t n i vo,
n s khai bo:
B
1
peers
1
IP address
n i dung
2) A tm ki m Hello
3) A yu c u file t B
3
1
2
1
A
P2P: H n ch c a th m c t p trung
Tnh ch u l i
Hi u nng
B n quy n: s b truy t
Chia s file l phn
tn song thng tin
v n i dung l t p
trung
Query flooding: Gnutella
hon ton phn tn
khng c my ch t p
trung
giao th c public
c nhi u phin b n
client Gnutella cng ci
t giao th c ny
overlay network: th
X v Y c m t c nh
n u gi a chng c m t
lin k t TCP
Cc my ang ho t
ng v cc c nh t o
nn th
c nh: lin k t logic
thng th ng c t hn
10 lin k t cho m i
peer
Gnutella: protocol
Thng i p yu c u c qu ng b
trn t t c cc c nh
Thng i p c chuy n ti p
QueryHit
s c g i tr v theo ng ng c l i
Q
y
er
u
Q
t
Hi
y
er
u
Query
QueryHit
Tnh m r ng:
Flooding c gi i h n
Qu
er
y
File transfer:
HTTP
Query
QueryHit
Qu
ery
So snh ki n trc client-server v P2P
V n : Th i gian g i m t file t i N my
tnh khc?
us: bng thng upload
c a server
Server
ui: bng thng upload
us
File, kch
th c F
u1
d1
u2
c a client/peer i
d2
di: bng thng upload
c a client/peer i
dN
uN
M ng
(d th a bng thng)
Client-server: th i gian chia s file
Server
server l n l t g i
N copies:
NF/us
client i m t F/di
download
F
us
dN
u1 d1 u2
d2
Network (with
abundant bandwidth)
uN
Th i gian g i t i N clients = dcs = max { NF/us, F/min(di) }
i
T tuy l n tnh v i N
(v i N l n)
P2P: th i gian chia s file
Server
server g i m t copy:
F/us time
client i m t F/di t i
xu ng
NF bits ph i c t i
xu ng (t ng c ng)
F
us
dN
u1 d1 u2
d2
M ng
(Gi s khng b t c)
uN
t c upload cao nh t c th (gi s
t t c cc nt g i cng cc o n file t i
cng m t my): us + ui
i=1,N
dP2P = max { F/us, F/min(di) , NF/(us + ui) }
i
i=1,N
So snh ki n trc Client-server, P2P
Minimum Distribution Time
3.5
P2P
Client-Server
3
2.5
2
1.5
1
0.5
0
0
5
10
15
20
N
25
30
35
P2P Case Study: BitTorrent
Chia s file P2P
tracker: tm t t c cc my
trong torrent
l y danh
sch my
trao i file
peer
torrent: nhm cc my
chia s cng m t nhm
file
BitTorrent (1)
file c chia thnh 256KB (chunks).
m t my tham gia vo torrent:
khng c chunks, nhng s tch ly d n theo th i gian
ng k v i tracker l y danh sch cc my v connect
n cc my bn cnh
khi download s ng th i upload n cc my khc .
cc my c th gia nh p/r i b m ng
Khi my l y file xong, n c th r i m ng ho c ti p t c
tham gia chia s
BitTorrent (2)
L y chunks
T i m i th i i m, cc my
khc nhau s c cc o n
file khc nhau
th ng xuyn h i cc my
bn c nh.
A tm cc o n cn thi u
rarest first
G i chunks: Bnh t- bnh quy
A g i cc o n file t i top 4
my cho A v i t c cao
nh t
nh gi l i top 4, c 10
secs
Kho ng 30 secs: ch n ng u
nhin 1 my khc v g i
o n file
cho php cc my m i
tham gia vo top 4
P2P Case study: Skype
P2P (pc-to-pc, pcto-phone, phone-topc) Voice-Over-IP
Skype
(VoIP)
login server
IM
Giao th c ng d ng
ring
M hnh phn c p
Skype clients (SC)
Supernode
(SN)
Skype: thi t l p cu c g i
User kh i t o Skype
SC ng k v i SN
Danh sch SNs
SC ng nh p
Skype
login server
Call: SC lin l c v i SN,
g i ID ng i c g i
SN lin l c v i SNs khc
tm ID c a ng i kia,
sau tr l i cho SC
SC lin l c tr c ti p v i nhau, qua TCP