AP3



TPDUTCP

49152 —65535

FTP
Telnet
SMTP
DNS
TFTP
HTTP
SNMP
SNMP(trap)

21
23
25
53
69
80
161
162
IP
socket API socket
UDPIP
UDP UDP


UDP 5100
5.2 UDP
UDP UDP IP UDP IP UDP
UDP UDP UDP
IP
IP
IP
UDP
UDP
UDP
——
00000000 00001111 → 15
00000100 00111111 → 1087
00000000 00001101 → 13
00000000 00001111 → 15
10010110 11101101 →
01101001 00010010 →

TCP
()TPDU
(64K,1500)
TCP
TCP
ARQ


TCP
TCP
TCP
IP
IP


——


——


——


—— 4 TCP TCP “” 32 4
——


——


——


ACK —— ACK 1 ACK 0
——


PSH (PuSH) —— TCP PSH = 1
——


RST (ReSeT) —— RST 1 TCP
——


——


——



——


—— 2 TCP 12
——


——


—— TCP MSSMSS TCP“ MSS ”
MSS (Maximum Segment Size)

—— 3 STCP (16 + S) S
——10 4 4
—— 5.6.3


P2 – P1 =

——
TCPIP
RFC29881/8
RTTD
RTTD
——
——
= 1001
L1 = 1501
L2 = 3501
R1 = 3001
R1 = 4501
——
A
B
A 101 200 200
A 301 400 100
A 1 100 300
A 401 500
A
A 501 600
A 600

Nagle

1

1

2

3

4

2

3

4

5

6

7

8

5

6

7

8

1



2

3

4



5

6

7

8






4Byte



——
cwndMSS
ACK
ssthresh ssthresh64
Slowstart algorithm
“”
2
4
6
8
10
12
14
16
18
20
0
0
4
8
12
20
24
22
16
“”
2
4
6
8
10
12
14
16
18
20
0
0
4
8
12
20
24
22
16
“”
2
4
6
8
10
12
14
16
18
20
0
0
4
8
12
20
24
cwnd 1 M1 M2
22
16
“”
2
4
6
8
10
12
14
16
18
20
0
0
4
8
12
20
24

cwnd 1 cwnd 2 4 4
22
16
“”
2
4
6
8
10
12
14
16
18
20
0
0
4
8
12
20
24
22
16
“”
2
4
6
8
10
12
14
16
18
20
0
0
4
8
12
20
24

cwnd ssthresh cwnd = 16
22
16
“”
2
4
6
8
10
12
14
16
18
20
0
0
4
8
12
20
24

ssthresh 12 24 1


ssthresh
——
RED
THmin THmin THmaxTCPRTTTHmax THmax=2×THmin
Lav=(1-δ)×Lav+ δ ×
p=Ptemp/(1-count ×Ptemp)count
Ptemp=Pmax ×(Lav-THmin)/(THmax-THmin)
LAV Thmin p = 0
LAV Thmax p = 1
THmin LAV THmax 0 p 1
0 pmax
5.8 TCP
——
x

ack = x 1 seq = y
SYN = 1, seq = x
——
ack = y 1
SYN = 1, seq = x


——
TCP



——



——
SYN0ACK1TCP


TCPFIN=1TCPFIN
TCP
——
TCP
FIN = 1, seq = u
seq = v
B A
FIN = 1, seq = u

TCP
FIN = 1, ACK = 1, seq = w, ack= u 1





FIN = 1, ACK = 1, seq = w, ack= u 1





——
seq = u + 1
FIN = 1, seq = u
FIN = 1, ACK = 1, seq = w, ack= u 1





FIN = 1, ACK = 1, seq = w, ack= u 1
FIN-
WAIT-1
CLOSE-
WAIT
FIN-
WAIT-2
LAST-
ACK


ESTAB-
LISHED
ESTAB-
LISHED
A
B



CLOSED
2MSL
A ACK B
“”A ACK 2MSL
——
TCP
TCP——
ACK
FIN, SEQ = u
FIN, ACK, SEQ = v, ACK = u + 1
ACK, SEQ = u + 1, ACK = v + 1
TIME_WAIT
CLOSE_WAIT
SYN_RCVD
ESTABLISHED