-2006-6-10

TCPTCPNagle

()TCPTCPTCP

TCP ()

TCPTCPTCPTCP

1PCA(C)PCB(S)SYNSYN+ACKSYNC/SServerClient TCP

TCPW.Richard Stevens TCP/IP 20004

24TCPFlags SYNACK Flags FINACK

3--MSS(Option)

Maximum Segment Size +--------+--------+---------+--------+ |00000010|00000100| max seg size | +--------+--------+---------+--------+ Kind=2 Length=4Maximum Segment Size Option Data: 16 bits02 04 05 b4

3(MTU) 1500: 46AST

35MSS = MTU IP TCP =1500 - 20 - 20 = 1460 --3TCP --5,3IPTCP=( IP(16 bits) - IP(4 bits)*4 - TCP(4 bits)*4 )IPTCP32bits(4bytes)

tcpsndwnddata.txt,

3 4 5

0 1 2 3 4 5 6 7 8 9 n-1 n

3 4 5 6 7 8

= min[cwnd, rwnd]

0 1 2 3 4 5 6 7 8 9 n-1 n

3 4 5 6 7 8 9 n-1

rwnd

3 4 5

6(1)

0 1 2 3 4 5 6 7 8 9 n-1 n

0 1

= min[cwnd, rwnd] = 2*MSS

2*MSS

0 1 2 3 4 5 6 7 8 9 n-1 n

0 1

= min[cwnd, rwnd] = 2*MSS

0 1 2 3 4 5 6 7 8 9 n-1 n

2 3 4

= min[cwnd, rwnd] = 3*MSS

3*MSS

0 1 2 3 4 5 6 7 8 9 n-1 n

2 3 4

= min[cwnd, rwnd] = 3*MSS

4

0 1 2 3 4 5 6 7 8 9 n-1 n

4 5 6 7

= min[cwnd, rwnd] = 4*MSS

3*MSS

0 1 2 3 4 5 6 7 8 9 n-1 n

4 5 6 7

= min[cwnd, rwnd] = 4*MSS

6 7

0 1 2 3 4 5 6 7 8 9 n-1 n

6 7 8 9

= min[cwnd, rwnd] = 5*MSS

3*MSS

6(3) 6(3)DATAACK

6(3)DATADATADATA

3 4 5

0 1 2 3 4 5 6 7 8 9 n-1 n

3 4 5 6 7 8 9 n-1

rwnd

3 4 5 6

0 1 2 3 4 5 6 7 8 9 n-1 n

3 4 5 6 7 8 9 n-1

rwnd

6(3)ACKACKACK

3 4 5

0 1 2 3 4 5 6 7 8 9 n-1 n

3 4 5 6 7 8

= min[cwnd, rwnd] = 6*MSS

5

0 1 2 3 4 5 6 7 8 9 n-1 n

5 6 7 8 9 n-1

= min[cwnd, rwnd] = 7*MSS

ACKACKACKDATADATADATA6553565535ACKcwndrwnd = + min [ cwnd , rwnd ]

6(2)

6(2)1/2

0 1 2

0 1 2 3 4 5 6 7 8 9 n-1 n

rwnd = 65535

3 4 5

6 7 8 9 n-1

0 1 2 3 4

0 1 2 3 4 5 6 7 8 9 n-1 n

rwnd = 65535

5 6 7

8 9 n-1 n

6(2)2/2

9 n-1

0 1 2 3 4 5 6 7 8 9 n-1 n

rwnd = 5000

0 1 2 3 4 5 6 7 8

n

0 1 2 3 4 5 6 7 8 9 n-1 n

rwnd = 0

6(2)6553565535

X1

6(4)6(2)

n n+1 n+2 n+3 n+4 n+5 n+6 n+7 n+8 n+9 2n-1 2n

n n+1 n+2 n+3

rwnd = 5840

6(4)

0 1 2 3 4 5 6 7 8 9 n-1 n

0 1 2 3 4 5 6 7 8

rwnd = 65535

7Keep-AliveKeep-Alive

11(1)

NagleMSSNagleNagle

11(2)X>=1*MSS

PPT

8(1)sthread=65535snd_cwnd=2RFC2581snd_cwnd*1460< ssthread snd_wnd = min [ cwnd , rwnd ]rcv_wnd=65535snd_cwnd*1460=2920snd_wnd = min [snd_cwnd , rcv_wnd] = snd_cwnd*1460=2920snd_wnd_right = snd_wnd_left + snd_wnd

8(2)ssthread=65535ACKsnd_cwnd1snd_cwnd*1460< ssthreadACKsnd_cwnd1MSSRTT

8(2) 2DATA3DATAsnd_wndDATA1ACK2DATAACKsnd_wnd2DATAACKcwnd1cwndrwndsnd_wndcwndsnd_wnd11DATA3DATA

8(2)2DATA3DATA 2DATAACK

--snd_wnd = min [snd_cwnd , rcv_wnd] = 2*MSSsnd&noAck_data = 0*MSSuseable_wnd = 2*MSS1MSS

0 1 2 3 4 5 6 7 8 9 n-1 n

0 1

= min[cwnd, rwnd] = 2*MSS

2*MSS

--12DATAsnd_wnd = 2*MSS snd&noAck_data = 2*MSSuseable_wnd = 0*MSS1ACKsnd_wnd = snd_wnd_old + 1*MSS = 3*MSS snd&noAck_data = snd&noAck_data_old 2*MSS = 0*MSSuseable_wnd = 1*MSS + 2*MSS = 3*MSS

0 1 2 3 4 5 6 7 8 9 n-1 n

0 1

= min[cwnd, rwnd] = 2*MSS

0 1 2 3 4 5 6 7 8 9 n-1 n

2 3 4

= min[cwnd, rwnd] = 3*MSS

3*MSS

--23DATAsnd_wnd = 3*MSS snd&noAck_data = 3*MSSuseable_wnd = 0*MSS1ACKsnd_wnd = snd_wnd_old + 1*MSS = 4*MSS snd&noAck_data = snd&noAck_data_old 2*MSS = 1*MSSuseable_wnd = 1*MSS + 2*MSS = 3*MSS

0 1 2 3 4 5 6 7 8 9 n-1 n

2 3 4

= min[cwnd, rwnd] = 3*MSS

4

0 1 2 3 4 5 6 7 8 9 n-1 n

4 5 6 7

= min[cwnd, rwnd] = 4*MSS

3*MSS

--33DATAsnd_wnd = 4*MSS snd&noAck_data = 4*MSSuseable_wnd = 0*MSS1ACKsnd_wnd = snd_wnd_old + 1*MSS = 5*MSS snd&noAck_data = snd&noAck_data_old 2*MSS = 2*MSSuseable_wnd = 1*MSS + 2*MSS = 3*MSS

0 1 2 3 4 5 6 7 8 9 n-1 n

4 5 6 7

= min[cwnd, rwnd] = 4*MSS

6 7

0 1 2 3 4 5 6 7 8 9 n-1 n

6 7 8 9

= min[cwnd, rwnd] = 5*MSS

3*MSS

--43DATAsnd_wnd = 5*MSS snd&noAck_data = 5*MSSuseable_wnd = 0*MSS1ACKsnd_wnd = snd_wnd_old + 1*MSS = 6*MSS snd&noAck_data = snd&noAck_data_old 2*MSS = 3*MSSuseable_wnd = 1*MSS + 2*MSS = 3*MSS

--n3DATAsnd_wnd = (n+1)*MSS snd&noAck_data = (n+1)*MSSuseable_wnd = 0*MSS1ACKsnd_wnd = snd_wnd_old + 1*MSS = (n+2)*MSS snd&noAck_data = snd&noAck_data_old 2*MSS = (n-1)*MSSuseable_wnd = 1*MSS + 2*MSS = 3*MSS

8(3)Xssthread=max(cwnd/22*MSS)RFC2001cwnd=1 ssthreadcwndACK1snd_cwnd*1460 ssthread

9RTO KarnRTO = 2 * RTO_old

9(1)RTORTTRTTACKDATAACKKarn

9(2)RTO1RTO2RTTRTTACKRTTRTOKarnRTTACKACKACKRTTRTOKarnRTTRTT

9RFC1122RTTRTORTT=0RTO=3Linux10SRTT=0RTO=300RTO20012020 12000LinuxRTT808

10ACKACKDATAACK

10(1)X5X6X7

10(2)ACKssthread=max(cwnd/22*MSS)RFC2001cwnd= min [cwnd , + + 3]RTTRTOACKRTTRTO

10(3)ssthreadcwnd= min [cwnd , + + 3]ACKACKssthreadcwndRTTSMSS*SMSS/cwndsnd_cwnd*1460> ssthread

4.2 TCPTCP ACKTCP

TCP

shutdown()

3 4 5

0 1 2 3 4 5 6 7 8 9 n-1 n

3 4 5 6 7 8

= min[cwnd, rwnd]

0 1 2 3 4 5 6 7 8 9 n-1 n

3 4 5 6 7 8 9 n-1

rwnd

3 4 5

63DATAACK65535TCP