TCP

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TCP
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Todays topics

• TCP
• Functions provided by TCP
• TCPs error recovery
• TCPs congestion control
• TCP performance analysis
• Application Layer
• DNS
• FTP, Telnet, WWW browsing, email
• Intranet Extranet

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TCP is a connection for the two end hosts
A
B
Full duplex connection
TCP
TCP

• Connectionless IP network (not aware of TCP
  connection)

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Functions provided by TCP

• Clocks
• Buffer status
• Sequencing packets
• Duplication reminder
• ACK generate
• Retransmit lost packets (reliable service)
• Adapt transmission speed (congestion control)

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Connection established
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TCP Sliding window
Sender side (in bytes) 17 18 19 20 21 22 23 24
25 26 27
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TCP header
Flags URG ACK PSH RST SYN FIN
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UDP Header
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TCP Tunnel
If the sender launcher a new packet every time it
receives an ACK, then it will deliver data at
exactly the same rate of the bottleneck link.
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TCP bandwidth as a function of Window Size and RTT

• TCP BW WS/RTT

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Delayed ACK

• Suppose that delayed ACK is set. When does the
  receiver send ACK upon receiving a packet?
• There is a data packet to send
• 200ms expires
• Receiver buffer increased by 2 segments (Thus one
  ACK is send for every other packet received)
• Out of order packet received

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Slow start through the use of congestion window

• Sender wants to be conservative, I.e. not to send
  a whole window-worth data
• At the beginning of a new connection
• After a packet loss
• This is called slow start, it uses a advertised
  window and congestion window.

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TCP throughput

• TP win/RTT, winmin (adv_win, cwnd)
• RTT includes propagation and queueing delays
• Bandwidth-Delay product link_rate 2propgation

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????????TCP??

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CR(????X)
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CR(????X)
CC(????Y ??X)
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?????TCP?UDP
???????Internet?

• UDP(User Datagram Protocol)
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• TCP(Transport Control Protocol)
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TCP??

• TCP???????????
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• TCP??????
• 1.???????TCP???????????????,?????????????????????
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TCP?
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TCP?????

• 2. ????TCP???????????????????????,????????
• 3. ????????????,????????????????????????????

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1 2 3 4 5 6 7 8 9
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TCP/IP?????????
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TCP/IP??????

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• ?????????Internet?????????????