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Transcript 
ELEN 602 Lecture 15
• More on IP
• TCP
1
TCP Streams
Application
Application
byte stream
byte stream
segments
Transmitter
Receiver
Send buffer
Receive buffer
ACKs
2
TCP end-to-end Flow control
Transmitter
Send Window
Receiver
Receive Window
Slast+Wa-1
...
Octets
transmitted Slast
and ACKed
...
Srecent
Rlast
Rlast+WR+1
...
Rnext Rnew
Slast+Ws-1
Slast oldest unacknowledged octet
Srecent highest-numbered transmitted octet
Slast+Wa-1 highest-numbered octet that
can be transmitted
Slast+Ws-1 highest-numbered octet that
can be accepted from the application
Rlast highest-numbered octet not yet read
by the application
Rnext next expected octet
Rnew highest numbered octet received
correctly
Rlast+WR-1 highest-numbered octet that
can be accommodated in receive buffer
3
TCP Segment
0
4
10
16
Source Port
24
31
Destination Port
Sequence Number
Acknowledgement Number
Header
Length
Reserved
UAP R S F
R C S S Y I
GKH T NN
Checksum
Window Size
Urgent Pointer
Options
Padding
Data
4
TCP Pseudoheader
0
8
16
31
Source IP Address
Destination IP Address
00000000
Protocol = 6
TCP Segment Length
5
3-way Handshake for connection establishment
Host A
Host B
6
Sequence numbers
Host A
Host B
Delayed segment with
Seq_no = n+2
will be accepted
7
TCP application example
Host A (Client)
socket
connect (blocks)
Host B (Server)
socket
bind
listen
accept (blocks)
connect returns
write
read (blocks)
accept returns
read (blocks)
read returns
write
read (blocks)
read returns
8
TCP Window control
Host A
Host B
t0
t1
t2
t3
t4
9
TCP Header overhead
Data
20 bytes of
TCP header
20 bytes of
IP header
TCP
Header
IP
Header
10
Connection Termination
Host A
Host B
Deliver 150 bytes
11
TCP State
diagram
CLOSED
passive open,
create TCB
applic.
close
LISTEN
SYN_RCVD
applic.
close,
send
FIN
receive SYN,
send ACK
SYN_SENT
applic. close
or timeout,
delete TCB
ESTABLISHED
CLOSE_WAIT
FIN_WAIT_1
CLOSING
LAST_ACK
FIN_WAIT_2
TIME_WAIT
2MSL timeout
delete TCB
12
Routing for mobile hosts
Foreign
network
Home
network
Foreign
agent
Mobile
host
2
Home
agent
Internet
3
1
Correspondent
host
13
IP to IP Encapsulation
Outer IP Header
IP Header
IP Header
IP Payload
IP Payload
14
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