Data Transmission flow using TCP protocol

Declaration
Reference: Andrew S. Tanenbaum - Computer Networks
• This Lecture Material is prepared for
Delivering Data Transmission by ML
• Notes were taken from Text Book: “Andrew
S. Tanenbaum - Computer Networks”
•
5/7/2024 1

5/7/2024 Reference: Andrew S. Tanenbaum - Computer
Networks
2
Outline
Transmission Control Protocol

Networks
3
Transport Layer 1/2

Networks
4
Transport Layer 2/2
Process-to-process delivery

Networks
5
Transport Layer Addressing
Addresses
•Data link layer  MAC address
•Network layer  IP address
•Transport layer  Port number (choose among multiple
processes running on destination host)

Networks
6
Port Numbers
•Port numbers are 16-bit integers (0  65,535)
Servers use well know ports, 0-1023 are privileged
Clients use ephemeral (short-lived) ports
•Internet Assigned Numbers Authority (IANA) maintains a list of
port number assignment
Well-known ports (0-1023)  controlled and assigned by
IANA
Registered ports (1024-49151)  IANA registers and lists
use of ports as a convenience (49151 is ¾ of 65536)
Dynamic ports (49152-65535)  ephemeral ports
For well-known port numbers, see /etc/services on a UNIX or
Linux machine

Networks
7
Socket Addressing
•Process-to-process delivery needs two identifiers
IP address and Port number
Combination of IP address and port number is called a
socket address (a socket is a communication endpoint)
Client socket address uniquely identifies client process
Server socket address uniquely identifies server process
•Transport-layer protocol needs a pair of socket addresses
Client socket address
Server socket address
For example, socket pair for a TCP connection is a 4-tuple
Local IP address, local port, and
foreign IP address, foreign port

Networks
8
Multiplexing and Demultiplexing
Multiplexing
Sender side may have
several processes that
need to send packets
(albeit only 1 transport-
layer protocol)
Demultiplexing
At receiver side, after
error checking and
header dropping,
transport-layer delivers
each message to
appropriate process

Networks
9
Transmission Control Protocol 1/10
•TCP must perform typical transport layer functions:
Segmentation  breaks message into packets
End-to-end error control since IP is an unreliable Service
End-to-end flow control  to avoid buffer overflow
Multiplexing and demultiplexing sessions
•TCP is [originally described in RFC 793, 1981]
Reliable
Connection-oriented  virtual circuit
Stream-oriented  users exchange streams of data
Full duplex  concurrent transfers can take place in both
directions
Buffered  TCP accepts data and transmits when appropriate
(can be overridden with “push”)

Networks
10
•Reliable
requires ACK and performs retransmission
If ACK not received, retransmit and wait a longer time for
ACK. After a number of retransmissions, will give up

Networks
11
•TCP uses a sliding window mechanism for flow control
•Sender maintains 3 pointers for each connection
Pointer to bytes sent and acknowledged
Pointer to bytes sent, but not yet acknowledged
Sender window includes bytes sent but not acknowledged
Pointer to bytes that cannot yet be sent

Networks
12
•Flow Control
Tell peer exactly how many bytes it is willing to accept
(advertised window  sender can not overflow receiver buffer)
Sender window includes bytes sent but not acknowledged
Receiver window (number of empty locations in receiver buffer)
Receiver advertises window size in ACKs
Sender window <= receiver window (flow control)
Sliding sender window (without a change in receiver’s advertised
window)
Expanding sender window (receiving process consumes data faster than
it receives  receiver window size increases)
Shrinking sender window (receiving process consumes data more
slowly than it receives  receiver window size reduces)
Closing sender window (receiver advertises a window of zero)

Networks
13

Networks
14
•Flow Control
TCP Flow Control
□receive side of TCP connection has a receive buffer:
□ The app process may be slow at reading from buffer
flow control
sender won’t overflow receiver’s
buffer by transmitting too much, too
fast
□speed-matching service: matching the send rate to
the receiving app’s drain rate

Networks
15
•Flow Control
TCP Flow control: how it works
(Suppose TCP receiver
discards out-of-
order segments)
□spare room in buffer
= RcvWindow
= RcvBuffer-[LastByteRcvd
- LastByteRead]
□ Rcvr advertises spare room by
including value of RcvWindow in
segments
Sender limits unACKed data to
RcvWindow
0 guarantees receive buffer doesn’t
overflow

Networks
16
TCP Connection Establishment
SYN: Synchronize
ACK: Acknowledge
Three way handshake:
Step 1: client host sends TCP SYN segment to
server
O specifies initial seq #
O no data
Step 2: server host receives SYN, replies with
SYNACK segment
O server allocates buffers
O specifies server initial seq. #
Step 3: client receives SYNACK, replies with ACK
segment, which may contain data
Recall: TCP sender, receiver
establish “connection” before
exchanging data segments
□ initialize TCP variables:
O seq. #s
O buffers, flow control info (e.g.
RcvWindow)
□ client: connection
initiator Socket clientSocket =
new Socket("hostname","port
number");
□ server: contacted by
client Socket connectionSocket =
welcomeSocket.accept();

Networks
17
TCP Connection Establishment
Closing a connection:
client closes socket:
clientSocket.close();
Step 1: client end system sends TCP FIN
control segment to server
Step 2: server receives FIN, replies with
ACK. Closes connection, sends FIN.
Step 3: client receives FIN, replies with
ACK.
O Enters “timed wait” - will respond with ACK to
received FINs
Step 4: server, receives ACK. Connection
closed.
Note: with small modification, can handle
simultaneous FINs.
client server
close
timed
wait

Networks
18
State Transition Diagram 1/4
Typical TCP
states visited
by a TCP
client

Networks
19
Typical
TCP
states
visited by
a TCP
server

Networks
20
State Description
CLOSED There is no connection.
LISTEN The server is waiting for calls from the client.
SYN-SENT A connection request is sent; waiting for acknowledgment.
SYN-RCVD A connection request is received.
ESTABLISHED Connection is established.
FIN-WAIT-1
The application has requested the closing of the
connection.
FIN-WAIT-2 The other side has accepted the closing of the connection.
TIME-WAIT Waiting for retransmitted segments to die.
CLOSE-WAIT The server is waiting for the application to close.
LAST-ACK The server is waiting for the last acknowledgment.
Can use netstat command to see some TCP states

Data Transmission flow using TCP protocol

More Related Content

Similar to Data Transmission flow using TCP protocol

Recently uploaded

Data Transmission flow using TCP protocol