The document discusses the User Datagram Protocol (UDP) and the Transmission Control Protocol (TCP). UDP is a connectionless protocol that provides process-to-process communication over IP. TCP is connection-oriented and establishes a virtual connection between hosts to reliably send data using flow and error control. TCP numbers data bytes and uses sequence numbers and acknowledgments to ensure reliable in-order delivery. Connection establishment and termination with TCP uses three-way and four-way handshaking protocols. TCP guarantees in-order delivery of data to processes and handles lost packets.

1. Yarmouk University – Faculty of Information
Technology and CS Computer Science
Department
Transport Layer

2. 23-2 USER DATAGRAM PROTOCOL (UDP)
The User Datagram Protocol (UDP) is called a
connectionless, unreliable transport protocol. It does
not add anything to the services of IP except to provide
process-to-process communication instead of host-to-host
23.2
communication.

3. 23.3
Table 23.1 Well-known ports used with UDP

4. Figure 23.9 User datagram format
23.4

5. 23.5
UDP length
= IP length – IP header’s length
Note

6. 23-3 TCP
TCP is a connection-oriented protocol; it creates a
virtual connection between two TCPs to send data. In
addition, TCP uses flow and error control mechanisms
at the transport level.
23.6

7. 23.7
Table 23.2 Well-known ports used by TCP

8. 23.8
The bytes of data being transferred in each connection are numbered by TCP.
The numbering starts with a randomly generated number.
USING sequence number and the acknowledgment number FIELDS. These two
fields refer to the byte number and not the segment number.
Note

9. Figure 23.16 TCP segment format
23.9

10. Field Description
Source port address. This is a 16-bit
Destination port
address
This is a 16-bit field
Sequence number This 32-bit field defines the number assigned to the first byte of data contained in this segment.
Acknowledgment
number
This 32-bit field defines the byte number that the receiver of the segment is expecting to receive from the
other party. If the receiver of the segment has successfully received byte number x from the other party, it
defines x + I as the acknowledgment number.
Header length This 4-bit field indicates the number of 4-byte words in the TCP Header. The length of the header can be
between 20 and 60 bytes. Therefore, the value of this field can be between 5 (5 x 4 =20) and 15 (15 x 4 =60).
Reserved This is a 6-bit field reserved for future use
Control This field defines 6 different control bits or flags
Window size This field defines the size of the window, in bytes, that the other
party must maintain. Note that the length of this field is 16 bits, which means that
the maximum size of the window is 65,535 bytes. This value is normally referred
to as the receiving window (rwnd) and is determined by the receiver.
Checksum This 16-bit field
Urgent pointer •This l6-bit field, which is valid only if the urgent flag is set, is
used when the segment contains urgent data. It defines the number that must be
added to the sequence number to obtain the number of the last urgent byte in the
data section of the segment
Options There can be up to 40 bytes of optional information in the TCP header

11. Figure 23.17 Control field
23.11
These bits enable flow control, connection establishment and termination,
connection abortion, and the mode of data transfer in TCP.

12. 23.12
Table 23.3 Description of flags in the control field

13. Connection establishment using three-way handshaking
Random
With the connection now established, the client will send data whose first byte will be
given sequence number 4,568. The server's first byte of data will be numbered 12,999.

14. Connection establishment using three-way handshaking

15. Figure 23.18 Connection establishment using three-way handshaking
23.15

16. Note
• A SYN segment cannot carry data, but it consumes one sequence number.
• A SYN + ACK segment cannot carry data, but does consume one sequence number.
• An ACK segment, if carrying no data, consumes no sequence number.
23.16

17. simultaneous Connection establishment using three-way handshaking
It will not require a 3rd ACK segments. It will be handled in 2 way handshake

18. Figure 23.19 Data transfer
23.18

19. Connection termination using three-way handshaking
23.19

20. Note
• The FIN segment consumes one sequence number if it not carry data.
• The FIN + ACK segment consumes one sequence number if it does not carry data.
23.20

21. Simultaneous Connection termination

22. Connection termination using Half-close Four-way handshaking

23. Connection termination using Half-close Four-way handshaking

24. Connection termination using Half-close Four-way handshaking
23.24
One End can stop sending data
while receiving data.
And normally issued by the
CLIENT
The termination can be only for
the outbound connection (i.e.
Sorting) for the client
(requester) and the server can
terminate the inbound
connection and maintain the
outbound
Request for the
termination but the 3rd
way is not initiated yet.
Until the server finishes
the processing and send
a FIN back to the client.
In the half closed
connection, the client
closes outbound, thus
cannot send out data
only ACK. And server
closes inbound
connection, thus he still
can send data if
needed.

25. Note
• ACK segments do not consume sequence numbers and are not acknowledged.
• Data may arrive out of order and be temporarily stored by the receiving TCP, but
TCP guarantees that no out-of-order segment is delivered to the process.
23.25

26. Figure 23.24 Normal operation
23.26

27. Figure 23.25 Lost segment
23.27

28. 23.28
The receiver TCP delivers only ordered data to the process.
Note