1. Transport Layer

2. Learning Outcomes
Understanding of end-to-end delivery and port address
Understanding of well-known port numbers
Understanding of different service types in the transport layer
List of two transport layer protocols
List of applications of UDP and applications of TCP
Understanding of TCP connection/termination procedure

3. Topics discussed in this section:
1. INTRODUCTION
The transport layer is responsible for process-to-process delivery (or also called end-to-end delivery) – the delivery of a packet, part of a message, from one process to another. Two processes communicate in a client/server relationship, as we will see later.
Topics discussed in this section:
Client/Server Paradigm Multiplexing and Demultiplexing
Connectionless Versus Connection-Oriented Service
Reliable Versus Unreliable
Two Protocols

4. Note
The transport layer is responsible for process-to-process (or also called end-to-end) delivery.

5. Types of data deliveries

6. Transport layer protocol + port number
Port numbers
OS assigns applications when socket() is invoked.
bind() with applications.
Transport layer protocol + port number

7. IP addresses versus port numbers

8. A bit different from different OSes.
IANA ranges
(client port numbers)
A bit different from different OSes.

9. TCP UDP Services Connectionless Connection-oriented Block transfer
Byte streaming
Unreliable
Reliable
TCP
UDP

10. Position of UDP, TCP, and SCTP in TCP/IP suite

11. Topics discussed in this section:
2. USER DATAGRAM PROTOCOL (UDP)
The User Datagram Protocol (UDP) is called a connectionless, unreliable, block transfer protocol. It does not add anything to the services of IP except to provide process-to-process communication instead of host-to-host communication.
Topics discussed in this section:
Well-Known Ports for UDP User Datagram
Checksum
UDP Operation
Use of UDP

12. Note:
UDP is a connectionless, unreliable, block transfer protocol that has no flow and error control. It uses port numbers to multiplex data from the application layer.

13. Well-known ports used with UDP

14. User datagram format

15. Note:
UDP is a convenient transport-layer protocol for applications that provide flow and error control. It is also used for short message transfer and by multimedia applications.

16. Topics discussed in this section:
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.
Topics discussed in this section:
TCP Services TCP Features
Segment
A TCP Connection
Flow Control
Error Control

17. TCP service
Connection-oriented
Full-duplex
Byte streaming
Reliable

18. Well-known ports used by TCP

19. Any size Any size Any size Byte stream delivery No overwriting,
not like UDP

20. The numbering starts with a randomly generated number.
Note
The bytes of data being transferred in each connection are numbered by TCP.
The numbering starts with a randomly generated number.

21. Numbering bytes Sequence number and acknowledge number Why do we need?
Independent in each direction: full-duplex mode
Not segment numbers, but byte numbers
0 ~

22. TCP segment format

23. TCP segment format Source port address Destination port address
Sequence number for the first byte of the payload
Acknowledge number [Q] How to know whether ACK is valid?
Header length: unit 4B
Reserved
Control field
Window size
With acknowledgement
The size of the window, in bytes, of the opponent for flow control
Maximum bytes
The unit could be changed by using an option
Checksum
16 bit checksum
Urgent pointer
Used when the urgent flag is set
It points to the last byte of the urgent data
Options

24. When the payload needs to be sent out of order,
Control field
When the payload needs to be sent out of order,
e.g., it wants to abort the sending application, but it has already
sent a huge amount of data.
u.p.
u.d.
payload
When the payload needs to be delivered without buffering
that is used to increase the efficiency of TCP,
called delayed transmission.
E.g., SSH terminal session

25. Description of flags in the control field

26. Connection establishment using three-way handshaking
8001
Initial window size of the opponent included
for flow control.

27. Data transfer

28. Connection termination using three-way handshaking
X +1

29. Half-close
x+1

30. to control the flow of data so that the destination does not become
Note
A sliding window is used to make transmission more efficient as well as
to control the flow of data so that the destination does not become
overwhelmed with data. TCP sliding windows are byte-oriented.
What kind ARQ algorithm for error control?
Selective Repeat ARQ