1. CPEG514 Advanced Computer Networkst
University of Nizwa
Faculty of Engineering and Architecture
Electrical and Computer Engineering
CPEG514 Advanced Computer Networkst
Week 12
Atef Abu Salim
Spring 2014/2015

2. Transport Layer Layer 4. The transport layer is responsible for:
CPEG514 Advanced Computer Networks
Transport Layer
Layer 4.
The transport layer is responsible for:
the delivery of a message from one process to another
( Process-to-Process delivery ).
Port addressing : get the message to the correct process on the computer via port address.
provides virtual end-to-end links between peer processes.
Segmentation and reassembly : a message is divided into transmittable segments each segment containing a sequence no.
Connection Control: connection oriented or connectionless.
Flow control :
Error control:

3. Process-to-Process delivery
CPEG514 Advanced Computer Networks
Process-to-Process delivery

4. Process-to-Process delivery cont.
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Process-to-Process delivery cont.
The transport layer is responsible for Process-to- Process delivery , the delivery of a packet, part of a message, from one process to another.
The process communication in a client/ server relationship.

5. CPEG514 Advanced Computer Networks
Port Address
At the transport layer, we need a transport layer address called Port Number, to choose among multiple processes running on the destination.
The destination port number is needed for delivery.
The source port number is needed for reply.
In the internet model , the port numbers are 16- bit integer between 0 and

6. CPEG514 Advanced Computer Networks
IANA range
The IANA(Internet Assigned Number Authority) has divided the port numbers into three ranges: Well known port: (assigned and controlled By IANA).
Registered ports :1024 – 49151(registered with IANA).
Dynamic ports: – 65535, they can be used by any process.

7. CPEG514 Advanced Computer Networks
Socket address
The socket address is the combination of IP address and UDP/TCP port number.

8. Connectionless Versus Connection-Oriented Service
CPEG514 Advanced Computer Networks
Connectionless Versus Connection-Oriented Service
A transport layer protocol Can either be connectionless or connection-oriented.
Connectionless service:
*The packet are sent from one to another with no need for connection establishment or connection release.
* The packet are not numbered ; they may be delayed or lost or may arrive out of sequence.
* There is no acknowledgment either.
UDP is connectionless

9. Connectionless Versus Connection-Oriented Service cont.
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Connectionless Versus Connection-Oriented Service cont.
connection-oriented service:
*In a connection-oriented service, a connection is first established between the sender and receiver.
* Data are transferred.
* At the end , the connection is released.
TCP and SCTP are connection-oriented protocol.

10. User Datagram Protocol (UDP)
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User Datagram Protocol (UDP)

11. User Datagram Protocol (UDP) cont.
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User Datagram Protocol (UDP) cont.
UDP (User Datagram Protocol) creates a transport layer connection between two processes.
The UDP is called a connectionless, unreliable transport protocol.
It does not add anything to the service of IP except to provide process-to-process communication, also it performs very limited error checking.
UDP is a very simple protocol using a minimum of overhead and faster than TCP.

12. User Datagram Protocol (UDP) cont.
CPEG514 Advanced Computer Networks
User Datagram Protocol (UDP) cont.
If a process wants to send a small message and does not care much about reliability , it can use UDP.
Sending a small message by using UDP takes much less interaction between the sender and receiver than using TCP and SCTP.
The port number identifies the process, or
running application program. So using the port number, UDP directs the packet to the correct location.
No flow control. No ack of received packets. Only error control is if a checksum error is detected, it quietly drops the packet.

13. User Datagram Protocol (UDP) cont
CPEG514 Advanced Computer Networks
User Datagram Protocol (UDP) cont
UDP works well with apps that have their own error and flow control; works well with multicasting, SNMP, FTP,TFTP and RIP.
No error control mechanism in UDP except the checksum.
When the receiver detect the an error through the checksum, the user datagram is silently discarded.

14. CPEG514 Advanced Computer Networks
Example
Example: a user wants to know the day and time from a remote machine. Daytime client port # = , but Daytime server port # = 13.

15. Well-known ports used with UDP
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Well-known ports used with UDP

16. CPEG514 Advanced Computer Networks
User datagram format
Checksum : This failed is used to detect errors over the entire user datagram (header and data).

17. User datagram format cont.
CPEG514 Advanced Computer Networks
User datagram format cont.
Ethernet Frame
IP Datagram
UDP Datagram
Ethernet Header
IP Header
UDP Header
UDP Data
UDP Length = IP length – IP header’s length

18. Multiplexing and De-multiplexing
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Multiplexing and De-multiplexing
Port 1
Port 2
Port n
UDP: Multiplexing IP

19. Multiplexing and De-multiplexing cont.
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Multiplexing and De-multiplexing cont.
Port 1
Port 2
Port n
UDP: De-multiplexing
Based on port number IP

20. Transmission Control Protocol (TCP)
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Transmission Control Protocol (TCP)

21. Transmission Control Protocol (TCP) cont.
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Transmission Control Protocol (TCP) cont.
TCP provides a process-to-process (program-to- program) communication service using port numbers.
TCP is a connection oriented protocol; it creates a virtual connection between 2 TCPs to send data.
TCP uses the flow, error control and congestion control mechanisms at the transport level.
The TCP packet is called a segment

22. Transmission Control Protocol(TCP) cont.
CPEG514 Advanced Computer Networks
Transmission Control Protocol(TCP) cont.
TCP is called reliable transport protocol , it adds connection-oriented and reliability to the services of IP.
TCP can create a full-duplex service.

23. Well-known ports used by TCP
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Well-known ports used by TCP

24. TCP Services: Process-to-process communication: Reliable services:
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TCP Services:
Process-to-process communication:
Reliable services:
Connection-Oriented service:
Full-Duplex Communication:
TCP can create a full-duplex service. Data can flow in both directions at the same time

25. TCP Services cont. Sending and Receiving Buffers:
CPEG514 Advanced Computer Networks
TCP Services cont.
Sending and Receiving Buffers:
Buffers on each side hold the data to be transmitted , sent and received.
Stream Delivery service:
TCP provides a stream delivery service. It breaks up the data stream into segments of variable size. Each segment receives a header and is handed off to the IP layer.

26. TCP Services cont. Segments:
CPEG514 Advanced Computer Networks
TCP Services cont.
Segments:
breaks up the data stream into segments of variable size. Each segment receives a header and is handed off to the IP layer.

27. CPEG514 Advanced Computer Networks
TCP segments

28. CPEG514 Advanced Computer Networks
TCP segment format