1. 6 Transport Layer Computer Networks Tutun Juhana
Telecommunication Engineering
School of Electrical Engineering & Informatics
Institut Teknologi Bandung
Computer Networks

2. Transport Layer Services

3. Process-to-Process Communication

4. Addressing: Port Numbers
To define the processes, we need identifiers called port numbers
In the TCP/IP protocol suite, the port numbers are integers between 0 and 65,535

5. In client-server paradigm:
Client program defines itself ephemeral port number  Short lived  recommended to be greater than 1,023
Server process must use well-known port numbers

8. ICANN Ranges

9. Socket Addresses
Socket address is the combination of an IP address and a port number

10. Encapsulation and Decapsulation

11. Multiplexing and Demultiplexing

12. Flow Control

14. Although flow control can be implemented in several ways, one of the solutions is normally to use two buffers. One at the sending transport layer and the other at the receiving transport layer

15. Error Control Detect and discard corrupted packets.
Keep track of lost and discarded packets and resend them.
Recognize duplicate packets and discard them.
Buffer out-of-order packets until the missing packets arrive.

17. Sequence Numbers

18. We can use both positive and negative signals as error control
Acknowledgment
We can use both positive and negative signals as error control
The receiver side
can send an acknowledgement (ACK) for each or a collection of packets that have arrived safe and sound
can simply discard the corrupted packets
The sender can detect lost packets if it uses a timer
When a packet is sent, the sender starts a timer; when the timer expires, if an ACK does not arrive before the timer expires, the sender resends the packet.
Duplicate packets can be silently discarded by the receiver. Out-of order packets can be either discarded (to be treated as lost packets by the sender), or stored until the missing ones arrives.

19. Combination of Flow and Error Control

21. Congestion Control
Congestion control refers to the mechanisms and techniques to control the congestion and keep the load below the capacity

22. Open-Loop Congestion Control
Retransmission Policy
Window Policy
Acknowledgment Policy

23. Closed-Loop Congestion Control
Closed-loop congestion control mechanisms try to alleviate congestion after it happens

24. Connectionless and Connection-Oriented Services

26. TRANSPORT-LAYER PROTOCOLS

27. Simple Protocol

28. Stop-and-Wait Protocol

30. Efficiency
The Stop-and-Wait protocol is very inefficient if our channel is thick and long
By thick, we mean that our channel has a large bandwidth (high data rate)
by long, we mean the round-trip delay is long
The product of the above two is called the bandwidth-delay product
We can think of the channel as a pipe. The bandwidth-delay product then is the volume of the pipe in bits
The pipe is always there. If we do not use it, we are inefficient.
The bandwidth-delay product is a measure of the number of bits a sender can transmit through the system while waiting for an acknowledgment from the receiver.

32. Pipelining
In networking and in other areas, a task is often begun before the previous task has ended  This is known as pipelining
There is no pipelining in the Stop-and-Wait protocol because a sender must wait for a packet to reach the destination and be acknowledged before the next packet can be sent

33. Go-Back-N Protocol

37. Timers Resending packets
Although there can be a timer for each packet that is sent, in our protocol we use only one. The reason is that the timer for the first outstanding packet always expires first. We resend all outstanding packets when this timer expires.
Resending packets
When the timer expires, the sender resends all outstanding packets

42. Selective-Repeat Protocol

47. Bidirectional Protocols: Piggybacking