Important points for Chapter 4

The purpose of the transport layer is to ensure that data travel successfully from one end to another end across the network. The port numbers indicate the application the data belongs to. At the transport layer, the port numbers are added into or removed from the original data

When the client communicate to the HTTP server, the well known port 80 is used as the destination port. For the source port, the PC will assign a random port number. The address and port number combination forms a socket. The port numbers are reversed on the return path.

In the transport layer, there are two types of protocols

The slow and steady protocol
TCP is a reliable protocol which sequence data packets before sending and acknowledge it once the packets are received. Due to the amount of acknowledgements needed, it is too slow for streaming applications. It is useful for application which requires accurate and reliable data.
Window size - Max number of bytes received before sending ack
Sequencing - Data packets are arranged in the right order after receiving

The fast and furious protocol
UDP is a non reliable protocol which has no sequence numbers or acks. The main purpose of this protocol is to allow fast data transmission. Packet loss during transmission are ignored by the end devices.

The key information at transport layer is the port numbers. The port numbers indicate the data belong to which application. For example, port 25 is SMTP and it is used by the email client. On the other hand, port number 53 is DNS and it is used by the resolver nslookup to resolve domain names.

In order for applications to send and receive data concurrently across the network, we need to multiplex the data. By multiplexing the data, we mean that the data is divided into segments and and take turns to be transported across the network. This appears to the user that the application are running concurrently.

To start a TCP session, the end devices need to perform a 3 way handshake. For UDP session, it is not needed. TCP reorder packets while UDP does not reorder. If there are packet losses during transmission, TCP request for retransmission while UDP does not.

When connected to servers running on TCP or UDP, the well known ports are used while random ports are assigned to the PCs.

Chapter 4 slides uploaded

Hello ! The presentation slides for Chapter 3 are as follows:

Summary Slides (Beginner)
https://www.dropbox.com/s/08ohn1ubdv6w1tz/Chapter_4_Overview.ppt?m
Slightly Detailed Slides (Intermediate)
https://www.dropbox.com/s/wx0kcmo39ah22g9/Expl_NetFund_chapter_04_Trans_Layer.ppt?m
Detailed Slides (Advanced)
http://ibizzone.ite.edu.sg/elearning/mod/resource/view.php?id=1293
Quiz
http://ibizzone.ite.edu.sg/elearning/mod/quiz/view.php?id=1302

Follow your skill level and go through the slides. If you feel comfortable, go through the higher level slides as well and finally, attempt the quiz