1. Reference model

2. Goal: 2 message exchange between application processes

3. What we should do? message Electrical signal message Where is the destination station? How to reach the station? What if error happens? What if congestion happens? How to make electrical signal? ………..

4. Reference model message Electrical signal message

5. Reference model Divide and conquer; divide the whole work into separate small tasks – layers Each layer is independent of other layers. Each layer in a station is communicating with the same layer in the corresponding station.

6. Introduction1-6 analogy: overseas air travel Each task is working independently. ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing

7. Introduction1-7 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Reference model for the travel layers: each layer has its own mission. – Each layer works independently. – Lower layers provide services to the very higher layer.

8. Reference model application transport network link physical application presentation session transport network data link physical OSI 7 layers Internet layers

9. Application layer Application process has its own task to provide some services. – Web client/server, email, ftp, DNS etc. Then how can processes exchange messages to provide some services.

10. Transport Layer Transport layer delivers all messages from several application processes to the corresponding transport layer. – Then, how they can differentiate all messages? network access 1 IP Transport network Access 2 IP transport network access1 access2 IP subnet 1 end-to-end subnet 2 AP1AP2AP3AP1AP2AP3

11. Network layer node-to-node delivery How to find the path to reach the destination.

12. Link layer Link layer takes the responsibility of delivering data between two nodes which are connected by the same physical link. 4.1212

13. Link layer The data unit to be delivered at the link layer is called a frame. goal – How to know where the frame begins and ends? In addition, – Is there any error during transmission? – Is there any frame loss because of the processing speed difference between a sender and a receiver? – And others.

14. Physical layer How to make a data frame into an electrical signal? (coding)

15. Physical layer and link layer

16. How is the data unit (PDU) at each layer delivered to its lower or higher layer at the boundary? – encapsulation PDU consists of data part and header part. The header has the information with which each layer can do its own functions. encapsulation

17. Introduction1-17 source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch message M HtHt M HnHn frame

18. encapsulation

19. Communication protocol

20. Common protocol TCP connection req TCP connection response Hi Got the time? 2:00 time

21. How to specify in protocol Procedure to exchange messages What kind of information should be exchanged to do jobs. How these information is contained in the header.