Contents

1. Introduction Example: a diplomatic negotiation Principles of a layered model Connection oriented and connectionless communications Communication networks according to a layered model Contents

2. Connection Oriented Communications Typical example: A telephone conversation 3 step process: • 1. Establish connection • using the signaling protocol • 2. Use connection • using an informal protocol • being billed for duration of usage • 3. Terminate connection • using the signaling protocol

3. Connection Oriented Communications A temporary communication channel is built through the telephone network

4. Network has a state : the list of active connections Network can guarantee Quality of Service Reservation of transmission capacity at connection establishment Monitoring of data transfer and correction of transmission errors by retransmission Network is fragile : state can be lost. Application domain : Very efficient for transferring high volumes of data Mandatory if stringent Quality of Service requirements Poor initial response times due to connection setup Inapplicable if nodes have high failure rate. Connection Oriented Communications

5. Connectionless Communications Typical example: The postal service Letters, with an address and a stamp, are individually carried from a Post office box to a personal mailbox

6. Connectionless Communications No connections are needed to carry mail

7. The network is stateless. No guaranteed Quality of Service. No reservation of transmission capacity No error correction by retransmission Network is robust : No state stored in any node Each node operates almost independently from others Application domain : Whenever single message response times are critical Whenever nodes are unreliable Connectionless Communications

8. Connection PolicyLayer independance Connectionless protocol Level (n+1) entity Level (n+1) entity Connection oriented protocol Level (n) entity Level (n) entity Level (n-1) Service Provider

9. Introduction Example: a diplomatic negotiation Principles of a layered model Connection oriented and connectionless communications Communication networks according to a layered model Contents

10. Interoperability A two layers model. Applications Layer Connectivity Networks Layer

11. Interoperability A three layers model. Applications Layer Internet & Transport Layer Connectivity Networks Layer

12. Applications Layer Transport Layer Internet Layer Networks Layer Internet & Transport Layers

13. WWW Transport Layer TCP TCP Internet Layer IP IP SKYNET UUNET Networks Layer Internet & Transport LayersExample

14. Layered communications system protocol = horizontal convention Service access point & address Connection Oriented vs. Connectionless Communications Applications and networks layers Connectivity : service offered by lower layers Interoperability : full communications services Internet & Transport layers Introduced concepts

15. Fred Halsall Data Communications, Computer Networks and Open Systems Fourth Edition Addison-Wesley 1995. ISBN 0-201-42293-X BibliographyTo know More about network modeling Recommended for this chapter