Telecommunications Concepts

1. Chapter 1.2 Communications Systems Modeling TelecommunicationsConcepts

2. Introduction Example: a diplomatic negotiation Principles of a layered model Communication networks according to a layered model Side-tracks: Connection oriented vs. Connectionless networks. The seven layers of the OSI model Contents

3. Introduction Example: a diplomatic negotiation Principles of a layered model Communication networks according to a layered model Side-tracks: Connection oriented vs. Connectionless networks. The seven layers of the OSI model Contents

4. The problem: Complexity of networked systems The solution: Decomposition into independent subsystems Layered network model Introduced by IBM (SNA, 1971) Standardized by ITU (X200) and ISO (7498) Method universally adopted Standards not really obeyed in practice Layered Network Models

5. Introduction Example: a diplomatic negotiation Principles of a layered model Communication networks according to a layered model Side-tracks: Connection oriented vs. Connectionless networks. The seven layers of the OSI model Contents

6. A diplomatic negotiation Political arguments Service Access Points Translation Cryptography Transmission

7. A diplomatic negotiation Political arguments Service Access Points Single language messages Cryptography Transmission

8. A diplomatic negotiation Political arguments Service Access Points Single language messages Encrypted messages Transmission

9. A diplomatic negotiation Political arguments Service Access Points Single language messages Encrypted messages Electromagnetic waves

10. Introduction Example: a diplomatic negotiation Principles of a layered model Communication networks according to a layered model Side-tracks: Connection oriented vs. Connectionless networks. The seven layers of the OSI model Contents

11. Layered Model Definitions Level (n+1) entity Level (n+1) entity Virtual level n+1 communication path using a level n+1 protocol Physical Communication Path Level n Service Access Points Level (n) entity Level (n) entity Virtual level n communication path using a level n protocol Level n Addresses Level (n-1) Service Provider

12. Layered Model DefinitionsExample: The Telephone Service Virtual Interpersonal communication path Physical Communication Path Telephone Service Access Points Telephone Numbers Telephone Network

13. Layered Model DefinitionsProtocol Data Units (n+1)PDU Level (n+1) entity Level (n+1) entity (n)PDU Level (n) entity Level (n) entity Level (n-1) Service Provider

14. Layered Model DefinitionsLayer overhead Level (n+1) entity Level (n+1) entity Connection oriented protocol Level (n) entity Level (n) entity Level (n-1) Service Provider

15. Introduction Example: a diplomatic negotiation Principles of a layered model Communication networks according to a layered model Side-tracks: Connection oriented vs. Connectionless networks. The seven layers of the OSI model Contents

16. Connection oriented communication 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

17. Connection oriented communication A temporary communication channel is build through the telephone network

18. 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 communicationMain points

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

20. Connectionless communication No connections are needed to carry mail

21. 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 communicationMain points

22. Introduction Example: a diplomatic negotiation Principles of a layered model Communication networks according to a layered model Side-tracks: Connection oriented vs. Connectionless networks. The seven layers of the OSI model Contents

23. A two layers model. Applications Layer Interoperability Networks Layer Connectivity # Interfaces = # Applications * # Networks

24. A three layers model. Applications Layer Internet & Transport Layer Interoperability Networks Layer Connectivity # Interfaces = # Applications + # Networks

25. Applications Layer The Internet & Transport Layer Transport Layer Internet Layer Networks Layer

26. The Internet & Transport LayersExample: www http TCP IP IP SKYNET UUNET Networks Layer

27. Introduction Example: a diplomatic negotiation Principles of a layered model Communication networks according to a layered model Side-tracks: Connection oriented vs. Connectionless networks. The seven layers of the OSI model Contents

28. Networks Layers The 7 OSI layers 7 : Application Applications Layers 6 : Presentation 5 : Session Internet & Transport Layer 4 : Transport Interoperability 3 : Network 2 : Data Link Connectivity 1 : Physical

29. Layered communications system protocol = horizontal convention Service access point & address Connectivity : service offered by lower layers Interoperability : full communications services Connection Oriented Communications Connectionless Communications Introduced concepts

30. 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