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Chapter 2
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  1. Chapter 2 Communications Systems Modeling

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

  3. Introduction Example: a diplomatic negotiation Principles of a layered model Connection oriented and connectionless communications Communication networks according to a layered 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 Connection oriented and connectionless communications Communication networks according to a layered 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 Connection oriented and connectionless communications Communication networks according to a layered 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 PDUencapsulation (n)PDU Level (n) entity Level (n) entity Level (n-1) Service Provider

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

  15. 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

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

  17. 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

  18. 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

  19. Connectionless Communications No connections are needed to carry mail

  20. 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

  21. 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

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

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

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

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

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

  27. 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

  28. 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