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Contents • • • • • Introduction Example: a diplomatic negotiation Principles of a layered model Connection oriented and connectionless communications Communication networks according to a layered model Postacademic Interuniversity Course in Information Technology – Module C1 p1 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 Postacademic Interuniversity Course in Information Technology – Module C1 p2 Connection Oriented Communications A temporary communication channel is built through the telephone network Postacademic Interuniversity Course in Information Technology – Module C1 p3 Connection Oriented Communications • 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. Postacademic Interuniversity Course in Information Technology – Module C1 p4 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 Postacademic Interuniversity Course in Information Technology – Module C1 p5 Connectionless Communications No connections are needed to carry mail Postacademic Interuniversity Course in Information Technology – Module C1 p6 Connectionless Communications • 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 Postacademic Interuniversity Course in Information Technology – Module C1 p7 Connection Policy Layer independance Level (n+1) entity Connectionless protocol Level (n+1) entity Connection oriented protocol Level (n) entity Level (n) entity Level (n-1) Service Provider Postacademic Interuniversity Course in Information Technology – Module C1 p8 Contents • • • • • Introduction Example: a diplomatic negotiation Principles of a layered model Connection oriented and connectionless communications Communication networks according to a layered model Postacademic Interuniversity Course in Information Technology – Module C1 p9 A two layers model. Networks Layer Postacademic Interuniversity Course in Information Technology – Module C1 Interoperability Connectivity Applications Layer p10 A three layers model. Networks Layer Postacademic Interuniversity Course in Information Technology – Module C1 Connectivity Internet & Transport Layer Interoperability Applications Layer p11 Internet & Transport Layers Applications Layer Transport Layer Internet Layer Networks Layer Postacademic Interuniversity Course in Information Technology – Module C1 p12 Internet & Transport Layers Example WWW Transport Layer TCP TCP Internet Layer IP SKYNET IP UUNET Networks Layer Postacademic Interuniversity Course in Information Technology – Module C1 p13 Introduced concepts • 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 Postacademic Interuniversity Course in Information Technology – Module C1 p14 Bibliography To know More about network modeling Fred Halsall Data Communications, Computer Networks and Open Systems Fourth Edition Addison-Wesley 1995. ISBN 0-201-42293-X Recommended for this chapter Postacademic Interuniversity Course in Information Technology – Module C1 p15