09-07-K.Steenhaut & J.Tiberghien - VUB 1 Telecommunications Concepts Chapter 1.2 Communications Systems Modeling

09-07-K.Steenhaut & J.Tiberghien - VUB 2 Contents 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

09-07-K.Steenhaut & J.Tiberghien - VUB 3 Contents 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

09-07-K.Steenhaut & J.Tiberghien - VUB 4 Layered Network Models 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

09-07-K.Steenhaut & J.Tiberghien - VUB 5 Contents 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

09-07-K.Steenhaut & J.Tiberghien - VUB 6 A diplomatic negotiation Translation Cryptography Transmission Service Access Points Political arguments

09-07-K.Steenhaut & J.Tiberghien - VUB 7 A diplomatic negotiation Cryptography Transmission Service Access Points Political arguments Single language messages

09-07-K.Steenhaut & J.Tiberghien - VUB 8 A diplomatic negotiation Political arguments Transmission Service Access Points Single language messages Encrypted messages

09-07-K.Steenhaut & J.Tiberghien - VUB 9 A diplomatic negotiation Political arguments Service Access Points Encrypted messages Single language messages Electromagnetic waves

09-07-K.Steenhaut & J.Tiberghien - VUB 10 Contents 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

09-07-K.Steenhaut & J.Tiberghien - VUB 11 Layered Model Definitions Level (n+1) entity Level (n+1) entity Level (n) entity Level (n) entity Level (n-1) Service Provider Level n Service Access Points Level n Addresses Virtual level n+1 communication path using a level n+1 protocol Virtual level n communication path using a level n protocol Physical Communication Path

09-07-K.Steenhaut & J.Tiberghien - VUB 12 Layered Model Definitions Example: The Telephone Service Telephone Network Telephone Service Access Points Telephone Numbers Virtual Interpersonal communication path Physical Communication Path

09-07-K.Steenhaut & J.Tiberghien - VUB 13 Layered Model Definitions Protocol Data Units Level (n+1) entity Level (n+1) entity Level (n) entity Level (n) entity Level (n-1) Service Provider (n+1)PDU (n)PDU

09-07-K.Steenhaut & J.Tiberghien - VUB 14 Layered Model Definitions Layer overhead Level (n+1) entity Level (n+1) entity Level (n) entity Level (n) entity Level (n-1) Service Provider Connection oriented protocol

09-07-K.Steenhaut & J.Tiberghien - VUB 15 Contents 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

09-07-K.Steenhaut & J.Tiberghien - VUB 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

09-07-K.Steenhaut & J.Tiberghien - VUB 17 Connection oriented communication A temporary communication channel is build through the telephone network

09-07-K.Steenhaut & J.Tiberghien - VUB 18 Connection oriented communication Main points 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.

09-07-K.Steenhaut & J.Tiberghien - VUB 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

09-07-K.Steenhaut & J.Tiberghien - VUB 20 Connectionless communication No connections are needed to carry mail

09-07-K.Steenhaut & J.Tiberghien - VUB 21 Connectionless communication Main points 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

09-07-K.Steenhaut & J.Tiberghien - VUB 22 Contents 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

09-07-K.Steenhaut & J.Tiberghien - VUB 23 A two layers model. Applications Layer Networks Layer Connectivity Interoperability # Interfaces = # Applications * # Networks

09-07-K.Steenhaut & J.Tiberghien - VUB 24 A three layers model. Applications Layer Internet & Transport Layer Networks Layer Connectivity Interoperability # Interfaces = # Applications + # Networks

09-07-K.Steenhaut & J.Tiberghien - VUB 25 The Internet & Transport Layer Applications Layer Internet Layer Transport Layer Networks Layer

09-07-K.Steenhaut & J.Tiberghien - VUB 26 The Internet & Transport Layers Example: www TCP Networks Layer http SKYNETUUNET IP

09-07-K.Steenhaut & J.Tiberghien - VUB 27 Contents 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

09-07-K.Steenhaut & J.Tiberghien - VUB 28 The 7 OSI layers Applications Layers Internet & Transport Layer Networks Layers Connectivity Interoperability 1 : Physical 2 : Data Link 3 : Network 4 : Transport 5 : Session 6 : Presentation 7 : Application

09-07-K.Steenhaut & J.Tiberghien - VUB 29 Introduced concepts 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

09-07-K.Steenhaut & J.Tiberghien - VUB 30 Bibliography To know More about network modeling Fred Halsall Data Communications, Computer Networks and Open Systems Fourth Edition Addison-Wesley ISBN X Recommended for this chapter