Postacademic Interuniversity Course in Information Technology – Module C1p1 Chapter 2 Communications Systems Modeling

Postacademic Interuniversity Course in Information Technology – Module C1p2 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 C1p3 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 C1p4 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

Postacademic Interuniversity Course in Information Technology – Module C1p5 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 C1p6 A diplomatic negotiation Translation Cryptography Transmission Service Access Points Political arguments

Postacademic Interuniversity Course in Information Technology – Module C1p7 A diplomatic negotiation Cryptography Transmission Service Access Points Political arguments Single language messages

Postacademic Interuniversity Course in Information Technology – Module C1p8 A diplomatic negotiation Political arguments Transmission Service Access Points Single language messages Encrypted messages

Postacademic Interuniversity Course in Information Technology – Module C1p9 A diplomatic negotiation Political arguments Service Access Points Encrypted messages Single language messages Electromagnetic waves

Postacademic Interuniversity Course in Information Technology – Module C1p10 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 C1p11 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

Postacademic Interuniversity Course in Information Technology – Module C1p12 Layered Model Definitions Example: The Telephone Service Telephone Network Telephone Service Access Points Telephone Numbers Virtual Interpersonal communication path Physical Communication Path

Postacademic Interuniversity Course in Information Technology – Module C1p13 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 PDU encapsulation

Postacademic Interuniversity Course in Information Technology – Module C1p14 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 C1p15 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 C1p16 Connection Oriented Communications A temporary communication channel is built through the telephone network

Postacademic Interuniversity Course in Information Technology – Module C1p17 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 C1p18 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 C1p19 Connectionless Communications No connections are needed to carry mail

Postacademic Interuniversity Course in Information Technology – Module C1p20 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 C1p21 Connection Policy Layer independance Level (n+1) entity Level (n+1) entity Level (n) entity Level (n) entity Level (n-1) Service Provider Connection oriented protocol Connectionless protocol

Postacademic Interuniversity Course in Information Technology – Module C1p22 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 C1p23 A two layers model. Applications Layer Networks Layer Connectivity Interoperability

Postacademic Interuniversity Course in Information Technology – Module C1p24 A three layers model. Applications Layer Internet & Transport Layer Networks Layer Connectivity Interoperability

Postacademic Interuniversity Course in Information Technology – Module C1p25 Internet & Transport Layers Applications Layer Internet Layer Transport Layer Networks Layer

Postacademic Interuniversity Course in Information Technology – Module C1p26 Internet & Transport Layers Example Internet Layer Transport Layer Networks Layer WWW SKYNETUUNET TCP IP

Postacademic Interuniversity Course in Information Technology – Module C1p27 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 C1p28 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