1 K. Salah Module 1.0: Introduction Definition Communication Model Type of networks –WAN –MAN –LAN, WLAN –PAN, WPAN Networking Technologies Network Switching Types TCP/IP Reference Model

2 K. Salah Definition A computer network technogloy is often a practical application/consequence of science and engineering concepts related to computer networks.

3 K. Salah Network Topologies Point-to-point Bus Ring Star

4 K. Salah What a Network Does Provides communication that is –Reliable –Fair –Efficient –From one application to another –Automatically detects and corrects  Data corruption  Data loss  Duplication  Out-of-order delivery –Automatically finds optimal path from source to destination

5 K. Salah A Communications Model Source –Generates Data to be Transmitted Transmitter –Converts Data into Transmittable Signals Transmission System –Carries Data Receiver –Converts Received Signal into Data Destination –Takes Incoming Data

6 K. Salah Simplified Communications Model - Diagram

7 K. Salah Classes of Computer Networks –Wide Area Network (WAN) –Metropolitan Area Network (MAN) –Local Area Network (LAN), Wireless LAN –Personal Area Network (PAN), Wireless PAN

8 K. Salah Classification of Interconnections

9 K. Salah Wide Area Networks Large Geographical Area Rely in Part on Common Carrier Circuits (e.g., T1 & T3 by STC). Available Technologies –Circuit Switching –Packet Switching –SMDS & X.25 –Frame Relay –Asynchronous Transfer Mode (ATM) –Integrated Services Digital Network (ISDN)

10 K. Salah Switching (1) Circuit Switching: –Dedicated Communications Path Established for the Duration of the Conversation –Example - Public Switched Telephone Network Packet Switching: –Data Sent Out of Sequence –Small Chunks (Packets) of Data at a Time –Packets Passed from Node to Node between Source and Destination –Used for Terminal to Computer and Computer to Computer Communications Note: CO vs. CL –Connection Oriented  Modeled after the telephone system  When PDUs are sequenced, I.e. logical connection –Connectionless  Modeled after the postal system  When PDUs are not sequenced

11 K. Salah Switching (2) Telecommunication networks Circuit-switched networks FDM TDM Packet-switched networks Networks with VCs Datagram Networks

12 K. Salah SMDS & X.25 (SMDS) Switched Multimegabit Data Service –Designed by Bellcore in the 1980s –Connecting LAN to LAN through leased lines –Connectionless protocol carrying packets –Standard speed is 45Mbps. X.25 –Developed by CCITT in 1970s to specify the interface between public packet-switched networks and customer LANs. –Connection-oriented protocol supporting both switched virtual circuit (SVC) and permanent virtual circuit (PVC). –As opposed to SVC, PVC are never torn down. –Operates at speed of 64 kbps

13 K. Salah Frame Relay Packet Switching Systems were built on unreliable communication lines, and thus had Large Overheads to Compensate for Errors Modern Systems Are More Reliable Errors Can Be Caught in End System (Applications) Most Overhead for Error Control is Stripped Out You can think of FR as permanent virtual circuit FR operates at 1.5 Mbps. The concept of committed rate and uncommitted rate.

14 K. Salah Asynchronous Transfer Mode ATM Evolution of Frame Relay Little Overhead for Error Control Fixed Packet Length (Called Cells) Anything From 10Mbps to Gbps Constant Data Rate Using Packet Switching Technique

15 K. Salah Integrated Services Digital Network ISDN Designed to Replace Public Telecom System Wide Variety of Services Entirely Digital Domain

16 K. Salah Local Area Networks Smaller Scope –Building or Small Campus Usually Owned by Same Organization as Attached Devices Data Rates Much Higher Usually Broadcast Systems –IEEE – Logical Link Control –IEEE Ethernet –IEEE Token bus –IEEE Token ring –IEEE – Wireless –GigE & 10GigE

17 K. Salah Monolithic vs. Structured Communications is a Complex Task Too Complex for Single Unit Structured Design Breaks Down Problem into Smaller Units Layered Structure – Why? –explicit structure allows identification, relationship of complex system’s pieces –modularization eases maintenance, develop, updating of system  change of implementation of layer’s service transparent to rest of system  e.g., change in gate procedure doesn’t affect rest of system

18 K. Salah Layering Concept To reduce design complexity, network architectures are organized as a series of layers (principle of divide-and- conquer) Layer N+1 Layer N Computer AComputer B peer protocol interface protocol

19 K. Salah Typical Functions of a Protocol Encapsulation Segmentation and reassembly Connection control Ordered delivery Flow control Error control Addressing Multiplexing Transmission services

20 K. Salah Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical Each layer: distributed “entities” implement layer functions at each node entities perform actions, exchange messages with peers

21 K. Salah Layering: logical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data E.g.: transport take data from app add addressing, reliability check info to form “packet” send packet to peer wait for peer to ack receipt analogy: post office – register mail. data transport ack

22 K. Salah Layering: physical communication application transport network link physical application transport network link physical application transport network link physical application transport network link physical network link physical data

23 K. Salah Protocol layering and data Each layer takes data from above adds header information to create new data unit passes new data unit to layer below application transport network link physical application transport network link physical source destination M M M M H t H t H n H t H n H l M M M M H t H t H n H t H n H l message segment packet frame

24 K. Salah Some Protocols in TCP/IP Suite