K. Salah 1

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

K. Salah 2

Definition

•A computer network technogloy

is often a practical application/consequence of science and engineering concepts related to computer networks.

K. Salah 3

Network Topologies

Point-to-point Bus

RingStar

K. Salah 4

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

K. Salah 5

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

K. Salah 6

Simplified Communications Model - Diagram

K. Salah 7

Classes of Computer Networks

– Wide Area Network (WAN)

– Metropolitan Area Network (MAN)

– Local Area Network (LAN), Wireless LAN

– Personal Area Network (PAN), Wireless PAN

K. Salah 8

Classification of Interconnections

K. Salah 9

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)

K. Salah 10

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

K. Salah 11

Switching (2)

Telecommunicationnetworks

Circuit-switchednetworks

FDM TDM

Packet-switchednetworks

Networkswith VCs

DatagramNetworks

K. Salah 12

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

K. Salah 13

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.

K. Salah 14

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

K. Salah 15

Integrated Services Digital Network

• ISDN

• Designed to Replace Public Telecom System

• Wide Variety of Services

• Entirely Digital Domain

K. Salah 16

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 802.2 – Logical Link Control– IEEE 802.3 - Ethernet– IEEE 802.4 - Token bus– IEEE 802.5 - Token ring– IEEE 802.11 – Wireless– GigE & 10GigE

K. Salah 17

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

K. Salah 18

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+1

Layer N Layer N

Computer A Computer B

peer protocol

interfaceprotocol

K. Salah 19

Typical Functions of a Protocol

• Encapsulation

• Segmentation and reassembly

• Connection control

• Ordered delivery

• Flow control

• Error control

• Addressing

• Multiplexing

• Transmission services

K. Salah 20

Layering: logical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

Each layer:

• distributed

• “entities” implement layer functions at each node

• entities perform actions, exchange messages with peers

K. Salah 21

Layering: logical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

dataE.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

transport

ack

K. Salah 22

Layering: physical communication

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

networklink

physical

data

data

K. Salah 23

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

applicationtransportnetwork

linkphysical

applicationtransportnetwork

linkphysical

source destination

M

M

M

M

Ht

HtHn

HtHnHl

M

M

M

M

Ht

HtHn

HtHnHl

message

segment

packet

frame

K. Salah 24

Some Protocols in TCP/IP Suite