Telecommunications Chapter 5 Chapter Objectives Understand the role

Telecommunications Chapter 5

Chapter Objectives • Understand the role of telecommunications in organizations • Describe the evolution and types of computer networks • Understand networking fundamentals • Explain the role of the Open System Interconnect (OSI) model and network operating systems

The Role of Telecommunications in Organizations • Work Group Communication – E-mail – Video conferencing • Emerging Business Applications – Electronic Commerce • Uses the World Wide Web – Electronic Data Interchange (EDI) • Allows computer-to-computer links between trading partners

Building Blocks of Data Communication • All communications require three things: – Senders and receivers that have something to share • Coded by sender • Decoded by receiver – A pathway or transmission media to send the message – Rules or protocols of communication

Human vs Computer Communication

Computer Networks • Computers and other devices connected by a communications channel – Share files and other resources between users • Channel: the transmission media • Bandwidth: carrying capacity of the media • Protocols: the physical and logical rules for transmission • Modem: sends signal over telephone line – Converts digital signal to analog and back again

Modems

Evolution in Computer Networking • Centralized computing – Uses mainframes and “dumb” terminals • Distributed computing – Uses separate computers • Collaborative computing – Uses two or more networked computers • Networks today include all three models

Centralized Computing Model

Distributed Computing Model

Collaborative Computing Model

Classifications of Networks • Private Branch Exchange (PBX) – A privately owned telephone switch • Local Area Network (LAN) – Usually confined to a single building or site • Wide Area Network (WAN) – Enterprise network - one organization – Global network

Private Branch Exchange

Local Area Network

Enterprise Network

Networking Fundamentals • • • Servers, Clients, and Peers Network Services Transmission Media Network Topologies Network Access Control Methods Major Standards

Servers, Clients, and Peers • Server-centric networks – Server • A network computer that makes services available to users – Client • Uses services provided by a server • Peer-to-peer networks – Allow any computer or device to provide and request services

Servers, Clients, and Peers

Network Services • Offered by the network operating system – File services • Store, retrieve, and move data – Print services • Control access to printers and fax machines – Message services • Deal with communication between network users – Application services • Run software for network clients

Transmission Media • The physical pathway that carries signals • Media characteristics – Bandwidth - transmission capacity stated in megabits per second (Mbps) – Attenuation - weakening of signal over distance – EMI - electromagnetic interference • Two forms – Cable media – Wireless media

Cable Media • Twisted Pair – Two or more pairs of insulated copper wires • Coaxial – Inner copper conductor surrounded by plastic insulation with outer braided foil shield • Fiber Optic – Uses pulses of light to send data – Glass or plastic core surrounded by cladding with a tough outer sheath

Wireless Media • Infrared Line of Sight – Light waves transmit data on unobstructed path • High-Frequency Radio – Radio signals up to 39. 6 meters • Microwave Line of Sight – Terrestrial uses earth-based antennas – Satellite sends signals between antennas on earth and orbiting satellites

Network Topologies • Star Network – All nodes attached to center a hub – Messages must pass through the hub • Ring Network – A closed loop – Messages move in one direction • Bus Network – An open-ended line – Nodes receive message at the same time

Star Network

Ring Network

Bus Network

Network Access Control Methods • Distributed Access Control – Token passing • Circulating electronic token prevents collisions • Must possess the token to transmit a message • Random Access Control – CSMA/CD • “Listen” for quiet line; then send message • Collision occurs with simultaneous messages • Must wait and resend

Token Ring Operation

Major Standards • To ensure the interoperability and compatibility of networks • Three major standards for LAN – Ethernet – Token-Ring – ARCnet

Connectivity Hardware • Computers can be physically connected in many ways • Each device must be connected to the medium

Key Components of a Local Network • • Transmission Media Connectors Network Interface Cards (NIC) Modems (MOdulator/DEModulator) Repeaters Hubs Bridges Mutiplexers (MUX)

Key Components for Internetworking • • Routers Brouters Channel Service Units (CSU) Gateways

Connectivity Software • The OSI Model • Network Operating Systems

The OSI Model • Protocol representing a group of specific tasks that allow data communication between two computers • Each higher layer builds on the functions of the layers below

The OSI Model

The OSI Model and Message Passing

Network Operating Systems • Client/server architecture LANs – The system software runs on the file server – Part of the NOS runs on each workstation • Peer-to-peer networks – NOS is installed on each attached workstation – Runs on top of the local operating system