Transcript Chapter 5: Telecommunications

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
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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
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Transmission Media Connectors
Network Interface Cards (NIC)
Modems (MOdulator/DEModulator)
Repeaters
Hubs
Bridges
Mutiplexers (MUX)
Key Components for
Internetworking
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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