Chapter 10
Data Communications
Data Communications
Communication Basics
Communication Basics
Computer communications is at
Computer communications is at
three levels
three levels
– Application level Application level – Computer levelComputer level
– Communication channelCommunication channel
Protocol
Protocol
– Set of rules for communicationsSet of rules for communications
OSI Reference Model
OSI Reference Model
Layer Name Purpose
7 Application Layer Application-to-application communication 6 Presentation Layer Manage data representation conversions
5 Session Layer Establish and maintain communication channel 4 Transport Layer Guarantee end-to-end integrity of transmission 3 Network Layer Route data between network addresses
ISO Website
Protocols for Computer
Protocols for Computer
Communication
Communication
Early computersEarly computers
– TerminalsTerminals – Sneaker netSneaker net
System Network Architecture (SNA)System Network Architecture (SNA)
– Established by IBM in 1974Established by IBM in 1974 – ProprietaryProprietary
Token-RingToken-Ring
Protocols for Computer
Protocols for Computer
Communication
Communication
Ethernet
Ethernet
– Xerox working with Intel and Digital Xerox working with Intel and Digital
Equipment Corporation developed this protocol Equipment Corporation developed this protocol – Non-proprietaryNon-proprietary
– Defined by IEEEDefined by IEEE
Packets
Packets
Piece of the total data to be communicated,
Piece of the total data to be communicated,
combined with the address of the destination
combined with the address of the destination
computer for the data and other control
computer for the data and other control
information.
information.
Network Addresses
Network Addresses
Address
Address
– Four-part set of numbers Four-part set of numbers – Each from 0 to 255Each from 0 to 255
Internet Service Providers (ISPs)
Internet Service Providers (ISPs)
– User connects through common carrierUser connects through common carrier
Serial Line Internet Protocol (SLIP) and
Serial Line Internet Protocol (SLIP) and
Point-to-Point Protocol (PPP)
Point-to-Point Protocol (PPP)
Protocols for Public Phone
Protocols for Public Phone
Systems
Systems
X.25
X.25
– analoganalog
– older protocololder protocol
Integrated Services Digital Network (ISDN)
Integrated Services Digital Network (ISDN)
– Digital Digital
Protocols for Public Phone
Protocols for Public Phone
Systems (cont.)
Systems (cont.)
Frame Relays
Frame Relays
– Move to fiber opticsMove to fiber optics
Asynchronous Transfer Mode (ATM)
Asynchronous Transfer Mode (ATM)
– Smaller packet sizeSmaller packet size
Data Communications Links the
Data Communications Links the
General Systems Model Elements
General Systems Model Elements
Standards
Management Information
processor Environment
Networks
Networks
Each device must be connected to the
Each device must be connected to the
communications medium via a network
communications medium via a network
interface card (NIC)
Types of Networks
Types of Networks
LAN (local area network)
LAN (local area network)
– Limited area but could include 100 or so microsLimited area but could include 100 or so micros – Facilitates office automationFacilitates office automation
MAN (metropolitan area networks)
MAN (metropolitan area networks)
– spans one city/metropolitan areaspans one city/metropolitan area
WAN (wide area network)
WAN (wide area network)
– Covers a large geographic areaCovers a large geographic area
Common LAN Topologies
Common LAN Topologies
Star
Common LAN Topologies
Common LAN Topologies
Ring
Common LAN Topologies
Common LAN Topologies
Bus
Satellite Satellite Earth Earth station station Earth Earth station station Telephone Telephone company company central office central office Telephone Telephone company company central office
central office Telephone
Types of Networks (cont.)
Types of Networks (cont.)
Internet
Internet
– Collection of networksCollection of networks – PublicPublic
Intranet
Intranet
– Uses Internet network protocolsUses Internet network protocols – Limits accessibilityLimits accessibility
– FirewallFirewall
Extranet
Extranet
Control of Data
Control of Data
Communications Networks
Communications Networks
Centralized
Centralized
– Point-of-sale terminalsPoint-of-sale terminals – Data collection terminalsData collection terminals
Distributed processing
Distributed processing
– Receiving computer runs programs that use dataReceiving computer runs programs that use data
Client/server processing
Client/server processing
– Mixes centralized and decentralized processing Mixes centralized and decentralized processing
strategies
Legend:
A Network of Terminals
Legend:
A Distributed Processing
A Distributed Processing
Network
Communications Hardware
Communications Hardware
ModemModem
– Converts digital to analog and vice versaConverts digital to analog and vice versa
– Bits per second determines transmission speedBits per second determines transmission speed – Local loopLocal loop
Hub Hub
– Receives a data packet from a computer at one end of Receives a data packet from a computer at one end of
one spoke of the star topography and copies its
one spoke of the star topography and copies its
contents to all other computers
Data Communications with a
Data Communications with a
Modem
Modem
Computer
Computer
Modem
Modem ChannelChannel ModemModem
Computer
Computer
Communications Hardware
Communications Hardware
(cont.)
(cont.)
Router
Router
– Device that connects many LANsDevice that connects many LANs – More sophisticated than a bridgeMore sophisticated than a bridge
– Process header information of a packetProcess header information of a packet
Switch
Switch
– Filters data not intended for a computer on a Filters data not intended for a computer on a particular network
Communications
Communications
Connections
Connections
Private Lines
Private Lines
– Circuit that is always open to communications Circuit that is always open to communications traffic
traffic
– Also called leased line or dedicated lineAlso called leased line or dedicated line – Two typesTwo types
» T-1 - Maximum speed just over 1.5 MbpsT-1 - Maximum speed just over 1.5 Mbps » T-3 - Maximum speed 43 MbpsT-3 - Maximum speed 43 Mbps
Communications
Communications
Connections (cont.)
Connections (cont.)
Virtual Private Networks (VPNs)
Virtual Private Networks (VPNs)
– Tunneling software makes Internet connections Tunneling software makes Internet connections more secure
more secure
– Privacy through authenticationPrivacy through authentication
Network Management
Network Management
Digital nervous systems of an organization
Digital nervous systems of an organization
Network planning
Network planning
– Anticipates firm’s network needsAnticipates firm’s network needs – Monitor’s performanceMonitor’s performance
Network Control
Network Control
– Determines faultsDetermines faults
Network Management
Network Management
(cont.)
(cont.)
Network managerNetwork manager
– Planning, implementing, operating, and controlling a Planning, implementing, operating, and controlling a
firm’s data communications network(s)
firm’s data communications network(s)
StaffStaff
– Network analysts (a type of systems analyst)Network analysts (a type of systems analyst) – Software analysts Software analysts
– Data Communication Technicians (specialize in Data Communication Technicians (specialize in
hardware)
hardware)
Wireless Networks
Wireless Networks
Cellular networks
Cellular networks
– Hand held telephonesHand held telephones – Primarily for voicePrimarily for voice
Wireless LANs
Wireless LANs
– Extensions of regular LANsExtensions of regular LANs
Wide-area wireless networks
Wide-area wireless networks
Wireless Networks (cont.)
Wireless Networks (cont.)
Paging networks
Paging networks
– Receive only capabilityReceive only capability
Personal Communications Network (PCN) is the networking infrastructure for wireless.
A Network with Mobility
A Network with Mobility
Capability
Capability
MSS = mobile support station
MU MU MU
MU MU MU MU MU MU
MU MU MU
MSS
MSS MSS
MSS
Fixed host
Fixed host
Fixed host
Summary
Summary
Data communications enable computers to
Data communications enable computers to
share information and applications
share information and applications
Networks
Networks
– LANsLANs – MANsMANs – WANsWANs
Summary [cont.]
Summary [cont.]
Basic Hardware
Basic Hardware
– HubsHubs – RoutersRouters – BridgesBridges – SwitchesSwitches
