Transcript Chapter 11

Data Communications
The Basic Communication
Model
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Sender
Coder
Channel
Decoder
Receiver
Send
Sender
Coder
Coder
Channel
Decoder
Receiver
The Basic Communication Model
Computer-based Data
Communications
Data communications definition:
The movement of coded data and information
from one point to another by means of
electrical or electromagnetic devices, fiberoptical cables, or microwave signals. Also
called teleprocessing, telecommunications,
telecom, and datacom.
The Basic
Data Communications Schematic
Terminal
Modem
Channel
Modem
Computer
Basic Data
Communications
Schematic
Terminal
to Modem
to Channel
to Modem
to Computer
A modem is always required between a
telephone and a digital computer.
Types of Networks (interconnected
datacom devices)
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WAN (wide area network)
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LAN (local area network)
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Covers a large geographic area
Includes a wide variety of circuits
Usually includes host computers
Limited area but could include 100 or so micros
Facilitates office automation
MAN (metropolitan area networks)
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spans one city/metropolitan area
An Expanded Data
Communications Network
Visual display terminals
Hard copy terminals
Multiplexer
Cluster
control
unit
Other
types of
terminals
Modem
Channel
Multiplexer
Modem
Front-end
processor
Host
computer
Terminal Types
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Keyboard
CRT - Cathode Ray Tube
VDT - Video Display Terminal
Hardcopy terminal
Teleprinter terminal
Terminal Types (continued)
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Keyboard terminals
Push-button telephone
Point-of-Sale (POS)
Data collection
Special purpose
Other Data
Communications Hardware
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Cluster control unit -- controls multiple
terminals in an area
Modem -- rated speed of bits per second
determines transmission speed. Like a pipe
determines water flow.
Multiplexer -- allows multiple terminals to
share a single channel.
Channel
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n
WAN channel components
Local loop
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Typical circuitry
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Twisted pair (4 wires)
Coax (buried)
IXC circuit (interexchange)
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Typical circuitry
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Microwave
Fiber-optical cable
The Channel of a
Wide Area Network
Satellite
User’s
modem
IXC circuit
Local
loop
Earth
station
(interexchange
channel)
Earth
station
Telephone
company
central office
Microwave
tower IXC circuit
(interexchange
channel)
Telephone
company
central office
Telephone
company
central office
Microwave
tower
Local
loop
Telephone
company
central office
User’s
modem
Front-end Processor
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Ports
Serial versus parallel transmission
Message switching, store and forward
Host
The Front-end Processor
Software
Channel
Interface Units
Host Computer
Interface
Serial
transmission
Parallel transmission
To host
Secondary
storage
Data Communications Software
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Host (telecommunications monitor or TCM)
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Front-end processor (network control
program)
Telecommunications Monitor (TCM)
Host
Prioritize
message
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4
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Maintain
security log
DBMS
Interface
with DBMS
Backup and
restart
Security
log
Primary
storage
status
Network Control Program (NCP)
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Poll terminals such as roll call polling
Maintain a record of activity; date and time
stamps
Convert codes
Editing such as error checking and
reformatting
Add and delete routing codes
Maintain a history file of messages
Maintain statistics on network use
Data Communications Links the
General Systems Model Elements
T = terminal
Standards
Management
T
Input
T
Information
processor T
Transformation
T
Output
T
Environment
T
Basic Network Approaches
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Timesharing
Distributed processing
Client/server computing
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Clients are users, typically using workstations
networked to form LANs
Server is a mainframe, mini, or even a micro
Basic Network Approaches
(continued)
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Complex software permits resource sharing
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Combines central computing (MIS, DP)
with end-user computing
A Timesharing Network
Legend:
Computer
Terminal
A Distributed Processing Network
Legend:
Central
Computer
Distributed
Computer
Common Carriers
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Services
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Public-measured
Private (a.k.a. leased or dedicated line)
Integrated services digital network (ISDN)
ISDN- Integrated Services Digital
Network
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Simultaneous multimedia transmissions
Two types of channels
Data
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B channel carries data
D channel carries signals
Signals
Two Standard Structures
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Basic access (typically residential)
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B channels @ 64 kbps ea.
D channel @ 16 kbps
Primary access (typically business)
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B channels @ 64 kbps ea.
D channel @ 64 kbps
Local Area Networks
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File server, network server
Peripherals
Circuitry
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Owned by using firm
Twisted pair is least expensive
Coax handles videoconferencing
Fiber-optics is most secure
LAN Software
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Novell (NetWare) and Microsoft (Windows
NT) are leading vendors of LAN software
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Software allows servers and peer-to-peer
connections
Workstation
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Manager 1
Letter Quality
Printer
Workstation
2
Users
Network
Server
Secretary 1
Workstation
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Plotter
Secretary 2
Hard
Disk
Workstation
4
Manager 2
A Local Area Network
LAN Control Methodologies
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Contention-based (Ethernet)
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First-come, first-served
Collisions occur when load is heavy
Token-passing (IBMs Token Ring Network)
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Token -- set of data bits required to send a
message
Highlights in MIS
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Mobile computing
Wireless networks
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cellular
wireless Lans
wide-area wireless
paging networks
A Network with Mobility Capability
MU MU MU
MU MU MU
Fixed host
MSS
Fixed host
MSS
Fixed
network
Fixed host
MSS
MSS
Fixed host
MU MU
MSS = mobile support station
MU = mobile units
MU MU MU MU
Network Management
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1. Network planning
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Capacity planning
Staff planning
Performance monitoring
2. Network control
3. Network manager
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Staff
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Network analysts (a type of systems analyst)
Software analysts (specialize in datacom software)
Datacom technicians (specialize in hardware)
LAN managers
The Intranet
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Intranet applications
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policy and procedure manuals
Product and pricing information
Employee information
Job openings
Documents needing signatures
Schedules and calendars
Access to databases
Access to groupware
The Intranet (continued)
n
Steps to a successful Intranet
1. Determine information needs
2. Establish Intranet policy
3. Build an Intranet staff
4. Provide for end user document preparation
5. Determine whether to outsource the Intranet service
6. Select the Intranet outsourcer
7. Provide datacom services
8. Build in Intranet security
9. Monitor system performance
Intranet Implementation Steps
1. Determine
information needs
2. Establish
Intranet policy
Yes
No
5. Outsource?
6. Select the Intranet outsourcer
7. Provide datacom
resources
3. Build an
Intranet staff
8. Build in Intranet security
4. Provide for end user
document preparation
9. Monitor system
performance