Transcript Networks and Telecommunications

Chapter 6
Networks and Telecommunications
The Strategic
Management of
Information
Technology
Transaction Processing
System
Input
Process
Systems Development
Communication
Information
Output
Local Area Networks
Local Area Networks:
A Definition
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Provides access to shared resources such as
printers, data, and applications
Increases controllability and consistency in
applications and data
Increases access to shared applications and
databases in large computers with many users
Provides a vehicle for electronic mail
Shares access to external resources through
communication lines
Local Area Networks:
Reason
Performance
 Change Management
 Systems Management
 Network Management
 Direct Communication
 Ease in Installation and Maintenance
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Network Protocols
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1.
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Physical Layer
Interfaces between Network Medium and Network Drives
Defines Electrical and Mechanical Characteristics of Network
Bad Plug
Network Protocols
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Logical Link Layer
Frames Packets
Controls Physical Layer Data Flow
Data Colision
Network Layer
Addresses and Routes Packets
Handles Fragmentation and Reassembly of Data
Broadcast Storm
Transport Layer
Manages Network Layer Connections
Provides Reliable Packet Delivery Mechanism
Multiple ACKS
Network Protocols
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Session Layer
Provides Remote Procedure Call Support
Reports Lower-Layer Errors
Protocol Error
Presentation Layer
Specifies Architecture-Independent Data Transfer Format
Encodes and Decodes Data; Encrypts and Decrypts Data;
Compresses Data
Misdirected Data
Application Layer
Provides Interface to End-User Processes
Provides Standardized Services to Applications
Incompatible Software
Communication according to the Open
System Interconnection Reference Model
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Application Layer
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Presentation Layer
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Session Layer
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Transport Layer
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Network Layer
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Data Link Layer
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Physical Layer
Physical Layer
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Hardware Description:
The interface to the physical cable medium
is described; layout of connectors, signals
on each connector, voltage levels.
The physical connection to the network, how
connections are established and maintained,
and how error conditions in data medium are
handled.
Physical Layer
Data Link Layer
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Software Description:
Transmit blocks of data from the data link layer
in one computer to another.
Detect errors in data blocks and either correct
the errors or ensure retransmissions of the
effected data blocks.
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Data Link Layer
Protocols
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Token Passing (IBM)
– All blocks of data carried around the network with a source and destination
address
– Traffic is guided physically from unit to unit around the ring
– IEEE 802.5; ISO IS 8802-5
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Token Bus
– Traffic is guided on a common data bus, which directly connects all units in
the network
– All units are part of an organized logical sequence
– All units at any point in time know the address of the unit before and after in
logical sequence.
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CSMA/CD (ethernet)
– All units connected to the common bus can come in at any point in time
after the unit has tested and found out no one else is using the network.
– When collisions happen, both units resend the data after a short break.
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Protocols
Medium Access Control
– Interfaces to the actual transport media to enable applications to
communicate
– IEEE 802.5; ISO IS 8802-5
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Logical Link Control
– Insures that all software implemented on the top five layers of the OSI
Model remains independent of which physical network is implemented in the
bottom of the model.
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NETBIOS
– Constructs, maintains, and uses a table of relations between the Token Ring
addresses and the defined names of units and services in the network; this
enables real names to be used.
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Advanced Program to Program Comm.
– Supports program to program communications between different systems
through the Token Ring.
– Specific implementation of the IBM Systems Network Architecture (SNA)
Logical Unit (LU) 6.2 architecture.
Topologies
Star Topology
 Bus
 Ring
 Physical Star, Logical Ring
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Topologies
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Star Topology
– Connections are made from all connected machines to one central place.
– Control unit controls traffic in the network.
– Computer in the middle has absolute control over traffic in the machine.
Topologies
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Bus Topology
– One cable passed throughout entire implementation and to which each unit
is connected.
– Network cannot be centrally controlled.
BUS
Topologies
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Token Ring Topology
– Signals in the network are passing from machine to machine.
– This gives controlled and stable data traffic in the network.
– No central control or configuration of the traffic.
RING
Topologies
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Token Ring Topology
– IEEE 802.5; ISO IS 8802-5
– Uses the Baseband Transmission Technique
 Signal is directly on the transmission medium without modulating a
carrier signal.
 Information occupies entire bandwidth in the medium.
– Token format:
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SD AC
Starting delimiter (one byte)
Access control (one bit)
Frame control
Destination address
Source address
Routing information
Information Field
Frame check sequence
Ending delimiter
Frame status
– Address Recognized Bit
– Frame Copied Bit
FC
DA SA
RI
INFO
FCS
ED
FS
Topologies
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Token Ring Topology
– 4 Millionbits/s versus 15 Millionbits/second
 16 Mbits/s is for large data transfer
– Each individually attached unit can only work at its speed
 The lower speed of the individual machine limits the data transfer rate.
Topologies
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Physical Star, Logical Ring Topology
– Each cable connection consists of two wires and provides two ways for the
signal to pass in the one cable.
– Logical connection in a ring insures stability of the traffic.
– Configuration and management from a central place.
Wiring
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Telephone Twisted Pair
– Unshielded and susceptible to noise
– Not for higher data rates or long distances
– Inexpensive
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Coaxial Cable
– Central core with shield around it
– Shield insures radio frequency noise is not generated
– High data rates at long distances
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Fiber Optic Cable
– Light signals transmitted by light emitting diodes are immune to electrical
and magnetic noise
– High data rates at long distances
Cost-effective ways to increase access
Multistation Access Unit (MAU)
 Controlled Access Unit (CAU)
 Fiber Distribution Data Interface (FDDI)
 Advanced Peer-to-Peer Networking (APPN)
 Bridges, Gateways, and Routers
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Cost-effective ways to increase access:
Multiple Access Units
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Multistation Access Unit (MAU)
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Passive Ring Concentrator
Includes room for 8 connected units
Forms a ring segment
Passes signal back to ring
Ring Out/Ring In (can be connected in series)
Controlled Access Unit (CAU)
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Active Ring Concentrator
Contains logic for control functions
Passes signal back to ring
Ring Out/Ring In (can be connected in series)
Acts as Primary Input, Primary Output, and Secondary Adapter
Cost-effective ways to increase access:
FDDI and APPN
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Fiber Distribution Data Interface (FDDI)
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100 Million bits/second
Fiber connections enable larger geographic dispersion
Stations can attach directly to a ring or through a concentrator
Can connect to both the primary and secondary ring simultaneously
Advanced Peer-to-Peer Networking
(APPN)
– Programs capable of comunicating with other programs running on other
machines on the network can be automatically set in session with each
other.
– Network nodes know all APPC resources in both themselves and in end
nodes
– Each network node maintains a topology database of APPC resources and
available routes through the network.
Cost-effective ways to increase access:
Bridges, Gateways, and Routers
 Bridges
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Gateways
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Connection between two local rings.
Unexpected physical breakdown in one ring will only affect this ring and not other rings.
Discourage users on one ring to use resources on another ring.
Operates in only the lowest levels of the OSI Model.
Connection between two token ring networks.
Units that connect a Token Ring Network to a computer system or network that uses
communications protocols other than Token Ring protocols.
Establish connections between units in the token ring network and units that are not
directly attached to the Token Ring Network.
Handles/Requires protocol conversion
Operates in all seven layers of OSI Model.
Routers
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Allow for selected higher level protocols to communicate through the network.
LAN-to-LAN WAN Program.
Remote NETBIOS Access Facility.
Network Layer
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Responsible for buffering and routing packets
throughout the network. (Virtual Circuits)
Essential in Wide Area Networks, not used in
bus-topology LANs.
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Network Layer
Network Layer
Network
Operating
System
Novell
UNIX
Microsoft/NT
OS/2
Default
Prtocol
IPX/SPX
Wide Area
Network
NDS
Internet Packet Exchange/
Sequence Packet Exchange
(lower/higher)
Naming Convention
TCP/IP
DCE
Transmission Control Protocol/
Internet Protocol
(higher/lower)
Net/BIOS
Basic In Out System
Addtitional Security
Transport Layer
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Partitions long messages arriving from upper
session layers into data packets. On the receiving side, reassembles messages from
collections of packets received.
Below Transport Layer, a data packet is a
unit of information handled bu the network.
Above it, messages are the information units.
Transport Layer
Session Layer
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Session Layer
Responsible for providing a communication
session between two user processes running
on two separate network nodes. Responsible
for determining whether a session can begin,
be maintained, or terminated.
Presentation Layer
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Presentation Layer
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Converts user messages from the
form used bu the application layer
to that used by all lower layers.
Below this layer, the meaning of data
fields of messages and packets does
not influence their processing.
Application Layer
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Application Layer
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Boundary between the OSI network
and the application (user) processes.
If a LAN operates as a distributed
system, the application layer is
responsible for direct communication
with elements of the distributed
operating system.
Architectural Layers and Tiers
Architectural Layers
Client
User
Interface
Function
Set
Database
Access
Network
Server
Communication
Protocol
Data
Dictionary
Translation
Layer
Data
Objects
Data
Transport
Data
Partitioning
Architectural Layers and Tiers
Tiered-Architecture
Presentation
Processing
Data
Functionality
Server
Client
Remote
Procedure
Calls
Functionality
Server
Database
Functionality
Server
Client
Database
Functionality
Server
Architectural Layers and Tiers
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Two-Tier Architecture
– Advantages
Application Development Speed
 Ability to model data and populate a database
on a remote server
 Robust
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– Disadvantages
Version control and redistribution problems
 System security complications
 Client tools and middleware are volatile
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Architectural Layers and Tiers
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Three-Tier Architecture
– Advantages
Separates Presentation, Processing, and Data
into separate, distinct software tiers
 Middle tier is programmed in portable C code
 Remote Process Call for calling technique
 Overall flexibility in resource allocation
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– Disadvantages
Lack of development tools
 More code in more places
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Local Area Networks
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Important Mechanism to Integrate:
– Hardware
– Software
– Application Development Environment
Communication according to the Open
System Interconnection Reference Model
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Application Layer
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Presentation Layer
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Session Layer
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Transport Layer
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Network Layer
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Data Link Layer
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Physical Layer
Communication according to the Open
System Interconnection Reference Model
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Application Layer
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Presentation Layer
5
Session Layer
4
Transport Layer
3
Network Layer
2
Data Link Layer
1
Physical Layer
Changes In The Marketplace
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The quality imperative
Consumer computing
Deregulation of some major industries
Crossing industry boundaries
Traditional customers are “leaving”
Crossing national boundaries
Production is becoming global
New product and service development cycles
are shortening
Cooperative Processing
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Cooperative Processing means that processes on two or
more geographically dispersed computers cooperate in
order to complete a task. In a primitive way, we have had
a form of cooperative processing with this broad definition
for several years, in the form of terminals connected to
host (usually mainframe) computers.
Client/Server Systems are a form of cooperative
processing where client and server machines share a
processing workload.
Attributes of Cooperative
Processing
Distributed processing
 Connectivity among processors
 Distributed databases
 System-wide rules
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Connectivity Elements
Technical connectivity means that it is
technically possible to interconnect two
units so that they can communicate
 Procedural connectivity means that
procedures are in place to permit and
encourage connectivity
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Building Cooperative
Processing Systems
Benchmark and prototype new
technologies to verify vendors’
claims.
 An open architecture works on
mission-critical applications.
 Large distributed system projects
need a vendor coordinator.
 Use of CASE was mandatory.
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Components Of Cooperative
Processing Systems
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Operating Systems - provide the processing capabilities. They
need to be designed for networking and powerful workstations to
be useful in distributed systems.
Mainframes - likely to continue as the primary database servers,
because their database management systems are highly
sophisticated, and reliable distributed database technology is not
yet available.
Workstations - the focal point in cooperative processing, because
they initiate the requests for services that are provided across the
networks.
Servers- generally perform specialized functions, such as image
servers, electronic mail servers, video servers, voice mail
servers, credit card servers, expert system servers, etc..
Superservers - support hundreds of workstations each,
performing mission-critical processing at the node and handling
heavy traffic.
Forms Of Cooperative
Processing
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Host-driven terminal emulation is where the desktop computer
runs an application that connects to a host as a standard “dumb”
terminal.
Host-driven front ending is where the desktop computer runs a
host-based application by providing a graphical interface for the
user, making the system easier to use.
Host-driven client/server computing is where the desktop runs an
application that turns it into a server capable of receiving
messages form the host to perform some tasks.
Desktop-driven client/server computing is where the host
functions as a transaction processing server and the desktop
submit queries to it.
Peer-to-peer computing is where processing occurs
simultaneously on both the desktop and host, with control
switching between the two.
Cooperative Processing
Permits lower-cost computing
 Makes the end user the focus of
computing
 Expands the computing universe by
aiming at work groups
 Supports new organizational
structures via its connectivity
 Increases organizational flexibility
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Guidelines For Building
Networks
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Create an overall architecture - meaning a set of
company policies and rules which, when
followed, are expected to lead to the network
environment that is desired
Stress connectivity - the goal today is not a
single, coherent network, but rather finding a
means to interface many dissimilar networks
Use standards - Most complications in
networking are caused by incompatibilities which
can be reduced by using standards. In fact,
standards should be the foundation of an overall
architecture.
Network Connectivity
Components
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Bridges
– Link two similar networks together
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Routers
– provide additional translation and route
selection features
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Gateways
– link dissimilar networks
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Smart hubs
Network Architecture
Not a diagram or a set of diagrams
 Not one utopian solution for all network
problems
 Set of policies, principles, and
guidelines that will lead to more
widespread connectivity
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OSI’s Seven Layers
The Physical Layer
 The Data Link Layer
 The Network Layer
 The Transport Layer
 The Session Layer
 The Presentation Layer
 The Application Layer
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Broadband
Telecommunications
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Where more than one signal travels
over a communication medium at one
time. As organizations put more kinds
of data on computers, they need greater
bandwidth to whip this data around.
How a Telecommunications System Is
Analagous To a Highway System
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The Flows - The flow of information within and between the
corporate office, departments, and individuals is analogous
to the traffic flow in the highway system within and
between cities.
Building of Systems - Information systems departments
are responsible for designing, building, and maintaining the
information system in the same way that governments are
responsible for building and maintaining streets, roads,
and highways for cars and trucks.
Managed by Users - Once built, both systems are
managed not by builders but by users or drivers.
Standards - Government agencies provide standards and
laws for regulating the flow of highway traffic, that are
enforced by police. Similarly, the information systems
function develops and enforces the telecommunications
standards for message traffic.
“Facts of Life” in the Telecommunications
Industry
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Organizations have a multitude of networks
The reach of networks is expanding organizationally
The telecommunications industry is being
destabilized
Global network services are emerging
New technologies are improving bandwidth utilization
The focus of network designers is now
interconnecting LANs
Electronic mail provides a new communication
infrastructure
Murray’s Eight Phases to a Totally Distributed System
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Phase 1: The first phase is characterized by host-based, real-time query and update.
This phase is traditional on-line information system processing, where dumb
terminals access host-based applications to view and update data
Phase 2: The second phase provides additional query capabilities through file
transfers to PCs.
Phase 3: The third phase adds batch updating form PC data. This phase reverses
the philosophy of Phase 2 by making the PC database the master.
Phase 4: The forth phase enables real-time query and update from either host or
PC. This phase extends the capabilities of the PCs by allowing them to update the
host on-line.
Phase 5: The fifth phase introduces homogeneous cooperative processing without
two-phase commit, that is, like databases run on the same hardware and system
software platforms. This phase adds true distributed databases, across similar or
identical platforms.
Phase 6: The sixth phase moves to heterogeneous cooperative processing without
two-phase commit, that is, databases run on a mix of platforms. This phase extends
the previous one by permitting distributed databases across mixed platforms.
Phase 7: This seventh phase adds the all-important two-phase commit capability (to
homogeneous databases), going a system a true distributed database.
Phase 8: This phase extends Phase 7 to heterogeneous databases.
Personal Communications
Networks
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Permit person-to-person rather than location-to-location.
Each person will have his or her own personal phone
number associated with a lightweight telephone that he or
she carries around.
Each person will not only transmit telephone conversations
but also computer-based information, voice mail, electronic
messaging, call screening, and other personal from
anywhere.
Important technology for
– emergencies
 natural disasters
– special events
 political conventions and sporting events
Wireless LANs Will Likely be
the Best Alternative
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Wireless LANs have the advantage in hazardous
environments, in historic buildings where wiring
ducts are full, for disaster recovery, and in
temporary installations. Furthermore, there are
many instances where temporary
communications are needed, and wireless are
much easier to reconfigure. Wireless LANs use
either light (in the form of infrared) or radio (in
the form of narrowband or spread spectrum)
technologies to transmit signals.
T-Carriers Hierarchy and
Difference
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A T1 line is equivalent to a group of 24 voice
grade lines, which means its capacity is 1.544
million bits per second (mbps).
A T2 trunk has a capacity of 96 voice circuit
equivalent (6.312 mbps), T3 has a 672 voice
circuit equivalent (44.736 mbps) and T4 has a
4,032 voice circuit equivalent (139.264 mbps).
T-carriers are used mainly to carry analog voice
signals that have been digitized, while the
nomenclature of DS represents the arrival of true
end-to-end digital circuits.
Fast Packet Switching
Technologies
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Frame relay uses variable-length packets and is
slated to replace the workhorse of today’s data
networks, X.25. It is most appropriate for
sending large bursts of data.
Cell relay is faster than frame relay because it
transmits fixed-length packets, which require less
processing. It is most appropriate for transmitting
packets that must be received in sequence and
at standard intervals, such as voice and video.
Network Components
Network File Server
 Network Operating System
 Network Interface Card
 Workstation Software
 Connection
 Network Wiring Hub
 Backup Device
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Network Advantages
Sharing Printers and Other Devices
 Providing Mass Storage
 Sharing Data
 Providing Network Security
 Providing Communication Services
 Sharing Software
 Facilitating Group Interaction
 Permitting Distributed Processing
 Enhancing Software Support and
Training
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Key Client/Server Issues
Ability to Build Graphical User Interfaces
 Compenent Re-Use
 Team Development
 Deployment Scalability
 Cross Platform Delivery
 Adaptability
 Design/Integration
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Key Issues
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Strategic Business Objectives
Software Fit
Software Customization
User Productivity
Information Access
Flexibility and Adaptability
Software Implementation
System Performance
Customer Service
Cost of Ownership
Client/Server Evaluation
Object-Oriented Technology
 Integration of Third Party Components
 Application Partitioning
 Interpreted or Compiled Code
 Multiplatform GUI and Operating Systems
 Team Development
 Ease in Application Maintenance
 Open Connectivity to Multiple Databases
 On-Line Transaction Processing Applications
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SONET
The transport network for broadband
services will be SONET (synchronous
optical network), a set of international
standards for transmission over fiberbased networks at speeds of 51.84 mbps
(above T3) to a shopping 13 gigabytes
per second. its importance lies with the
fact that SONET will allow networks to
use equipment from different vendors due
to its “mid-span meet”-an information
model and messages sets for making
translations among equipment.
FDDI
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FDDI (fiber distributed data interface) is
an international standard for operating a
fiber optic cable network at 100 mbps
(nearly T4 speed). It is most
appropriate for backbone networks that
link LANs in a building or between
buildings, because it can support up to
500 workstations up to two kilometers
(1.2 miles) apart.