Transcript Telecom

TELECOMMUNICATIONS
TELECOMMUNICATIONS
SYSTEM
 A telecommunications system is a collection
of compatible hardware and software
arranged to communicate information --text,
graphics, images, voice, or video-- from one
location to another.
COMPONENTS
 Computers to process information, terminals and
other input/output devices to send or receive data
 Communications channels (telephone lines, fiber
optic cables, coaxial cables, wireless transmission) to
link sending and receiving devices in networks
 Communications processors (modems, multiplexers,
front-end processors) to provide support functions for
data transmission
 Communications software to control input and output
activities and to manage other functions of the
communications network
PRINCIPAL FUNCTIONS
 Transmission of information
 Establishing an interface between sender and
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receiver
Routing messages along the most efficient path
Processing information to get the right message to
the right receiver
Checking and editing transmitted information for
errors and formats
Converting messages from the speeds and codes of
one device to those of another
Controlling the flow of information, routing messages
and maintaining overall network structure
COMM. CHANNELS
 Communication channels are means by
which data are transmitted from one device in
a network to another.
 A channel can utilize different kinds of
transmission media.
COMM. CHANNELS
 Twisted Pair (Shielded Twisted Pair and
Unshielded Twisted Pair)
 Twisted wire consists of strands of copper wire
twisted in pairs. Shielded twisted pair uses a special
braided wire, which surrounds all the other wires,
which helps to reduce unwanted interference.
 The features of twisted pair cable are:
 Low cost
 Slow transmission (interference with high-speed
transmission)
 10 MBps (baud rate)
COMM. CHANNELS
 Coaxial Cable
 Thickly insulated copper wire that can transmit a
larger volume of data than twisted wire can.
 The general features of coaxial cable are:
 Up to 200MBps
 Fast
 Interference free
 Hard to wire
 Does not support analog signals
COMM. CHANNELS
 Fiber Optic
 Consists of thousands of strands of clear glass fiber
(human hair thick) which are bound into cables. Data
are transformed into pulses of light, and sent by a laser
device at a rate of 500KBps to several billions per
second.
 High-speed [large bandwidth requirements like video,
large database systems] long distances and
interconnecting networks.
 It costs more than either twisted pair or coax, and
requires special connectors and jointing methods.
 Durable, used for backbones [linking LAN’s together] or
rings (100Mbps)
COMM. CHANNELS
 Wireless Transmission
 Send signals through air or space
 (cellular phone, microwave transmission-high
frequency radio signal-25 to 30 miles apart not to be
affected by earth curvature, communication satellitemicrowave signal bounced off satellite, etc.).
COMM. DEVICES
A modem is a device that translates digital signals into analog form (and
vice versa) so that computers can transmit data over analog networks
such as telephone and cable networks.
NETWORK TYPES
 LAN (Local Area Network)
 Small networks are often called Local Area
Networks. A LAN is a network allowing easy
access to other computers or peripherals.
 The typical characteristics:
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physically limited (< 2km)
high bandwidth (> 1mbps)
inexpensive cable media (coax or twisted pair)
data and hardware sharing between users
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NETWORK TYPES
 Metropolitan Network
 These are networks used inside cities and
metropolitan areas.
 Connections are done by fiber optic cabling
for short distances or by modems. These also
connect LANs together.
 The use of these networks is to send data
(files or faxes) from central office to
distributors outside the city.
NETWORK TYPES
 Wide Area Networks (WAN)
 These networks can be regional, national or
even international. They supply the
organization with sound and video
communications.
 Communication is performed by satellites or
microwaves as well as modems. For
international networks communication
requires some standards which are named as
protocols. Internet is an example to WANs.
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NETWORK SEGMENT
 A network segment is a length of cable that
devices can be attached to, which has its own
unique address and has a limit on its length
and the number of devices, which can be
attached to it.
NETWORK SEGMENT
 Large networks are made by combining
several individual network segments together,
using appropriate devices like routers and/or
bridges. Bridge is used to allow traffic from
one network segment to the other.
 Each network segment is considered unique and has its own
limits of distance and the number of connections possible.
NETWORK SEGMENT
 When network segments are combined into a
single large network, paths exist between the
individual network segments. These paths
are called routes, and devices like routers
and bridges keep tables, which define how to
get to a particular computer on the network.
 When a packet arrives, the router/bridge will
look at the destination address of the packet,
and determine which network segment the
packet is to be transmitted on in order to get
to its destination.
NETWORK TOPOLOGY
 Topology refers to the way in which the
network of computers is connected. Each
topology is suited to specific tasks and has its
own advantages and disadvantages.
 The choice of topology is dependent upon:
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type and number of equipment being used
planned applications and rate of data transfers
required response times
cost
BUS TOPOLOGY
 All workstations connect to the same cable segment
commonly used for implementing Ethernet at 10mbps
the cable is terminated at each end wiring is normally
done point to point a faulty cable or workstation will
take the entire LAN down two wire, generally coax.
 Devices can be attached or detached from the
network at any point without disturbing the rest of the
network
 Overall performance declines as more users and
devices are added, because all message traffic must
flow along the central bus
 Today, the bus design is much less popular
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RING TOPOLOGY
 Can be thought of as a bus network with the ends
connected. The physical wiring can resemble a star pattern
using a central device called Multistation Access Unit
(MAU) wiring workstations into a logical ring.
 One disadvantage of a ring network is that if a network
device fails (such as a PC or a server), the devices
downstream from the failed device cannot communicate
with the network
 Token ring protocol is used for controlling station access to
the ring. A short message (called a token) is circulated
around the ring, being passed from station to station (it
originates from a controller or master station, which inserts
it onto the ring.
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FDDI
 Fiber Distributed Data Interface (FDDI) is
based on two counter-rotating 100-Mbit/sec
token-passing rings.
 The rings consist of point to point wiring
between nodes, which repeat the data as it is
received.
FDDI
STAR TOPOLOGY
 All wiring is done from a central point (the server or
hub) has the highest cable lengths of any topology.
 Each workstation is wired in star fashion back to a
concentrator-wiring centre (hub/switch). With 32/64..
ports. One of these ports is connected to a server, or
the output of the hub can be connected to other hubs.
 Disadvantage of the star design is that the entire
network is dependent on the switch
 However, in most large star networks, backup
switches are available immediately in case of
hardware failure
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Network Models
 Routers
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Routers differ from switches in that they
connect networks
Gateway can connect to a larger, dissimilar
network, such as the Internet
Proxy server provides Internet connectivity for
internal LAN users
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Components of a Simple Computer Network
Illustrated here is a very simple computer network, consisting of computers, a
network operating system residing on a dedicated server computer, cabling (wiring)
connecting the devices, network interface cards (NIC), switches, and a router.
Corporate Network Infrastructure
Today’s corporate
network
infrastructure is a
collection of many
different networks
from the public
switched
telephone network,
to the Internet, to
corporate local
area networks
linking workgroups,
departments, or
office floors.
Client/Server Architecture
 Today’s interconnected world requires an
information architecture that spans the entire
enterprise
 Whether you are dealing with a departmental
network or a multinational corporation, as a
systems analyst you will work with a
distributed computing strategy called
client/server architecture
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Client/Server Architecture
 Overview
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Client/server architecture refers to systems that
divide processing between one or more
networked clients and a central server
The client submits a request for information
form the server, which carries out the operation
and responds to the client
Many early client/server systems did not
produce expected savings
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Client/Server Architecture
 Client/Server Tiers
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Two-tier design; UI on client, data on server,
application on both or on each
Three-tier design; UI on client, data on server,
application on middle layer (application server),
because it provides the application logic, or
business logic
Three-tier designs also are called n-tier designs
The middle layer is more efficient and costeffective in large-scale systems
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