Lecture6 Data Networking.pptx

Data Networking and
Communications

TELECOMMUNICATIONS
 Communications is an activity associated with distributing
or exchanging information while Telecommunications refers
to the technology of communications at a distance that
permits information (today it, involves Data: digital and
analog, Voice: spoken word and Video: telecommunication
imaging) to be created any where and used everywhere
with little delay.
 Networking refers to the interconnection of two or more
computers and/ other data transmitting equipment (such as
mobile phones, printers etc). LANs, MANs and WANs are
examples of computer networks.

Networks
 Computer Networks are categorized into three: that is,
LAN, MAN and WAN
 Local Area Networks (LAN)
 Metropolitan Area Networks (MAN)
 Wide Area Networks (WAN)

Local Area Network (LAN)
 Small interconnected of personal computers or
workstations and printers within a building or small area up
to 10 kilometers.
 Small group of workers that share common application
programs and communication needs. LANs are capable of
very high transmission rates (100s Mb/s to G b/s).
 LAN equipment is usually owned by organization. Medium
may be owned or leased from telephone company provider
or common carrier.

WANs
 WANs were developed to communicate over a large
geographical area (e.g. lab-to-lab; city-to-city; east coast-
to-west coast; North America-to-South America etc).
 WANs require the crossing of public right of ways (under
control and regulations of the interstate commerce and
institute of telephone and data communications established
by the government and international treaties).

 WANs around the world rely on the infrastructure
established by the telephone companies (“common
carrier”) or public switched telephone network (PSTN).
WANs consist of a number of interconnected switching.
 Transmission signals are routed across the network
automatically by software control to the specified
destination.
 The purposes of these nodes are to route messages
through switching facilities to move data from node to node
to its destination.

Network Topologies
 Network topology refers to the way that your computer
network is arranged.
 The network can have a physical or a logical topology. The
physical topology describes the layout of computers and
where the workstations are positioned.
 The logical network topology describes how the information
flows through the network. Ring, Star, Bus, Mesh and
Hybrid are examples of Network Topologies.

Bus Topology
 Each node is daisy-chained (connected one right after the
other) along the same backbone.
 Information sent from a node travels along the backbone
until it reaches its destination node.
 Each end of a bus network must be terminated with a
resistor.

 The Nodes can be computers or any other devices that are
able to communicate (share data) in a Computer Network.
 The Backbone is a communication media: that is, the
means of connection between the communicating devices.
 Twisted pair cables, coaxial cable and fiber optic cables
are good instances of communication media.

Ring Topology
 Similar to a bus network, rings have nodes daisy chained,
but the end of the network in a ring topology comes back
around to the first node, creating a complete circuit. Each
node takes a turn sending and receiving information
through the use of a token.

 The token along with any data is sent from the first node to
the second node which extracts the data addressed to it
and adds any data it wishes to send.
 Then second node passes the token and data to the third
node, etc. until it comes back around to the first node
again.
 Only the node with the token is allowed to send data. All
other nodes must wait for the token to come to them.

Star Topology
 In a star network, each node is connected to a central
device called a hub.
 The hub takes a signal that comes from any node and
passes it along to all the other nodes in the network. In a
star network, each node is connected to a central device
called a hub.
 The hub takes a signal that comes from any node and
passes it along to all the other nodes in the network.

Hybrid network
 A Star network topology can be blended with network
topologies like the Ring and to Bus topology to form a
hybrid network topology.

Basic transmission medium
concepts
 Medium is the physical path between transmitter and
receiver in a data transmission system. In Guided Medium,
the waves are guided along a solid medium path (twisted
pair, coaxial cable, and optical fiber).
 In Unguided medium, the waves are propagated through
the atmosphere and inner/outer space (satellite, laser, and
wireless transmissions).

Medium examples by type
 Conductive: twisted pairs and coaxial cables
 Electromagnetic: microwave
 Light: lasers and optical fibers (need clear line of sight)
 Wireless – inner/outer space; satellite (Omni directional 
security issues)

Coaxial cable
 This is the widely used medium and is installed for use in
business and corporation Ethernet and other types of
LANs. It consists of inter copper insulator covered by
cladding material, and then covered by an outer jacket.

Applications of Coaxial cable :
 TV distribution (cable TV); long distance telephone
transmission; short run computer system links
 Local area networks

Twisted Pair Cables
 Each wire with copper conductor
 Separately insulated wires
 Twisted together to reduce cross talk
 Often bundled into cables of two or four twisted pairs
 If enclosed in a sheath then is shielded twisted pair
(STP) otherwise often for home usage unshielded

Optical Fibers
 Multimode fiber is optical fiber that is designed to carry multiple
light rays or modes concurrently, each at a slightly different
reflection angle within the optical fiber core.
 It is used for relatively short distances because the modes tend
to disperse over longer lengths (this is called modal dispersion).
 For longer distances, single mode fiber (sometimes called
monomode) fiber is used. In single mode fiber a single ray or
mode of light act as a carrier

Physical Description of optic fiber
 Glass or plastic core of optical fiber = 2 to 125 µm
 Greater capacity; 2 Gb/s over 10’s of Km
 Smaller size and lighter weight
 Cladding is an insulating material
 Jacket is a protective cover
 Laser or light emitting diode provides transmission light
source
 Greater repeater spacing – fewer repeaters, reduces line
regeneration cost

Wireless Transmission
 Satellite is a microwave relay station. Satellite ground
stations are aligned to the space satellite, establishes a
link, broadcast at a specified frequency.
 Ground station normally operates at a number of
frequencies. Satellite space antenna is aligned to the
ground station establishes a link and transmits at the
specified frequency.
 Satellites are capable of transmitting at multiple
frequencies simultaneously, full duplex.
 To avoid satellites from interfering with each other, a 4

Network Devices
 Network devices are components used to connect
computers or other electronic devices together so that they
can share files or resources like printers or fax machines.
 Devices used to setup a Local Area Network (LAN) are the
most common type of network devices used by the public.
 A LAN requires a hub, router, cabling or radio technology,
network cards, and if online access is desired, a high-
speed modem.

Hubs
 A hub is the central component place where data
converges from one or more directions and is forwarded
out in one or more directions in a LAN.
 There are four components in a basic wired hub network:

These are :
1) Ethernet cable: This is the physical cable that links the
computers together, enabling them to communicate. The
Ethernet cable, also called twisted pair, or 10-Base T, plugs
into a network card located in each computer on the LAN.
2) Network Interface Cards (NICs): One of these cards
goes into a vacant PCI slot inside each computer. The
back of the card features a port for one end of an Ethernet
cable. Newer computers normally have a networking card
built-in.

3) Networking Hubs: The networking hub is a junction box
with several ports in the back for receiving the Ethernet
cables that are plugged into each computer on the LAN.
With Ethernet cables going from each NIC to the hub, all
computers are connected to the hub.
4) Networking Software: Most operating systems today
come with networking software built-in, but the software is
also available from third parties. The software works with
the hardware to create a networking environment on each
computer, allowing the user to see shared files and
recourses. It also allows for administration of the network.

 With a group of computers wired to the hub and the
software installed, the computers can talk to each other.
 Networking hubs will broadcast all traffic that comes
through the hub to all machines or nodes connected to the
LAN.
 Each computer/node on the LAN will have its own address,
called a MAC (Medium Access Control) address. Each
node will ignore any traffic not addressed to its MAC
address.

 Networking hubs are simple devices that are fine for home
use in most cases, but not considered optimal for
workplace environments.
 Networking hubs can only operate in half-duplex mode -- a
computer cannot receive and send transmissions at the
same time.
 Another drawback is that networking hubs broadcast traffic
indiscriminately to all machines on the LAN. This opens the
door to security issues, making it easy to use so-called
"packet sniffers," for instance, to snoop on all network
traffic.

Gateway
 A gateway is a network point that acts as an entrance to
another network. On the internet, in terms of routing, the
network consists of gateway nodes and host nodes.
 Host nodes are computer of network users and the
computers that serve contents (such as Web pages).
Gateway nodes are computers that control traffic within
your company’s network or at your local internet service
provider (ISP).
 A gateway interconnects dissimilar protocols and servers,

Router
 A router is a device or a software in a computer that
determines the next network point to which a packet should
be forwarded toward its destination.
 Allow different networks to communicate with each other.
Routers create and maintain a table of the available routes
and their conditions and use this information along with
distance and cost algorithms to determine the best route
for a given packet.
 A packet will travel through a number of network points
with routers before arriving at its destination. A router

Bridge
 A bridge is a product that connects a local area network
(LAN) to another local area network that uses the same
protocol (for example, Ethernet or token ring). A bridge
examines each message on a LAN, "passing" those known
to be within the same LAN, and forwarding those known to
be on the other interconnected LAN (or LANs).
 A bridge interconnects two LANs that use the SAME logical
link control protocol but may use different medium access
control protocols.

Switch
 A networking switch is the central device in a wired or
wireless LAN (local area network).
 It receives signals from each computer on the network via
Ethernet cables in a wired network or radio waves in a
wireless LAN.
 In both cases, the networking switch directs traffic across
the LAN, enabling the computers to talk to each other and
share resources.
 It allows different nodes of a network to communicate

 A networking switch runs in full-duplex mode, meaning a
machine on the LAN can receive and transmit data
simultaneously.
 This is much faster than a networking hub, an alternate
device that serves the same purpose as a switch but
operates in half-duplex mode, allowing each machine or
node either to send or receive at any given time.
 Another key difference between a networking switch and a
hub is that the switch sends traffic discriminately, using
addresses to direct traffic packets exactly where they are
supposed to go.

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