Unit_1.pptx

Unit 1
Fundamentals of Computer Network
Definition, uses of computer network,
Network Devices: Bridge, Switch, Router, Gateway, Access Point,
Network Topologies: Bus, Star, Ring, Tree, Mesh, Hybrid,
Types of Network: LAN, MAN, WAN, PAN, Ad-Hoc Network, Networks Software,
Protocol, Design issues for the Network layers.
Types of Transmission Media: Guided Media, Unguided Media.
Network Architecture: Client-Server, Peer To Peer, Hybrid.
Network Models: OSI and TCP/IP Model,
Types of Addressing: Physical addressing, Logical addressing, Port addressing and other
addressing.

Computer Networks
• A computer network is a system for communicating between two or more computers and
associated devices
• A popular example of a computer network is the internet, which allows millions of users to share
information.
• Computer networks can be classified according to their size:
– Personal area network (PAN)
– Local area network (LAN)
– Metropolitan area network (MAN)
– Wide area network (WAN)

Primary objective of Computer Networks
Transfer data from machine A to machine B
Facilitate access to remote information
Facilitate sharing of data
Facilitates person to person communication
Facilitate Interactive Entertainment
Not every machine is connected to every other machine
 Establish connection between a pair of machines
to Transfer data
 Enable machines of different speeds to communicate with each other
10/31/2022

Applications of Networks
Resource Sharing
Hardware (computing resources, disks, printers)
Software (application software)
Information Sharing
Easy accessibility from anywhere (files, databases)
Search Capability (WWW)
Communication
Email
Message broadcast
Remote computing
Distributed processing (GRID Computing)
10/31/2022

Network hardware components-
Devices
Hubs, bridges, switches, routers, gateways, Access point

Devices and the layers at which they operate
Layer Name of Layer Device
3 Network Routers, layer 3
switches
2 Data Link Switches,
bridges, NIC’s
1 Physical Hubs

Hubs
Hub is Multiport repeater containing multiple ports
to interconnect multiple devices

Hubs
• Hubs regenerate and retime network signals
• Hubs propagate signals through the network
• They cannot filter network traffic
• They cannot determine best path
• used as network concentration points
• Uplink port – crossover mode or straight through mode

Bridges
• A layer 2 device designed to create two or more LAN segments, each
of which is a separate collision domain.
• The purpose is to filter traffic on a LAN, to keep local traffic local, yet
allow connectivity to other segments of the network.
• Filter traffic by looking at the MAC address
• Frame filtering

Bridges
• Filtering database
• Collection of data created and used by a bridge that
correlates the MAC addresses of connected workstations
with their locations
• Also known as a forwarding table

Bridges
• A bridge can also be used to connect two closely similar LANs.
• It is a media access control method used most especially in LAN
using early Ethernet technology LAN and a token ring LAN.
• The bridge examines the destination address in a frame and either
forwards this frame onto the next LAN or does not.
• The bridge examines the source address in a frame and places this
address in a routing table, to be used for future routing decisions.

Switches
• Subdivide a network into
smaller logical pieces

Network Switch
• Network switches appear nearly identical to network hubs, but a
switch generally contains more "intelligence" (and a slightly higher
price tag) than a hub
• Network switches are capable of inspecting data packets as they are
received, determining the source and destination device of that
packet, and forwarding it appropriately
• By delivering each message only to the connected device it was
intended for, a network switch conserves network bandwidth and
offers generally better performance than a hub

What is a Router?
• Routers are physical devices that join multiple wired or wireless
networks together
• Technically, a wired or wireless router is a Layer 3 gateway, meaning
that the wired/wireless router connects networks together
• A Gateway is a device that acts like a security guard and only allows
data in or out if it has the right network headers

Routers
• Home “networkers” often use an Internet Protocol (IP) wired or
wireless router
• IP is the most common OSI network layer protocol
• Protocols are the rules governing the transfer of data information.

Network Topology
The network topology defines the way in
which computers, printers, and other
devices are connected. A network
topology describes the layout of the wire
and devices as well as the paths used by
data transmissions.

Bus Topology
Commonly referred to as a linear
bus, all the devices on a bus
topology are connected by one
single cable.

Bus Topology
 Single cable connects all network nodes without intervening
connectivity devices
 Devices share responsibility for getting data from one point to another
 Inexpensive, not very scalable
 Difficult to troubleshoot, not fault-tolerant

Advantages of Bus Topology
 Works well for small networks
 Relatively inexpensive to implement
 Easy to add to it

Disadvantages of
Bus Topology
 Management costs can be high
 Potential for congestion with network traffic

Star Topology
The star topology is the most commonly
used architecture in Ethernet LANs.
Larger networks use the extended star
topology also called tree topology.

Star topology
 Every node on the network is connected through a central device

Star
 Any single cable connects only two devices
 Requires more cabling than ring or bus networks
 Easily moved, isolated, or interconnected with other networks

Advantages of Star Topology
 Good option for modern networks
 Low startup costs
 Easy to manage
 Offers opportunities for expansion
 Most popular topology in use; wide variety of equipment available

Disadvantages of Star Topology
 Hub is a single point of failure
 Requires more cable than the bus

Ring Topology
A frame travels around the ring, stopping at each node. If
a node wants to transmit data, it adds the data as well as
the destination address to the frame.
The frame then continues around the ring until it finds
the destination node, which takes the data out of the
frame.
Single ring – All the devices on the network share a
single cable
Dual ring – The dual ring topology allows data to be
sent in both directions.

 Ring topology
 Each node is connected to the two nearest nodes so the entire network forms a circle
 One method for passing data on ring networks is token passing
 Active topology
 Each workstation transmits data

Advantages of Ring Topology
 Easier to manage; easier to locate a defective node or cable problem
 Well-suited for transmitting signals over long distances on a LAN
 Handles high-volume network traffic
 Enables reliable communication

Disadvantages of Ring Topology
 Expensive
 Requires more cable and network equipment at the start
 Not used as widely as bus topology
 Fewer equipment options
 Fewer options for expansion to high-speed communication

Mesh Topology
The mesh topology connects all devices (nodes) to each
other for redundancy and fault tolerance.
It is used in WANs to interconnect LANs and for
mission critical networks like those used by banks and
financial institutions.
Implementing the mesh topology is expensive and
difficult.

Hybrid Topology
combination of two or more topologies
Advantages of Hybrid Topology
1) Reliable : Unlike other networks, fault detection and troubleshooting is easy in this type of topology.
2) Scalable: Its easy to increase the size of network by adding new components, without disturbing existing
architecture.
3) Flexible: Hybrid Network can be designed according to the requirements of the organization and by
optimizing the available resources.
4) Effective: Hybrid topology is the combination of two or more topologies, so we can design it in such a
way that strengths of constituent topologies are maximized while there weaknesses are neutralized.
Disadvantages of Hybrid Topology
1) Complexity of Design: One of the biggest drawback of hybrid topology is its design. Its not easy to
design this type of architecture and its a tough job for designers. Configuration and installation process
needs to be very efficient.
2) Costly Hub: The hubs used to connect two distinct networks, are very expensive. These hubs are
different from usual hubs as they need to be intelligent enough to work with different architectures and
should be function even if a part of network is down.
3) Costly Infrastructure: As hybrid architectures are usually larger in scale, they require a lot of cables,
cooling systems, sophisticate network devices, etc.

7.36
Classes of transmission media

Transmission Media
 Conducted or Guided media
 use a conductor such as a wire or a fiber optic cable to move the signal from
sender to receiver
 Wireless or Unguided media
 use radio waves of different frequencies.

Details
 Guided media – provide a physical path (wire)
 Unguided – employ an antenna for transmission (wireless)
 Characteristics and quality determined by medium and signal
 For guided, the medium is more important in determining the limitations
on transmission.
 For unguided, the bandwidth produced by the antenna is more important
 Key concerns are data rate and distance
 The greater the data rate and distance the better.

Guided Transmission Media
 Transmission capacity depends on the distance and on whether the medium is
point-to-point or multipoint
Types
 twisted pair wires
 coaxial cables
 optical fiber

Twisted Pair
 A wire pair acts as a single communication link.
 A number of these pairs are bundled to gather into a cable by wrapping them in a
tough protective sheath.
 On long-distance links, the twist length typically varies from 5 to 15 cm.
 The wires in a pair have thickness of from 0.4 to 0.9 mm.

Twisted Pair - Applications
 The most common medium for analog and digital signals is twisted pair.
 Telephone network
 Between house and local exchange (subscriber loop, also called local loop)
 Within an office building
 To the in-house private branch exchange (PBX)
 For connections to a digital data switch or digital private branch exchange within a building.
 A data rate of 64 kbps is common.
 For local area networks (LAN)
 10Mbps or 100Mbps; now support up to 1 Gbps.

Twisted Pair – Adv. and Disadv.
 Much less expensive than the other commonly used guided transmission media.
 Easy to work with (install and debug)
 Low data rate; comparing with other guided transmission medium.
 Short range

Unshielded and Shielded TP
 Unshielded Twisted Pair (UTP)
 Ordinary telephone wire
 The least expensive of all the transmission media.
 Easiest to install
 Suffers from external electromagnetic interference
 Provides low data rate.
 Shielded Twisted Pair (STP)
 Metal shielding that reduces interference
 More expensive
 Harder to handle (thick, heavy)
 Support higher data rate.

Categories of unshielded twisted-pair cables

Coaxial Cable Applications
 Like twisted pair, coaxial cable consists of two conductors.
 Most versatile medium
 Television distribution
 Ariel to TV
 Cable TV
 Long distance telephone transmission
 Can carry 10,000 voice calls simultaneously
 Being replaced by fiber optic
 Short distance computer systems links
 Local area networks

Coaxial Cable - Transmission Characteristics
 Analog
 Amplifiers every few km
 Closer if higher frequency
 Up to 500MHz
 Digital
 Repeater every 1km
 Closer for higher data rates

plastic jacket glass or plastic
cladding
fiber core
Fiber Optic Layers
 consists of three concentric sections
Plastic Jacket glass or plastic
claading Fiber core

Optical Fiber - Benefits
 Greater capacity
 Data rates of hundreds of Gbps over tens of kilometers.
 Smaller size & weight; thinner than coaxial cable or bundled twisted-pair
cable.
 Lower attenuation and is constant over a wide range.
 Electromagnetic isolation; optical fiber are not affected by external
electromagnetic field. Thus, no interference, impulse noise, or crosstalk.
 Fibers do not radiate energy.
 High degree of security from eavesdropping.

Optical Fiber - Applications
 Metropolitan trunks
 Rural exchange trunks
 Subscriber loops
 LANs

LAN, MAN & WAN
Network in small geographical Area (Room, Building or a Campus) is called LAN
(Local Area Network)
LAN covers 100 m
Network in a City is call MAN (Metropolitan Area Network)
MAN covers more than 100 m
Network spread geographically (Country or across Globe) is called WAN (Wide Area
Network)
WAN covers more than 1000 m

• A LAN is a network that is used for communicating among computer
devices, usually within an office building or home
• LAN’s enable the sharing of resources such as files or hardware devices
that may be needed by multiple users
• Is limited in size, typically spanning a few hundred meters, and no more
than a mile
• Is very fast, with speeds from 10 Mbps to 10 Gbps
• Requires very little wiring, typically a single cable connecting to each
device
• Has lower cost compared to MAN’s or WAN’s
Local Area Network

LAN basics
• LAN’s can either be made wired or wireless. Twisted pair, coax or fiber optic cable can be
used in wired LAN’s
• Nodes in a LAN are linked together with a certain topology. These topologies include:
• Bus
• Ring
• Star
• A node is defined to be any device connected to the network. This could be a computer, a
printer etc.
• A Hub is a networking device that connects multiple segments of the network together
• A Network Interface Card (NIC) is the circuit board that is used to connect computers to
the network. In most cases, this is an Ethernet card plugged in a computer’s motherboard

MAN
A metropolitan area network, or MAN, covers a city. The best known
example of a MAN is the cable television network available in many
cities.

WAN
•WANs have a large capacity, connecting a large number of computers over a large
area, and are inherently scalable.
•They facilitate the sharing of regional resources.
•They provide uplinks for connecting LANs and MANs to the Internet.
•Communication links are provided by public carriers like telephone networks,
network providers, cable systems, satellites etc.

Personal Area Network
• A PAN is a network that is used for communicating among
computers and computer devices (including telephones) in
close proximity of around a few meters within a room
• It can be used for communicating between the devices
themselves, or for connecting to a larger network such as
the internet
• PAN’s can be wired or wireless

Ad-hoc Network
• The term ad hoc is a Latin word that literally means "for this”
• Temporary Network created for a specific purpose

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