Basic Intro to Computer Networks ..........

1. Computer Network
A computer network :-> It is a group of two or more computers
connected to each electronically. This means that the computers can
"talk" to each other and that every computer in the network can send
information to the others. Usually, this means that the speed of the
connection is fast - faster than a normal connection to the Internet.
A computer network, often simply referred to as a network, is a
collection of computers and devices interconnected by
communications channels that facilitate communicationsand allows
sharing of resources and information among interconnected devices.
 Put more simply, a computer network is a collection of two or more
computers linked together for the purposes of sharing information,
resources, among other things. Computer networking or Data
Communications (Dotcom) is the engineering discipline concerned
with computer networks.

2. Computer Network
Computer networking is sometimes considered a sub-discipline of
electrical engineering, telecommunications computer science
information technology and/or computer engineering since it relies
heavily upon the theoretical and practical application of these
scientific and engineering disciplines.
Networks may be classified according to a wide variety of
characteristics such as medium used to transport the data,
communications protocol used, scale, topology, organizational
scope, etc.

3. Application of computer netw
Technology
Local networks use Ethernet or Wi-Fi.
Most computer networks use Ethernet or Wi-Fi as the LAN technology.
Wi-Fi is also know as IEEE 802.11. In the wide area, almost all networks
use TCP/IP to connect between sites. TCP/IP packets are put inside
Ethernet or Wi-Fi frames to transport them over the local area.
Computer software uses TCP/IP to create connections between
computers and share information.
Print Sharing
The first application for computer networks was to share printers
attached to a personal computer in a small office. Many modern printers
attach directly to the network and no longer need a host computer to
operate. Anyone connected on the network can use any printer on the
network, providing they have correct permissions.

4. Application of computer netw
File Sharing
The second common application for computer networking was to
share files and disk space. Files created on one computer can be
used by someone working on another computer accessing the file
over the network. This is the simplest form of electronic collaboration.
This concept has been extended to create file servers. These are
computers with the main purpose of storing and sharing files.
Wide Area File Sharing
NFS and CIFS are systems that work well in a local area with high
speed links between the computers. They do not work well over long
distances where bandwidth between the computers may be limited. The
File Transfer Protocol (FTP) was designed to transfer files over long
distances at slow or unpredictable speeds. Transferring files is not as
interactive as sharing files, but it still allows for collaboration.

5. Application of computer netw
World Wide Web and Beyond
In the late 1990s, the Hyper Text Transfer Protocol (HTTP) gained
widespread acceptance. This allowed information to be posted on a
server in a standard markup language called the Hyper Text Markup
Language (HTML). HTML also provides a mechanism for input. This is
one of the main applications of computer networks since the year
2000. Web pages can display information in a standard format and
receive input from the users to create surveys, shopping on line and
many other applications
Real Time Applications
As 2010 approached, there was more interest in using computer
networks to provide voice and video services. IP phones and IP TV
became an alternative to the traditional phone system and cable TV
system. We can expect to see more of these applications as the
network continually grows.

6. Transmission Media
 There are 2 basic categories of Transmission Media:
 Guided
 Unguided.
Many transmission media are used as communications channels.
For telecommunications purposes in the United States, Federal Standar
1037C, transmission media are classified as one of the following:
Guided (or bounded)—waves are guided along a solid medium such as
a transmission line.
Wireless (or unguided)—transmission and reception are achieved by
means of an antenna.

7. Guided Media
 Guided Transmission Media uses a "cabling" system that guides the data
signals along a specific path. The data signals are bound by the "cabling"
system.
 Guided Media is also known as Bound Media. Cabling is meant in a
generic sense in the previous sentences and is not meant to be interpreted
as copper wire cabling only.
 There 4 basic types of Guided Media:
→ Open Wire
→ Coaxial Cable
→ Twisted Pair
→ Optical Fibre

8. Un Guided Media
 Unguided Transmission Media consists of a means for the data
signals to travel but nothing to guide them along a specific path. The
data signals are not bound to a cabling media and as such are often
called Unbound Media.
 Also called wireless communication. It transports electromagnetic
Waves without using a physical conductor. Signals are broadcast
through the air ( in some cases water). There are available to
anyone who can receive them.
 Radio Frequency Allocation – the selection of the electromagnetic
spectrum defined as radio communication is divided into 8 ranges,
called bands, each regulated by government. These bands are
rated from very low frequency (VLF) to very high frequency (EHF)

9. OSI Model
 Open Systems Interconnection (OSI) is a set of
internationally recognized, non-proprietary standards
for networking and for operating system involved in
networking functions.
 Open Systems Interconnection
 Standard model for data communications
 Specified by international standards organization (ISO)
 Adopted by CCITT/ITU
 Official model explained in X.200 series
 Layered approach to communications
 Seven layers altogether
 Each layer performs a unique function
 Each layer has its own protocol
 Protocol messages in upper layer is data to layer below

10. 7 Layers
Layer Name Description Examples
Application User Level Processing Telnet, FTP, Mail
Presentation Data Representation & Syntax ISO Presentation
Session Sync Points and Dialogs ISO Session
Transport Reliable End to End TCP
Network Unreliable Thru Multi-Node Network X.25 Pkt, IP
Link Reliable Across Physical Line LAPB, HDLC
Physical Unreliable Wire, Telco Line RS232, T1, 802.x
10

11.  LAYER 7 – The APPLICATION Layer
• The top layer of the OSI model
• Provides a set of interfaces for sending and receiving applications to gain
access to and use network services, such as: networked file transfer,
message handling and database query processing
 LAYER 6 – The PRESENTATION Layer
• Manages data-format information for networked communications (the
network’s translator)
• For outgoing messages, it converts data into a generic format for network
transmission; for incoming messages, it converts data from the generic
network format to a format that the receiving application can understand
• This layer is also responsible for certain protocol conversions, data
encryption/decryption, or data compression/decompression
 LAYER 5 – The SESSION Layer
• Responsible for initiating, maintaining and terminating sessions
• Responsible for security and access control to session information(via session
participant identification)

12.  LAYER 4 – The TRANSPORT Layer
• Manages the transmission of data across a network
• Manages the flow of data between parties by segmenting long data
streams into smaller data chunks (based on allowed “packet” size for
a given transmission medium)
• Reassembles chunks into their original sequence at the receiving end
 LAYER 3 – The NETWORK Layer
• Handles addressing messages for delivery, as well as translating logical
network addresses and names into their physical counterparts
• Responsible for deciding how to route transmissions between computers
• This layer also handles packet switching and network congestion control
 LAYER 2 – The DATA LINK Layer
• Handles special data frames (packets) between the Network layer and
the Physical layer
• At the receiving end, this layer packages raw data from the physical
layer into data frames for delivery to the Network layer

13.  LAYER 1 – The PHYSICAL Layer
• Converts bits into electronic signals for outgoing messages
• Converts electronic signals into bits for incoming messages
• This layer manages the interface between the the computer and the network
medium (coax, twisted pair, etc.)
• The bottom layer of the OSI model

14. Computer Networking device
(Hard Ware)
 Computer networking devices are units that mediate data in a computer network ,
Computer networking devices are also called network equipment, Intermediate
Systems (IS) or InterWorking Unit (IWU). Units which are the last receiver or
generate data are called hosts or data terminal equipment.
 List of computer networking devices
•Router: A specialized network device that determines the next network point to which it can
forward a data packet towards the destination of the packet.unlike a gateway, it
cannot interface different protocols. Works on OSI layer 3
•Bridge: A device that connects multiple network segments along the data link
layer. Works on OSI layer 2.
•Switch: A device that allocates traffic from one network segment to certain lines
(intended destination(s)) which connect the segment to another network
segment. So unlike a hub a switch splits the network traffic and sends it to
different destinations rather than to all systems on the network. Works on
OSI layer 2.

15. •Hub: Connects multiple Ethernet segments together making them act as a
single segment. When using a hub, every attached all the objects,
compared to switches, which provide a dedicated connection between
individual nodes.works on OSI layer1.
•Repeater: Device to amplify or regenerate digital signals received while sending
them from one part of a network into another. Works on OSI layer 1.
 Some hybrid network devices:
•Multilayer Switch : A switch which, in addition to switching on OSI layer 2,
provides functionality at higher protocol layers.
•Protocol Converter: A hardware device that converts between two different
types of transmissions, such as asynchronous and
synchronous transmissions.
•Bridge Router : Combines router and bridge functionality and are therefore
working on OSI layers 2 and 3.

16.  Other hardware for establishing networks or dial-up connections:
•Multiplexer: Device that combines several electrical signals into a single
signal
•Network Card: A piece of computer hardware to allow the attached
computer to communicate by network
•Modem: Device that modulates an analog "carrier" signal (such as
sound), to encode digital information, and that also
demodulates such a carrier signal to decode the transmitted
information, as a computer communicating with another
computer over the telephone network
•ISDN terminal adapter : A specialized gateway for ISDN
•Line Driver: A device to increase transmission distance by amplifying the
signal. Base-band networks only.

17. Networking Soft Ware
 Network Software is a set of primitives that define the protocol between two
machines. The network software resolves an ambiguity among different types of
network making it possible for all the machines in the network to connect and
communicate with one another and share information.
 Network software is the information, data or programming used to make it possible
for computers to communicate or connect to one another.
 Network software is used to efficiently share information among computers. It
encloses the information to be sent in a “package” that contains a “header” and a
“trailer”. The header and trailer contain information for the receiving computer,
such as the address of that computer and how the information package is coded.
Information is transferred between computers as either electrical signals in electric
wires, as light signals in fiber-optic cables, or as electromagnetic waves through
space.

18. Types of Cable in Networking
 Cable is the medium through which information usually moves from
one network device to another. There are several types of cable
which are commonly used with LANs. In some cases, a network will
utilize only one type of cable, other networks will use a variety of
cable types.
 The type of cable chosen for a network is related to the network's
topology, protocol, and size.
 Understanding the characteristics of different types of cable and how
they relate to other aspects of a network is necessary for the
development of a successful network.
 Types of cables used in networks :-
 Coaxial Cable
 Fiber Optic Cable
 Unshielded Twisted Pair (UTP) Cable
 Shielded Twisted Pair (STP) Cable

19. 1 ) Coaxial Cable :-
 Coaxial cabling has a single copper conductor
at its center. A plasticlayer provides insulation
between the center conductor and a braided
metal shield (See fig. 1). The metal shield helps to
block any outside interference .
Fig. 1. Coaxial cable
 Although coaxial cabling is difficult to install, it is highly resistant to signal
interference. In addition, it can support greater cable lengths between
network devices than twisted pair cable.
 The two types of coaxial :-
1) Thin coaxial cable is also referred to as thinnet. 10Base2 refers to the
specifications for thin coaxial cable carrying Ethernet signals. The 2 refers to
the approximate maximum segment length being 200 meters. In actual fact the
maximum segment length is 185 meters.
2) Thick coaxial cable is also referred to as thicknet. 10Base5 refers to the
specifications for thick coaxial cable carrying Ethernet signals. The 5 refers to
the maximum segment length being 500 meters.

20. Thick coaxial cable has an extra protective plastic cover that helps keep
moisture away from the center conductor. This makes thick coaxial a great
choice when running longer lengths in a linear bus network. One
disadvantage of thick coaxial is that it does
 Coaxial Cable Connectors :-
 The most common type of connector used with
coaxial cables is the Bayone-Neill-Concelman
(BNC) connector (See fig. 2).
Fig. 2. BNC connector
 Different types of adapters are available for BNC connectors, including a T-
connector, barrel connector, and terminator. Connectors on the cable are the
weakest points in any network. To help avoid problems with your network,
always use the BNC connectors that crimp, rather

21. 2 ) Fiber Optic Cable :-
 Fiber optic cabling consists of a center glass core
surrounded by several layers of protective
materials (See fig. 3). It transmits light rather than
electronic signals eliminating the problem of
electrical interference.
Fig. 3. Fiber optic cable
 This makes it ideal for certain environments that contain a large amount of
electrical interference. It has also made it the standard for connecting
networks between
 Fiber optic cable has the ability to transmit signals over much longer distances
than coaxial and twisted pair. It also has the capability to carry information at
vastly greater speeds. This capacity broadens communication possibilities to
include services such as video conferencing and interactive services.
 The center core of fiber cables is made from glass or plastic fibers (see fig 3).
A plastic coating then cushions the fiber center, and kevlar fibers help to
strengthen the cables and prevent breakage. The outer insulating jacket
made of teflon or PVC.

22. 3 ) Unshielded Twisted Pair (UTP) Cable :-
 Twisted pair cabling comes in two varieties :-
shielded and unshielded. Unshielded twisted pair
(UTP) is the most popular and is generally the best
option for school networks (See fig. 4).
Fig.4. Unshielded
twisted pair
 The quality of UTP may vary from telephone-grade wire to extremely high-
speed cable. The cable has four pairs of wires inside the jacket. Each pair is
twisted with a different number of twists per inch to help eliminate interference
from adjacent pairs and other electrical devices.
 The tighter the twisting, the higher the supported transmission rate and the
greater the cost per foot. The EIA/TIA (Electronic Industry
Association/Telecommunication Industry Association) has established
standards of UTP and rated six categories of wire (additional categories are
emerging).

23.  Categories of Unshielded Twisted Pair
Category Speed Use
1 1 Mbps Voice Only (Telephone Wire)
LocalTalk & Telephone (Rarely
2 4 Mbps
used)
3 16 Mbps 10BaseT Ethernet
4 20 Mbps Token Ring (Rarely used)
100 Mbps (2 pair) 100BaseT Ethernet
5
1000 Mbps (4 pair) Gigabit Ethernet
5e 1,000 Mbps Gigabit Ethernet
6 10,000 Mbps Gigabit Ethernet

24.  Unshielded Twisted Pair Connector :-
 The standard connector for unshielded twisted pair
cabling is an RJ-45 connector. This is a plastic
connector that looks like a large telephone-style
connector (See fig.5).A slot allows the RJ-45 to be
inserted only one way.
Fig. 5. RJ-45 connector
 RJ stands for Registered Jack, implying that the connector follows a standard
borrowed from the telephone industry. This standard designates which wire
goes with each pin inside the connector.

25. 4 ) Shielded Twisted Pair (STP) Cable :-
 Although UTP cable is the least expensive cable, it
may be susceptible to radio and electrical
frequency interference (it should not be too close
to electric motors, fluorescent lights, etc.).
Fig.6. Shielded
twisted pair
 If you must place cable in environments with lots of potential interference, or if
you must place cable in extremely sensitive environments that may be
susceptible to the electrical current in the UTP, shielded twisted pair may be
the solution. Shielded cables can also help to extend the maximum distance
of the cables.
 Shielded twisted pair cable is available in three different configurations :
 Each pair of wires is individually shielded with foil.
 There is a foil or braid shield inside the jacket covering all wires (as a
group).
 There is a shield around each individual pair, as well as around the entire
group of wires (referred to as double shield twisted pair).