This is a continuation of my series of articles on the terms
and concepts that are frequently asked in IT interviews. This article is an
attempt to discuss the salient terminologies and concepts related to Computer
networking that are often asked in interviews. Although an article on Computer
Networking concepts and terms would run for many pages, I have discussed only
important ones to make it fit in one article.
A Computer Network implies two or more computers those are
linked together through some software, hardware, etc for the purpose of exchanging
data and information.
The Internet is a network of networks. It is "the
worldwide, publicly accessible network of interconnected computer networks that
transmit data by packet switching using the standard Internet Protocol (IP)."
World Wide Web
The World Wide Web or WWW is a hypertext based distributed
information system. It "is the global network of hypertext (HTTP) servers
that allow text, graphics, audio and video files to be mixed together." It
is an "information space in which the items of interest, referred to as
resources, are identified by global identifiers called Uniform Resource
Identifiers (URI)." According to Tim Berners-Lee, inventor of the World
Wide Web, "The World Wide Web is the universe of network-accessible
information, an embodiment of human knowledge."
A modem is a modulator-demodulator device that is used for
converting the transmission signals from digital to analog for transmission
over voice-grade phone lines. While the digital signals are converted to a form
suitable for transmission over analog communication at the source, the reverse
happens at the destination where these analog signals are returned to their
original digital form.
Network Interface Controller
A network card, network adapter or the Network Interface Controller
(NIC) is a piece of computer hardware that facilitates the systems in a network
When the information transfer is from one system to many
systems using the same means of transfer then such a network is known as a
Broadcasting or Multicasting.
When the information transfer is from one system to any
other single system using the same means of transfer then such a network is
known as Point-to-Point or Unicasting.
Network bandwidth or network throughput is a measure of the data
transfer rate or the amount of data that can pass through a network interface
over a specific period of time. This is expressed in bits per second or bps.
This is a wide-band technology that is capable of supporting
voice, video and data. It is "a transmission medium capable of supporting
a wide range of frequencies, typically from audio up to video frequencies. It
can carry multiple signals by dividing the total capacity of the medium into
multiple, independent bandwidth channels, where each channel operates only on a
specific range of frequencies."
Integrated Services Digital Network (ISDN)
Integrated Services Digital Network, an international
standard for end-to-end digital transmission of voice, data, and signaling
facilitates very high-speed data transfer over existing phone lines.
Network Load Balancing
Network Load Balancing may be defined as a technique that
"distributes the network traffic along parallel paths to maximize the
available network bandwidth while providing redundancy."
Local Area Network
LAN also known as Local Area Network are networks restricted
on the bases of the area they cover. These networks stretch around an area of
10 meters to 1 km. "LANs enabled multiple users in a relatively small
geographical area to exchange files and messages, as well as access shared
resources such as file servers and printers." The commonly used LAN
devices include repeaters, hubs, LAN extenders, bridges, LAN switches, and
Metropolitan Area Network
MAN also known, as Metropolitan Area Network is a network
that is larger than LANs spreading across an area of 1 km to 10kms. A simple
example for this type of network is the branches of a bank spread across the
city and are connected for information exchange.
Wide Area Network
WAN also known, as Wide Area Network is a network that is
larger than a MAN, it spreads across an area of 100kms to 1000 kms. "A WAN
is a data communications network that covers a relatively broad geographic area
and that often uses transmission facilities provided by common carriers, such
as telephone companies. WAN technologies generally function at the lower three
layers of the OSI reference model: the physical layer, the data link layer, and
the network layer." A simple example for these networks is the network of
a huge IT company, which contains branches all over the world with all its
branches connected to each other.
Wireless Networks are those networks wherein the
interconnection between two systems is not physical. The computers that
interchange information are not physically linked with wires.
Bluetooth is a wireless network that has a short range and
can be used to connect a system with its internal components like monitor,
mouse, CPU, etc without actually having a plug in. Components that support the
Bluetooth technology can be detected whenever they are in the detectable range.
When there are multiple paths between the sender and the
receiver the best path for sending the information has to be chosen. The choice
is made based on a number of criteria like the number of hops between the
systems or on the physical distance between the systems. This process of
finding the best path is known as routing.
Network topology refers to the arrangement of the nodes in a
network. The following are the major types of network topologies:
The Media Access Control or MAC address is the Network
Interface Card address and is composed of 12 hexadecimal characters (0-9, A-F)
and is defined as a unique identifier used to identify most network equipments
and is used as the source and destination addresses for data packets on a LAN.
Every network device in the world has a unique MAC address. The first 6
characters of the MAC address are unique to the manufacturer of the device.
Every system that is connected to the internet is called a
node and it is identified by a unique 32 - bit numeric address called the IP
address or the Internet Protocol address. These addresses are created and
governed by the Internet Assigned Numbers Authority or the IANA.
A subnet is an identifiably separate part of an organization's
network and is defined as "an interconnected, but independent segment of a
network that is identified by its Internet Protocol (IP) address."
"A Virtual LAN, commonly known as a VLAN, is a method
of creating independent logical networks within a physical network."
A Virtual Circuit may be defined as a logical circuit that ensures
that there is a reliable communication between two network devices. It is
"a network service that provides connection-oriented service regardless of
the underlying network structure."
Domain Naming Service
Domain Naming Service or DNS is a naming service that is
used to name the nodes over a network for simplicity reasons. The domain name
is actually a textual name that identifies a host in a network. The DNS servers
have the DNS names stored along with their corresponding IP addresses.
A Network Protocol implies that rules and regulations that
govern how two devices can communicate in a network for the purpose of sharing
data and information exchange. Network protocols are in other words, the
language of communication amongst two network devices in a network. Typical
examples of protocols include TCP/IP, SMTP, HTTP, SNMP, Telnet, FTP, etc.
Ethernet was designed and developed by the Xerox
Corporation, DEC and Intel Corporation way back in 1976. It is a local-area
network that uses the uses carrier sense multiple access collision detects
(CSMA/CD) technology and the bus topology to provide a very reliable and fast
data communication in a small geographic area.
Carrier Sense Multiple Access / Collision Detection
Carrier Sense Multiple Access is a set of rules that govern
how the network devices respond at the time when a collision is detected, i.e.,
when two devices attempt to use a data channel simultaneously.
Secure Sockets Layer
Secure Sockets Layer or SSL is a frequently used protocol
for managing the security of message transmission over the internet. It
facilitates this by enabling the server and the client systems to exchange
public keys to enable them to encode and decode the data and information that
they exchange between themselves.
A socket is the end point of a two way communication between
two systems running over a network.
A port implies an unsigned integer that uniquely identifies
a process running over a network. The following are some of the well known port
FTP (Data) 20
FTP (Control) 21
A router is a device that is used to route network data
packets between two networks using some predefined algorithms. These algorithms
are commonly known as routing algorithms.
A repeater may be defined as a device that "regenerates
and propagates the electric signals between two network segments."
A Network Firewall comprises one or a group of two or more
systems that prevents unauthorized network accesses by restricting the unwanted
or unauthorized incoming or outgoing network traffic.
A gateway joins two or more networks using a combination of
the necessary hardware and software. "A gateway can translate information
between different network data formats or network architectures."
A packet may be defined as a formatted block of data and or
information for transmission over a network. These packets are broken into
smaller packets for facilitating the transmission over the Internet. A network
packet consists of the following:
While the header and the trailer mark the beginning and the
end of the packet, the payload contains the actual data to be transmitted.
A network switch is defined as a hardware device that is
used to join multiple systems together at a low-level network protocol layer.
It is a computer networking device that "connects network segments. It
uses the logic of a Network bridge but allows a physical and logical star
topology. It is often used to replace network hubs. A switch is also often
referred to as an intelligent hub."
A network bridge is used to connect two systems in a network
that have identical configuration. It is an "abstract device that connects
multiple network segments along the data link layer. An example of a bridge in
a computer network is the network switch."
Open Systems Interconnection or OSI Model
The International Standards Organization or the ISO, proposed
the OSI Reference Model, and it is known as Open Systems Interconnection as it
is designed for systems that are open for communication. "The Open System
Interconnection (OSI) reference model describes how information from a software
application in one computer moves through a network medium to a software
application in another computer. The OSI reference model is a conceptual model
composed of seven layers, each specifying particular network functions." This
is a seven layered design that depicts the typical network architecture and a
conceptual framework for communication and how data can pass through one layer
to another in such an architecture, the protocols involved, etc.
The OSI Layers
The OSI model describes the following seven layers in its
The Physical layer
The Data Link Layer
The Network Layer
The Transport Layer
The Session Layer
The Presentation Layer
The Application Layer
The following diagram depicts the seven layers of the OSI
The Physical Layer
This is the lowest layer in the OSI model and deals with the
transfer of raw bits across the network. "The physical layer defines the
electrical, mechanical, procedural, and functional specifications for
activating, maintaining, and deactivating the physical link between
communicating network systems."
The Data Link Layer
The main function of the data link layer is to break up large
amounts of information into packets and send the packets sequentially across a
no error transmission medium and receive the acknowledgement packets from the
receiver for the same. Another important function of this layer is to make the
sender and the receiver compatible with each other by synchronizing the
information between the two to avoid a fast sender – slow receiver problems and
vice – versa
The Network Layer
The function of the Network layer is to see that all the
packets that are sent or received have an error free network or an error free
medium for the exchange of packets in general to have a good quality of service
is the major function of the network layer.
The Transport Layer
The transport layer collects the information, splits it into
packets and sends it to the network layer. It ensures that the data transferred
is devoid of any errors and in the right sequence.
The Session Layer
The session layer is instrumental in establishing,
controlling and terminating communication sessions. It should be noted that the
"communication sessions consist of service requests and service responses
that occur between applications located in different network devices."
The Presentation layer
The Presentation Layer of the OSI Model converts the incoming
and outgoing data from one presentation format to another so as to ensure that
it is readable across application layers of other systems.
The Application Layer
"This is the layer at which communication partners are
identified, quality of service is identified, user authentication and privacy
are considered, and any constraints on data syntax are identified."