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.

Computer Network

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.

Internet

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."

Modem

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 to communicate.

Broadcasting

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.

Unicasting

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.

Bandwidth

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.

 

 

Broadband

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 routers.

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

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

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.

Routing

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.

 

Topology

Network topology refers to the arrangement of the nodes in a network. The following are the major types of network topologies:

·         Ring

·         Bus

·         Star

MAC Address

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.

IP Address

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.

Subnet

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."

Virtual LAN

"A Virtual LAN, commonly known as a VLAN, is a method of creating independent logical networks within a physical network."

Virtual Circuit

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.

Protocol

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

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 (CSMA)

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.

Network Socket

A socket is the end point of a two way communication between two systems running over a network.

Network Port

A port implies an unsigned integer that uniquely identifies a process running over a network. The following are some of the well known port numbers:

Http              80

Telnet           23

SMTP            25

SNPP            444

DNS             53

FTP (Data)     20

FTP (Control) 21  

Router

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.

Repeater

A repeater may be defined as a device that "regenerates and propagates the electric signals between two network segments."

Firewall

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.

Gateway

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."

Packet

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:

·         A header

·         A trailer

·         A payload

While the header and the trailer mark the beginning and the end of the packet, the payload contains the actual data to be transmitted.

Network Switch

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."

Network Bridge

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 architecture:

·         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 Model.

Figure 1

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."