A computer network consists of two or more computers that are interconnected with each other and share resources such as printers, servers, and hardware and exchange the data in the form of files, facilitating electronic communication. Computers on a network can be connected through twisted pair cables, telephone lines, radio waves, satellites or optical fiber cables. The first computer network designed was the ‘Advanced Research Projects Agency Network (ARPANET)’ by the United States Department of Defense. Since then, myriads of new computer networking technologies have been designed. This tutorial only covers the first three network technologies i.e LAN, WAN and MAN. However, currently there are multiple networking technologies in use which have been enlisted below.

• Local Area Network (LAN)
• Wide Area Network (WAN)
• Metropolitan Area Network (MAN)
• Wireless Local Area Network (WLAN)
• Storage Area Network (SAN)
• Controller Area Network (CAN)
• Personal Area Network (PAN)
• Global Area Network (GAN)
• Internet Area Network (IAN)

 

 

Local Area Network (LAN)

A Local Area Network (LAN) is a network that is restricted to smaller physical areas e.g. a local office, school, or house. Approximately all current LANs whether wired or wireless are based on Ethernet. On a ‘Local Area Network’ data transfer speeds are higher than WAN and MAN that can extend to a 10.0 Mbps (Ethernet network) and 1.0 Gbps (Gigabit Ethernet).

LAN networks can be implemented in multiple ways, for example twisted pair cables and a wireless Wi-Fi with the IEEE 802.11 standard can be used for this purpose. One end of the twisted pair cable is plugged into switches using ‘RJ-45 connectors’ whereas the other end is plugged to a computer or in another network. All new routers use the b/g/n IEEE 802.11 standards. The ‘b’ and ‘g’ operate in the 2.4 GHz spectrum, and ‘n’ operates in 2.4 and 5.0 GHz which allows better performance and less interference.

Computers and servers (provides services to other computers like printing, file storage and sharing) can connect to each other via cables or wirelessly in a same LAN. Wireless access in conjunction with wired network is made possible by Wireless Access Point (WAP). Devices with WAP functionality provide a bridge between computers and networks. A WAP is able to connect hundreds or even more of wireless users to a network. Servers in a LAN are mostly connected by a wire since it is still the fastest medium for network communication. But for workstations (Desktop, laptops, etc.) wireless medium is a more suitable choice, since at some point it is difficult and expensive to add new workstations into an existing system already having complex network wiring.

Token Ring and Fiber Distributed Data Interface (FDDI)

With Ethernet, ‘Token Ring’ and ‘Fiber Distributed Data Interface (FDDI)’ are also considered the major ‘Local Area Network’ technologies. In Token Ring network all computers are connected in a ring or star topology for prevention of data collision and with a data transfer rates of either 4 or 16 megabits per second by IEEE 802.5 standard version. In FDDI for data transmission optic fiber are used that extend the range of a LAN up to 200km and supports thousands of user.

Wide Area Network (WAN)

Wide Area Network is a computer network that covers relatively larger geographical area such as a state, province or country. It provides a solution to companies or organizations operating from distant geographical locations who want to communicate with each other for sharing and managing central data or for general communication.

WAN is made up of two or more Local Area Networks (LANs) or Metropolitan Area Networks (MANs) that are interconnected with each other, thus users and computers in one location can communicate with users and computers in other locations.

In ‘Wide Area Network’, Computers are connected through public networks, such as the telephone systems, fiber-optic cables, and satellite links or leased lines. The ‘Internet’ is the largest WAN in a world. WANs are mostly private and arebuild for a particular organization by ‘Internet Service Providers (ISPs)’ which connects the LAN of the organization to the internet. WANs are frequently built using expensive leased lines where with each end of the leased line a router is connected to extend the network capability across sites. For low cost solutions, WAP is also built using a ‘circuit switching’ or ‘packet switching’ methods.

Metropolitan Area Network (MAN)

A Metropolitan Area Network (MAN) is a network that connects two or more computers, communicating devices or networks in a single network that has geographic area larger than that covered by even a large ‘Local Area Network’ but smaller than the region covered by a ‘Wide Area Network’. MANs are mostly built for cities or towns to provide a high data connection and usually owned by a single large organization.

A Metropolitan Area Networks bridges a number of ‘Local Area Networks’ with a fiber-optical links which act as a backbone, and provides services similar to what Internet Service Provider (ISP)  provide to Wide Area Networks and the Internet.

Major technologies used in MAN networks are ‘Asynchronous Transfer Mode (ATM)’, ‘Fiber Distributed Data Interface (FDDI)’ and ‘Switched Multi-megabit Data Service (SMDS, a connectionless service)’. In most of the areas, these technologies are used to replace the simple ‘Ethernet’ based connections. MANs can bridge Local Area Networks without any cables by using microwave, radio wireless communication or infra-red laser which transmits data wirelessly.

‘Distributed Queue Dual Bus (DQDB)’ is the Metropolitan Area Network (MAN) IEEE 802.6 standard for data communication. Using DQDB, networks can extend up to 100km-160km and operate at speeds of 44 to 155Mbps.

Conclusion

LAN is a private network used in small offices or homes usually within 1km range with high speed transfer data rate and fulltime service connectivity in low cost. WAN covers a large geographical area for example, a country or a continent. Its data transfer data is usually low as compared to LAN, but it is compatible with a variety of access lines and has an advanced security. MAN covers an area bigger than LAN within a city or town and serves as an ISP for larger LAN. It uses optical fibers or wireless infrastructure to link the LANs therefore, providing high speed regional resource sharing.

 

 

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WAN

In the field of computers, the wide usage of group connections have become inevitable, which lead to the introduction of LANs (Local Area Networks). These LANs come under the category of small scale networks within a single building or campus.

WANs are Wide Area Networks which cover a wider area such a city, or a limited area greater than LAN. Wireless Personal Area Networks (PANs) are the next step down from WLANs, covering smaller areas with low power transmission, for networking of portable and mobile computing devices such as PCs, Personal Digital Assistants (PDAs).

Fundamentals of WLANs

The technical issues in WLANs must be understood in order to appreciate the difference between wired networks and wireless networks. The use of WLANs and their design goals are then studied. The types of WLANS, their components and their basic functionalities are also detailed.

IEEE 802.11 Standard

This section introduces a prominent standard ion WLANs, the IEEE 802.11 standard. The medium access control (MAC) layer and the physical layer mechanisms are explained. This section also covers some of the optional functionalities such as security and quality of service (QoS).

HIPERLAN Standard

This section describes another WLAN standard, HIPERLAN standard, which is a European standard based on radio access.

Bluetooth

This section deals with the Bluetooth standard, which enables personal devices to communicate with each other in the absence of infrastructure.

WLAN Fundamentals

While both portable terminals and mobile terminals can move from one place to another, portable terminals are accessed only when they are stationary.

Mobile Terminals (MTs), on the other hand, are more powerful, and can be accessed when they are in motion. WLANs aim to support truly mobile work stations.

WLAN Uses

Wireless computer networks are capable of offering versatile functionalities. WLANs are very flexible and can be configured in a variety of topologies based on the application. Some possible uses of WLANs are described below.

• Users would be able to surf the Internet, check e-mail, and receive Instant Messages on the move.

• In areas affected by earthquakes or other disasters, no suitable infrastructure may be available on the site. WLANs are handy in such locations to set up networks on the fly.

• There are many historic buildings where there has been a need to set up computer networks. In such places, wiring may not be permitted or the building design may not be conductive to efficient wiring. WLANs are very good solutions in such places.

Design Goals

The following are some of the goals which have to be achieved while designing WLANs −

• Operational simplicity − Design of wireless LANS must incorporate features to enable a mobile user to quickly set up and access network services in a simple and efficient manner.

• Power efficient operation − The power-constrained nature of mobile computing devices such as laptops and PDAs necessitates the important requirement of WLANs operating with minimal power consumption. Therefore, the design of WLAN must incorporate power-saving features and use appropriate technologies and protocols to achieve this.

• License-free operation − One of the major factors that affects the cost of wireless access is the license fee for the spectrum in which a particular wireless access technology operates. Low cost of access is an important aspect for popularizing a WLAN technology. Hence the design of WLAN should consider the parts of the frequency spectrum. For its operation which does not require an explicit

• Tolerance to interference − The proliferation of different wireless networking technologies both for civilian and military applications have led to a significant increase in the interference level across the radio spectrum.

  The WLAN design should account for this and take appropriate measures by way of selecting technologies and protocols to operate in the presence of interference.

• Global Usability − The design of the WLAN, the choice of technology, and the selection of the operating frequency spectrum should take into account the prevailing spectrum restriction in countries across the world. This ensures the acceptability of the technology across the world.

• Security − The inherent broadcast nature of wireless medium adds to the requirement of security features to be included in the design of WLAN technology.

• Safety requirements − The design of WLAN technology should follow the safety requirements that can be classified into the following.

  • Interference to medical and other instrumentation devices.
  • Increased power level of transmitters that can lead to health hazards.

  A well-designed WLAN should follow the power emission restrictions that are applicable in the given frequency spectrum.

• Quality of service requirements − Quality of Service (QoS) refers to the provisioning of designated levels of performance for multimedia traffic. The design of WLAN should take into consideration the possibility of supporting a wide variety of traffic, including multimedia traffic.

• Compatibility with other technologies and applications − The interoperability among different LANS is important for efficient communication between hosts operating with different LAN technologies.

Network Architecture

Network architecture describes the types of WLANs, the components of a typical WLAN and the services offered by a WLAN.

Infrastructure based versus Ad Hoc LANs

WLANs can be broadly classified into two types, namely Infrastructure networks and Ad hoc LANs, based on the underlying architecture.

Infrastructure networks

Infrastructure networks contain special nodes called Access Points (APs), which are connected via existing networks.

• APs are special in the sense that they can interact with wireless nodes as well as with the existing wired network.
• The other wireless nodes, also known as Mobile stations (STAs), communicate via APs.
• The APs also act as bridges with other networks.

Ad hoc LANs

Ad hoc LANs do not need any fixed infrastructure. These networks can be set up on the fly at any place. Nodes communicate directly with each other for forward messages through other nodes that are directly accessible.