Ways of securing computer networks

• Access authorization restricts access to a computer to group of users through the use of authentication systems. These systems can protect either the whole computer - such as through an interactive logon screen - or individual services, such as an FTP server. There are many methods for identifying and authenticating users, such as passwords, identification cards, and, more recently, smart cards and biometric systems.

• Anti-virus software consists of computer programs that attempt to identify, thwart and eliminate computer viruses and other malicious software (malware).
• Application with known security flaws should not be run. Either leave it turned off until it can be patched or otherwise fixed, or delete it and replace it with some other application. Publicly known flaws are the main entry used by worms to automatically break into a system and then spread to other systems connected to it.
• Backups are a way of securing information; they are another copy of all the important computer files kept in another location. These files are kept on hard disks, CD-Rs, CD-RWs, and tapes. There is also a fourth option, which involves using one of the file hosting services that backs up files over the Internet for both business and individuals.
• Encryption is used to protect the message from the eyes of others. It can be done in several ways by switching the characters around, replacing characters with others, and even removing characters from the message. These have to be used in combination to make the encryption secure enough, that is to say, sufficiently difficult to crack.
• Firewalls are systems which help protect computers and computer networks from attack and subsequent intrusion by restricting the network traffic which can pass through them, based on a set of system administrator defined rules.

• Honey pots are computers that are either intentionally or unintentionally left vulnerable to attack by crackers. They can be used to catch crackers or fix vulnerabilities.
• Intrusion-detection systems can scan a network for people that are on the network but who should not be there or are doing things that they should not be doing, for example trying a lot of passwords to gain access to the network.
• Pinging:The ping application can be used by potential crackers to find if an IP address is reachable. If a cracker finds a computer they can try a port scan to detect and attack services on that computer.
• Social engineering awareness keeps employees aware of the dangers of social engineering and/or having a policy in place to prevent social engineering can reduce successful breaches of the network and servers.

Computer Network Notes

Computer Network

In connection with the information technology and computers a network is a way to connect computers together so that they can communicate, exchange information and pool resources or a network is a communicating system connecting two or more computers. Network connects people as close as the next office and as for as halfway around the world.

In business networks have revolutionized the use of computer technology. Many businesses that used to relay on a centralized system with mainframe and a collection of terminals now use computer networks in which every employee who needs a computer has personal computer connected to the network. In education, schools, colleges and universities have also shifted to strategies built around networked personal computers.

Configurations or Topologies Networks

A network can be arranged or configured in several different ways. This arrangements is called the network's topology. The four principal network topologies are

1. Star Network

2. Bus Network

3. Ring Network

4. Hierarchical Network

1. Star Network

In a star network small computers or peripheral devices are linked to a central unit. This central unit may be a host computer or a file server. All the communications pass through this central unit. Control is maintained by polling. Each device is in turn allowed to send the message.

One particular advantage of the star form of network is that it can be used to provide a time-sharing system. i.e several users can share resources (time) on a central computer. The star is a common arrangement for linking several microcomputers to a mainframe that allows access to an organizations database.

2. Bus Network

In a bus network each device in the network handles its own communication control. There is no host computer. All communications control travel along a common connecting cable called a bus. As the information passes along the bus it is examined by each device to see if the information is intended for it.

The bus network is typically used when only a few microcomputers are to be linked together. The bus network is not as efficient as the star network for sharing common resources. However it is less expensive and is in very common use.

3. Ring Network

In a ring network, each device is connected with two other devices forming a ring. There is no central file server or computer. Messages are passed around the ring until they reach correct destination. With microcomputers ring network is the least frequently used arrangement. However it is often used to link mainframes specially over wide geographical areas.

A ring network is useful in a decentralized organization because it makes possible a distributed data processing system i.e. computers can perform processing tasks at their own dispersed locations.

4. Hierarchical Network

This type of networks are also called hybrid network. It consist of several computers linked to a central host computer just like a star network. However these computers are also hosts to other smaller computers or to peripheral devices. The host at the top of the hierarchical network could be mainframe. The computers below the mainframe could be minicomputers and those below microcomputers. This network allows various computers to share database processing programs and different output devices. It is useful in a centralized organizations.

Strategies of Networks

Every network has a strategy or a way of coordinating the sharing of the information and resource. The most common network strategies are terminal, peer-to-peer and client/server systems, terminal network system. In this system processing power is centralized in one large computer, usually the mainframe. The nodes (a node is any device connected to network) connected to this host computer are terminals (a terminal is a input or output device) with little or no processing capability. Most airline reservation systems are terminal systems.

Peer-to-Peer Network System

In a peer-to-peer network, nodes can act both as servers and clients. There are several advantages of using this type of strategy. The networks as inexpensive and easy to install and they usually work well for smaller systems with less than ten nodes. As the number of nodes increases, however the performance of the network declines.

Client/Server Network System

Client/Server network system uses to coordinate and supply services to all other nodes on the network. The server provides access to centralized resources such as databases, applications software and hardware. This strategy is based on specialization. Server nodes coordinate and supply specialized services and client nodes request services.

One advantage of client/server network system is its ability to handle very large networks efficiently. Another advantage is the powerful management software that monitors and controls networks activities. The major disadvantage of it is the high cost of installation and maintenance.

Advantages of Network

Networks provide tremendous benefits. The most compelling advantages of network are as follows.

1. Networks allow users simultaneous access to shared programs and data.

2. Network also allows users to share peripheral devices such as printers and hard disks.

3. Network usually includes the capacity to send e-mail and many e-mail systems let users to attach files to their messages.

4. Connecting computers to form a network makes it easier to perform backups of the data on all the network hard disks.

Types of Networks

Communications differ in geographical size. Three important types are LANs, MANs, WANs.

Local Area Networks (LANs)

Network with computers and peripherals devices in close proximity within the same building are called local area networks (LANs).

The figure shows an example of a LAN. This type of arrangement has two benefits.

1. People can share different equipment, which lowers the cos of equipment.

2. LAN also features a network gateway. i.e. a LAN may be linked to other LANs or to large networks in this manner.

Metropolitan Area Network (MANs)

These network are used as links between office buildings in a city. Cellular phone systems expand the flexibility of MANs by allowing links to car phones and portable phones.

Wide Area Network (WANs)

Wide area networks are countrywide and worldwide networks. Among other kinds of channels they use microwave relays and satellites to reach users over long distances. One of the most widely used WANs is Internet. Which allows users to connect to other users and facilities worldwide.

Uses of Internet

The most common uses of Internet are

1. Communicating

Sending and receiving e-mail is the most popular internet activity. You can send and receive e-mail to and from you friends and family located almost anywhere in the world. You can join an listen to discussions and debates on a wide variety of special interest topics.

2. Shopping

One of the fastest growing applications of Interest is electronic commerce. You can visit a cyber mall for making purchases.

3. Researching

Internet provides you to have one of the world's largest libraries available from home.

4. Entertainment

Do you like music, the moves and reading or playing computer games? You can find them all on Internet waiting for you to locate and enjoy.

What are the characteristics of client/server architecture

The basic characteristics of client/server architectures are:

1) Combination of a client or front-end portion that interacts with the user, and a server or back-end portion that interacts with the shared resource. The client process contains solution-specific logic and provides the interface between the user and the rest of the application system. The server process acts as a software engine that manages shared resources such as databases, printers, modems, or high powered processors.

2) The front-end task and back-end task have fundamentally different requirements for computing resources such as processor speeds, memory, disk speeds and capacities, and input/output devices.

3) The environment is typically heterogeneous and multivendor. The hardware platform and operating system of client and server are not usually the same.Client and server processes communicate through a well-defined set of standard application program interfaces (API's) and RPC's.

4) An important characteristic of client-server systems is scalability. They can be scaled horizontally or vertically. Horizontal scaling means adding or removing client workstations with only a slight performance impact. Vertical scaling means migrating to a larger and faster server machine or multiservers.

What is the full form of ISDN? Explain use of ISDN in Internet

Integrated Services Digital Network (ISDN) is an upgraded phone line that can be used for faster Internet access and for regular voice calls. Using one line, you can talk on the phone while you’re surfing the Web. ISDN is all digital, which means that data doesn’t have to be converted to an analog signal for transmission.

The ISDN service intended for residential use is Basic Rate Interface (BRI). On one ISDN line, BRI provides two 64Kbps channels, or B channels, and one 16Kbps channel, or D channel.

The D channel is mostly used for signaling—for instance, to indicate that the line is busy.

The B channels are where the action is. When the B channels are combined, you have a 128Kbps line to the Internet. That’s over twice the speed of the fastest analog modem, 56Kbps. If you want to talk on the phone or send a fax, your Internet access drops down to one 64Kbps B channel while the other B channel is used for voice.

How does a Token-Passing Protocol works

The token-passing protocol relies on a control signal called the token. A token is a 24-bit packet that circulates throughout the network from NIC to NIC in an orderly fashion. If a workstation wants to transmit a message, first it must seize the token. At that point, the workstation has complete control over the communications channel. The existence of only one token eliminates the possibility of signal collisions. This means that only one station can speak at a time.

Logical Ring Physical Star topology for Token-Passing Standard.

It is sure that any break in the ring at any point will interrupt communications for all machines. To solve this problem, IBM developed a modified ring topology, which they called the logical ring physical star. The central point of the physical star configuration is Token Ring hub called the multi-station access unit (MSAU, pronounced as masow). Workstations and servers attached to the MSAU through special STP adapter cables. IBM converted stars into a logical ring by connecting all MSAU hubs together through special ring-in (RI) and ring-out (RO) ports.

Advantages of Token Ring.

Here are Token ring's most useful advantages:

a. It offers excellent throughput under high-load conditions.

b. Token Ring facilitates LAN-to-LAN mainframe connections especially for interfacing with IBM's broader connectivity strategies.

c. It has built-in troubleshooting mechanisms such as beaconing and auto-reconfiguration and may now be used with UTP cabling.

d. It has the most reliable protocol (token-passing), the most trouble-free configuration (physical star) and the fastest connectivity scheme (r or 16 mb/s).

Disadvantages of Token Ring.

Few of the disadvantages of Token Ring are:

a. Token Ring is very expensive. All topology components cost much more than other more popular standards.

b. It is relatively proprietary. Token Ring's complexity is built into the hardware components. This means hat you need to choose a manufacturer and stick with it.

c. Engineers must have considerable expertise to manage and troubleshoot token ring components.

What is Proxy Server

A server that sits between a client application, such as a Web browser, and a real server. It intercepts all requests to the real server to see if it can fulfill the requests itself. If not, it forwards the request to the real server.

Proxy servers have two main purposes:

# Improve Performance: Proxy servers can dramatically improve performance for groups of users. This is because it saves the results of all requests for a certain amount of time. Consider the case where both user X and user Y access the World Wide Web through a proxy server. First user X requests a certain Web page, which we'll call Page 1. Sometime later, user Y requests the same page. Instead of forwarding the request to the Web server where Page 1 resides, which can be a time-consuming operation, the proxy server simply returns the Page 1 that it already fetched for user X. Since the proxy server is often on the same network as the user, this is a much faster operation. Real proxy servers support hundreds or thousands of users. The major online services such as America Online, MSN and Yahoo, for example, employ an array of proxy servers.

# Filter Requests: Proxy servers can also be used to filter requests. For example, a company might use a proxy server to prevent its employees from accessing a specific set of Web sites.

What is a Router in Computer Network

Router is used to send data to the next network. Routers are Computer Network device that is used for  delivering and forwarding information.

Types of Routers

Many kinds of Routers are present in the current market that are depending on the need of the any enterprises. Cisco is the major manufacturer of router mostly Cisco router are used to set up network of large corporation and even of the ISPs. Broadly Routers are divided into three categories that depending upon the corporate needs.

1. Internet connectivity routers

These routers are used in Border Gateway Protocol for exchange information. These type of routers are further divided into four more categories.

1.1. Edge router

A Edge router or edge device is routes data packets between LANs and an Asynchronous Transfer Mode (ATM) network.

1.2. Subscriber edge router (SER)

Subscriber edge router (SER) Also known as Customer Edge router.Customer Edge router use EBGP protocol, it used in (enterprise) organization.

1.3. Inter provider border router

Inter provider border router are used for Interconnecting ISPs. Inter provider border router use BGP protocol to speake.

1.4. Core router

When a router become the integral part of the LAN(Local Area Network) is called core router. Core router uses internal BGP protocol.Core routers have specialized functions in VPN,that is based on a combination of BGP and Multi-Protocol Label Switching protocols.

One Another Type of Router is SOHO routers. It is used for connection other networks in small geographical area it is known as SOHO connectivity.

How Routers Works

Routers are interconnectivity devices that is used to transfer the datum packets along networks by visualizing the networks path. Routers visualizing the networks path to many networks such as Electronic networks, Transport networks and phone networks. Two ways are exist for routers operation using either control plane or forwarding plane. In control plane the router sends the precise data packets to their specific location. On the other hand in forwarding plane router does not remember the sending or receiving information about the packets.

Advantages of Routers

Routers route the data in an organized way. Routers generate a reliable connection between hosts. Routers is used for alternatively incase the main is fail to transfer data.

What is an Ethernet topology? How an Ethernet Worked

The Ethernet topology was developed at the University of Hawaii to connect computers on the various Islands. It was radio based design.  Ethernet is one of the most popular Computer Network or LAN technologies in use today covering more than 85% of the computer networks. Ethernet system consists of three basic elements:

1. The physical medium use to carry Ethernet signals between computers on the network

2. A set of rules (protocols) embedded in each Ethernet interface that will decide how multiple computers on the network will have access to the data on the medium.

3. An Ethernet frame that consists of a standardized set of bits used to carry data over the system.

The operation of Ethernet can be described in simple terms as follows:

Each computer on the Ethernet Network, also known as a node, operates independently of all other nodes. All nodes attached to an Ethernet are connected to a shared medium over which the Ethernet signals travel serially, one data bit at a time.

To send data a station first listens to the channel and when the channel is idle the station transmits its information in the form of an Ethernet frame, or packet. The Ethernet rules (protocol) are defined in such a way that every node gets a fair amount of frame transmission opportunity.

As each Ethernet frame is sent out on the shared medium, the Ethernet interfaces inside the node look at the destination address. The interfaces compare the destination address of the frame with their own address. The Ethernet interface with the same address as the destination address in the frame will read the entire frame and all other network interfaces will ignore the information.

Medium Access Control of Ethernet

The set of rules which ensures that every node in an Ethernet gets a fair amount of frame transmission opportunity, are called the "Medium Access Control" mechanism. The Medium Access Control mechanism is based on a system called Carrier Sense Multiple Access with Collision Detection (CSMD/CD).

Ethernet Frame.

The heart of Ethernet system is the Ethernet Frame, which is used to deliver information between the computers. The frame consists of a set of bits organized into several fields. These fields include address fields, a data field and an error checking field that checks the integrity of the bits in the frame to make sure that the frame has arrived intact.

Advantages of Ethernet.

Ethernet's major advantages are:

1. It is an inexpensive way to achieve high speed LAN transmissions (10 to 100 MB/s)

2. It is a proven technology that supports various writing configurations.

3. It works well with a large number of LAN and micro-to-mainframe applications.

4. It is easy to install.

Disadvantages of Ethernet Cabling

The Ethernet cabling ahs the following disadvantages:

1. Ethernet is not a high-level performer in high-load environments. This protocol (CSMA/CD: Carrier Sense Multiple Access/Collision Detection) can slow down dramatically if hundreds of workstations are competing for the same cabling trunk

2. Its linear bus cabling system can sometimes make it difficult to isolate problems.

The networks Type Based on Transmission Technology

The networks Type Based on Transmission Technology

The Computer networks can be classified on various properties. The Computer networks can also be classified on the basis of Computer network technology used by them. There are two types of Computer networks in this category.

1. Broadcast Networks. In broadcast networks, a single communication channel is shared among all the computers of the network. This means, all the data transportation occurs through this shared channel. The data is transmitted in the form of packets. The packets transmitted by one computer are received by all others in the network. The destination of packet is specified by coding the address of destination computer in the address field of packet header. On receiving a packet, every computer checks whether it is intended for it or not. If the packet is intended for it, it is processed otherwise, it is discarded. There is another form of broadcast networks in which the packets transmitted by a computer are received by a particular group of computers. This is called as "Multicasting".

2. Point to Point or Store and Forward Networks. This is the other type of networks on the basis of transmission technology. The store and forward networks consist of several interconnected computers and networking devices. The data is transmitted in the form of packets. Each packet has its own source and destination address. To go from a source to a destination, a packet on this type of network may first have to visit one or more intermediate devices or computers that are generally called as "routers". The packets are stored on an intermediate router unless the output line is free. When the output line is free, it is forwarded to the next router. The routing algorithms are used to find a path from the source to destination. The routing algorithms play a very important role in this type of network.

What are the different types of servers

File servers. -With a file server, the Computer Network client passes requests for computer network files or file records over a computer network to the file server. This form of computer network data service requires large bandwidth and can slow a computer network with many users down considerably. Traditional LAN (Local area Network) computing allows users to share resources, such as data files and peripheral devices, by moving them from standalone PCUs onto a Networked File Server (NFS).

Database servers-In database servers, clients passes SQL (Structured Query Language) requests as messages to the server and the results of the query are returned over the network. The code that processes the SQL request and the data resides on the server allowing it to use its own processing power to find the requested data, rather than pass all the records back to a client and let it find its owndata as was the case for the file server.

Transaction servers- Clients invoke remote procedures that reside on servers which also contains an SQL database engine. There are procedural statements on the server to execute a group of SQL statements (transactions) which either all succeed or fail as a unit. The applications based on transaction servers are called On-line Transaction Processing (OLTP) and tend to be mission-critical applications which require 1-3 second response time, 100% of the time and require tight controls over the security and integrity of the database.

The communication overhead in this approach is kept to a minimum as the exchange typically consists of a single request/reply (as opposed to multiple SQL statements in database servers). Application servers are not necessarily database centered but are used to server user needs, such as. download capabilities from Dow Jones or regulating a electronic mail process. Basing resources on a server allows users to share data, while security and management services, which are also based in the server, ensure data integrity and security.

Explain Client Server Networking Model

A Computer networking model where one or more powerful computers (servers) provide the different computer network services and all other user's  of computer  network (clients) access those services to perform user's tasks is known as client/server computer networking model. Client-server computer networking model became popular in the late 1980s and early 1990s as many applications were migrated from centralized minicomputers and mainframes to computer networks of persona computers.

The design of applications for a distributed computing environment required that they effetely be divided into two parts: client (front end) and server (back end). The network model on which they were implemented mirrored this client-server model with a user's PC (the client) typically acting as the requesting machine and a more powerful server machine to which it was connected via either a LAN or a WAN acting as the supplying machine. It requires special networking operating system. It provides user level security and it is more expensive.

What is Internetworking

Internetworking started as a way to connect disparate types of computer networking technology. Computer network term is used to describe two or more computers that are linked to each other. When two or more computer networks or computer network segments are connected using devices such as a router then it is called as computer internetworking. Internetworking is a term used by Cisco. Any interconnection among or between public, private, commercial, industrial, or governmental computer networks may also be defined as an internetwork or Internetworking. In modern practice, the interconnected computer networks or Internetworking use the Internet Protocol. Two architectural models are commonly used to describe the protocols and methods used in internetworking. The standard reference model for internetworking is Open Systems Interconnection (OSI).  Internetworking is implemented in Layer 3 (Network Layer) of this model The most notable example of internetworking is the Internet (capitalized). There are three variants of internetwork or Internetworking, depending on who administers and who participates in them :

Extranet

Intranet

Internet

Intranets and extranets may or may not have connections to the Internet. If connected to the Internet, the intranet or extranet is normally protected from being accessed from the Internet without proper authorization. The Internet is not considered to be a part of the intranet or extranet, although it may serve as a portal for access to portions of an extranet.

Extranet : An extranet is a network of internetwork or Internetworking that is limited in scope to a single organisation or entity but which also has limited connections to the networks of one or more other usually, but not necessarily, trusted organizations or entities .Technically, an extranet may also be categorized as a MAN, WAN, or other type of network, although, by definition, an extranet cannot consist of a single LAN; it must have at least one connection with an external network.

Intranet : An intranet is a set of interconnected networks or Internetworking, using the Internet Protocol and uses IP-based tools such as web browsers and ftp tools, that is under the control of a single administrative entity. That administrative entity closes the intranet to the rest of the world, and allows only specific users. Most commonly, an intranet is the internal network of a company or other enterprise. A large intranet will typically have its own web server to provide users with browseable information.

Internet : A specific Internetworking, consisting of a worldwide interconnection of governmental, academic, public, and private networks based upon the Advanced Research Projects Agency Network (ARPANET) developed by ARPA of the U.S. Department of Defense also home to the World Wide Web (WWW) and referred to as the 'Internet' with a capital 'I' to distinguish it from other generic internetworks. Participants in the Internet, or their service providers, use IP Addresses obtained from address registries that control assignments.

Types of Networks

Computer Networks fall into three classes regarding the size, distance and the structure namely: LAN (Local Area Network), MAN (Metropolitan Area Network), WAN (Wide Area Network). A LAN links a small group of functionally similar workstations within a local geographic area such as a series of adjacent cubicles or offices on the same floor. Once the Computer network expands to include other floors or divers office within a metropolitan area, it becomes a MAN. Finally, a WAN is simply a LAN of LANs. WANs expand the boundaries of computer networking to a global or even galactic scale.

Types of Networks - Common examples of area network types are:

LAN (LAN is a Local Area Networking)

A Local Area Network is a computer network covering a small Networks geographical area, like a home, office, or groups of buildings e.g. a school Network. For example, a library will have a wired or wireless LAN Network for users to interconnect local networking devices e.g., printers and servers to connect to the internet. The defining characteristics of LANs Network, in contrast to Wide Area Networks (WANs), includes their much higher data-transfer rates, smaller geographic range, and lack of need for leased telecommunication lines. Although switched Ethernet is now the most common protocol for Networks. Current Ethernet or other IEEE 802.3 LAN technologies operate at speeds up to 10 Gbit/s.IEEE has projects investigating the standardization of 100 Gbit/s, and possibly 40 Gbit/s. Smaller Networks generally consist of a one or more switches linked to each other - often with one connected to a router, cable modem, or DSL modem for Internet access. LANs Network may have connections with other LANs Network via leased lines, leased services.

Types of LAN

There are basically two types of Local Area Networks namely: Arcnet and Ethernet.

ARCNET (Attached Resource Computer NETwork)

ARCNET is one of the oldest, simplest, and least expensive types of Local-Area Network (LAN) protocol, similar in purpose to Ethernet or Token Ring. ARCNET was the first widely available networking system for microcomputers and became popular in the 1980s for office automation tasks. ARCnet was introduced by Datapoint Corporation in 1977. A special advantage of ARCNET (Attached Resource Computer NETwork ) is that it permits various types of transmission media - twisted-pair wire, coaxial cable, and fiber optic cable - to be mixed on the same network.The specification is ANSI 878.1. It can have up to 255 nodes per network.

A new specification, called ARCnet Plus, will support data rates of 20 Mbps

Ethernet is a family of computer networking technologies for local area networks (LANs) commercially introduced in 1980. Standardized in IEEE 802.3, Ethernet has largely replaced competing wired local area network (LAN) technologies.Ethernet uses a bus or star topology Network and supports data transfer rates of 10 Mbps.Ethernet Network uses the CSMA/CD access method to handle simultaneous demands. It is one of the most widely implemented LAN standards.A newer version of Ethernet Network, called 100Base-T (or Fast Ethernet), supports data transfer rates of 100 Mbps. And the newest version, Gigabit Ethernet supports data rates of 1 gigabit (1,000 megabits) per second. Ethernet is a physical and data link layer technology for local area networks (LANs). Ethernet Network was invented by engineer Robert Metcalfe.

MAN (Metropolitan Area Networks)

MAN stands for Metropolitan Area Networks is one of a number of types of networks. A MAN ( Metropolitan Area Networks ) is a relatively new class of network. MAN is larger than a local area network (LAN) and as its name implies, covers the area of a single city. MANs ( Metropolitan Area Networks ) rarely extend beyond 100 KM and frequently comprise a combination of different hardware and transmission media.

The two most important components of MANs ( Metropolitan Area Networks ) are security and standardization. Security is important because information is being shared between dissimilar systems. Standardization is necessary to ensure reliable data communication.

A MAN ( Metropolitan Area Networks ) usually interconnects a number of local area networks (LANs) using a high-capacity backbone technology, such as fiber-optical links, and provides up-link services to wide area networks (or WAN) and the Internet.

MAN ( Metropolitan Area Networks ) adopted technologies from both LAN (local area networks) and WAN (Wide Area Networks) to serve its purpose. Some legacy technologies used for MAN ( Metropolitan Area Networks ) are ATM, FDDI, DQDB and SMDS. These older technologies are in the process of being displaced by Gigabit Ethernet and 10 Gigabit Ethernet. At the physical level, MAN links between LANs (local area networks) have been built on fibre optical cables or using wireless technologies such as microwave or radio.

The Metropolitan Area Networks (MAN) protocols are mostly at the data link level (layer 2 in the OSI model ), which are defined by IEEE, ITU-T, etc.

WAN (Wide Area Networks)

A wide area network (WAN) is a telecommunication network. A wide area network is simply a LAN of LANs or Network Of Networks. WANs connect LANs (Local Area Networks) that may be on opposite sides of a building, across the country or around the world. WANS (wide area networks) are characterized by the slowest data communication rates and the largest distances. WANs (wide area networks) can be of two types: an enterprise WAN (wide area networks) and Global WAN (wide area networks).

Computers connected to a Wide Area Networks are often connected through public networks, such as the telephone system. They can also be connected through leased lines or satellites. The largest WAN (wide area networks) in existence is the Internet. Some segments of the Internet, like VPN (Virtual Private Networks) based extranets, are also WANs (wide area networks) in themselves. Finally, many WANs (wide area networks) are corporate or research networks that utilize leased lines.

Numerous WANs have been constructed, including public packet networks, large corporate networks, military networks, banking networks, stock brokerage networks, and airline reservation networks.

Organisations supporting WANs (wide area networks) using the Internet Protocol are known as Network Service Providers (NSPs). These form the core of the Internet.

By connecting the NSP WANs together using links at Internet Packet Interchanges (sometimes called "peering points") a global communication infrastructure is formed.

WANs (wide area networks) generally utilize different and much more expensive networking equipment than do LANs (Local Area Networks). Key technologies often found in WANs (wide area networks) include SONET, Frame Relay, and ATM.

Clarify Enterprise WANs.

An enterprise WAN (wide area networks) connects an entire organization including all LANs (Local Area Networks) at various sites. This term is used for large, widespread organizations such as corporations, universities and governments.

Clarify Global WANs.

Global WANs (wide area networks) also span the world but they do not have to connect LANS (Local Area Networks) within a single organization. The Internet is an example of a global WAN. It connects diverse locations, organizations and institutions throughout the world. Global WANS (wide area networks) can be public or private. Private WANs (wide area networks) are called Intranet which belongs to an organization. Public WANs (wide area networks) are open to everybody so that anybody can connect and use the resources and services available.

WLANs - Wireless Local Area Networks

WLANs (Wireless Local Area Networks or sometimes referred to as LAWN, for local area wireless network) provide wireless network communication over short distances using radio or infrared signals instead of traditional network cabling.WLANs (Wireless Local Area Networks) is one in which a mobile user can connect to a local area network (LAN) through a wireless (radio) connection.

Norman Abramson, a professor at the University of Hawaii, developed the world’s first wireless computer communication network,

A WLAN typically extends an existing wired local area network. WLANs (Wireless Local Area Networks) are built by attaching a device called the access point (AP) to the edge of the wired network. Clients communicate with the AP using a wireless network adapter similar in function to a traditional Ethernet adapter.

Network security remains an important issue for WLANs (Wireless Local Area Networks). Random wireless clients must usually be prohibited from joining the WLAN. Technologies like WEP raise the level of security on wireless networks to rival that of traditional wired networks.

The IEEE 802.11 group of standards specify the technologies for wireless LANs. 802.11 standards use the Ethernet

WLAN (Wireless Local Area Networks) hardware was initially so expensive that it was only used as an alternative to cabled LAN in places where cabling was difficult or impossible.

All components that can connect into a wireless medium in a network are referred to as stations. All stations are equipped with wireless network interface controllers (WNICs). Wireless stations fall into one of two categories: access points, and clients. Access points (APs), normally routers, are base stations for the wireless network. They transmit and receive radio frequencies for wireless enabled devices to communicate with. Wireless clients can be mobile devices such as laptops, personal digital assistants, IP phones and other smartphones, or fixed devices such as desktops and workstations that are equipped with a wireless network interface.

WLAN (Wireless Local Area Networks) types

Private home or small business WLAN

Commonly, a home or business WLAN employs one or two access points to broadcast a signal around a 100- to 200-foot radius. You can find equipment for installing a home WLAN in many retail stores.

With few exceptions, hardware in this category subscribes to the 802.11a, b, or g standards (also known as Wi-Fi); some home and office WLANs now adhere to the new 802.11n standard. Also, because of security concerns, many home and office WLANs adhere to the Wi-Fi Protected Access 2 (WPA2) standard.

Enterprise class WLAN

An enterprise class WLAN employs a large number of individual access points to broadcast the signal to a wide area. The access points have more features than home or small office WLAN equipment, such as better security, authentication, remote management, and tools to help integrate with existing networks. These access points have a larger coverage area than home or small office equipment, and are designed to work together to cover a much larger area. This equipment can adhere to the 802.11a, b, g, or n standard, or to security-refining standards, such as 802.1x and WPA2.

Examples:

For WLANs that connect to the Internet, Wireless Application Protocol (WAP) technology allows Web content to be more easily downloaded to a WLAN and rendered on wireless clients like cell phones and PDAs.

Storage Area Network (SAN) :

A storage area network (SAN) is a type of local area network (LAN) is a high-speed special-purpose network. A SAN typically supports data storage, retrieval and replication on business networks using high-end servers, multiple disk arrays and Fibre Channel interconnection technology.

Storage Area Networks (SANs) technology is similar but distinct from network attached storage (NAS) technology. While SANs traditionally employ low-level network protocols for transfering disk blocks, a NAS device typically works over TCP/IP and can be integrated fairly easily into home computer networks.

The term SAN can sometimes refer to system area networks instead of a storage area network. System area networks are clusters of high performance computers used for distributed processing applications requiring fast local network performance. Storage area networks, on the other, are designed specifically for data management.

SANs support disk mirroring, backup and restore, archival and retrieval of archived data, data migration from one storage device to another and the sharing of data among different servers in a network. SANs can incorporate sub networks with network attached storage (NAS) systems.

Storage Area Networks Make Your Life Easier

Simplification of Storage Administration is now possible because of Storage Area Networks cause cables and storage devices doesn’t need to be moved physically. Moving data from one server into another is now a breeze. Thanks to Storage Area Networks. Life is much easier.

Before, storage area networks process can take as little as half an hour. But this was before and now we can accelerate it.

The boo-table features of Storage Area Networks can also be effective and enable during recovery of data because of certain disaster such as server failure or human error. Storage area networks are great tools in recovering important data and back ups. Distant location doesn’t effect the storage area networks as long as the secondary storage array is working. This enables storage replication either implemented by disk array controllers, by server software, or by specialized SAN devices. Since IP WAN’s are often the least costly method of long-distance transport, the Fibre Channel over IP (FCIP) and iSCSI protocols have been developed to allow SAN extension over IP networks.

In the old model like in physical SCSI layer, it supported a few meters of distance and no guarantee of business continuity when disaster strike.In storage area networks, the disk arrays has accelerated and consolidated in the features like I/O caching, volume cloning and snap shotting making business continuance possible or BCV’s (Business Continuance Volumes).

Campus Area Network (CAN)

A campus area networks (CANs) is a computer network interconnecting a few local area networks (LANs) within a university campus or corporate campus Network.Campus area network may link a variety of campus buildings.A campus area network is larger than a local area network but smaller than a metropolitan area network (MAN) or wide area network (WAN). CAN can also stand for corporate area network.

Personal Area Network (PAN)

A personal area network is a computer network organized around an individual person. Personal area networks typically involve a mobile computer,Personal area networks can be constructed with cables or wirelessly.Personal area networks generally cover a Network range of less than 10 meters (about 30 feet).

PAN (Personal Area Network) first was developed by Thomas Zimmerman and other researchers at M.I.T.'s Media Lab and later supported by IBM's Almaden research lab.

Wireless Personal Area Network (WPAN) which is virtually a synonym since almost any personal area network would need to function wirelessly. Conceptually, the difference between a PAN ( personal area network ) and a wireless LAN ( Local Area Network) is that the former tends to be centered around one person Network while the latter is a local area network (LAN) that is connected without wires Network and serving multiple users.

What is a computer network? Advantages of Network . Explain Network Services.

A computer network consists of two or more computers that are linked in order to share resources such as printers and CD-ROMs, exchange files, or allow electronic communications. The computers on a computer network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.

A computer network consists of two or more computers that are linked in order to share resources such as printers and CD-ROMs, exchange files, or allow electronic communications. The computers on a computer network may be linked through cables, telephone lines, radio waves, satellites, or infrared light beams.

Computer network can be classified on the basis of following features :

By Scale : Computer networks may be classified according to the scale :

Local Area Network (LAN)

Metropolitan Area Network (MAN)

Wide Area Network (WAN)

By Connection Method : Computer networks can also be classified according to the hardware technology that is used to connect the individual devices in the network such as Optical fibre, Ethernet, Wireless LAN.

By Functional Relationship (Network Architectures) : Computer networks may be classified according to the functional relationships which exist between the elements of the network. This classification also called computer architecture. There are two type of network architecture :

Client-Server

Peer-to-Peer Architecture

By Network Topology : Network Topology signifies the way in which intelligent devices in the network see their logical or physical relations to one another.Computer networks may be classified according to the network topology upon which the network is based, such as :

Bus Network

Star Network

Ring Network

Mesh Network

Star-Bus Network

Tree or Hierarchical Topology Network

Advantages of Network

The following are the distinct notes in favor of computer network.

a. The computers, staff and information can be well managed

b. A network provides the means to exchange data among the computers and to make programs and data available to people

c. It permits the sharing of the resources of the machine

d. Networking also provides the function of back-up.

e. Networking provides a flexible networking environment. Employees can work at home by using through networks ties through networks into the computer at office.

Explain Network Services

1. Network services are the thing that a network can do. The major networking services are

2. File Services: This includes file transfer, storage, data migration, file update, synchronization and achieving.

3. Printing Services: This service produces shared access to valuable printing devices.

4. Message Services: This service facilitates email, voice mails and coordinate object oriented applications.

5. Application Services: This services allows to centralize high profile applications to increase  performance and scalability

6. Database Services: This involves coordination of distributed data and replication.