KINDS OF NETWORKS

Peer-to-Peer Networks

In a peer-to-peer network, there are no dedicated servers, and there is no hierarchy among the computers. All the computers are equal and therefore are known as peers. Each computer functions as both a client and a server.

And there is no administrator responsible for the entire network. The user at each computer determines what data on that computer is shared on the network. Below figure shows a peer-to-peer network in which each computer functions as both a client and a server.

Computers in a peer-to-peer network are called peers. In a peer-to-peer network, all computers are considered equal; they all have the same abilities to use the resources available on the network. Each computer can function both as a client and a server. Computers are not dedicated to function as servers. They use the network to share resources among the independent peers. The computer whose applications are required by the other networked computers functions as a server. The other computers function as clients. Therefore, a dedicated administrator is not assigned for network management.

A peer-to-peer network is a small group of people using a network. Peer-to-peer networks members usually perform similar tasks, which necessitates the sharing of resources. The peer-to-peer networks support 10 computers. The users in a peer-to-peer network are located in the same geographical area. Operating systems, such as Microsoft Windows 98 or Microsoft Windows XP, can be used to set up a peer-to-peer network. Additional software is not required because peer-to-peer networking is built into the systems.

Another important point of peer-to-peer networks is that the users of each computer plan and control the security of their resources. The users determine the resources on their computers, which can be shared on the network. The shared network resources, such as disk space, printers or faxes, can be used by anyone who has access to the network. This is possible only if the shared network resources are not password protected. Peer-to-peer networks have weak and intrusive security because a central server is not used to administer and secure the network. In addition, some users may not implement security.

A peer-to-peer network does not support a central login process. This implies that a user who logs on to one peer can access any shared network resource, which is not controlled by a specific password. Peer-to-peer networks are relatively simple. Because each computer functions as a client and a server, there is no need for a powerful central server or for the other components required for a high-capacity network. Peer-to-peer networks can be less expensive than server-based networks.

Peer-to-peer networks are simple and inexpensive to install and maintain. The cost of implementing peer-to-peer networks is low because a central server is not used to administer the network. In addition, the components for a high-capacity network are not required in a peer-to-peer network.

In a peer-to-peer network, the users handle administration. This means that all the users need to be trained in how to share files, folders, and printers. In a peer-to-peer network, suddenly shutting down your computer can cause one of your colleagues to be unable to print.

Peer-to-peer networks are appropriate for environments where all the users are located in the same geographical area and the network security is not an important factor. In addition, these networks are useful when the network expansion is limited.

Advantages of a peer-to-peer network:

Less initial expense - No need for a dedicated server. Setup - An operating system (such as Windows XP) already in place

may only need to be reconfigured for peer-to-peer operations.

Disadvantages of a peer-to-peer network:

Decentralized - No Centralized server. Security - Does not provide the security available on a peer-to-peer

network.

Server Based Networks

A dedicated server is one that functions only as a server and is not used as a client or workstation. Server based networks (see below Figure) have become the standard models for networking.

In a server-based network, clients rely on the services that the server provides, such as file storing and printing. Client computers are generally less powerful than server computers.

A server-based network using network operating system is that the networks are organized into domains. A domain is a collection of networks and clients that share security information. Domain security and logon permissions are controlled by special servers called domain controllers. Users cannot access the resources of servers in a domain until a domain controller has authenticated them.

In server-based networks, a network administrator centrally manages the resource security. The administrator defines and manages user access to network resources.

Another beneficial of server-based networks is central file storage. Server-based networks provide easy backup of critical data. Data backup is another useful characteristic of server based networks.

Server based networks can support a larger number of users than peer-to-peer networks. To support a large number of users, server-based networks use monitoring and network management tools. Servers must perform varied and complex tasks. (See below figure)

Security is often the primary reason for choosing a server-based approach to networking. In a server-based environment, one administrator who sets the policy and applies it to every user on the network can manage security. (see below figure)

Advantages of a client/server network

Centralized - Resources and data security are controlled through the server.

Security - More security then Peer-to-peer network. Flexibility - New technology can be easily integrated into system. Interoperability - All components (client /server) work together. Accessibility - Server can be accessed remotely and across multiple

platforms.

Disadvantages of a client/server network

Expense - Requires initial investment in dedicated server. Maintenance - Large networks will require a staff to ensure efficient

operation. Dependence - When server goes down, operations will cease across

the network.

A LAN is a network with two or more computers connected to each other in a single location

Wired Local Area Network (LAN)

It is the simplest type of network in which computers are connected to each other by cables.

Each of the computers on the LAN is also called a node .

A LAN is characterized by three primary attributes:

Topology

The topology is the pattern used to connect the computers together. With a bus topology, a network cable connects each computer to the next one, forming a chain. With a star topology, each of the computers is connected to a central nexus called a hub/Switch. A ring topology is essentially a bus network with the two ends joined together. (You will see more about network topologies in Chapter 6)

Medium

Four basic types of media are used in local-area networks; coaxial cable, twisted-pair wires, fiber-optic cable, And wireless.

Each medium has its advantages and disadvantages relative to cost, speed, and expandability. Coaxial cables provide high speed and low error rates. Twisted-pair wires are cheaper than coaxial cables, can sustain the speeds common to most personal computers, and are easy to install. Fiber-optic cable is the medium of choice for high-speed local-area networks. Wireless local-area networks have the advantage of expandability. (You will see more about network medium in Chapter 5.2)

Protocols

The topology and the medium used on a particular network are specified by the protocol. (You will see more about protocol in Chapter 8).

LAN computer networks that usually cover a limited range, say, within the boundary of a building. A LAN computer network is two or more computers that communicate with each other through some medium.

The primary usage of local-area networks (LANs) is the sharing of hardware, software, or information, such as data files, multimedia files, or electronic mail. Resource sharing provided by local-area networks improves efficiency and reduces overhead.

There are a number of ways in which nodes can communicate over a network. The simplest is to establish a dedicated link between the transmitting and receiving stations. This technique is known as circuit switching. A better way of communicating is to use a technique known as packet switching, in which a dedicated path is not reserved between the source and the destination. Data are wrapped up in a packet and launched into the network. In this way, a node only has exclusive access to the medium while it is sending a packet. During its inactive period, other nodes can transmit. A typical packet is divided into preamble, address, control, data, and error-check fields.

The computers in a LAN are connected by using cables. This method cannot be used to connect computers that are in different locations, for example, in buildings across a town or city. Therefore, a LAN is not suitable for large businesses with offices in several locations.

Wireless Local Area Network

The term wireless networking refers to technology that enables two or more computers to communicate using standard network protocols, but without network cabling.

Peer-to-peer wireless network consists of a number of computers each equipped with a wireless networking interface card. Each computer can

communicate directly with all of the other wireless enabled computers. They can share files and printers this way, but may not be able to access wired LAN resources, unless one of the computers acts as a bridge to the wired LAN using special software.

A wireless network can also use an access point, or base station. In this type of network the access point acts like a hub, providing connectivity for the wireless computers. It can connect the wireless LAN to a wired LAN, allowing wireless computer access to LAN resources, such as file servers or existing Internet Connectivity.

There are two types of access points:

Hardware access points (HAP)

Hardware access points offer complete support of most wireless features, but check your requirements carefully.

Software Access Points

Software Access Points which run on a computer equipped with a wireless network interface card as used in peer-to-peer wireless network. The software routers that can be used as a basic Software Access Point, and include features not commonly found in hardware solutions.

Connected wireless LAN to wired LAN

To do this you will need some sort of bridge between the wireless and wired network. This can be accomplished either with a hardware access point or a software access point.

Hardware access points are available with various types of network interfaces, such as Ethernet or Token Ring, but typically require extra hardware to be purchased if you're networking requirements change. If networking requirements go beyond just interconnecting a wired network to a small wireless network, a software access point may be the best solution.

A software access point does not limit the type or number of network interfaces you use. It may also allow considerable flexibility in providing access to different network types, such as different types of Ethernet, Wireless and Token Ring networks. Such connections are only limited by the number of slots or interfaces in the computer used for this task. Further to this the software access point may include significant additional features such as shared Internet access, web caching or content filtering, providing significant benefits to users and administrators.

Wireless networking offers a cost-effective solution to users with difficult physical installations such as campuses, hospitals or businesses with more than one location in immediate proximity but separated by public thoroughfare.

This type of installation requires two access points. Each access point acts as a bridge or router connecting its own LAN to the wireless connection. The wireless connection allows the two access points to communicate with each other, and therefore interconnect the two LAN's.

Wireless network range

Each access point has a finite range within which a wireless connection can be maintained between the client computer and the access point. The actual distance varies depending upon the environment; manufacturers typically state both indoor and outdoor ranges to give a reasonable indication of reliable performance. Also it should be noted that when operating at the limits of range the performance may drop, as the quality of connection deteriorates and the system compensates.

Typical indoor ranges are 150-300 feet, but can be shorter if the building construction interferes with radio transmissions. Longer ranges are possible, but performance will degrade with distance. Outdoor ranges are quoted up to 1000 feet, but again this depends upon the environment.

There are ways to extend the basic operating range of Wireless communications, by using more than a single access point or using a wireless relay /extension point. Multiple access points can be connected to a wired LAN, or sometimes even to a second wireless LAN if the access point supports this.

In most cases, separate access points are interconnected via a wired LAN, providing wireless connectivity in specific areas such as offices or rooms, but connected to a main wired LAN for access to network resources, such as file servers.

If a single area is too large to be covered by a single access point, then multiple access points or extension points can be used. Note that an "extension point" is not defined in the wireless standard, but have been developed by some manufacturers.

When using multiple access points, each access point wireless area should overlap its neighbors. This provides a seamless area for users to move around in using a feature called "roaming.” See Roaming for further information.

Some manufacturers produce extension points, which act as wireless relays, extending the range of a single access point. Multiple extension points can be strung together to provide wireless access to far away locations from the central access point.

Roaming

A wireless computer can "roam" from one access point to another, with the software and hardware maintaining a steady network connection by monitoring the signal strength from in-range access points and locking on to the one with the best quality.

Usually this is completely transparent to the user; they are not aware that a different access point is being used from area to area. Some access point configurations require security authentication when swapping access points, usually in the form of a password dialog box.

Access points are required to have overlapping wireless areas to achieve this as can be seen in the following diagram.

A user can move from Area 1 to Area 2 transparently. The Wireless networking hardware automatically swaps to the Access Point with the best signal.

Sharing an internet connection in wireless network

To share an Internet connection across a LAN you need two things:

an Internet sharing hardware device or software program a LAN

If your LAN is wireless. You need hardware or software access point and a wireless LAN. Any computer equipped with a wireless network card running suitable Internet sharing software can be used as a software access point. A number of vendors offer hardware access points.

A hardware access point may provide Internet Sharing capabilities to Wired LAN computers, but does not usually provide much flexibility beyond very simple configurations.

If an existing wired LAN already has an Internet connection, then the hardware access points simply connect to LAN and allow wireless computers to access the existing Internet connection in the same way as wired LAN computers.

Wireless Network security

Wireless communications obviously provide potential security issues, as an intruder does not need physical access to the traditional wired network in order to gain access to data communications. However, 802.11 wireless communications cannot be received much less decoded by simple scanners, short wave receivers etc. This has led to the common misconception that wireless communications cannot be eavesdropped at all. However, eavesdropping is possible using specialist equipment.

To protect against any potential security issues, 802.11 wireless communications have a function called WEP (Wired Equivalent Privacy), a form of encryption which provides privacy comparable to that of a traditional wired network. If the wireless network has information that should be secure then WEP should be used, ensuring the data is protected at traditional wired network levels.

IEEE 802.11

Wireless networking hardware requires the use of underlying technology that deals with radio frequencies as well as data transmission. The most widely used standard is 802.11 produced by the Institute of Electrical and Electronic Engineers (IEEE). This is a standard defining all aspects of Radio Frequency Wireless networking.

Also it should be noted that traditional Virtual Private Networking (VPN) techniques will work over wireless networks in the same way as traditional wired networks.

Wide Area Network (WAN)

A wide area network (WAN) is a telecommunications network, usually used for connecting computers, that spans a wide geographical area. WANs can by used to connect cities, states, or even countries.

An example of a WAN connection would be a company with two offices in distant cities, each with its own LAN and connected by a leased telephone line. This type of WAN is illustrated in below figure. Each end of the leased line is connected to a router and the routers are connected to individual LANs. Any computer on either of the LANs can communicate with any one of the other computers at the other end of the WAN link or with a computer on its own LAN.

WANs are often used by larger corporations or organizations to facilitate the exchange of data and in a wide variety of industries, corporations with facilities at multiple locations have embraced WANs. Increasingly, however, even small businesses are utilizing WANs as a way of increasing their communications capabilities.

Although WANs serve a purpose similar to that of local area networks (LANs), WANs are structured and operated quite differently. The user of a WAN usually does not own the communications lines that connect the remote computer systems; instead, the user subscribes to a service through a telecommunications provider. Unlike LANs, WANs typically do not link individual computers, but rather are used to link LANs. WANs also transmit data at slower speeds than LANs.

WANs have existed for decades, but new technologies, services, and applications have developed over the years to dramatically increase their efficacy for business. WANs were originally developed for digital leased-line services carrying only voice, rather than data. As such, they connected the private branch exchanges (PBXs) of remote offices of the same company. WANs are still used for voice services, but today they are used more frequently for data and image transmission (such as video conferencing). These added applications have spurred significant growth

in WAN usage, primarily because of the surge in LAN connections to the wider networks.

WANs are either point-to-point, involving a direct connection between two sites, or operate across packet-switched networks, in which data is transmitted in packets over shared circuits. Point-to-point WAN service may involve either analog dial-up lines, in which a modem is used to connect the computer to the telephone line, or dedicated leased digital telephone lines, also known as "private lines." Analog lines, which may be either part of a public-switched telephone network or leased lines, are suitable for batch data transmissions, such as congruent order entry and point-of-sale transactions. Dedicated digital phone lines permit uninterrupted, secure data transmission at fixed costs.

Point-to-point WAN service providers include both local telephone companies and long distance carriers. Packet-switched network services are typically chosen by organizations which have low volumes of data or numerous sites, for which multiple dedicated lines would be too expensive.

Depending on the service, WANs can be used for almost any data sharing purpose for which LANs can be used. Slower transmission speeds, however, may make some applications less practical for WANs. The most basic uses of WANs are for electronic mail and file transfer, but WANs can also permit users at remote sites to access and enter data on a central site's database, such as instantaneously updating accounting records.

New types of network-based software that facilitate productivity and production tracking, such as groupware and work-flow automation software, can also be used over WANs. Using groupware, workers at dispersed locations can more easily collaborate on projects. WANs also give remote offices access to a central office's other data communications services, including the Internet.

Wireless Fidelity Wi-Fi

A typical Wi-Fi setup contains one or more Access Points (APs) and one or more clients. An AP broadcasts its SSID (Service Set Identifier, "Network name") via packets that are called beacons, which are usually broadcast every 100 ms. The beacons are transmitted at 1 Mbit/s, and are of relatively short duration and therefore do not have a significant effect on

performance. Since 1 Mbit/s is the lowest rate of Wi-Fi it assures that the client who receives the beacon can communicate at least 1 Mbit/s. Based on the settings (e.g. the SSID), the client may decide whether to connect to an AP. If two APs of the same SSID are in range of the client, the client firmware might use signal strength to decide which of the two APs to make a connection to.

The Wi-Fi standard leaves connection criteria and roaming totally open to the client. This is a strength of Wi-Fi, but also means that one wireless adapter may perform substantially better than the other. Since Wi-Fi transmits in the air, it has the same properties as a non-switched ethernet network.

Wi-Fi Devices

Wireless Access Point (WAP)

A wireless access point (AP) connects a group of wireless stations to an adjacent wired local area network (LAN). An access point is similar to an ethernet hub or switch, but instead of relaying LAN data only to other LAN stations, an access point can relay wireless data to all other compatible wireless devices as well as to a single (usually) connected LAN device, in most cases an ethernet hub or switch, allowing wireless devices to communicate with any other device on the LAN.

Wireless Routers

A wireless router integrates a wireless access point with an IP router and an ethernet switch . The integrated switch connects the integrated access point and the integrated ethernet router internally, and allows for external wired ethernet LAN devices to be connected as well as a (usually) single WAN device such as cable modem or DSL modem . A wireless router advantageously allows all three devices (mainly the access point and router) to be configured through one central configuration utility, usually through an integrated web server .

Wireless Ethernet Bridge

A wireless Ethernet bridge connects a wired network to a wireless network. This is different from an access point in the sense that an access point connects wireless devices to a wired network at the data-link layer . Two wireless bridges may be used to connect two wired networks over a wireless link, useful in situations where a wired connection may be unavailable, such as between two separate homes.

Advantages of Wi-Fi

Allows LANs to be deployed without cabling, typically reducing the costs of network deployment and expansion. Spaces where cables cannot be run, such as outdoor areas and historical buildings, can host wireless LANs.

Wi-Fi silicon pricing continues to come down, making Wi-Fi a very economical networking option and driving inclusion of Wi-Fi in an ever-widening array of devices.

Wi-Fi products are widely available in the market. Different brands of access points and client network interfaces are interoperable at a basic level of service. Products designated as Wi-Fi CERTIFIED by the Wi-Fi Alliance are interoperable and include WPA2 security.

Wi-Fi networks support roaming, in which a mobile client station such as a laptop computer can move from one access point to another as the user moves around a building or area.

Wi-Fi networks support roaming, in which a mobile client station such as a laptop computer can move from one access point to another as the user moves around a building or area.

Wi-Fi is a global set of standards. Unlike cellular carriers, the same Wi-Fi client works in different countries around the world.

Disadvantages of Wi-Fi

Wi-Fi can be interrupted by other devices, notably 2.4 GHz cordless phones and microwave ovens.

Power consumption is fairly high compared to some other standards, making battery life and heat a concern.

The most common wireless encryption standard, Wired Equivalent Privacy or WEP, has been shown to be breakable even when correctly configured.

Wi-Fi Access Points typically default to an open ( encryption -free) mode. Novice users benefit from a zero configuration device that works out of the box but might not intend to provide open wireless access to their LAN.

Wi-Fi networks have limited range. A typical Wi-Fi home router using 802.11b or 802.11g with a stock antenna might have a range of 45 m (150 ft) indoors and 90 m (300 ft) outdoors. Range also varies with frequency band, as Wi-Fi is no exception to the physics of radio wave propagation. Wi-Fi in the 2.4 GHz frequency block has better range than Wi-Fi in the 5 GHz frequency block, and less range than the oldest Wi-Fi (and pre-Wi-Fi) 900 MHz block. Outdoor range with improved antennas can be several kilometres or more with line-of-sight.

Wi-Fi networks can be monitored and used to read and copy data (including personal information) transmitted over the network when no encryption such as VPN is used.