Differences Between WLAN and LAN

Although WLANs and LANs both provide connectivity between the end users, they have some key differences that include both physical and logical differences between the topologies. In WLANs, radio frequencies are used as the physical layer of the network. Differences also exist in the way the frame is formatted and in the transmission methods, detailed as follows:

■ WLANs use carrier sense multiple access with collision avoidance (CSMA/CA) instead of carrier sense multiple access collision detect (CSMA/CD), which is used by Ethernet LANs. Collision detection is not possible in WLANs, because a sending station cannot receive at the same time that it transmits and, therefore, cannot detect a collision. Instead, WLANs use the Ready To Send (RTS) and Clear To Send (CTS) protocols to avoid collisions.

■ WLANs use a different frame format than wired Ethernet LANs use. WLANs require additional information in the Layer 2 header of the frame. Radio waves cause problems not found in LANs, such as the following:

■ Connectivity issues occur because of coverage problems, RF transmission, multipath distortion, and interference from other wireless services or other WLANs.

■ Privacy issues occur because radio frequencies can reach outside the facility. In WLANs, mobile clients connect to the network through an access point, which is the equivalent of a wired Ethernet hub. These connections are characterized as follows:

■ There is no physical connection to the network.

■ The mobile devices are often battery-powered, as opposed to plugged-in LAN devices. WLANs must meet country-specific RF regulations. The aim of standardization is to make WLANs available worldwide. Because WLANs use radio frequencies, they must follow country-specific regulations of RF power and frequencies. This requirement does not apply to wired LANs.

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Characteristics of a Network

Many characteristics are commonly used to describe and compare various network designs. When you are determining how to build a network, each of these characteristics must be considered along with the applications that will be running on the network. The key to building the best network is to achieve a balance of these characteristics. Networks can be described and compared according to network performance and structure, as follows:

■ Speed: Speed is a measure of how fast data is transmitted over the network. A more precise term would be data rate.

■ Cost: Cost indicates the general cost of components, installation, and maintenance of the network.

■ Security: Security indicates how secure the network is, including the data that is transmitted over the network. The subject of security is important and constantly evolving. You should consider security whenever you take actions that affect the network.

■ Availability: Availability is a measure of the probability that the network will be available for use when required. For networks that are meant to be used 24 hours a day, 7 days a week, 365 days a year, availability is calculated by dividing the time it is actually available by the total time in a year and then multiplying by 100 to get a percentage.

For example, if a network is unavailable for 15 minutes a year because of network outages, its percentage availability can be calculated as follows:

([Number of minutes in a year – downtime] / [Number of minutes in a year]) * 100 = Percentage availability

([525600 – 15] / [525600]) * 100 = 99.9971

■ Scalability: Scalability indicates how well the network can accommodate more users and data transmission requirements. If a network is designed and optimized for just the current requirements, it can be very expensive and difficult to meet new needs when the network grows.

■ Reliability: Reliability indicates the dependability of the components (routers, switches, PCs, and so on) that make up the network. Reliability is often measured as a probability of failure, or mean time between failures (MTBF).

■ Topology: Networks have two types of topologies: the physical topology, which is the arrangement of the cable, network devices, and end systems (PCs and servers), and the logical topology, which is the path that the data signals take through the physical topology.

These characteristics and attributes provide a means to compare different networking solutions. Increasingly, features such as security, availability, scalability, and reliability have become the focus of many network designs because of the importance of the network to the business process.

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Network User Applications

The key to utilizing multiple resources on a data network is having applications that are aware of these communication mechanisms. Although many applications are available for users in a network environment, some applications are common to nearly all users.

The most common network user applications include the following:

■ E-mail: E-mail is a valuable application for most network users. Users can communicate information (messages and files) electronically in a timely manner, to not only other users in the same network but also other users outside the network (suppliers, information resources, and customers, for example). Examples of e-mail programs include Microsoft Outlook and Eudora by Qualcomm.

■ Web browser: A web browser enables access to the Internet through a common interface. The Internet provides a wealth of information and has become vital to the productivity of both home and business users. Communicating with suppliers and customers, handling orders and fulfillment, and locating information are now routinely done electronically over the Internet, which saves time and increases overall productivity. The most commonly used browsers are Microsoft Internet Explorer,

Netscape Navigator, Mozilla, and Firefox.

■ Instant messaging: Instant messaging started in the personal user-to-user space; however, it soon provided considerable benefit in the corporate world. Now many instant messaging applications, such as those provided by AOL and Yahoo!, provide data encryption and logging, features essential for corporate use.

■ Collaboration: Working together as individuals or groups is greatly facilitated when the collaborators are on a network. Individuals creating separate parts of an annual report or a business plan, for example, can either transmit their data files to a central resource for compilation or use a workgroup software application to create and modify the entire document, without any exchange of paper. One of the best-known traditional collaboration software programs is Lotus Notes. A more modern web-based

collaboration application is a wiki.

■ Database: This type of application enables users on a network to store information in central locations (such as storage devices) so that others on the network can easily retrieve selected information in the formats that are most useful to them. Some of the most common databases used in enterprises today are Oracle and Microsoft SQL Server.

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