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Friday, August 26, 2011

Comparison of LANs and WANs

LANs (Local Area Networks) and WANs (Wide Area Networks) are two basic types of networks used in digital communications. Typically, LANs are used within a private campus, where as WANs require regional government permission for laying and may cover very long distances.


LANs (Local Area Networks) and WANs (Wide Area Networks) are two basic types of networks used in digital communications. We try to distinguish between LAN and WAN by comparing both technologies.
Property LAN WAN
Protocols commonly used Ethernet, Token Ring, FDDI, etc. X.25, Frame Relay, ISDN, Leased line etc.
Communication method Shared Media Point-to-point
Main Advantage Offer high speeds over short distances. Since LANs spread over short distances (typically a fraction of a kilometer), they offer very high speeds. The signal strengths offered by LAN devices is good, and LANs typically require less expensive equipment for transmission, and reception of signals. Offer relatively low speeds over longer distances. With WAN, the media becomes expensive since it had to traverse over several kilometers (sometimes 100s or 1000s of Kilometers). Attenuation and noise become significant over such large distances. Hence, high power transmitters, and highly sensitive receivers are used with WANs. These equipment tend to be very expensive because they use signal modulation and frequency conversions.
Common Usage 1. Within a building, campus, or city
2. Used to connect several host computers within a building or campus together. 1. Between cities or any points that are geographically separated by a large distance (several kilometers or more)
2. WAN is normally used for connecting LANs separated by a large distance (say, several hundred kilometers)
Speeds Up to 1 Gbps typical. Normally, all of LAN bandwidth is available to a single user (or host) at any given time. The communication is burst in nature. Up to several Gbps shared. Though todays WANs offer very high bandwidths, the bandwidth is typically shared among several customers.
Cost Very low cost per Mbps High cost per Mbps.
Comments Both LAN and WAN are used in different circumstances, and they both complement each other.
As a case study to demonstrate the use of LAN and WAN, assume that an institution, Aurobindo Institute, has several departments and a centralized applications server. Each department needs to access the central server to access any application such as Microsoft Word or Excel. These applications are bandwidth intensive, and require high bandwidth over a shorter distance. All these departments need to be connected and should have access to the central application server. We need a Local Area Network for this purpose. A LAN may be confined to a small room, or a building, or a big campus depending on the requirement.
Now, assume that Arabindo has an email server, and a sister institute, Shanti situated in a different city needs access to your email server. You can't provide a LAN connection, since it is typically limited to a fraction of a kilometer (or a few kilometers with signal conditioners). Another reason for unsuitability of LAN is that you can't lay cables over public property without explicit permissions. One feasible solution for this is to have a WAN connection. For example, both Aurobindo and Shanti can have a link to ISP at both ends, and setup a virtual LAN over the the WAN. By using WAN, you can have your LAN spread across a large geographical regions. Without WAN, it would have been impossible to provide email access to the school. Internet is an example of a Wide Area Network spreading across continents.

Please visit Networking Protocols section of CCNA Tutorials available at SimulationExams.com for more information on networking protocols and their use.

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