Cisa Exam Notes - Wan

Topics: OSI model, Point-to-Point Protocol, Packet switching Pages: 15 (5277 words) Published: March 3, 2013
Compiled by A.K.Asokan. (

Page Nos.1 of 16

Local Area Network can be easily understood since typically every office has a LAN. One could personally see the switches connecting various computer nodes and may be a router to which the switches are connected. Also we can see the Network Interface Card (NIC) at the back of the computer where we plug in the cable with the RJ45 connector, the blinking light etc. on the card. (Sometimes when it is not working, we pull out the cable from the card and plug it again to try our luck!!) All that we know. But how will you establish a connectivity between your Head office located in Chennai and the Branch office in Singapore? What are all the possibilities and whom to approach? We know that there is no way to lay a cable all the way to Singapore! That will be extremely difficult and not a good idea in terms of cost and feasibility also. So, let’s first understand what makes the difference between a LAN and a WAN. The general and immediate answer comes to our mind is that LAN is ‘local’ and WAN is a “wide” area network. The Distance!. But now-a-days we have the wireless LAN technology which can really cover a ‘wide’ area. Then is it the Bandwidth? Again we see the competition at our door step that we can get gigabit broadbands from various service providers at much, much cheaper rates. This is not either. What then? Generally, to set up a LAN, we buy computers, switches, cables, connectors, routers etc. But do you buy any equipment or wire to connect your Branch office located at Singapore or Delhi or Bombay? The answer is No. So we own the LAN infrastructure but we generally lease WAN infrastructure from any third party Service Providers or from a Telephone company. WANs generally carry a variety of traffic types such as voice, data and video. Imagine in your office there are 25 telephone extensions. So you have 25 telephone instruments placed on each officer’s desk wired and you own the infrastructure. If you want to call your three Branch offices at Singapore, USA and Canada do you own the infrastructure? i.e. the wires, telephone instruments connected till your branch offices? No. you ‘lease’ them. To make it more clear, you take a telephone line from the telephone company with ISD facility. Now that using your telephone company’s infrastructure, you can call to Singapore or any other branch offices anywhere in the world!. Similarly we own the LAN infrastructure and we ‘lease’ the infrastructure of a third party provider or a Telco for Wide Area Network (WAN) communication. If you carefully read the previous notes on LAN communication, we came across lot of terminologies. Like that here also we have to learn some terminologies. Let us first understand the WAN connection types.

Compiled by A.K.Asokan. (

Page Nos.2 of 16

WAN Technolologies Imagine you have a branch office in Delhi and another one in Canada. Your requirement is that every two minutes, you will communicate with each branch office. You must therefore have an always up connectivity for this at the same time cost effective. You can go for a dedicated line (a synchronous serial connectivity) so that it will be always on. But to establish a dedicated line, you will have to spend lot of money. If in case you are not using the full capability of the dedicated line and it happens that sometimes you will communicate with your branch offices only for 3-4 hours a day, then spending so much on a dedicated line is not a feasible solution. The alternative is a dial up line. Then every time you communicate, you have to dial and bring the line up and then send the data. It is tedious and though cost effective when compared to dedicated line, the bandwidth is also not guaranteed!. What we need is a connectivity, which is always ON at the same time cost effective also. One of such services is called Fame Relay. Frame relay is a Technology and not a...
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