Thread: LAN Question

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    LAN Question

    Dear Network Experts,
    please guide me how to solve the following questions,I am really lost, thanks in advance.

    (a) Implement a LAN for a company that has 50 employees, each has a notebook attached to the LAN.
    Recommend a suitable data rate for the LAN if the typical use of the LAN is as shown below.
    Justify your answers by working out the load for each requirement.
    State any assumption(s) that you have made in your answers.
    You can assume that 1 MBytes = 1000, 000 bytes, 1Kbps= 1000 bits per sec and 1KBytes= 1000 bytes.

    i. Each employee needs to retrieve a file of average size of 1 MBytes. An employee may do this on average 3 times during the 8 hours working time.
    ii. Each employee needs to access the internet at 1 Mbps. This can happen for 10 employees simultaneously.
    iii. Each employee may receive 20 emails per hour with an average size of 100KBytes. Half of the employees may receive email simultaneously.
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    The question is basically about figuring out the load on the network. How much data will one person want to use? How often? Will many people need data at the same time? How long should it take for them to get the data?
    Note that below I use 'B' for bytes and 'b' for bits, so 1MB/s = 8Mb/s.

    For example, part (i) is about downloading a 1MB file. One person doing it 3 times a day means 50 people will do it 3*50=150 times a day. Over 8 hours that's about once every 3 minutes.
    Now consider how long it could take to get the file. 1KB/s would need 1000 seconds, which is ridiculous regardless of load. 100KB/s is 10 seconds. Is that reasonable for a user? What happens to the network's load? What happens if two or more people want to get a file at the same time?

    Part (ii) is about some number of people wanting simultaneous access. 1Mb/s for 10 people means 10Mb/s total, but that's really just between the office and the internet. How does each person connect to the LAN? If they have their own dedicated connection then each one providing 1Mb/s would be sufficient, but if multiple people use (eg) a switch then the upstream link needs to support 1Mb/s * the number of people behind the switch. Pick something reasonable as your assumption.

    Part (iii) is similar to the first part in that there is sporadic activity, except this time it's much more likely that people need to use data at the same time. 20 emails/hour = average 1 email every 3 minutes, times 100KB is 100KB/3 minutes, times 25 people at once is 2.5MB/3 minutes = 111Kb/s. On average. Again, how long should it take a user to get their emails? Is it okay if it takes a bit longer when lots of people are getting emails at once?

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