Chapter Two Homework
1. What are some typical technical goals for organizations today?
Scalability, availability, Performance, Security, Usability, manageability, adaptability, affordability.
2. What does availability mean?
It’s can be expressed as a percent uptime per year, month, week, day, or hour compared to the total time in that period. It does also be expressed as a mean time between failure (MTBF) and mean time to repair (MTTR).
3. If a network is up for 835 hours in five weeks, what is the availability?
In the week = 24 x 7 = 168 hour in one week
So, 168 x 5 = 840 hour
So the availability is 835 / 840 = 0.994 x 100 = 99.4 %
4. Using the five nines availability, what is the down time in second per four weeks?
One weeks in second = 60 x 60 x 24 x 7 = 604800 second
4 Weeks = 604800 x 4 = 2419200 second
Availability = 1 – 0.99999 = 0.000001 second
So the downtime is 0.000001 * 2419200 = 24.192 second.
5. What does the term hot-swapping means, and what the reasons for using it?
6. A customer requires 99.999% availability, how would you carry out maintenance for such a network? Assume that hot-swapping is not possible
7. What are the typical bit error rate BER of a fiber link & copper link?
8. If a load is 115kbps where a packet switch needs to transmit it over an ISDN circuit (128kbps), what is the utilization? How many packets in the queue?
Utilization = 115/128 = 0.898%
Average number of packets in queue = (0.898) / 1-0.898) = 8,804 Packets
9. How do bandwidth and throughput differ?
Bandwidth: is a data carrying capacity of a circuit, usually specified in bits per second
Throughput is the quantity of error free data transmitted per unit of time, usually specified in packets per second
10. How can one improve network efficiency?
More the packet is larger more the efficiency of the network will be.
11. What are the security threats if a network device is compromised?
Data flowing through the network can be intercepted, analyzed, altered, or deleted, compromising integrity and confidentiality.
Additional, related network services, which rely on trust among network devices, can be compromised. For example, bad routing data or incorrect authentication information could be injected into the network.
User passwords can be compromised and used for further intrusions and perhaps to reach out and attack other networks.
The configuration of the device can be altered to allow connections that shouldn’t be allowed or to disallow connections that should be allowed.
12. What tradeoffs may be necessary in order to improve network efficiency?
Implementing good throughput for one application might cause delay problems for another application. The cause of the efficiency of the (network) throughput is the packet size, so if one application have large packet size to make it efficiency the other packet for another application may don’t have capacity on the network.
13. Redundancy is not one of the network goals, what is meant by redundancy? Explain to what network goal is related and why?
Redundancy means adding duplicate links or devices to a network to avoid downtime.
Redundancy is linked to Availability, but redundancy is not a network goal, but redundant network topologies are becoming more and more significant for many networks design client who want to make certain business continuity after a major fault or disaster.