CSC8513 Assignment 3
This assignment will be marked out of 100 and is worth 30% of the entire course.
Question 1
(10 marks)

Figure 1. A network of which we need to find some shortest paths.
Determine all the shortest paths from node A to the other nodes of the network shown in Figure 1, using Dijstra's algorithm. The labels on the links in the figure show the link costs (or distances). Create a routing table for node A.
You are encouraged to check the shortest paths using the Netml system and find the routing table at node A.
Marking Criteria
• The Dijkstra algorithm has been carried out and demonstrated in a Table.
• The minimum distance node, amongst all temporary nodes, is the one made permanent in each step.
• The correct end-to-end shortest distances have been calculated for all nodes.
• The routing table is correct.
Question 2
(10 marks)
Service type Mean Standard Dev. Growth rate (p.a.)
File services 12 Mbit/s 8 Mbit/s 10%
Internet access 20 Mbit/s 10 Mbit/s 40%
Database access 5 Mbit/s 20 Mbit/s 4%
Telephony 4 Mbit/s 1 Mbit/s 2%
Videoconferencing 2 Mbit/s 20 Mbit/s 10%
Table 1. Traffic Mix
Suppose the mean, standard deviation, and growth rate of different classes of traffic is as shown in Table 1. Create another table, with the same structure, with the mean, standard deviations, and growth rates in four years time, assuming that the growth rates are correct and do not change.
Marking Criteria
• The mean traffic in four years time in each category has been correctly estimated.
• The standard deviation of the traffic in four years time, in each category, has been correctly estimated.
Question 3
(10 marks)
Suppose an organisation has 280 employees who work, on average 8 hours each day, and during the busy hours (approximately 10-11 and 14.00-15.00), they are using their phones 20% of the time, of which half are to other staff within the organisation. Estimate the internal and external telephone traffic in Erlangs. Choose an encoding rate, which will be used for these calls, and estimate, from this, the mean and standard deviation of the required bit rate for the external calls. From this, estimate the capacity which would be required on a link dedicated for the external calls.
Marking Criteria
• The traffic, in Erlangs, due to external calls, has been correctly estimated.
• A sensible encoding rate for the calls has been chosen and the consequent mean traffic, in bits/s, has been estimated.
• The consequent standard deviation of the traffic, in bits/s has also been correctly estimated.
• The link capacity needed to carry this traffic has been correctly estimated.
Question 4
(10 marks)
Determine the minimum spanning tree network for the network shown in Figure 1. Use one of the standard algorithms and make sure to explain each step of the algorithm so that it is clear that you understand how the algorithm works.
Marking Criteria
• The method used to calculate a minimal spanning tree has been identified.
• The method used to calculate a minimal spanning tree has been correctly used.
• The actual minimal spanning tree is shown in a diagram.
Question 5
(30 marks)
A company needs to choose, install, and maintain communication facilities between two of its sites. The traffic which needs to be carried comprises telephony, video-conferencing, and TCP/IP traffic.
The telephone traffic is contributed by 30 employees at one site and 90 at the other site and it has been estimated that these employees are on the phone on average 30% of their time, during the busiest periods of 10-11 in the morning and 2-3 in the afternoon. Half of all the calls they make are between the two sites.
The video-conferencing sites make use of 512 kbit/sec, full-duplex, of synchronous digital transmission capacity when it is in operation, which can be at any time of the day, including the periods when the telephone traffic is busiest. This facility is in use, on average, for 5 hours per week.
The TCP/IP traffic, provides file-server and database access for the smaller of the two sites, to the main file-server and database servers, which are at the larger site. This traffic has been estimated currently to have a mean of 50 kbit/sec and standard deviation of 500 kbit/sec, when measured over a 1 second interval.
The number of employees is growing at a rate of 5% per year; the video-conferencing service will not be changed for the forseeable future, i.e. it will continue to operate at the same rate and there will remain just the two locations which are used for video-conferencing exclusively with each other. The TCP/IP traffic is estimated to be growing at a rate of 35% per year.
The link must be available up to 50% of its nominal required capacity at least 99.9% of the time.
The following facilities for connecting the two sites are available:-
• A spread-spectrum line-of-sight transmission facility operating at 4 Mbit/sec, which will cost $10,000 to install (special aerials are required) and $1,000 per year to maintain; however, this facility becomes inoperable in certain weather conditions, which occur 2% of the time during business hours. It is possible to install two of these facilities, however the problem with weather will affect them both at the same time.
• a digital leased-line facility, as listed in Table 2. These services are claimed to be available 99.9% of the time.
• an Internet VPN tunnel, the cost of which is incurred through usage charges with an internet service provider (ISP), which charges $50 per gigabyte for all data. This facility is claimed, by the ISP, to have a capacity of 2 Mbit/sec available 99% of the time, and of 4 Mbit/sec 90% of the time.
Interface type Module Size Layer Cost (p.a.)
E1 2 Mbit/s 1 $6,000
E3 34 Mbit/s 1 $18,000
STM1 155 Mbit/s 1 $65,000
STM4 620 Mbit/s 1 $160,000
STM16 2.45 Gbit/s 1 $400,000
STM64 9.92 Gbit/s 1 $900,000
Fast Ethernet 100 Mbit/s 1 $15,000
Gigabit Ethernet 1 Gbit/s 1 $24,000
10xGigabit Ethernet 10 Gbit/s 1 $100,000
Wavelength 10 Gbit/s 0 $18,000
Table 2. Transmission technologies available
Identify and describe a single facility or a combination of facilities which can provide the required service between the two sites at the prescribed level of service over the next 5 years at the minimum total cost. Use a discounting rate of 20% to compare all plans by present-value $. You should assume that all the costs indicated above remain constant for the entire period.
Marking Criteria
• A plan has been prepared, in the form of a table, for the next five years, which shows the traffic in each of the three categories, and the total traffic, including mean and standard deviation.
• The capacity required on the link has been calculated for each of the 5 years.
• The cost required, for each service, based on the rental, installation, or service charges, has been correctly calculated and taken into account in the report.
• A combination of services which can deliver the required availability at the required capacity has been correctly identified.
• A clear argument has been given that the present-value dollar cost for the selected plan is smaller than any other plan which meet the performance criteria.
Question 6
(30 marks)
Imagine that you are asked to design a network for the Ipswich campus of USQ.
So far in this course, you have focused on:-
• The identification of individual traffic flows.
• The derivation of performance requirements from identified individual traffic flows. (These performance requirements include the specification of required throughput, loss, delay, reliability and security).
• Projecting these performance requirements into the future.
• Comparing the choice of network layouts and equipment which would satisfy future performance requirements for each of the individual and combined traffic flows.
This assignment question focuses on just how does one come to know about these traffic flows.
Based on the -Real World Problem- seminar, outline steps that you would carry out in order to get a realistic knowledge of these traffic flows. Where would you begin? Who should you talk to? What guides your choice of who to listen to? What tools would help you to verify your knowledge of these traffic flows.
Hints
Stakeholders:-
• How to identify the stakeholders?
• What is the benefit to the stakeholder?
• What influence does the stakeholder have?
Your Report
Your report should have at least 500 words. It should have an introduction, a main body and a conclusion.
Assignment Submission
Your submission should take the form of a single PDF document. The document should be properly formatted, complete with headings and page numbers. The questions should appear in order in the submitted PDF document.