Telecommunication Networks Assignment, SP2 2017 Network dimensioning for a large organisation This assignment is intended to test your ability to apply the simple components of knowledge gained throughout the course to a “real‐life” problem. You will need to be able to make realistic assumptions, justify them, and then translate them into the design of your system. Please note that in practice each set of assumptions made by individual students will be unique. There is no one correct set of assumptions, one correct method to solve each problem, or one correct answer to the task you will be asked to carry out. However, to score well, you need to be able to provide convincing justification of your choices of assumptions as well as methods used to produce a design that is consistent with these assumptions. Note that for the telephone lines dimensioning tasks you may have to locate an Erlang B calculator that does not have the limitations on the traffic intensity and number of circuits – there are many calculators like this available on the www. Please remember that this is an individual assignment work that has to be carried out by individual students without external help. Also, please remember that this is NOT a huge task that requires hundreds of hours of effort and tens of pages of reporting. You can finish the assignment within no more than 10‐15 hours, and prepare a complete report no longer than 6‐10 pages. 1. The scenario Consider a large organisation with two buildings A and B. Building A is where all central IT facilities (PABX, VoIP server, Intranet server) are located. Buildings are connected with each other and with the outside world as shown in the figure below. The central servers include, depending on the scenario, PABX, Intranet www and file servers, mail server etc. The I/F denotes interface equipment to the connecting link or circuit group. Depending on the scenario, it might be a PDH multiplex interface, IP router, etc.Building A Building B I/F I/F I/F Central servers (PABX, intranet, email …) Interface equipment (routers, concentrators, PDH circuit group interface) To/from outside network AB and BA Common assumptions: 1. All employees of the organisation have a telephone and computer on their individual desk. 2. There are 2000 staff located in building A. These are the management, administration, marketing, sales, support etc. staff. Assume that all of them generate the same telephone and data traffic. During the working day, they generate and receive many phone calls to/from outside world as well as a few phone calls to/from other employees of the organisation. However, most of their moderate data traffic is internal (accessing web applications running on the internal server and exchanging internal emails), and only small proportion of data traffic is external (mostly emails). 3. There are 3000 staff located in building B, all of them employed in the engineering and product development departments of the organisation. Assume that all of them generate the same telephone and data traffic. During the working day, they generate and receive a few phone calls to/from other employees of the organisation as well as outside world, but their use of telephone is significantly less frequent as that of building A employees. However, in addition to a moderate internal data traffic (emails and access to web based applications running on the organisation’s server), they generate significant external data traffic resulting from browsing and downloading technical data, standards, engineering/research literature etc. 4. Assume that all telephone and data traffic generated by employees of the organisation can be considered Poisson. This is a crude assumption (please check the slides on Internet traffic), but necessary for simplicity. 5. When considering internal telephone traffic, assume (for simplicity) that there is the same volume of internal telephone traffic flowing between any two employees of the organisation, regardless of the departments they work in. For example, the volume of traffic flowing between Liz from engineering and James from administration will be the same as traffic flowing between Natalie from marketing and Chris from product development.2. Your tasks Task 1: Make realistic assumptions as to the traffic generation behaviour of an individual employee (in accordance with assumptions 2 and 3, you need to differentiate between employees from building A and employees from building B when considering external telephone traffic and data traffic). In other words, assign numbers to the following: a) Average arrival rate of external telephone calls to/from each staff member’s telephone λiAext and λiBext (for buildings A and B respectively). Assume that this includes both outgoing and incoming calls and will have the same value for all staff in the same building. b) Average arrival rate of internal telephone calls to/from each staff member’s telephone λi. Assume that this includes both outgoing and incoming calls. Note that in accordance with assumption 5 above, this will be the same for all employees regardless of the building they are located in. c) Average call holding time (for simplicity, assume the same value for all calls, external and internal). d) The average external downlink data traffic (file and email downloads, web pages) per staff member located in building A in bps (or kbps or Mbps – whatever suits the purpose). e) The average external downlink data traffic (file and email downloads, web pages) per staff member located in building B in bps (or kbps or Mbps – whatever suits the purpose). f) The average external uplink data traffic (emails sent, web page requests, TCP ACKs) per staff member located in building A in bps (or kbps or Mbps – whatever suits the purpose). g) The average external uplink data traffic (emails sent, web page requests, TCP ACKs) per staff member located in building B in bps (or kbps or Mbps – whatever suits the purpose). h) The average internal downlink data traffic (file and email downloads, web pages) per staff member located in building A in bps (or kbps or Mbps – whatever suits the purpose). i) The average internal downlink data traffic (file and email downloads, web pages) per staff member located in building B in bps (or kbps or Mbps – whatever suits the purpose). j) The average internal uplink data traffic (emails sent, web page requests, TCP ACKs) per staff member located in building A in bps (or kbps or Mbps – whatever suits the purpose). k) The average internal uplink data traffic (emails sent, web page requests, TCP ACKs) per staff member located in building B in bps (or kbps or Mbps – whatever suits the purpose). Provide rationale for each assumption (i.e. explain briefly why you consider it realistic).Task 2: For this task, only consider telephone traffic. Assume that all telephone traffic is circuit‐ switched as in the traditional PSTN. The relevant scenario is illustrated in the figure below. The “central servers” become a PABX, the “interface equipment” at building B becomes a telephone line concentrator with PDH multiplex equipment, and the interface at building A becomes PDH multiplex equipment, as in the figure. Building A Building B I/F I/F I/F PABX PDH circuit group interface To/from outside network AB and BA PDH circuit group interface a) Given the assumptions made in Task 1 a,b,c, map the total telephone traffic flows (in Erlangs) onto circuit group A‐B and the external circuit group. Show the reasoning leading to the answer you gave. b) If we require that the end‐to‐end GoS probability of loss for each call (internal and external) be no greater than 0.01 (1 in 100), what are the GoS probabilities of loss allowed for each of the two groups of circuits? c) Given the results in a and b above, what are the required numbers of circuits in each group? Task 3: For this task, only consider data traffic as specified in Task 1 d‐k. As illustrated in the figure below, the “central servers” now become the email/www servers, and the “interface equipment” is simply IP routers. Building A Building B I/F I/F I/F SERVERS router To/from outside network AB and BA routersa) Map the total flows of data (in kbps or Mbps) generated by staff onto the links connecting building B with A and building A with outside world. Please assume that both links are part of WAN (leased from external providers), not part of the organisation’s Ethernet. As a consequence, for each link you have to state separately the downlink and uplink traffic. Provide rationale (explanation) for your answer. b) Given the traffic flows obtained in a above, state the data rate capacity (in Mbps) required for each link (separately in the downlink and uplink directions), under the condition that average packet delay for each link cannot exceed 2 ms. Assume that the internal data transfers between servers, hosts and routers located in the same building incur negligible delay, and that the processing delay at servers and routers is also negligible. Note: you may need to make a realistic assumption regarding the average packet length (why?) c) Calculate the buffer sizes required on the link AB and the link BA to ensure that the packet loss in no more than 1 in 2000. Task 4: For this task, assume that all telephony needs of the organisation are served with the VoIP solution. Assume that the VoIP codec rate is 64 kbps. Assume that the modem transmits data only when there is a talkspurt, and that it does not transmit anything during the silence period. Assume the average talkspurt duration of 0.6 s and the average silence duration of 0.4 s, and that in a typical phone call 50% of talkspurts are transmitted in one direction and 50% in the other (i.e. that the two people involved in the call will talk, on average, for the same amount of time). This results in the symmetry of downlink and uplink traffic loads incurred by a VoIP call. a) Calculate the additional VoIP data traffic (in kbps or Mbps) loading each of the two links (external, A‐B) in each (uplink and downlink) direction. b) Given that all traffic in the organisation is now data traffic, calculate the total data traffic for each link in each direction (i.e. add the VoIP traffic to the data traffic resulting from Task 3a). c) Will the addition of VoIP traffic to the remaining data traffic make significant difference to the dimensioning of the data links? Justify your answer.