--- title: "Role of traffic engineering" subject: "Telecommunications" chapter: 6 key: "semester_8/telecommunications:role-of-traffic-engineering" source: https://www.bctengineer.com/q/semester_8/telecommunications/role-of-traffic-engineering site: BCT Engineering --- # Role of traffic engineering Telecommunications · Chapter 6: Telephone Traffic - Asked in: 2069 Chaitra, 9 marks - Video: [Lec-18_Traffic Engineering | Telecommunication Engineering | ICT Engineering](https://www.youtube.com/watch?v=9Rc_XrgN9kA) — Computer_IT_ICT Engineering Department : LJIET - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_8/telecommunications/role-of-traffic-engineering - Whole chapter: https://www.bctengineer.com/md/semester_8/telecommunications/chapter-6 ## Question Explain the role of traffic engineering in case of telecommunications. ## Short answer Traffic engineering uses teletraffic theory to measure, forecast, and dimension network resources (trunks, switches) so that the required grade of service (e.g., blocking probability) is met at minimum cost. It determines the number of circuits needed during the busy hour, designs routing plans, and monitors performance to handle overloads and plan growth. ## Answer **Traffic engineering** applies probability theory (queueing and teletraffic theory) to measured traffic so that a telecommunication network is built with just enough equipment to give a required quality of service at the lowest cost. Subscribers do not all call at once, so an exchange is built with far fewer paths than subscribers; traffic engineering decides how many. #### Why it is needed - A network with one trunk per subscriber would be very expensive and mostly idle. - Too little equipment causes blocking, long dial-tone delays and lost revenue. - Traffic is random and varies with time of day, day of week and season, so planning must use statistics. #### Roles of traffic engineering 1. **Traffic measurement and characterisation.** Measure the number of calls, holding times and busy-hour traffic (in erlang) on each route, and find the busy hour (CCITT E.600). 2. **Forecasting.** Predict future traffic from subscriber growth, new services (data, mobile) and tariff changes, so equipment is ready in time. 3. **Choice of grade of service.** Fix the acceptable blocking probability, e.g. 1% on local routes, 0.5% on final routes, and delay targets such as dial tone within 3 s for 95% of calls. 4. **Dimensioning.** Using Erlang B (loss systems), Erlang C (delay systems), Engset or binomial (finite sources), calculate the number of: - trunks on each route, - switching paths and network stages, - common-control equipment: registers, markers, processors, signalling links, - radio channels in a mobile cell. 5. **Switching network design.** Calculate blocking of multistage (e.g. Clos) networks using the Lee graph or Jacobaeus methods. 6. **Routing plans.** Design high-usage and final routes with alternate (overflow) routing so trunks are used efficiently. 7. **Processor and queue performance.** Find delays in stored-program control processors, message queues and data networks with queueing models (M/M/1, M/M/n). 8. **Performance monitoring and overload control.** Compare measured blocking with target and add capacity or apply call gapping when traffic exceeds design values. 9. **Cost optimisation.** Balance equipment cost against lost-call revenue and customer satisfaction. #### Example A route carries 10 E in the busy hour. For GoS 0.01, Erlang B gives about 18 trunks. Without traffic engineering, one might install 30 (wasteful) or 12 (blocking about 12%). The table shows the main tools used: | Situation | Model | |---|---| | Lost calls cleared, many sources | Erlang B | | Calls wait in queue | Erlang C, M/M/1 | | Few sources | Engset, binomial | | Switch fabric blocking | Lee, Jacobaeus | Thus traffic engineering links traffic demand, quality of service and cost, and is the basis of planning every exchange, trunk route and mobile cell. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. What is the main aim of traffic engineering? A. Provide one trunk for every subscriber B. Provide just enough equipment for the required quality of service at lowest cost C. Eliminate all blocking completely D. Maximise the number of subscribers per exchange Answer: B. It uses probability theory on measured traffic to build with enough, not excess, equipment to meet the required quality of service. (Key point: Aim of traffic engineering) 2. Why must network planning use statistical methods? A. Because traffic is random and varies with time of day, week and season B. Because all subscribers call at the same time C. Because holding times are always constant D. Because equipment never fails Answer: A. Traffic is random and varies, so only probability theory can give the required equipment. (Key point: Why statistics are needed) 3. Which model is used to dimension trunks for lost calls cleared with many sources? A. Erlang C B. Engset C. Lee graph D. Erlang B Answer: D. Erlang B applies to loss systems; Erlang C is for delay systems and Lee graphs for switch fabric blocking. (Key point: Models for dimensioning) 4. A route carries 10 E and the GoS target is 0.01. Which statement matches the example? A. About 30 trunks are required B. About 12 trunks give GoS 0.01 C. About 18 trunks are required; 12 would give about 12% blocking D. About 10 trunks are enough because load equals trunks Answer: C. Erlang B gives about 18 trunks for 10 E at 1% blocking; fewer trunks such as 12 cause heavy blocking. (Key point: Grade of service) ## Related in Telecommunications - [Short note: Telephone traffic engineering](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Ashort-note-traffic-engineering) — Telecommunications, chapter 6, asked 2× - [Traffic engineering objectives; Engset formula](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Atraffic-objectives-engset) — Telecommunications, chapter 6 - [Traffic engineering goals; E.600 busy hours](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Atraffic-engineering-busy-hour-e600) — Telecommunications, chapter 6 - [Importance and unit of traffic engineering](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Atraffic-engineering-importance-unit) — Telecommunications, chapter 6 - [Role of hybrid transformer](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Ahybrid-transformer-role) — Telecommunications, chapter 2 - [Traffic numerical: 800 calls, 50 lost](https://www.bctengineer.com/question.md?key=semester_8%2Ftelecommunications%3Agos-800-calls-50-lost) — Telecommunications, chapter 6, asked 6× ## Related in other subjects - [Traffic engineering; road user characteristics and HVE](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Ate-definition-road-user-hve) — Transportation Engineering II, chapter 1 - [Traffic engineering; road users and vehicular characteristics](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Ate-definition-road-users-vehicular) — Transportation Engineering II, chapter 1 - [Parallelism, IPC deadlock and OS role](https://www.bctengineer.com/question.md?key=semester_4%2Fmicroprocessor%3Aparallelism-deadlock-os-role) — Microprocessor, chapter 6 - [Traffic control devices and traffic signs](https://www.bctengineer.com/question.md?key=semester_7%2Ftransportation_engineering_ii%3Atraffic-control-device-requirements-signs) — Transportation Engineering II, chapter 1, asked 2×