Task 1- Calculate the VoIP traffic load in access trunks to the Internet
You will calculate the phone service traffic load in Erlangs on the access links connecting the company's location with the Internet through the ISP. The following assumptions are given.
1. The PSTN connection is only used as a backup. No phone calls will go to the PSTN trunk, which is only used in case of packet network WAN failure.
2. There are 510 phones at the company's location, including IP phones, soft phones, and analog phones.
3. Sixty percent of the phones generate simultaneous call attempts in the busy hour, with an average duration of 7 minutes per call.
Q1. What is the number of call attempts during the busy hour at the company's location?
Q2. What is the traffic load in Erlangs during the busy hour? Show calculation and units.
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Minutes of traffic in the hour
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=
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number of calls x duration
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Minutes of traffic in the hour
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=
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306 x 7
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Minutes of traffic in the hour
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=
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2142
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Hours of traffic in the hour
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2142 / 60
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Hours of traffic in the hour
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=
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35.7
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Traffic figure
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=
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35.7 Erlangs
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Q3. What is the dimension of traffic measurement unit Erlang?
Task 2-Calculate the number of SIP trunks and access link bandwidth required for VoIP calls to the Internet
You will calculate the access bandwidth and the number of SIP trunks required to meet the company's objective. Use the busy-hour traffic load to the Internet that was calculated in Task 1. The following assumptions are given.
1. The call-blocking probability during busy hour should not exceed 1% (i.e., 0.01).
2. Use the G.711 codec with a 20-millisecond payload duration per packet.
3. Use the Erlang-to-VoIP bandwidth calculator
Q4. What is the difference between a completed call and a call attempt?
Q5. What is the number of SIP trunks (lines from the online calculator) required to meet company's needs?
Q6. What access link bandwidth (Kbps from the online calculator) is required to connect the company's location to the Internet?
Q7. If T1 bandwidth is 1.544 Mbps, T3 bandwidth is 44.736 Mbps, and there are 28 T1 in a T3, what access connection(s) does the company need to lease in terms of T1 and/or T3?
Q8. Include a screenshot below showing the results from the Erlang-to-VoIP bandwidth calculator.
Task 3-Calculate the number of backup access channels to the PSTN
ABC Inc. is concerned with performance degradation and service interruptions due to the Internet availability. It decides to have a backup connection to the PSTN in case of any disruptions of phone services through the packet network.
You will calculate the number of analog lines the company needs to lease from a telephone service provider (TSP) as a backup in case of packet network failures. The following assumptions are given.
1. Use the same busy-hour traffic load as in Task 1.
2. The call blocking should not exceed 10% (i.e., 0.01).
3. Use the Erlang B calculator.
Q9. How many analog lines does the company need to subscribe from a TSP? Include a screenshot below that shows the calculator results.
Q10. Assume that each analog line can carry 1 Erlang of voice traffic. What is the utilization of the PSTN trunks if an Internet failure occurs during the busy hour? Show the calculation.
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Minutes of traffic in the hour
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=
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number of calls x duration
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Minutes of traffic in the hour
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=
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306 x 7
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Minutes of traffic in the hour
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=
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2142
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Traffic figure = 1 Erlang
Utilization of the PSTN trunk=1 x 60
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Utilization of the PSTN = 60
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