Calculate a bandwidth for a live event?
Question: Complete the following calculations: Calculate bandwidth requirements for a live event that is streamed over the Internet based on the information below.
You are the network administrator for an Internet Service Provider (ISP). Your company has been asked to provide bandwidth for a live event produced by one of your clients.
You have been asked to calculate the total data transfer required for the event. You have also been asked to verify that your Internet connection can support the maximum estimated concurrent listeners. You have a 45-megabits-per-second (Mbps) connection to the Internet (a T3 circuit).
Time of the event: 6:00 P.M.-8:00 P.M.
Encoding rate: 22 kilobits per second (kbps)
Average length of play: 60 minutes
Total listeners: 1,500
Concurrent listeners: 1,200
Calculation 1: Calculate the total data transfer for the live event.
Calculation 2: Calculate the required internet connection bandwidth
Answer:
TCP/IP doesn't use stop and start bits. There must be some confusion here with serial connections (eg. modems). And routers won't 'cache' packets. Proxies and the like MAY cache them but don't count on that helping the numbers. If anything, they may hurt more than help.
What will be important to know if what the video application says it will require, throughput-wise, for each video stream based on the codec used to encode the data. You mentioned the encoding rate of 22kb/s so I will assume that is what the application says it needs in throughput for one video stream
Assume each video stream requires 22kb/s (roughly half the speed of an analog modem so we are talking...pretty slow). We now know the required throughput but we need to consider a few other items. First, packet size. Smaller packets have larger IP and TCP overhead. Second, retransmissions because of lost packets, etc. Those will cut into the available throughput as well. If the video application's contention of 22kb/s is taking into account average IP and TCP overhead, then we just need to get a handle on retransmissions. Let's say there will be a 5% retransmission rate. Now the expected throughput requirement jumps to about 23kb/s.
If there are 1200 concurrent users requesting 23kb/s from your server(s), then we can just multiply to get 27,600 kb/s (or around 27.6 Mb/s). Now the DS3 is about 61% filled. To quote a famous author on the matter: "For wide area networks (WANs), optimum average network utilization is about the same as for token ring networks--70 percent". So...you should be ok.
As for the total data transferred in this two hour span...(2.875 KB) * (1500 users * 3600 seconds) = 15525000 KB...or around 15.525GB
1) Take Concurrent listeners x Encoding rate x 3600 to give you total bits. Divide that by 8 to find bytes.
2) Take the total listeners x encoding rate. Divide this by 1000 to show it as Mbps then compaire to the T3 rate.
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