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Let's say you wanted to build the world's most popular mobile messaging product, and you needed to estimate how much network bandwidth would be used in a year. How would you go about doing this?
Interviewer: Let's say you wanted to build the world's most popular mobile messaging product, and you needed to estimate how much network bandwidth would be used in a year. How would you go about doing this? Interviewee: I’m going to ask you 3 questions to clarify, is that okay? Interviewer: Sure. Interviewee: First, what metrics would you say are important for popularity? Downloads, engagement, or retention. Interviewer: What would you say? Interviewee: I’d say it depends. An app with high volume of downloads can be perceived as highly popular. However, it the users never use the app (not engaged) then it’s not quite that popular. Retention on the other hand wouldn’t be a useful metric to measure because if there is a low volume of downloads and low engagement, then the app is not popular. Engagement on the other hand, without a high volume of downloads would make it not popular (engaged user base but not enough traction to gain popularity). However, for the sake of the discussion let’s assume that the app will have high downloads and engagement is the most ideal metric to measure for “popularity”. Interviewer: Okay, I follow your logic. Let’s assume high downloads and say engagement is the metric for popularity. Interviewee: Second, when you say, “network bandwidth” I’m assuming you mean the bandwidth that is used in app, correct? Interviewer: Correct. Interviewee: Great, that further confirms that engagement is the right metric to track because downloads happens outside of the app on the app store / google play network / servers. Interviewee: Lastly, if this is a messaging app can we assume that we store and transfer messages. Interviewer: Yes. Interview: Okay, I’m going to move forward and go with a top-down approach. Assuming the world’s population stays constant at 7,800,000,000. We know that out of the 7.8B people in the world 1/5 own a smartphone that is capable of using a mobile messaging app. Out of these 1/5 of users, let’s say that 30% of them will prefer to use a mobile messaging application (rather than SMS) and also have the funds to purchase the data necessary. Based on this calculation (7,800,000,000 * .20) * (.30) = 468,000,000 Lets say out of these 468,000,000 users each user on average will send 30 messages daily. There are also 365 days in a year. Based on this calculation 468,000,000 * 30 = 14,040,000,000 message sent daily For each message lets assume on average it is 20 characters. Each character is roughly 1byte. Therefore, on average each message is 20bytes of information. We also know that each 1GB is roughly 1,000,000,000. On average 1byte = 8 bits. 1Gbps = 1,000,000 bps Based on this calculation 14,040,000,000 * 20byte = (280,800,000,000 * 8bit) = 2,246,400,000,000,000bits transferred per day. There are 24 hrs in a day, 60 minutes in an hour, 60 seconds in a minute. 24 * 60 * 60 = 86,400 seconds in a day 2,246,400,000,000,000/86,400 = 26,000,000,000 / 1,000,000,000 = 26Gbps * 365 = 9490Gbps For the case of network bandwidth of a popular mobile messaging app we can estimate that we need to be able to have a data transfer rate of 9490Gbps/year.
Hey there Richard Lin, thanks for the thoughtful answer. However, at one point you say "1Gbps = 1,000,000 bps" This isn't accurate right? was this a typo? Thanks.