February 15, 2005

Skype Math Anxiety

Yesterday Stuart did a simple arithmetic on Skype usage to ask (rhetorically) whether mobile operators can keep up with Skype usage. This note is not related to that question specific, but an attempt to understand the arithmetic.

First a recap of his observations:

  • 2M active users concurrently online
  • Skype serves 3M minutes per hour

His assumption:
  • An user logs on for 12 hours in a day

My assumptions (due to lack of knowledge of precise definition):
  • Active user and logged on user are the same
  • One minute call between two users contribute to 1 minute to served minutes count (I doubt it because double counting is straight forward; but this assumption is against me, so I will take it.)

Stuart builds his analysis the following way:
  • Each user generates 1.5 minutes per hour
  • Or 36 minutes per day
  • Since the user is active only 12 hours, a user generates 72 minutes per day

Me thinks:

  • At any time 1M calls going on and they generate 3M minutes in an hour
  • So each user generates 3 minutes per hour
  • Since the user is active only for 12 hours per day, each user generates 36 minutes per day.

So what gives? Also note that if they are double counting the minutes (as I suspect) then each user generates only 18 minutes per day.

There is an unobserved nugget buried in Stuart’s assumptions. If a Skype user is logged on for 12 hours per day, then 4M users log on per day out of 70.5M downloads – 5.7%. Just an observation, with nothing implied.

Posted by aswath at February 15, 2005 02:09 PM
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Good point re potential to double count. I kept tracking the minutes for the 24 hour period. Call it 36 million for the day. I'm not sure where you get the 1 million calls going on.

In Skype the "users online number" is those that are logged in. Thus it isn't representative of the number of active users or current active calls from what I understand. It's a Kazaa like number.. people on the network. There are dialups and other reasons to log off. Thus the lower the number participating daily the higher the average call time. The on twelve hours is probably conservative..(too long) but then is just a guess. Let's assume it is actually six million users using Skype per day. then the average call time is 6 minutes per hour for 24 hours. That provides a number that is close to two hours unless we are double counting then we are back to an hour which is easier to digest.

Probably means the number logging on is twice the six million. Thus we would still be looking at an average call time per day of well over 30 minutes.

That's where the numbers again become weird. We hear Skype has some 24 million registered users. That doesn't mean active only means they downloaded it and created a profile. Some of these profiles are no doubt double counted users with multiple profiles. The 70 million download number is just bogus and meaningless. Provide a new rev and get more downloads.

So by which ever measure or logic... Skype users (a hypothectical average, the heavy users will go hours) are running up a thousand minutes per month. I suspect it is much higher. So how can mobile operators create a package that enables you and me average to do an additional 1000 minutes or more per month for free?

Posted by: Stuart Henshall at February 15, 2005 07:34 PM

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