Skype on School Networks

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Question: Should a school network be able to handle a class with 15 Skype connections or is Skype too bandwidth intensive? How does Skype compare to a YouTube download or an iTunes podcast stream?

The IT Guy says:
Whether or not your school network can handle that many Skype calls will depend on your outside connection to the Internet. The Skype software will change the level of bandwidth it needs depending on a variety of conditions (including how much bandwidth is available.) At the highest end, a single Skype call requires 128 kilobits of data per second, while at the low end it uses 24 kilobits per second. That's a pretty wide range, obviously! For fifteen students, then, you are looking at between 360 and 1,920 kilobits per second (or .36 and 1.92 megabits per second).

For just the network inside your school, this shouldn't be that big a deal. Most Ethernet networks now handle 100 megabits per second, so this is pretty small potatoes. However, the connection out from the school to the district network or to the Internet may be far more limited - at least in our region, it's not uncommon for a school building to be using what's called a T-1 line for that outgoing connection. That is slightly more than 1.5 megabits per second. Under those circumstances, your Skype impact can be pretty significant.

If you're lucky, your district has upgraded to a higher-capacity service, such as a T-3 line or fiber optic. A T-3 connection is almost 37 megabits per second (24 times the rate of a T-1), and fiber optic can be even more. Check with your tech support staff to find out what you have. (You may find out that your tech support staff will discourage you from using services such as this, regardless of how much you have available. Sometimes they feel like the lone knight at the drawbridge, fighting the bandwidth-devouring dragons that seek to overrun the castle and bring the whole network crashing to the ground.)

To compare Skype to other services, iTunes radio broadcasts run from 56 to 128 kilobits per second. A YouTube video runs about 2.5 megabytes per minute of video, which translates to roughly 20 megabits of data. The exact bandwidth impact depends on how long it takes to download; if you download 20 megabits in 30 seconds, that's 660 kilobits per second. If it takes a minute, it's 330 kilobits per second, and so on.

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