Networking 101

Copyright Priscilla Oppenheimer

Study Topics 1

Time to transfer data example 1

What is the best-case estimate of how much time it would take to send a 50 MB JPEG photo to your grandma if you only have a 40 kbps modem line?

• There are 8 bits in a byte.
• Multiply Megabytes (MB) times eight to get Megabits (Mb).
• 50 MB = 400 Mb.
• To ensure that we use compatible units of measurement, convert Megabits (Mb) to Kilobits (kb).
• There are 1,000 kilobits in one Megabit.
• Multiply Mb times 1,000 to get kb.
• 400 Mb = 400,000 kb.
• Time = size divided by bandwidth.
• Time = 400,000 kb divided by 40 kbps.
• Time = 10,000 seconds.

This is also equal to 166 minutes or 2.7 hours. You better be patient as you send that photo (or compress it better before sending it!)

For you sticklers:

Network bandwidth and throughput are specified in bits per second, not bytes per second. In addition, in the networking world, Mega means one million precisely and kilo means one thousand precisely. When we talk about data storage, on the other hand, Mega often means 1,024 x 1,024. Similarly, kilo often means 1,024. Don't worry about this. Although it's true that the 50 MB file might really be 50 x 1024 x 1024 x 8 bits, we aren't trying to be so precise that this matters to us.