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The Technology Explained: What is
Bandwidth and Throughput?
The term bandwidth
refers the size of the "pipe" that carries data. While often mistakenly
used interchangeably with the term bandwidth, throughput refers to a
measure of the amount of data flowing through the "pipe" over a given
period of time. These 2 concepts are important when troubleshooting
performance problems such as slow downloads or web pages taking to long
to load. The table below shows the different connection types and their
speeds.
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Connection
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Speed
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Medium
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Description
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Dial-up connection (POTS)
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Up to 56 Kbps
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Twisted pair
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Rapidly being replaced by faster
technologies.
|
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T-1
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1.544 Mbps
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Twisted-pair, coaxial cable,
or optical fiber
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Large company to ISP
ISP to Internet infrastructure
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E-1
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2.048 Mbps
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Twisted-pair, coaxial cable,
or optical fiber
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32-channel European equivalent
of T-1
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T-2
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6.312 Mbps
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Twisted-pair, coaxial cable,
or optical fiber
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Large company to ISP
ISP to Internet infrastructure
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Digital Subscriber Line (DSL)
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256 Kbps to 8 Mbps
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Twisted-pair
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Home, small business, and enterprise
access using existing phone lines
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Cable modem
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512 Kbps to 52 Mbps
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Coaxial cable
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Home, business, school access
|
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E-3
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34.368 Mbps
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Twisted-pair or optical fiber
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European version of T-3 that
carries 16 E-l signals
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T-3
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44.736 Mbps
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Coaxial cable
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ISP to Internet infrastructure
Smaller links within Internet infrastructure
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OC-1
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51.84 Mbps
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Optical fiber
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ISP to Internet infrastructure
Smaller links within Internet infrastructure
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OC-3
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155.52 Mbps
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Optical fiber
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Large company backbone
Internet backbone
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Asynchronous Transfer Mode (ATM)
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622.08 Mbps
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Optical fiber
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Internet backbone
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When discussing
speed, a common task is the calculation of download times. There is
a conversion process involved in this since connection speeds are measured
in Bits Per Second (Bps) and file sizes are measured in bytes. The formula
for calculating download times is a follows: Download time = file size
/ connection speed.
Let's take a look at an example - Let's say you wish to find out how
long it will take to download a 1mb file over a 56K dial-up modem connection.
The first thing we need to do is convert the connection and the file
size into a common measurement - as is most commonly done, we will use
bits. Our 56 Kilobit connection is easily converted to bits by multiplying
by 1000 which gives us a 56000 bits per second connection. To convert
the file size to bits, you need to remember that there are 8 bits in
a byte and our file is 1 megabyte in size. 1 Megabyte = 1024 Kilobytes
and 1 Kilobyte = 1024 Bytes. Thus, we multiply 1 x 1024 x 1024 x 8 which
equals 8,388,608. We now plug our number into our formula such that
8,388,608/56,000 = 149.78 seconds which comes to 2 minutes and 30 seconds
(rounded).
It is probably still a little confusing so let's do one more example.
This time we want to find out how long it will take to download a 25Mb
file on a T-1 connection. A T-1 connection operates at 1.544 Mbps which
is 1,544,000 bits. Our file is converted to bits by multiplying 25 x
1024 x 1024 x 8 which equals 209,715,200 bits. We then plug these numbers
into our formula as follows: 209,715,200/1,544,000 = 135.83 seconds
or 2 minutes and 16 seconds (rounded).
[What is a network?] [Buying Networks 1] [Buying Networks 2] [Hubs vs. Switches] [What is a Router?] [Cabling] [Patch Cables] [Cable vs DSL] [Oversubscribing] [Search Engines] [What is Bandwidth?] [Computer Viruses: A Global Threat] [Kernel's: Win2k vs. Linux] [Interrupts] [Plug and Play] [Backups] [TCP and IP] [Harddrive Buyers Guide] [Laptops vs Desktops] [Vista Upgrades]
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