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Explaining Network Speeds
How often have you wondered
what the what kbps really means. Ever wonder how
fast a 10Mbps Ethernet is? How long SHOULD it take to
copy a file from one computer to another over different kinds
of networks? How long should a download take over a
modem? Is a 1mb network like Home PNA fast enough for
your home? In this article I will attempt to clarify modem,
broadband, and common networking speeds in a practical easy
to follow way.
Foreword: To keep this article clear
and simple, I have chosen to ignore the 1000/1024 'base 2'
issues.
Definitions
BIT:
abbreviated to a small b (Kbps), unit of measurement in a
computer representing a 1 or a 0
BYTE:
abbreviated to a capital B (KBps), another unit of measurement
in a computer, 8 bits are in a single byte. Other lengths
are possible like 16, 32, 64, etc but network communications
is based on 8 bit lengths.
Kbps: kilobits per second,
or 1000 bits per second
Mbps: Megabits per second
or 1,000,000 bits per second
Is It Bytes or Bits?
The small b in Kbps lets us know the unit of measurement is
bits. A capital B would let us know the measurement
is in Bytes.
Even though the metric system uses a small
k for kilo, the computer industry has chosen to use a capital
K in most cases.
Definition Examples:
56Kbps 56 X 1000 bits per
second = 56,000 ones and zero's
128Kbps 128 X 1000 bits per second
= 128,000 ones or zero's
460Kbps 460 X 1,000 bits per second
= 460,000 ones or zero's
1Mbps
1 X 1,000,000 bits per second = 1 million
one's or zero's
10Mbps 10 X 1,000,000 bits per
second = 10 million one's or zero's
Use:
So far so good. It would appear
that you have enough information to start figuring out how
long it takes to transfer files but you have to remember that
these speeds are in BITS not BYTES. When we look
at a file size we look at the number of BYTES not the number
of bits. Using this information we can build the
chart below.
Theoretical Maximum Speeds
| Common Name |
Used With |
Bits per Second |
Bytes per Second |
| 28.8Kbps |
Modems |
28,800 |
3,600 |
| 56.6Kbps |
Modems |
56,600 |
7,200 |
| 128Kbps |
ISDN |
128,000 |
16,000 |
| 460Kbps |
Cable Modem |
460,000 |
57,500 |
| 1Mbps |
Home PNA 1.0 |
1,000,000 |
125,000 |
| 1.6Mbps |
HomeRF |
1,600,000 |
200,000 |
| 10Mbps |
Ethernet |
10,000,000 |
1,250,000 |
| 100Mbps |
Fast Ethernet |
100,000,000 |
12,500,000 |
Aprox Theoretical Transfer Times:
| Common Name |
Used With |
Time to Transfer 1 Megabyte |
Time to transfer 50 Megabytes |
| 28.8Kbps |
Modems |
4.5 Min |
3.8 Hrs |
| 56.6Kbps |
Modems |
2.3 Min |
2 Hrs |
| 128Kbps |
ISDN |
1 Min |
50 Min |
| 460Kbps |
Some Cable Modems |
17 Sec |
14.5 Min |
| 1Mbps |
Home PNA 1.0, Cable Modes |
8 Sec |
6.5 Min |
| 1.6Mbps |
HomeRF |
5 Sec |
4 Min |
| 10Mbps |
Ethernet |
1 Sec |
40 Sec |
| 100Mbps |
Fast Ethernet |
1 Sec |
4 Sec |
Theoretical vs Real times:
So many factors go into real transfer
times that it is very difficult to wrap blanket numbers around
them. Once you get over ISDN speeds, network latency,
protocol overhead, driver efficiency, and all kinds of other
technical things get in the way. In general, expect
transfer speeds of 40 to 80% of the maximum speed.
Aprox Real Transfer Times:
| Common Name |
Used With |
Time to Transfer 1 Megabyte |
Time to transfer 50 Megabytes |
| 28.8Kbps |
Modems |
6-12 Min |
4.8-9.6 Hrs |
| 56.6Kbps |
Modems |
3-6 Min |
2.4-4.8 Hrs |
| 128Kbps |
ISDN |
1-3 Min |
1-2.1 hrs |
| 460Kbps |
Some Cable Modems |
22-43 Sec |
18-36 Min |
| 1Mbps |
HomePNA 1.0**, Some Cable Modes |
10-20 Sec |
8-16 Min |
| 1.6Mbps |
HomeRF** |
6-13 Sec |
5-10 Min |
| 10Mbps |
Ethernet, HomePNA 2.0** |
1-2 Sec |
50-100 Sec |
| 100Mbps |
Fast Ethernet |
1 Sec |
5-10 Sec* |
*PCI Bus inefficiency
can easily make this 9-14 seconds
**Often, these systems run at 1/2 speed
because of interference
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