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Explaining Home Network
Speeds
Published: 17-Nov-2000
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, boradband, and common networking speeds in a practical easy to
follow way.
Foreward: To keep this
article clear and simple, I have chosen to ignore the 1000/1024 'base 2'
issues.
Definitions
BIT: abreviated
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 goood. 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 easly
make this 9-14 seconds
**Often, these systems run at 1/2 speed because of
interference
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