How does 56K
Works?
To understand 56K, it's necessary to take a brief look at how
traditional analog modems work. -- Information inside your computer is in digital format:
all of the data is stored as 1s and 0s. Normal phone lines are analog: they transmit data
as a series of peaks and valleys. Your "modem" is a MOdulator / DEModulator: it
modulates outgoing data from digital to analog, and demodulates incoming data from analog
to digital. Above a certain threshold (called Shannon's Limit) the signal-to-noise ratio
of any medium becomes too low to reliably transfer data. The analog phone line is the
limiting factor in the speed of data transmission because of the inherent noise it
contributes. -- Today's telephone network is increasingly digital. In particular, the
portion of the phone connection between the phone company and the Internet Service
Provider (ISP) is often digital. Digital lines still have noise, and are still subject to
Shannon's limit, but they have less noise and a higher ceiling. -- Several companies have
created techniques that take advantage of the digital portion of the phone network to
achieve higher speeds than were possible with a purely analog pathway. These new
techniques treat the phone system as a mostly digital network that just happens to have an
analog portion. -- There are several consequences to the reliance on a half-digital
connection. Your Internet service provider (ISP) must have digital phone lines to the
public switched telephone network (PSTN). That's the easy part: if your ISP offers 56K,
they've got the digital lines.56K is for Download Only
A 56K connection is asymmetric: it's faster for downloading than
for uploading. Downloading means receiving data from another computer (for example,
viewing a Web page or receiving email). Uploading means sending data to another computer
(for example, sending email or uploading files to your Web page.) The download speed can
be as much as 56K, but the upload speed will initially be only 28.8K or 33.6K. Many other
high-speed technologies (e.g. ADSL and cable modems) also have asymmetric rates. V.34
modems (28.8K and 33.6K) support asymmetric connections to compensate for poor line
quality in one direction, but the upload and download rates are usually very close to one
another. The lower upload speed isn't significant for most users. Most Internet surfers
spend far more time downloading than uploading. The upload limitation does limit the
utility of 56K for certain uses. In particular, it makes 56K impractical for low-end
server use, or for videoconferencing. For those applications, ISDN is superior.
Why is there a limit on upload for
56K?
When downloading over a 56K connection, data is changing from a digital signal to
an analog signal. Digital-to-analog conversions are perfectly accurate, so downloading at
speeds up to 56K is possible. When uploading, data is changing from an analog signal to a
digital signal. Analog-to-digital conversions are imperfect, so noise is introduced into
the signal.
Does 56K modem deliver the
speed you need?
56 Kbps modems can dramatically cut the amount of time you have to
wait to view a web page, or to download a large file. But there is still a significant
differences between the speeds achieved by the x2 and K56Flex modem. It usually depends on
how well the 56K engine is develop and for the modems, different firmware or drivers, the
performance can be different. Improvements is still under development.
What kind of speed will I
gain with 56kbps modem?
Many who buy 33.6 analog modems are surprised that they don't
necessarily connect at the full 28800 (or 33600) speed. Connections at 26400 or 24000 are
common. Because the part of the connection between your computer and the phone company is
analog, 56K modems will still suffer from line noise. The good news is that with 56K
connections the part of the connection between the phone company and the Internet service
provider is digital, which has much less noise. How much faster? Even if you can't get a
28.8K or 33.6K connect now, you may be able to get a much higher connect speed with 56K.
Early test results indicate most people will be able to get speeds between 38K and 48K. As
with 28.8K and 33.6K modems, the exact performance will depend on the line quality in your
area. It was found that a majority of their users (81.3%) connected at between 40 and 50K,
with 58.2% connecting between 45 and 50K:
Speed
52000
50666
49333
48000
46666
45333
44000
42666
41333
40000
38666
37333
36000
33333
32000
29333 |
# Calls
2
10
71
159
567
317
132
189
82
39
24
72
45
126
20
60 |
Percentage Connected
0.1%
0.5%
3.7%
8.3%
29.6%
16.6%
6.9%
9.9%
4.3%
2.0%
1.3%
3.8%
2.3%
6.6%
1.0%
3.1% |
|
Will 56k Modems
increase speed in direct modem-to-modem hookups?
No, there is no gain of increase speed. All 56 Kbps modems have
inherent limitations. For instance, if you are planning to upgrade for faster direct
modem-to-modem hookups -- for videoconferencing, telecommuting, playing games with a
friends in another state and so on -- 56k modem does not helps. This is because you can
achieve the high transmission rates only when you're receiving data from the Internet
Service Provider Server modem, which sends out digital signals that are converted into
cleaner analog waves -- that is, without the distortion that limits the speed of
conventional modems.Can
I connects 56K modem to another 56k modem?
Yes, at 33.6Kbps or slower, x2 and K56Flex modems can communicate
with each other because they switch to the standard protocol, V.34bis or V.34.
56k Speed Limited
Because of FCC limitations, 56k modem will be effectively limited
to 53K in the U.S. This isn't a huge problem, as most people probably wouldn't connect at
the full 56K anyway, due to the phone line impediments that prevent many people from
connecting at 28.8, and that prevent most people from connecting at 33.6K. And, really,
it's just a 6% difference.
There is quite a bit of mis-understanding on this subject.
Here's some clarification:
 | Only x2 modems are affected. K56flex modems are not
affected. |
| The FCC's rules apply only in the U.S. Other countries are
not affected. |
| The FCC does not limit modem speeds. Instead, it limits the
amount of power that can be sent through the phone line in order to prevent interference
with other electrical devices. |
| It's possible that the FCC may grant a waiver in the future
that would allow speeds of 56K or higher in the U.S. It's very likely that the final ITU
standard for 56K will not have this limitation. |
| The 53K limitation is not built into the modems you buy.
Instead, it is enforced in the server equipment at the online service or Internet service
provider you're dialing into. A software change at the ISP could remove the limitation,
and equipment shipped overseas does not have the limitation. |
56K reality for ISP ?
If you were one of the first people to buy a 28800 modem, you may
have discovered that most of the places that you called still used 14400 modems, so you
could only connect at 14400. It's always been this way with modems: they can only connect
at the highest speed supported by both modems. 56K throws a new twist into the story. Yes,
both you and your Internet service provider (ISP) must have 56K modems. Otherwise, you'll
only connect at a maximum of 28.8K or 33.6K. There's more to it than that, though. The
whole concept of 56K technology depends on the ISP having digital phone lines connecting
their modems to the phone company. The digital lines are much clearer than analog phone
lines, so higher connection speeds are possible. And the real beauty of 56K is that the
ISP has to have special phone lines, but you don't. 56K modems will work with the regular
analog phone lines you have now. So the ISP needs digital phone lines. Is that a problem?
Maybe. Many ISPs already have digital PRI lines to support customers using ISDN. Even more
use a digital T1 line to bring in analog phone calls from their customers' modems. Those
ISPs are well on their way to offering 56K service. The problem will mostly be with
smaller ISPs who can't afford the investment needed to rebuild their infrastructure. The
ISP market has become more competitive, with rates dropping and big fish eating little
fish. The arrival of 56K will provide further competitive pressure, and may accelerate the
consolidation of the ISP market. How do you know if your ISP has digital lines and digital
equipment? You can probably call your ISP and get the answer, but if the service offers
ISDN, that's a good sign. They definitely have digital lines and digital equipment if they
use Ascend MAX terminal servers.
Why 56K modem Fails to connects
56Kbps?
| Excessive electronic interference introduces noise
on phone line.
This will limit your modem connections to a slower speed and may cause the
modem connection to drop out. |
| Only one A/D conversion allowed.
There's one requirement that will prevent some people from using 56K. For
56K to work, you can have at most one analog-to-digital conversion between your home or
office and the Internet service provider (ISP). If there's more than one, you can't use
56K, and your connection will be limited to V.34 speeds (a maximum of 33.6K).
 | If your office is on a PBX, you may have problems getting
speeds higher than 28.8 or 33.6K. Many offices use PBX (private branch exchange) telephone
systems, a sort of electronic receptionist and switchboard. If your office telephone has
its own extension, or if you must dial a number (usually 9 in the U.S.) to get an outside
line, you are probably on a PBX. PBXes are also common in hotels. It's likely that most
PBX systems will prevent 56K modems from working by introducing extra analog-digital
conversions. Workarounds include getting a separate phone line for the modem, or plugging
the modem into the same phone jack as the fax machine, which is probably plugged into a
direct outside line, because fax machines also have problems with PBX systems. |
| If your neighborhood's phone circuit has multiple A/D
conversions, your only option is to move to another neighborhood. For instance, some
suburban phone companies use Subscriber Link Concentrators (SLCs) to turn ordinary analog
lines into digital ones, which may require several analog/digital conversion. You're free
to complain to the phone company, but don't get your hopes up. The only 100% guaranteed
test is to borrow a 56K modem and dial into your local ISP from your home or office. Be
sure to install the drivers that come with the modem. |
| Voice Enhancers that boost sound quality on a line, such as
AT&T's TrueVoice, can cause an extra analog/digital conversion that will limit your
connection speed to 33.6kbps or lower. |
|
| Your are incorrectly connecting to the Internet
Service Provider's Server Modem.
K56Flex modem connects to the ISP's x2 or 33.6 modems pool and x2 modem connects to
the ISP's K56Flex or 33.6 modem pool. |
| Oversea phone connections.
You may not be able to connect at 56kbps to a ISP using international lines because
of noises and conflicting digital-conversion technology. |
How to test my phone lines for 56K
connections?
3COM V.90/x2 Line Test
http://www.3com.com/56k/need4_56k/linetest.html
Is there any listing of 56K
ISP?
http://www.56k.com/isps/56k/
1998, the year for 56K Modem
to follow ITU standards.
The ITU has officially designated the recommended international 56K
standard as V.90. This replaces the working title of V.pcm.
|
