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datarate greater than 4kB on voice channel..?

the bandwidth of voice channel is 4k actually data rate is less than 4kB per second in voice channel. Then how does download accelerator softwares download files at the rate greater than 4kB.Infact the data rate on a telephone line does not exceed 3.5kBps.Theoratically the data rate cannot acceed 4kBps on a local loop (voice channel).
Ur opinion is appretiated.
thanks
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info_expert
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1 Solution

Commented:
One word : Compression
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Commented:
One word : Compression
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Commented:
64k = 1 ds0
there are 8 bits in a byte.
64 divided by 8 = 8
64kbps = 8kBps
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Commented:
Also,
What kind of voice circuits are you talking about?
POTS (Plain Old Telephone Service) = 28k to 56k Bandwidth
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Commented:
Since compression is used, the less compressed the data already is, the faster the download accelerators work.
For example :
Try downloading an MP3, notice it doesn't pull down quite as fast as, say, a bitmap or a wav file.
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Author Commented:
i know that compression is used but what if an already compressed file downloads at a rate greater than 4kBps. E.G. 96MB downloaded in 5 hours.
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Author Commented:
i know that compression is used but what if an already compressed file downloads at a rate greater than 4kBps. E.G. 96MB downloaded in 5 hours.
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Commented:
I would suggest that the theoretical data limit on a pure "voice" channel is significantly less than 8Kb/s , unless you can talk *really* fast - if you are suggesting running a data channel over a voice line, then t1n0m3n has provided the figures already...  If you are trying to find the minimum bandwidth necessary to provide minimal voice service (over a data line), then your originally supplied figures may be correct, given the appropriate software.

Cheers,
-Jon
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Author Commented:
According to the shannon theorem
channel capacity = C = B log base 2 (1+SNR)
SNR in telephone lines is 1000.
effective bandwidth is 3100Hz so,
c= 3100 * log base 2 (1001) = 30894 bits/sec is nearly less than 4kB/sec
NOW??????????

thanks for ur response
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Commented:
Holy homework questions, batman!

Are you trying to make something work and/or looking for real world experiences (and if so, what exactly do you require that has not already been stated), or do you just have a paper due?

Cheers,
-Jon
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Commented:
Yes Info Expert,
Your shannon theorem holds water only when talking about a pure analog line.  Digital technology has changed the landscape of that theorem.  I.E. V.90 and X2.
If you look at my answer you will see that 28Kbps = 3.5KBps
I stick to my guns.  Answer = Compression
Just because a "compressed" file is compressed doesnt mean that it cannot be further compressed by some other compression algorithm.

If you have a purpose for wanting the answer, please state them, we could probably help you work around a bandwidth issue.  But if this is just for homework.....you have your answer.
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Commented:
The only ways I can think of to speed up a fixed rate connection are:

1.)  Optimization.  Optimize your machine to reduce routing protocol overhead.
2.)  Compression.  Compress uncompressed or poorly compressed data, routing protocol headers
4.)  New math.  If you calculate 1KB as 1000 bits and not 1024 bits.  By switching back and forth on how you do your calculations, you can gain (or lose) download speeds.  It doesn't amount to much, but hey, that wasn't the question.

#3 is most likely the real magic behind download accelerators and is probably the answer you are looking for.  When in doubt, PFM (Pure F!#\$in' Magic) is always the answer...  ;-)

Hope it helps!
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Commented:
Yeah, #3 is a real bite when trying to determine your bandwidth speed (my IE seems to do this kind of thing by default).

mbruner - I entirely agree with your comments (#4 was amusing - I created a 50000 byte test file (forgive me that I'm too lazy to multiply by 1024 as needed) on a fast server to test download rates [see above] - guess what - IE says it's not 50M, but something around 47.6 - yay!  I already gained a savings of 5% in no time hehe)...

Cheers,
-Jon
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Commented:
In any case, a good reason to suspect you are encountering #3 is if your bandwidth rate starts out incredibly high (I've seen it try to convince me that I'm getting 2.5 megabytes/second off my cable connection [yeah, right]), and falls off geometrically as the download progresses...

Cheers,
-Jon

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Author Commented:
It is very nasty behaviour that if someone has a question in his mind then you assume that he has a homework given by the school
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Author Commented:
thanks a lot.
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Commented:
There is always the possibility of a question being a homework problem, particularly if it tends to be wholly theoritical in nature - I admit, such rather topically general TAs like this one tend to attract that kind of question more than others, but that is no reason to go on the defensive when asked for your motives...  I was mostly kidding when I asked about the homework - that's why I said 'Holy homework questions, Batman!' rather than 'Please explain your practical implementation, as this smells like a homework question'.  Also, we still have no idea what you are trying to accomplish - I'm gussing this indeed *was* a homework question, as you have yet to provide this info, and just accepted an answer when we asked for clarification (smells fishy to me).

The AUP says no homework questions are allowed, but it is up to the experts to identify them - if you have a problem with that, please take it up with EE management.

In any case, feel free to put your money where your mouth is, and post your motivation for asking this question.  I'm betting if you do, you will get an even better answer than the one you accepted, even though the pts have already been assigned (I volunteer, for one).  If all you are asking is how a download accelerator works, why didn't you accept mbruner's excellent explanation (other than he's a bit confused about what constitutes a 'routing protocol')?

I'm waiting...

Cheers,
-Jon
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Author Commented:
To The--Captain

Dear the actual matter is that. One day a student in our class asked the same question to the teacher. Our teacher was not very much sure about what happens in download accelerator so he said it might be a compression. So i wanted actual answer then i asked the question here and waited several days and did not found appropriate answer except compression which was firstly given 't1n0m3n'. then I saw that some persons feel that i have a homework due, so i had no choice except 't1n0m3n'.
AND
>>>why didn't you accept mbruner's excellent explanation (other than he's a bit confused about what constitutes a 'routing protocol')?

The reason is simple, the answer of compression was firstly given by 't1n0m3n'. the remaining 3rd and 4th points are not able to be agreed on.
Thanks for your response.
Regards !
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Commented:
I'm not confused by what constitutes a "routing protocol", although I suspose I could have chosen better wording in my explanation.

Thanks for the compliment, none-the-less.  =)

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Commented:
mbruner - Yes, you are - a routing protocol is OSPF, BGP, ISIS, RIP, etc - not too many folks that use download accelerators ever see a packet of those protocol types.  Sorry to take you to task, but you asked for it hehe

If you were referring to IP protocol headers, I am in agreement - just don't call them routing protocol headers...

info_expert - you see, we were not too far off - although it was *not* a homework question, it was an academically generated question - these are almost impossible to distinguish from actual homework questions, hence our questioning - I for one, feel vindicated.  No need to get so defensive...

In any case, I have no problem with t1n0m3n's answer, but you should be aware that, IMO, mbruner's answer was "more correct", in that he points out that compression is only a part of the answer - in fact, most download accelerators don't compress data any more than it already is (how could they?), but in fact rely more on mbruner's #3 and #4.

I might offer a #5 - multiple connections.  Many new download accelerators designed for broadband users have the ability to perform multiple simultaneous connections to different sites containing the same file - rather than overloading a single server, the accelerator requests only pieces of the file from several different servers all known to have the same exact file - the data requested from each server is minimal, and tends to migrate bandwidth bottlenecks closer to the proverbial last mile (and the data arrives more in parallel, rather than sequentially).

In any case, I'm sure your theory holds water at some basic hardware level - however, once you start piling on upper layer tech, the amount of data you can receive per unit of time goes wayyy up due to all the factors we have mentioned, even on "analog" circuits (just look at DSL [yes, I'm aware that this is turning your analog line into an albeit noisy digital one]).

Cheers,
-Jon
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Commented:
The real point of all this is that you can't get more out of your fixed rate circuit than your fixed rate (if implemented correctly by the telco), _unless_ you use compression or some sort of advanced packet prediction technology (which I have yet to see).  Everything else just works to make sure you use your available badwidth and computing resources as efficiently as possible.  This is why t1n0m3n deserved the points on this question.

Fair enough about the use of the term "routing protocol".  I won't waste everyone's time arguing over semantics, other than to say that I was using the term with an incorrect, yet generally accepted, definition in mind.
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Author Commented:
i appretiate the response of both of you and and by the way i dont have dsl.
I give complementary points to mbruner by the titel 'points for mbruner'
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Commented:
Wow.  Thanks.
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