david@elroy.jpl.nasa.gov (David Robinson) (12/04/89)
From the discussion so far it appears that modems do not take up
anymore phone network resources than a normal voice call, you get the
same ~4KHz bandwidth whether you are talking or using a modem.
The only valid argument for charging a modem different is that they
tend to be use the line for longer periods of time. But a person
sitting on a modem reading news for two hours is no different than a
teen talking to their friend for two hours, both tie up the network.
I think the phone companies will argue that as more modems are
appearing total network usage will rise and their current physical
plant and rate structure cannot support this, thus they propose a
surcharge.
It can easily be shown that a surcharge for modems is not fair, many
modem users do not tie up lines for long periods of time. A better
proposal would be to modify the current rate structure. Now we
currently pay more for the first minute (anyone still pay more for the
first 3 minutes?) and a cheaper flat rate for the rest of the call.
If long duration calls are a problem, why not propose a rate that
increases after a certain amount of usage, either linearly or
non-linearly if you really want to curb long usage. I think this
would be more fair and more accurately represent the problem. People
will quickly change their usage habits if you start to effect their
wallets.
David Robinson elroy!david@csvax.caltech.edu ARPA
david@elroy.jpl.nasa.gov ARPA
{cit-vax,ames}!elroy!david UUCP
Disclaimer: No one listens to me anyway!jbayer@ispi.com (Jonathan Bayer) (12/05/89)
david@elroy.jpl.nasa.gov (David Robinson) writes: > From the discussion so far it appears that modems do not take up >anymore phone network resources than a normal voice call, you get the >same ~4KHz bandwidth whether you are talking or using a modem. Sorry, you're wrong. The telephone network is designed to work with human voices. As such the equipment multiplexes many conversations onto a single wire. Human conversation has many gaps that the network can use to multiplex other conversations using the same frequency. A modem is on continously, tying up a frequency full-time. Assuming that a wire can handle 100 different conversations at one time, and further assuming that 10 % of the conversations is quiet, that means that with the proper equipment a single wire could handle 110 conversations at the same time. However, you use modems and all of a sudden the network loses some of its excess capacity. I am sure that my numbers are not correct, but the method is valid. I do not support the idea of extra charges for modem usage, and the phone companies' numbers will have to be looked at very carefully, however you cannot deny that modems _do_ take up bandwidth that conversations do not. Jonathan Bayer Intelligent Software Products, Inc. (201) 245-5922 500 Oakwood Ave. jbayer@ispi.COM Roselle Park, NJ 07204
ted@uunet.uu.net (Ted Schroeder) (12/05/89)
In this discussion nobody has mentioned the fact that modems place a
continuous carrier on the line, unlike human voices that pause between
sentences and words. There is a form of compression called DSI (and
there may be other forms also) that allow this "dead space" to be
used. You might put 12 calls on 8 lines and assume the "dead space"
would allow you to compress bandwidth this way. I know this is done
quite frequently in fully digital private networks, but I don't know
how the public networks work and whether they use this type of
technology.
Does anyone out there know about this?
Ted Schroeder ted@Ultra.com
Ultra Network Technologies ...!ames!ultra!ted
101 Daggett Drive
San Jose, CA 95134
408-922-0100
Disclaimer: I don't even believe what I say, why should my company?sgf@cs.brown.edu (12/05/89)
I tried to stay out of this, but... david@elroy.jpl.nasa.gov (David Robinson) writes: > From the discussion so far it appears that modems do not take up >anymore phone network resources than a normal voice call, you get the >same 4KHz bandwidth whether you are talking or using a modem. jbayer@ispi.COM (Jonathan Bayer) writes: >Sorry, you're wrong. The telephone network is designed to work with >human voices. As such the equipment multiplexes many conversations Well, you're both half right. If your modem traffic is passing through trunks (not just confined to two local loops served by the same end office) you're going digital. A modem conversation is one continuous scream and definitely (depending on how the signal is modulated/ compressed) takes up more trunk and switch bandwidth than the circuit held by two people who have fallen asleep after phone sex. If, however, your local loop (assumed still analog) is connected to another local loop at the same end office via an analog switch, what you've got is similar to an operator sitting in front of a patchboard - an electrical circuit which doesn't care what it's carrying (you get your 4KHz). Then there's ISDN with digital local loops.... _/**/Sam_Fulcomer sgf@cfm.brown.edu sgf@browncs.bitnet
rupeb@uunet.uu.net (Bernard Rupe) (12/06/89)
In article <1798@accuvax.nwu.edu> jbayer@ispi.com (Jonathan Bayer) writes: >X-Telecom-Digest: Volume 9, Issue 551, message 1 of 11 >Sorry, you're wrong. The telephone network is designed to work with >human voices. As such the equipment multiplexes many conversations >onto a single wire. Human conversation has many gaps that the network >can use to multiplex other conversations using the same frequency. A >modem is on continously, tying up a frequency full-time. Assuming >that a wire can handle 100 different conversations at one time, and >further assuming that 10 % of the conversations is quiet, that means >that with the proper equipment a single wire could handle 110 >conversations at the same time. However, you use modems and all of a >sudden the network loses some of its excess capacity. >...however you cannot deny that modems _do_ take up bandwidth that >conversations do not. Although I haven't been following this subject consistently, I think I can shed some light on the situation. Voice calls in today's network are indeed restricted to 3400 Hz. These calls are sampled at 8 kHz and converted to a digital rate of 64 Kb/s. These 64 Kb/s channels are then multiplexed and sent into the telephone network. Today's technology does not take advantage of any silent passages in conversation (although it could be done, it would be very expensive). Modem data is converted into the same 64 Kb/s and is multiplexed into the telephone network just like a voice call (otherwise, how could you use a regular phone line for a modem call?). The result, then, is that a modem call and a voice call take up exactly the same bandwidth in the telephone network. Bernie Rupe uunet!motcid!rupeb
john@zygot.ati.com (John Higdon) (12/06/89)
In article <1799@accuvax.nwu.edu>, ames!ultra!ted@uunet.uu.net (Ted Schroeder) writes: > In this discussion nobody has mentioned the fact that modems place a > continuous carrier on the line, unlike human voices that pause between > sentences and words. There is a form of compression called DSI (and > there may be other forms also) that allow this "dead space" to be > used. You might put 12 calls on 8 lines and assume the "dead space" > would allow you to compress bandwidth this way. I know this is done > quite frequently in fully digital private networks, but I don't know > how the public networks work and whether they use this type of > technology. There are two major problems with this. Long distance companies rarely do this anymore (it was too disconcerting to the customers) and local telcos *NEVER* do this between local offices. And remember, it's the local telcos that want to put the extra charges onto modem users. The drift has been lost here. Every justification for discerning between modems and the human voice would apply to LD carriers, not the metallic circuit that runs between your PC and your local central office. You already pay for long distance; is someone suggesting that modem calls should be charged at a higher rate? But the original question concerned whether lines used for modems should have higher *local* charges applied across the board. John Higdon | P. O. Box 7648 | +1 408 723 1395 john@zygot.ati.com | San Jose, CA 95150 | M o o !
deej@bellcore.bellcore.com (David Lewis) (12/07/89)
In article <1798@accuvax.nwu.edu>, jbayer@ispi.com (Jonathan Bayer) writes: > david@elroy.jpl.nasa.gov (David Robinson) writes: > > From the discussion so far it appears that modems do not take up > >anymore phone network resources than a normal voice call, you get the > >same ~4KHz bandwidth whether you are talking or using a modem. > Sorry, you're wrong. The telephone network is designed to work with > human voices. As such the equipment multiplexes many conversations > onto a single wire. Yes, but the multiplexing method you describe is not the one used in general. > Human conversation has many gaps that the network > can use to multiplex other conversations using the same frequency. A > modem is on continously, tying up a frequency full-time. Assuming > that a wire can handle 100 different conversations at one time, and > further assuming that 10 % of the conversations is quiet, that means > that with the proper equipment a single wire could handle 110 > conversations at the same time. > I am sure that my numbers are not correct, but the method is valid. Valid, perhaps. Used, no. (OK, before someone jumps on me and starts throwing "statistical TDM" around... not used by the public switched telephone network in any major applications.) > I do not support the idea of extra charges for modem usage, and the > phone companies' numbers will have to be looked at very carefully, OK, let's clarify some terms. A two-way voice conversation includes energy in the frequency band 20-20000 kHz. The majority of this energy is below 4000 Hz. An intelligible voice conversation, therefore, can be considered to include energy in the frequency band 300-3300 Hz. It also includes a large amount of dead air. A telephone voice channel is capable of carrying energy in a frequency band from about 300 to about 3300 Hz. This channel is constantly available, end to end, to the user. Regardless of the fact that no energy may be carried at a given point in time, the capacity is immediately, fully, directly available to the end user at any given point in time, and is not used by the network for any other purpose. This is true whether you're talking an analog loop, an analog trunk, a time-division multiplexed digital trunk (on any medium), an ISDN loop... doesn't matter. The 3000Hz of capacity is not used by the network for any other purpose. Therefore, it matters not whether that 3000Hz of capacity is 100% utilized, 90% utilized, or 10% utilized -- the resources are fully available to the end user, and you should not charge the end user more because he's able to make more efficient use of the channel provided him. > however you cannot deny that modems _do_ take up bandwidth that > conversations do not. Yes, I can. I can't deny that modems make more efficient use of the available bandwidth -- but I certainly can deny that modems "take up bandwidth conversations do not". A modem, be it a 300bps Bell 103, a 1200 bps Bell 212a, or a 9600 bps V.32, uses 3000 Hz of bandwidth. Period. A conversation uses 3000 Hz of bandwidth. Period. David G Lewis ...!bellcore!nvuxr!deej (@ Bellcore Navesink Research & Engineering Center) "If this is paradise, I wish I had a lawnmower."
kebera@alzabo.uucp (Krishna E. Bera) (12/08/89)
ames!ultra!ted@uunet.uu.net (Ted Schroeder) writes: >In this discussion nobody has mentioned the fact that modems place a >continuous carrier on the line, unlike human voices that pause between >sentences and words.... Has anyone in the modem protocol design business considered dropping the carrier when the line is idle, and picking it up again when there is data to be sent? Can't modems be made to recognize the difference between on and off-hook? This would render moot the whole 'separate charge for modem use' issue, as modems would have the same line usage as human voice as far as the phone company was concerned. Krishna E. Bera "Programmer on the loose" Voice: (613) 238-4101
shri@ccs1.cs.umass.edu (H.Shrikumar{shri@ncst.in}) (12/12/89)
In article <1799@accuvax.nwu.edu> ames!ultra!ted@uunet.uu.net (Ted Schroeder) writes: >X-Telecom-Digest: Volume 9, Issue 551, message 2 of 11 >In this discussion nobody has mentioned the fact that modems place a >continuous carrier on the line, unlike human voices that pause between Interesting ... to remember that PEP modems like the Telebit Trailblazer put out essentially half duplex packets, with fast turnaround to simulate full duplex. Now if only the modems will keep silent when there no data to send, (except perhaps for a keep alive packet every second or so) then ... what is the difference if any at all between these modems and human conversation ? Will the (now being discussed) modem-service-charge apply in that case ? :-) shrikumar ( shri@ccs1.cs.umass.edu, shri@ncst.in )