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Modem Speed

Dial up speed

Newsgroups: comp.os.linux.networking
Date: 2003-10-05 18:17:52 PST

> I use wvdial to dial up to Internet. I noticed that whenever I was
> connected, wvdial would say connection speed to be 115200. It has
> never been changed. However, when I was connecting to the same ISP
> using Windows, the connection speed would vary from time to time.
> Sometimes it is 46000, sometime 44000, 40000, or 36000, etc.
>
> I'm wondering, if the wvdial gives me a faked connection speed, or I
> can enjoy some kind of previlage while connecting via Linux?

The serial interface (UART chip) on a PC handles many different internal data transfer rates. The highest rate it handles is 115200. This means that applications can communicate with the _modem_ at that speed, but not necessarily what's outside the modem.

The rates of 46000, 36000 etc. are normal and you're not going to see higher connection rates with Linux. I'm not familiar with wvdial but you could configure your modem's initialization string (e.g. AT&F1 for factory defaults on a US Robotics) to have the modem itself report the negotiated rate.

You could do a 'wget' to a fast site to see what speed you can actually download at.

By the way, it is still possible to see extremely fast data transfers (e.g. 115200) with a modem connection. The way it works is: let's say the modem is connected with another modem at 48000 but receiving some kind of highly compressable text. If the modem/link has built in compression support, that data could be decompressed at your computer and actually fed to your application at a tremendous rate.

Jem Berkes

Dial up speed

>>115200 is modem-to-computer speed.  Modem-to-modem speed is 56K or less
>>(hence, 56k modem).  You can set modem to report modem-to-modem speed,
>>something like "CONNECT 48000".  With my external modem, I use 'w2' to
>>get modem connect speed..

> Actually didn't the FCC limit "56K" to an actual 53K?

There's a FCC regulation limiting line radiation. An analog modem operating at speeds beyond about 53 kb/s causes line radiation that exceeds that limit.

> Also, the actual pipe seems to be assymetric just like with
> DSL or cable modem. Meaning you may get 53K down but never more
> than 33K up using an analog line dialing into an ISDN modem.
> The practical corrolary of this seems to be that two purely
> analog modems linked together never get more than 33K.

That's for V.90 modulation and V.42bis compression. For V.92 the up and down speeds can both be configured for 48 kb/s - according to a USR paper. From another source, V.92 has V.44 compression which, for normal web browsing, "out-performed V.42(bis) by up to 60%".

> As the previous poster points out, you need to talk to the
> modem at higher speeds like 115200 in order to take maximum
> advantage of the compression in the modem. With pure-text
> streams it will likely get you higher throughputs.

And on rare occasions the speed may exceed 11520 B/s, nominally the greatest rate at which the usual 115200 b/s PC serial device can transfer data between it and pppd. The modem to ISP DCE data transfer rate at 53 kb/s is only 6625 B/s, not counting PPP frame and networking protocols' overhead.

Clifford Kite

Modem speed reporting

,----- [ John Riggs ]
|
| Depending on your modem settings, it will either report speed in DTE
| or DCE speed.  DTE speed is the speed at which the PC sends and
| receives data from the modem and is usually reported as 115,200.
| DCE speed is the speed at which the modems speak to each other.
| This speed is usually something less than the maximum advertised
| modem speed, e.g., 56k or 33.6k.  It is the DCE speed that most
| people are interested in.
|
| If your modem is reporting DTE speed and you want DCE instead, you
| need to issue an AT command to reset your modem.  The command to
| report DCE speed is usually W2.  An easy way to ensure your modem is
| reporting DCE speed is to add the W2 command in the chat script.
| For example:
|
| OK ATH0
|
| could be changed to:
|
| OK ATH0W2
|
`-----

,----- [ Clifford Kite ]
| Look in your modem manual for the AT command, in the old Hayes
| command set ATW1s95=47 would cause the modem to report initial DCE
| connect speed (and other things as well).
`-----

,----- [ Michael Meissner ]
| You also need to make sure your modem reports the modem speed when
| connected.  This is modem specific, and you will need to read the
| friendly manual.  For my Courier, the commands are:
|
|  ATQ0V1X7&A3
|
| where:
|
|  AT Hayes (RIP) modem control sequence header
|  Q0 send result codes
|  V1 return results as words
|  X7 extended result codes
|  &A3 indicate error correction/modulation
|
| I think AT&W will then set those options in NVRAM so that ATZ won't
| reset them -- but I don't have the FM in front me.
|
| I also put ATI6I11 in my chat script before dialing, so that I get a
| copy of the modem statistics for the last call dumped in my syslog.
| This way, I can look at it if I suspect getting bad connections and
| look at retransmits and BLERs.
`-----

Modem speed limit

,----- [ Bill Unruh ]
| 56k modems can only work with a digital-- direct to line modems on
| the other side. Two 5k modems can only connect at max of 33K.
`-----

,----- [ David Efflandt ]
| The fastest connection you can get between any 2 analog modems
| (V.34) on perfect normal phone lines is 33.6K.  Due to line quality
| 24-28K may be the best you can do.  It takes special digital
| hardware and digital line directly from the phone company to run a
| 56K (V.90 or V.92) server.
|
| I often see people wanting to dialin to their home or office to use
| their DSL or cable connection, but it would be faster to simply use
| a dialup ISP.
`-----

Modem speed monitoring

,----- [ Michael Meissner ]
| I believe that X-Isp also includes connection speed.  The web page
| is at:
|
|  http://users.hol.gr/~dbouras/[]
`-----

,----- [ Alan J. Wylie ]
| for a GUI display under X, try pload
|
| http://www.engr.utk.edu/~mdsmith/pload/[]
|
| or pppstats, which comes with the ppp package.
`-----

,----- [ Rootman ]
| I ran kdevmon on the KDE desktop on the server so as to monitor the
| ppp0 connection.  Instead of reporting just the connect speed it
| does a running computation of speed every so many millieconds and
| reports a top, current and average speed - which should give you an
| indiaction of what is going on with the dialup - speeds can drop and
| rise as the connection ages, get it at:
| http://apps.freshmeat.net/homepage/947602271/[]
`-----