Tips & Hints
Speed tips
Trouble-shooting
CRC errors
ISP Bandwidth
 
Related Links
Port and line speed

Tips and trouble-shooting hints

Speed tips

Basic tips on how to improve your speed

  1. DTE rate - Set this as high as possible. Usually 115,200 bps on recent PCs (even using Windows 3.1). 230,400 bps will likely become the norm on newer PCs. If nothing happens when you 'log on' change the setting to a slower rate and try again.
  2. Compression - Make sure that compression is used on your connections.
  3. Error Control - Make sure your modem is set to LAPM (V.42) error control rather than MNP which is around 20% slower.
  4. Modem Line Rate - Force your modem to connect at a lower speed (2400 or 4800 bps less) if it retrains (pauses transmission and re-negotiates the connection) often or your calls break down frequently. Many modems, by default, disconnect after a certain number of re-transmits of a data block. A stable connection at a lower speed can often give more data throughput than an unstable connection. Check your modem's handbook to find out how to set the maximum line rate.


Trouble-shooting

  1. Using FTP - Probably the best way to test you modem's actual speed is to download a compressed file, a ZIP file for example, from your ISP's server using an FTP program, such as CuteFTP. If possible, you should dial directly into your ISP's server rather than dialling into a Point-Of-Presence (POP). This call may cost more than dialling into a POP, but, it avoids possible congestion on the link between the POP and the server.

  2. Recording log files - If you are using Windows 95/98 you could record log files.
    The modemlog.txt file logs interaction between your PC and your modem while your connection is being set-up and disconnected. From this file you can determine at what speed you modem connects, and what type, if any, of error correction is used, and if compression is enabled. Look out for a connection string such as "CONNECT 28800 LAPM COMPRESSED", which confirms that error correction and compression are used.
    A connection string containing "38400", "57600", "115200" or "230400" indicates the DTE speed (port speed), and suggests that the modem has not been set-up correctly.
    The ppplog.txt file logs Point-to-point protocol activity, and records instances of errors such as CRC errors, overrun errors and incomplete packets.
    You can use a Modemlog File Viewer and a Ppplog File Viewer to monitor and trouble-shoot your calls.

  3. System Monitor - The Windows 95/98 System Monitor can be used to measure data throughput on your modem. The utility (Start | Programs | Accessories | System Tools | System Monitor), is useful for indicating the peak data throughput. In Windows 95, you must be on-line before you can add your modem to the items list in System Monitor. The version of DUN with Windows 98

  4. Initialisation String - If you are not sure that you have the correct INF file for your modem you could set-up your modem as a Standard 28800 bps modem. The initialisation string for this type of modem is ATE0V1. Alternatively, add &F to the extra settings part of the Advanced Connection Settings window. For most modems, this re-loads the factory settings, cancelling the Dial-Up Networking setting changes. Default settings for most recent modems are suitable for Internet connections, but, you could also refer to the user manual of the modem, and add other commands to the extra settings part of the Advanced Connection Settings window.

  5. Link diagnostics - Some modems monitor a connection and store information about the link operations, such as the last rate before disconnection, disconnection reason and number of retrains. This information can be helpful in isolating the source of problems. Examples are 3Com/U.S.Robotics' ATI6 and ATI11, Rockwell's AT&V1 and MultiTech's ATL8. After an Internet connection use any terminal emulation program such as Windows 95's HyperTerminal or Windows 3.1's Terminal to check your modems diagnostics information.
    Note: In Windows 95/98, it may be necessary to change a setting in your system registry to prevent Dial-Up Networking from resetting your modem.
    You can also dial your ISP's access number using a terminal program, enter three pluses (+ three times in quick succession), wait one second for an OK response, enter ati6 and press the enter key.
    This example demonstates link diagnostics on a 3Com/U.S.Robotics modem:

    at&f
    OK
    atdt123456789
    CONNECT 33600/ARQ
    ~}#!}!}!} }9}"}&} }*} } }#}%#
    }%}&} }<^3}'}"}(}"L}^~~}#!}!}"}
     }9}"}&} }*} } }#}%#}%}&} }<^3}
    '}"}(}"}~
    OK
    ati6
    U.S. Robotics 56K Message Link Diagnostics...
    
    Chars sent         3   Chars Received   219
    Chars lost         0
    Octets sent        3   Octets Received  146
    Blocks sent        3   Blocks Received    7
    Blocks resent      0
    
    Retrains Requested 0   Retrains Granted   0
    Line Reversals     0   Blers              0
    Link Timeouts      0   Link Naks          0
    
    Data Compression       V42BIS 2048/32
    Equalisation           Long
    Fallback               Enabled
    Protocol               LAPM
    Speed                  33600/33600
    Current Call           00:00:10
    
    Online
    
    OK
    ath
    OK
    

    The strange characters above are associated with setting up protocols, and the three pluses won't be echoed back to you. Instead of hanging-up using the ath command, you can re-enter ati6 repeatedly, although your ISP's modem may disconnect you after a couple of minutes.

  6. Line Diagnostics - Using a Communications program, such as Windows Terminal or HyperTerminal, dial your ISP's access number. When you get the CONNECTED message type +++ (three pluses). The modem should respond with OK. Type AT%L and press the enter key. Next type AT%Q and press the enter key.
    If all goes well (and your modem supports these commands) your screen should look something like this:

    CONNECT 33600
    OK
    at%l
    018
    
    OK
    at%q
    044
    
    OK
    

    The line level reading is in -dBm, where 018 is -18dBm. If you have a short line you should expect to get between -13dBm and -16dBm. Longer lines will give readings between -17dBm and -60dBm, although most modems quote -43dBm as the minimum required level. A level of -30dBm may sustain a 28.8Kbps connection, but, 14.4Kbps could be as high as possible from a -35dBm reading.
    The line quality reading represents the number of re-transmissions the modem has performed over a specific period of time. The lower this figure is the better, although at speeds above 9600bps you probably won't get zero, even on a good line, since the number of transmissions goes up as the speed goes up. I normally measure between 40 and 60 on a known good line at 33,600bps. If the quality figure goes too high (99 on some modems) the modem retrains and may re-connect at a lower speed which should have a better quality figure.

  7. Your modem's speaker - It is not uncommon to have a line fault or synchronisation problems in the telephone exchange or switching centre. This can cause your modem to retrain repeatedly, and in extreme instances, force the connection to dis-connect. By adding m2 to the extra settings part of the Advanced Connection Settings window, your speaker remains on for the duration of the connection. The sound should remain constant, with retrains, if they occur, being easily recognisable. Typically, a retrain causes an interruption in data flow lasting around 8 seconds.

    You can download 10 second samples of a normal connection and a connection with a retrain. Both Microsoft ADPCM WAV files are 55KBytes, and the expected download time for each file is less than 20 seconds at 28,800bps.


  8. A complete swap - Temporarily swap your computer and modem with another computer and modem that doesn't have connection problems. If the other computer uses the same ISP and dials into the same point-of-presence, this should help prove that the problem lies with the line (or internal wiring), or with the computer and modem.

  9. Common problems - Some modems have two sockets, one for the line and the other for a telephone, but, many recent modems just have one socket (less manufacturing costs), and use a special adapter which plugs into the telephone wall socket or modem socket. If the adapter is not used, the line is, effectively, short-circuited once the cable is plugged into the modem. A workaround is to re-terminate the telephone plug using only the inside pair of wires, but, ideally, the proper adapter should be used.

CRC Errors

CRC errors, as recorded in the Point-to-Point Protocol log file PPPLOG.TXT, are errors found in the PPP packets. Put simply, as you download data, the data is broken-up into blocks of data, up to 1500 bytes in size. A mathematical calculation is applied to the data in a block and a checksum is derived. This checksum is sent along with the data in the PPP packet. At the receiving end the same calculation is applied to the block and compared to the checksum. If the checksums don't match then an error is recorded and the packet must be resent.This method of data verification is said to be 99.95% reliable.

Ideally, your PPPLOG.TXT file should not record any CRC errors. If the line is noisy, but error control is used by the modems, all packets should eventually be delivered intact. Alternatively, if error control is not being used by the modems, occurrences of line noise will cause CRC errors which will be recorded in the PPPLOG.TXT.

Overrun errors, which are also recorded in the PPPLOG.TXT file, will also be recorded as CRC errors since the CRC checksums from incomplete packets will not match.

I recently had a problem that I only experienced with Internet Explorer while downloading JPG graphic files. An apparent pause during downloads seemed to coincide with CRC errors recorded in the Point-to-Point Protocol log file. Click here for more details.

ISP Bandwidth

The bandwidth that your Internet Service Provider offers can greatly affect your speed. An ISP may have one or more T1 (1.544Mbps) or E1 (2.048Mbps) to the back-bone of the Internet, but this is of little use if they only feed your POP (Point-of-Presence) with a 64Kbps data line and you are not the only user on-line. When you are connected to your POP you ultimately share bandwidth with all other users connected to the POP a that time. So, even if two users' modems connect to their ISP's modems at 56Kbps, if the POP is served by a 64Kbps data line, they both share this 64K bandwidth. If dialling directly into the server, rather than going through a POP,
or going through the POP at quiet times of the day, is much faster there
may be not enough bandwidth to that POP.


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