Why does my 3COM^® U.S. Robotics^® modem connect at high-speed (V.90), but is slow at browsing or downloading?

Question or Problem:

3COM (U.S. Robotics) modems that achieve high-speed (V.90) connections may still have slow browsing and downloading speeds. A connection faster than 31,200 BPS (bits per second) is generally considered a high-speed connection.

Discussion:

A 3-COM U.S. Robotics X2 or V.90 client modem calling an ISP (Internet Service Provider) which answers with X2 or V.90 host modems can negotiate a connection speed that is "too aggressive." This type of connection can result in your modem attempting to use sections of the bandwidth that would be available in a "perfect" telephone connection, regardless of whether the sections are actually free or clear from noise. The connection speed does not always dictate how quickly a modem can download or how quickly a web page can load.

NOTE: The connection speed can be viewed with either the 3COM Modem Manager: click Start | Programs | 3COM US Robotics | 3COM Modem Manager, or by placing your mouse cursor over the Connection (modem) icon in the Taskbar.

NOTE: If the modem manager is not installed, place the blue 3COM driver CD in the CD-ROM drive and click Install Modem Manager when it begins to Autoplay.

If a modem selects a connection speed that is too aggressive, errors may occur so frequently that the modem is "busy" re-sending packets that are damaged or corrupted by impediments in the public telephone system. Throughput, which is the ability of a modem to send or receive data in a timely manner, is affected when a modem must continually re-send packets.

Your modem will allow you to "adjust" the initial connection speed in order to work with the nature of the V.90 standard and to work around the ever-changing public telephone system. (V.90 is the standard that allows a connection speed above 33600 bps.) The V.90 standard defaults to the fastest possible connection, but the public telephone system contains many impediments that will obstruct a high-speed connection.

NOTE: Want to know more? See the section titled MORE INFORMATION.

Solution:
 

Use the following process to limit how aggressively your modem negotiates a connection with the host modem (ISP modem). The process is simple; just two questions, one test download, and few mouse clicks! Then you can test the new settings and recycle the process as needed!

The following two questions will help determine what steps to take and configuration changes to make. You may need to call your ISP for some of the answers, such as what standard, KFLEX or V.90, they support. Dell will not have information about the Internet service you have chosen, or how it is provided to you.

NOTE: Dellnet is fully compliant with the V.90 standard.

Write down the answers to the following questions for use later in this process.

Question 1.
Do you suffer poor throughput with every one of the phone numbers or providers you are dialing? (Most ISP's have more than one access number.) If the modem moves data more quickly (while browsing or downloading) when you use an alternative number, you are probably selecting a host modem that is the same brand as, or more compatible with, the modem in your system. You can stop here if using an alternative number provides you with satisfactory performance.

Question 2.
Does your ISP support V.90/X2; or is this a KFLEX provider?

NOTE: V.90 is the newest standard. X2 is the older U.S. Robotics standard. KFLEX or K56FLEX is the older Lucent^® or Rockwell^® standard.

NOTE: This process is written for the 3COM U.S. Robotics line of modems. To check if you have a 3COM U.S. Robotics modem, click Start | Settings | Control Panel, then double-click on the Modems icon.

You begin the process by decreasing the modem connection speed and performing a download in order to establish a performance benchmark. Next, you check for errors, such as BLERS (Block Errors) and LINK NAKS (Link Negative Acknowledgments). These errors, which the modem monitors, may result in low throughput. After you have established the benchmark, you must go through a cycle of incrementally increasing the modem connection speed. After each increase in the connection speed, you will need to monitor for increases in the download speed and the number of errors. Your goal is to balance speed and errors for maximum throughput.

Click Start | Settings | Control Panel, then double-click the Modems icon.

Click Properties | Connection | Advanced | Extra Settings.

Slow the modem connection speed to 37333 by typing AT&F1S13=64&N24 into the Extra Settings box.

NOTE: For All 3COM U.S. Robotics modems, this string reloads the default settings, disables fast retrains (the term fast retrains is explained in the MORE INFORMATION section), and slows the V.90 connection speed to 37333.
 

Use your answer to Question 1 to determine the appropriate string from the following list:

• If your ISP supports only X2, add S32=66 to the end of the line in the Extra Settings box (this disables V.90, but allows X2).
• If your ISP supports V.90, add S32=34 (this disables X2, but allows V.90.)
• If your ISP supports only KFLEX and you have a 3COM/US Robotics modem, then your fastest connection speed will be 33,600 or lower.


When you are finished, the Extra Settings line may look something like this:

AT&F1S13=64S32=34&N24

This string is a great place to start when troubleshooting connection problems with the 3COM U.S. Robotics modems, but do not skip Question 1, as not all ISPs are the same.

NOTE: It is not important which command comes after AT&F1.

• Click the OK button until you reach the Modem Properties box, then click Close.
• Test your modem. Connect to your ISP and download a test file. Browse to: http://support.dell.com/filelib/ and click File Library | FTP | Miscellaneous Files.
• There are two test files in the list: Dell.bmp and Dell.doc. Double-click on one of the files.
• When the File Download dialogue box opens, click Save this file to disk and then click OK.
• When the Save as window opens, save the file in your Desktop. Disconnect from the Internet when the download is finished.
• As the file downloads, the File Download box reports the size of the file, the average download speed (throughput) and how long it took to move the file to your Desktop from the Dell web page. Record the time and download speed; these will be two of the benchmarks you are trying to improve. If you have the Modem Manager installed, check for the download throughput by clicking on:

Start | Programs | 3COM Modem Manager | Diagnose | Log.
• Now, we will check for errors:

Click Start | Programs | 3COM Modem Manager | Diagnose | Terminal.

NOTE: You may also launch a HyperTerminal window to perform the following tests.

• In the open Terminal or HyperTerminal window, type ATE1I6 (A TEE E ONE EYE SIX) and press [Enter]. If the terminal returns Error, type AT and press [Enter]. You will see data returned similar to:


OK U.S. Robotics 56K Voice Win Link Diagnostics...
Chars sent 16848 Chars Received 875378
Chars lost 0 Octets sent 10771 Octets Received 70654
Blocks sent 1519 Blocks Received 963
Blocks resent 0 Retrains Requested 1 Retrains Granted 0
REJs Received 0 Blers 3
Link Timeouts 0 Link Naks 0
Data Compression V42BIS 2048/32
Equalization Long
Fallback Disabled
Protocol LAPM
Speed 26400/26400
Last Call 00:02:08
Disconnect Reason is DTR dropped

• Record the following: Blers and Link Naks; these are the other two benchmarks that you are trying to improve.


NOTE: Blers are Block Errors and Link Naks are Link Negative Acknowledgments. Both should be kept as low as possible. It is rare to have 0 Blers errors, but try to keep them under 5 Blers per 3 to 5 minute test download.

• Now that the benchmarks have been established, repeat the steps. With each cycle, increase the modem connection speed "one notch" higher than the current speed. Use Table 1 to determine the correct AT Command string (&N__) to change in the Extra Settings box (Step 3) in order to increase the modem speed one level. Continue this process until the errors begin to increase.


Table 1
AT Command : Connection Speed
&N8 : 14400 bps
&N9 : 16800 bps
&N10 : 19200 bps
&N11 : 21600 bps
&N12 : 24000 bps
&N13 : 26400 bps
&N14 : 28800 bps
&N15 : 31200 bps
&N16 : 33600 bps
&N17 : 28000 bps
&N18 : 29333 bps
&N19 : 30666 bps
&N20 : 32000 bps
&N21 : 33333 bps
&N22 : 34666 bps
&N23 : 36000 bps
&N24 : 37333 bps
&N25 : 38666 bps
&N26 : 40000 bps
&N27 : 41333 bps
&N28 : 42666 bps
&N29 : 44000 bps
&N30 : 45333 bps
&N31 : 46666 bps
&N32 : 48000 bps
&N33 : 49333 bps
&N34 : 50666 bps
&N35 : 52000 bps
&N36 : 53333 bps
 

In a perfect world, you are shooting for a download of the Dell.doc file in 60 seconds or less, and the Dell.bmp file in two minutes.

NOTE: The .bmp file cannot be compressed by the modem; the .doc file can. This explains why files the same size will download at different speeds.

Downloading the two test files in the times listed will probably translate to a "perfect" telephone line and low congestion on the Internet. Watch the Blers and Link Naks, and try to keep them as low as possible. Your download speeds will vary with the normal daily Internet congestion. You will find that your download speeds will increase late at night.

MORE INFORMATION:

Standard analog telephone lines can only transmit raw data (zeroes and ones) at around 3429 bps (bits per second). Improvements in compression (coding the data to make it use less room) pushed the data speeds to 9600 (very simple compression), 14,400, 28,800 and finally 33,600 baud (very complex compression). For many years, 33,600 was considered to be the absolute speed limit on modem transmissions. To conquer this limit, two competing standards (X2 and KFLEX) were created using compression methods based on Digital Technology to achieve greater effective speeds. These two standards were then unified into one common standard, V.90.

The V.90 standard defaults to the fastest possible connection, but impediments in the public phone system may obstruct the actual throughput of the modem. Physical defects in the composition of the telephone line, electronic switching devices installed by the phone company, and weather effects can all negatively impact the bandwidth available to your modem.

If the client modem (your modem) does not detect these impairments during the initial negotiation or if the line conditions change, a retrain will occur. A retrain is triggered by a modem "losing" data or sensing data corruption. During the initial "handshake", the host modem (your ISP's modem) will work with the client modem, using the capabilities of the phone line, by generating a DIL (Digital Impairment Learning) data burst. This "discovery" is a V.8 DIL data burst. You know it as the funny sounding "BONG" during a modem handshake. The "BONG" sound is an equal mix of sound that is spread across 150 Hertz to 3750 Hertz. The client modem will listen to the sound and try to locate the "bad spots" (noise or static) or impairments and avoid placing data into them.

In most cases when a modem is losing data, it will train down. Line conditions are dynamic and will vary during the call as well as from call to call. In a case where a client modem makes an aggressive connection, there may be so much noise on the telephone line that the modem spends a large portion of the time re-sending data that was corrupted or damaged, or re-training to overcome this condition. This is one of the causes of low throughput.

It is very common during peak telephone usage that a call to a number right next door be routed across town, or to a different city and back. While this helps the phone company deal with increased demand, it can create a potential for low-quality modem connections. Due to these considerations, almost all local telephone companies only guarantee 9600 Baud for data transfers.

If you spend a lot of time online or your business depends on fast Internet data transfers, you may want to look into the services that are designed for data, not voice (the public telephone system). ADSL/DSL (Asynchronous Digital Subscriber Line),
ISDN (Integrated Services Digital Network) and cable modems are not voice devices. They were designed to transfer data at high speeds and are becoming very common in the average household. These services are "the way to go" if you are serious about moving data rapidly to or from the Internet.

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