 How 56k Modems Work (I have a 56k Modem but can't connect at 56k speeds, why?) |
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Introduction
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We wrote this article to help our 99main customers understand the differences in modem technology without boring you to death with tons technical details. Currently there are a variety of modem types, everything from hardware based modems, software based modems and modems that wish they were modems. Although all of the modems do basically the same job, which is connect to an Internet Service Provider, not all modems work in every situation and often a modem that will not work in one place will work like a charm in another. The only exception to the rule seems to be good old fashion hardware based modems which seem to have the ability to adapt it's self to pretty much every line condition.
Part 1: Types of Modems
Part 2: How 56k Modems Get 56k Speeds
Part 3: Connection Speed Vs. Throughput
Part 4: Common Problems and Solutions
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Part 1: Types of Modems
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There are a few different types of modems out on the market nowadays. The three most common are Hardware Modems, Controllerless modems and HSP/HCF Modems. These parts must be on every modem, one way or another, in order for a modem to function.
- The Data Pump is the part of the modem which does the majority of the Modulation/Demodulation. This part may also be called the Digital Signal Processor (DSP) and it does the calculations for interpreting the digital signals.
- The Data Controller is the second part. This is the part that controls how the modem communicates, what type of modem it is, error correction coding, basic information about connection protocols such as V.90, X2, Kflex, V.34, etc; data compression and also for interpreting and extra AT commands its given by the user or the computer.
So what's the difference?
Hardware Modems: The Real Deal
There are a few major parts on all modems that must be present in one way or another in order to work properly most notably are the Data Pump and the Data Controller. All hardware based modems contain both parts making it capable of handling all of the communication process by itself. The only thing that would be required of the computer's operating system is to tell the modem what number it is calling, when to make the call and when to hang up. Hardware based modems work with every operating system from Apple Macintosh, DOS, Windows 3.1, Window 95/98/ME, Windows NT 3.5/4.0/2000, Unix, Linux, BEOS and so on. Because all the communication is up to the modem it often handles bad/fluctuating phone line conditions much better than software based modems.
Hardcore gamers should note that a hardware based modem will be your best friend when playing online action games such as Half-Life, Quake and Unreal Tournament. A hardware based modem does not rely on the computer's CPU to do the processing of the information to send over the net. Because a Hardware modem requires nothing more from the computer's CPU after it is connected, the modem is much better at sending and receiving packet information and correcting errors. If reliability, speed and a quick ping are required to fit your connection needs we highly suggest you run out and buy a hardware based modem. All external modems we have seen have been hardware modems which connect to your system's serial port through a cable and sit outside your main computer.
Controllerless Modems: Only Half There
The best example of a controllerless modem would be 3COM USRobotics Winmodem. The Winmodem still contains a hardware datapump but does all its Data Controller functions in software. This has two main advantages. The first big reason is that by excluding one of the main chips from the modem it cuts the cost for producing those modems by $25-$50 making it cheaper for you to buy. The second is that the modem can be more easily upgraded to newer firmware by simply installing new software provided by the manufacturer.
With the advantages of a controllerless modem come some disadvantages. Because a major part of the modem is based in software it is required that your computer be running a Microsoft Windows 95/98 type operating system and your computer be at least a Pentium 133mhz machine to work properly. These modems may not work in Window NT 4 or 2000 environments and will not work in any Linux or Unix based operating system. Additionally, a controllerless modem sometimes has difficulties with phone lines that are not optimal or have frequent changes in conditions causing slowdowns, disconnections or even not being able to negotiate a connection unless they are slowed to a non-56k protocol such as v.34.
I give the USRobotics Winmodem as an example because it is one of the better of the Controllerless modems. It seems to perform fairly well in a variety of conditions. So if you don't need the best but still demand a reliable connection, 3com's USRobotics Winmodems seem to be the way to go.
NOTE: LT Winmodems are also decent and have excellent driver support. However we still find 3COM's Winmodem to be more stable and have better driver and technical support for their product.
Software HSP/HCF Modems: No One Home
Techs across the country cry out in fear when they hear a customer with an HSP/HCF modem is having connection problems. These modems are typically the worst type of modem you can have. Both the Data Pump and the Data Controller are removed from the modem and emulated in software. Removing these chips causes the modem to become slightly more than a glorified phone jack meaning it contains only the basic circuitry to connect to the telephone network. Nearly every other function is done by the computer and the CPU.
Because the modem is now basically a piece of software, conditions need to be written into the software to tell the modem how to react under various circumstances. If a condition on a phone line does not match a condition it is programmed with the modem reacts very poorly causing disconnects, slow connections, constant retains and often achingly slow speeds. If you have any of these types of problems your first action should be to locate a firmware or driver update which may have more programmed variables then your current version.
So if there are so many problems with this type of modem why does it continue to sell? Because it's inexpensive to manufacture and incredibly cheap to sell which is important in the current times where sub-$1000 PCs are popular. Currently major manufacturers such as Hewlett-Packard, Compaq, Gateway, Packard Bell, Acer will put HCF/HSP modems in your computer unless you choose otherwise (usually costing more - but it's worth the cost, trust us).
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Part 2: How 56k Modems Get 56k Speeds
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Due to the nature of 56k modems, they are very sensitive to phone line conditions both inside your house and outside on the telephone company's network. Your computer is a digital machine meaning that it transmits data in 1's and 0's (On and Off) to each component within. Telephone lines on the other hand are Analog meaning that they transmit data by sound. Modems work by taking a digital signal and transforming that into analog (sound) over a phone line. In order for 56k modems to work the way they are intended there must be no more than one Analog to Digital (A/D) conversion between your computer's modem and our service at 99main. If there are any more A/D conversions than one you will not achieve 56k connections due to the decreased integrity of the signal.
The way your modem sends data to us is:
[Your Computer] > [Digital signal] > [Your Modem] > [Analog signal] > [Telephone Company] > [Digital signal] > [99main]
We send data back to you like this skipping an additional Analog to digital conversion:
[99main] > [Telephone Company] > [Analog Signal] >[Your Modem] > [Digital Signal] > [Your Computer]
In order to achieve connections higher than 33.6Kbps, modem companies have invented a technology to use to their advantage the all digital connectivity between the server modems (99main) and the Public Switch Telephone Network (PSTN). In order to achieve 56k speeds on the downstream (data going to you from the internet), 99main uses our all digital connection with the telephone company to keep the signal in tact until it reaches your local phone line, eliminating one of two Analog to Digital conversions. This will allow modem download speeds as high as 56Kbps. A 56k modem connection is only one way; 33.6Kbps is still the limit for the upload rates because of the additional Analog to Digital conversion. (Note: To prevent "cross talk" or noise spilling over from one phone circuit to another separate phone circuit, the FCC has limited the connection speed for 56k modem to 53k)
If along the way back from 99main to you the telephone company has old equipment or an additional A/D conversion you will not receive a 56k connection. The fact is that the telephone system is designed to host voice phone calls which require far less quality than a data connection requires. Therefore in some locations where population has not required the telephone company to upgrade their equipment you may have equipment that will not support 56k quality connections very well or even at all. On the other hand having a population boom in one area may not be enough for the telephone company to upgrade it's equipment either. If a phone company is running low on phone lines it may decide to install a device called a SLC (pronounced "Slick") what this device does is basically split up a phone line channel into two separate channels in order to accommodate the growing need for phone lines in your area. In this case you could be getting 56k class speeds one day and then the next day they could install one of these SLC's into your local central office doubling their available phone lines but effectively cutting your bandwidth in half.
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Part 3: Connection Speed Vs. Throughput
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Throughput is more important than connection speed. No matter what your modem reports to you as your connection speed it may not be the true speed. Both phone line quality and modem type play a major part in the actual data throughput you receive when downloading data from the Internet.
A common misconception many people believe is once you connect to your ISP at a certain speed it remains that speed the entire time you are connected. This is incorrect assumption. You probably noticed during the initial connection process all of the hissing and screeching sounds the modem makes before it goes quiet. The hissing and screeching is called training or synching. It is during this part of the connection process that your modem and our modem are talking to each other to figure out at what speed they can reliably send and receive data to one another. After this process is completed windows shuts off the modem's speaker so you won't have to listen to all the noise it makes. What you won't know is that your modem can and will go through a retrain or resynch process if it detects a change in the phone line conditions. While it is retraining no data will flow through the connection which is why sometimes things just seem to stop working and the modem lights won't flash. In most cases the modem will start sending data again after it is done with the retraining process, which usually takes anywhere from 15-30 seconds, sometimes it will disconnect if the retrain attempt failed.
So what does this have to do with your connection? Well, different modems have different ways of handling phone line noise and retraining. Some modems will connect lower and then as time passes it will slowly work it's way up while other modems may connect high and then train down over the duration of the call. Windows only reports the connection speed you initially connected with so there is no real way for you to know what your throughput is using that information. Instead one thing you can do is get a program that monitors your incoming and outgoing data through the modem in real time. DUmeter and NetMedic are two such programs that are available for download to try out. Check out 56k=V.Unreliable which is an excellent source of information regarding throughput. You can link directly to their article on throughput here if you would like to see an example of a typical modem connection.
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Part 4: Common Problems and Solutions
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This section is for the people who are having difficulties with their connections. Symptoms usually include: Frequent disconnects, slow web surfing, high ping times in games, trouble establishing a connection and error codes from dialup networking.
If Your Modem Does Not Dial and No Connection Box Pops Up (but it used to)
Check to make sure that windows is still set to auto dial. To find out click the Start button >> Settings... >> Control Panel. Find the Internet or Internet Options icon and double click it. Click on the Connection tab on the top of the window. In the middle of the window should be three option circles. One of them should be called "Always Dial My Default Connection". This option should be marked, if it is not then it's most likely the problem you are having.
If Your Modem gives you the "No Dial Tone" Error
- This sounds silly but make sure your line is still plugged in on both the back of the modem and in the phone jack on the wall. Sometimes the wire can be kicked enough to nock it loose when sitting at the computer. Try unplugging and then reinserting the phone cords on all connections.
- If you have any other devices between your modem and wall jack like caller ID boxes, faxes or surge suppressors; try removing them temporarily and run the phone line directly from the modem to the wall jack.
- Make sure that you phone line is plugged into the modem and that it is plugged into the correct phone jack. There are usually two phone jack slots on the back of a modem very close to each other and it can be easy to miss and plug it into the wrong one. The jack that you must plug it into will be marked Line or Telco, NOT Phone. Once this is confirmed make sure that the other end is plugged snuggly into the correct phone jack on the wall.
- If you would like to have a handset telephone next to the computer you can plug the handset into the back of the modem marked Phone. If you do plug in a handset you can then pick up the phone and check by ear to see if there is a dial tone; if there is a dial tone then the modem is plugged in correctly. See Step 2 about Additional Devices.
- If you still did not get a dial tone, unplug your modem wire from the wall jack and plug a normal telephone into it. If you hear a dial tone now you should replace the cord that is going between your modem and the wall jack then try connecting again.
- Another thing that we typically see is Modems often give the "No Dial Tone" error when they have been hit by lightning. If you have had a lightning storm in the area recently and your modem was working before the storm this is most likely the cause. This happens when a lightning strike hits the part of the modem responsible for picking up the line so the modem can dial out. If this happened, you now you have an excuse to pick up a good hardware modem. =)
Slow or Sluggish Internet Performance
- First thing you should find out is what type of modem you have in your computer. To find this out click Start >> Settings >> Control Panel. Once in the Control Panel find the Modems icon and double-click it to open it. In the box in the center should be the Modem you have. Once you know what type of modem you have, check your modem manufacturer's website for updated firmware or drivers. If they do, this could be the only thing you need to do to fix the problem which is particularly important for software based modems. You can find many driver links at Windrivers.com, 56k.com and 56k=V.Unreliable.
- If that doesn't fix the problem try to remember when the problem started. If it happened recently try to recall if there were any new devices like caller ID boxes, cordless phones, fax machines or extremely long phone extension cords attached to the house wiring around the same time this problem started. If your not sure try removing every other phone or device from the house's phone wiring and then try again. Too many devices on a phone line can drain the available power to your house phone wire causing connection problems.
- You should use the phone cord provided by the modem manufacturer to connect your modem. This cord is usually no longer then 6 feet which is the optimum length. This should go straight into the houses phone jack without passing through any phone line splitters, Caller ID, Fax machines or surge suppressors.
- If you have more then one phone line try hooking it up to the other line and connect to see if there is any difference. If you have only one phone line try a different phone jack in the house.
- Try looking at the modem lights when you are connected. The modem lights should be in your System Tray down by your clock and look like two little computers when you are connected. The bottom most light is the Transmit light (Sending data to the Internet) the top most light is the Receive light (Receiving Data from the Internet) When you send a request for a web page normal modem light operation should be a quick burst from the Transmit light, a short wait (usually a second or two), then a near solid Receive light with several very quick flashes (sometimes solid) from the Transmit light as it is downloading the web page. If you request a web page but your transmit and receive lights are flashing back and forth with neither one of them staying on for any length of time there may be something flaky with the driver or the modem. Try a different website and if this repeats try disconnecting and then connecting again to see if the connection improves.
- Check what speed you are connected at by double clicking the two little computers by the clock. If you are connected at anywhere between 34k to 41k you may have a phone line that barely supports 56k. In most cases this works fine but if you are having constant disconnects or slow performance you may want to try disabling 56k protocols. By disabling 56k protocols you may actually increase your reliability and throughput due to your modem no longer trying to retrain the connection to a higher speed that it cannot reliably sustain. You can limit your connection speed by looking in the manual provided with your modem for a command to turn off V.90 and KFlex or X2. Alternatively you can check out 56k=V.Unreliable for a modem string that may work for your modem. Check the page at 56k=V.Unreliable by clicking here.
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Sunday, December 22
99main