=-=-=-=-=-=-=- Av-Sync Bulletin 8 : Line Noise & You -=-=-=-=-=-=-= Download as ALLNOIS3.ZIP Updated 9-17-89 This was a difficult bulletin to put together. So many people have mis-conceptions of what line noise is. Most often, they blame it on the place they are calling rather than looking within their own back yard, or the environment from point A to point B. "What happens between your modem and the other end?" We will try to answer most common questions covering these areas: AV-Sync Calls from HOME Calls from the OFFICE LD Services (Name your calling card!) Multiplexing on a local level Weather A typical connect path We are not super-moguls of communications, but after many calls to the right people, some accurate info has been obtained which may be useful. All of this is designed to educate the novice while not insulting the people who have a full understanding of modem communications. AV-Sync: We run a fairly large system here. The concern is always for the user. As usual, we try to apply the latest technology we can afford. Because there is such a turn-around in the industry, we prefer to wait rather than "jump" onto a new product, version of software, modem, etc. Once the product has proven itself, we will consider it. AV-Sync runs with either Hayes SmartModems (2400) or USR HST 9600, Depending on the node. The main dial-in number operates via Hayes 2400 since that is the top speed for most first-time callers. The modem has proven itself to be reliable and bullet-proof to most problems generated by outside callers and MA BELL. The next number (in rotary) and all other numbers run with USR HST modems. We decided on USR because they seem to be the front-runner so far as 9600 access goes. One (1) V.32 CCITT standard is on line for users who want to experiment. We don't plan to expand to more V.32's any time soon. The market just doesn't warrant it. As well, USR is always making upgrades and changes to their modems. This doesn't really impact on the caller, but the host (BBS) may be in deep water. Changes in various phone companies' data rate transmissions have a large effect on how well a call goes through. Then the AT&T breakup came about, no one really took a long hard look at what effect it would have on the consumer OWING TO THE FACT THAT YOU ARE NOW DEALING WITH THE LOCAL STORE instead of a national entity. We'll address that later. Statistics as of 9-16 indicate: 1200 baud callers @ 31% 2400 baud callers @ 43% 9600 baud callers @ 20% 300 baud callers @ 2% ODD baud callers @ 4% Lines HERE: All incoming lines to AV-Sync are among the cleanest in Atlanta. We have the circuits checked weekly as a policy. Rarely, there will be noise on these lines owing to bad weather (humidity does strange things to copper wire), or when the local exchange (404-32) is replacing equipment. Other users of this exchange include the National CDC, Emory University, and National Data Corp's Atlanta hub. If you have line noise....... It isn't the local phone company's obligation to tell us if service may be interrupted for installation of a new trunk or some internal switch. They aren't obligated to tell us when THEIR software fouls up; (usually at the daily exchange scan, if at all). Funny thing: While one local caller will have tons of noise on one call and the next one will be clean from the same calleron the same line, there are callers from New Zealand at 9600 every day, Germany at 2400 every day, the UK at 1200 & 2400 every day, and NO problems with noise or wierdness. And then there's ITALY.... lots of problems from Italy. Most callser are at 1200 baud, but an occasional 2400 caller. More of the 2400 calls from there have problems. We tracked that down to the system and routing they use to get to the U.S. A "NO ANSWER" here may mean one of two things: The caller is using an automatic dialer to access the system, and the system is getting modem errors, causing it to try a reset WHILE the caller is dialing repeatedly. This isn't usually productive, but many people don't understand that. A node is down in the rotary, and the software (ours) failed to place the modem "OFF-HOOK", causing a busy signal which would tell the phone company to go to the next line in the rotary. Instead, a "dead ringer" happens, and users may only access AV-Sync if some unfortunate person is calling the dead line, thus tying it up and forcing the rotary to the next free node. This isn't a regular situation, but it does happen on occasion. This problem is common on many systems. The local phone company (YOURS or OURS) may also cause this to happen. That's why you might call a VOICE number sometimes, expecting an answer, and it just rings and rings. "I tried to call you, but there was no answer!". >> "That's funny, I was here all the time and didn't hear the phone ring!" This is just the way many phone companies (BOC's) cache their services and resources. On occasion, a few users go to NOWHERE LAND inside the all powerful MA BELL. Calls from HOME: The MOST common problem we've experienced from home-based callers is line noise or dis-connects induced by someone picking up the phone, or the user forgetting to cancel CALL WAITING where available. Your local phone company will have that information. Some BOC's provide different codes for call waiting. They range from CANCEL until user says ACTIVATE again to CANCEL for THIS CALL ONLY. The SECOND thing that has cropped up is that many BOC's (local stores) have gone to multiplexing in some areas where there aren't enough lines to go around. This is usually in a rural area, or in small townships where the local phone company has decided it is cheaper for them to add this feature INSTEAD of running extra lines or upgrading service. In most cases of this nature, the ADPCM or Pulse Code Modulation system crunches data to 7 bits instead of the normal 8 bits in order to cram more traffic into the existing system. NOTE: This has nothing to do with your modem parameters (N-7-1/N-8-1). With ADPCM, anything above around 4800 baud may not be possible. If you ask your local phone office whether they are using this or not in your area, dumb looks are still free. The office personnel don't know these things, but they may be VERY HAPPY to install a dedicated DATA line for your modem at a whopping premium. In some cases, this only amounts to their adding a filter or resistor inthe line, etc., or offsetting their expenses of un-dedicating one of the existing lines on your circuit so that it is a regular line like you used to have. The PSC can handle some complaints as far as price gouging if you get a bum deal. Many who are just beginning to use modems have purchased the best buy at their local computer outlet. Often, these "best buys" can provide nothing but headaches. Typically, they are discontinued models because the manufacturer either found a bug or dumped a line for better technology. The reseller received a good liquidation deal and passed the modem, along with its problems, to YOU. This isn't true in all cases, but the range of compatibility and potential problems is enormous. CAVEAT! : You may have received a communications program with your modem. Depending on what it is, you may have more problems by using THAT program than one which is shareware/registered or purchased. In the majority of cases, we have seen more problems from people using certain versions of (for example) Crosstalk and BITCOM which comes with some EVEREX modems. This is only an observation, not a judgement on the integrity of either program. There are also complaints from users of Smartcom from Hayes. Several good shareware or purchased programs are avialble either on bulletin boards or in stores. You should make sure you have the latest version in either case. Surveys from here indicate: TELIX, BOYAN, QMODEM & PROCOMM as being the most popular programs used. If you bought got a bargain basement brand, usually 1200 or 300 baud, the only thing that the manufacturer had to do in most cases to claim HAYES compatibility was to include the AT command and other very basic modem communications standards. Then, most of them will go in their own directions with "& this & that & whatever". This is not to say that you should buy the latest and greatest modem, but a few opinions from friends wouldn't help. Though most newer models aren't entirely perfect, the average is better these days. One of the best investments against line noise is an MNP modem. Level 5 is the most popular. This feature will do a lot better with noisy lines, and file transfers will be better. If a line is too noisy, some MNP modems will connect at a lower baud rate than your original call. Often, some forget to reset their dialing directories to the highest baud rate when buying/upgrading to a new modem. Always consult your communications program's manual and the manual which came with your modem to be sure that the strings are correct. In many cases, the modem's default string is sufficient. In others, these items must be changed to achieve the full capabilities of the unit. If you have a known GOOD modem, you may have a configuration problem with the software you are using to call out. Understanding of proper FILE TRANSFER PROTOCOLS is important. The best two averages are YMODEM and ZMODEM. Others are good, but less reliable in many cases. Again, AV-Sync prefers to go with tried and true protocols rather than the latest thing out there. Check your configurations carefully, and insure that your download (Receive Files) paths are set up properly, and that you are loading these files to a disk which has sufficient space available for the file(s). Users with only floppy disks should make sure that each session starts with a clean formatted disk in the download drive. It can be a disaster to place all of your downloads in the same directory as your communications program. Once you decide to clean it out, you stand a good chance of deleting some of the programs along with the files you no longer need. It may be wise to create a separate download directory, specifying it in your COMM program's setup. This keeps the comm program clean and free. If you do a lot of perusing and trial of files, it may be good to create yet another WORK directory on your hard disk, only utilizing the files you wish to try one at a time. Returning to the BACK YARD: If you live in an older house, the phone wiring may be ancient. While good for voice calls, it may be insufficient for data calls. Many BOC's offer an inside maintenance service whereby they agree to maintain wiring inside your house or apartment for X amount per month. This doesn't mean that they will come in and re-wire the whole place, but they WILL fix any problems. Unless you order a data line in many areas of the country, MA BELL doesn't guarantee a perfect connection. Then if you DO order a data line, a few filters are installed, and you get the bill every month, normally paying the cost of the filters and labor in 2 months' time. A house is one thing for access to wiring. Apartments often have problems due to the way a builder may have installed things. The telco wiring code for apartments requires that X amount of lines or "pairs" be provided to each apartment. If one pair is bad, another can be used, or an extra line installed as needed. If you experience consistent connection problems with a modem, you may have a wiring malady from your house to the phone company. It's a good idea to have them check your lines if you suspect this may be the problem. NOTE: A VOICE call may seem clean, but a modem call may be dirty. ome problems do not show up in your receiver. LINE NOISE in BOTH directions is usually an indication of a problem with your line between the house and the exchange, or a problem within the exchange itself. There are still some old "stepper" or mechanical exchanges in some areas of the country. Since the break-up of AT&T, there is no pressure for a local BOC to upgrade. All they are bound to do is provide voice service. These older exchanges can be a cause of constant headaches for modem users. Calls from the OFFICE: Another can of worms......... You are now at the mercy of what your company uses for a communications system. The local phone company is no longer involved (unless you are using their equipment) once the wires or fibers connect to their terminal in your building. If you are on a "Polling" system, you may get spurious line noise or disconnects regularly. Some systems allow dedicated lines which are inde- pendent of the regular system. These are the lines that normally work when others will not due to system failure or a power interruption. Although they may go through the same inter-office service, they have priority, and are not subject to some restrictions. Your company may be using a system which saves $$ by finding the cheapest carier for a call. Most often, the cheapest carrier/path may be the worst for a modem call. You can't control this one without a little hutspah. If you are calling from an extension that BEEPS you when someone else is trying to call in, the same may happen. Then there's always someone picking up the phone you may be using to call out. In an office environment, the BEST bet is a dedicated line for modem use, or at least a line you can control. NOTE: Some newer internal systems compress "data" to a point where it may be impossible to call out at a higher baud rate. The worst we have heard is 1200 so far. Many LD services do the same during heavy traffic times (per area). Long Distance services and connections: I don't want to fault US Sprint, but they make a good example. I use them myself, and have found them to be good most of the time.... .............however........ saying that you're a "fiber optic network" doesn't guarantee anything. NO long distance service can guarantee you'll have the cleanest connection possible, because they can't guarantee the lines you are using to get TO them. In one city, I can rig the line in my hotel room to call out (many don't provide extra outlets or modular connectors) and if the hotel's system is noisy, so is my connection.... ... even with an MNP modem! Try again in 5 minutes.... perfect (9600 baud) connection! .......Why?....... The amount of traffic on many phone exchanges dictates what type of connection you may get. That also accounts for how loud and clear or faint & weak a voice call may be at any time. Modems can't always HEAR things well either. If the connection is weak, there's no telling what will happen. NOTE: This can be a common problem, no matter WHO you use for a carrier. Just like some office setups, cariers will go for X path first and if it's tied up, they may opt for the next one, and it may be bad or good. During off-hours, it's pot luck much of the time. In many cases, the least expensive line will be chosen first. Next, the more expensive line and so on. It all has to do with traffic patterns locally or across the nets which are commonly used by all phone companies. A few alternatives are in the works, but not cost effective or perfected yet. Most of these are quelling heavy data users' problems with existing services. Even on LOCAL services, an exchange which may have problems may be the cause of noise even if the surrounding exchanges are clean. If the call must pass through a dirty exchange, the CLEANEST and BEST paths on either end won't make much difference. These items are all additive, and will certainly play on the quality of your call. WEATHER: In Atlanta, just as other areas, phone connections sometimes get noisy during high humidity (rain & murky weather). Corrosion on copper wires tends to do its worst during these periods. In a few hours or days, these problems go away. Again, it depends on where you are calling from or to, and how well the local BOC is taking care of its hardware. It's almost impossible to shield everything from the elements. In cases where a noise problem is found on a home line, it is normally traced to a corroded wire or connection outside or in the path to the exchange. Generally, all LOCAL calls are clean, unless a microwave link is involved. Again, inclement weather may cause problems. Peak SUNSPOT activity tends to disrupt MICROWAVE and SATELLITE transmissions, not to mention radio and 2-way comunications. Sspots can send wide-band bursts of RF (Radio Frequency) interference which will interupt almost any transmission. Common Practice: If you experience noise more often than not, have your phone lines checked first. Next, check your modem and its setup for your COM program. If you have trouble connecting to certain areas of the country, keep a log of the trouble areas and contact your long distance supplier. If you have CONSISTENT trouble connecting with one service or BBS in a city, and no problem connecting with another service or BBS in the SAME city (excepting locales where the area codes have been modified for growth), leave a message to the service you have the most problems with and let THEM check it out from their end. This only works well where two services are within the same area code and city. One phone exchange handles several prefixes. In ALL cases, periods of heavy sunspot activity can cause hassles with every form of communication. Most effected are cellular phones, microwave, some satellite transmisions, and long lines in some rural areas. A TYPICAL PATH: You are at the computer in Oregon and decide to call Miami. When you dial the number, it goes through the local exchange, to a major area hub for MA BELL, then may be microwaved or sent via satellite to a major hub on the other end, with all traffic and switching in between. When that hub gets the call, it routes it to the exchange which is the home for the number you called. This is a typical path, but you have gone through a lot of potential problem areas: Wiring to your exchange, Wiring or microwave from the exchange to the hub. Satellite or microwave from the hub to destination. Destination hub to target exchange. Target exchange to the modem you called. Any number of things can happen on either end or in between. Add switching of lines by vendors, carriers, local BOC quality control and weather factors to that, and you have the formula for line noise. Courtesy of AV-Sync Atlanta (404) 320-6202