By Joe Rinehart
I wrote this article in Oct of 1999 to help people using modems for dial-up Internet access in rural America and ISP's understand some of the issue with dial-up modems. and the potential to resolve them.
I’ve used modems ever since the days of 1200 baud back in the eighties. These days I’m a little more fortunate to have 1.56MB per second high speed T-1 access from work, but I still use a modem from my home or outside the office. As more people are signing up on the ‘net I’ve been asked more often about the dreaded “drop carrier” and if everything is OK with our system. This is why I’ve decided to write an indepth article to detail the causes of problem and some potential solutions.
To detail the exact meaning of what a “drop carrier” is, I’d offer this explanition: A dropped carrier is the loss of a connection after the point of username and password being accepted by a server. This article does’nt attempt to detail all of the reasons a connection isn’t made! Password errors are too common and just don’t count. A dropped carrier has the same effect as hanging up the phone on either end.
There are many causes of disconnections or dropped carriers. I’ve created a list to work by in the order I believe solutions are achieved faster. These include:
- a storm or other foul weather
- picking up a phone extension in another room
- caller rudeness (opp’s I meant call waiting;)
- reverse phone line wiring
- bandwidth consumption by too many users
- incompatible or cheap modems
- poor modem settings
- outdated modem drivers
- modem protocol version incompatibilities
- outdated remote access server hardware
- improper gateway setting
- server side idle timeout settings
- server side session timeout setting
- consumer side idle timeout setting
- a bad phone company trunk line
- distance to the phone company central office, a server reboot, & other
- network hardware and software maintenance
- security alarm system
The details of each item on the list and their solutions include:
A storm or fould weather is likely the most common cause of dropped carriers. Dampness can basically short circuit the connections and often times a human ear can hear the static in the line. The fact is there isn’t much that can be done to improve this situation except ride out the weather until it’s better.
It is worth mentioning that it’s important to protect your equipment during storms with good surge protection. Without any protection, you are better to be off-line and don’t forget to unplug the phone, computer, monitor, printer, etc… since they can get zapped even if they aren’t on should lightning strike.
Config.Com servers use both surge protection and a battery backup system designed to shutdown the system in the event of an electrical failure. When the power is restored, the system automatically goes back on-line.
picking up a phone extension in another room
Another popular cause for getting disconnected is someone in another room picking up an extension to make a telephone call. ABout the only solution to prevent this from happening is to buy phones with LED lights which show lines in use.
caller rudeness (opp’s I meant call waiting;)
Many phone companies offer additional services these days including call waiting, distinctive ring, call forwarding, etc… These services are operated on digital networks. computers are digital beasts. The modems which convert analog to digital signals back and forth see the tones emitted from services like call waiting as hangup commands (ATH0). The solution is to either turn off the service in your modem settings before dialing out or if the telephone line is dedicated for computer usage, then remove the service from the line and save a few bucks;^)
The reverse polarity of a phone line can also cause poor connections. Your local electronic store offers a “line polarity tester” for about $5.00. This is something worth checking even on voice lines as it will improve the quality of your telephone service.
bandwidth consumption by too many users
Bandwidth consumption is also a popular cause of dropped carriers. Only so much data can be transmitted through a “pipe” at any one time. A full T-1 can handle about 100 simutanious network users transmitting data at the same time. If an Internet service provider (ISP) has several hundred phone lines on a single T-1 and everyone would update their browsers or otherwise participate in video or sound conferencing, the users would first start to see slow transmissions, then as consumption increases, dropped carriers.
Config.Com makes the bandwidth consumption statistics available for our network subscribers peace of mind. At present we have much more bandwidth than can be used at any one time. We aim to maintain bandwidth carefully as our network grows to assure clean connectivity for all users.
It’s a well know fact among old time modem users that two of the same type of modems connecting to each other offer the best throughput. If you connect two of the same brand name cheap modems they will likely be fine. The problem lies in that the Internet service providers offerring dial-in access often are not using inexpensive modems. The quality of their connections may be determined by the type of modems they use.
We believe that if people are getting computers these days to surf the net they should get a good modem worthy of the task. You may skimp on memory, video, sound, etc, but if you are concerned about the quality of your connection, then you should consider the modem as important as the computer itself!
Now, that we’ve cleared the air on quality modems, we run into another problem. There are several types of quality modems. To ease the confusion, we simply recommend asking your Internet provider what type of modems their service uses. If it’s 3COM/USRobotics then buy a good robotics modem. If it’s Cisco router, then buy a Rockwell chipset modem. In all cases we do NOT recommend buying a WIN modem because of it’s inexpensive pricing, because they depend of your computers processor to make them run better, rather than having their own 16550 AFN/AN UART buffer chip.
Config.Com uses 3COM/USRobotics modems because they are the World’s largest manufacturer of modems!
Not much to say here other than try to stay with factory defaults. If you play with your modem settings and don’t understand them, you are asking for trouble. If you’ve already done the damage by playing with them, bring a terminal widow up then type in “AT&F”. If this doesn’t worf for your modem then you’ll need to read the manual or contact your modem manufacturer.
This is one of those tricky things to determine if it’s the right version for your ISP. Modem drivers used to not be a problem until the speeds of modern modems got faster. Every time a new protocol is invented, there is always some lag time before a standard is produced. The most extreme of this was when 56k was invented by US Robotics which is known as X2. It wasn’t long before Rockwell released their version of 56k which is known as 56K-Flex. After a period of months the V.90 standard was agreed on and many modem manufacturers rushed to jump on the higher speed bandwagon. Since Feb. of 1998 when the V.90 standard was first released there have been several updated versions released. It is important to have the same version as the modem you are connecting to to assure the cleanest connection possible.
Config.Com uses the most recent X2 and V.90 protocol versions available! Our service contract with 3Com includes notification of new releases and upgrades to better keep our dial-in service the highest quality possible.
modem protocol version incompatibilities
This is very closely related to outdated modem drivers. If you have the first release of V.90 and I have the 5th, well, they are going to have differences in them. The solution is again to update your drivers to be sure they are current.
outdated remote access server hardware
This is a very important factor in not only possible drop carriers, but the quality of a 56k or ISDN 128k connection! Many networks established before 1999 we using equipment designed for 28.8k or 33.3k modems. Of course, as protocols were invented so were upgrades for these remote access servers, but, here’s where the problem lies: A Cisco 5200 router was designed using an Apple 20Mhz processor. In order to even attempt to offer 56K and ISDN access the 5200 Cisco must have several upgrades to it. These include:
1. Must be using Mica modems
2. Must be maxed out with memory, &
3. Must use the latest operating system.
Even after these three critical upgrades are made, there are no guarentees of clean connections. especially after reaching about 50% of the servers capacity. I have heard it from a system administrator authority that this is the reason a major telephone company spent a large chunk of change to upgrade their entire network to use Cisco 5300 remote access servers! We’d like to note that the processor speed has double from the Cisco 5200 to the Cisco 5300.
Config.Com specifically designed it’s network for high speed access! Not only for 56K and ISDN, but to allow for ease of upgrading to the forthcoming xDSL standards.
We choose to use the 3COM/USRobotics Total Control remote access server for dial-in access. Our phone lines are digital Primary Rate Interface (PRI) DS1/T1 rather than Basic Rate Interface (BRI) lines. Sure, BRI service will still work with 56k and ISDN modems, but PRI works better.
We selected the Cisco 2610 for routing our Internet packets due to it’s faster processor speed, and other quality features. All of our equipment was purchased in 1999 with the maximum memory available so we’d better meet the demands of 100% high speed capacity access and to take our network down less for upgrades;^) The fact is our Cisco router has more flash memory that it will ever utilize!
These are examples of how we didn’t cut costs at the expense of the quality of our dial-in network to achieve a higher profit margin!
While most ISP’s can set their remote access servers to override the Domain Name Services (DNS) and gateway settings, I’ve seen cases where this was done but the user had the wrong settings and encountered problems. Blame it on Uncle Bill… but whatever the reason, it’s worth checking into.
server side idle timeout settings
ISP’s have the ability to set a remote access server to disconnect a user if no characters are transmitted from the keyboard for a particular period of time. There are ways to override this from the user side, but it’s often frowned upon by the ISP’s. If you added up the cost of the modem, phone line, bandwidth, and other overhead involved with just a single access line, it is a lot more than the value of one users account. ISP’s offer dedicated connections for people that need 24 hour access.
Some ISP’s have changed their access accounts and method of marketing to only offer 200-300 hours monthly due to abuse or being taken advantage of by a few users who insist on tieing up resources to the point of losing money for the ISP. One published community ISP model that did this was http://www.delaware.net who did lose about 2% of their user base when they made the change. The quality of their network improved, since those they lost were mostly users that attempted dedicated access were also the largest consumers of bandwidth. Now that ISP make a higher profit due to lower user to modem ratios ;^)
server side session timeout setting
Ahh, this one is a sensitive topic in these days of marketing “Unlimited Access”. I’d like to point out that config.com markets using the phrase “Unlimited Attended Access”. That being said, the fact is some ISP’s will set a session timeout wich causes a disconnection after the specific period of time is reached. No known why to overcome this obsticle as it will require the caller to dial in again, even if the user is using automation to do so.
Config.Com uses the session timeout of 24 hours when dial-in network capacity reaches 75%. This means that a user account will be disconnected after being active for 24 hours. He must re-connect to continue using the account. During periods when network capacity is lower after expand the network infrastructure we lenghten the limits. You may always telephone or email the system administrator to extend these limits for very large file transfers or something like a family emergency.
consumer side idle timeout setting
The Microsoft default settings are something like 15 minutes. We recommend these be extended to at least meet the ISP’s or to have enough time to go to the bathroom, eat lunch, make a quick run to the store, or even accept a telephone call. This settin is under the users control and are accessed by going to my computer, then dial-in networking properties.
a bad phone company trunk line
Not much can be done about this excepting a complaint to the telephone company. This type of problem is more likely to be found in rural areas and have a tendency to exist between communities. If after everything possible has been tried and determined to not be at fault under the users and ISP’s control, then by all means contact the phone company.
I’d suggest to not tell the phone company that you are having problems with your computer, but rather have static on the line or get garbled faxes too often. The reason to keep data transmission out of he pictue is that they will say there is no guarentee for data connections unless you purchase one and frankly, that’s the job of an ISP or ISDN user who wishes high speed connectivity;^)
Your best hope is that enough people will complain in the same geographical area that the phone company will send their specialist out to investigate, and hopefully, find the problem. The down side of this is… In my experience, I believe we’ve pinpointed two sections of our county that users seem to have problems with drop carriers or poorer connections more than normal, but we’ve not succeeded in seeing them solved after three years of helping people get connected 
distance to the phone company central office,
The further distance from your modem to the closest phone company central office or sub-station the more likely you are to have a poor connection. Technically, there are ways to solve this, but frankly they can get more costly than the average consumer can afford. The best solution is to buy the best modem possible for your connection to your ISP.
Well, this speaks for itself. Can’t do much to prevent it, but your ISP can plan and try to limit it to some degree. Operating systems have to be upgraded from time to time and there may other emergency situations which require a system to be booted. Some ISP’s make their “uptime” stats available which is something to consider when selecting an ISP. Config.Com’s present uptime record for a server is 183 days. As soon as all the servers have their Operating system upgraded, we are going to shoot for a longer record!
other network hardware and software maintenance
This is related to booting servers, but not limited to it. Hardware and software needs upgraded from time to time. You ISP may plan to do this all at once, as grow occurs, or technology is outdated.
Config.Com presently manitains a state of the art network with regard to hardware. A few software upgrades are always being made, but more often than not software upgrades don’t require booting unless it’s an operating system.
Lastly, and very importantly, config.com has designed as much redundancy as possible and will continue to strive for that kind of commitment to quality. Frankly, we haven’t reached the perfection of having multiple T-1 Internet connections, but then I don’t think any other service “to our community” has reached that point either. We have achived a dial-in network design which allows our mail server and radius server to be rebooted without logging users off, because we add the user names and passwords in both our UNIX radius server and our 3COM remote access server.
Security alarm systems
This cause had to be added as it was quite a learning experience for me. We had a user who was getting dropped about every three minutes religiously. When he brought the system into our office, it worked fine. After several months, he telephoned me to inform me that the problem turned out to be due to having his computer modem plugged into the same line that his home security alarm system was on. The bottom line is: If you have a security alarm system, you should not use it for your modem!
It is my sinere desire that this article helps you understand the many causes of dropped carriers and might offer some solutions to help you limit their occurances.
Joe Rinehart,
Operations Designer & Network Administrator
Config.Com, Inc.
124 East Spruce Avenue
Ravenna, Ohio 44266-3048
330.297.9595
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Last Updated on Sunday, 05 July 2009 11:55
