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PCI-RAS General Questions
Do I need any special phone line to use with my modem connection?
The most common modem connection problems with analogue modem connections are phone line related. Check your phone line. Today's phone lines were initially designed to carry analogue voice signals, not digital data. Modem devices enable data to be transmitted over these lines by converting (or MODulating) the digital data streams from the computer into an analogue form that can be sent down a phone line. At the receive end of the line the modem then DEModulates these analogue signals coming in from the telephone line, reconverting them back into data. Unfortunately, the faster information gets transmitted down the phone line, the more susceptible the whole process becomes to line noise. Today’s V.90 modems requires good quality, low noise phone line connections to be able to consistently transfer data at 53Kbps. Poor connections and noisy lines will degrade the performance of the modem connection.
Modern modem technology is sophisticated enough to deal with this degradation gracefully. When presented with a noisy line connection, the modems at each end renegotiate the speed at which they transmit and receive data. The result is a drop back in connection speed. The success of this process is largely dependant on the quality of the modems at each end. Also if the noise is sporadic or comes in bursts, then data being sent over the line may be corrupted during transmission. The modem receiving the data will detect the damage and request the transmitting modem to resend the information. The result is that while the reported connect speed of the modem may remain high, the actual data transmission speed may be significantly reduced due to the continual need to resend data.
In the worst case, a poor line connection will cause the modems to disconnect from the line, or it may prevent the modems from establishing a connection at all. Different modems are better at dealing with noise than others, and again cheaper lower quality modems can exacerbate the problem. So if you having connection problems the first step always is to check your phone line:
· The phone wiring within your premises can effect on your Dial Up Networking and Internet modem connection. It is worth trying to eliminate sources of line noise. Listen to the phone line during voice conversations. Does the line sound clear?
· Sometimes the noise can originate in your own home or office. If you are using a long phone extension cord, try a shorter one. Make sure the phone line is not near any potential noise source, such as a monitor. And don’t operate your computer with the case open, as the case shields the noise created by the computer. Other noise sources could include desk fans, fridges, washing machines — the list goes on. Finding the source of noise is basically a process of elimination. Make sure the modem is at least three feet away from any fluorescent lamps. The electrical static generated by the fluorescent light may interfere with your modem connection. Electronic dimmers also radiate signals. Make sure these are off, or at least at full intensity.
· Problem can arise when you have other equipment on the same phone line as the modem. Avoid using a line splitter, a duplex adapter, a coupler or anything other than one continuous cable between your wall jack and your modem. Try disconnecting any other telephones, answering machines, fax machines and modems on the same phone number to see if performance improves. You may have, for instance, a poor cable on a telephone handset that doesn't stay entirely "on hook." A single uninterrupted connection between the jack and the modem often improves performance.
· Interference can come from the oscillators or transmitters in radios or television sets being near your modem. Some cheap modems (and televisions) are not properly shielded when manufactured. If you notice problems when a television is turned on or when a radio transmitter is activated, then you have a shielding problem. Monitors can also emit significant electro- magnetic fields. This can also interfere with an improperly shielded modem. Never place a modem on top of a TV or video display monitor. If you suspect this type of interference is causing your problem, try orientating the modem and its cables in different positions to see if that helps.
· Placing an internal modem close to a source of internal computer radiation can induce problems into the modem's phone amplifiers. Try moving the modem to another PC slot to minimize this problem. Make sure your computer equipment is FCC Part 15 approved. This means that the computer and components have been tested and meet standards that insure your equipment will not adversely affect the operation of other electronic devices (such as modems, computers, TV's and radios).
· Avoid using modems on phone lines that are switched through your office PBX as this can cause problems.
· If you have call waiting on your telephone line, disable it.
· If possible, try your modem on a computer in another location, or try someone else’s modem on your computer. Try dialing another ISP (perhaps using a free introductory offer kit).
· Sometimes faults at your local telephone exchange can cause connection problems. In such a case the quality of the connection will vary. Hanging up and redialing usually fixes the problem. However, in this instance the consistency of your problem would suggest that this is not the cause. Lastly, if you've established that phone line inside your office are satisfactory but the line performance still is a problem, then call your telephone company and get them to test the state of your telephone lines. Most carriers undertake to make all their lines capable of at least maintaining a 9600-baud connection.
· Selective interference can occur when you call only certain numbers or exchanges. Your telephone company routes signals from local exchanges/central offices to other exchanges/central offices. Sometimes certain exchanges cannot connect to others without line noise problems. If you see a pattern like this, notify the telephone company of the problem. Cross-talk on a telephone line can cause serious modem communication problems. Your telephone company is obligated to check out service problems that can be specifically isolated to certain exchanges or conditions. Do not be put put off if the telephone company tries to sell you a digital (e.g. ISDN) service or a dedicated (leased) line as the solution. They generally have an obligation to provide a basic level of service.
My modem dials out but it won't successfully complete the connection.
There are a number of problems that can prevent your modem out dialing successfully:
· If your modem fails to make a particular connection then the problem may well be with the telecom line or with the modem at the other end. Retry making the connection (and if possible try making the call with a standard phone connected to see if you can establish a voice call over the line).
· Sometimes problems arise because of incompatible modems at each end. In theory all modems meet the international telecommunication standards and they can be assured of speaking to each other. With popular name brand modems this is the case. However there are many cheap modems on the market that may not reliably interconnect.
· Also check the modem configuration at the other end. If the modem at the other end does not have error correction then you will need to disable error correction at your PCI-RAS end by issuing to each modem port:
· Another common problem with failure to connect is timeouts. High-speed modems can require a long time to recognize, negotiate and properly connect to other modems. Ensure you are allowing at least 60 seconds per call attempt. Also set your modems S7 register to = 255. By default, S7 allows only 30 seconds of waiting before disconnecting. Setting S7=255 allows your communication program to have complete control over the process.
Problem: My modem link looses data with high speed connections
This problem can have a number of causes:
· The most common is a poor dial up connection so redial and check the line condition.
· Ensure that your modem and dialer program are also using hardware flow-control (RTS/CTS ON).
· For Wave modems make sure the modem cable you are using supports hardware flow-control.
· Set the COM port speeds to run at (or faster than) the maximum modem connect speed. e.g. 38400 is a good port speed for a 33.6kbs modem links but use 155kbps for 56K connections.
· For Wave modems ensure the serial port it is attached to has at least a16550 serial UART device.
Will my modem work with call waiting?
Unfortunately the tones generated by the exchange to inform you that another call is coming in, will interfere with the modem communication, and may drop the connection. To get around this problem simply turn off Call Waiting on your phone before you dial out with your modem.
To turn it off select the Modem device in the Control Panel. Then in the Dialing Properties add the command to turn off call waiting to your modem's dialing string by checking Disable Call Waiting. This will prevent call waiting from hanging up your connection!
In USA the general command to add to your dial-up string is *70, (i.e. asterisk 70 comma). In Australia the general command string is *43# (i.e. asterisk 43 hash) and to turn the Call Waiting back on just dial ‘*43#’ when you are finished. If you are unsure check with your telephone company or a phone book for the appropriate command characters.
If possible, try your modem on a computer in another location, or try someone else’s modem on your computer. Try dialing another ISP (perhaps using a free introductory offer kit).
Can I use my modem through a PBX?
PCI-RAS modems were designed to be used on the standard 2-wire analogue PSTN telephone system. If your PBX conforms to this specification for its internal lines then the modem will work properly. Most PBX’s also require you to place a ‘0,’ or a ‘9,’ in front of the number to get an outside line.
PCI-RAS modems will not work on Digital PBX systems and may be damaged if connected to such a network.
How do I determine if my modem supports fax Class 1 or Class 2?
All current models of PCI-RAS modems support both fax Class1 and fax Class 2. However the Rockwell modem chip hardware and firmware used in these products sometimes only offer fax Class 1 support (particularly the early revisions of new releases). To determine the fax capabilities of your PCI-RAS modem, access the port using a terminal emulator program (e.g. HyperTerminal in Programs/Accessories in Windows NT/95/98) or use cu under Unix, and issue the following commands:
If the modem is a Class 2 modem, then you can issue further AT commands to determine the fax microcode revision etc.
Can other PCs on the network share my PCI-RAS multi-modem to get online to the Internet or send faxes?
Yes. If your modem is installed in a PC running Windows 95 or Windows98, you will need to install third party software to do this. Windows 95/98 does not offer offer any modem pooling, modem sharing or proxy server gateway facilities. If your modem is installed in an NT server then you can set up RRAS (routing and remote access service) to allow other PCs to access the Internet through the modem link on your PC. However no support is available for modem pooling or modem sharing.
One way to enable PC's on your network to share the Internet modem connection on your PC, is to set up your PC as a proxy server. Proxy server is an application that will let your PC act as a server that all the other PCs on the network can use to get online to the Internet. All the other PCs will then use your PC server as their gateway to the Internet. There's a wide selection of proxy server and gateway software available. Popular packages include MidPoint, WinProxy and Wingate . Many others can be found at ZDNet Software Library. The most popular package for small networks is Wingate and for a two PC network it is free!
One hidden cost with gateway software is the fact that the proxy server application can place a huge burden on the PC with the modem. Often this load necessitates the PC server being as the gateway to the network - running no other applications. Also the gateway solution will allow all the PCs on the network to route their Internet traffic through the proxy server's modem link to the ISP. However it does not allow the PCs to have more general access to the modem. Some PCs on the network may need to run other dial-out or dial-in communications software (e.g. to dial the local bank branch for electronic banking). Modem sharing is not a service offered by proxy server software.
Modem polling or modem sharing is the other alternative to allow all the PCs on the network to access the modem on your PC. With modem pooling any PC can effectively claim use of the shared modem on your PC. One user at a time. All the communications software is running back on the PCs that is using the modem, so the load on your PC is minimal. The most popular modem pooling package is SAPS (SpartaCom Asynchronous Port Sharing), which allows peer to peer sharing of COM ports between LAN workstations. Another popular package is WinPool from Moreton Bay. The freeware version will allow an unlimited number of users to access a single modem on the network.
What is Data Compression? Error Correction? Flow-Control?
Data compression is a system by which the modem tries to compress the data before sending it via the phone line and thus improve the throughput of the transmission. PCI-RAS modems use the ITU-T V.42bis protocol for data compression. It can give a throughput increase of up to 400%. This means that although for a modem that can only go as high as 33600 bps on the telephone line, you can achieve theoretical effective speeds of 115,200 bps. In most cases with normal files that have not been compressed already you can get reliable transmission rates of about 50,000 bps.
Error correction is a system by which modems try to eliminate errors on the line. The data is encoded in a certain manner that allows errors to show up clearly. When this happens the modem will automatically ask the other end to resend the data. This helps to ensure error free data transfer between devices. A by product of this encoding is that the modem makes more efficient use of the line and can thus get up to about 110% of rated raw throughput from the modem. PCI-RAS multi-modems support the ITU-T V.42 specifications for error correction protocols.
Flow Control is like a set of traffic lights between the modem and the computer. Because the modem does not know what the computer is doing at any given time and vice versa, there needs to be a system in place to let each other know when they are busy. Flow control allows the computer (or modem) to stop the flow of data while it is busy doing other operations and then start it back up again, thus not lose any of the data being sent.
There are 3 types of flow control in common use at the moment. They are No flow control, XON/XOFF (also known as Software) and RTS/CTS (also known as Hardware). All high-speed modems require a form of flow control whether XON/XOFF or RTS/CTS. The Banksia Wave modem defaults to RTS/CTS as it is deemed to be the most reliable. PCI-RAS modem ports are all hardwired with RTS/CTS. The PCI-RAS communications engine manages this flow control at the chip level on the card - so there is no chance of losing data.