|
|
 |
 |
 |
|
|
|||
|
||||
|
||||
Re: 56 kbs modemsFrom: Dean Huffman (perinatl@slip.net)Sat Dec 27 11:36:34 1997
A couple of points about 56 KBS modems. 1) The modem can transfer data at 56 KBS in only one direction. Since the data flow is usually greatest from ISP to user (unless you are operating a server of some sort), the modems are set up so that data can flow at 56 KBS from ISP to user (not the other way around). 2) Clearly, the ISP has to have 56 KBS modems at their site in sufficient numbers to handle the calls that come in. If the caller is connected to a 28.8 (or 33.6) modem, then the maximum data transfer in either direction is 28.8 (or 33.6). Many ISP's do NOT provide 56 KBS. I believe AOL falls into that group although they are upgrading. (Hey, they have enough trouble even at 28.8!) Others charge extra for 56 KBS, some as much as $6.00 per hour. Some provide it at no additional charge. 3) There are two 56 KBS protocols, X2 and KFlex. The user and the ISP have to both be using the same protocol. Otherwise the data flow will fall back to 28.8 or 33.6. Some providers have both protocols, but give different phone numbers for each. It is possible (but I do not know whether it is being done) that the ISP could automatically switch calls to the appropriate modem depending upon which protocol the caller is using. 4) There will be a new, protocol, probably this summer, that will become the international standard. It will probably not be compatible with either of the existing protocols. If you buy a new modem, be sure that it is made by a company that will promise a free upgrade (and by a company that is likely to still be in business this summer). 5) Because of FCC restrictions on amount of decibels that can be used on American phone lines, 56 KBS is really functional only at about 48 KBS. It will never reach 26 KBS until the FCC changes its regulations. 6) Phone lines might not be of sufficient quality to support 56 KBS modems. Major modem manufacturers offer "800" numbers you can call with your 28.8 or 33.6 modem to "test" whether or not your local phone company will be able to support 56 KBS. Local phone companies can fail to support 56 KBS for multiple reasons. 7) The 56 KBS protocol works because of certain digital to analog (D to A) conversion characteristics at the local phone company. "Analog" telephone signal are carried in analog fashion only between the local phone company and the home, the so called "last mile". The remainder of the phone call, whether it be between switching stations in the same local community or between stations across the country, are carried as digital signals at 64 KBS. (Twenty-four such lines make up the so-called T-1 line which can carry digital data at approximately 1.5 MBS or mega (million) bits per second.) When the signal is converted from digital back to analog at the local switching station, a signal is created that the 56 KBS modem can read at (or close to) that speed. If there is an intervening analog to digital conversion (e.g., as in a office or hotel PBX) then the 56 KBS advantage is lost and the signal falls back to 28.8 or 33.6, which is why 56 KBS modems generally do not work in hotels and motels. 8) There is at least one company that claims to be able to transfer data at 63 to 64 KBS (in one direction). They are promoting a system whereby the user sets up TWO such modems and two analog phone lines, and the ISP does the same. One modem works at 64 KBS for INCOMING signals and the other for OUTGOING signals. Hence one can have up to 64 KBS going simultaneously in both directions, or about 96 KBS (33.3 + 63) going in one direction. There is special software that splits the signals between the two modems on each line. The advantage? Near ISDN speeds (two B lines) for the cost of two analog lines. Since ISDN is grossly overpriced in most markets, this can make for big savings. For more information about ISDN, do a search on your favorite search engine or check out: http://www.microsoft.com/windows/getisdn/whatis.htm 9) There are a number of new technologies coming up to compete with 56 KBS and ISDN. Some are expensive, some are inconvenient, and some are very spotty in availability. Some, however, may provide a significant improvement over POTS (plain old telephone service). One is ASDL that can provide 2 - 4 MBS data rates. It uses ordinary telephone lines. At each end there must be a special unit, called a CSU/DSU, similar to a modem. Some LBOC's (local Bell operating companies) are gearing up to offer it. (If you can get your phone company to install a "burglar alarm line" from your home to the ISP, and if both are close enough to the same telephone switching station, and if they will install a CSU/DSU, you can get T-1 or better rates. This is a well kept secret -- the phone company does not want you to know about this. There are "cable modems" that provide very high data rates, but are still in the developmental stage. If you are willing to set up a satellite dish, for $19.95 per month (after the dish is set up) you can get 200 KBS incoming data by satellite, after 5:00 PM in the evening (until ?? 8:00 AM ??), and all day weekends and holidays. The catch is that you have to have a second ISP to take your outgoing calls at 28.8 (they cannot go through the satellite). Hence, after set-up, it actually costs $39.90 per month. However, you do not have to depend upon having cable or high quality phone service nearby -- it works from anywhere that you can receive the satellite signal. The problem is that the outgoing call to the local ISP might be a toll call (for those who live in the boonies). There are other services begin set up such as radio (Ricochet), etc. 1998 or 1999 should see significant increases in internet availability.
>Hi: The limit is the maximum bps of your internet service provider. I
-- ================================================================== Dean G. Huffman Phone: 217 787-3745 FAX 217 787-0680 (Home) perinatl@slip.net 217 782-9666 217 524-2432 (Office)
|
|
Return to
|
Mail a New Message to the Forum: ob-gyn-l@obgyn.net Forum Administrator: geffrey.klein@obgyn.net Report Technical Problems: webmaster@obgyn.net Last Updated: Wed Dec 2 05:22:32 2009 |
The American Medical Association is no longer designating CME hours for AMA Category II CME credit. However, physicians themselves may self designate learning activities as Category II CME credit hours if they feel it is of sufficient educational merit and meets the formal definitions of continuing medical education. OBGYN.net believes these interaction in this forum meets these criteria. For further information see the AMA web site.