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Setup | >> MODEM V90 <<
Q: What is V.90? A: V.90 is the new official ITU international standard for "56K" analog modems. Previously there were two competing proprietary 'defacto' standards-- K56flex (from Rockwell) and X2 (from 3COM/USR). Recently introduced is also "V.92" which offers quicker connect times and useful, faster upstream connections if you are transmitting lots of data.
Q: Which modem should I buy? A: Buy a modem that is V.90 or V.92 compliant now. And buy one of the top name brands. They are already in the stores. Do not buy a no-name or "house brand".
Q: How fast are V.90 modems? A: With a reasonably good phone line and if you live within 3 1/2 miles from your central office (local phone company building), you should get connect speeds between 40K and 53K. See our Speed charts. Some lines have impairments on them, like digital pads or robbed bit signaling (RBS), which decreases the highest achievable speeds. However if you are getting pretty good V34 connections, you should be able to significantly benefit from a V90 modem.
Q: If these modems can't really connect at 56K, why are they called 56K? A: It was an unfortunate misnomer. The FCC limits legal speed on the Telephone network to 53Kbps. Actual speeds vary according to your phone line conditions. (...your actual mileage may vary)
A: This is to insure compatibility with your existing ISP. When your ISP upgrades their modems, your modem will be able to switch automatically into V.90 mode, but for now will continue to operate in K56flex or X2 mode. This is important for the near future. The new modem you buy should support TWO 56K protocols, V.90 plus another, because ISP's are running X2 or K56flex right now.
A: If you have a V.90 modem, and your ISP has deployed V.90 equipment, yes (Virtually all ISPs now support V.90, though few support V.92).
A: Make sure you are calling a phone number that has a compatible 56K modem at your Internet Service Provider. Some phone numbers only have V34 modems on them and you cannot get 56K speeds calling these. Also, make sure you are calling a compatible line. If your ISP has K56flex running, you will not be able to get an X2 modem to connect at K56 speeds and visa versa.
A: Many homes and businesses are attached to the central office by a "SLICK" or "Subscriber Loop Carrier" system, such as SLC-96 or SLC Series 5. If such a system is present, the line from a subscriber's phone first goes to a SLC "remote terminal" (which is typically in an underground vault in the neighborhood, in the basement of the office building, etc.). At that point the analog signal is converted to 64Kbps digital; then 24 of these are put on two pairs (one for sending, one for receiving) and then this goes to the central office. At the central office there are several ways of attaching to the switch, but in so-called "universal SLC", the 24 signals go to a "CO-terminal", where they are demultiplexed and converted back to analog before attaching to the switch. A SLICK creates a D to A conversion then an A to D conversion. The later A to D conversion will not allow you to get 56K (PCM) rates. None of the protocols (V.90, K56Flex or X2) will give you 56K rates with the extra A to D conversion.
Q: Don't modems need 10 bits to transfer a byte (at least with the normal 8N1 settings), so the speed of a 33600 bps modem is actually 3360 bytes per second? A: No, this is a common misconception. The 33600 speed is the DCE speed which is the speed between your modem and the modem you are calling. This is an analog connection and there are no start or stop bits. The DTE speed is the speed between your PC and your modem. If it is an external modem, it is the speed of data transfer over the serial cable connecting your modem to your PC. Serial connections do have start and stop bits, but since the DTE speed is usually 115200 bps it is not a limiting factor over the DCE speed.
Q:
What advantages does v90 have over X2 technology?
A: I recently bought two Logicode 56K bps (using x2) modems at a good price. They are Quicktel model 56W-P modems that are supposed to be software upgradable to the new V.90 ITU standard. My dilemma is that Logicode has gone out of business! Will there be (or is there now) a "generic, plain vanilla" software upgrade for X2 modems to the V.90 standard? US Robotics has a download for their modems, but it doesn't work with other manufacturers' modems. Will anyone (ITU, for instance) be offering such upgrades to us unfortunates?
Q: What kind of performance can you expect with v.90? A: With a reasonably good phone line and if you live within 3 1/2 miles from your central office (local phone company building), you should get connect speeds between 40K and 53K. Some lines have impairments on them, like digital pads or robbed bit signaling (RBS), which decreases the highest achievable speeds. However, if you are getting pretty good V34 connections, you should be able to significantly benefit from a V90 modem.
Q: What is the basic requirement that is needed to upgrade to v.90 standard? A: --Flash --Most vendors have promised to deliver software upgrades for their modems.
Q: How do I update my K56-Flex or X2 modem to run v.90? A: For most modems, simply download the flash utility software and upgrade.
Q: Will upgrading to v.90 make my X2 modem K56-Flex-compatible or make my K56-flex modem X2-compatible? A: No.
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