Last week’s article about 56K modems prompted a variety of responses. A few readers praised the performances of their 56 Kbps modems, while others weren’t so lucky. For example, one person reported buying a K56Flex modem because his ISP had adopted that technology. "Wonder of wonders," he writes, "the highest speed attainable for me is 31.2 Kbps! What gives?"
In this case, the fault may lie with the phone company’s wiring. To take advantage of 56K technology, you must have uninterrupted copper wire running from your house through the cross-connect point (your neighborhood wiring hub) to the central office (or CO). If the phone company runs short of copper from the cross-connect point to the CO, they may start using tricks like squeezing two lines onto one, which is fine for voice-quality transmissions, but noisy for high-speed modem communications. For more detailed information, see the FAQtoids later in this issue.
Other readers pointed out many modem manufacturers are hedging their bets with new 56K modems by making them upgradable to whichever 56K standard is adopted in the coming year. Global Village Communications seems to be offering the most flexibility to its customers by selling both a K56Flex modem and an X2 modem, both of which can be flash-upgraded to the new standard.
Jon Rust <[email protected]> wrote to clarify a bit about the FCC-imposed voltage cap on phone lines that limits X2 throughput to 53 Kbps instead of the full 56 Kbps:
K56Flex is not limited to 53 Kbps. X2 is limited, but the developers at Lucent and Rockwell did their homework. They do not break FCC regulations when they run at top speed. Of course, in the real world, you’d never see a 56 Kbps connection anyway. Phone lines just aren’t that good yet. An additional point in favor of K56Flex is the lower latencies. As TidBITS pointed out recently, latency is what’s killing modems. (See TidBITS-367.) With my K56Flex connection, I typically see ping times at around 90 ms. Compared to the 130 to 140 ms ping times from X2 (I’ve heard from several people, but never tried myself) and all 33.6 modems, this is quite an improvement. It’s still short of ISDN though (about 25 ms). Quake is much more playable with 90 ms pings.
For more information on the K56Flex technology, see the Rockwell white paper below, which has moved to a different URL than the one reported last week.