ISP Information:
This allows for the appearance of light reflecting off an object when represented on 3D computer graphics. White or light-colored pixels are blended into darker areas to provide these highlights.
ISP Glossary:
Specular Highlights - lars.homlung@semcon.com (Lars Homlung) wrote:I did some modem tests on a network to a company that had someproblems when they used V.90 and V.34 modems. I did some changes tothe network, and to see how clean the connection was I run the modemsin buffermode and disabled the error/ flowcontrol. I got a cleanconnection on the V.34 and on 40000 with the V.90 modem, but if I usedhigher speeds on the V.90 I got some bursts (0.01% when I run trafficfor 20 min). I have tried to find out why this happens and I haven'tfound a direct answer but I think it's because of the high samplingrate and/or that the analog and the digital modem are doing somespeed/level negotiation.The sampling rate is the same regardless of the speed. And almostcertainly it isn't due to speed/level negotiations.The higher the speed the more unique values have to be recognized,which means finer granularity in the PAM signal. That makes, atthe lower voltage steps, the noise on the cable much more significantat higher speeds than at lower speeds. Another factor, which ishard to estimate, might be the quality of the codec in the telco'sline card for any given line. The telco installs thousands of linecards, and has no need to use high quality codecs that are intendedfor low error rate data! Instead they save thousands of dollars byusing codecs that are good enough for voice grade... which meansthat some of them are probably very good, and some aren't. Henceit is possible that what you are seeing is also nothing more thanvariations in the output voltage from the telco's codec.Whatever, given a 50666 bps connection, I'm hard pressed to seewhat point there is in wasting time figuring out why it isn't fasteror less "noisy". To put it mildly, you have a fabulous line.--Floyd L. Davidson Ukpeagvik (Barrow, Alaska) floyd@barrow.com
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