ZyXEL Elite 2864 User Guide - Page 211

cal modem both provide V.54 Remote Digital Loopback capability. The Control Level field of the LCD screen of the initiating modem will indicate RLBST, and that of the accepting modem will indicate LDL. This test can be initiated by either modem when the modems are on-line. Local Modem DTE A C Transmitter Receiver RLBST B ~~~~ Remote Modem Transmitter B A Receiver LDL Line Condition Status Display The screen displays of this section only apply to the LCD models. Regarding data being transmitted over telephone line circuits, there are many kinds of line impairments that can affect the data being received by the remote modem. The 2864 modem can measure four major line impairments. From the impairment readings, you can understand the current line condition. The 2864 also logs line events over a long period, so you know what the line condition has been. We will describe these readings and logs as follows: > PJ= 0.4 FO=-0.6 Note: The readings displayed are just for reference and not to be taken for measurements. Signal to Noise Ratio (S/N) This reading is expressed in 0.1 dB resolution. The higher the speed, the higher the S/N ratio required. The modem measures the S/N ratio by measuring the distance between the demodulated signal point and the ideal signal point. For V.32/V.32bis, the modem-measured S/N ratio is generally about 2 dB higher than what is actually on the line because the modem rejects some of the out-of-band noise. For V.22/ 22bis, the difference can be as high as 8 dB because the modem only uses part of the 3KHz bandwidth and rejects more than half of the voice band noise. 18-5