Black Box 34336, MD885AE-R2, MD885C-R2, MD885A-R3 user manual 122

Modem 34336

NOTE

The ALBX test may result in errors or may fail altogether even where conditions are satisfactory for normal operation. The test channel presented to the modem during the ALBX test includes all impairments of both the inbound and outbound channels (ampli-tude distortion, delay distor-tion, noise, etc.). The main purpose of the ALBX test is to verify that the Modem is connected to the leased line and the leased-line circuit is complete. The test is not meant to assess the suitability of the leased line.

Initiate the ALBX test using the Modem’s front-panel controls, as explained in the following paragraphs.

Make sure the local modem is not in communication with the remote modem, the data rate is the same as the DTE’s data rate, and the DTR circuit is on. (If TR is present on the EIA status screen, the DTR circuit is on.)

From the second page of the LCD MAIN MENU, select TEST. Go to the second page of the LOCAL TEST menu. Select ALBX.

The ANALOG LOOP(EXT) screen is displayed, with ON and OFF as the possible selections.

Select ON to activate the test. In general, the "DSR during ALB test" option discussed in Chapter 2 should be left ON (default selection) to avoid disrupting the DTE and DTE software operations.

The EIA status screen is displayed while the test is being conducted. If no external loopback is present, the status screen displays an IDLE message. If a loopback is present, handshake sequence codes appear (H-01, etc.), followed by the modem speed. Ensure that test data is being generated and watch for data errors. By transmitting test data and comparing it with the received copy, the DTE and modem are checked for proper operation. During the ALBX test, RD (receive data) may appear on the status screen even though no data is being received.

On a flat line, the Modem in ALBX test mode trains and remains running across the following range of signal loss: in V.32 mode, 0-51 dBm (0-52 dBm at 12,000 bps); for V.33 operation, 0-47 dBm; and for Bell 208A/B operation, 0-37 dBm. If signal loss exceeds the limits, the test may not start or may be halted.

During the ALBX test, the modem attempts to retrain upon loss of carrier. In switched carrier mode, the modem attempts to retrain upon loss of RTS.

To end the test, press the ENT pushbutton to return to the ANALOG LOOP(EXT) screen. Then select OFF.

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