Paradise P300 specifications Set G.703 line code ? 1=AMI 2=HDB3 Normal

For the first three options the dialogue terminates here, for G.703 it proceeds to the line code selection:

Set G.703 line code: [?] 1=AMI 2=HDB3 (Normal)

Change, Terr-Intfc, Electrical Menu, Line Code (if G.703)

For E1 G.703 the line code selection is as shown above (AMI=Alternate Mark Inversion or HDB3=High Density Bipolar 3). For T1 G.703 the line code selection is between AMI and B8ZS (Binary 8 Zero Substitution). In both cases the NON-AMI option is most common so select this if in any doubt.

The NON-AMI options for T1 and E1 are both different means to achieve the same objective, which is to limit the number of contiguous zeros which may be transmitted on the G.703 line. This is necessary with G.703 as with AMI a `mark` (logic one) is sent as a pulse on the line, and a `space` (logic zero) is set as the absence of a pulse on the line. If there are too many contiguous spaces the G.703 receiver fails to recover the clock properly (as there are no incoming pulses for a while) and it causes data errors. HDB3 and B8ZS are both methods of ensuring that no more than three or eight zeroes respectively occur on a G.703 line by substituting strings of more than this number of zeroes with another code, in turn this code is detected at the end of the G.703 line and replaced with the correct number of zeroes again.

If the line code is set incorrectly you will almost continuously see “Tx Warn: Tx line code violations detected” which indicates the modem is receiving line code violations and most probably set for AMI but receiving a B8ZS/HDB3 coded signal. Intermittent occurrences of the warning however are more likely to be caused by line noise corrupting the signal. Note that if the modem is incorrectly set for B8ZS/HDB3 and the other equipment expects AMI, then there will be no warning on the modem.

Finally, and only for T1 G.703 cards the following screen is shown:

Set T1 line length: [?]ft

1=<133' 2=<266' 3=<399' 4=<533' 5=<655'

Change, Terr-Intfc, Electrical Menu, Line Length (if T1 G.703)

This screen allows the signal to be pre-compensated to cope with differing lengths of standard `ABAM` cable. We would suggest you select option 1, less than 133 feet by default (no compensation).

P300H P300 Series Modem Installation and Operating Handbook Page 97