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P300H P300 Series Modem Installation and Operating Handbook Page 97
Set G.703 line code: [?]
1=AMI 2=HDB3 (Normal)
Change, Terr-Intfc, Electrical Menu, Line Code (if G.703)
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)
For the first three options the dialogue terminates here, for G.703 it proceeds to the line code selection:
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:
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).