Recommendations for Trunk Descriptor Settings
For best performance, analog trunks to the local exchange or Central Office should operate
with an attenuation in the range of 0 dB to -8 dB. Higher attenuation will degrade the signal
(both acoustic and DTMF dialing) and may make some connections, such as long-distance,
difficult to use. Short loops provide the best performance.
The following trunk descriptors are recommended based on the amount of attenuation
presented by the trunk line:
Table 20: LS Trunk Specifications
Trunk Functions Parameters
Min. operating loop current 18 mA
Max. operating loop current 100 mA
Reversal detector Detects CO battery polarity
Loop detect for CO disc. (no battery) < 2V across Tip and Ring
Ring Detect Threshold ASU ASU II AMB
for Ringing Frequency = 20 Hz 16 Vrms 30 Vrms 30 Vrms
for Ringing Frequency = 25 Hz 16 Vrms 25 Vrms 25 Vrms
for Ringing Frequency = 50 Hz 16 Vrms 20 Vrms 20 Vrms
Table 21: Attenuation Levels for Short and Long CO Trunks
Trunk Category (CO Trunk Circuit Descriptor form) Attenuation on Trunk Line
Short 0 dB to -3 dB
Long -3 dB to -6 dB
Long
(some additional signal loss will occur with lines of this
length)
-6 dB to -8 dB
Caution: Near maximum
attenuation
Long
(additional signal loss will occur with lines of this length;
some connections will be difficult to use)
Greater than -8 dB
Not acceptable
Extra Long
(this setting is valid when used with AMB/AOB or AX/ASU II
LS trunks)
This setting should only be used in situations where the
attenuation on the trunk line is greater than -8 dB and the trunk is
presenting usability problems.
This connection provides additional gain with respect to the Long
setting, but this additional gain is only applied on the signal
transmitted from the CO to the ICP. This setting is identical to the
Long setting for signals transmitted from the ICP to the CO.
Greater than -8 dB
Not acceptable
Note: Use the LSMeasure Tool to determine the line settings for Loop Start (LS) trunks that are
connected to an Analog Board in the controller, to a Universal ASU, or to an ASU II. Refer to the 3300
ICP Technician’s Handbook or the System Administration Tool online help for details.
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