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THE DIGITAL LOSS PLAN
switch will have value only after verification of this switch’s port-to-port loss specification.
Conformance with ANSI standards greatly simplifies this process and reduces the likelihood of
compatibility problems.
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The loss between switches is 0 dB over digital facilities, 1 dB for combination facilities, and VNL
for analog facilities.
If the losses in a switch network have been verified correct and specific problems associated with
the loss plan remain, the appropriate transmission engineering organization should be consulted.
DS1/DMI/ISDN-PRI PORT LOSSES
All DS1/DMI/ISDN-PRI circuit-pack channels, regardless of the type of port for which they are used,
are transparent (zero loss) and preserve digital bit integrity. All connection losses are inserted in the
switch network in conformance with the digital loss plan and dependent on switch administration
options.
TERMINATING A DS1 AT A CHANNEL BANK
The DS1/DMI-BOS channels that leave the switch in digital form and are converted to analog form
by a channel bank are called combination channels. Three basic types are described below.
Tie Trunk Ports
To obtain the required channel unit losses for combination tie trunks, extended-range E&M channel
units (or their equivalent) should be used. The attenuators on this channel unit are set as follows: the
transmit (A-to-D) attenuator should be set to (15.5-Lc) dB, where Lc is defined as the loss in the
interconnecting cable between the channel bank and the analog switch, and the receive (D-to-A)
attenuator should be set to (12.5-Lc) dB, where Lc is as above. Setting the channel unit attenuators
to these values will meet the requirement for combination tie trunks. This requirement specifies a net
gain of 2 dB in the A to D direction and a net loss of 4 dB in the D to A direction.
CO DID Trunk Ports
Digital ground-start CO, loop-start CO, and Direct Inward Dial (DID) trunks may (optionally)
terminate on channel banks located at a CO. If this is the case, it is the CO's responsibility to set the
channel unit losses. As a guideline, the net loss should range from 1 to 3 dB. Also, the loss should
be the same in both directions.