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LOOP-START TRUNKS:
WHEN TO USE LOOP-START TRUNKS
There are two times when you consider the use of loop-start facilities: when you
should
use loop-start
facilities and when you
must
use loop-start facilities.
Proper Loop-Start Facility Applications
If loop-start facilities are prone to problems such as glare why are they still in use?
Most of the problems associated with loop-start facilities only come into play with automated PBXs.
Loop-start facilities are perfectly acceptable for use with single-line telephones, key systems, and manual
(cordboard or switchboard) attendant operated PBXS.
3
Some PBXs, especially those that cannot be
administered by the customer, can operate properly with with loop-start facilities for one-way incoming and
one-way outgoing trunks, that must be handled by an attendant.
Besides, the cost of converting all of the loop-start customer and CO equipment currently installed to
ground-start operation would be an incremental expense.
Note:
Loop-start trunks
are not recommended
for use with the MERLIN LEGEND configured for PBX
mode operation. Ground-start trunks are
always
preferred.
Unavoidable Loop-Start Facility Applications
One situation that will require the use of loop-start facilities on the LEGEND system would be the
connection of Centrex lines to the PBX. In some regions, Centrex is also called Essex or Centron lines.
Most operating companies will provide Centrex service only on loop-start facilities. Some operating
companies may consider converting the lines to ground-start facilities as an extra-cost special assembly, but
this is at the operating company’s option. Currently, the LEGEND system does not support the use of GS
Centrex.
Consider the case of a state government. In the early seventies the state linked all departments, large and
small, in one Centrex system in order to control inter-departmental message unit expenses. The individual
departments terminate their Centrex lines in large, non-uniform key systems.
Now, departments like Motor Vehicles and the State Police, have grown to the size of small companies and
occupy their own buildings. The Centrex is no longer capable of providing efficient internal
communications for the large departments, and traffic demands from large departments are swamping
service to smaller departments. The state would like to keep Centrex for convenient interdepartmental
calling without message unit charges. The larger departments, however, need PBXs like the LEGEND
system to take the load off the Centrex and for better internal communications. The local operating
company will only provide Centrex service on loop-start facilities. In this case, some loop-start Centrex
lines will terminate in the Legend system. Glare may occur on the Centrex lines. In general,
ground-start
facilities are always preferred.
3. Some true manual PBXs are probably still present in the field. but you are not likely to encounter one during the installation of a
modern PBX. On a true manual PBX all calls, both incoming and outgoing, must be handled by an attendant. there is no way to
dial a code such as “9” for an outside line. h is this close supervision by the attendant that makes loop-start facilities acceptable for
use with manual PBXs.