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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.
