Tomas
Regular Member
imported post
Aaron1124 wrote:
Brief background: Since the early days of telephony on of the built in features of switching systems has been "Line Load Control." At it's simplest in the old systems ALL telephones lines were assigned more or less at random to a "service class." Usually there were three classes, "A," "B," and "C." 20% of the lines were assigned to "A," and 40% to each of the other two classes. "Essential Service" (police, doctors, hospitals, fire, public coin phones, etc.) were given priority to Class "A" assignments.
When the phone system was overloaded or there was a disaster or by government order, "Line Load Control" could be locally activated, and ONLY Class "A" lines would be able to get dial tone and originate calls. (In most of the old Bell System this took 4th level management approval or higher.)
Calls in progress would not be interrupted, and new calls from Class "A" phones could be made to any class phone (assuming it was operational).
As conditions got better, Class "B" and Class "C" lines would be alternated between and allowed dial tone for periods of time. Finally, all classes would be allowed dial tone as conditions warranted restoral.
Modern electronic systems have much finer control, but the ability to restrict service to only the approved Essential Service lines still exists.
(This also applies to cellular devices... See also: http://www.fcc.gov/pshs/emergency/priorityservices.html )
(I my 25 years with the Bell System I was only involved with activating LLC twice - both as a result of system overloads due to natural disaster.)
Aaron1124 wrote:
Just a quick aside, here, from an old telco engineer. It's not OC but it answers the asked question. If you are not interested, please just skip this post. Thanks!
Brief background: Since the early days of telephony on of the built in features of switching systems has been "Line Load Control." At it's simplest in the old systems ALL telephones lines were assigned more or less at random to a "service class." Usually there were three classes, "A," "B," and "C." 20% of the lines were assigned to "A," and 40% to each of the other two classes. "Essential Service" (police, doctors, hospitals, fire, public coin phones, etc.) were given priority to Class "A" assignments.
When the phone system was overloaded or there was a disaster or by government order, "Line Load Control" could be locally activated, and ONLY Class "A" lines would be able to get dial tone and originate calls. (In most of the old Bell System this took 4th level management approval or higher.)
Calls in progress would not be interrupted, and new calls from Class "A" phones could be made to any class phone (assuming it was operational).
As conditions got better, Class "B" and Class "C" lines would be alternated between and allowed dial tone for periods of time. Finally, all classes would be allowed dial tone as conditions warranted restoral.
Modern electronic systems have much finer control, but the ability to restrict service to only the approved Essential Service lines still exists.
(This also applies to cellular devices... See also: http://www.fcc.gov/pshs/emergency/priorityservices.html )
(I my 25 years with the Bell System I was only involved with activating LLC twice - both as a result of system overloads due to natural disaster.)