Call collision
40830
191945850
2008-02-16T23:01:03Z
Jim.henderson
2255048
Subcat ->teletraffic
In [[telecommunication]]s, a '''call collision''' (commonly known as '''glare''') is one of two things:
#The [[contention]] that occurs when a [[terminal (telecommunication)|terminal]] and [[data]] [[Telecommunication circuit|circuit]]-terminating equipment ([[DCE]]) specify the same [[channel (communications)|channel]] at the same [[time]] to [[transfer]] a [[call]] request and handle an incoming call. When call [[collision]] occurs, the DCE proceeds with the call request and cancels the incoming call.
#The condition that occurs when a [[trunk]] or channel is seized at both ends simultaneously.
If you have ever tried to make a call out on a PBX, and been accidentally connected to an incoming call, you have experienced glare. This can sometimes happen at home too, if you pick up your phone to make a call out at the exact second that a call is about to start ringing in.
[[Multi-line hunting]] generally avoids glare by picking trunks in opposite preference order so the highest numbered line, which is last choice for incoming calls, is first choice for outgoing calls, like so:
<pre>incoming-->1
2
3
4
5
6
7
8<-- outgoing</pre>
For PBX trunks, glare can further be reduced by using [[ground start]] trunking. IE: Nortel BSP discourages using [[loop start]] trunks for this and other reasons. Long Distance exchanges in the 1950s and 60s incorporated Glare Detectors to alleviate the problem.
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[[Category:teletraffic]]