Can you group multiple ERLs under one ELIN?

Answered Question
Feb 22nd, 2008

We have a new building with 6 floors, approximately 200 rooms and an average of 2 phones per room. I have read the CER Admin manual and have started the design for CER. I would like to define each room/office as a single ERL in the building. However, I cant afford to allocate over 200 DIDs to ELINs. My understanding is that the ELIN DID must be a unique DID and not assigned to a phone. So, if my understanding is correct, can I lump multiple ERLs into one ELIN to cut down on the requirement?

This is incorrect. You can have multiple ELINs per ERL, but you can only have one ERL per ELIN. The ERL defines the location to the local emergency authority. Typically you would define one ERL per physical location. If the location is large and can be logically sub-divided, you could define multiple ERLs. In your case, it may make sense to define one per floor or one for the building. You also need to know the local laws for the CER location. e911 legal requirements regarding location identification can be different from one location to another.

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Correct Answer

This is incorrect. You can have multiple ELINs per ERL, but you can only have one ERL per ELIN. The ERL defines the location to the local emergency authority. Typically you would define one ERL per physical location. If the location is large and can be logically sub-divided, you could define multiple ERLs. In your case, it may make sense to define one per floor or one for the building. You also need to know the local laws for the CER location. e911 legal requirements regarding location identification can be different from one location to another.

jeffrey.girard Fri, 02/22/2008 - 09:35

Thanks for your reply, I sorta answered my own question by using a large whiteboard and mapping the flow of an E911 call. However, I still have a question on the return and how the CER can route the call from the PSAP to the originator. I understand that the CER caches a mapping between originator DN and the ELIN used for up to 3 hours. However, on the return call from the PSAP, by using the Xlation pattern, the CER is presented with 913 and 10 digit number via the 913 CTI Route Point. Now, I know that the last 4 digits of the 10 digit number are the key, but how does the CER know that?

jeffrey.girard Fri, 02/22/2008 - 09:46

Got it. I went back and re-read the Admin Guide. When initially setting up the CER, one of the configurations made is to set the digit strip pattern. That reveals the original ELIN which is then bounced against the cache to find the original caller.


Thanks for the help!

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