RE: [Ieprep] Diffserv Code Point for Emergency calls

"GOLDMAN, STUART O (STUART)" <> Sun, 30 October 2005 01:03 UTC

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To: Janet P Gunn <>, "James M. Polk" <>
Subject: RE: [Ieprep] Diffserv Code Point for Emergency calls
Date: Sat, 29 Oct 2005 20:02:44 -0500
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What Janet say is of course exactly correct but only when SS7 is in fact used. If the call is routed to the PSAP via MF trunking this indicator is not present. 

James is correct about the typical use of a small number of trunks for the routing which makes sense if you think about the equally small number of call takers at the PSAP. Having significantly more trunks doesn't help with completion if the limiting factor is the human call takers.

So you are all right! 

Stu Goldman
Lucent Technologies
5531 E. Kelton LN
Scottsdale,AZ 85254
602 493 8438 home office
623-582-7136 voicemail  

-----Original Message-----
From: [] On Behalf Of Janet P Gunn
Sent: Monday, October 24, 2005 5:51 AM
To: James M. Polk
Cc:;; ken carlberg
Subject: RE: [Ieprep] Diffserv Code Point for Emergency calls


The PSTN DOES give emergency (911) calls priority in a small way.

The SS7 signaling messages have an associated priority, called MTP.  When an SS7 "server" is congested, it will shed MTP 0 messages before it sheds MTP 1 messages.

Normal call request messages ( ISUP IAMs) are MTP 0.
Emergency (911), NS/EP. and MLPP call request messages are MTP 1.

Janet wrote on 10/23/2005 11:42:34 PM:

> Reinaldo
> Actually, the PSTN does not give better priority to 911 calls (vs. 
> normal

> calls), they just use separate cirucuits once the 911 call gets to the 
> first Class-5 switch.  Typically, a Class-5 Switch will have a small
> of dedicated circuits that connect directly to a 911 Selective Router 
> (which is a special instance of a Class-5 switch). 911 calls are 
> routed over these dedicated circuits towards the SR to then be routed 
> to the appropriate PSAP. This isn't really anything special - since 
> the circuit world is not bandwidth contending, they are circuit contending.

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