I have been working to deploy a new private WAN for a customer that
services E911 emergency calls delivered over VoIP. While working on
this, I learned that their DSCP markings for SIP control traffic are
AF12, not AF31 or CS3 which is what I typically see from our other
enterprise customers. Media is still marked EF.
These markings appear to have been standardized by a body called NENA,
National Emergency Number Association. Googling 'NENA SIP "AF12"'
returns the relevant PDFs. Below is a sample from their standards
guide.
DSCP | Use | PHB
-----+----------------------------------+--------
0 | Routine Traffic | Default
1 | 9-1-1 Signaling | AF12
2 | 9-1-1 Text Media | AF12
3 | 9-1-1 Audio Media | EF
4 | 9-1-1 Video Media | AF11
5 | 9-1-1 Non-human-initiated Call | AF21
6 | Intra ESInet* Events | AF21
7 | Intra ESInet Other 9-1-1 Traffic | AF22
(* Emergency Services IP Network)
Does anyone know the reasoning behind specifying SIP as AF12 instead of
AF31? While developing these standards, was NENA aware that AF12 tends
to be prioritized lower than AF31 on most networks?
Just trying to get some background on the decision.
Thanks,
-Brian
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