[asterisk-users] PJSIP call Delay DNS/Realtime

Nick Olsen nick at floridavirtualsolutions.com
Thu May 16 12:52:42 CDT 2019

Hello all,

I'm migrating a box from PJSIP with normal Flatfiles to ODBC/Realtime, Also 16.0.1 to 16.3.0. After adding a few peers to the new RT box, I noticed a delay in call processing. All I had done thus far is added a few endpoints for upstream carriers, And one downstream for the legacy PBX it was replacing. After a bit of troubleshooting I found the issue to be related to having the identify section matching a domain name (Instead of an IP). Each endpoint with match=domain.name.here (The specific name didn't really matter) added a bit of noticeable latency. Once you were up to 4-5 of them, It was a ~5 second delay from the time the invite came in until the time the call was routed and stood up with audio. Even when you were routing between unrelated (non-dns matched) endpoints. Looking at the debug logs, It seems like Asterisk looks these peers up on some kind of time interval. As well as during _every_ inbound call. This also explains why the delay increased with every single DNS based endpoint I added. Each extra peer means another DNS lookup and process.

To further test my theory, I stood up a local caching DNS resolver and this significantly improved the delay. But it was still ~1 second with 5 DNS based endpoints. Even with a caching resolver, This doesn't scale. Doing a large number (and growing with scale) of DNS lookups for every call (Maybe even every packet) just doesn't fly.

So my questions are:  
1. Anyone have any idea why asterisk does this when using realtime but NOT when using flatfiles?
2. Is there not a way to cache this in Asterisk without having to do a DNS lookup every time?
3. Any other tweaks I can make to asterisk to speed this up (Not really looking to match based on other objects, like header or username).

Nick Olsen
Network Engineer
Office: 321-408-5000
Mobile: 321-794-0763

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