[VoiceOps] Acme STUN

[Alex Balashov]

Parkin, Tyler wrote:
> Has anybody used the STUN functionality of the Acme SD?  I posed the 
> following questions to our SE and engineer, but if anybody has actual 
> experience with it I’d be curious to know how it works.
> 
>  
> 
> -Does it work? J
> 
> -Re: performance, is STUN less costly than a very short registration 
> refresh rate (<30 seconds)?  Some impact on performance of a fully 
> loaded  SD 4000 would be appreciated.
> 
> -Is it a better solution than their hosted NAT traversal?

No, you'd be better off doing far-end NAT traversal on the Acme.  You 
don't necessarily need to use frequent re-registrations for this if 
you think that it taxes the registrar;  the Acme can, as most SIP 
network elements, send periodic OPTIONS pings to peers to determine if 
they're reachable, which also has the side effect of renewing the 
expiration timer on NAT gateways' state mappings for the UDP pinholes 
created by the registration and/or other activity.

STUN is a giant science project, unless you have tight control over 
the CPE that the customers will use and it is very simple to provision 
it for STUN.  Far-end NAT traversal, on the other hand, will work with 
almost anything.

It is almost certain that the Acme can also do draft-comedia style 
media port detection[1], which is also necessary for far-end NAT 
traversal.

Don't know about the performance metrics, but the ease of 
configurability and standardisation argument points solidly in favour 
of not using STUN, IMHO.  STUN is not a common approach to this 
problem anymore for most service providers - at least, in my 
experience.  I don't think most of my ITSP customers even remember 
what STUN is anymore.

-- Alex

[1]  This is where the RTP port advertised in the SDP body received
      from the NAT'd endpoint is ignored, and the media relay agent
      instead waits to see what the *actual* source port of incoming
      media is before sending any of it sown, because that's where
      media needs to be sent in order to reach the endpoint.  The SDP
      body will advertise the local source port (if the endpoint does
      symmetric RTP, which is generally the case), but the NAT gateway
      will remap it to some other port on the external interface.

-- 
Alex Balashov - Principal
Evariste Systems
Web     : http://www.evaristesys.com/
Tel     : (+1) (678) 954-0670
Direct  : (+1) (678) 954-0671