> 1) The help text on the new NAT traversal page instructs
> the admin to open ports on the firewall used by the Media
> Relay. Where are these ports configured and where can I see
> what the currently configured range is?
I will let Ranga field that one.
> 2) As far as I understand the media relay used by NAT traversal is
> shared with sipXbridge.
Correct. BTW, the Media Relay function is called the Symmitron (tm) :)
> Is it a requirement for the the NAT traversal
> feature to work that an instance of sipXbridge is configured on the
> SBC page?
No, the sipXbridge which includes the Media Relay function (the
Symmitron) is started automatically at start-up even when it is not
configured as an SBC. This is analogous to the call park server being
launched even when no park orbits are defined.
> If so, sipXconfig should not only tell the user but also verify
> the availability of a media relay before the admin can enable NAT
traversal.
>
> 3) Max concurrent relays: If it is correct that the media relay is
> shared with sipXbridge then max concurrent relays would limit the
> total number of remote worker sessions, but not the max number of
> relays used for SIP trunking. Correct?
Right. The Symmitron offers a certain quantity of relays of out which
'Max concurrent relays' are set aside for the NAT traversal feature.
Media relays are used every time a NAT separates media endpoints or when
3PCC calls are detected. This means that the following conditions will
use up one media relay:
- a call to/from Remote Workers
- When sipXecs is itself located behind a NAT along with some local
phones then calls between said local phones and other endpoints on the
public side of the NAT will use up a media relay.
- Music-on-hold due to 3PCC nature of the call
- Most calls to devices whose locations are unknown. These are
typically registration-less devices such as gateways.
Now, each media relay used by the NAT traversal feature requires 4 ports
(2 for relaying RTP and 2 for relaying RTCP). This means that the
theoretical maximum number of relays that the Symmitron can offer is (
'Symmitron UDP port range Upper bound' - 'Symmitron UDP port range Lower
bound' ) / 4.
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