Page 372 - Asterisk™: The Future of Telephony

trunktimestamps (channel)
Specifies whether or not Asterisk should send timestamps for the individual sub-
frames within trunk frames. There is a small bandwidth penalty for sending these
timestamps (less than 1 kbps/call), but they ensure that frame timestamps get sent
end-to-end properly. If both ends of all your trunks go directly to TDM and your
trunkfreq equals the frame length for your codecs, you can probably suppress
these. The receiver must also support this feature, although it does not also need
to have it enabled:
trunktimestamps=yes|no

Retrieving Dialplan Information from a Remote Asterisk Box

Asterisk can retrieve dialplan information from another Asterisk box with the use of a
switch => statement. When this occurs, the Asterisk IAX channel driver must wait for
a reply from the remote box before it can continue with other IAX-related processes.
This is especially troubling when you have multiple switch statements nested through-
out multiple boxes: if a switch statement has to traverse several boxes, there could be
an appreciable delay before a result is returned.
When the global iaxcompat option is set to yes, Asterisk will spawn a separate thread
when the switch lookup is being performed. The use of this thread allows the main IAX
channel driver to continue on with other processes while the thread waits for the reply.
A small performance hit is incurred with this option:
iaxcompat=yes|no

Registering to Other Servers with register Statements
The register switch (register =>) is used to register your Asterisk box to a remote server
—this lets the remote end know where you are, in case you are configured with a
dynamic IP address. Note that register statements are used only when the remote end
has you configured as a peer, and when host=dynamic.
The basic format for a register statement is:
register => username:password@remote-host
The password is optional (if not configured on the remote system).
Alternatively, you can specify an RSA key by framing the appropriate RSA key name †
in square brackets ([]):
register => username:[rsa-key-name]@remote-host

† Asterisk RSA keys are typically located in /var/lib/asterisk/keys/. You can generate your own keys using the
astkeygen script.

344 | Appendix A: VoIP Channels