Asterisk 21 is scheduled to become the next major release.  As part of that process there are a number of modules being removed, see: wiki.asterisk.org.

Channel drivers:

chan_alsa
chan_mgcp and res_pktccops
chan_skinny
chan_sip

Resource modules:

res_monitor

Application modules:

app_osplookup
app_macro

The removal of chan_sip also requires changes to the Asterisk test suite.  This falls under two categories, tests that need to be converted to use chan_pjsip and tests that can now be removed.

Patches can be obtained via the individual reviews linked to each issue listed above.

Of the modules removed, three stand above the rest in terms of complexity and required actions.

• chan_sip – deprecated as of Asterisk 17, chan_sip has finally been removed from Asterisk as of version 21.  If you have not yet moved your systems to chan_pjsip, please see the following wiki page regarding the migration.
• app_macro – deprecated in Asterisk 16 but has remained longer than usual due to it’s extensive use in examples, documentation, and production. Another module that has a replacement – see Gosub; for some time.
• res_monitor – deprecated in Asterisk 16, also saved from removal due to continued use.  MixMonitor has long since been in use in it’s stead.

Please plan accordingly using the above references and stay current with asterisk.org for all released Asterisk versions.