Port over the Cisco Call Manager functionality currently available in chan_sip
(see https://usecallmanager.nz/documentation-overview.html), to chan_pjsip.
This will entail not a single patch but lots of smaller patches adding the individual functionality to upstream Asterisk to enable putting all the pieces together. A small Cisco 794x lab should be used for testing along.
Personal advice from Gareth Palmer, the author of the chan_sip version:
A good place to start would be to add a cisco_usecallmanager=yes configuration option and then have that enable an equivalent re-implementation of buggymwi=yes which was the first change made to chan_sip to start supporting those phones.
You must be