Hi, how could I know which variables related to SIP are writable variables and 
which ones just read variables?
For example, I'm trying to set the From domain and User-Agent in leg B by 
doing:

<action application="bridge" 
data="{sip_invite_domain=${sip_from_host},sip_user_agent=CUSTOM}sofia/gateway/gw1/xxx@xxxxxx.xxx"/>

Unfortunatelly just the From domain is set while the User-Agent remains the 
value in 'user-agent-string' of the Sofia profile.