[Asterisk-Users] Sip flow diagram?

[Rich Adamson]

Does anyone have a high level flow diagram showing acceptable sip
messages exchanges?

For exampe:
  Source         Dest
  Invite   ->    
           <-    Trying
  Ok       ->

I'm specifically trying to debug an issue with various hangups, prior
to call completion, after call completion, "calling" vs "called" party
hold, etc, and getting rather confused watching the various packets
flowing between sip devices with a sniffer (and no reference document).

Rich