How can 'log.sipd' registration statistics be interpreted?

The following is an example from 'log.sipd' of SIP Endpoint registration cache entries:

    May 12 17:06:43.246 [SIP] REG[546/546] new=311 fwd=311 ref=56 tmo=0

[SIP] REG[xxx/yyy]

 where xxx is Local Contacts <Active> and yyy is Local Contacts for /<Period-High>

new=xxx

 count of all new registrations which are not in cache for the window. This does not include registers which are responded to with 401 challenges. De-register messages are not counted in either new or fwd counters.

fwd=311

 count of every register message sent on core side, whether it is initial one or after a challenge or a forwarded one after half life time expiry. De-register messages are not counted in either new or fwd counters.