Cisco TelePresence Administrator's Manual page 96

Registration control
Re-registrations
All endpoints must periodically re-register with the VCS in order to keep their registration active. If you do not
manually delete the registration, the registration could be removed when the endpoint attempts to re-register,
but this depends on the protocol being used by the endpoint:
H.323 endpoints may use "light" re-registrations which do not contain all the aliases presented in the initial
n
registration, so the re-registration may not get filtered by the restriction policy. If this is the case, the
registration will not expire at the end of the registration timeout period and must be removed manually.
SIP re-registrations contain the same information as the initial registrations so will be filtered by the
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restriction policy. This means that, after the list has been activated, all SIP registrations will disappear at
the end of their registration timeout period.
The frequency of re-registrations is determined by the Registration expire delta setting for
(Configuration > Protocols >
H.323).
Cisco VCS Administrator Guide (X8.1.1)
SIP) and the Time to live setting for
SIP
H.323 (Configuration > Protocols >
About registrations
Page 96 of 507