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Landslide: Why SIP Re-registration happens based on 1/2 the value of the Expires (s) parameter

Environment/Versions
Landslide has a configuration of Expires for SIP Registration. Default value is 600000 second but you could change it to any value you want. Expires is used to trigger SIP reregistration.

Some people think LS should do SIP reregistration when expires value expired, for example, if expires is 60, they think SIP reregistration should happen after 60 seconds of the registration. But that’s not the truth.

 
Answer
Expires means the Server consider SIP client isn’t there any more, it’s the deadline for reregistration, not the time to start re-registration, so Client must do reregistration before the expires, normally the re-registration will occur based on 1/2 the value of the Expires (s) parameter.

 From TS 24.229

Unless either the user or the application within the UE has determined that a continued registration is not required the UE shall reregister an already registered public user identity either 600 seconds before the expiration time if the previous registration was for greater than 1200 seconds, or when half of the time has expired if the previous registration was for 1200 seconds or less, or when the UE intends to update its capabilities according to RFC 3840 [62] or when the UE needs to modify the ICSI values that the UE intends to use in a g.3gpp.icsi-ref media feature tag or IARI values that the UE intends to use in the g.3gpp.iari-ref media feature tag.

 

Product : Landslide Client