Hello I have a question about the interval between re-registration of a client and the expiration of a registration at the server. Clearly, the client and the server cannot both use the exact timeout negotiated during the REGISTER transaction as that would create a race between the expiration and refreshment of a registration. I hope the SIP RFC does mandate some procedure to prevent this (i.e. the client having to re-register some time before the registration expires). But I can't find the part that addresses this.
Some background: Our company is developing operational communication systems where external components (like public address interfaces and gateways to radio networks) are communicating using SIP with a custom soft-PBX. Registration using SIP REGISTER is used not only to route calls but also to detect whether a specific component is available and take appropriate actions (like alerting staff) if it's not. So the expiration of a registration is not a silent event but does trigger actions by our system, which should of course be minimized if they're not necessary. I know that DHCP implementations use the procedure where the client will refresh it's binding after half of the expiration interval has passed. But working with different SIP implementations I see that some clients start the re-registration after the full interval has passed (sometimes even a few seconds later). Thanks! Michael _______________________________________________ Sip-implementors mailing list [email protected] https://lists.cs.columbia.edu/cucslists/listinfo/sip-implementors
