Registration is the event where your IP Phone (UA) contacts our system and tells it where you can be reached for incomming calls. The registration interval is the time (measured in minutes or seconds) between when your UA re-registers. Registration is required before you can make PSTN calls (see the Knowledge Base article on Error 205.)

We recommend a registration interval set to around 300 seconds or 5 minutes. If you set it any lower than this, then your UA spends a lot of time re-registering, needlessly waisting bandwidth and other resources. If it is set too much higher, then you might be waiting around for an expiration that should have happened sooner (like when you move a portable UA between networks.)