RAM memory is divided into Unprotected & Protected data, & Program store. Unprotected data is for call registers which are used for each call with data like call state(established, ringing etc), timeslot, orig & term TNs, digits dialed. Also for each set or trunk used on a call, a block of tempoaryb (unprotected) memory is required. This is the area of memory that is wiped clean in an INI. The 1st offhook after an INI will obtain a new Unprot. memory block.
Calls stay up because they use the network card memories to interchange timeslot TDM samples.
Protected data in memory contains set information that doesn't change until a MAC is done, same for CDBs RDBs, CFN etc - INI doesn't chg this data. The other RAM stores the call processing programs & is like protected data.
INIs can occur due to 1- manual button push, 2- watchdog timeout = a software proc is taking too long to finish ie a sanity timer - otherwise nothing else gets done, & 3-Response timeout means a hardware device has failed to respond in a timely fashion.
The bottom line is seconds vs minutes to keep the speechpaths going, & ensure the hardware & software vagaries are handled quickly without Reloading if possible which puts the machine out of commission for ~ minutes.
