What is SER? The short answer is SER is a "softswitch". However, the term softswitch is a word used mostly by marketing and sales people because it really has no defined technical meaning. In other words there is no RFC or other technical document that specifies exactly what a "softswitch" is.

Some marketing and sales people typically use this name when referring to an integrated PSTN gateway with a PSTN switch while others use it for any call processing entity. SER would fall in to the latter case and so you may consider SER to be a "softswitch".

In reality the closest technical names for SER are "registrar", "proxy server", and "redirect server". In some circumstances, SER can also act as SIP User Agent because it can initiate and terminate SIP transactions.

For a complete description of what SER really is you should refer to the offical IPtel documentation at http://old.iptel.org/ser/doc/seruser/seruser.html#ABOUTSER [1]

Credits: This information was adapted from contributions from Jiri Kuthan.