[Serusers] Server Capacity

Hi all,

I'm new to SER and was reading the admin guide and came across this:

"With a $3000 dual-CPU PC, the SIP Express Router is able to power IP telephony services in an area as large as the Bay Area during peak hours."

My question about this, is what is this measuring? For example, is it only measuring SIP registrations? Maybe the same SER server is connected to a few IPTSPs and SER is acting as both a registrar and a proxy server? May be all of the above, while still allowing every UA registered in the server to talk to one another? Maybe it's also providing some more advanced features like voicemail to all those Bay Area users?

Can someone please clarify this for me?

Thanks, Waldo