[asterisk-users] Role of asterisk

[Valentin Bud]

Hello list,

 When you have an asterisk box connected between the VoIP
phones and an PSTN gateway what is the role of asterisk. Proxy server:
stateful or stateless?

 From what i read in the: "Understanding the SIP, second edition" from
Alan B. Johnston
i think that asterisk is a stateful proxy server as well as
registration server. Am I right?
Can asterisk be configured to work as redirect server or stateless
proxy or i am totally
in the dark and don't understand correctly?

 And if you know other (better) books for SIP please tell me.

thank you and have a great day,
v