This chapter contains sections titled:

• Prerequisites for Operation in the IMS

• IPv4 and IPv6 in the IMS

• IP Connectivity Access Network

• P-CSCF Discovery

• IMS-level Registration

• Subscription to the reg Event State

• Basic Session Setup

• Application Servers: Providing Services to Users

• Changes due to Next Generation Networks (NGN)

• Interworking

• Combinational Services

• Basic Sessions Not Requiring Resource Reservation

• Globally Routable User Agent URIs (GRUU) in IMS

• IMS Communication Service Identifier (ICSI)

• IMS Application Reference Identifier (IARI)

• NAT Traversal in the IMS