194 ◾ IP Communications and Services for NGN
tools that collectively can be used as a secure replacement for traditional IP. IPSec
is most commonly used in architectures in which a set of hosts or administra-
tive domains have an existing trust relationship with one another. IPSec is usually
implemented at the operating system level in a host, or on a security gateway that
provides confidentiality and integrity for all traffic it receives from a particular
interface (as in a VPN architecture). IPSec can also be used on a hop-by-hop basis.
In many architectures, IPSec does not require integration with SIP applications;
IPSec is perhaps best suited to deployments in which adding security directly to
SIP hosts would be arduous. UAs that have ...