HP-UX Java SIP Stack Programmer's Guide (February 2008)

E.164 Number Mapping
In voice over IP (VoIP) networks, an endpoint is identified by an IP address and a
telephone number. When a user calls a SIP remote end point from a PSTN network,
only the telephone number is known. The SIP uniform resource identifiers (URI) is
unknown. Therefore, it is important to translate the telephone number into the SIP URI
for the call to be established. While the SIP user agents or proxy servers can be statically
provisioned by mapping the destinations corresponding to particular telephone numbers
or telephone number ranges, considering the size and complexity of a complete
mapping, it is preferable if SIP user agents can query a destination that is appropriate
for a particular telephone number.
E.164 Number Mapping (ENUM) is a standard that enables the translation of telephone
numbers to SIP URIs. The ENUM feature performs the translation using the existing
Internet domain name server (DNS) query mechanism. The ENUM mechanism is used
in cellular IP Multimedia Subsystem (IMS) networks, and also for fixed and mobile
operators.
Parsing Different URIs
A SIP address can be described in different URI formats. A tel URI describes a SIP
end point that is using a phone number. A pres URI is a SIP address used for presence
user agents (UAs). An im URI is used for instant messaging. Each URI can appear in
many variations in a SIP message. Therefore, parsing these URIs is important. The SIP
stack parses the different URIs and provides the data to the application in a friendly
data structure.
Additional SIP Extensions
The SIP stack supports a variety of features to implement a number of extensions to
SIP. The following extensions are supported:
• General uniform resource locator (URL) scheme support – This extension is a
general framework to support any type of URL scheme, such as im: and tel:.
• INFO method – This extension is used for mid-call information exchange without
changing the call state. For more information about this extension, see RFC 2976
(The SIP INFO Method).
• MESSAGE method – This extension is used for instant messaging. For more
information about this extension, see draft-ietf-sip-message-0x (SIP Extensions for
Instant Messaging).
• UPDATE method – This extension is used to enable a client to update the parameters
of a session (such as the set of media streams and their codecs) without changing
the dialog state. For more information about this extension, see RFC 3311 (The
Session Initiation Protocol (SIP) UPDATE Method).
44 JSR32 JAIN SIP APIs