■■ Java platformshave been extended for the development of SIP [17].
There is extensive literature available on this topic as well.ENUM
ENUM was initially meant to stand for E. 164 NUMber translation to IP, but
now correctly stands for E.164 to URI Dynamic Delegation Discovery Systems
(DDDS) Application [18] and is a service that allows users to have only one
single phone number on their business card. The ENUM user may have multi-
ple PSTN, mobile and PBX phone and fax numbers, at home, at work, and in
autos or boats, as well as several IP devices such as PCs, laptops, and palm
computers, and SMS. ENUM can use the Domain Name System (DNS) in com-
bination with SIP user preferences, so if someone uses the single number on a
business card, the call, SMS page, voicemail, or e-mail can be directed to the
device of preference of the called party.
Using a single telephone number to be reached anywhere is a valid concept
at present, since many phone calls originate on circuit-switched networks
using PSTN or PBX-type telephones. However, telephone numbers need not
be the preferred contact address everywhere and for all times. As communica-
tions over the Internet and in 3G/4G mobile networks gain more and more
user acceptance, the single contact address in the form of a URI (such as an
e-mail address) may become the more practical choice.
ENUM allows callers from circuit-switched networks that are predominant
at present to reach any device on either on another circuit-switched network or
on the Internet. ENUM service with SIP is described in Chapter 4, “DNS and
ENUM.”
SIP Interworking with ITU-T Protocols
Much work has been dedicated by the Internet Engineering Task Force (IETF),
the International Telecommunications Union Telecommunications Standard-
ization Sector (ITU-T), and the European Telecommunications Standards Insti-
tute (ETSI) for interworking of SIP with other protocols, such as those shown
in Table 2.7.
Table 2.7 SIP Interworking with ITU-T Protocols
ENUM: E.164 to IP address mapping using DNS
SIP-H.323 [18] Interworking
(continued)Internet Communications Enabled by SIP 27