TCP/IP Tutorial and Technical Overview - IBM Redbooks

Operational support system
OSS provides user account setup, VoIP service provision, and fulfillment. If there
are any issues in VoIP services, OSS provides trouble ticketing, troubleshooting,
and service assurance. OSS also provides billing and other operational supports.
20.2 Session Initiation Protocol (SIP) technologies
Developed in 1996, the Session Initiation Protocol was originally designed as a
means of notifying or inviting users to Internet multicast and broadcast sessions.
This design, an early form of Internet signalling, made SIP very useful for
signalling in VoIP, and thus most VoIP developers have adopted SIP as the core
IP telephony standard. The most current RFC definition for SIP, published in
2002, is RFC 3261. However, it has been updated several times since 2002, as
illustrated in Table 20-1.
Table 20-1 RFC updates to SIP
Update description RFC Year
SIP-Specific Event Notification 3265 2002
S/MIME Advanced Encryption Standard for SIP 3853 2004
Discussion of problems identified with SIP’s Non-INVITE
Transaction
SIP provides control over multimedia sessions. Implemented at the application
layer, it is capable of establishing, modifying, and terminating sessions. In the
context of IP telephony, these sessions are the VoIP “calls” themselves, and SIP
is used to place the calls, modify them in-session (for example, inviting other
users for features such as three-way calling), and to hang up. Also integrated
into SIP’s design is mobile capability, because SIP handles name mapping and
redirection servers. This allows users to use IP telephony without regard to their
physical or network location.
Primary SIP functions include:
User location and name translation
User location and name translation is used to ensure that
the call reaches the user.
User availability User availability determines whether the called party is
willing to engage in communication.
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