Sip Functions And Features - HP FlexNetwork MSR Series Configuration Manual

For example, when receiving a request from a calling UA, the redirect server searches for the
location information of the called UA and returns the location information to the UA. This location can
be that of the called UA or another proxy server, to which the UA can initiate the session request
again. The subsequent procedure is the same as that for calling a called UA directly or for calling a
proxy server.
Location server
A location server is a device that provides UA information to proxy and redirect servers; it retains UA
information received by a registrar. The location server and registrar can located on the same device
as two logical components or located on different devices.
Registrar
A registrar receives UAs' registrations. The registration information (for example, the local telephone
number) is usually stored on the location server for future retrieval. The location server and the
registrar are both logical components and are usually co-located.

SIP functions and features

Functions
SIP supports the following facets of establishing and terminating multimedia communications:
•
Locating called SIP endpoints, the most powerful function of SIP. For this purpose, SIP can use
the registration information of SIP endpoints on the registrar. In addition, it can enhance its user
location service by using other location services provided by the domain name server (DNS)
and lightweight directory access protocol (LDAP).
•
Determining user availability, making sure whether a called endpoint can participate in a
session. SIP supports multiple address description and addressing styles, including SIP-URI
(for example, SIP: 123456@172.18.24.11), Tel-URL (for example, Tel: +1312000), and
SIPS-URI (SIPS: 123456@172.18.24.11). Thus, a SIP caller can identify whether a callee is
attached to a PSTN network by callee's address, and then initiate and set up the call to the
callee through the gateway connected to the PSTN.
•
Determining user capabilities, that is, the media type and media parameters of a called
endpoint. In a message exchange process, each SIP endpoint sends such information in
transmitted messages so that all other participants can learn about its capabilities.
•
Setting up a session, or session parameters, at both callee and caller sides. Two parties can
select the appropriate capabilities for session setup through negotiation about media type and
media parameters to be used.
•
Managing sessions by modifying session parameters or terminating sessions.
Features
SIP delivers the following features:
•
Open standards—Can accommodate new functions, products, and services introduced by
different service providers.
•
Flexible configuration—Accommodates a wide range of dialup, wire, and wireless devices,
allows highly flexible configurations, and can work with other systems.
•
Scalable system—Allows expansion as enterprises grow.
•
Support to remote users—With SIP, an enterprise network can extend to all its users,
wherever they are.
•
Competitive advantage potentials—More SIP-based services are emerging.
•
Consistent communication method—Management becomes easier as the result of
consistency in dialup mode and system access method used by branches, SOHOs, and
traveling personnel.
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