VoIP Signaling Protocols
VoIP uses several ascendancy and call-signaling protocols. Among these are:
■ H.323: H.323 is a accepted that specifies the components, protocols, and procedures
that accommodate multimedia advice services, real-time audio, video, and data
communications over packet networks, including IP networks. H.323 is allotment of a
family of International Telecommunication Union Telecommunication Standardization
sector (ITU-T) recommendations alleged H.32x that provides multimedia communication
services over a array of networks. H.32x is an awning of standards
that ascertain all aspects of synchronized voice, video, and abstracts transmission. It also
defines end-to-end alarm signaling.
■ MGCP: MGCP is a adjustment for PSTN aperture ascendancy or attenuate accessory control.
Specified in RFC 2705, MGCP defines a agreement that controls VoIP gateways that
are affiliated to alien alarm ascendancy devices, referred to as alarm agents. MGCP provides
the signaling adequacy for less-expensive bend devices, such as gateways, that
might not accept implemented a abounding voice-signaling agreement such as H.323. For example,
anytime an event, such as off-hook, occurs on a articulation anchorage of a gateway, the
voice anchorage letters that accident to the alarm agent. The alarm abettor again signals the voice
port to accommodate a service, such as dial-tone signaling.
■ SIP: SIP is a abundant agreement that specifies the commands and responses to set up
and breach bottomward calls. SIP additionally capacity appearance such as security, proxy, and transport
control agreement (TCP) or User Datagram Agreement (UDP) services. SIP and its partner
protocols, Session Announcement Agreement (SAP) and Session Description
Protocol (SDP), accommodate announcements and advice about multicast sessions to
users on a network. SIP defines end-to-end alarm signaling amid devices. SIP is a
text-based agreement that borrows abounding elements of HTTP, application the aforementioned transaction
request and acknowledgment archetypal and agnate attack and acknowledgment codes. It also
adopts a adapted anatomy of the URL acclamation arrangement acclimated aural e-mail that is
based on Simple Mail Transfer Agreement (SMTP).
■ SCCP: SCCP is a Cisco proprietary agreement acclimated amid Cisco Communications
Manager and Cisco IP Phones. The end stations (telephones) that use SCCP are
called Skinny clients, which absorb beneath processing overhead. The applicant communicates
with the Cisco Unified Communications Manager (often referred to as Call
Manager, abbreviated UCM) application connection-oriented (TCP-based) communication
to authorize a alarm with addition H.323-compliant end station.