Introduction To Voip; Voip System; Basic Voip Call Flow - 3Com MSR 50 Series Configuration Manual

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Introduction to VoIP

VoIP System

Basic VoIP Call Flow

V O
OICE VERVIEW
VoIP makes it possible that voice services such as plain old telephone service
(POTS) can be carried over the IP network. VoIP is implemented via voice packets.
In VoIP, the voice gateway segments the voice signal into frames and stores them
in voice packets to transmit.
Currently, interworking between PSTN and Internet is implemented via VoIP
gateways. Meanwhile, the PC-to-telephone, telephone-to-PC, and
telephone-to-telephone technologies are mature and the call quality has been
improved greatly. Therefore, VoIP can completely meet the commercial
requirements.
H.323 and session initiation protocol (SIP) are two common protocols used in VoIP.
For details about H.323 and SIP, refer to
For POTS, all functions from the call originator to the call receiver are implemented
by the public switched telephone network (PSTN). VoIP is different from POTS.
Figure 647 VoIP system
Gateway
PSTN
Telephone
In Figure 647, the VoIP gateway provides interfaces for communication between
the IP network and PSTN/integrated services digital network (ISDN), users connect
to the originating VoIP gateway through PSTN, the originating VoIP gateway
converts analog signals into digital signals and compresses them into voice packets
that can be transmitted over the IP network, and the IP network transmits the
voice packets to the terminating VoIP gateway, which reduces the voice packets to
recognizable analog signals and transmits them to the receiver. This is a complete
telephone-to-telephone communication process. In practice, a gatekeeper (GK)
server or SIP server may be applied in the VoIP system to implement the functions
of routing and access control.
The following describes a basic VoIP call flow:
1 A user picks up a telephone and the modular voice card detects the user's
off-hook action in real time
2 The modular voice card transmits the off-hook signal to the VoIP signal processing
module on the VoIP gateway.
"Voice Protocols" on page
Gateway
IP
PSTN
GK server / SIP server
2238.
Telephone