Chapter 12. Voip; Introduction - Draytek Vigor2500V Manual

Vigor2500V series
Chapter 12
VoIP

12.1 Introduction

Voice over IP network (VoIP) enables you to use your broadband
Internet connection to make toll quality voice calls over the Internet.
There are many different call signaling protocols; methods by which VoIP
devices can talk to each other. The most popular protocols are SIP, MGCP,
Megaco and the older H.323. These protocols are not all compatible with
each other (except via a soft-switch server).
The Vigor2500V series support the SIP protocol as this is an ideal and
convenient deployment for the ITSP (Internet Telephony Service Provider)
and softphone and is widely supported. SIP supports peer-to-peer direct
calling and also calling via a SIP proxy server (a role similar to the
gatekeeper in H.323 networks). The MGCP protocol use a client-server
architecture, the calling scenario being very similar to the current PSTN
network.
After a call is setup, the voice streams transmit via RTP (Real-Time
Transport Protocol). Different CODECs (methods to compress and encodec
the voice) can be embedded into RTP packets. Vigor2500V series provides
Gvarious CODECs, including G.711 A/ -law and G.729 A & B. Each
CODEC uses a different bandwidth and hence provides different levels of
voice quality. The more bandwidth a CODEC uses the better the voice
quality, however the CODEC used must be appropriate for your Internet
bandwidth.
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