User's Manual

Chapter 15 VoIP
B222s User’s Guide
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1 A sends a SI P I NVI TE request t o B. This m essage is an invit at ion for B to part icipat e in a SI P
telephone call.
2 B sends a response indicat ing t hat t he t elephone is r inging.
3 B sends an OK response aft er the call is answered.
4 A t hen sends an ACK m essage to acknowledge t hat B has answered the call.
5 Now A and B exchange voice m edia ( talk) .
6 Aft er t alking, A hangs up and sends a BYE request .
7 B r eplies w it h an OK response confirm ing receipt of t he BYE request and the call is term inat ed.
Voice Coding
A codec (coder/ decoder) codes analog voice signals int o digit al signals and decodes the digit al
signals back int o analog voice signals. The LTE Device support s t he following codecs.
• G.711 is a Pulse Code Modulation ( PCM) waveform codec. PCM m easures analog signal
am plitudes at regular t im e int ervals and convert s t hem into digit al sam ples. G.711 provides very
good sound qualit y but requires 64 kbps of bandwidth.
• G.726 is an Adapt ive Differential PCM ( ADPCM) waveform codec t hat uses a low er bitrat e t han
st andard PCM conversion. ADPCM conver t s analog audio int o digit al signals based on the
difference bet w een each audio sam ple and a prediction based on previous sam ples. The m ore
sim ilar t he audio sam ple is t o t he prediction, the less space needed t o describe it . G.726 operat es
at 16, 24, 32 or 40 kbps.
• G.729 is an Analysis-by- Synthesis ( AbS) hybrid waveform codec that uses a filt er based on
inform ation about how t he hum an vocal t ract produces sounds. G.729 provides good sound
qualit y and reduces t he required bandwidth t o 8 kbps.
MWI (Message Waiting Indication)
Enable Message Waiting I ndication ( MWI ) enables your phone t o give you a m essage–wait ing
( beeping) dial t one when you have a voice m essage( s) . Your VoI P service provider m ust have a
m essaging syst em that sends m essage wait ing stat us SI P packets as defined in RFC 3842.
15.8.3 Quality of Service (QoS)
Quality of Service ( QoS) refers t o bot h a net work's abilit y t o deliver data wit h m inim um delay, and
the networking m et hods used t o provide bandwidth for real- tim e m ult im edia applicat ions.
Type of Service (ToS)
Net work t raffic can be classified by sett ing t he ToS ( Type of Service) values at t he data source ( for
exam ple, at the LTE Device) so a server can decide t he best m et hod of delivery, t hat is t he least
cost , fast est rout e and so on.