User guide

LTE TDD B2268H

User Guide

13 VoIP

Issue 01 (2014-01-15)

110

Figure 13-9 SIP Call Progression

Step 1 A sends a SIP INVITE request to B. This message is an invitation for B to participate in a SIP

telephone call.

Step 2 B sends a response indicating that the telephone is ringing.

Step 3 B sends an OK response after the call is answered.

Step 4 A then sends an ACK message to acknowledge that B has answered the call.

Step 5 Now A and B exchange voice media (talk).

Step 6 After talking, A hangs up and sends a BYE request.

Step 7 B replies with an OK response confirming receipt of the BYE request and the call is terminated.

----End

Voice Coding

A codec (coder/decoder) codes analog voice signals into digital signals and decodes the digital

signals back into analog voice signals. The LTE Device supports the following codecs.



G.711 is a Pulse Code Modulation (PCM) waveform codec. PCM measures analog signal

amplitudes at regular time intervals and converts them into digital samples. G.711

provides very good sound quality but requires 64 kbps of bandwidth.



G.726 is an Adaptive Differential PCM (ADPCM) waveform codec that uses a lower

bitrate than standard PCM conversion. ADPCM converts analog audio into digital signals

based on the difference between each audio sample and a prediction based on previous

samples. The more similar the audio sample is to the prediction, the less space needed to

describe it. G.726 operates at 16, 24, 32 or 40 kbps.



G.729 is an Analysis-by-Synthesis (AbS) hybrid waveform codec that uses a filter based

on information about how the human vocal tract produces sounds. G.729 provides good

sound quality and reduces the required bandwidth to 8 kbps.

MWI (Message Waiting Indication)

Enable Message Waiting Indication (MWI) enables your phone to give you a message– waiting

(beeping) dial tone when you have a voice message(s). Your VoIP service provider must have a

messaging system that sends message waiting status SIP packets as defined in RFC 3842.