VoLTE as the Technology of Choice for LTE Voice Transmission and SMS
GSM Association IR.92 specifications highlight specific standards to deliver voice and SMS services over an LTE network with IMS (IP Multimedia Sub-systems). WiFi as an “offload” is also an interesting concepts for many operators. VoLTE is essentially VoIP over 4G/LTE using IMS architecture.
In order for LTE UE to establish a voice call over IMS, the following steps are essential:
- UE RRC Connection Request to EPC & IMS
- PDN Connectivity Request
- Protocol Configuration Options IE
- P-CSCF address
- EPS Attach & P-CSCF Discovery
- UE initial IMS registration
KEY TECHNICAL REQUIREMENTS FOR VoLTE ARE:
- PCC rule authorization and QoS rule generation
- Multiple Bearers (Default, Dedicated)
- QoS Class Identifiers (QCIs)
- Semi-Persistent Scheduling
- Transmission Time Interval (TTI) Bundling
- Discontinuous Reception (DRX)
- Robust Header Compression (RoHC)
COMMON RTP PAYLOAD TYPES FOR VOLTE ARE:
- Audio AMR 8000
- Audio AMR-WB 16000
- Text T140 1000
- Video H.263 90000
- Audio EVRCB 8000
- Audio EVRCWB
- Video H.263-2000 90000
- Video H.263-2000 90000
- Video H.264
- Video MP4V-ES 90000
