Waves

Voice Codecs and DSP Resources

Cisco Aug 16, 2025

Voice Codecs

Codec G.711 (SD) G.722 (HD) G.729 (Compressed) iLBC iSAC
Bandwidth 64Kbps 64Kbps 8Kbps 13.3Kbps 10-32Kbps
w/overhead 82K+ 80K+ 26K+ 28K+ 16-64K+
MOS 4.3/5 4.5/5 3.92/5 4.14/5

MOS - Mean Opinion Score

PESQ - Perceptual Evaluation of Speech Quality

PEAQ - Perceptual Evaluation of Audio Quality

G.711 uncompressed, matches T1 lines

G.729 works best for latin based languages, not good for music on hold

Sample size default 20ms, 50 packets per second.

Calculating Per-Call Bandwidth

  1. Start with bytes per second for codec
  2. Add 40 bytes per packet for Layer 3 overhead
  3. Add Layer 2 overhead
    1. Ethernet 18
    2. Ethernet with VLAN Tag 22
    3. PPP 6-9
    4. Frame Relay 6
    5. ESP (IPSec VPN) 50-57
  4. Multiply by PPS
  5. Multiply by 8 to convert to bits

DSP Modules

  • Convert TDM and Analog voice calls into IP Packets
  • Sampling, encoding, and quantization
  • Transcoding
  • Conferencing
  • Media Termination Point (MTP)

DSPs can be directed using DSP Farms

voice-card 1
  dsp services dspfarm
	
dspfarm profile 1 conference
  codec g711ulaw

Tags

Craig Garnham

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