G.711

G.711 is the standard uncompressed audio codec used for VoIP telephony, delivering toll-quality voice at 64 kbps per direction. It is the default and most widely used codec in VICIdial deployments and virtually all telephony systems worldwide. G.711 comes in two variants: ulaw (mu-law), used in North America and Japan, and alaw (A-law), used in Europe and most other regions. Both provide the same audio quality but use different companding algorithms.

How It Works in VICIdial

G.711 encodes audio by sampling the analog voice signal 8,000 times per second (8 kHz sample rate) and encoding each sample into 8 bits using logarithmic companding. This produces a constant bitrate of 64 kbps. The logarithmic encoding emphasizes lower-amplitude signals (quiet sounds) and compresses higher-amplitude signals (loud sounds), optimizing the 8-bit range for human speech characteristics.

In VICIdial, G.711 is configured in the Asterisk SIP or PJSIP configuration for both carrier trunks and agent endpoints. When both sides of a call use G.711, Asterisk can pass the RTP audio through without transcoding — a “native bridge” that minimizes CPU usage and latency. If one side uses G.711 and the other uses a different codec like G.729, Asterisk must transcode, consuming significant CPU resources.

Each G.711 call consumes approximately 87 kbps of bandwidth per direction when accounting for IP, UDP, and RTP packet headers (64 kbps audio payload plus ~23 kbps overhead). For a VICIdial server handling 200 concurrent calls, this means approximately 35 Mbps of bidirectional bandwidth for audio alone. Call recordings stored in G.711 format consume approximately 480 KB per minute (or about 29 MB per hour).

Why It Matters

G.711 is the recommended codec for most VICIdial deployments for several reasons. It provides the highest voice quality achievable in standard telephony (MOS score up to 4.4), requires zero transcoding when used end-to-end, consumes minimal CPU, and is universally supported by every carrier, SIP device, and telephony platform. The only tradeoff is bandwidth — G.711 uses 8x more bandwidth than G.729.

For call centers with adequate network bandwidth (which includes most modern data center deployments), G.711 ulaw should be the default choice. The CPU savings from avoiding transcoding allow VICIdial servers to handle more concurrent calls, and the superior audio quality improves agent comprehension and customer satisfaction. Reserve bandwidth-efficient codecs like G.729 for remote agents on constrained connections or international routes where bandwidth costs are significant.