Bandwidth refers to the amount of data a communication line can transmit per unit of time, measured in bps (bits per second). In telephone communications, bandwidth is a critical factor that directly affects call quality.
Traditional analog phones used the 300 Hz-3,400 Hz voice band, equivalent to approximately 64 kbps (G.711 PCM) when digitized. In VoIP, the required bandwidth varies significantly depending on the codec used. G.711 requires about 80 kbps (including headers) for high quality but consumes more bandwidth, while G.729 requires about 30 kbps, saving bandwidth at the cost of slightly lower quality.
When bandwidth is insufficient, quality degradation occurs in the form of audio dropouts, increased delay, and noise. When deploying VoIP in an enterprise, total bandwidth must be estimated as simultaneous calls x bandwidth per call. For example, 20 simultaneous G.711 calls require approximately 1.6 Mbps for voice alone.
To prevent bandwidth shortages, QoS (Quality of Service) settings that prioritize voice traffic over other data are essential. Configuring high priority for voice packets on routers and switches maintains call quality even during concurrent large data transfers. Since actual bandwidth is lower than theoretical values, contracting for extra capacity is recommended. For example, if planning for 10 simultaneous calls, G.711 theoretically requires 870 kbps, but accounting for packet header overhead and network jitter, securing at least 2 Mbps is a practical guideline. When deploying cloud PBX, internet connection bandwidth is often the bottleneck for call quality, making pre-deployment bandwidth testing essential.