G.711 Codec
G.711 is the most widely supported telephone audio codec, available as ulaw (PCMU) and alaw (PCMA). It uses 64 kbit/s and is a common baseline on SIP devices.
Published 8 November 2026 · Updated 9 November 2026 · 1 min read · By SpaGreen Creative
Short answer
G.711 is the ITU-T standard for 8 kHz telephone-quality audio at 64 kbit/s, available as ulaw (PCMU, North America and Japan) and alaw (PCMA, most other regions).
G.711 is the codec the traditional telephone network uses, standardised by the ITU-T. It samples audio 8,000 times per second and stores each sample in 8 bits using a logarithmic curve, which gives 64 kbit/s of audio in each direction. There are two curves. Mu-law, written ulaw or PCMU, is used in North America and Japan. A-law, written alaw or PCMA, is used in Europe and most of the rest of the world. RFC 3551 assigns payload type 0 to PCMU and 8 to PCMA.
The codec is simple, adds almost no delay and is supported by nearly every SIP phone, softphone, PBX and provider. That near-universal support is its main value: it is the usual common baseline when two sides share no other codec. Whether a call uses it still depends on the codecs the server or trunk allows and on SDP offer/answer negotiation. The cost is bandwidth. With RTP, UDP and IP headers added, a G.711 call uses roughly 80 to 90 kbit/s per direction, which matters on constrained links.
Audio quality is the familiar telephone sound, limited to about 3.4 kHz. Wideband codecs such as G.722 and Opus sound noticeably clearer. Most PBX systems enable both G.711 variants by default, and softphones including SIPdia support both ulaw and alaw.
Sources and further reading
This article is published by SpaGreen Creative, the maker of SIPdia. Product names mentioned belong to their owners. Where it describes other software, treat the steps as general guidance and check the official documentation linked above.
