G.711 A-law encodes narrowband voice at 64 kbit/s and is commonly aligned with UK and European PSTN interworking. When UKDDI enables it and the network has capacity, it is normally the first codec to test because it avoids the extra quality loss of low-bitrate compression.
Settings used in this guide
These are public service values, not your password or account-specific authentication ID.
| Approved codec order | Confirm in your UKDDI activation email |
|---|---|
| Media security | SRTP |
What G.711 A-law does
G.711 is pulse code modulation for voice-frequency signals. The A-law variant, often shown as PCMA, is widely used in European telephony. It carries an encoded audio payload of 64 kbit/s and represents traditional narrowband telephone audio rather than HD voice.
Wide interoperability and low codec complexity, with no low-bitrate compression stage.
It consumes more network capacity than G.729 and does not extend speech bandwidth like G.722 or Opus.
Budget more than 64 kbit/s per call
The 64 kbit/s figure is only encoded audio. RTP, UDP, IP and link-layer headers are sent with each packet; SRTP, VLANs, IPv6, VPNs and tunnels can add more. Packetisation changes how often those headers repeat.
- Use the PBX or network calculator for the actual packet interval and encapsulation.
- Plan upload and download capacity for the maximum simultaneous calls plus headroom.
- Measure congestion, loss and jitter; clear audio on an idle speed test does not prove peak-hour quality.
- Apply call admission control rather than letting every new call contend on a full link.
When to prioritise G.711 A-law
The account codec order remains Confirm in your UKDDI activation email. If a downstream endpoint uses a different codec, decide deliberately where conversion occurs and confirm the PBX/SBC has capacity.
- The UKDDI activation profile includes G.711 A-law/PCMA.
- Most calls enter or leave the UK PSTN and the PBX/endpoints support it natively.
- The network has stable capacity and low packet loss rather than relying on extreme compression.
- Recording, voicemail, conferencing and IVR components can use it without transcoding.
Test a G.711 A-law deployment
- 1Confirm the negotiated codec
Check SDP and PBX call statistics for PCMA/G.711 A-law rather than assuming the first configured preference won.
- 2Test at peak load
Run simultaneous calls during a realistic busy period and watch loss, jitter, delay and WAN utilisation.
- 3Test voice applications
Verify IVR keypad input, hold, transfer, recording, voicemail and conferencing.
- 4Check secure media
Confirm SRTP remains active and that security settings did not force an unexpected fallback.