Problemi di Eco sulle porte FXO dei gateway Patton

The echo is commonly created on PSTN lines when analog lines are involved in the conversation. To minimize this sometimes very annoying phenomenon, Patton SmartNode gateways have an integrated echo canceller. Since they work in an adaptive way, only the really existing echo is canceled. The best place to cancel an echo is at the VoIP ports, between the IP network and the PSTN or PBX where it occurs. Therefore, it is generally recommended to always activate the echo canceller (default setting). There are some other conditions where the echo canceller cannot recognize an echo signal, as such, and therefore cannot cancel it. Under these conditions, the echo cannot be canceled and therefore remains perceptible:

• The echo is too strong
• The echo is delayed beyond the time window of the echo canceller (25ms in SmartNodes). Very long PSTN lines, which involve for example multiple analog-to-digital conversions, or satellite links may in fact have a longer delay.
• The echo is acoustically distorted. A distorted signal cannot be recognized as an echo, because it is not a faithful copy of the true signal.

Here are some Web options with which you can try to reduce or eliminate the echo:

Menu Telefony / PSTN profiles / default profile
Enable Echo Canceler (default)
Hybrid Loss 9
Non-Linear Processor Mode [activated] -> Adaptive
Output gain (Specifies the input gain from the PSTN) = 0
Input gain (Specifies the output gain towards the PSTN) = 0

NOTES: Output and Input gain respectively control the volume of the outgoing flow from the Patton to the telephone line and the volume of the opposite flow: sometimes it may be necessary to reduce them to lower the echo, but it is not advisable to go down to values ​​below -15dB since it could have negative repercussions on the volumes of the conversations and also on the recognition of the tones at the entrance of the responders.

If the echo is normally perceived in the IP terminals, start lowering the output gain: this will also lower the replica that comes back as an echo; if this is not enough, stop at a value of 115dB and slightly act on the value of the input gain, that is of the voice sent from the Patton to the PBX: lowering this volume will attenuate the general volume of the flow of external interlocutors but also of the replicas of the own echo.

Menu Telefony / VoIP Profiles / Profiles Default -> Voice
Silence Suppression set to “yes” on all codecs

Menu Telephony / VoIP Profiles / Profile default -> Dejitter Buffer
Mode = Adaptive
Voice = 20 ms

NOTES: in some cases, for best results, configure the mode parameter to silence. The dejitter buffer value may also vary from case to case: try different values ​​but don’t use values ​​higher than 100ms

Any background noise can be caused by the sensitivity of the phone’s microphone instead: some phones have very sensitive microphones that pick up a lot of background noise, or they are not directional enough to capture the speaker’s voice and instead pick up surrounding noises. A gain adjustment on the phones (if possible) is often useful as is a gain adjustment on the Patton. Instead, adjusting both the gain settings on the Patton and the gain settings on the phone can significantly improve the quality.

Other factors are outside of Patton, such as network delay or out-of-order packets. A ping across the network can help identify this scenario if ping times are high. Bandwidth usage is the other big culprit, and a traffic graph can pinpoint this, for example, if there is a lot of traffic it could interfere with voice packets if no QOS policy is set, which is used to prioritize voice packets. beyond the data.

For more information, see Patton’s original article (English language) at this address.