Troubleshooting Echo Problems between IP Phones and IOS Gateways

Publisher

Cisco

URL

https://www.cisco.com/c/en/us/support/docs/voice/voice-quality/19640-echo-ipphone-gateway.html

Published

2008-04-02

Updated

unknown

Accessed

2026-09-25

HTTP status

200

License

Cisco website terms of use; no-redistribution; short excerpts and locators only

Source notes citing this source

• When a PSTN user hears echo on a call with an IP phone, Cisco identifies the cause as acoustic coupling between the earpiece and the microphone of the IP phone handset. in context
• The 2008 Cisco echo technote gives the IOS gateway echo-cancel coverage default as 8 ms, adjustable up to 32 ms. disputed in context
• Cisco gives a target ERL of approximately 20 dB and a minimum of 15 dB when tuning to eliminate echo. in context
• Cisco states that ERL needs to be approximately 6 dB or higher for the gateway echo canceller to engage. in context
• On Cisco IOS voice ports, input gain is applied before the echo canceller sees the echo signal, and output attenuation is applied after the echo canceller sees the original output signal. in context
• For echo caused by PSTN hybrids that the IP phone user hears, Cisco places responsibility for preventing the echo on the voice gateways. in context
• Cisco attributes hybrid echo to an impedance mismatch in the hybrid circuit such as a two-wire to four-wire interface. in context
• Cisco states that the default voice-port impedance of 600 ohms is consistent with most PSTN and PBX lines. in context
• The 2008 Cisco technote says the fix for acoustic echo from an IP phone handset is a phone load with echo suppression on the handset and headset, and that the loads available then included echo cancellation only on the speakerphone. in context
• When the IP phone user hears echo, Cisco attributes it to hybrids in the PSTN network. in context
• The party who hears echo is not where it is generated. If the IP or VoIP user hears their own voice, look at the far-end TDM or analog tail and the gateway echo canceller facing it; if the PSTN or far-end user hears it, look at acoustic coupling at the IP endpoint. inferred in context
• Cisco explains that the packet segment of a VoIP call adds significant delay, typically 30 ms in each direction, which makes echoes from analog tail circuits perceptible when they were previously indistinguishable from sidetone. in context
• Cisco states that an echo must be delayed by at least 20 milliseconds before a user perceives it. in context
• Cisco states that in most telephones sidetone helps mask some of the echo. in context

Cite this source record

APA

WarmTransfer. (2008, April 2). Troubleshooting Echo Problems between IP Phones and IOS Gateways. WarmTransfer. https://warmtransfer.net/knowledge/sources/cisco-technote-19640-echo-ipphone-gateway

BibTeX

@misc{warmtransfer-cisco-technote-19640-echo-ipphone-gateway,
  title  = {Troubleshooting Echo Problems between IP Phones and IOS Gateways},
  author = {{WarmTransfer}},
  year   = {2008},
  url    = {https://warmtransfer.net/knowledge/sources/cisco-technote-19640-echo-ipphone-gateway},
  note   = {Cisco, accessed 2026-09-25}
}