Troubleshooting PRI circuits that are down or dropping calls

Verified 2026-10-02 · 5 sources · tier 2

Also known as pri-d-channel-down, t1-pri-down.

On Asterisk systems with Sangoma cards, pri show spans should report each PRI span as 'Up and Active', and Sangoma says to turn on PRI debugging for any span that does not 2. Sangoma lists 4 causes of a PRI bouncing up and down on its cards: a telco signalling issue, physical-layer instability, wrong clocking chosen at setup, and wrong HDLC configuration 4.

Checking span state on Asterisk

Run pri show spans and confirm that every PRI span reports 'Up and Active' 2. If a span reports anything else, Sangoma says to turn on PRI debugging for that span 2.

In the PRI debug output, check which direction the D-channel frames are travelling 1. If the output shows only outbound D-channel frames and nothing incoming, Sangoma says to contact the telco to confirm that the D-channel has been activated 1.

Diagnosing a PRI that bounces up and down

Sangoma lists 4 causes of a PRI bouncing up and down on its cards 4:

• A telco signalling issue 4.
• Physical-layer instability 4.
• Wrong clocking chosen at setup 4.
• Wrong HDLC configuration 4.

Watching physical-layer alarms

On Sangoma cards, wanpipemon -i wXg1 -c Ta shows physical-layer alarms 3. Sangoma suggests running this command under watch so you can see the alarms change over time 3.

Checking E1 framing (CRC4 and NCRC4)

Sangoma names a common cause of an E1 PRI bouncing: choosing NCRC4 in the FE_FRAME setting where CRC4 is needed, or choosing CRC4 where NCRC4 is needed 5. Sangoma says to fix this by editing the wanpipe configuration file and then restarting wanpipe 5.

See also

• PRI and TDM gateway interworking
• Carrier escalation evidence packages

Applicability

Applies to: Sangoma Asterisk and Sangoma Wanpipe. Deployments: on-premises. Sources checked 2026-10-02. The diagnostic commands and causes in this article are those Sangoma documents for its telephony cards, including Asterisk systems that use those cards 2 4.

What remains uncertain

How to diagnose calls that drop mid-call on a span that otherwise stays up is not covered by the sources below. Framing settings for T1 PRI circuits are not covered by the sources below. How to interpret PRI debug output beyond the outbound-only D-channel case is not covered by the sources below. Diagnostic procedures for PRI hardware or platforms other than Sangoma cards are not covered by the sources below.

WarmTransfer. (2026, October 2). Troubleshooting PRI circuits that are down or dropping calls. WarmTransfer. https://warmtransfer.net/knowledge/pri-circuit-troubleshooting

@misc{warmtransfer-pri-circuit-troubleshooting,
  title  = {Troubleshooting PRI circuits that are down or dropping calls},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/pri-circuit-troubleshooting},
  note   = {Verified 2026-10-02}
}