FXO disconnect supervision and calls that do not hang up

See also

Sources

1. 1
   On AudioCodes MediaPack 5xx v7.2, CurrentDisconnectDuration sets the current disconnect pulse duration, with a range of 200 to 1500 ms and a default of 900 ms, and a change requires a device reset.

   Answer and Disconnect Supervision Parameters · parameter CurrentDisconnectDuration · Checked 2026-10-14
2. 2
   On AudioCodes MediaPack 5xx v7.2, CurrentDisconnectDefaultThreshold sets the FXO line voltage threshold for current disconnect detection, with a range of 0 to 20 V and a default of 4 V, and a change requires a device reset.

   Answer and Disconnect Supervision Parameters · parameter CurrentDisconnectDefaultThreshold · Checked 2026-10-14
3. 3
   On AudioCodes MediaPack 5xx v7.2, DisconnectOnDialTone releases an FXO call when the PBX returns dial tone and is disabled by default.

   Answer and Disconnect Supervision Parameters · parameter DisconnectOnDialTone · Checked 2026-10-14
4. 4
   On AudioCodes MediaPack 5xx v7.2, GWMaxCallDuration caps gateway call duration in minutes (0 to 35791) and defaults to 0, meaning unlimited.

   Answer and Disconnect Supervision Parameters · parameter GWMaxCallDuration · Checked 2026-10-14
5. 5
   AudioCodes notes that whichever disconnect method is configured on the FXO device must be supported by the CO or PBX.

   Calls Termination by PBX · Calls Termination by PBX, note · Checked 2026-10-14
6. 6
   AudioCodes calls detection of polarity reversal or current disconnect the recommended FXO disconnect method; the device disconnects immediately when either appears on the Tel side.

   Calls Termination by PBX · Calls Termination by PBX, method 1 · Checked 2026-10-14
7. 7
   AudioCodes states that disconnecting on interruption of the RTP stream (DisconnectOnBrokenConnection with BrokenConnectionEventTimeout) works correctly only when silence suppression is not used.

   Calls Termination by PBX · Calls Termination by PBX, method 4 · Checked 2026-10-14
8. 8
   AudioCodes MediaPack 5xx v7.2 lists five ways an FXO device can detect call termination: polarity reversal or current disconnect, reorder/busy/dial/SIT tone detection, a special DTMF code, interruption of the RTP stream, and protocol termination from the IP side.

   Calls Termination by PBX · Calls Termination by PBX, numbered methods 1 to 5 · Checked 2026-10-14
9. 9
   AudioCodes states that tone-based FXO disconnect needs the correct tone frequencies and cadence defined in the Call Progress Tones file and is somewhat less reliable than polarity reversal or current disconnect.

   Calls Termination by PBX · Calls Termination by PBX, method 2 · Checked 2026-10-14
10. 10
    Cisco states that anytone disconnect detection operates only during call setup and that echo cancellation must be enabled with it so the router does not disconnect on its own ringback tone.

    Understanding FXO Disconnect Problem · section Configure Supervisory Disconnect Signaling, Cisco IOS 12.1(3)T subsection (anytone) · Checked 2026-10-14
11. 11
    Sangoma states that Asterisk needs a signal from the far end to detect that a call on an analog line has been hung up.

    Open Source - Why Won't Asterisk Disconnect a Call Over Analog Lines? · opening explanatory paragraph · Checked 2026-10-14
12. 12
    Cisco describes battery reversal as the PBX reversing battery polarity when the far end answers and restoring normal polarity when the far end disconnects, with the reversal also used by the PBX to start billing.

    Understanding FXO Disconnect Problem · section Battery Reversal · Checked 2026-10-14
13. 13
    In the Cisco IOS releases covered by tech note 8120, battery reversal detection is not a default feature and must be configured with the battery-reversal voice-port command.

    Understanding FXO Disconnect Problem · section Battery Reversal · Checked 2026-10-14
14. 14
    In the chan_dahdi sample configuration, busydetect enables listening for the busy pattern and busycount, the number of busy cycles required, defaults to 3.

    chan_dahdi.conf.sample (Asterisk sample configuration) · [channels] section, options busydetect and busycount · Checked 2026-10-14
15. 15
    The chan_dahdi sample configuration says that without busypattern Asterisk accepts any regular sound-silence pattern as busy, and gives 500,500 as a commented example.

    chan_dahdi.conf.sample (Asterisk sample configuration) · [channels] section, option busypattern · Checked 2026-10-14
16. 16
    The chan_dahdi sample configuration describes callprogress as highly experimental and warns that it can easily detect false answers.

    chan_dahdi.conf.sample (Asterisk sample configuration) · [channels] section, option callprogress · Checked 2026-10-14
17. 17
    Cisco tech note 8120 is dated 2006 and names only IOS 11.3MA to 12.2(2)T on 1750, 2600, 3600, 3700 and MC3810 hardware, so it does not establish command defaults or hardware support on current IOS XE routers.inferred

    Understanding FXO Disconnect Problem · header revision history and platform lists in each method section · Checked 2026-10-14
18. 18
    Calling party control (CPC), also called forward disconnect, is a central office signal telling subscriber equipment that the calling party has hung up, so that answering machines stop recording; it may be implemented by an open switching interval or by polarity reversal.

    Supervision (telephony) · section Calling party control · Checked 2026-10-14
19. 19
    For Cisco IOS 12.1(5)XM and 12.2(2)T, Cisco recommends first trying supervisory disconnect dualtone mid-call with a predefined country cptone locale before attempting custom tone configurations.

    Understanding FXO Disconnect Problem · section Configure Supervisory Disconnect Signaling, Cisco IOS 12.1(5)XM and 12.2(2)T subsection · Checked 2026-10-14
20. 20
    The Asterisk chan_dahdi sample configuration lists the signalling values fxs_ls (loop start), fxs_gs (ground start) and fxs_ks (Kewl Start), and states that the overall signalling default is auto.

    chan_dahdi.conf.sample (Asterisk sample configuration) · [channels] section, signalling option list · Checked 2026-10-14
21. 21
    The chan_dahdi sample configuration documents dialtone_detect as disabled by default, and describes yes as looking for dial tone for 10000 ms after answer.

    chan_dahdi.conf.sample (Asterisk sample configuration) · [channels] section, option dialtone_detect · Checked 2026-10-14
22. 22
    Because the sample configuration describes dialtone_detect=yes as watching for dial tone only for 10000 ms after answer, Sangoma's use of it as a general fix for lines held after inbound hangups may not catch hangups later in a long call.inferred

    chan_dahdi.conf.sample (Asterisk sample configuration) · [channels] section, option dialtone_detect; compare sangoma-kb-asterisk-analog-disconnect workaround steps · Checked 2026-10-14
23. 23
    From Cisco IOS 12.1(3)T, supervisory disconnect dualtone can detect disconnect tones either throughout the call with the mid-call keyword or only during call setup with the pre-connect keyword, with custom tones defined in a voice class dualtone.

    Understanding FXO Disconnect Problem · section Configure Supervisory Disconnect Signaling, Cisco IOS 12.1(3)T subsection · Checked 2026-10-14
24. 24
    Across the vendors reviewed, the electrical disconnect signals (loop current interruption or polarity reversal) are the primary methods and tone detection is the fallback, so a stuck FXO port is best diagnosed by first finding out which electrical signal, if any, the line provides.inferred

    Calls Termination by PBX · Calls Termination by PBX, methods 1 and 2; compare cisco-technote-8120-fxo-disconnect method sections · Checked 2026-10-14
25. 25
    Cisco describes four supervisory disconnect methods an FXO port can detect: ground-start signalling disconnect, power denial, battery reversal and tone-based supervisory disconnect.

    Understanding FXO Disconnect Problem · section Understand Supervisory Disconnect Signaling Methods · Checked 2026-10-14
26. 26
    One cisco-voip list participant reported that the battery-reversal command did not appear in the running configuration on IOS 15.5M and concluded it was already a default there.field report

    [cisco-voip] FXO Disconnect Detection · quoted reply dated Sep 11 2016 within the 2016-09-21 message · Checked 2026-10-14
27. 27
    Community advice on both the cisco-voip list and the Asterisk forum is to ask the carrier which disconnect method the line uses, or to have disconnect supervision enabled on it, before tuning tone detection.field report

    [cisco-voip] FXO Disconnect Detection · quoted reply dated Sep 12 2016 within the 2016-09-21 message · Checked 2026-10-14
28. 28
    A field test suggested on the Asterisk forum for whether a line has disconnect supervision: connect a line-powered phone with a backlit keypad, call a mobile, hang up the mobile, and watch the keypad go dark for about a second.field report

    Hangup not detected · reply by IronHelix · Checked 2026-10-14
29. 29
    Asterisk forum users report that busy-tone detection as a hangup workaround leaves the line off-hook until the carrier's busy tone starts, which can take roughly 30 to 60 seconds after the far end hangs up.field report

    Hangup not detected · reply by IronHelix following the busydetect report · Checked 2026-10-14
30. 30
    A 2016 cisco-voip list report describes a US carrier that confirmed disconnect signalling was sent from the CO but did not pass through a DSLAM between the CO and the premises after a softswitch migration.field report

    [cisco-voip] FXO Disconnect Detection · message of 2016-09-21 by the original poster, carrier update paragraph · Checked 2026-10-14
31. 31
    Practitioners on the cisco-voip list advise identifying a carrier's disconnect tone by capturing PCM or DS0 audio, or by recording the busy or congestion tone, and then defining that frequency and cadence on the router.field report

    [cisco-voip] FXO Disconnect Detection · quoted replies dated Sep 12 2016 within the 2016-09-21 message · Checked 2026-10-14
32. 32
    Cisco notes that FXS ports normally reverse battery on call connection and advises disabling battery reversal on an FXS port that is connected to an FXO port without battery reversal detection.

    Understanding FXO Disconnect Problem · section Battery Reversal · Checked 2026-10-14
33. 33
    Cisco states that on a ground-start connection the switch removes the ground at disconnect and the FXO port goes on-hook, which requires a switch able to provide ground-start.

    Understanding FXO Disconnect Problem · section Ground-start Signaling Disconnect · Checked 2026-10-14
34. 34
    On the Grandstream HT813 FXO port, Current Disconnect Threshold sets the minimum line power drop counted as a disconnect, with a default of 100 ms and a range of 50 to 800 ms; Enable Current Disconnect is meant for providers that signal call completion by dropping line power.

    HT813 – Administration Guide · section FXO Port Page Definitions, settings Enable Current Disconnect and Current Disconnect Threshold · Checked 2026-10-14
35. 35
    On the Grandstream HT813 FXO port, Enable PSTN Disconnect Tone Detection uses a tone as the disconnect signal, and the PSTN Disconnect Tone defaults to the North American busy tone f1=480@-32, f2=620@-32, c=500/500.

    HT813 – Administration Guide · section FXO Port Page Definitions, settings Enable PSTN Disconnect Tone Detection and PSTN Disconnect Tone · Checked 2026-10-14
36. 36
    Grandstream advises setting Enable Polarity Reversal on the HT813 FXO port to Yes only if the line subscribes to a polarity reversal service from the PSTN provider, warning that calls will fail otherwise; the default is No.

    HT813 – Administration Guide · section FXO Port Page Definitions, setting Enable Polarity Reversal · Checked 2026-10-14
37. 37
    On the Grandstream HT813, PSTN Ring Timeout detects a PSTN hangup when the FXO port has not answered, with a range of 2 to 10 seconds and a default of 6.

    HT813 – Administration Guide · section FXO Port Page Definitions, setting PSTN Ring Timeout (sec) · Checked 2026-10-14
38. 38
    Grandstream's HT813 technical specifications list its disconnect methods as Busy Tone, Polarity Reversal/Wink and Loop Current.

    HT813 – Administration Guide · section HT813 Technical Specifications, Disconnect Methods row · Checked 2026-10-14
39. 39
    The chan_dahdi sample configuration documents hanguponpolarityswitch for FXO ports, noting that in some countries a polarity reversal signals the disconnect of a call.

    chan_dahdi.conf.sample (Asterisk sample configuration) · [channels] section, option hanguponpolarityswitch · Checked 2026-10-14
40. 40
    Sangoma states that in North America analog hangup is signalled by a voltage drop of about half a second, which is loopstart with disconnect supervision and which Asterisk calls Kewlstart.

    Open Source - Why Won't Asterisk Disconnect a Call Over Analog Lines? · opening explanatory paragraph · Checked 2026-10-14
41. 41
    Cisco states that on a loop-start FXO connection the switch side provides no disconnect supervision because the switch always supplies battery, so the FXO port depends on the switch to signal when to hang up.

    Understanding FXO Disconnect Problem · section Understand the FXO Disconnect Problem · Checked 2026-10-14
42. 42
    An open switching interval (OSI), also called open loop disconnect, is a period during which central office battery is removed from a telephone line, and it can be used to signal disconnect supervision.

    Supervision (telephony) · section Open switching interval · Checked 2026-10-14
43. 43
    Cisco defines power denial as an interruption of line power from the switch or PBX to the FXO port lasting at least 350 ms, which the router treats as a disconnect.

    Understanding FXO Disconnect Problem · section Power Denial-based Supervisory Disconnect · Checked 2026-10-14
44. 44
    In Cisco IOS from 11.3MA, the voice-port command supervisory disconnect signal enables power denial recognition and is the default.

    Understanding FXO Disconnect Problem · section Configure Supervisory Disconnect Signaling, Cisco IOS 11.3MA subsection · Checked 2026-10-14
45. 45
    Cisco's rule of thumb is that a router originating a call from its FXO port can provide the local disconnect, while a router receiving a call on its FXO port needs the connected switch to provide the disconnect signal.

    Understanding FXO Disconnect Problem · section Common Scenarios · Checked 2026-10-14
46. 46
    Wikipedia describes the open switching interval as the North American disconnect method on analog loop-start trunks and an analog disconnect tone as the method used in many South American countries.

    Supervision (telephony) · sections Open switching interval and Analog disconnect tone · Checked 2026-10-14
47. 47
    When lines stay occupied after an inbound caller hangs up on kewlstart, Sangoma's suggested workaround is to set dialtone_detect=yes in chan_dahdi.conf before the channel definitions and restart Asterisk.

    Open Source - Why Won't Asterisk Disconnect a Call Over Analog Lines? · workaround procedure, steps 1 to 4 · Checked 2026-10-14
48. 48
    Cisco lists the symptoms of missing FXO disconnect supervision as phones that keep ringing after the caller has hung up and FXO ports that stay busy after the call should have cleared.

    Understanding FXO Disconnect Problem · section Understand the FXO Disconnect Problem · Checked 2026-10-14
49. 49
    Sangoma notes that some telcos support only basic loopstart and so cannot signal Asterisk that a call has ended.

    Open Source - Why Won't Asterisk Disconnect a Call Over Analog Lines? · paragraph following the Kewlstart explanation · Checked 2026-10-14
50. 50
    Cisco tech note 8120 gives the defaults as 30 seconds for timeouts wait-release and 60 seconds for timeouts call-disconnect on the FXO voice port.

    Understanding FXO Disconnect Problem · section Configure Supervisory Disconnect Signaling, Cisco IOS 12.1(5)XM and 12.2(2)T subsection · Checked 2026-10-14
51. 51
    Cisco calls the default wait-release and call-disconnect timers potentially excessive and suggests about 5 seconds for both, adjusted to local conditions.

    Understanding FXO Disconnect Problem · section Configure Supervisory Disconnect Signaling, Cisco IOS 12.1(5)XM and 12.2(2)T subsection, example and following text · Checked 2026-10-14
52. 52
    In Cisco IOS 11.3MA, configuring no supervisory disconnect signal turned off power denial support and enabled basic tone disconnect, which could detect only a 600 Hz tone.

    Understanding FXO Disconnect Problem · section Tone-based Supervisory Disconnect and Configure Supervisory Disconnect Signaling, Cisco IOS 11.3MA subsection · Checked 2026-10-14
53. 53
    Cisco notes that the supervisory tones a PBX plays to indicate call release differ in most countries, so tone-based disconnect has to be matched to the local tone.

    Understanding FXO Disconnect Problem · section Tone-based Supervisory Disconnect · Checked 2026-10-14
54. 54
    Cisco's comparison table shows the original VIC-2FXO card does not support battery reversal detection, while VIC-2FXO-M1, VIC-2FXO-M2, VIC2-2FXO and VIC2-4FXO support all four disconnect methods.

    Understanding FXO Disconnect Problem · section Comparison among FXO Voice Interface Cards (VICs) · Checked 2026-10-14
55. 55
    Voicemail and auto attendant ports reached through an FXO gateway are on the receiving side of inbound calls, so under Cisco's rule of thumb they rely entirely on the switch's disconnect signal and stay off-hook after a caller hangs up if the line provides none.inferred

    Understanding FXO Disconnect Problem · section Common Scenarios, Scenario 2 and the closing rule of thumb · Checked 2026-10-14
56. 56
    On Yeastar P-Series analog FXO trunks, Busy Count sets how many busy tones to wait for before disconnecting, defaults to 4, and Yeastar warns that detection may fail if the value is too high.

    Analog FXO Trunk Settings · section Hangup Detection, setting Busy Count · Checked 2026-10-14
57. 57
    Yeastar P-Series Appliance Edition analog FXO trunks offer Busy Tone, Polarity Reversal and Loop Current Disconnect as hangup detection methods.

    Analog FXO Trunk Settings · section Hangup Detection, setting Hangup Detection Method · Checked 2026-10-14

Documents

Cite this page

WarmTransfer. (2026, October 14). FXO disconnect supervision and calls that do not hang up. WarmTransfer. https://warmtransfer.net/knowledge/fxo-disconnect-supervision

@misc{warmtransfer-fxo-disconnect-supervision,
  title  = {FXO disconnect supervision and calls that do not hang up},
  author = {{WarmTransfer}},
  year   = {2026},
  url    = {https://warmtransfer.net/knowledge/fxo-disconnect-supervision},
  note   = {Verified 2026-10-14}
}