Troubleshoot PDD in Webex Calling with Premises Based PSTN

Introduction

This document describes how to troubleshoot a call failure when PSTN provider takes more than 12 seconds to answer with the Ringing.

Prerequisites

Requirements

Cisco recommends that you have knowledge of these topics:

• Basic SIP.
• Access to a Cisco Local Gateway.

The information in this document was created from the devices in a specific lab environment. All of the devices used in this document started with a cleared (default) configuration. If your network is live, ensure that you understand the potential impact of any command.

Background Information

Post Dial Delay (PDD), which refers to the duration it takes for a caller to hear a ring back tone after the initiation of a call. This delay typically corresponds to the time it takes to receive either a 180 Ringing or 183 Session Progress response to a SIP Invite.

On occasions, users have reported experiences such as dead air or dropped calls, as the caller does not hear any response after dialing, confusion ensues.

In the context of Webex calling withLocal Gateway, if the PSTN provider exceeds a Post Dial Delay of 12 seconds, the call is automatically canceled from the Webex Calling side.

Get the logs from LGW

The steps to get the logs from the Local Gateway are the next:

Step 1. Log in to Local Gateway using Putty.

Step 2. Enable debug in Local Gateway.

gw-wxc# conf t

lgw-wxc(config)# no logging console

lgw-wxc(config)# no logging monitor

lgw-wxc(config)# no logging rate-limit

lgw-wxc(config)# no logging queue-limit

lgw-wxc(config)# logging buffer 400000000 debug

lgw-wxc(config)# end

lgw-wxc# clear log

lgw-wxc# debug ccsip messages. ===>> SIP Call messages tracing is enabled

lgw-wxc# debug voice ccapi inout ===>> voip ccapi in/out debugging is on

Step 3. Start recording the Putty session.

Go to Settings > Session > Logging  and set:

Session logging: Select All session output.

Log file Name: Select Browse and select the directory where you want to save the file and the name.

Start Recording

Step 4.Attempt to recreate or reproduce the outgoing call to PSTN.

Step 5. Get the output of the logs.

lgw-wxc# Terminal length 0

lgw-wxc# sh log

Step 6. Stop recording Putty session and Save the file.

Go to Settings > Session > Logging  and Set:

Session logging: None.

Stop Recording

Step 7. Stop the debugs.

lgw-wxc# Undebug all  

Troubleshoot the LGW Logs

Step 1. Open the log you took using a text plain program like Notepad.

Step 2. Look the Invite coming from Webex Calling, in the next example you can see the Invite arrives at 12:09:48.

125670: *Jul 21 12:09:48.231: //-1/xxxxxxxxxxxx/SIP/Msg/ccsipDisplayMsg:
Received:
INVITE sip:+1XXXXXXXXXX@XX.XX.XX.XX:5061;transport=tls;dtg=sbc_lgu SIP/2.0
Via:SIP/2.0/TLS XXX.XXX.XX.XX:8934;branch=z9hG4bKBroadworksSSE.-XXX.X.XXX.XXV40413-0-100-1704852021-1689966652299-
From:<sip:+1XXXXXXXXXX0@XXX.XXX.XX.XX;user=phone>;tag=1704852021-1689966652299-
To:<sip:+1XXXXXXXXXX@XXXXXXXX.cisco-bcld.com;user=phone>
Call-ID:SSE191052299210723-1072365917@XXX.XXX.XX.XX
CSeq:100 INVITE
Contact:<sip:XXX.XXX.XX.XX:8934;transport=tls>
P-Asserted-Identity:<sip:+1XXXXXXXXXX@XX.XX.XXX.XXX;user=phone>
Privacy:none
P-Access-Network-Info:6307694336
Allow:ACK,BYE,CANCEL,INFO,INVITE,OPTIONS,PRACK,REFER,NOTIFY,UPDATE
Recv-Info:x-broadworks-client-session-info,x-cisco-mute-status
X-BroadWorks-Correlation-Info:64b1f41c-5b24-4865-9b00-c5a9acd0c1d8
Accept:application/media_control+xml,application/sdp,multipart/mixed
Supported:
Max-Forwards:69
Session-ID:7202892d00105000a000ac7e8ab6b729;remote=00000000000000000000000000000000
Content-Type:application/sdp
Content-Length:2260

Step 3. Look the Invite is sent immediately to PSTN Provider at 12:09:48.

125749: *Jul 21 12:09:48.238: //2058481/FED4647C9552/SIP/Msg/ccsipDisplayMsg:
Sent:
INVITE sip:+1XXXXXXXXXX@XXX.X.XXX.XX:5060 SIP/2.0
Via: SIP/2.0/UDP XXX.X.XXX.XX:5060;branch=z9hG4bK11B7E01FDE
Remote-Party-ID: <sip:+1XXXXXXXXXX@XXX.X.XXX.XX>;party=calling;screen=yes;privacy=off
From: <sip:+1XXXXXXXXXX@XXX.X.XXX.XX>;tag=91790161-DA8
To: <sip:+1XXXXXXXXXX@XXX.X.XXX.XX>
Date: Fri, 21 Jul 2023 19:09:48 GMT
Call-ID: FED527FA-273011EE-9558C2C2-D591E4CC@XXX.X.XXX.XX
Supported: 100rel,timer,resource-priority,replaces,sdp-anat
Min-SE: 1800
Cisco-Guid: 4275332220-0657461742-2505228994-3583108300
User-Agent: Cisco-SIPGateway/Cisco IOS 16.12.5
Allow: INVITE, OPTIONS, BYE, CANCEL, ACK, PRACK, UPDATE, REFER, SUBSCRIBE, NOTIFY, INFO, REGISTER
CSeq: 101 INVITE
Timestamp: 1689966588
Contact: <sip:+1XXXXXXXXXX@XXX.X.XXX.XX:5060>
Expires: 180
Allow-Events: telephone-event
Max-Forwards: 68
Session-ID: 7202892d00105000a000ac7e8ab6b729;remote=00000000000000000000000000000000
Session-Expires: 1800
Content-Type: application/sdp
Content-Disposition: session;handling=required
Content-Length: 666

Step 4. After 12 seconds at 12:10:00 you can see Webex Calling send to Local Gateway a Cancel.

125757: *Jul 21 12:10:00.218: //-1/xxxxxxxxxxxx/SIP/Msg/ccsipDisplayMsg:

Received:
CANCEL sip:+1XXXXXXXXXX@XXX.X.XXX.XX:5061;transport=tls;dtg=sbc_lgu SIP/2.0
Via:SIP/2.0/TLS XXX.XXX.XX.XX:8934;branch=z9hG4bKBroadworksSSE.-XXX.X.XXX.XXV40413-0-100-1704852021-1689966652299-
From:<sip:+1XXXXXXXXXX@XXX.XXX.XX.XX;user=phone>;tag=1704852021-1689966652299-
To:<sip:+1XXXXXXXXXX@XXXXXX.cisco-bcld.com;user=phone>
Call-ID:SSE191052299210723-1072365917@XXX.XXX.XX.XX
CSeq:100 CANCEL
X-BroadWorks-Correlation-Info:64b1f41c-5b24-4865-9b00-c5a9acd0c1d8
Max-Forwards:69
Session-ID:7202892d00105000a000ac7e8ab6b729;remote=00000000000000000000000000000000
Content-Length:0

Step 5. In this instance, it is crucial to open a Webex Calling case to extend the PDD beyond 12 seconds. Include the Local Gateway trace for further analysis.

Step 6. This is the graphics trace of the call.

Trace

Related Information

• Technical Support & Documentation - Cisco Systems