Issue: Duplicate SIP Messages Detected in Softphone Logs

Overview

This article covers the issue of duplicate SIP messages observed in softphone logs, which may result in unexpected call behavior such as dropped calls or call routing anomalies. This issue has primarily been observed in environments with remote users using VPN or multiple devices logged in under the same SIP credentials.

Affected System

• EvoVoice Softphone

• Evo Console

• SIP Server Configuration

Reported Symptoms

• Incoming calls drop with the error: Call answered elsewhere

• Softphones ring and immediately disconnect

• Users miss calls despite phones being active

• SIP logs show each SIP INVITE message duplicated

Example Log Behavior

When reviewing SIP logs for an affected user, you may see something like this:

INVITE sip:13002@... [timestamp A]
INVITE sip:13002@... [timestamp A]
ACK sip:13002@... [timestamp B]
ACK sip:13002@... [timestamp B]

This means the SIP INVITE was sent twice, possibly due to two active sessions or registration sources.

Possible Causes

1. Double Registration of a SIP Account:

   • Same SIP extension is logged into two devices (e.g., softphone + physical phone)

   • Same extension is active in two apps (softphone + console)

   • Same extension used on multiple PCs

2. Network-Level Duplication:

   • The user is connected via VPN and local internet simultaneously

   • SIP packets are routed via two interfaces (i.e., multiple NICs or tunnel+LAN)

3. Software Glitch:

   • Rare softphone bugs can cause retry loops or ghost sessions

   • SIP stack does not correctly drop old sessions

Troubleshooting Steps

🧪 Step 1: Confirm SIP Extension Usage

• Ask user which devices they're using (PC, mobile, desk phone, console, etc.)

• Make sure the same extension is not logged into multiple softphones

🧪 Step 2: Check for Active Sessions

• On the SIP server or PBX, run a session/registration list to identify if the extension appears more than once

• If using a hosted SIP provider, request a registration dump

🧪 Step 3: Review Network Setup

• Is the user connected via VPN?

  • If yes, disable VPN temporarily and retest

• Use ipconfig /all (Windows) or ifconfig (macOS/Linux) to check for multiple active interfaces

🧪 Step 4: Collect SIP Logs

• Reproduce the issue and collect logs from:

  • Softphone logs (.pcap or internal trace)

  • SIP server logs if available

Resolution Steps

✅ Option 1: Disconnect Other Devices

• Ask user to log out from all devices using the same SIP extension

• Reboot softphone and reconnect on only one device

✅ Option 2: Assign Unique Extensions

• Avoid using a shared SIP extension on multiple endpoints

• If multiple users share a workstation, assign separate extensions

✅ Option 3: Disable VPN or Isolate SIP Traffic

• If VPN is essential, set up split tunneling to exclude SIP traffic

• Alternatively, configure softphone to bind to a specific interface/IP

✅ Option 4: Re-register Softphone

• Fully close the softphone app

• Remove SIP profile if applicable

• Re-enter credentials and reconnect to clean the session state

✅ Option 5: SIP Server Tuning (Admin-only)

• Limit max simultaneous registrations per SIP extension

• Enable SIP session timeout to clear ghost sessions after 1–2 mins of inactivity

Prevention Tips

• Always assign 1 SIP account = 1 device

• Avoid dual-login setups unless call forking is explicitly configured

• Instruct users to avoid using VPN unless required, and ensure they're not double-routing SIP traffic