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Knowledge Base

PC Client Fails to Initiate a Call Through Wireless Access

Publication Date:  2019-12-31  |   Views:  45  |   Downloads:  0  |   Document ID:  EKB1100043733

Contents

Issue Description

After a PC client logs in and registers through a wireless network, the client fails to initiate audio and video calls. Other terminals that access through a wired network can successfully initiate audio and video calls.

Handling Process

1. On the PC client, capture the network packets when calling is abnormal. The INVITE request sent by the PC client receives a "502 bad gateway" response.

2. Trace the signaling on the U1900 and capture the login signaling of the PC client. Check the Contact field to obtain the registration IP address corresponding to the terminal's SIP number. (Alternatively, run the show sipue eid SIP number command on the voice gateway.)

3. Trace the signaling when the PC client initiates a call, and check the layer-3 source address of the INVITE message.

4. Signaling analysis finds that the IP address in the Contact field of the registration message is different from the original address of call initiation.

5. Check the networking. The Wi-Fi AP used by the PC has the router and NAT functions enabled.

6. Change the AP mode to bridge mode and disable NAT.

7. After the PC client connects to the Wi-Fi network again, it can successfully initiate calls.

Root Cause

1. When a terminal initiates a registration request with the U1900, the U1900 uses the IP address in the Contact field of the registration message as the registration address of the SIP number.

2. When this SIP number initiates a call, the layer-3 source address of the INVITE message is converted to an address of the Wi-Fi side as NAT is enabled. As a result, the original address of the INVITE message identified by the voice gateway is different from the IP address of the registration address of the terminal.

3. In this case, the U1900 gateway returns a "502 bad gateway" error, resulting in call failure.

Check method:

1. On the voice gateway, run the show sipue eid SIP number command to check the IP address registered by the current number.

2. On the gateway, trace the signaling for a call and check the source IP address of the INVITE message.

3.  Check whether the registration address is the same as the signaling source address.

Solution

Step 1. Deploy an SBC or set up a VPN tunnel between the PC client and the voice gateway to implement NAT traversal. Or change the AP to bridge mode (without NAT).
Step 2. Log in to the PC client again and initiate a call.