U1900 intra-office IP phones occasionally fail to call each other.

【Issue description】

In the networking where
Huawei U1930, IP phone, and SBC are deployed, there is a possibility that U1930
intra-office users fail to call each other, the called phone does not ring, and
the calling party cannot hear any ring back tone.

【Possible Cause】

1、The IP network is in poor condition, packet loss occurs,；

2、he SBC is configured incorrectly；

3、the U1930 and IP phone configurations are incorrect.

【Handling Procedure】

1、Capture and analyze the network packets on the SBC side. The SBC does not forward the INVITE message forwarded by the U1930 to the IP phone. As shown in Figure 1.

Figure 1：Capture network packets on the SBC side

2、Further analyze the data packet. It is found that the SBC does not forward the invite message because it considers that the port of the terminal is unreachable. As shown in Figure 2.

Figure 2 ：Analyzing data packets

3、Send the data packet to the SBC expert for analysis. The SBC considers that the port of the IP phone is unreachable because the port on the SBC is updated because the port reservation time on the SBC is 1800s. If no call is made or no registration message is sent within the time, the port number of the IP phone on the SBC is updated.

4、 Check the registration timeout interval of the IP phone. The default value is 3600s, which exceeds the timeout interval for resending registration messages on the SBC.

5、Change the registration timeout interval of the IP phone to 1800s. After several weeks of observation, no intra-office call is connected, and the problem is solved.

【Suggestion and conclusion】

It is recommended that the registration timeout period on the IP phone be the same as the SBC timeout period.