/mcplistens to the user, the user can hear the customer without issue. With this information, you know to focus only on the RTP packets that travels from the user side to the customer side. Step 2. Once you have the topology written out, the first step is to take packet captures on one side of the topology and work your way to the other end of the topology. a. Take the first capture with a port span of the switch port that the IP Phone is plugged into. Use Wireshark to decode the RTP stream and play back the audio. If there is an issue with the audio (the users voice is not clear) the focus can be placed on the cabling from the phone to the switch, the phone equipment (handset, headset, speakerphone), and the phone itself. If there is no issue with the audio (the users voice is clear), you can eliminate the phone, cabling from the phone to the switch, and the phone equipment (handset, headset, speakerphone) as the source of the poor quality. At this point move to Step (b) if there is no issue with the audio. b. Take a packet capture at router_A (ingress and egress), then decode and play back the audio streams. If there is an issue with the audio at ingress you have isolated the issue, as you know that the audio entered switch_A without issue but entered router_A with an issue. If there is no issue with the audio at ingress and the audio quality was poor on egress, you have isolated the issue to router_A. If there is no issue with the audio move to Step (c), continue to gather packet captures along the RTP path. c. Take a packet capture at router_B (ingress and egress), then decode and play back the audio streams. If there is an issue with audio at the ingress of router_B, and you know that there was no audio issue at the egress of router_A from previous packet captures, you have isolated the issue and know that the issue is between router_A and router_B (the WAN in this example). If there is no issue with the audio at ingress and the audio quality was poor on egress, you have isolated the issue to router_B. If there is no issue with the audio move to Step (d) to gather more packet captures. d. At this point in the troubleshoot process you have determined that the audio quality is good from the IP Phone, switch_A, router_A, the WAN, and the egress of router_B. The next packet capture must be taken from the GW. If there is a problem with the audio at the ingress of the GW the issue has been isolated to switch_B. If there is an audio issue with audio quality at egress, you have isolated the issue to the GW. If there is no issue with audio quality at egress the issue is likely on the PSTN/Provider side, contact your Provider, provide them with a packet capture with the audio that leaves the GW without issue would be the next step in the troubleshoot process. Additional Resources