When troubleshooting static issues, it is essential to understand where static comes from and what the possible causes can be. There seems to be a general misconception that static can stem from a Networking issue.

Typical causes of Static Include:
  • Faulty Hardware (Handset, Headset, or Base)
  • Poor Physical Connection (Handset or headset cord)
  • Voltage Input/Poor power connection (AC adapter or PoE)
Less common causes of static:
  • Echo Cancellation (gone wrong)
  • Voice Activity Detection
  • Codec Mismatch between G.711U and G.711A (there are protection and logic on most equipment that prevents this).
Things that don't cause static:
  • Networking, except for faulty Networking equipment on the premise.
  • Packet loss, Jitter, PDV. While these cause audio quality issues static is not one of them.
Quick TIP: In our experience, Static usually stems from a bad handset, headset, or bad handset cord. Simply switching the call to speakerphone can prove if that's the case.

Troubleshooting Steps

Some essential questions that need to be asked when dealing with static. Remember there are two audio paths in a typical SIP call; one sending, and one receiving.

The Questions
  • Who heard the static on the call? One party or both parties? We need to identify the source of the static, remember it is possible it came from the PSTN caller.
  • Do all calls from the device have static? Was this a one-time thing?
  • Do all calls from the location have static? Possible Electronic interference, bad cabling or network equipment.
Who heard the static?
  1. Did both parties on the call hear the static?
    • In this case, RTP-Sight should clearly show what side of the call the static was coming from. You can look at the RTP streams and determine the IP address. Remember that the Switch relays media, so if you see static from a Switch IP, this means the static came from the far-side or the call. Open a ticket with Support.
  2. Did your customer hear the static?
    • You can listen to the call from RTP-Sight to determine if there was static from the other side of the call. In most cases you will hear clear audio at the switch, indicating this is something inside your customer's Network.
  3. Did the other side of the call complain about hearing static?
    • It's possible static came from the microphone connection from your customer's phone, but will clearly be shown in RTP-Sight when listening to the call. If there is no static in RTP-Sight, this indicates a problem on the far end of the call. If it happens to more than one destination, submit a ticket with Support.
What to do!

In most cases, you will find that the source of the static was inside of your customer's Network. So you will need to do some troubleshooting to find the culprit. It will help if you are able to do packet captures from the phone, switch, and Firewall, but some troubleshooting can be done without it. Once you have the packet captures; You can listen to the traffic using Wireshark from each location to determine where the static originated.

If the static is coming from your customer's Network:

  1. Start with the phone! Remember to test speakerphone vs handset. While this is usually caused by a handset/headset, it's possible there is something wrong with the phone itself. If you do a packet capture from the phone, and the phone is sending bad audio from the speakerphone and handset: you have a bad phone. 
  2. If you don't hear static from here, move to the Switch or Firewall to listen for traffic.
    1. If you don't hear static from the Firewall, the problem could be at the ISP's modem or equipment. Restart, and if the issue persists contact Support for more guidance.
    2. If you do hear the static at the Firewall, try plugging the phone directly into it. If the static goes away, this means the problem is somewhere on the Network between the phone and firewall (cabling, or switch).

If your customer hears the static:

  1. It's still a good idea to start with the phone. Do a packet capture to see if the received audio has static in it. If the packet capture doesn't show static, this points to an issue with the phone's hardware. If you do hear static from the inbound audio, try to do a packet capture to the firewall to locate the static inside the Network.
  2. If you don't have the ability to do a packet capture on the Firewall or Switch, try plugging the phone directly into the firewall or modem to see if the issue persists.

If both sides hear the static:

Again, in this case, it should be easy to see who is sending the staticky RTP Stream in RTP-Sight.

What about Hum?

Hum is technically different than static, but can easily be mistaken for static. Hum comes from electromagnetic interference, the typical cause for Hum is having your cell phone too close to your phone. Right before you receive a phone call or a text, you get a buzzing/humming noise in the earpiece. Other equipment can cause this outside of cell phones, but the fix when it occurs is to move the phone away from other electronics.

If you need assistance, please contact the control tower for more assistance.