What does UDP Timeout mean?
UDP Timeout refers to the amount of time a UDP Pinhole stays open on a Firewall or Router. Depending on your equipment this timeout can range from a few seconds to many minutes. Most devices fall under the minute(s) range.
We recommend UDP Timeout to be set at 30 or 60 seconds. Please be aware that leaving a UDP Port open for an extended period of time can be a security risk for some network devices.
Brief Explanation of UDP Timeouts
UDP Ports must be opened from the Inside of your customer Network (explanation below), that port will timeout within a set timeframe after the last message was transmitted.
- Your Phone Registers using local port 5060 sending it's registration to the Switch.
- As registration passes through your Firewall, the Firewall assigns a random UDP Port for the external connection (sometimes will use the same internal port).
- The Switch keeps this as Registration data and knows it can contact the phone at this Port, as long the port doesn't close or change.
- Re-registration or Keep-Alive can be sent to keep this port open. Typically the port doesn't change often.
- If the UDP Timeout is too short, the firewall will close the port before Re-registration occurs. In time period; SIP messaging from the Switch would be sent to a port that has already been closed by the Firewall, and the packets will be dropped. Picture Example Below.
What are the Symptoms of UDP Timeouts?
- Incoming Call Goes straight to Voicemail, or doesn't ring certain phones in a ring group.
- Calls drop at exactly 17 minutes, 32 minutes, 47 minutes..
- Calls Randomly Drop.
- Firewall Port (registration port) for SIP Traffic changes frequently.
What are NOT Symptoms of UDP Timeouts?
- Phone appears to have lost registration. The phone and the Switch are unaware of the Firewalls UDP Timeout Length, both sides will think Registration is Active.
- Not able to place Outbound calls. The phone will always open the firewall port itself because it's inside the Network, the switch will always respond to the same port.
- Call Quality issues.
How do I recognize UDP Timeouts on my Network?
Outside of the normal symptoms mentioned above, it is easily recognizable on a SIP Trace of a failed or dropped call. You will see 5 duplicated SIP Messages such as an INVITE, all sent quickly with no response. Followed by a BYE from the Switch either right away or two minutes later.