UDP Packet Fragmentation


By default, the Skyetel Network communicates using UDP. This is the preferred method by many PBXs, and it is what we recommend. However, as VoIP has evolved over the last 10 years, the packet sizes supported by UDP have become insufficient. Many networks on the PSTN will provide too much information for a single UDP packet, and when this happens, it becomes fragmented. This usually is resolved by your ISP - they will stitch the broken SIP packet back together again and provide it back to the PBX as if nothing happened. However, there are cases where the ISP does not do this. 

In cases when your PBX is experiencing UDP packet fragmentation, the endpoint health section will show your PBX as green, but calls to your PBX may route to the technical difficulties message. 

How To Fix This

Switch to TCP

The easiest solution is to switch to TCP on IP Authentication from within our Portal (please note that we do not support SIP Registration via TCP). In almost all cases that will resolve any packet fragmentation as TCP allows for much larger packet sizes.

To do that, simply switch the protocol on your Endpoint Group to TCP:


Please Note - Switching to TCP takes our network about 5 minutes to propagate during which time your Endpoint's Health will be Orange. Once it goes green, you are good to go. More info here: https://support.skyetel.com/hc/en-us/articles/360041178573-Endpoint-Health

Once you switch to TCP on our network, please make sure you enable TCP on the PBX and open the relevant ports on your firewall. 

Move the PBX to the Cloud

If your PBX requires UDP, then the next best option would be to move the PBX onto a cloud provider like Digital Ocean, Linode or AWS. All three of these providers support Jumbo Frames, and it's probably a good idea to move the PBX to the cloud anyway. 

Talk to your ISP

You may also attempt to work with your ISP and ask them to enable Jumbo Frames on your internet connection and networking equipment.


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