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Default Invite packet size over 1500 MTU
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Bryan Nelson Offline

Posts: 71
Joined: Feb 2013
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Default Invite packet size over 1500 MTU

Just wanted to post this for others who may have issues using these phones with the default codec set.

I couldn't figure out why my authenticated INVITES were not working from this phone, and it turns out that with all the default video codecs enabled, the INVITE ends up being over the 1500 MTU packet size, and will get fragmented. While there are re-assembly standards, they don't always works so well (Google Compute couldn't properly re-assemble until recently).

Using TCP or simply disabling some codecs resolves the problem.

The original invite sent out is under the 1500 MTU, but we challenge for nonce and the additional authentication information added to the new INVITE generated by the T-49 ends up being slightly over. While the phone isn't technically doing anything incorrect, this was frustrating to troubleshoot.

Suggest that at least one of the default active codecs is disabled to help avoid this troubleshooting for others Wink
(This post was last modified: 06-09-2016 02:41 AM by Bryan Nelson.)
06-09-2016 02:41 AM
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Default Invite packet size over 1500 MTU - Bryan Nelson - 06-09-2016 02:41 AM

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