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Default Invite packet size over 1500 MTU
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Bryan Nelson Offline
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Post: #1
Default Invite packet size over 1500 MTU
Hello,

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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Karl_Yealink Offline
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Post: #2
RE: Default Invite packet size over 1500 MTU
Please send the PCAP file to us, so we can check.
Please email to me(karl@yealink.com). Note that you need to copy the link of this forum, so I can know the problem.
06-23-2016 10:50 AM
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someone Offline
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Post: #3
RE: Default Invite packet size over 1500 MTU
(06-23-2016 10:50 AM)Karl_Yealink Wrote:  Please send the PCAP file to us, so we can check.
Please email to me(karl@yealink.com). Note that you need to copy the link of this forum, so I can know the problem.

I have the same problem (using 3CX) and a T58V:
If I reduce the Codecs to alaw, and ulaw, the packet size is 1508. That works, but, if I add G729, G722, and more, the packet size goes up to 1538.
Normally that is not of a big problem, but, depending on the receiving party or in my case I have a remote phone connected through a VPN tunnel. I simply cannot start a call.
A good SBC will most likely filter the header, and will remove unnecessary talk. But in my case this is a remote location with only one phone.

It the email address still correct?
(This post was last modified: 11-20-2018 06:04 PM by someone.)
11-20-2018 06:03 PM
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