Peer gets unreachable in short time?

Why peer gets unreachable short time?(stays reachable around 30 second or 1 minute than debug log says it is unreachable) Peer is same local network with asterisk. But i try to test TLS. It can be about TLS?

Not sure if is the TLS , But I was reading on this forum about a bug that make sip peers unrechable I will try to look for the info , and if I find it, I will pass it to you. Anyway my sugestion is :test without the LTS and verify if the same problem happen

Phone-A: This ip phone is in public field and under the nat.(Only one router)(forexample public ip:,
Phone-B: This ip phone is same local network with asterisk and under the 2 natted routers.( public ip:

when i call from Phone-A to Phone-B so it is not working. But When i call from Phone-B to Phone-A so it is working.

If i exchange the Phone network locations so in both direction is working!!!(I mean, Phone-A is located to Phone-B’s network location, and Phone-B was located to Phone-A’s network location)

When i typed, sip show peer Phone-A and sip show peer Phone-B so there is only one differences. Difference is only “TLS” word. One of them writing like “tls”, in another one write like “TLS”

Output of the sip show xxx
Useragent : Yealink SIP-T28P 00:15:65:13:76:a7
Reg. Contact : sip:502@;transport=TLS

Useragent : Tesan E52/E52P
Reg. Contact : sip:503@;transport=tls

Problem is about phone software implementation?