Hello, Peplink community!
We are exploring SIP feature implementation, a long-requested addition. As we progress, we have a few questions for you. We asked these questions to some of you, but it never hurts to double check 
The POTS Adapter currently supports G.711, G.729AB, AMR-NB, and AMR-WB. However, for SIP, additional codecs may be required. Which of the following codecs are mandatory for a minimum viable product?
G.722, G.722.1, G.723.1, G.726, G.728, Opus, iLBC, iSAC
Which of these are mandatory codecs? We are trying to decide on a minimum, must have codec list.
Next, regarding security, the POTS Adapter supports TLS 1.2. We would like to know if TLS 1.3 is a mandatory requirement for SIP implementation.
Finally, please let us know if thereās anything else important we should be aware of during this development.
Our services support G.722, G.711u, G.729a and GSM. I think you are already āthereā in this regard, from what I can see.
TLS: Most of what we have works with 1.2 just fine; one particular application needs 1.3. If I were going to do this Iād ensure 1.2 and 1.3 are supported.
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I would really like to see Opus as a supported codec here for various reasons assuming the hardware can support it. It will provide a lot of efficiency over G.729 on a cellular connection.
Regarding TLS, 1.3 shouldnāt be mandatory for implementations today in 2025, however, it is better performing and more secure than TLS1.2. One of the big things you can do to āextendā TLS1.2 is to disable/prevent the use of insecure cipher suites / handshake methods. For example, using ECDHE with TLS1.2 makes it fine to use, but deciding to use PSK with TLS1.2 is a no-no. Last thing to note is that this may not be up to you/the POTS adapter, as it requires certain support mechanisms on the PBX side. That being said, I donāt see any PBX requring TLS1.3 over TLS1.2 at this point in time.
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