add a *get_sotdma_comm_state* method

[M0r13n]

Related to #17

[anttinousiainen]

Maybe default values for SOTDMA-radio-fields should be something not valid for the actual message?

ie. UTC hours and minutes default to zero, which is a valid value for them, so it is not easy to see if it really UTC 00:00.

I see in real messages UTC reported as 24:60 when not available, but would -1 be a good default?

[anttinousiainen]

Also:

• parser/decoder should check whether radio_state is infact SOTDMA
• optionally parser/decoder should handle ITDMA, FATDMA and RATDMA data fields where present as well. Quick glance on the spec (*) suggest maybe only ITDMA radio_status is present in the messages (in addition to SOTDMA)

(*) RECOMMENDATION ITU-R M.1371-1

[M0r13n]

@anttinousiainen

Maybe default values for SOTDMA-radio-fields should be something not valid for the actual message?

Totally right. In Python it is common to just use None for none available fields. Therefore, I decided to just set all fields to None by default.

parser/decoder should check whether radio_state is infact SOTDMA
optionally parser/decoder should handle ITDMA, FATDMA and RATDMA data fields where present as well. Quick glance on the spec (*) suggest maybe only ITDMA radio_status is present in the messages (in addition to SOTDMA)

You are right. I added a method named get_itdma_comm_state(). I also added the required logic to distinguish between ITDMA and SOTDMA messages.