How to properly parse a TCP packet?

Question

C++ / C#

Good afternoon!
Please tell me, I'm trying to write a packet parser from a satellite monitoring terminal, and I ran into such a problem, I don't understand how to extract IMEI from a packet, without extraneous characters.
There are no problems with receiving packets, I do it via msdn.
Here is the description of the protocol from the manufacturer:

After converting the first packet from the terminal

data = System.Text.Encoding.ASCII.GetString(bytes, 0, i);

I get:

B863000000113045                                              z

The length of the first packet is 66 bytes.
How to remove extra characters and what do they mean judging by the description of the protocol?
I will be very grateful for links to examples on my subject, tk. it is clear that I do not understand something ... but what?
Thank you!

Answer 1

I advise you to run wireshark, it will probably be more clear how to parse