Reading and Writing to I/O tags

[ShaliniBanerjee]

I am reading and writing to I/O tags in Logix5571 using pycomm. While dissecting using Wireshark, I could see that the Symbol Class(0x6b) is being accessed with Service Codes 0x4c and 0x4d. I am confused about the following:

Is this the convention in which I/O tags are accessed, as in using the Symbol Class? Is it not Assembly Class? I have read that while doing implicit messaging, Assembly Class is used to access the I/O tags, is it different for the explicit messaging?