Using the Preferences | Protocols feature adds more analysis capabilities to Wireshark. Just be careful here not to add too many capabilities, as that will slow down packet capture and analysis.

For TOS and DiffServ, go to Chapter 10,  Network Layer Protocols and Operations.

SNMP is a protocol used for network management. The SNMP Object Identifier (OID) is used to identify objects and their location in the Management Information Base (MIB). An object can be a counter that counts interface input packets, an IP address of a router interface, a device name or location, CPU load, or any other entity that can be presented or measured.

The SNMP MIB is built in a tree structure, as you can see in the next diagram. Top-level MIB object IDs belong to different standard organizations. Vendors define private branches, including managed objects, for their own products:

When resolving SNMP MIB, Wireshark shows not only the object ID, but also its name, which helps to understand the monitored data.