Ok, you said it yourself. gRPC is an environment in which RPC is used for communication. RPC is not Protobuf , but instead Protobuf can use RPC , and gRPC is actually Protobuf over RPC.
You do not need to use Protobuf to create RPC services in your application. This is a good idea if you are building small to medium sized libraries / applications. Also, you do not need to learn Protobuf syntax to create your services.
Protobuf , , , REST. Protobuf. , Protobuf , Go. , - Java, Protobuf RPC , net/rpc, ( Go Java)
, Protobuf . .