The gRPC protocol is an RPC protocol on top of HTTP2.

While the most common type of RPC receives only one request message and returns only one response message, the protocol also supports RPCs that return multiple individual messages in a streaming fashion, RPCs that accept a stream of request messages, or RPCs with both streaming requests and responses.

Conceptually, each gRPC call consists of a bidirectional stream of binary messages, with RPCs of the "non-streaming type" sending only one message in the corresponding direction (the protocol doesn't make any distinction).

Each RPC uses a different HTTP2 stream, and thus multiple simultaneous RPCs can be multiplexed transparently on the same TCP connection.