ready to send and receive RPCs.
Parameters:
      * name (str) -- a globally unique name of this node.
        (e.g., "Trainer3", "ParameterServer2", "Master", "Worker1")
        Name can only contain number, alphabet, underscore, colon,
        and/or dash, and must be shorter than 128 characters.
  * **backend** (*BackendType**, **optional*) -- The type of RPC
    backend implementation. Supported values is
    "BackendType.TENSORPIPE" (the default). See Backends for more
    information.

  * **rank** (*int*) -- a globally unique id/rank of this node.

  * **world_size** (*int*) -- The number of workers in the group.

  * **rpc_backend_options** (*RpcBackendOptions**, **optional*) --
    The options passed to the RpcAgent constructor. It must be an
    agent-specific subclass of "RpcBackendOptions" and contains
    agent-specific initialization configurations. By default, for
    all agents, it sets the default timeout to 60 seconds and
