Flow control of messages to/from clients and services in a remote access system. Within the remote access system a layered architecture may be provided that includes a client layer at a client device, a service layer associated with a service, and a server layer that is a communications proxy for messages sent between the client device and the service. The service layer may have a receive queue for messages received from the client device and a send queue of messages destined for the client device. The server layer may include an outbound queue of messages destined for the client device. Full duplex communications between the client layer and the server layer may be implemented using a service protocol in a first channel for communication between the client layer and the server layer and a second channel for communication between the server layer and the client layer.