Sending Channel and Receiving Channel

Each IN channel or OUT channel has two parties: a sender and a recipient. This section specifies an abstract data model that senders and recipients MUST adhere to in order to implement flow control for this protocol. This protocol specifies that only RPC PDUs are subject to the flow control abstract data model. RTS PDUs and the HTTP request and response headers are not subject to flow control. Implementations of this protocol MUST NOT include them when computing any of the variables specified by this abstract data model.

The following sections define the separate protocol variables that are part of the receive windows and flow control data model.

Sending Channel


Implementations of this protocol MUST maintain a Boolean value named PlugState to represent if the Sending Channel is in the Plugged Channel Mode or the Unplugged Channel Mode.


In the context of receive windows and flow control, a sender MUST maintain a queue of PDUs that are required to be sent. The size and maximum length of the SendQueue are implementation-specific and on Windows implementations, bounded by available system memory.


The sender MUST keep track of the total bytes sent over the IN channel or OUT channel instance it uses to send PDUs. This abstract variable is called BytesSent. This variable MUST be the integer count of bytes that the connection has sent. BytesSent will have the inclusive range of zero and two gigabytes (the max of ChannelLifeTime).

Sender AvailableWindow

The sender MUST keep track of the local size, in bytes, of the available ReceiveWindow. This variable is called Sender AvailableWindow.


The sender MUST keep track of the size, in bytes, of the maximum receiving channel's ReceiveWindow.