Two parameters directly affect the flow of data across a virtual circuit: Window Size and Packet Size. Window Size is the maximum number of unacknowledged packets that can occur in a call. Packet Size is the maximum number of data bytes that can fit in the user data field of a packet.
You can use the Flow Control Parameter Negotiation facility to allow the Window Size and Maximum User Packet Size parameters to be negotiated in each direction on a per-call basis.
See Default Packet and Window Size Configuration for more information about setting default packet and window sizes.