RFC 1859 ISO Transport and Flow Control October 1995 requirements of the upper layer. Use of class 2 Non-use of Explicit Flow Control is suitable when the use of separate virtual data channels for normal and expedited Data are desirable or when an explicit disconnection of the Transport connection is desirable. Hosts which choose to implement this extension are expected to listen on the well-known TCP port number 399. It is recommended that the well-known RFC 1006 TCP port 102 not be used. This recommendation is done to minimise impact to an existing RFC 1006 implementation. The memo also describes the use of this extension within the DIGITAL Network Architecture (DNA). 2. The protocol The protocol specified by this memo is fundamentally equivalent to the protocol ISO 8073 Transport Class 2 Non-use of Explicit Flow Control, with the following extensions: - Expedited Data service is supported. - Splitting and Recombining may be used for Expedited Data transmission. - The Network Service used is provided by TCP. The ISO 8073 Transport protocol Class 2 allows Multiplexing. It is recommended that this capability not be use for performance reasons. The ISO 8073 Transport protocol exchanges information between peers in discrete units of information called transport protocol data units (TPDUs). The protocol defined in this memo encapsulates these TPDUs in discrete units called TPKTs. The structure of these TPKTs and their relationship to TPDUs are discussed in the next sections. 2.1 TCP service as a Network Service - The Primitives The mapping between the TCP service primitives and the service primitives expected by ISO 8073 Transport when operation over Connection-oriented network service is straightforward. Pouffary Informational