The Enhanced Communications Transport Protocol (ECTP) is a transport protocol designed to support Internet multicast applications running over multicast-capable networks. ECTP operates over IPv4/IPv6 networks that have the IP multicast forwarding capability with the help of IGMP and IP multicast routing protocols. ECTP could possibly be provisioned over UDP. ECTP is targeted to support tightly controlled multicast connections.

This Recommendation | International Standard defines the protocol which provides reliability control in the simplex multicast case, adopting a tree-based approach. Other Recommendations | International Standards in the ECTP family will define the QoS management functions for the simplex case and will define reliability control and corresponding QoS management functions for the duplex case and the N-plex case.

The sender is at the heart of multicast group communications. A single sender in the simplex multicast connection is assigned the role of the connection owner. The connection owner is responsible for overall connection management by governing connection creation and termination, connection pause and resumption, and join and leave operations.

For tree-based reliability control, a hierarchical tree is configured during connection creation. The sender is the root of the control tree. The control tree can define a parent-child relationship between any pair of tree nodes. This tree-based structure can result in local owners occurring at lower levels in the tree hierarchy as the control structure extends. Each local owner created becomes the root of its own local control tree. The connection owner will then be the root of the overall control tree. Error control is performed for each local group defined by a control tree. Each parent retransmits lost data, in response to retransmission requests from its children.