About RTMFP multicasting

HTTP and RTMP are both application-level protocols built on TCP (transmission control protocol). Using TCP is a standard method to obtain reliable data transfers over the web. However, the reliability of TCP comes at the cost of potentially high data latency.

Services that require low latency, as for live interaction with voice over IP or for online games, use the UDP protocol. UDP (user datagram protocol) is an alternative to TCP that delivers data rapidly. UDP is also compatible with packet broadcast (sending to all nodes on a local network) or multicast (sending to all subscribers).

Using UDP multicast, you can build a media player to

  • broadcast enterprise-scope information, such as a company meeting

  • broadcast video within and beyond your network without a content delivery network (CDN)

  • allow internal network clients to participate in a peer-to-peer (P2P) group, to help ensure high-quality video delivery

Using UDP, Adobe has developed the Real-Time Media Flow Protocol (RTMFP), an alternative to TCP-based RTMP and HTTP. To use RTMFP multicast, clients must run an application built for Adobe Flash Player 10.1 or greater or Adobe® AIR®. There are three forms of multicast that RTMFP supports:

Native IP multicast.
With IP multicast, a multicast address is associated with a group of interested receivers. The sender sends a single datagram to the multicast address. Then, the intermediary routers copy the message and send the copies to receivers who’ve registered their interest in data from that sender.

P2P (application-level) multicast.
P2P multicast uses Flash Player applications within the multicast group to route and relay data. Because the RTMFP protocol supports groups, this enables an application to segment its users to send messages and data only between members of the group. Application-level multicast provides one-to-many (or a few-to-many) streaming of continuous live video and audio.

Fusion multicast.
With Fusion multicast, native IP multicast and P2P/application multicast are combined. Clients can receive content via native IP multicast or fall back to P2P/application multicast if IP multicast is not available.

RTMFP is a managed connection that requires the authorization of a Flash Media Server 4.0 instance to make the introductions. Clients must remain connected to the server to retain the direct connection. Additionally, the server provides a script that handles publish/unpublish requests and republishes the live stream into a target Flash group. For further information on RTMFP, see the Building Peer-Assisted Networking Applications in the Flash Media Server 4 Developer's Guide.

Note: Dynamic streaming and DVR functionality (such as pausing or stopping a video) are not supported with RTMFP multicast at this time.