Transport Options

Despite the widespread use of RTP over UDP for audio and video streaming, the experts are still at work on Transport layer options that address the fundamental unsuitability of either TCP or UDP for streaming situations.

Stream Control Transmission Protocol (SCTP), which is described in RFC 2000 and later documents, is a connection-oriented transport protocol (and thus more similar to TCP), but, like UDP, SCTP is more message-oriented. SCTP also offers the capability to maintain several message streams in parallel through a single connection.

Datagram Congestion Control Protocol (DCCP), which is described in RFC 4340, also borrows features from both TCP and UDP. DCCP is connection-oriented (like TCP), with fast but unreliable delivery (like UDP).

Both SCTP and DCCP perform something called congestion control. As you can see by the name, DCCP is especially interested in providing a congestion control mechanism. Congestion control is a means for reducing the kinds of retransmission issues associated with TCP and providing more efficient use of the bandwidth. Algorithms used by the protocol adjust the characteristics of the data flow to optimize throughput and reduce the number of retransmitted packets.

Implementations of SCTP and DCCP are available now. SCTP has been around for a little longer, and is perhaps better known to developers, but DCCP shows promise.