Structured Stream Transport (SST)
Just like other transport protocols aim to improve upon TCP, Structured Stream Transport (SST) is no exception. SST is an experimental protocol that adds stream management on top of TCP to allow systems to effectively perform streaming reception and interactive connections simultaneously. SST started development in 2006 and 2007, but in almost 10 years, hasn't garnered significant support to become a mainstream transport protocol. SST is an example of how a protocol has a tough road to join the likes of TCP and UDP in mainstream adoption.
Stream Control Transmission Protocol (SCTP)
SCTP is yet another transport-layer protocol that combines some of the features of TCP with some of the features of UDP. In 2012, I wrote an article titled "What About Stream Control Transmission Protocol (SCTP)?" that described SCTP and its message-oriented approach compared with TCP's stream-oriented approach. There are many implementations of SCTP and seemingly a lot of potential for this protocol. However, TCP and UDP have considerable momentum and there is gravity for developers to consider these two traditional transport layer protocols. Without major operating system support by Microsoft and Apple, this protocol is destined to be another footnote in the Internet's history book.
Datagram Transport Layer Security (DTLS)
Transport Layer Security (TLS) (previously known as SSL) has been used for many years to secure web sites using HTTPS. There was an industry-wide desire to provide privacy for connections datagram protocols like UDP. Datagram Transport Layer Security (DTLS) in an IETF protocol (originally RFC 4347) that provides for confidentiality and non-repudiation for UDP streams. DTLS is used with the Cisco AnyConnect SSL VPN client. DTLS version 1.2 was originally conceived for use as a way to secure UDP streams (RFC 6347), but DTLS can also be used with other protocols such as DCCP (RFC 5238), with SCTP (RFC 6083), and with SRTP (RFC 5764).
Secure Real-time Transport Protocol (SRTP)
Similar to DTLS, SRTP has the goal of providing encryption and message authenticity for real-time communications using UDP or multicast. SRTP is an extension of the Real-time Transport Protocol (RTP) that is frequently used for streaming media transport and frequently accompanies the RTP Control Protocol (RTCP) that provides for management of those streams. SRTP also provides a secure form of RTCP called Secure RTCP (or SRTCP). The Secure Real-time Transport Protocol (SRTP) and SRTCP were defined in 2004 by the IETF with RFC 3711. SRTP has been augmented with the RFCs titled "Encryption of Header Extensions in the SRTP" (RFC 6904) and "Support for Reduced-Size RTCP: Opportunities and Consequences" (RFC 5506).
Reliable User Datagram Protocol (RUDP)
RUDP aimed to provide a compromise between the connectionless lightweight UDP transport protocol and the connection-oriented heavyweight TCP protocol. RUDP provided for ordered packet delivery and acknowledgement of receipt and retransmissions. It is very likely that you haven't heard of RUDP. That is because it was originally created by Bell Labs as a new addition to their Plan 9 operating system. Eventually, Plan 9 was released by Lucent Technologies as a free open source operating system, but it didn't gain the industry-wide adoption of Linux and Android. Cisco integrated RUDP into their SS7 Cisco PGW 2200 Softswitch node Signalling Link Terminal (SLT)
Summary
It is human nature to try to improve upon inventions of others and to try to optimize systems and improve efficiency. IPv4 and the protocols above the Internet layer continue to develop, despite the steamily ubiquitous use of the Internet Protocol. TCP/IP will never be finalized; it will continue to evolve and improve as we think of new ways to communicate.
These optimizations to TCP and UDP and IP have potential to improve the efficiency and performance of internet communications. However, each of these new transport layer protocols need to be implemented into host operating systems, and integrated into applications such as web browsers and web server software. Wikipedia has an excellent table that compares and contrasts many of these transport layer protocols. It remains to be seen which of these protocols will dominate. Some of these protocols have potential to gain mainstream adoption, while others will wither away as research projects. Other protocols have already gained momentum and you may already be using them today.
This story, "12 extensions to TCP/IP that optimize internet connections" was originally published by Network World.