The “Experimental” status of Multipath TCP

http://blog.multipath-tcp.org/blog/html/2017/01/04/experimental.html

January 04, 2017

Multipath TCP is defined in RFC 6824 and I recently heard feedbackfrom someone working for industry who mentioned that Multipath TCP should notbe considered for deployment given its Experimental status. I was surprisedby this comment and I think that it would be useful to clarify some facts aboutthe maturity of Multipath TCP.

First, from a administrative viewpoint, the Experimental status ofMultipath TCP was decided at the creation of the IETF MPTCP workinggroup. At that time, it was unclear whether it would be even possible tospecify a protocol like Multipath TCP and the IESG wantedto encourage experiments with the new protocol. By selecting this option ,the IESG prepared a future standardisation of theprotocol and this is happening right now with the definition of a standards-trackversion of Multipath TCP in RFC6824bis . According to the milestones of the IETF MPTCP workinggroup, this revision should be ready in 2017.

Second, from a technical viewpoint, the maturity of a protocol cannot be inferred from the status of its specification. The best way to measure this maturity isto observe the interoperable implementations and the deployment of the protocol. From thesetwo viewpoints, Multipath TCP is a clear success. There are endhost implementations on Linux, FreeBSD, Apple iOS, MacOS and Oracle Solaris. Multipath TCP is also supported on various middleboxes including Citrix Netscaler, F5 BIG-IP LTM and Ericsson.

From a deployment viewpoint, Multipath TCP is also a huge success. Hundreds of millions of users of Apple devices (iPhone, iPad, laptops) use Multipath TCP every time they use the Siri voice recognition application. In Korea, a dozen of models ofhigh-end smartphones from Samsung and LG include a port of the reference implementation of Multipath TCP in the Linux kernel and use SOCKS proxies to bond WiFi and fast LTE. Several network operators provide those proxies as a commercial service. Other companies such as Swisscom or OVH also rely on SOCKS proxies to bond different types of links together. Another emerging use case are hybrid access networks. In various countries, network operators are require to provide fast broadband services, even in rural areas where deploying fiber is too expensive. Many of these operators want to combine their xDSL and LTE networks in order to improve the bandwidth to their customers. Tessares has already deployed a pilot hybrid access network solution that leverages Multipath TCP in Belgium.

Posted by Olivier Bonaventure