This document specifies an application proxy, called Transport Converter, to assist the deployment of TCP extensions such as Multipath TCP. This proxy is designed to avoid inducing extra delay when involved in a network-assisted connection (that is, 0-RTT). This specification assumes an explicit model, where the proxy is explicitly configured on hosts. The proxy can be installed in managed networks by a network operator, for instance to help the deployment of Multipath TCP.
Working Group Summary
While Multipath TCP is an important use case, the Convert Protocol can actually be used for several TCP extensions. As the protocol is highly related to TCP standards and not specific to Multipath TCP, it was decided to home this document in the TCPM working group. The TCPM working group requests publication as Experimental document because the protocol targets controlled environments in which all network attachments are managed by the same administrative entity.
The document has been presented and discussed repeatedly in TCPM and as a result the protocol has changed several times. One frequently discussed design choice is whether and how to use TCP Fast Open (TFO). Appendix C explains the rationale for the final solution. There have also been some discussions whether such a proxy is really useful and needed. Some few contributors to the working group were not convinced by the MPTCP use case. During WGLC, Philip Eardley (chair of the MPTCP WG) has performed a comprehensive review, which was subsequently addressed in a number of document updates. The shepherd has reviewed the document before WGLC and verified that all WGLC comments are addressed. In addition to that, several contributors from vendors and network operators have explicitly expressed their support before and during WGLC. It has also been mentioned that the protocol is of interest to 3GPP. In TCPM, there is very strong but not unanimous support for publication as experimental document.
There is at least one known implementation: Tessares has an open-sourced a library (https://github.com/Tessares/libconvert) and a closed-source Hybrid Access Gateway (HAG) that uses this library directly to act as an MPTCP Converter. Korea Telekom (KT) has reported to TCPM the results of a PoC using these implementations (see https://tessares.pr.co/181810-kt-tessares-successfully-test-5g-low-latency-multi-radio-access-technology-in-a-commercial-5g-network). Other vendors have also expressed interest, but there is no publicly known second implementation.
The document shepherd is Michael Scharf. The responsible Area Director is Mirja Kuehlewind.