An Initial Prototype of Multi-Connection TCP Transport

Within the G-Lab NETCOMP project [1], we have developed Multi-Connection TCP (MCTCP) transport as a new multipath transport solution. MCTCP aggregates multiple Transmission Control Protocol (TCP) connections between potentially different addresses into a single session that can be accessed by an application like a single TCP connection. MCTCP encodes control information, as far as possible, in the payload of the TCP connections and therefore requires only minor changes in the TCP implementations, and it is transparent in the singlepath case. MCTCP is proposed to the IETF as a simple, modular, and extensible mechanism for multipath transport [2]. As shown in Figure 1, MCTCP starts with an initial TCP connection. As long as multiple paths are not used, an MCTCP transfer is identical to a standard TCP transfer, except for a new TCP option in SYN segments that signals MCTCP support between the session endpoints. Once multi-connection transfer is enabled, data chunks are sent over several TCP connections with a new type-length-value (TLV) framing format. This framing also permits the exchange of control information. The multiple TCP connections operate independently, but the MCTCP session coordinates their congestion control states. Applications can use MCTCP exactly like a single TCP connection, as described in [3]. In summary, MCTCP overcomes the limitations of other multipath transport protocols that currently discussed in the IETF.