Multipath TCP (MPTCP)
Multipath TCP (MPTCP), defined in RFC 8684 (obsoleting the earlier RFC 6824), extends ordinary TCP so a single connection can use more than one network path at the same time -- for example, a phone's WiFi and cellular radios together -- instead of being tied to one source and destination address pair for its entire lifetime. After the initial TCP handshake, either side can negotiate additional "subflows" over other available address pairs, and MPTCP schedules application data across whichever subflows are currently open, reassembling it in order at the receiving end so the application still sees one ordinary TCP socket. Because MPTCP signals itself through TCP options that an unaware middlebox can strip without the connection actually failing, a path that drops those options silently downgrades the connection to plain single-path TCP rather than breaking it outright, which makes partial MPTCP support hard to notice from the outside. Apple has used MPTCP for the Siri voice assistant since iOS 7, and several network operators use it to bond WiFi and LTE/5G for a single faster connection. Each subflow runs its own Path MTU Discovery independently, since different paths can have different MTUs.
By AdminKit team, Netbase JSC · Updated