Hello, I have an idea about Flexible Session Protocol, and wrote a preliminary concept implementation available at https://github.com/jaglee/FSP Abstract: FSP is a connection-oriented transport layer protocol that provides mobility, multihoming and multipath support by introducing the concept of 'upper layer thread ID', which was firstly suggested in [Gao2002] <https://mailarchive.ietf.org/arch/msg/ietf/u-6i-6f-Etuvh80-SUuRbSCDTwg> Authencity of an FSP packet is usually crytographically protected by some algorithm that requires a shared secret key. The upper layer thread ID is assigned roughly the same semantics as the Security Parameter Index (SPI) in MOBIKE [RFC4555] to index the secret key. The secret key is assumed to be installed by the upper layer application. FSP facilitates such secret key installation by introducing the concept of 'transmit transaction', which makes it flexible for the application layer protocols to adopt wide range of key establishment algorithm. I wonder if it could resolve some concerns in research. Best Regards, Jason Gao