[multipathtcp] primary/secondary path concept in mptcp?

[Yoshifumi Nishida <[e-mail]>]

Hi,
While I'm reading the recent threads in mptcp WG ML, I start wondering
there might be a need for primary/secondary path concept in mptcp path
managements, which is similar to the one in SCTP.

The mptcp spec already allows us to set backup flag to the path. But, in
this case, failover will happen only when the regular path becomes
unavailable. I think this will mean it can take longer time unless the
regular path can correctly sends RST.

The primary/secondary path idea is more light-weight approach than the
backup mode. When packets has been lost on the primary, it tries to utilize
the secondary path while checking the status of the primary (e.g. by
sending keep alives). Once the primary has been recovered, it starts using
the primary again.

A potential use case for this approach would be wifi and LTE combination.
While wifi link has intermittent connection failure (e.g due to handover or
minor connection problems), it uses LTE and after the wifi link has been
recovered, it starts using it again.

Some folks may say a well sophisticated path scheduler can handle this kind
of situations, but I'm not very sure yet because it may need complex
controls to be effective.

Thanks,
--
Yoshi