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[babel] Babel Hellos [was: Open issues with draft-ietf-babel-rtt-extension]

Juliusz Chroboczek <jch@irif.fr> Fri, 26 July 2019 21:53 UTC

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Date: Fri, 26 Jul 2019 23:53:51 +0200
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From: Juliusz Chroboczek <jch@irif.fr>
To: Baptiste Jonglez <baptiste.jonglez@imag.fr>
Cc: Toke Høiland-Jørgensen <toke@toke.dk>, babel@ietf.org
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Subject: [babel] Babel Hellos [was: Open issues with draft-ietf-babel-rtt-extension]
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> I also think unicast/unscheduled Hellos can make (a) work without further
> hacks, but indeed it feels somewhat uncomfortable that Hello messages are
> used for several roles (neighbour discovery and maintenance, link quality
> estimation, RTT estimation).

The logic is that:

  - Hello TLVs carry link-local information about the sending peer;
  - IHU TLVs carry link-local information about the receiving peer.

From that point of view, the local timestamp belongs in the Hello packet.

The apparent complication is that Hello packets are also used to carry
negative information: missing enough Hellos indicates that the sending
node has died or moved away.  Hence the need to carry a timeout.

An unscheduled Hello is simply a Hello that opts out from the timeout
subprotocol.

-- Juliusz

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