Re: [Qirg] Additional comments on Rodney draft

[Bruno Rijsman <[e-mail]>]

Ah yes, with apologies to Dave, I knew that this was going to be a controversial statement. Preference for soft-state vs hard-state appears to be like a preferred religion or preferred editor - once someone has an opinion on the matter, it is hard to convince them otherwise (and yes, I myself am guilty as charged ;-)

Just one minor correction: I do think you need a hop-by-hop control plane for the classical channel. Any simple control protocol will do (standard OSPF, BGP, whatever…). For the classical channel, you don’t need anything fancy like RSVP. I am only advocating RSVP-like constructs for the quantum channel.

— Bruno

> On Nov 20, 2019, at 2:35 PM, Dino Farinacci <[e-mail]> wrote:
> 
>> (4) In the QIRG meeting someone made an argument for using soft-state. I know this is going to be a controversial statement, but I think that hard-state is *much* better. Soft-state is the main reason that RSVP has problems scaling when we are creating a full mesh of LSPs between N edge nodes, where N large (say more than 100). You end up with 100^2 = 10,000 LSPs, and all the soft-state refreshing just kills the control plane. Hard-state protocols, such as BGP and the now-defunct CR-LDP, only need to advertise state once, and then it stays valid until the state is explicitly withdrawn or the transport connection breaks. The complexities of cleaning up the state are greatly exaggerated by soft-state proponents, and this is a well-solved problem (use TCP + one keep-alive per TCP connection, not per circuit).
> 
> Dave Oran said this and he is right. That is if you feel you need a control protocol hop-by-hop in the underlying classical network, which I think you don’t.
> 
> Soft state refreshes are more robust for failures and redundancy and allow state to time out gracefully (given there is no time budget to time out state, as Dave stated). 
> 
> Soft state refreshes in the last 10 years have gotten a bad name because when there is no state change, people think you waste bandwidth.
> 
> Dino
>