Re: WG ACTION: 1 week to discuss [LL37] Aggressive Time-outs

> From: "Mika Liljeberg" <[email protected]>

> I see what you and kre are saying, but I don't buy the number game. The
> fact remains that three is a wholly arbitrary number and likely to be
> wrong for most environments. Who is to say one probe is not enough? It
> all depends on the link error rate and the number of nodes supported by
> the link.
> 
> For instance, a Bluetooth PAN piconet (radio range 10 meters) supports a
> maximum of 7 nodes and the link layer is reliable. Three probes is
> completely unnecessary and at the same time constitute a usability
> problem, since many of the use cases involve quick ad-hoc interactions.

Link layer reliability is not the issue. Experience shows that in many networks the single most common cause of lost packets is busy hosts dropping them on input. A reliable link layer just ensures that both hosts know that the packet was received. There is no guarantee that a packet delivered is a packet processed. Either the new host sending the ARP probe, or the holder of a conflicting address could miss a packet this way.

Does Bluetooth's link layer reliability extend to broadcast probes?

I would accept that the number of probes could be a symbolic parameter NUM_PROBES rather than a hard coded number, but for this spec NUM_PROBES=3 is appropriate. A subsequent document for Bluetooth piconets (or whatever), could then specify NUM_PROBES=0 or 666 or anything appropriate.

Philip