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OT: Re: [bluetooth-dev] IP over Bluetooth - current structure notso clean



On Mon, 30 Oct 2000, Andrew Worsley wrote:
>   Also the cheap frequency hopping approach is not that suitable for
>   connectionless, data transmission. It's cheaper (I understand) but
>   in it's present form means that you can potential have long delays
>   before you discover a device, like up to 10 seconds, from memory.

That is for a unit totally out of sync though. If the devices have been in
contact in a not-so distant past, it's much faster to get synchronized
(sync. in the long hopping pattern sequence - if you've been in contact
recently you know approx. where in the pattern the peer is).

The design is optimized for stand-by power-consumption, AFAIK. You can
make a time-slot protocol use many powers-of-10 lower energy than the
comparable CSMA/CA wireless schemes, since you don't have to have the
receiver enabled other than at the exact times you _know_ you can get a
timeslot sent to you or an inquiry/broadcast. And this has it's
implications elsewhere of course.

Re. your concerns below. I think everybody who wants to use BT as a full
wireless network shares them. The problem again is that it was more
designed as a cable-replacement for personal cells, very low standby power
and a very robust voice-carrier. You can get around all of the problems by
having suitably clever access points, taking up / taking down links,
repeaters god knows what however :) It'll be interesting to see what
"work-arounds" will be most popular.. (and the guys in the
interop-departments will probably get their hands full :) 

/Bjorn

>   So you can't do a whole lot of IP like things. Broadcast an IP packet -
>   like a SNMP trap or ARP or such like in any easy way, when something
>   goes wrong. First you have to form a pico net, which can take time
>   and then some, more to negotiate connections, PPP what ever.
> 
>   With each piconet you can only have 7 devices with one master how how are you
>   going to have lots of embedded devices next to each other in a house? i.e.
>   your kitchen area or audio/visual entertainment system? Surely a more
>   practical system is to establish connectionless links so they can mostly
>   stay quiet and quickly send data when they have something to say to an
>   arbitrary device?
> 
>   Also if you want to send a message to a particular bluetooth device, how do
>   you refer to it. Typically in Internet land you have a domain name which
>   stays relatively constant, an IP address which can change occasionally (but
>   which DNS will map the domain name to automatically) with the link address
>   only usable by immeadiate neibours.

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