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Re: [ecf-dev] Central remote server strategy

On 10/15/2013 12:58 PM, Markus Alexander Kuppe wrote:
On 10/15/2013 07:18 PM, Scott Lewis wrote:
More generally though...in a 'group' computing model (i.e. >= 2 group
'members'), there's a long-standing problem called 'distributed
consensus'.   Distributed consensus [1] is basically the ability of all
parties in a group to agree on the value of some data.    As simple as
this sounds, it's not simple in general...as with some topologies (e.g.
a network of links between group members), it can be very difficult to
define a protocol that guarantees that all group members reach consensus
about something as simple as what the current group membership is (i.e.
who's 'there' or 'present' in the group).
What kind of consensus do peers in our example chat application even
need to reach?

Well, one sort of consensus that would frequently be expected in a chat session would be a reliable indication of who is actually participating in the chat...i.e group membership. That's one form of consensus...i.e. having all participants (eventually) agree on the group membership.

0f course, if that's not expected/required for this use case then it doesn't need to be provided. But group membership...aka presence...is frequently expected in real-time chats.

The current design simply allows peers to send a message
and no guarentee is given whether this message is (eventually) received
by 1 to n other peers. This problem is too simple to even require
consensus whatsoever and thus qualifies for a basic peer to peer design.

Ok...if such info is not guaranteed for this sample app then that's fine. I'm just pointing out that if such info is to be provided (e.g. presence/membership) then consensus through some means would be needed.

Scott




M.
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