[Spread-users] Algorithms used by Spread

[anders.lindstrom at ubs.com]

Hi,

I've been reading the papers 'The Spread Wide Are Group Communication System' and 'The Totem Single-Ring Ordering and Membership Protocol' as well as 'Extended Virtual Synchrony'.

I am particularly interested in the Ring protocol. In the 'Spread' paper it says that

  ...the Ring protocol is a modification of the ring protocol used in Totem and Transis. In Totem and Transis, the Ring protocol
  is used to provide reliability, global flow control and global ordering.

  Spread uses the ring protocol for one main purpose: packet-level reliability and flow control within the local site, and one
  secondary purpose: message-level stability within members of the ring. The crucial point is that the same token is used for both
  these functions. In the same token circulation, the ring aru calculation algorith updates both the packet and message are fields.

I'm not exactly sure what this is saying. It seems to imply that Ring improves on Totem because it uses the same token for packet-level
and message-level parts of the protocol. I can't say this for sure because the Totem paper doesn't mention packet-level issues (at least, I couldn't find anything).

It also seems to be saying that message-level stability is less important (i.e. 'secondary') within Ring than within Totem. Is that true? I don't see how stability can be of secondary importance. I would have thought that it is of equal importance unless your not using safe delivery.

Cheers,

Anders.


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