[asterisk-users] dundi network - redundancy / fault tolerance ?

[Ex Vito]

  Hi list,

  I'm planning a private DUNDi network for a cross-country
  distributed PBX. Initially it will be composed of about 10
  systems, growing to about 20.

  Current requirements point to a topology of two interconnected
  "DUNDi hubs", each peering with half the PBXs... This would
  lead to two interconnected / inter-peered stars.

  Example:

  - Consider PBXs A to H
  - C and E will be hubs and peer with each other
  - A, B and D peer with C
  - F, G and H peer with E

  This leads to a maximum three hop lookup and will make
  good use of current network topology / bandwidths. Of course,
  should any of the hubs be unavailable and the lookup capability
  is severely compromised.

  Now, how to move on to acheive some kind of fault tolerance ?
  According to the docs we've studied, DUNDi does not like loops
  (which we assume one can limit with low enough TTLs).

  Our doubts are:

  - Should one use the "order" peer parameter to specify alternate
    lookup paths / peers ? Is that its purpose ? If not, what is it used
    for ?

  - Alternatively, should one create loops in the DUNDi topology and
    limit them via TTL ?

  - If both options are possible, which would be the trade-offs between
    them ? (Not clear at all to us!)

  - Assuming any of the above is possible as a means to acheive
    redundancy, which of the following topologies would your prefer ?
    (hmmm, maybe I need to refresh my graph theory...) ;-)

    #1 - Peer each PBX with both hubs
    #2 - Duplicate both hubs and peer each PBX with its hub and
          its hub dup

    For better understanding, take a look at:

    #1 - http://www.2photosharing.com/images/qhpnzycd7j7kf26j2f.png
    #2 - http://www.2photosharing.com/images/npzbwvgnr4t079laou0.png

  Thanks in advance for review and feedback.
  Cheers,
--
  exvito