Re: M2PA (SIGTRAN) and multi-homing

Brian,


Refer to the Sigtran scenario's specification (e.g. ETSI EG 202 360
v1.1.1(2004-12)),
chapter 4.3...

In case there is only a single M2PA link in the link set, the messages
formerly sent out in parallel over different links are now serialized over
one channel, as M2PA makes no use of the " streams" concept provided by
SCTP...
Advise is: To avoid that messages are not delivered (message loss) in case
of retransmission, more than one link using M2PA should be used to form a
linkset.

That is why I design more than 1 M2PA link between two STP's (for
telecommunication SG, not internet host)

Regards,
Robby Pocornie





2006/12/11, Brian F. G. Bidulock <[email protected]>:
>
> Robby,
>
> Robby Pocornie wrote:                                               (Wed,
> 06 Dec 2006 15:12:50)
> >
> >    Hi Brian,
> >    Hi All,
> >
> >    Is it useful to have SCTP multihoming on M2PA links between
> Signalling
> >    Transfer Points/Gateway (STPG)?
> >
> >    I  see  in  the  IETF RFC that multihoming on M2PA has been taken
> into
> >    account as a possibility.
> >    Is this possibility advisible, without being harmful for the Network
> ?
>
> SCTP multihoming is not harmful to the network (otherwise it would not
> have
> been included in SCTP).
> >
> >    I also read that It is possible that transmission of M2PA messages
> MAY
> >    be  delayed  by  SCTP  slow  start under certain conditions, like
> Path
> >    failure (multi-homing) if SCTP switches to a new path.
> >    (<draft-ietf-sigtran-m2pa-09.txt >)
>
> Yes, they may be delayed.  But M2PA runs its own ack timer to ensure that
> the link is still viable.
>
> >
> >    I'm  now  in doubt,  because  a supplier  of STPG's told me that
> often
> >    customers  do  not  use  multi-homing  for  M2PA  associations
> because
> >    redundancy is already provided at MTP Layer 3 (Changeover
> procedures).
>
> That is an engineering decision.  If there exists sufficient link
> redundancy
> at MTP3, multihoming might be unecessary.
>
> >
> >    The   supplier   claim   that   M2PA  multi-homing
> can  actually  make
> >    configuration  more  complicated  because  of  timers for RTT (at
> SCTP
> >    level) and COO, CBO at MTP layer 3.
>
> It is true in practice that if SCTP protocol paramters are not set
> carefully
> that they can interact negatively with MTP3.  This is one reason why we
> recommended only 1 M2PA link between hosts, because if multiple M2PA links
> existed between hosts and all fail at the same time, MTP3 could thrash
> between links.  MTP3 pretty much assumes that links fail independently and
> is designed to accomodate only a single link fialure in a network.  In
> regular SS7, multiple link failures are extremely rare.
>
> >
> >    Do you have any argumentation or practical explanation to this claim?
> >    Who  can  advise  me why  to  Implement  Multihoming  OR NOT
> Implement
> >    Multihoming in a Sigtran M2PA Network connection?
>
> Unfortunately, there is no golden rule.  These are operational decisions
> that
> must be made with full knowledge of the topologies involved.  If you have
> little operational experience of your own upon which to rely, it might be
> a
> good idea to rely partly upon the operational experience of your vendor.
>
> --brian
>
>
> --
> Brian F. G. Bidulock
> [email protected]
> http://www.openss7.org/
>

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