In message <E2D27064CD59574F88D05AEF5728396D159D56@PH01SRV02.photuris.com>, Lea
h Zhang writes:
> Curtis,
>
> I have one inline comments.
>
> Leah
Leah,
If the major ingress and egress of traffic are A-E and A-F, then
creating two tunnels B-C-D and B-D has no effect.
You can create more than one LSP from A-E or A-F and further subdivide
the traffic to get a better load split. You may be able to improve
load balancing by splitting either of them into two equal LSP. You
can get a better load balance through an unequal split. You need to
know apriori which LSP need to be divided in this way and the optimal
percentage of the split. This is just fine in theory but in practice
is considered difficult to manage in a network of any practical size.
Curtis
> > -----Original Message-----
> > From: Curtis Villamizar [mailto:curtis@workhorse.fictitious.org]
> > Sent: Wednesday, May 09, 2001 8:18 AM
> > To: Yufei Wang
> > Cc: 'curtis@workhorse.fictitious.org'; 'van@packetdesign.com';
> > 'xiaoxipe@cse.msu.edu'; 'irtf-rr@puck.nether.net'
> > Subject: Re: interesting Infocom paper on traffic engineering via
> > routing metrics
> >
> > MPLS can put the A-E traffic on one leg and the A-F traffic on the
> > other leg but cannot accurately balance the load.
>
> I do not believe that this is the case. IF we build two MPLS tunnels,
> A-B-D-F and A-B-C-D-E, we
> can put the A-E traffic on the leg, and A-F traffic on the other leg. But
> there are other
> ways of building the tunnels for load balancing. For example, we can build
> two tunnels from
> B to D, B-C-D and B-D. Since these two tunnels share the same source and
> destination nodes, we
> can set the bandwidth of these two tunnels to be the same to do equal load
> balacing between
> B-C-D and B-D.
>
>
> > The only technique
> > so far that can accurately balance the load is OMP. With lots of MPLS
> > LSP, the CR based MPLS/TE load balance is generally not as good but
> > "good enough". With OSPF and ECMP metrics can be set so that load
> > balance is not as good as MPLS/TE. Some consider the ability of the
> > IGP to load balance to be good enough. Others don't consider it good
> > enough and consider IGP load balance too hard to manage and that was a
> > principle motivation for MPLS/TE.
> >
> > With IGP load balance there can also be extremely poor load balance
> > after a failure in the topology until all of the costs are changed.
> >
> > Curtis
> >
> >
> > > > Many simple topologies cannot be optimized by setting IGP
> > metrics but
> > > > can easily be optimized using MPLS. For example:
> > > >
> > > > C E
> > > > / \ /
> > > > A---B---D--F
> > > >
> > > > The largest traffic contributors are A-E and A-F. The
> > bottlenecks are
> > > > B-C or B-D where the available capacity of B-C and B-D
> > are unequal and
> > > > the flows A-E and A-F are unequal. It is easy to pick values that
> > > > where neither ECMP or putting all of the flows on one leg
> > would do as
> > > > well as a traffic engineered solution.
> >
>
This archive was generated by hypermail 2b29 : Mon Aug 04 2003 - 04:10:03 EDT