Subject: [mpls] On Preemption in a DiffServ aware MPLS-TE environment

From: Fahad Dogar <[email-masked]>
Date: Fri, 18 Nov 2005 20:37:54 +0500

Hi,
 Regarding preemption, I wonder if anyone can comment on how likely is that
we will need to preempt several LSPs to accommodate a new LSP?
 We are currently considering the problem of preemption in a DiffServ aware
MPLS environment. Various preemption schemes exist (in literature) some of
which try to minimize the number of preempted LSPs. All such schemes assume
that the average bandwidth of lower priority requests is *much* smaller as
compared to the mean size of higher priority requests and, therefore, imply
that multiple lower priority requests need to be preempted to accommodate a
higher priority request. Is it reasonable to assume that in a multi-class
environment, large variation in traffic patterns of different classes would
exist? Any measurements or studies out there? Any justifications for
assuming different mean sizes for traffic requests belonging to different
classes?
 In contrast to the popular assumption, if the traffic distribution of
different classes is similar in terms of mean bandwidth, it is very *likely*
that accommodating one high-priority LSP would require preempting just one
low-priority LSP, especially when the number of LSPs is large. This
significantly reduces the complexity of preemption algorithm.
 How likely is it that for a given traffic request, typically we would need
to preempt several LSPs (and not just one) in order to accommodate the new
request.
 Thanks in advance,
Fahad
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