The MPLS WG Archive

[Fahad Dogar <fahad.dogar@gmail.com>]

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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