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Optimal QoS path provisioning of
coexisted and aggregated traffic in networks is still
demanding problem. All traffic flows in a domain are
distributed among LSPs (Label Switching Path)
related to service classes, but the congestion problem
of concurrent flows (traversing the network
simultaneously) can appear. For LSP creation the
IGP (Interior Getaway Protocol) uses simple on-line
routing algorithms (e.g. OSPFS, IS-IS) based on
shortest path methodology. In the presence of
premium traffic where some links may be reserved
for certain traffic classes or for particular set of users
it becomes insufficient technique. On other hand,
constraint based explicit routing (CR) based on IGP
metric ensures traffic engineering (TE) capabilities. It
may find a longer but lightly loaded path better than
the heavily loaded shortest path. In this paper a new
approach to explicit constraint-based routing is
proposed. LSP can be pre-computed much earlier,
possibly during SLA (Service Level Agreement)
negotiation process. It could be a very good solution
for congestion avoidance and for better loadbalancing
purpose where links are running close to
capacity. To be acceptable for real applications such
complicated routing algorithm can be significantly
improved. Further improvements through heuristic
approach are made and comparisons of results are
discussed.

Keywords - intra-domain QoS routing, traffic
engineering in DiffServ/MPLS networks, constraintbased
routing