Table 1 Sources of IIU and how they are dealt with in the heuristic

High complexity of the routing problem

Inaccuracy (the

Different mechanisms of the heuristic

P-M2-S2

solutions are

resolution in its present version (HMOR-S2 _PAS)

inherently

approximate)

Simplifications and approximations

Imprecision

The focus is on the relative value of the results

assumed in the stochastic model for

of the traffic model; small differences between o.f.

the traffic in the links, leading to an

values can be disregarded when comparing solutions

approximate model, unavoidable for

(this is a achieved by using adequate numerical traffic

computational tractability reasons

calculation procedures); scenario evaluation with

different traffic matrices

Instability phenomenon potentially

Imprecision

Criterion for choosing candidate paths for possible

arising in the path selection procedure

and uncertainty

routing improvement, embedded in the main

if the MMRA-S2 is applied successively to

heuristic ‘optimization’ cycle

all the end-to-end flows of each

service type

Numerical errors in the calculations of

Imprecision

‘Robust’ and well-tested numerical algorithms

marginal implied costs and blocking

(namely the Kaufman/Roberts algorithm and

probabilities of all the flows, propagating

fixed-point iterators)

throughout the resolution procedure

Stochastic nature of the traffic offered

External

Periodical update of traffic flows means via a

to the network

uncertainty

statistical estimate (first-order moving average)

based on real-time measurements; sensitivity/

robustness analysis; scenarios evaluation.

Uncertainties in the identification

Specific form

Definition of dynamic preference thresholds

of the ‘virtual decision maker’ in a

of internal

in the o.f. space, combined with the use

fully automated decision application

uncertainty

of reference points

environment