s. If the call is successful then this tandem node remains the currently nominated tandem node p,(n+1)=(1-a)p,(m) (5.58) for overflow calls. Otherwise, if the call is rejected by this two-link route the call is lost and the tandem node for future overflow calls However, if the call fails, then Equations 5.59 and 5.60 are used. is re-selected by choosing at random from amongst the set of feasible tandem nodes for that source destination node pair. Note p,(n+1)=(1-e)p,(n) (5.59) that the tandem node is not re-selected if the call is successfully routed on either the direct route or the two-link alternative route. (5.60) The term sticky random routeing has been coined to emphasise this p,(n+1)=(1-E)p(n)+ j x i property of the strategy. The design of the DAR strategy attempts to construct a random The learning parameter, a, and the penalty parameter, E are two search algorithm to find and then efficiently utilise spare capacity parameters of the scheme such that 0<E<a<1 and E is small available within a network under varying conditions of traffic and compared to a. The value a is typically small SO that the updating capacity mismatches. step is gradual. If B is the probability that a call is blocked on route The simplicity of DAR permits us to extend the Erlang fixed point r then it can be shown that the Lo_scheme tends to approximately models of Section 5.3 to model DAR's long run average behaviour. equalise blocking probabilities, B_, while an LR-p scheme (where E Suppose that n. is the birth and death process for the utilization of = a) equalises the blocking rates B P. over routes r = 1,2, R. the link (i, ,j). Then as in Equations 5.25 and 5.26, Equations 5.61 In practice, in a fully connected network it is preferable to first try and 5.62 may be obtained where C. and r are the (i, j) link the direct route between two nodes and then apply the automaton to capacities and trunk reservation parameters respectively. the choice of two-link overflow routes, rather than to use the automaton to include the single link di