Blocking probability Overload situations in circuit switched networks -need to block calls Blocking probability Adverse impact on QoS Key performance measure for design and dimensioning
Blocking probability • Overload situations in circuit switched networks—need to block calls • Blocking probability • Adverse impact on QoS • Key performance measure for design and dimensioning 6
Alternate routing > Reduce blocking probability Primary Path If the shortest path is unavailable Origin Node the call can try other paths Destination Nor 0 · Edge-disjoint Problem Alternate 1) Alternate traffic usually use more pa resources than primary traffic 2)This inefficiency may lead to increase in blocking probability. Solution 1)Limit the number of choices of alternate paths 2) Add threshold to the alternate traffic certain capacity is exclusively reserved for primary traffic
➢ Reduce blocking probability If the shortest path is unavailable, the call can try other paths. • Edge-disjoint Problem: 1) Alternate traffic usually use more resources than primary traffic. 2) This inefficiency may lead to increase in blocking probability. Solution: 1) Limit the number of choices of alternate paths. 2) Add threshold to the alternate trafficcertain capacity is exclusively reserved for primary traffic. Alternate Routing Origin Node Destination Node Primary Path Alternate path 7
Alternative routing Hierarchical Ranked into several tiers Non-hierarchical More flexible and efficient Accommodate sudden strong increase traffic of any od pair · Reduce cost Mutual overflow strong dependency Instability can be mitigated by trunk reservation
• Alternative routing – Hierarchical • Ranked into several tiers – Non-hierarchical • More flexible and efficient • Accommodate sudden strong increase traffic of any OD pair • Reduce cost • Mutual overflow • strong dependency • Instability – can be mitigated by trunk reservation 8
Approximation of circuit switched networks with non-hierarchical alternative routing Generally does not admit product form solution Rely on accurate approximation No robust methodology is available that captures the overflow-induced state dependency
Approximation of circuit switched networks with non-hierarchical alternative routing • Generally does not admit product form solution • Rely on accurate approximation • No robust methodology is available that captures the overflow-induced state dependency 9
Erlang fixed Point Approximation (EFPA >decoupling a given system into independent server groups >total traffic offered to any server follows a Poisson process all individual input streams all overflow attempts
Erlang Fixed Point Approximation (EFPA) ➢decoupling a given system into independent server groups ➢total traffic offered to any server follows a Poisson process ▪ all individual input streams ▪ all overflow attempts 10