Discuss the 5-level switching hierarchy recommended by CCITT.

Hierarchical networks are able of handling heavy traffic where needed, and at similar time use minimal number of trunk groups. Within a strictly hierarchical network, traffic by subscriber A to Subscriber B and vice versa flows by the highest level of hierarchy that is quaternary centres. A traffic route through the highest level of hierarchy is termed as final route

1. End offices are the switching offices to that individual subscriber are directly connected

2. Toll offices are the switching offices utilized to interconnect the end offices.

Intercity calls are routed through toll office.

3. A very populous area, like a large city will have several end offices. A lot of the traffic involves calls among subscribers in the city and therefore between end offices. To make possible this end office to end office traffic a Tandem switching office may be given for one group of end offices.

CCITT hierarchical structure

LA = Local area

PA = primary area

SA = secondary area

TA = Tertiary area

QA = Quaternary area

E = Exchange

TE = tandem exchange