Problem A $$ Requirements and initial requirement engineering

A large telecommunication company wanted to expand its Internet Protocol $($IP$)$ network to support $$carrier$-$class

services$,$ and more specifically high$-$quality voice over IP $($VOIP$)$ systems. One important aspect to achieve this goal

was synchronization of VOIP servers and other equipment. Poor synchronization results in low quality of service $($QoS$),$

degraded performance, and unhappy customers. To achieve the required level of synchronization, the company wanted

to deploy a network of time servers that support the Network Time Protocol $($NTP$).$ Time servers are formed into groups

that typically correspond to geographical regions. Within these regions, time servers are organized hierarchically in

levels, where time servers placed in the upper level of the hierarchy are equipped with hardware that provides precise

time. Time servers in the lower hierarchy use NTP to request time from servers in the upper levels or from peers.