The company has now finished deploying the VoIP system for 1,800 employees in five main offices across the country.
To prepare for the change, it had to replace its existing frame relay network ready to carry high-quality voice and data traffic with MPLS. The network was provided by its incumbent telecoms operator, Cable and Wireless.
"MPLS was an essential forerunner for VoIP and has the unique feature of quality of service [QoS] which allows for voice transfer without getting broken services," said Richard Hodkinson, IT and operations director at Irwin Mitchell.
With the move to MPLS came a switch in the company's network topology, away from a star topology centring on its main Sheffield office, and towards a more resilient one where every site is connected to every other in a mesh configuration.
The company linked five main offices: Sheffield, Newcastle, Birmingham, Leeds and London, with the principal offices in Sheffield moving to a single state-of-the-art building housing 1,000 people. It also connected its satellite office in Marbella to the network.
"Everyone's become more risk-conscious and business continuity was a requirement," said Hodkinson. "With MPLS, if Sheffield was lost, we'd still have a telephone network. Also, each site could have its own internet connection, which reduces traffic between sites, and you get continuity of service and better performance."
He added that MPLS provides more bandwidth but does cost more - about 500,000 more than the previous network. "But you get network bandwidth, resilience and QoS."
Soon after the network was ready, the law firm completed its migration to VoIP, with Cisco call managers and Cisco IP Contact Center (IPCC), which routes calls and carries out network-to-desktop computer telephony integration (CTI). Each of the 1,800 employees received handsets.
Hodkinson said that VoIP products had matured to such a degree that the risks of adoption were low. "Cost savings weren't the driver for VoIP, and the unified messaging and other features were not enough to drive usage," he said.
Hodkinson added that it was time to retire the firm's ageing Meridian, BT and Nortel PBXs, which were well over 10 years old.