Sun Stable is a global insurance company with headquarters located in Houston， Texas. Thecampus there is made up of a number of office buildings located within the same vicinity. In 2003，a new building. Building 331B was added. The additional building houses approximately 1000 employees. Ratherthan deploy a private branch exchange （PBX） in the new building， Sun Stable has decided toimplement an IP telephony solution. External calls will be carried across a MAN link to anotherbuilding， where a gateway connects into the worldwide PBX network of Sun Stable. Voice mail andunified messaging components are required and all IP phones and workstations should be on separate VLANs and IP subnets. ActualTests.comWhich IP telephony deployment best suits their need？（）