Over-provisioning or Differentiated Services - A Case Study on integrating services over IP

A key question when integrating voice traffic into a corporate data network is cost versus benefit. Will an Integrated Services network save WAN link capacity which determines network costs? Does the complexity of additional explicit quality of service enablers like Differentiated Services (DiffServ) pay off its capacity savings? In a case study we have simulated the busy hour of a bank’s Intranet with ns-2 to determine the capacity needed with and without integration, with and without DiffServ. Due to online processing requirements we modeled all data traffic as web traffic with stringent response time requirements. Voice traffic was modeled as of ITU-T G.711 PCM type without silence suppression. For our business case we find that neither over-provisioning a one service class network nor a two class DiffServ network brings any savings. Only when relaxing the response time requirement for some of the web traffic, which is more realistic than adding additional traffic to the Intranet, we find that a three class DiffServ may save up to 60% of capacity. The amount of savings depends on the amount of traffic without QoS requirements in the Intranet.