As a major supporter of IP multicast, Microsoft has implemented one of the world's largest multicast networks. Microsoft uses its company network to develop and test Microsoft IP multicast applications, and the company also fully uses multicast in daily operations. Microsoft primarily uses Cisco internetworking equipment in its network. Based on the company's current and projected future IP multicast support from Cisco and Microsoft's vendor-interoperability requirement, Microsoft sees Protocol Independent Multicast (PIM) as the most viable choice for its IP multicast routing protocol.

Cisco is PIM's major vendor advocate. Cisco supports Protocol Independent Multicast-Dense Mode (PIM-DM) and Protocol Independent Multicast-Sparse Mode (PIM-SM) and interoperability between the two protocols in its routers. Cisco also provides PIM-to-Distance Vector Multicast Routing Protocol (DVMRP) interoperability. Microsoft uses PIM-DM in its corporate LAN, and PIM-SM in its WAN and regional backbones. Microsoft also uses PIM-DM to link global PIM-SM regions. In addition to PIM, Microsoft uses DVMRP to tunnel its network to Multicast Backbone (MBone) and interconnect its legacy networks that run Multicast Open Shortest Path First (MOSPF). In its switched Ethernet environment, Microsoft uses Cisco's Catalyst switches to manage IP multicast traffic at layer 2. Cisco developed Cisco Group Management Protocol (CGMP) for its Catalyst switches, which deliver multicast data only to switch ports that connect to multicast group members. Traditionally, layer 2 switches flood multicast data to all ports.

Microsoft uses Windows Media Service's NetShow for company communications, distance learning, news delivery, and file transfer. Approximately 12,000 employees participated in one Bill Gates NetShow presentation. Microsoft also extensively uses NetShow for distance learning and training. Salespeople, consultants, and engineers working in the field don't need to travel to Redmond, Washington, or wait for training books and CDs to come to them via snail mail. These employees can use NetShow to view recorded training sessions and learn about new products through the network. Microsoft updates company news about its regional business units by multicast to deliver the news quickly and save network bandwidth. And as I was writing this article, Microsoft was planning to use multicast for file replication.