Win2K is the first commercial product to support MADCAP. The Win2K DHCP service includes both unicast DHCP and MADCAP services. You can configure the MADCAP service on the same DHCP server that allocates unicast addresses or a dedicated DHCP server that assigns only multicast addresses. In Win2K's DHCP manager GUI, which Figure 5 shows, you can create one or more multicast address scopes on a DHCP server. To create a multicast address scope, right-click the DHCP server node in the DHCP manager GUI, and click New Multicast Scope, which brings up a multicast scope wizard that walks you through the creation of a multicast address scope. In the wizard, you can define a range of multicast addresses that a client can lease from the scope, the client's TTL value, and the duration of a limited lease or an unlimited lease duration. Give the defined scope a meaningful name, such as 1 Day scope, and specify a scope lifetime. The DHCP server will remove the scope from the server's service at that time and date. By default, a scope's lifetime is infinite.
If you have a MADCAP server in your network, a MADCAP client can lease a multicast address from that server. Figure 6 illustrates this process. Before the client can lease a multicast address, it must have had a unicast IP address (i.e., static or dynamic) for IP communication. To discover MADCAP servers in the network, a client multicasts a discovery message to 239.255.255.254. Win2K MADCAP servers always listen to this multicast address. All MADCAP servers that receive the discovery message unicast an offer message to the client. The offer message contains a list of multicast address scopes that the server offers and the servers' IDs. After the client receives all available multicast address scopes, it must choose the scope it wants. In a multicast application, a user can manually select a multicast scope or the application can automatically select a scope. The selection method depends on the application implementation. The client then multicasts a request message that includes the scope name, number of multicast addresses the client needs, and the MADCAP server's ID to 239.255
.255.254. In a unicast acknowledgment message, only the MADCAP server that contains the requested scope and the matching server ID replies to the client. The reply contains one or more of the multicast addresses that the client requested.
When a MADCAP server and client reside in different subnets, you don't need to configure the DHCP agent or helper configuration in the router that connects the subnets to relay DHCP messages that use unicast DHCP. However, you need to make sure that your network supports multicast because the MADCAP discovery and request messages use multicast. If you've set up scope-based boundaries in your network, ensure that each area contains at least one MADCAP server because a scope-based boundary will block messages to the local scope address 239.255.255.254 if the MADCAP server resides in a separate area.
Although Microsoft's Phone Dialer and Exchange 2000 Server conferencing application are two of the few MADCAP-enabled applications available, future multicast applications will include MADCAP support to ease multicast address management. In addition, Microsoft provides seven MADCAP API functions in its Platform Software Development Kit (SDK—http://msdn.micro
soft.com/library/psdk/network/mdhcp_ref_09rn.htm) to help software developers build MADCAP-enabled multicast applications. If you develop Windows-based multicast applications, add MADCAP support to your products. If you buy multicast applications from vendors, ask for MADCAP-enabled products.
Phone Dialer
Win2K provides a built-in multimedia application called Phone Dialer that lets you make voice calls and conduct video and audio conferences over IP networks. Phone Dialer provides multicast functionality through its video and audio conferencing capabilities, and the application supports MADCAP as a client. To use Phone Dialer, click Start, Programs, Accessories, Communications, Phone Dialer.
To host or participate in a video or audio conference, you must have working video and audio devices in your Win2K system, a MADCAP server, and Microsoft Site Server Internet Locator Service (ILS) on a Win2K Server system in your network. ILS is a component of Win2K's Network Services and requires Microsoft IIS to run. Phone Dialer uses ILS to publish and locate conferences. Phone Dialer conferences don't require Active Directory (AD), but it can benefit Phone Dialer by automatically locating the ILS server if the ILS server and Win2K computer running Phone Dialer are in AD. To find published conferences, in the Phone Dialer window, which Figure 7 shows, select Internet Directories, My Network, Conferences, which is the default location. To change this location, you must manually configure the ILS server's location in Phone Dialer. To do so, right-click My Network, select Add Directory Server, and enter the ILS server's DNS name or IP address when the system prompts you for a directory name.
If you originate a conference, you can manually set up user access permissions, and you can modify the conference properties or delete the conference. By default, the conference owner has all permissions and everyone who has the necessary system configuration in your network can join the conference.
To host a conference, click the New icon in Phone Dialer's toolbar. In the resulting Conference Properties window, which
Figure 8 shows, name the conference and specify the conference's start and stop time. As a MADCAP client, Phone Dialer lists all multicast address scopes that it received from the MADCAP servers. Select a scope in the Conference Scope section. Be sure that the scope you choose has an address lease that is longer than the duration of your conference. For example, in Figure 8, the conference duration is 1 day and 8 hours, so you need to select 2 Day Scope. Thus, when you create multicast address scopes in the MADCAP server, giving each scope a user-friendly and meaningful name is important. Phone Dialer leases two multicast addresses, one for video and one for audio. If Phone Dialer doesn't find a MADCAP server, it will randomly generate two multicast addresses and use them for the conference. You define user permissions for the conference on the Permissions tab of the Conference Properties window.
Joining a conference is easy. First, find the conference you want to view in the Conferences folder under the My Network or ILS server directories, then highlight it. Click the Join icon in Phone Dialer's toolbar, and Phone Dialer will display the conference if you have the necessary permissions. Even if you're the owner or originator of the conference, you use this process to join the conference.
Prime Time for IP Multicast
Win2K's IP multicasting components let you easily integrate Win2K into your corporate multicast network infrastructure. This functionality makes now the prime time to use IP multicast in your Win2K network.