Introducing Microsoft NetShow Live
After you understand the principles of IP multicasting and check your
support, you can use Microsoft NetShow Live to implement an IP multicasting
application, such as the CEO audio conference.
NetShow Live delivers prerecorded wave sound audio, live audio, and files
over an intranet and the Internet. It contains NetShow Live Server and NetShow
Live Client. NetShow Live Server is always the source of multicasting. It
requires NT Server 4.0. You can install NetShow Live Client in an NT 4.0 or a
Win95 computer to receive multicast information through IE 3.0 or later. You
also need a sound card if a NetShow Live computer plays audio. To implement
NetShow Live, you must set up the server, the client, the Web page, and the
session.
1. Server Setup. You can
download NetShow from http://www.microsoft.com/netshow. Simply copy file
nslservr.exe to an empty directory on the server and expand the file. The
program automatically installs NetShow Live Server.
2. Client Setup. You don't need
to manually install any software on a client computer. When a computer displays
a Web page that contains a NetShow Live ActiveX control, the program on the
server automatically installs the client files, msrtp.dll and ws2stub.dll, to
the Windows System32 directory on the client computer.
The client directory of NetShow Live on the server contains two NetShow
Live ActiveX controls, nlaudio.ocx and nlfile.ocx. nlaudio.ocx plays audio on
the client computer, and nlfiles.ocx stores a multicast file on the
client computer. The control files must reside in a directory (e.g., the same
directory as client Web pages) that the Web browser can find.
3. Web Page Setup. You can
embed a NetShow Live ActiveX control in a Web page. To create such a Web page as
an audio player or file transfer for clients, you need basic knowledge of HTML,
Microsoft ActiveX Control (see http://www.microsoft.com/activex for more
information about ActiveX), and a scripting language such as Microsoft Visual
Basic Scripting Edition (VBScript--you can download VBScript from
http://www.microsoft.com/vbscript).
The Web page must include three key components: object information, form,
and scripting code. Listing 1, is an example of the HTML file for the
CEO audio conference; Screen 1 displays the corresponding Web page. An HTML file
for file transfer is similar. More information about file transfer is available
in the NetShow Live SDK documentation that ships with NetShow Live.
The Object ID section of Listing 1 provides the object information to the
browser; that is, it tells the browser which control to load when a client opens
the Web page. The control is nlaudio for audio player or nlfile for file
transfer. To load either control, specify version -1,-1,-1,-1, as shown in the
listing. You must include all the parameters shown in the Object ID section of
the listing.
The Form section of Listing 1 defines the form that the control uses. A
form defines a user interface of a Web page and generally contains buttons and
text boxes. The form in the listing has three buttons: Play starts the audio
player, Stop stops the audio player, and About displays the current version of
the audio control.
The Script Language section of the listing, written in VBScript, contains
all subroutines of scripting codes to implement the functions defined in the
Form section. For example, when you click Play, the program executes subroutine
BtnPlay_OnClick. The subroutine first stops any previous audio player; joins the
multicast group by IP multicast address 239.100.20.30 and port number 25050;
uses the sound format IMA ADPCM, Mono (Monophonic), 8.000kHz and 4 bit, which
are represented by numbers in NLAudio.SetCodec(17,1,8000,4) respectively; and
then starts playing audio.
4. Session Setup. NetShow Live
Administrator is the utility for setting up a multicast session on the server.
With the administrator, you can create, modify, delete, start, stop, and save an
audio, live audio, or file transfer session.
Screen 2 displays the properties of the CEO live audio session. All
computers participating in the session must use the same IP multicast address.
In addition, NetShow Live must specify a port number for a specific session. The
port number is a UDP port that identifies an IP process in a computer. This can
range from 1 to 65535. You can use the numbers 5000 and above for user
applications. Microsoft requires that the port number for audio be an even
number in the range of 16384 to 32768. For the session to run successfully, the
attributes of the Sound Format in the property of the live audio session must
match those in NLAudio.SetCodec(17,1,8000,4) in Listing 1, and the IP address
and port in the property of the live audio session must match those in
NLAudio.SetSocket ("239.100.200.30", 25050) in Listing 1. In this
example, obviously, you need to set the sound format to IMA ADPCM, Mono,
8.000kHz and 4 bit by clicking Change and then choosing this setting. Enter
239.100.200.30 in the IP Address field and 25050 in the Port field.
You can also define the multicast range of this session in the Time to Live
(TTL) area in the properties of the session. The multicast range can be on your
local network (the subnet where the NetShow Live server resides), your intranet,
or the Internet within a scope specified by the TTL number. TTL=32 in the
example means that you can forward the CEO audio from the server to a client in
a maximum of 32 hops.
Be Well Prepared
Now you know the basics of IP multicasting and Microsoft NetShow Live, an IP
multicasting application. IP multicasting reduces the demand for network
bandwidth for applications, such as video and audio conferencing, that are well
suited for this technology. Integrate support for IP multicasting into the
design and upgrade of your network infrastructure. When your management and user
community require multicasting applications, you can offer a good solution and
preserve your network.
Microsoft NetShow Live is Microsoft's first IP multicasting application for
the NT network. You can expect more from Microsoft and third parties as NT gains
more market share. Be well prepared.
The complete source and executable code is available for downloading from
Windows NT Magazine's Web site at http://www.winntmag.com.