Chapter 11: Multicasting Live Streams

Multicasting helps you conserve bandwidth. It requires a specially configured network. In this chapter, you'll see how to set up RealProxy to multicast.

Overview

Multicasting is a way of sending a single live stream to multiple clients, rather than sending a stream to every single client.

Multicasting

In contrast, regular unicasting transmission sends a stream to each client that requests it.

Unicasting

To take advantage of multicasting, both RealProxy and clients, as well as the routers between them, must be multicast-enabled. For this reason, multicasting is mostly used with intranets where routers can be configured for multicasts. Multicast delivery can be done over the Internet only where intermediary network devices have been multicast-enabled.

Multicast is automatically used (when available and configured) for pull split streams. It is not used with passthrough or cache mode.

Multicast Methods

This method of multicasting uses the RTSP protocol to send control information over a TCP channel. RealProxy maintains a control connection for each client. The data channel is multicast to all clients. RTSP multicast provides the following features:

• Connection statistics—RealProxy can receive client connection information.

• SureStream—these multiply-encoded files are supported.

  	Note
  	RTSP multicasting works only with RealSystem G2 clients.

Setting Up Multicasting

Before you set up multicasting, you need to do two things:

• Configure the network for multicasting.

• Select the addresses you'll use for your multicasts.

Setting Up the Network for Multicasting

Before setting up RealProxy, verify the following items with your network administrator:

• Routers in your network are multicast-enabled.

• The computer running RealProxy is correctly configured for multicast support.

In addition to network settings, clients must be configured to request multicast transmission of live material. Consult the client software's user guide for information on configuring the client.

As noted earlier, both RealProxy and clients, as well as the routers between them, must be multicast-enabled in order for you to distribute presentations using the multicast features. This section describes only what is required to enable RealProxy for multicast broadcasting.

Allocating Addresses and Port Numbers in RealProxy

There are two factors to take into account when establishing the addresses and port numbers that RealProxy will use for multicasting:

• Select addresses from a legal range of available addresses. Valid ranges are between 224.0.0.0 and 239.255.255.255. The network administrator should know which multicast addresses are available on your intranet. On the Internet, certain ranges such as the addresses between 224.0.0.0 and 224.0.0.255 are reserved for other uses; see RFC 1700, "Assigned Numbers" for a complete list of restricted addresses.

• You must select enough addresses for the type of file you are multicasting. See "Determining Required Addresses and Port Numbers" for information on selecting the appropriate number. You'll need to know how many bit rates are included in each file that you are multicasting, and set aside the appropriate number.

Although the information in this document will help you calculate the number of addresses and port numbers you'll need for multicasting, you'll still need to consult with your network administrator regarding the actual addresses you'll use.

Determining Required Addresses and Port Numbers

For each file that you are transmitting via multicast, you must calculate the number of addresses you'll need. The number of addresses is based on the number of bit rates in the file. For simple RealVideo files, figuring the number of addresses and port numbers is relatively simple. SureStream files are more complex, as they can contain several bit rates, each with its own number of streams.

Unless you can find out the number of bit rates in the files that you are streaming, you'll have to guess. A safe number is six bit rates per file; the maximum number of bit rates that would be present in a single SureStream file is 14, yet files prepared for multicasts are likely to include only the higher encoding rates. A non-SureStream file would have at most one bit rate and two streams.

Setting Up Back-Channel Multicasting

Follow the instructions below to set up back-channel multicasting.

To set up back-channel multicasting:

1. In RealSystem Administrator, click Multicasting. Click Back-Channel.

2. In the RTSP Port box, type the port number to which RealProxy will direct its RTSP multicast streams. The value in this box refers to the client's port number. A typical value is 554.

3. Specify the range of addresses to which you want to multicast streams by filling in the Address Range box. RealProxy uses the first available address in this range. If your multicast streams are referenced in SMIL files, you will need one address for each stream.

   Refer to "Determining Required Addresses and Port Numbers" to calculate the exact number of addresses you'll need.

4. Indicate how far multicast packets can travel over a network by typing a value in the Time to Live box. Each time a multicast data packet passes through a multicast-enabled router, its Time to Live is decreased by 1. When the value is decremented to 0, the router discards the data packet.

   The value for Time to Live can range from 0 to 255. The larger the Time to Live, the greater the distance a data packet will travel.

   The default value of 16 is enough to keep multicast packets within a typical internal network.

   Time to Live (TTL) Values

   TTL Value	Packet Range
   0	Local host
   1	Local network (subnet)
   32	Site
   64	Region
   128	Continent
   255	World

5. To allow missing packets to be resent to clients that request them, select True from the Resend list. This setting is optional. It adds some overhead to the traffic on your network; however, clients receive better quality multicasts.

6. Indicate which clients will be able to view your multicast presentations by configuring the User List.

   To require that clients with IP addresses in the User List must connect in multicast mode, set Deliver Only to Yes. When this is selected, those clients not configured for multicast will not be able to receive the multicast, and will receive an error message instead. Use this feature when you want to restrict the multicast to a limited number of clients, or if you are multicasting a high-bandwidth presentation and do not want unicast to be an option.

   1. In the User List area, select Yes from the Delivery Only list.

   2. Click Add a User List.

   3. In the Rule Name box that appears, type a rule number. The rule number is used by RealProxy for sorting the address rules.

   4. Type the IP Address of the client allowed to receive the multicast in the IP Address box. To allow any client to access the multicast, type 0.0.0.0.

   5. Type the subnet mask for the client IP in the Netmask box.

      To indicate a single IP address, type 255.255.255.254 in the Netmask box. If you typed 0.0.0.0 in the To box, type the same thing in the Netmask box.

   6. Click OK.

   Repeat Step b through Step f for each set of clients that will be accessing your multicast.

7. Click Apply.

   	Note
   	Access Control rules are enacted before User List rules. A client that is excluded by Access Control will not be able to connect to any multicasts, regardless of the rules you create here. (IP Access Control is described in Chapter 9, "Limiting Access to RealProxy".)

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This file last updated on 12/07/00 at 16:37:38.