SL multicast notes

Sl4 adds two multicast client classes:

Udpanysourcemulticastclient: a client receiver that receives multicast traffic from any source, either source multicast (ASM) or Internet standard multicast (ISM)

Udpsinglesourcemulticastclient: from a single source ...... Source-specific multicast (SSM)

 

Security of SL Multicast:

The application must use a port greater than or equal to 1024;

Before you allow multicast clients to join a group, protocol checks are performed during the SL operation.

 

The two origins perform different security checks:

First case: before joining a single-source multicast group, the SL runtime sends the announcement to the source on UDP port 9430 through unicast, you can access any port of the source> = 1024 during the running.

Case 2: Sl application before joining any source multicast groupProgramHas the same access level for network resources and source sites.

If the local server can interact with multicast groups on the local network, the SL applications from this server also have the right to access the local multicast group;

For example, if a server on the Internet blocks interaction with a local multicast group, the SL application from the server is not authorized to access the local multicast group.

 

Three concepts are mentioned, including three physical objects: Sl Runtime (SL application), server (SL from this server), and multicast group source.

Simply put, whether an SL client can access multicast group sources depends on whether the server has the right to interact with multicast group sources.

 

For the SL cross-origin mentioned yesterday, does the SL application have the right to access other domains, including 80 (HTTP, sl4, and later versions) or 943 (socket) of other domains) whether the SL policy file or flash policy file is provided, and the file is accessible from the server, then the SL application from the server can access this domain.

 

Two similarities: access to an external domain or external source, controlled by this domain or the source, this domain or the source allows the server to access, then the SL application from the server has the right to access the domain or the multicast source.

 

Authorization process for SL applications:

Send the announcement. If you do not receive the authorization within 3 seconds, wait for 6 seconds and then send it again. If you do not receive the notification, wait for 3 seconds. If you do not receive the notification, wait for 12 seconds. If you do not receive the notification, the Policy Check will fail.

It may take up to 27 seconds for a successful authorization.

The next Policy Check is 60 seconds later. This is to prevent malicious or poor (as written in the original msdn article) programs from wasting traffic.

 

So what is multicast:

Key records:

Multicast is a point-to-multiple communication technology. It is currently used for network video or audio broadcasting, network video conferencing, multimedia distance education, and "push.

IP multicast address:

From 224.0.0.0-239.255.255.255

There are three types:

1. vro reservation:

224.0.0.0-224.0.0.255

2. Internet:

224.0.1.0-238.255.255.255

3. Private internal multicast IP Address:
239-0.0.0-239.00000000255