Multicast Question

PIM-SM/PIM-SSM are multicast routing protocols.  Internet hosts, such as servers running FMS and clients running Flash Player, do not typically implement Internet routing protocols.

Flash Media Server 4.0 can send IP multicast datagrams to any IPv4 or IPv6 multicast address, including those used for SSM (232.0.0.0/8 and ff30::/12).  no multicast routing or group maintenance messages are involved in FMS sending multicast packets.

when a client such as Flash Player subscribes to a multicast, it uses the native operating system APIs to add a multicast address/channel to a socket.  the host operating system will typically announce this membership to its routers with IGMP (for IPv4) and MLD (for IPv6).  Flash Player 10.1 can only subscribe to an any-source multicast.  Flash Player 10.2 can also subscribe to a source specific multicast on Windows and Linux (Mac OS X 10.6 and earlier does not provide the APIs and operating system support necessary to add an SSM channel to a socket).

routers receive IGMP and MLD messages from their directly connected clients to learn what multicast addresses they wish to receive.  routers may use any number of routing protocols, including PIM-SM/PIM-SSM, to work out how to forward the multicast packets from sources (FMS) to the clients.  the choice of PIM-SM/PIM-SSM or any other multicast routing protocol is an issue for the network designers and maintainers (example: your IT department).  it doesn't directly affect the operation of FMS or the clients, and neither the FMS nor the clients need to know (nor do they care) what kind of multicast routing protocols are used by the infrastructure.

Hi Steve,

FMS and Flash Player support multicast delivered via PIM Sparse Mode (SM) and Source-specific Multicast (SSM).  Any-sourced multicast (Sparse/Dense Mode) is supported in Flash Player 10.1. The caveats with SSM are:
a) it requires Flash Player 10.2 and you must supply the source address as the 3rd argument when you use the addIPMulticastAddress function on the GroupSpecifier class
b) it is not available on all platforms, namely Mac OS X, but newer Windows and Linux are ok.
c) FMS 4.0.x can publish for a SSM, but you'll need to build the groupspec string inside of Flash Player and pass that to FMS for publish.  The support for the "source" argument in GroupSpecifier.addIPMulticastAddress will be introduced in the next major version of FMS.

Hope this helps,

- brad

I think its PIM-SM because as of now we dont support SSM - though i would try to confirm my answer in few days.