Streaming Media Supplement sa2150 and sa2250

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Chapter 3 Understanding Media-IXT and RealNetworks
Normally, when Media-IXT splits an incoming stream into multiple outgoing streams, the transport protocol is
UDP, so Media-IXT must write UDP packets to the IP address of each client. If those clients can be reached via
multicast, then Media-IXT need only send out one stream of multicast packets to the multicast address, rather
than multiple streams of UDP packets (one stream to each client IP address).
Though attractive, multicast is rarely a practical option, because very few routers pass multicast packets, among
other reasons. Remember, too, that client players must be configured for multicast; otherwise, multicast streams
can not reach them. By default, RealPlayers are configured to attempt to use multicast. See RealNetworks
documentation for a fuller discussion of multicast, and instructions for configuring RealPlayer for multicast.
Understanding hierarchical live splitting and RealNetworks
The RealProxy component of Media-IXT performs the splitting of live streams in hierarchical deployments. To
configure Media-IXT for hierarchical live splitting, just configure Media-IXT for hierarchical proxy caching.
Understanding clustering and RealNetworks
Media-IXT supports management-only clustering, not full clustering. See “Understanding clustering” on
page 15.
Media-IXT supports caching of RealNetworks content in clustered configurations, but important limitations
apply:
• Traffic Manager remains unaware of the RealProxy component of Media-IXT
• the RealProxy GUI does not communicate with more than one node of the cluster
In more detail:
Cluster Management.
In a Media-IXT cluster, Traffic Manager provides a single management interface for
configuring and monitoring all nodes of the cluster. Traffic Manager does not configure or monitor RealProxy,
however. RealProxy’s own GUI works only on a single node and cannot configure or monitor RealProxy on
other nodes.
VIP failover.
VIP failover is a Media-IXT clustering feature. For RealNetworks, an explicit, management-only
cluster is the only supported deployment for VIP failover. See the next section of this chapter.
Understanding VIP failover and RealNetworks
VIP failover is a Media-IXT clustering feature. For RealNetworks, an explicit, management-only cluster is the
only supported deployment for VIP failover.
In a Media-IXT cluster, a pool of virtual IP addresses is assigned to the nodes in the cluster. When one node
fails, other nodes must take over the traffic going to the down node’s virtual IP addresses.
The node with the lowest IP address can assign another node to take over the traffic that would normally go to
the down node. This technique is called VIP failover (the VIP stands for Virtual IP address). The failover may
not complete quickly enough to avoid adding latency to client requests.
Media-IXT’s implementation of VIP failover for RealNetworks makes use of a small executable called
mixt_vip_config.
Upon failure of a node, Traffic Manager in another node calls mixt_vip_config, which in turn does the
following:
1. Edit rmserver.cfg to add another IP binding
2. Kill and restart the RealProxy so that the IP bindings are re-read
3. Call
mixt_vip_config to configure Traffic Server’s virtual IP failover mechanism
4. Take over all the traffic of the downed node