Streaming Media Supplement sa2150 and sa2250

55
Chapter 5 Understanding Media-IXT and QuickTime
Understanding live passthrough, live splitting, and
hierarchical live splitting for QuickTime
Media-IXT requires no special configuration to perform live passthrough for QuickTime.
Live splitting depends on the connection speed of the client.
The RTSP protocol contains information about the client connection speed, and not about the stream, so the
stream’s bit rate is irrelevant. Media-IXT splits the live stream into as many streams as it has clients of the same
connection speed. If a client of a different connection speed requests the live stream, Media-IXT pulls another
instance of the live stream from the origin QuickTime server.
Media-IXT requires no special configuration to perform live splitting for QuickTime. To configure hierarchical
live splitting only requires configuring the hierarchy itself.
QuickTime uses the RTSP control protocol, and the RTP data transfer protocol. RTP allows use of either TCP
or UDP as its underlying transport protocol. As data streams from an origin QuickTime server, through Media-
IXTs in a hierarchy, to client RealPlayers, both TCP and UDP are used at various times.
In hierarchical live splitting, a parent Media-IXT looks like an origin server to a child Media-IXT. So,
connections between the child and parent Media-IXTs in a hierarchy are over TCP, while the child Media-IXT
splits the live stream, directing the split streams to client QuickTime players over UDP. The live stream goes
from origin QuickTime server to parent Media-IXT over a TCP connection, and from parent Media-IXT to
child Media-IXT over a TCP connection, then is split into multiple streams which reach QuickTime Player
clients over UDP.
Like live splitting in a non-hierarchical deployment, hierarchical live splitting follows the principle that Media-
IXT splits the live stream into as many streams as it has clients of the same connection speed. For a given clip,
the number of separate streams that Media-IXT pulls from the origin server (or parent proxy) equals the number
of clients requesting the clip with different connection speeds.
How does the QuickTime player determine its connection speed? In its Preferences menu, the QuickTime
player has a Connection Speed sub-menu offering a choice of about eight or nine speeds. The
Connection Speed value is fixed for the duration of a streaming media session.
How are QuickTime player connection speeds represented by origin QuickTime servers and by Media-IXT?
Each connection speed maps to a different value for a Bandwidth header that the QuickTime player sends to
an origin server in the RTSP handshake that begins a session.
Understanding clustering and QuickTime
Media-IXT supports management-only clustering; there is nothing about a management-only cluster that makes
QuickTime streaming behave differently than in other deployment scenarios.
Understanding VIP failover and QuickTime
VIP failover is a Media-IXT clustering feature. For QuickTime, 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 VIP failover capability for QuickTime is built in. (The binary used for RealNetworks VIP
failover, mixt_vip_config, is not involved.)