Specifications

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Cisco Internet Streamer CDS 2.0-2.3 Software Configuration Guide
OL-13493-04
Chapter 1 Product Overview
Content Delivery System Architecture
The Windows Media Engine streams Windows Media content, with the capability of acting both as a
server and as a proxy. It streams prefetched content to the Windows Media Player, acts as a proxy for
client requests, splits a live stream into multiple live streams, and caches content requested from remote
servers.
Windows Media Engine acts as Windows Media Server for prefetched or cached content stored locally.
The request is served by means of RTSP and HTTP. Windows Media Engine checks with the storage
function on the Service Engine to see whether the content is stored locally; if the content is not found,
the Windows Media Engine engages the Windows Media Proxy.
The WMT Proxy works like the cache fill operation in the Web Engine. There are two options:
• Hierarchical Caching Proxy—If content is not found locally, the Windows Media Engine checks the
upstream Service Engines first before pulling the content from the origin server.
• Static Caching Proxy—The administrator statically configures Service Engines as upstream proxies.
The WMT Proxy accepts and serves streaming requests over RTSP and HTTP.
Fast Start
Fast Start provides data directly to the Windows Media Player buffer at speeds higher than the bit rate
of the requested content. After the buffer is filled, prefetched, cached, or live content stream at the bit
rate defined by the content stream format. Fast Start does not apply to content that is dynamically
ingested. Only Windows Media 9 Players that connect to unicast streams using MMS-over-HTTP or
RTSP can use Fast Start. The Fast Start feature is used only by clients that connect to a unicast stream.
With live content, the Windows Media Engine needs to hold the content in its buffer for a few seconds.
This buffer is used to serve Fast Start packets to subsequent clients that request the same stream as the
initiating first client request. The first client triggers the process, with the subsequent clients benefitting
from Fast Start.
Fast Cache
Fast Cache allows clients to buffer a much larger portion of the content before rendering it. Fast Cache
is supported only for TCP. It is not supported for RTP. The Windows Media Engine streams content at a
much higher data rate than specified by the stream format. For example, using Fast Cache, the Windows
Media Engine can transmit a 128-kilobit per second (Kbps) stream at 700 Kbps. This allows the client
to handle variable network conditions without perceptible impact on playback quality. Only
MMS-over-HTTP and RTSP requests for prefetched or cached content support Fast Cache. The speed is
determined by the client’s maximum rate and the configured Fast Cache rate—whichever is smaller.
Fast Stream Start
The first client requesting a live stream often experiences the longest wait time for the content to begin
playing. Users can experience long wait times because of the full RTSP or HTTP negotiation that is
required to pull the live stream from the source. Delays can also occur if the edge Service Engine has
not buffered enough stream data to fill the player’s buffer at the time the content is requested. When the
buffer is not filled, some data to the client might be sent at the linear stream rate, rather than at the Fast
Start rate. With Fast Stream Start, when a live stream is primed, or scheduled and pulled, a live
unicast-out stream is pulled from the origin server to a Service Engine before a client ever requests the
stream. When the first request for the stream goes out, the stream is already in the delivery service.
Live Stream Splitting
Live stream splitting is a process whereby a single live stream from the origin server is split and shared
across multiple streams, each serving a client that requested the stream. When the first client that
requested the stream disconnects, the Windows Media Engine continues to serve the subsequent
requesting clients until all requesting clients have disconnected. Live stream splitting using content that