Adobe's Emerging Rich Media Ecosystem, Part 3: Marketing, Service Level Agreements, and Security, Page 3
When a client request is received, the Edge server will handle the tasks it can, and then will make a connection to the Origin server for any additional data required. When the Origin server fulfills the request, the data is sent back to the Edge server, then on to the client. To the client, it appears that the connection is made directly to the application running on the Origin server.
The Edge server serves as a "traffic cop"—handling connection overhead, authentication, and other administrative duties—freeing up valuable system and network resources for the Origin server. Every connection and connection attempt consumes resources over and above the actual stream data flowing through the connection. As the number and frequency of connections increase, the load can be excessive; adversely affecting server performance.
The Edge server greatly reduces this load by aggregating connections. The Edge multiplexes the connections from a large number of clients into one connection to the Origin server. All communications between Edge and Origin servers are transparent to clients.
The Edge server also stores the prerecorded media content received from the Origin server in a cache, which is then made available to other clients that connect to the Edge server. Caching static content further reduces the load on the Origin server.
The Effects of Mobility on Wireless Media Streaming Performance
There are other examples that illustrated the need for and difficulty of capacity planning prior to the drafting of an SLA. In many cases, media is delivered from a streaming server on a wired network to mobile clients on a wireless LAN. There are two scenarios: with and without client mobility. Before releasing a new system, you should determine media streaming performance in best-case and worst-case scenarios for each case.
Two main points need to be understood: First, wireless media streaming performance can degrade significantly in the presence of user mobility. (Inconsistent wireless channel quality and intermittent connectivity can lead to excessive retransmissions, dynamic rate adaptation, and RTS/CTS negotiations on the WLAN. These delays degrade the performance of the wireless streaming application.)
Second, the performance degradation affects all clients in the WLAN, not just the clients who are mobile. This problem occurs because of the shared queue at the access point.
These observations highlight the many challenges for providing quality of service guarantees for wireless multimedia streaming. One possible solution is to use per-flow queuing at the access point, or a buffer management scheme that provides fairness.
Figure 2: Delivering media to mobile clients on a wireless LAN.
Another solution is to configure an access adaptor to accept or reject requests based on the number of clients currently connected or the amount of bandwidth currently being consumed.
The Recent FCC Auction of the 700 MHz Spectrum
The U.S. Federal Communication Commission (FCC) has been auctioning off part of the valuable 700 Mhz spectrum—this RF travels long distances and can penetrate thick walls—being "returned" by television broadcasters as they move to digital from analog signals in 2009. These frequencies will be accessible to customers using any device or software application.
At the same time, Google, Microsoft, and other tech companies are pushing for the ability to use these empty, unlicensed airwaves, known as white spaces, to provide high-speed Internet service that might be able to serve hard-to-reach rural regions and supplement other Internet services in cities. But opponents of this idea, namely television broadcasters who use adjacent airwaves, say white-space use can interfere with regular TV signals and could blot out over-the-air broadcasts.
I mention this controversy because, as we approach the next generation of wireless broadband services, there are new unresolved issues that could influence the quality of your broadcast media at its very source: For example, wireless microphones for sporting events, concerts, and churches, which use this unlicensed spectrum. TV broadcasters say this technology could put their productions at risk and support auctioning off those fallow airwaves and making them licensed in order to protect against interference. Stay tuned.
Flash Media Server distributes media streamed via RTMP, an Adobe-patented protocol that runs over TCP. Flash Media Server helps to further protect streamed media by encrypting it and tunneling it over HTTP. This new protocol is called RTMPE. Users view the streamed content via Flash Player. Similar in strength to Adobe's current SSL protocol (RTMPS), this enhancement can be leveraged by content owners and communication developers to add additional protection to their content. Additionally, SWF verification helps protect SWF files from being reused, modified, or hosted in alternate locations. And, Flash Media Server 3 also supports streaming of encrypted content to Adobe Media Player.
Figure 2 and the Appendix present an overview of the security options available in Flash Media Server 3.
Adobe's new Flash Media Rights Management Server (FMRMS) sits alongside the Flash Media Streaming Server or Flash Media Interactive Server and protects streaming content downloaded in FLV (Spark or VP6 codec) or MPEG4 (H.264 codec) format and played back on local desktops.
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