Audio and Video Streaming for the Masses

How one company used Linux to provide transmission of live audio and video over the Internet.
Electronic Commerce

E-commerce is all about web servers and databases. In addition to providing the page that the end user sees, web servers coordinate taking orders, verify credit card information and order fulfillment. The databases contain all information concerning the available merchandise and the static and dynamic content populating the served web page.

During the early stages of Global Media's growth, a third party handled this part of the business. Now that Global has a complete technical team, its web serving has been moved in-house. The web development firm was using a combination of Cold Fusion, SQL Server and Internet Information Server on NT. We found the whole situation less than ideal; it was ridiculously resource-intensive and slow. Scalability was also a concern.

The immediate concern when transferring the system, however, was to keep it running. Now that things are reasonably stable, the task of migrating the works to Linux has begun. Moving the static content to Apache on Linux is the first phase. Next, portions of the database will be moved from the SQL Server to Texpress for Linux. The final phase will be the transfer of financial transactions.

Although Texpress is a commercial database, it is worthy of a quick comment. It uses an interesting algorithm for text searches, building bit-pattern indexes. Lightning-fast, it is worth a look on some rainy day.

Network Operations Centre

Just as most of the broadcast network is located remotely—close to the audio sources—so most of the e-commerce network is far away, close to the big pipes. The Network Operations Centre is responsible for control and monitoring of all these remote machines.

For monitoring, we rely on SNMP (Simple network management protocal) and good old log files. We scan the logs in real time using the handy little utility swatch. When a message of interest is logged, swatch initiates the prescribed action. SNMP supplements and complements the log files by allowing an even finer-grained view of the inside of each box.

SNMP is the one place within the NOC where we were forced to find a solution outside of open source. On the broadcast network, the management end of the SNMP link uses HP OpenView on a Sun workstation. We did look at various Linux solutions for monitoring network and system information. Most of the functionality was available here and there, but not in a single tool, and it was not always stable. The state of the hardware in the audio-encoder boxes as well as the state of the encoding software and of the frame-relay link is fundamental to the success of our business. We needed something that could receive traps, discover network nodes, poll network nodes, and given the large number of nodes involved, graphically represent the whole. Commercial software seemed to be the only solution.

Nevertheless, the rest of the SNMP system runs on open systems. On the e-commerce side, where there are fewer nodes and polling is sufficient (i.e., no traps are used), NetSaint does the monitoring. Of course, the Linux boxes all use GNU SNMP agents. In fact, it is the open code that allows us to receive DMI (desktop managment interface) information from the audio boxes. The SNMP source code was modified so we could poll the encoder boxes for information concerning CPU temperatures, fan speeds and voltages.

Thanks to Linux, we did not need to make any expensive maintenance requests of vendors. Given these fine freely available tools, we can detect and fix trouble without the customer even knowing that anything was wrong.

One last Linux feature needs to be mentioned before closing. We shape the traffic on our pipe while the audio signal moves through our network toward the Internet. Sound quality depends on available bandwidth. One of the cornerstones of our business plan is high-quality sound; therefore, we have to protect the sound as far down the pipe as possible. The audio signal shares the pipe with monitoring and management traffic. Under normal circumstances, this should not present a problem. However, should a sudden surge in log activity occur or a new software package be sent back up the line, traffic shaping allows us to ensure it does not cut into the bandwidth required for our customer's broadcast.

Global Media Corporation produces the best audio signal possible for Internet listeners, while providing a cost-effective solution to broadcasters. Without Linux, we could not have achieved all we have as cheaply and effectively. Open source permits great independence. If the system had been built using a commercial operating system, we would have been subject to the cost and delay of vendor customizations, that is, if the vendor was even willing to consider making any modifications.

Many businesses still regard Linux and other open-source software with suspicion. It is still often perceived as a hacker toy unsuitable for real work. We hope our experience will help dispel such myths and encourage others to consider Linux as a viable work tool.

Gerald Crimp (gcrimp@globalmedia.com) is a software engineer at Global Media Corporation in Vancouver, BC, Canada. Debian is his distribution of choice. He looks forward to the day when Linux takes over the desktop.

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thanks good blog

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