The Next Quantum Leap in Speed

The age of anywhere, anytime, communication is here. The mobile user can send and receive e-mail, buy and sell stocks, get weather reports and surf the Web. However, the speeds currently available make these tasks less than a pleasure. Speed, more often called bandwidth, is a commodity that one can never have enough of. The explosive growth of the Internet and the general desire for timely information creates a need for more bandwidth and the efficient use of existing bandwidth. As speeds increase, the number and types of applications grow to use the available bandwidth. Multimedia is one such bandwidth-demanding application. To accommodate limited bandwidth, applications are often modified for the mobile user. Technologies and specifications such as the Wireless Application Protocol (WAP) and the Wireless Markup Language (WML) are a great aid in enabling the mobile user. They mitigate some of the limitations found in the wireless environment such as diminutive displays and restricted bandwidth.

Bandwidth to the desktop computer has made huge strides in the past few years. Cable modems and DSL bring speeds that make multimedia applications reasonable. The same cannot be said for the mobile user. Despite advertisements and hype to the contrary, speeds for the mobile user with a modem and cellular phone are limited. Sending and receiving a short e-mail is possible, but surfing web pages replete with graphics is impractical. All that will change when High Data Rate (HDR) is deployed.

HDR is a high-speed, high-capacity, wireless Internet technology. When it is introduced, it will represent a quantum leap forward in speed. It will provide high-speed wireless Internet access to the mobile user. Speeds of 2.4MBps will be possible and will make web surfing and other bandwidth-hungry applications heretofore limited to the desktop available to the mobile user. This article describes how Linux is playing a critical role supporting the development and deployment of HDR at Qualcomm, Inc.

Qualcomm, Inc. is a San Diego, California-based telecommunications company. Although Qualcomm is involved in virtually all aspects of digital wireless communication, it is known to many as the publisher of the Eudora e-mail client and the creator of the Code Division Multiple Access (CDMA) specification--the cornerstone of digital cellular communication in the United States and many other countries.

When it came to deciding the best platform to support the HDR subsystem and system-level software testing, Linux was chosen for good reasons. Linux is a well-supported, fast, flexible, easy-to-use, reliable, open-source operating system. It is also free, but cost was not a factor. The decision was based solely on technical merit.

Telecommunications is a highly competitive, fast-paced, cutting-edge industry. Time to market is crucial for success. A platform that provides flexibility and ease of use were the major factors in the decision to use Linux. The choice of Linux allowed the software development and test teams to implement an environment to test HDR quickly.

The test environment consists of a wide variety of hardware and software. For subsystem-level testing, there are more than 35 real-time operating system computers, 14 Windows NT systems and 6 Linux systems. At the system level, a similar configuration is used for testing.

Like all telecommunications applications, HDR is time-critical. To meet tight real-time requirements, VxWorks by Wind River Systems was chosen. To support high-level testing and simulate real-world mobile users, Windows machines were used. But Linux is the glue that holds it all together and is a key element in HDR development.

Linux is used in many ways to support HDR development and testing. One of the more crucial roles for Linux is to assign IP addresses to the test environment consisting of nearly 100 nodes. PCs and embedded system components installed in the system's base station are assigned addresses by several Linux DHCP servers. This allows devices to be easily added or removed to meet the dynamic needs of the test environment.

To monitor and control an embedded system, a standard RS-232 serial connection is used. However, due to the large number, an equally large number of serial interfaces is required. A terminal server (a.k.a. access server) is normally used for this purpose. However, after extensive research, no commercial terminal server was found that would allow multiple ``reverse'' Telnet connections. To meet this requirement, off-the-shelf multiport serial communication cards were added to the Linux machines. Using in-house developed multi-threaded software, the HDR team was able to do what no commercial product could do: allow multiple sessions to a single host. This allows several developers to connect simultaneously to the same source from multiple locations helping to make the testing process more productive.

When a software process crashes on an embedded system, hitting the hardware reset button on the board is often the only way to bring the system back to life. If the software developer is sitting next to the board, this is not a problem. However, it is more productive to allow HDR software engineers to develop and debug software from a quiet office with the embedded target residing remotely in a sometimes chaotic lab environment. To solve the problem of resetting a remote system that has crashed, a small remote reset box containing electromechanical relays was interfaced to the parallel port of the Linux machines. Using a web page interface and custom software, a software developer can remotely reset any of the target computers without leaving his or her office. In addition, due to the complexity of the system and large number of embedded targets, Linux allows all targets to be reset with a single mouse click. This has been a feature that has proven to be very useful and saves a great deal of time. It also means that software developers, who choose to, may work from home and reset the hardware remotely if necessary.

The Apache web server residing on each of the Linux systems is invaluable. Both static and dynamic pages provide software developers the means to monitor, control and coordinate testing.

After software components are released, they are distributed to clients for testing using the ftp server on Linux. Sufficient disk space is available for many versions of the software to remain on line. Changing to a new version is as simple as changing a soft link to point to the current version.

At the subsystem level, HDR messages are sent over an Ethernet network rather than over the air. This has the great advantage of simplifying the test environment, since sending packets over the air adds unnecessary complexity (i.e., fading, multipath, noise, etc.) to the testing environment. Transmitting messages over Ethernet allows HDR messages to be examined by monitoring network traffic. Linux serves as an excellent network sniffer. The standard tcpdump command is adequate for most diagnosis. For more complex searches and analysis of network traffic: ngrep, xipdump, tcptrace and xplot are used. The plethora of powerful networking tools available made our choice of Linux a wise one.