1. Bandwidth Limitations
The example presented in Table 5 is a simple document of a single box object, but as the number of objects increases, so does the associated XML structuring and
ultimately the XML file size. The file size of an XML document quickly becomes an issue when it is faced with the Network-Centric vision to push the internet deeper down range, and into the hands of individual sailor and soldier handheld devices or to remote fighting units. These devices and remote units generally do not have bandwidth support beyond that of a typical telephone dialup speed at best. The larger a file is, the longer it takes to send or receive on low-bandwidth devices, if able to transmit at all. Large XML means limits on the depth into the battlefield that information can be pushed using current connectivity.
Putting a dialup speed into perspective, Figure 9, adopted from Popovich (2005), describes the transfer times of a notional military file against a number of different bandwidth capabilities, assuming 100% dedicated bandwidth utilization.
Figure 9. Example of Transfer Time vs. Bandwidth (Data Rate) for a 100MB Video or Imagery File (From Popovich, 2005)
Military relevant files in XML format can quickly reach the multi-megabytes in size resulting in remote units unable to meet the bandwidth requirements to send or receive the XML format even though the fractional information within the XML document is within the limits of the remote unit’s transfer abilities.
2. Battery and Heat Limitations
To push networks deeper into the battlefield, handheld devices, similar to digital organizers, are the devices that are most likely to enable the push. These devices generally come with full-feature color interfaces that have a look-and-feel similar to an interface found on a desktop computer. They have through functionality but with specialized Application Programming Interfaces (API) designed specifically for their processors and display abilities. By matching a creative architecture design with a handheld API based on a few subtle limitations, handheld devices do almost all that a traditional desktop can, but within the palm of your hand.
Handheld processor limits are constrained by many things, from the number of operations per time-cycle, to the maximum storage ability, to the amount of power it requires to operate. The key things that set handheld devices apart from a desktop
computer are power consumption, heat dissipation and endurance. A desktop computer is connected to a constant power source, while a handheld device relies on the power
available in the attached battery which has a finite capacity.
a. Battery Power
A fundamental problem for handheld devices that is not present for desktop computers, at least not to the same level of importance, is a measurement of power consumption due to processor operations. Notionally, a desktop computer is evaluated on the number of operations it can perform in a specific time period, CPU clock-speed, along with its memory capacity, without consideration of power
for processor operations. A desktop if confronted by a complex file has essentially unlimited electrical power to throw at the problem. In contrast, the more complex a file a handheld device has to process, the faster that file drains the handheld device’s battery.
This reasonably simple to understand concept is often overlooked, and results in the premature demise of many handheld device applications because the application requires too much power to effectively operate.
The immediately hoped-for solution to this problem is to make better batteries. Moore’s law states that computer abilities double every 18 months. However, battery technology has not kept pace with Moore’s law, and the science behind battery technology indicates current technology may already be at its peak capacity (Ultra, n.d.).
Handheld devices for all intended purpose are nearly equivalent to desktop computers in terms of processing ability, but are limited unequally on electrical power. A powerful handheld device can quickly drain its battery and become useless on the battlefield. This is a potentially deadly situation if the devices are performing key mission functions.
Similarly, if a handheld processor is not able to perform the complicated tasks required of a battlefield mission, it becomes useless even before it can reach the battlefield.
b. Heat Dissipation
Compounding the power problem of handheld devices is heat dissipation.
A desktop computer has a fan to move air across the processor to cool the motherboard and other heat producing parts within the computer shell. Handheld devices have no fan to move air, relying only on natural airflow. Handheld devices are “held” while
operating, no air flows around the device to cool it. The designed operation of handheld device places them in a dangerous position to meltdown.
Handheld devices cannot dissipate heat at the same rate as a desktop computer so in addition to being limited by power, they are also limited by their rate of heat transfer, which is a function of power. The faster the battery is drained, the more heat it produces, the more heat that is produced, the faster the battery is drained.
E. CHAPTER CONCLUSION
While XML is the defacto data format for information exchange, its vices, particularly when being processed on handheld devices, can make XML too large and complex to be efficiently process. Due to XML’s verboseness, it prevents low-bandwidth devices from being able to receive and transmit XML documents. Due to the text-only format of XML, small devices are unable to process largely numeric XML documents due to the complexity of numerous text-to-number conversions. Complexity is further confounded within small devices by limited battery life, limited memory and small CPUs.
Handheld devices while nearly as functional as a desktop are limited by how long they can operate due to power and heat. The more complex an operation, the more power a handheld device will need. The more power a handheld device is using, the more heat it is producing. The more heat a handheld device produces, the faster it drains the battery.
Ultimately, the constraints of XML limit the network depth to which XML can be deployed due to the same design structure that has delivered XML’s successes.
F. CHAPTER SUMMARY
This chapter highlights the verboseness and complexity of XML processing that can prevent handheld and other small devices from being able to adequately process XML documents, limiting the network depth of XML.
THIS PAGE INTENTIONALLY LEFT BLANK
V. BINARY XML FORMAT RATIONALE: XBC
A. INTRODUCTION
This chapter discusses the history of the awareness of XML’s verboseness and parsing problems. Cases from DoD and the business world’s efforts to alleviate the limitations of XML are discussed. Based on the findings of the XML Binary
Characterization (XBC) working group, the overall purpose of this chapter is to discuss the technical challenges that an alternative XML format solution faces, and to discuss some of the general metrics to ensure that a successful alternative XML format is achieved.