ISBN: 0-471-41405 -0
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Bluetooth is a short -range radio technology that enables devices of many different shapes and functionalities and from different vendors to communicate. The technology operates in the 2.4GHz band and uses frequency hopping in order to ensure robustness against interference in this open frequency band. Profiles help ensure the interoperability between devices. Profiles indicate what functionality a device supports, and devices that feature the same profiles can communicate. Bluetooth is designed to be small and power-efficient and is expected to be included in a huge variety of devices (such as mobile phones, PDAs, computers, and so on).
Optimizing the Transmission
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any people initially viewed the mobile Internet as the Web without wires, meaning the same content and applications but without any fixed, wired connection to the user’s device. While this perception led to the creation of some flashy commercials and scenarios that people could relate to with their past Internet experiences in mind, it also created false expectations among users and wrong approaches among developers. Some companies just took the same applications and content that they presented to fixed Internet users and brought it to mobile Internet users. This approach was as bound for success as scanning the company archives to be presented on the Web in the early 1990s.
When the Internet as we know it today was built, its building blocks were constructed to work well with the network characteristics that were most prominent at the time. We could assume that a link had pretty much the same properties all of the time unless it got too loaded (congested). In case of congestion, all hosts on the network should act responsibly and back off to get the system out of the congestion. In this way, protocols such as the Transmission Control Protocol (TCP) and the Hypertext Transfer Protocol (HTTP) were designed with the Internet of past decades in mind. In TCP, a lost packet is treated as sign of congestion (that too many users are trying to use the network at the same time). Therefore, TCP backs off and reduces its transmission speed when it notices lost packets. These are some of the issues that we will address in this chapter, and we will explore some concrete ways to avoid getting into trouble when taking existing applications into the mobile Internet world. This process is not only about adapting the content, but also about adapting to the properties of the new networks.
Background and History
In the late 1960s, the United States Department of Defense and the Advanced Research Projects Agency (ARPA) established partnerships with U.S. universities and company research divisions in order to create a community for information sharing over computer networks. This goal required open, standardized protocols and a distributed multi -vendor architecture.
They created the first embryo of the Internet, called ARPANET, which was a packet-switched network with not-so-impressive bit rates of 56Kbps. This first network, which launched in 1969, consisted of four nodes and did not look much like the Internet that later would appeal so highly to the public. During the 1970s, this community of bright people worked on the architecture and protocol issues surrounding this network. In 1974, Vinton G. Cerf and Robert E. Kahn wrote a paper that outlined a design of a new protocol suite for the Internet. The proposal evolved into what we commonly call the TCP/IP Internet protocol suite, popularly just called TCP/IP after two of its components, TCP and the Internet Protocol (IP). After a few initial versions, work ended up with the commonly used version 4, which they finalized in 1979. IP version 4 is still, in the early twenty -first century, the protocol used on almost every computer on the Internet.
As more and more universities and other nodes became connected, capacity was running out, and the network was constructed piece by piece. In the late 1980s, T1 links of 1.544Mbps emerged, and T3s soon followed in early 1990. The universities continued to lead the Internet evolution as the use of e-mail became widespread in the early 1990s and was not only limited to researchers and computer students.
In the early 1990s, the Internet received a new face with the rapid spread of Web browsers that supported Hypertext Markup Language (HTML) over HTTP. Mosaic and Netscape were the early pioneers, and Internet Explorer later followed. Now, the common computer user could get a modem fairly cheaply and access the massive amount of information that was available. Again, universities led the way—and for every generation of students that graduated, the power of the Internet became more pervasive. With the takeup among consumers, people started to think about how to make money on this emerging opportunity.
In the second half of the 1990s, commercial interests became a bigger and bigger part of the Internet. People started to book trips and buy books and other goods online, and the Internet became an integral part of many people’s lives. From having been something that universities used for communication and