tailieunhanh - Optical Networks: A Practical Perspective - Part 4

Optical Networks: A Practical Perspective - Part 4. This book describes a revolution within a revolution, the opening up of the capacity of the now-familiar optical fiber to carry more messages, handle a wider variety of transmission types, and provide improved reliabilities and ease of use. In many places where fiber has been installed simply as a better form of copper, even the gigabit capacities that result have not proved adequate to keep up with the demand. The inborn human voracity for more and more bandwidth, plus the growing realization that there are other flexibilities to be had by imaginative use of the fiber, have led people. | This Page Intentionally Left Blank Introduction to Optical Networks AS WE ENTER THE telecommunications new millennium we are seeing dramatic changes in the industry that have far-reaching implications for our lifestyles. There are many drivers for these changes. First and foremost is the continuing relentless need for more capacity in the network. This demand is fueled by many factors. The tremendous growth of the Internet and the World Wide Web both in terms of number of users as well as the amount of time and thus bandwidth taken by each user is a major factor. A simple example of the latter phenomenon is the following An average voice phone call lasts about 3 minutes in contrast users connecting to the Internet via dialup lines typically stay on for an average of 20 minutes. So an Internet call brings in about six times as much traffic into a network as a voice call. Internet traffic has been doubling every four to six months and this trend appears set to continue for a while. Meanwhile we are seeing the ongoing deployment of broadband access technologies such as digital subscriber line DSL and cable modems which provide bandwidths per user on the order of 1 Mb s contrasted against the 28-56 kb s available over dialup lines. The impact of such deployments is quite significant. A 10 increase in penetration of DSL among the 100 million total . households will bring in another 1 Tb s of traffic into the network assuming that 10 of these users are on simultaneously. At the same time businesses today rely on high-speed networks to conduct their businesses. These networks are used to interconnect multiple locations within a company as well as between companies for business-to-business transactions. Large corporations that used to lease Mb s lines to interconnect their internal sites are commonly leasing 155 Mb s connections today. 1 2 Introduction to Optical Networks There is also a strong correlation between the increase in demand and the cost of bandwidth. .