Stratospheric Ozone Depletion and Its Effect on Skin Cancer Incidence E

Introduction This term paper is situated in an area of specific health related and environmental concern: the human dimensions of global change. For about a decade now there has been growing scientific interest in the global environmental changes resulting from anthropogenic activity. However most of this research has focused on the scientific bases of environmental transformations with little attention to how human social responses are linked to global change. As a result, scientists and researchers alike are beginning to ask questions about the symbiotic relationship between human well being and physical change. Abstract This research compilation plans to use one environmental health component of the global change phenomena - ozone depletion and skin cancer - to advance and deepen your understanding of the relationships between human wellness and environmental change. This project should deepen understanding by developing a framework for conceptualizing environmental health policy issues. In this way the relationships between scientists, policy makers and the public will be explored theoretically as the interactions of science, the state, and society as a whole. The Relationship of Skin Cancer Prevalence and the Increase in Ultraviolet-B Exposure due to Ozone Depletion Ultraviolet-B radiation damages the human skin: Acute exposure causes sunburn and chronic exposure results in loss of elasticity and increased aging. Increased absorption of UV-B triggers a thickening of the superficial skin layers and an increase in skin pigmentation (both of which act to protect the skin against future sunburns). This protective mechanism however, also makes the skin more vulnerable to skin cancer. Strong evidence exists of a dose... ...tion/2.html Mahaney, Francis X., "Nocturnal Animals Help Shed Light on Human Melanoma," __Journal of the National Cancer Institute__, 87 (21): (1 November 1995). Available on the World Wide Web at http://wwwicic.nci.ni h.gov/jnci/iss8721/87-1584.html. Roses, Daniel F., Stephen L. Gumport, Matthew N. Harris, and Alfred W. Kopf, __The Diagnosis and Management of Common Skin Cancers__ (Atlanta, Georgia: American Cancer Society, 1989), 89- 50M-No. 3373-PE. Schein, O.D. et al., "Ocular and Dermatologic Health Effects of Ultraviolet Radiation Exposure from the Ozone Hole in Southern Chile," __American Journal of Public Health__, 85 (4): 546-550 (April 1995). "Stat Bite: Trends in Melanoma Incidence," __Journal of the National Cancer Institute__, 87 (20): (1 November 1995). Available on the World Wide Web at http://wwwicic.nci.ni h.gov/jnci/iss8720/statbi20.jpg.

Wwii and Immigration

Following decades of isolationist policy, World War II was an essential time in the United States history because it gradually opened up American society to once again receive immigrants who are in search of better opportunity and refuge. In the early 19th century, the United States began to re-think about its stance on immigration. As the numbers of immigrants increased, questions about the leniency of the American government on immigration were raised by the â€Å"Progressive Movement†. Consequently, the United States began to employ a closed door policy of immigration.Chinese male immigrants, who had been coming in masses, inspired the implementation of the Chinese Exclusion Act of 1882, which forbade further immigration of laborers of Chinese descent. This act forced prohibited Chinese males from bring over their families and destroyed possibilities of citizenship for Chinese immigrants by making them permanent aliens. Furthermore, in 1907, adding to the isolationist stanc e of the U. S. , the city of San Francisco attempted to remove Japanese students from white schools and put them in segregated schools with Chinese students.The Japanese government was infuriated by with this comparison to the Chinese; this led to the establishment of the Gentleman’s Agreement. This was an informal agreement stating that the Japanese government would restrict further immigration of their people to the United States and, in return, Japanese children in San Francisco would be able to attend school with white children. Over the next half century, further restrictions on immigration were implemented, many based on racist assumptions that immigrants were inassimilable and could not be Americanized.However, we see examples in Nisei Daughter, where the children like Monica and her siblings became Americanized and came to detest the strict Japanese culture their parents were raised in. this contradicts the assumption that immigrants would not assimilate. Continued pr essure to limit immigration in the United States eventually led to the Immigration Act of 1917, which created the Asiatic Barred zone. This meant that people from the Asiatic zone, which included Japan, Korea, India, and Arabia were barred from coming to the United States. Furthermore, the Act restricted people who were illiterate and above the age of 16 from immigrating.As a result of the 1917 Act, the immigration process included a literacy test that only allowed people of a certain educational background to enter the United States under the assumption that they would be able to assimilate better with America’s progressive ideologies, provide skills for the work force, and contributing to the economy. Despite increased restrictions, in between the First and Second World War, immigration to the US was relatively high due to the scarcity of unskilled labor needed in mines and factories in the United States.After WWI, The Immigration Act of 1924 was passed which set a quota of a 165 thousand immigrants per year allowed into the United States. While there had been restrictions placed on Asian immigrants before 1924, there were still ways for students to come into America. Thus, the Second Quota Act was passed which stated that no Asians were permitted to come to the United States. There was an exception of 50 people per country provided those who came were racially white, jut just happened to be living in Asian countries.This act made it easier for people from Germany, France, and Great Britain to migrate to the United States because they were white and as such were thought to be able to assimilate more easily into the American Culture. The only region these quota restrictions did not apply to was the western Hampshire. These limitations did not apply to Mexican immigrants because there was a high demand for their labor in the south, and employers made it difficult for congress to restrict that labor. Overall, Before World War II, it was extremely hard to immigrate to the United States unless there was demand the labor of immigrants.By 1924, there was a clear racial hierarchy among immigrants in the United States based on skills as well as race. In Homestead: The Households of a Mill Town, Margaret Byington mentions the difficulties immigrant communities, such as the Slavs, faced as they tried to assimilate into the American culture. The government did not take any steps to address the hardships of these communities or help them assimilate into American culture. This is important because, after WWII, the United States went out of its way to welcome immigrants and develop programs to ease the adjustment process.The United States was very dissatisfied with their involvement in WWI; thus when the Great Depression occurred, they dealt with it by further isolating themselves from the rest of the world. The United States government focused on solving its economic difficulties at home and dealing with the decade long depression. Even after WWII began in Europe, the United States stayed true to its isolationist policies and wanted nothing to do with the war. However, the Japanese attack on Pearl Harbor in 1941 forced the United States to enter WWII. Success in WWII made the United States the leading power in the world.After the United States witnessed the devastation Hitler had caused in WWII, the American government vowed to never allow that to happen again. As a result, immediately after WWII, the lessons learned from Hitler were applied to Stalin in the cold war. Instead of turning away from communist Russia, the United States engaged in the Cold War. Their goal was to contain communism around the world. The United States began strengthening their relationship with their own allies by building programs that would help these countries with education and health in order to get their assistance in containing the spread of Communism.After WWII though, Americans, especially those in the executive branch who dealt with f oreign policy, increasingly saw immigration and naturalization policies as tools for shaping foreign relations and advancing American interest. One of the first acts passed in the interest of immigration reform was The McCarran Walter Act of 1952, which not only illuminated the category of aliens ineligible for citizenship. This was the category many of the Issei Parents in Nisei Daughter were placed in but now they were permitted to become American citizens like their Nisei children.Also, the restrictions of The Asiatic Barred Zone, was lifted. Now, all Countries including China, who had previously was not been allowed to send any immigrants to the United States, unless they were white, now have a small quota to send people to the United States regardless of their racial background. Also, there was recognition among Americans that there were more people who wanted to come to the United States than the country could accommodate. As a resold priority was given to those who had family in the United States and needed to be reunified with them.Although some of the restrictions on immigration were loosened with The McCarran Walter Act, the country still allowed only a small number of people to immigrate. President Truman was pushing for immigration reform for years and was not fully satisfied with the new policy so the United States government sought out ways to expand immigration while still keeping what was best for the country in mind. President Johnson, who succeeded Kennedy, signs in the passage of the immigration and nationalization act of 1965.This act reforms the country and erases the old system of discriminatory and restrictive quotas based on national original and race while replacing it with a much less racist system. It was a new way of thinking, not just about immigrant but toward the American society. To manage immigration now, the United States divided the world into western hemisphere which constituted North, Central and South America, and Eastern hemisphere which was everything else. Over 300 thousand immigrants are allowed to come to the United States yearly with this new cap.Certain people were given preference with 80 percent of the groups under the new cap coming under different forms of family unification. Because of our involvement with different wars around the world and our efforts to end communism, the United States was increasingly allowing people to come above the set cap to find refuge in our country. These new loose policies on immigration coincided greatly with the civil rights movement. The movement comes at the same time the US becomes conscious of its role as a world leader.When the United States sought out to stop communism, they needed to show the world that their system was better but they could not do that when the world saw America as segregated and racist against some of their own people. Unequal treatment among Americans led some countries to want to turn to communism as a better policy. Immigration r eform and the Civil Rights Movement reinforced one another and eventually left. In 1950s, more than half of immigrants came from Europe and there were more Canadians coming into the country than Mexicans but beginning with 1965, Asians and Mexicans have began to come in mass.Congress did not understand when they passed act of 1965 was just how large the number of immigrants coming in would become. This unexpected increase in immigrants scared some Americans. There was especially great number of people coming from Mexico who many entering the country illegally and not being counted in the quota. The Mexican population in the US jumped from 60 thousand people in the 1940s to 1. 6 million in the 1980s. Even though this high number of immigrants was brought up concerns about the current immigration policy, the country’s new understanding after WWII would not allow then to close their doors once again.

Digital Subscriber Line

C H A P T E R Chapter Goals †¢ †¢ †¢ †¢ †¢ Identify and discuss different types of digital subscriber line (DSL) technologies. Discuss the benefits of using xDSL technologies. Explain how ASDL works. Explain the basic concepts of signaling and modulation. Discuss additional DSL technologies (SDSL, HDSL, HDSL-2, G. SHDSL, IDSL, and VDSL). Digital Subscriber Line Introduction Digital Subscriber Line (DSL) technology is a modem technology that uses existing twisted-pair telephone lines to transport high-bandwidth data, such as multimedia and video, to service subscribers. The term xDSL covers a number of similar yet competing forms of DSL technologies, including ADSL, SDSL, HDSL, HDSL-2, G. SHDL, IDSL, and VDSL. xDSL is drawing significant attention from implementers and service providers because it promises to deliver high-bandwidth data rates to dispersed locations with relatively small changes to the existing telco infrastructure. xDSL services are dedicated, point-to-point, public network access over twisted-pair copper wire on the local loop (last mile) between a network service provider’s (NSP) central office and the customer site, or on local loops created either intrabuilding or intracampus. Currently, most DSL deployments are ADSL, mainly delivered to residential customers. This chapter focus mainly on defining ADSL. Asymmetric Digital Subscriber Line Asymmetric Digital Subscriber Line (ADSL) technology is asymmetric. It allows more bandwidth downstream—from an NSP’s central office to the customer site—than upstream from the subscriber to the central office. This asymmetry, combined with always-on access (which eliminates call setup), makes ADSL ideal for Internet/intranet surfing, video-on-demand, and remote LAN access. Users of these applications typically download much more information than they send. Internetworking Technologies Handbook 1-58705-001-3 21-1 Chapter 21 Asymmetric Digital Subscriber Line Digital Subscriber Line ADSL transmits more than 6 Mbps to a subscriber and as much as 640 kbps more in both directions (shown in Figure 21-1). Such rates expand existing access capacity by a factor of 50 or more without new cabling. ADSL can literally transform the existing public information network from one limited to voice, text, and low-resolution graphics to a powerful, ubiquitous system capable of bringing multimedia, including full-motion video, to every home this century. Figure 21-1 The Components of an ADSL Network Include a Telco and a CPE Core network Existing copper Server ADSL ADSL 1. 5 to 9 Mbps 16 to 640 kbps Internet ADSL connection ADSL will play a crucial role over the next decade or more as telephone companies enter new markets for delivering information in video and multimedia formats. New broadband cabling will take decades to reach all prospective subscribers. Success of these new services depends on reaching as many subscribers as possible during the first few years. By bringing movies, television, video catalogs, remote CD-ROMs, corporate LANs, and the Internet into homes and small businesses, ADSL will make these markets viable and profitable for telephone companies and application suppliers alike. ADSL Capabilities An ADSL circuit connects an ADSL modem on each end of a twisted-pair telephone line, creating three information channels: a high-speed downstream channel, a medium-speed duplex channel, and a basic telephone service channel. The basic telephone service channel is split off from the digital modem by filters, thus guaranteeing uninterrupted basic telephone service, even if ADSL fails. The high-speed channel ranges from 1. 5 to 9 Mbps, and duplex rates range from 16 to 640 kbps. Each channel can be submultiplexed to form multiple lower-rate channels. ADSL modems provide data rates consistent with North American T1 1. 544 Mbps and European E1 2. 048 Mbps digital hierarchies (see Figure 21-2), and can be purchased with various speed ranges and capabilities. The minimum configuration provides 1. 5 or 2. 0 Mbps downstream and a 16-kbps duplex channel; others provide rates of 6. 1 Mbps and 64 kbps for duplex. Products with downstream rates up to 8 Mbps and duplex rates up to 640 kbps are available today. ADSL modems accommodate Asynchronous Transfer Mode (ATM) transport with variable rates and compensation for ATM overhead, as well as IP protocols. Internetworking Technologies Handbook 21-2 1-58705-001-3 Chapter 21 Digital Subscriber Line Asymmetric Digital Subscriber Line Figure 21-2 This Chart Shows the Speeds for Downstream Bearer and Duplex Bearer Channels Downstream bearer channels n x 1. 536 Mbps 1. 536 Mbps 3. 072 Mbps 4. 608 Mbps 6. 144 Mbps 2. 048 Mbps 4. 096 Mbps x 2. 048 Mbps Duplex bearer channels C channel Optional channels 16 Kbps 64 Kbps 160 Kbps 384 Kbps 544 Kbps 576 Kbps Downstream data rates depend on a number of factors, including the length of the copper line, its wire gauge, the presence of bridged taps, and cross-coupled interference. Line attenuation increases with line length and frequency, and decreases as wire diameter increases. Ignoring bridged taps, ADSL perfo rms as shown in Table 21-1. Table 21-1 Claimed ADSL Physical-Media Performance Data Rate (Mbps) 1. 5 or 2 1. 5 or 2 6. 1 6. 1 Wire Gauge (AWG) 24 26 24 26 Distance (feet) 18,000 15,000 12,000 9,000 Wire Size (mm) 0. 5 0. 4 0. 5 0. 4 Distance (km) 5. 5 4. 6 3. 7 2. 7 Although the measure varies from telco to telco, these capabilities can cover up to 95 percent of a loop plant, depending on the desired data rate. Customers beyond these distances can be reached with fiber-based digital loop carrier (DLC) systems. As these DLC systems become commercially available, telephone companies can offer virtually ubiquitous access in a relatively short time. Many applications envisioned for ADSL involve digital compressed video. As a real-time signal, digital video cannot use link- or network-level error control procedures commonly found in data communications systems. Therefore, ADSL modems incorporate forward error correction that dramatically reduces errors caused by impulse noise. Error correction on a symbol-by-symbol basis also reduces errors caused by continuous noise coupled into a line. ADSL Technology ADSL depends on advanced digital signal processing and creative algorithms to squeeze so much information through twisted-pair telephone lines. In addition, many advances have been required in transformers, analog filters, and analog/digital (A/D) converters. Long telephone lines may attenuate signals at 1 MHz (the outer edge of the band used by ADSL) by as much as 90 dB, forcing analog sections of ADSL modems to work very hard to realize large dynamic ranges, separate channels, and Internetworking Technologies Handbook 1-58705-001-3 21-3 Chapter 21 Asymmetric Digital Subscriber Line Digital Subscriber Line maintain low noise figures. On the outside, ADSL looks simple—transparent synchronous data pipes at various data rates over ordinary telephone lines. The inside, where all the transistors work, is a miracle of modern technology. Figure 21-3 displays the ADSL transceiver-network end. Figure 21-3 This Diagram Provides an Overview of the Devices That Make Up the ADSL Transceiver-Network End of the Topology Downstream channel(s) Duplex channel(s) Mux Error control XMTR D/A and A/D Line coupler Channel separation (FDM or ECH) Basic telephone service splitter Line Demux Duplex channel(s) Error control RCVR Basic telephone service ADSL transceiver–network end (Premises end is mirror image) To create multiple channels, ADSL modems divide the available bandwidth of a telephone line in one of two ways: frequency-division multiplexing (FDM) or echo cancellation, as shown in Figure 21-4. FDM assigns one band for upstream data and another band for downstream data. The downstream path is then divided by time-division multiplexing into one or more high-speed channels and one or more low-speed channels. The upstream path is also multiplexed into corresponding low-speed channels. Echo cancellation assigns the upstream band to overlap the downstream, and separates the two by means of local echo cancellation, a technique well known in V. 32 and V. 34 modems. With either technique, ADSL splits off a 4-kHz region for basic telephone service at the DC end of the band. Internetworking Technologies Handbook 21-4 1-58705-001-3 Chapter 21 Digital Subscriber Line Signaling and Modulation Figure 21-4 ADSL Uses FDM and Echo Cancellation to Divide the Available Bandwidth for Services FDM Upstream Basic telephone service Downstream Frequency Echo cancellation Upstream Basic telephone service Downstream 1 Mhz Frequency 1 Mhz An ADSL modem organizes the aggregate data stream created by multiplexing downstream channels, duplex channels, and maintenance channels together into blocks, and it attaches an error correction code to each block. The receiver then corrects errors that occur during transmission, up to the limits implied by the code and the block length. At the user’s option, the unit also can create superblocks by interleaving data within subblocks; this allows the receiver to correct any combination of errors within a specific span of bits. This, in turn, allows for effective transmission of both data and video signals. Signaling and Modulation This section includes the following: †¢ †¢ CAP and DMT Modulated ADSL ADSL Standards and Associations CAP and DMT Modulated ADSL DMT and CAP are line-coding methods for modulating the electrical signals sent over the copper wire in the local loop. Carrierless Amplitude and Phase (CAP) is a common line-coding method. CAP is a well-understood technology because of its similarity with QAM. Although CAP is well-understood and relatively inexpensive, some argue that it is difficult to scale because it is a single-carrier modulation technique and is susceptible to narrowband interference. DMT uses multiple carriers. At this point, DMT is capable of more speed than CAP. This is one reason that the ANSI committee T1E1. accorded it standards status in document T1. 413. This standard calls for 256 subbands of 4 KHz each, thereby occupying 1. 024 GHz. Each subband can be modulated with QAM 64 for clean subbands, down to QPSK. If each of the subbands can support QAM-64 modulation, then the forward channel supports 6. 1 Mbps. On the return path are 32 subbands, with a potential for 1. 5 Mbps. Internetworking Technologies H andbook 1-58705-001-3 21-5 Chapter 21 Signaling and Modulation Digital Subscriber Line CAP and DMT Compared CAP is a single-carrier technique that uses a wide passband. DMT is a multiple-carrier technique that uses many narrowband channels. The two have a number of engineering differences, even though, ultimately, they can offer similar service to the network layers discussed previously. Adaptive Equalization Adaptive equalizers are amplifiers that shape frequency response to compensate for attenuation and phase error. Adaptive equalization requires that the modems learn line characteristics and do so by sending probes and looking at the return signals. The equalizer then knows how it must amplify signals to get a nice, flat frequency response. The greater the dynamic range, the more complex the equalization. ADSL requires 50 dB of dynamic range, complicating adaptive equalization. Only with recent advances in digital signal processing (number crunching) has it become possible to have such equalization in relatively small packaging. Adaptive equalization is required for CAP because noise characteristics vary significantly across the frequency passband. Adaptive equalization is not needed for DMT because noise characteristics do not vary across any given 4-KHz subband. A major issue in comparing DMT with CAP is determining the point at which the complexity of adaptive equalization surpasses the complexity of DMT’s multiple Fourier transform calculations. This is determined by further implementation experience. Power Consumption Although DMT clearly scales and does not need adaptive equalization, other factors must be considered. First, with 256 channels, DMT has a disadvantage regarding power consumption (and, therefore, cost) when compared with CAP. DMT has a high peak-to-average power ratio because the multiple carriers can constructively interfere to yield a strong signal. DMT has higher computational requirements, resulting in more transistors than the transceiver chips. Numbers are mostly proprietary at this point, but it is estimated that a single transceiver will consume 5 W of power, even with further advances. Power consumption is important because hundreds or thousands (as carriers dearly hope) of transceivers might be at the central office, or CEV. This would require much more heat dissipation than CAP requires. Latency Another issue for DMT is that latencies are somewhat higher than with CAP (15). Because each subband uses only 4 KHz, no bit can travel faster than permitted by a QAM-64. The trade-off between throughput and latency is a historical one in data communications and has normally been settled in the marketplace. Speed DMT appears to have the speed advantage over CAP. Because narrow carriers have relatively few equalization problems, more aggressive modulation techniques can be used on each channel. For CAP to achieve comparable bit rates, it might be necessary to use more bandwidth, far beyond 1 MHz. This creates new problems associated with high frequencies on wires and would reduce CAP’s current advantage in power consumption. Internetworking Technologies Handbook 21-6 1-58705-001-3 Chapter 21 Digital Subscriber Line Additional DSL Technologies ADSL Standards and Associations The American National Standards Institute (ANSI) Working Group T1E1. 4 recently approved an ADSL standard at rates up to 6. 1 Mbps (DMT/ANSI Standard T1. 413). The European Technical Standards Institute (ETSI) contributed an annex to T1. 413 to reflect European requirements. T1. 413 currently embodies a single terminal interface at the premises end. Issue II expands the standard to include a multiplexed interface at the premises end, protocols for configuration and network management, and other improvements. The ATM Forum and the Digital Audio-Visual Council (DAVIC) have both recognized ADSL as a physical layer transmission protocol for UTP media. Additional DSL Technologies This section discusses the following DSL technologies: †¢ †¢ †¢ †¢ †¢ †¢ SDSL HDSL HDSL-2 G. SHDSL ISDN Digital Subscriber Line (DSL) VDSL SDSL Symmetric Digital Subscriber Line (SDSL) is a rate-adaptive version of HDSL and, like HDSL, is symmetric. It allows equal bandwidth downstream from an NSP’s central office to the customer site as upstream from the subscriber to the central office. SDSL supports data only on a single line and does not support analog calls. SDSL uses 2B1Q line coding and can transmit up to 1. 54 Mbps to and from a subscriber, or can be configured to offer a variable range of bandwidth up to 1. 45 Mbps. The symmetry that SDSL offers, combined with always-on access (which eliminates call setup), makes it a favorable WAN technology for small to medium businesses and branch offices, and can be an affordable alternative to dedicated leased lines and Frame Relay services. Because traffic is symmetrical, file transfer, web hosting, and distance-learning applications can effectively be implemented with SDSL. HDSL Originally developed by Bellcore, high bit-rate DSL (HDSL)/T1/E1 technologies have been standardized by ANSI in the United States and by ETSI in Europe. The ANSI standard covers two-pair T1 transmission, with a data rate of 784 kbps on each twisted pair. ETSI standards exist both for a two-pair E1 system, with each pair carrying 1168 kbps, and a three-pair E1 system, with 784 kbps on each twisted pair. HDSL became popular because it is a better way of provisioning T1 or E1 over twisted-pair copper lines than the long-used technique known as Alternative Mark Inversion (AMI). HDSL uses less bandwidth and requires no repeaters up to the CSA range. By using adaptive line equalization and 2B1Q modulation, HDSL transmits 1. 544 Mbps or 2. 048 Mbps in bandwidth ranging from 80ntrast to the 1. 5 MHz required by AMI. (AMI is still the encoding protocol used for the majority of T1. ) Internetworking Technologies Handbook 1-58705-001-3 21-7 Chapter 21 Additional DSL Technologies Digital Subscriber Line T1 service can be installed in a day for less than $1,000 by installing HDSL modems at each end of the line. Installation via AMI costs much more and takes more time because of the requirement to add repeaters between the subscriber and the CO. Depending on the length of the line, the cost to add repeaters for AMI could be up to $5,000 and could take more than a week. HDSL is heavily used in cellular telephone buildouts. Traffic from the base station is backhauled to the CO using HDSL in more than 50 percent of installations. Currently, the vast majority of new T1 lines are provisioned with HDSL. However, because of the embedded base of AMI, less than 30 percent of existing T1 lines are provisioned with HDSL. HDSL does have drawbacks. First, no provision exists for analog voice because it uses the voice band. Second, ADSL achieves better speeds than HDSL because ADSL’s asymmetry deliberately keeps the crosstalk at one end of the line. Symmetric systems such as HDSL have crosstalk at both ends. HDSL-2 HDSL-2 is an emerging standard and a promising alternative to HDSL. The intention is to offer a symmetric service at T1 speeds using a single-wire pair rather than two pairs. This will enable it to operate for a larger potential audience. It will require more aggressive modulation, shorter distances (about 10,000 feet), and better phone lines. Much of the SDSL equipment in the market today uses the 2B1Q line code developed for Integrated Services Digital Network. The Bell companies have insisted that using this SDSL at speeds higher than 768 kbps can cause interference with voice and other services that are offered on copper wire within the same wire bundle. The biggest advantage of HDSL-2, which was developed to serve as a standard by which different vendors’ equipment could interoperate, is that it is designed not to interfere with other services. However, HDSL-2 is full rate only, offering services only at 1. 5 Mbps. G. SHDSL G. SHDSL is a standards-based, multirate version of HDSL-2 and offers symmetrical service. The advantage of HDSL-2, which was developed to serve as a standard by which different vendors’ equipment could interoperate, is that it is designed not to interfere with other services. However, the HDSL-2 standard addresses only services at 1. 5 Mbps. Multirate HDSL-2 is part of Issue 2 of the standard known as G. SHDSL, and is ratified by the ITU. G. SHDSL builds upon the benefits of HDSL-2 by offering symmetrical rates of 2. 3 Mbps. ISDN Digital Subscriber Line ISDN digital subscriber line (IDSL) is a cross between ISDN and xDSL. It is like ISDN in that it uses a single-wire pair to transmit full-duplex data at 128 kbps and at distances of up to RRD range. Like ISDN, IDSL uses a 2B1Q line code to enable transparent operation through the ISDN â€Å"U† interface. Finally, the user continues to use existing CPE (ISDN BRI terminal adapters, bridges, and routers) to make the CO connections. The big difference is from the carrier’s point-of-view. Unlike ISDN, ISDL does not connect through the voice switch. A new piece of data communications equipment terminates the ISDL connection and shuts it off to a router or data switch. This is a key feature because the overloading of central office voice switches by data users is a growing problem for telcos. Internetworking Technologies Handbook 21-8 1-58705-001-3 Chapter 21 Digital Subscriber Line Summary The limitation of ISDL is that the customer no longer has access to ISDN signaling or voice services. But for Internet service providers, who do not provide a public voice service, ISDL is an interesting way of using POTS dial service to offer higher-speed Internet access, targeting the embedded base of more than five million ISDN users as an initial market. VDSL Very-High-Data-Rate Digital Subscriber Line (VDSL) transmits high-speed data over short reaches of twisted-pair copper telephone lines, with a range of speeds depending on actual line length. The maximum downstream rate under consideration is between 51 and 55 Mbps over lines up to 1000 feet (300 m) in length. Downstream speeds as low as 13 Mbps over lengths beyond 4000 feet (1500 m) are also common. Upstream rates in early models will be asymmetric, just like ADSL, at speeds from 1. 6 to 2. 3 Mbps. Both data channels will be separated in frequency from bands used for basic telephone service and Integrated Services Digital Network (ISDN), enabling service providers to overlay VDSL on existing services. Currently, the two high-speed channels are also separated in frequency. As needs arise for higher-speed upstream channels or symmetric rates, VDSL systems may need to use echo cancellation. Summary ASDL technology is asymmetric, allowing more bandwidth for downstream than upstream data flow. This asymmetric technology combined with always-on access makes ASDL ideal for users who typically download much more data than they send. An ASDL modem is connected to both ends of a twisted-pair telephone line to create three information channels: a high-speed downstream channel, a medium-speed duplex channel, and a basic telephone service channel. ADSL modems create multiple channels by dividing the available bandwidth of a telephone line using either frequency-division multiplexing (FDM) or echo cancellation. Both techniques split off a 4-kHz region for basic telephone service at the DC end of the band Synchronous Digital Subscriber Line (SDSL) provides variable, symmetric, high-speed data communication up to 1. 54 Mbps. But SDSL doesn’t allow analog on the same line, as ADSL does. SDSL uses 2B1Q line coding, a technology employed in ISDN and T1 services. SDSL is a viable business option because of its capability to transmit high-speed data over longer distances from the CO and because of its ease of deployment made possible by its spectral compatibility. High Bit-Rate DSL (HDSL) is a symmetric version of DSL that uses 2B1Q like SDSL, but over two-wire pairs. HDSL is targeted at business deployment because it offers full-rate symmetrical 1. 5 Mbps service. HDSL-2 is a standards-based version of HDSL offering symmetrical 1. 5 Mbps service like HDSL, but with a single twisted pair of wires. HDSL is full-rate and does not offer variable rates. G. SHDSL does offer multirate service with symmetrical speeds of up to 2. 3 Mbps. ISDN digital subscriber line (IDSL) is similar in many ways to ISDN. The primary difference is that IDSL is always on and can reach speeds up to 512 kbps with compression. IDSL uses 2B1Q line coding and does not support analog. On the other hand, IDSL does allow data communications over longer distances than other DSL options (up to 26,000 feet) and is considerably less expensive than ISDN service, in most cases. Because IDSL supports existing ISDN CPE, it makes it easy to convert from ISDN to IDSL. Internetworking Technologies Handbook 1-58705-001-3 21-9 Chapter 21 Review Questions Digital Subscriber Line Very-High-Data-Rate Digital Subscriber Line (VDSL) transmits high-speed data over short distances through twisted-pair copper telephone lines. VDSL technology is still in the definition stage, but additional research is required before it can be standardized. VSDL and ADSL are similar technologies. However, although VSDL transmits data at nearly 10 times the rate of ADSL, ADSL is the more complex transmission technology. Review Questions Q – Name the current versions of DSL technology. A – ADSL, SDSL, HDSL, HDSL-2, G. SHDL, IDSL, and VDSL. Q – What are the two-line coding methods used for ADSL? A – DMT and CAP. Q – Which versions of DSL offer symmetrical service? A – SDSL, HDSL, and HDSL-2. Q – What symmetrical version of DSL offers multirate service over a single pair of wire? A – G. SHDSL Q – How far of a reach can IDSL achieve from the CO? A – 26,000 feet. Q – What downstream and upstream rates are proposed for VDSL? A – The maximum downstream rate under consideration is between 51 and 55 Mbps over lines up to 1000 feet (300 m) in length. Downstream speeds as low as 13 Mbps over lengths beyond 4000 feet (1500 m) are also common. Upstream rates in early models will be asymmetric, just like ADSL, at speeds from 1. 6 to 2. 3 Mbps. For More Information ADSL Forum (http://www. adsl. com/) Cisco DSL Depot (http://www. isco. com/warp/public/779/servpro/promotions/dsldepot/) Glossary Terms †¢ G. SHDSL – Asymmetrical Digital Subscriber Line. The upstream data rate is different from the downstream (typically the downstream is greater than the upstream). It is applicable to many DSL technologies offered today; however, this term typically assumes DMT as defined in the ANSI T1. 413 specification. CPE – Customer premises equipment, including devices such as CSU/DSUs, modems, and ISDN terminal adapters, required to provide an electromagnetic termination for wide-area network circuits before connecting to the router or access server. This equipment was historically provided by the telephone company, but it is now typically provided by the customer in North American markets. †¢ Internetworking Technologies Handbook 21-10 1-58705-001-3 Chapter 21 Digital Subscriber Line Glossary Terms †¢ CSU/DSU – Channel service unit/data service unit. Provides electromagnetic termination of the digital (WAN) signal at the customer premises. Performs line conditioning and equalization functions, and responds to loopback commands sent from the central office. In North America, the customer supplies the device providing CSU/DSU functionality; outside North America, the telecommunications service provider usually provides this device. DMT – Discrete Multitone is the ANSI specified modulation technique for G. SHDSL (ANSI-T1. 413). DMT is theoretically capable of more speed than CAP. The key providers of DMT are Alcatel, Amati, Aware/ADI, and Orckit. Downstream – Refers to the transmission of data from the central office (CO or COE) to the customer premise equipment (CPE). HDSL – High-speed Digital Subscriber Line. This is a symmetrical modulation technique that uses two or three pairs of wires. HDSL2 – High-speed Digital Subscriber Line. This is a symmetrical modulation technique that can achieve speeds in the T1 (1. 5 Mbps) range using one copper pair. POTS – Plain old telephone service. QAM – Quadrature amplitude phase modulation. RG. SHDSL – Rate Adaptive Digital Subscriber Line. This refers to the CAP2 and QAM technologies that use variable data rates to maximize the utilization of various loop lengths. SDSL – Symmetric Digital Subscriber Line. This indicates a subscriber line service that utilizes the same data rate for upstream and downstream. This term is applicable to MDSL and HDSL technologies. Upstream – Refers to the transmission of data from the customer premises equipment (CPE) to the central office equipment (CO or COE). VDSL – Very-High-Data-Rate Digital Subscriber Line. This is a high-speed asymmetrical service in the 10 to 25 Mbps range, typically limited to less than 5,000 feet. The targeted application for this technology is a hybrid fiber copper system (fiber to the neighborhood). †¢ †¢ †¢ †¢ †¢ †¢ †¢ †¢ †¢ †¢ Internetworking Technologies Handbook 1-58705-001-3 21-11 Chapter 21 Glossary Terms Digital Subscriber Line Internetworking Technologies Handbook 21-12 1-58705-001-3

Environmental Discourse Essay

Although environmental concerns have attained increasing currency within society, general coverage by the media fails to recognize that not all environmental discourses are alike. Different ideological strains exist and maintain different assumptions about not just the source of environmental problems, but the kinds of solutions that are necessary to solving environmental problems. In the latter half of the 20th century, when environmentalism arose as a distinct political and social ideology, the form of environmental discourse held by most of its proponents is what is now called deep green environmentalism. Deep green environmentalisms operate under the assumption that the dominant political and social ideologies such as unchecked growth, pervasive consumerism and extreme industrialism and capitalism are inherently flawed and contributive to ecological damage. They believe profound lifestyle changes and a willingness to confront dominant social institutions are needed to keep these problems in check. (Beder, 1991) By contrast, light green environmentalists are more common today: they have a casual concern regarding planetary welfare and do not view environmental protection as a distinct political ideology. They do not seek the political emasculation of industrialism and capitalism but instead emphasize environmentalism as a lifestyle alternative. They choose strategic consumption and a responsible modern living as the means to address environmental issues. As such, light green environmentalists make no pretense of possessing the same subversive aspirations of their dark or deep green counterparts. (Beder, 1991) Today, a new form of environmentalism has emerged: Bright green environmentalism. Bright green environmentalism holds that the guilt of modern living can be reconciled with environmental anxiety and sustainability is possible through tools and technology. The primary assumption is that it is difficult for individuals to go deep green and â€Å"turn their backs† on material luxury, and that the strategic consumption of light greens is ultimately trivial in relation to our ecological problems. To that end, bright green environmentalists embrace new forms of energy production, manufacturing, biotechnology, urban planning and other forms of sustainable design technologies as a means of retrofitting the present capitalist-industrialist mode of life rather than seeking to overthrow it. They celebrate the potential for economic abundance and material plenitude without compromising ecological sustainability. (Steffen, 2006) REFERENCES Beder, S. â€Å"Activism vs. Negotiation: Strategies for the Environment Movement. † Social Alternatives, Vol 10, No 4, pp. 53-56, December 1991. Retrieved on January 26, 2009 from: http://homepage. mac. com/herinst/sbeder/activism. html Steffen, A. (2006, May) â€Å"The Next Green Revolution. † Wired Magazine, 14. 05. Retrieved October 13, 2008 from: http://www. wired. com/wired/archive/14. 05/green. html

Transportation Planning Essay Example | Topics and Well Written Essays - 2500 words

Transportation Planning - Essay Example Much emphasis should be placed on the issue of transport planning with a view of expanding the planning boundaries from the conceptual to a practical based perspective. The rational Planning theory was a planning theory propounded after the World War two. It was majored in the core areas of knowledge in planning that were perceived to be essential to practice (Barrett 9). It led to development of the generic planning model in capitalistic democracies and was taken from views from different social disciplines in addition to the political and economic factors. It was used as an approach in solving problems in the public sphere (Brooks 39). Later, it was taken to the public policy due to its guiding principles. The rational planning theory had the following steps; a) the end to reductions and expansion, b) it calculated course of action, c) it evaluated the consequences, d) it provided alternatives to the existing challenge; e) it considered the implications of the existing alternate (J ohnson 67). This theory describes the problem solving mechanism in the transport planning. It was engineered with a view of serving the interest of the public and thus very populous (Brooks 47). Advocate Planner theory is based on the legal advocacy system as an analogy, where a member of a community approaches the planning authority and argues on the behalf of the public interest. Social learning theory puts emphasis on the responsibility of the planning authority to uniting the stakeholders and sharing the information with a view of learning from them (Barrett 22). This helps to develop social structures that meet the social expectations of the stakeholders. Transitive planning theory emphasized that the members of the community and the civic leaders be at the center of the planning process if at all the plan was to be implemented (Brooks 107). Communicative planning theory asserts that planners had to alert the members of the community (Johnson 21). This is believed to encourage

UC transfer personal Statement Example | Topics and Well Written Essays - 750 words

UC transfer - Personal Statement Example Volunteering in the computer club of my college gave me a deep insight in the extensive world of computers. I have a strong flare to work for social causes such as charity work which provides me with inner satisfaction and peace of mind. I feel proud to mention that I have been deeply involved in causes such as helping my professor clear trash on the beach several times. The complexity of computing and its use in the real world fascinates me, like helping the human genome plan for technical development, algorithmic skills for raising the effectiveness of economical markets to generating the digital transformation from the internet to other equipments that are wireless. Owing to my keen fascination with the subject I have had the advantages of reading some books on programming on my own which includes â€Å"The art of computer programming† by Donald Kuthe by Harold Abelson and Gerald Jay Sussman and â€Å"Programming pearls† by Jon Bentley. These books have provided me w ith a thorough knowledge of programming software and computing. I plan to have computing as my major in the university as my deep interest in the subject would guide me towards a bright future. Being a cool, calm and collected person, I take pleasure in the challenge of solving problem with explicit answers. My inventiveness assists me in accepting innovative ideas, these aspects of my personality compels me towards the field of computing and programming. As Gail Devers said â€Å"Keep your dreams alive. Understand to achieve anything requires faith and belief in yourself, vision, hard work, determination and dedication. Remember all things are possible for those who believe† I want to live my dream of leading a successful career in computing. Before enrolling in the Santa Barbara, I first studied in a language school called â€Å"Kaplan† for five months. For the past two years in SBCC I have

Personal ethics action plan Assignment Example | Topics and Well Written Essays - 2000 words

Personal ethics action plan - Assignment Example Professionally, I am a committed Operations Manager. I believe in team work and enjoy multi-tasking. I participate actively in group discussions. I possess leadership skills and do my best to motivate my team to achieve organizational goals. I am a keen negotiator and make every effort to maintain a high standard of quality and timeliness in my work. I believe in taking responsibility for the work I take up and give my very best to the work on hand. I would like to develop a strong work – life balance, in order to stably manage my personal and professional aspirations. I believe I would need to develop my observational and problem – solving skills in order to become a more complete professional. I would like to see myself in a decision – making role in a few years from now. My aim is to be the Director of a Multi-national company. I hope to be a well – balanced individual, with a successful personal and professional life! 2. Definitions: Ethics are a set o f values and principles that help one distinguish right from wrong. Ethics are the rules of one’s personal behavior that are often based upon laws, organizational policies, social norms, family, religion, and/or personal needs, and may be subject to differing interpretations. There is an old saying: â€Å"What is popular is not always right; what is right is not always popular.† Ethics govern the way people behave and influence their decisions on the 'right thing' to do. Our personal values contribute to the strength of our ethics. I believe that personal ethics influence our general ‘code of conduct’ in society and follow a process of continuous development. Leadership is a virtue that determines one’s ability to organize, guide and socially influence a group of people, in the accomplishment of a common  goal. Innate leadership qualities often emerge at a time of necessity, but these skills are not possessed in equal measures by all. Leadership i s influenced by one’s traits, intelligence, behavior, charisma, sense of authority, power and general temperament. Within an institution, each leader adopts a unique approach and style of leadership, for example: Transformational leadership or Situational leadership and gathers followers gradually. An effective leader plays the role of a mentor who encourages his team to think independently and guides the team towards achieving the outlined objectives. ‘Service’ may be defined as one’s personal willingness and voluntary contribution to any activity that does not have any direct financial or material compensation. One who is engaged in ‘service’ possesses a giving attitude, is dependable and is readily available to perform the task. In service, one must have the ability to work well ‘with others’, ‘for others’ and sometimes, ‘on behalf of others’. ‘Service’ to any organization requires active participation and a willingness to take on difficult responsibilities. Above all, the individual must represent his institution and perform committee work without a complaint, in the best interest of the organization and community. ‘Character’ refers to the innate traits, qualities and tendencies of an individual to think and act in different situations (known or unknown) with honesty, integrity, authenticity and responsibility. The pillars of character include trustworthiness, respect, responsibility, fairness, caring attitude and a sense of citizenship. Character is developed