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English to Serbian: Introduction to passive optical networks General field: Tech/Engineering Detailed field: Computers: Systems, Networks
Source text - English Chapter 1
Introduction
Cedric F. Lam
OpVista Inc.
The recent surge in bandwidth demand, driven by fast-growing video-on-demand (VOD) services and emerging applications such as network gaming,peer-to-peer downloading etc. has revitalized the optical communication in-dustry. After more than 20 years of active research, passive optical network(PON)-based broadband optical access systems are finally seeing wide-scaledeployments in Asia and North America. In Europe, carriers and serviceproviders are also actively looking into PONs as the next-generation broadbandaccess solutions.
1.1 HISTORY OF BROADBAND ACCESSNETWORKS AND PON
Access networks have been traditionally called last-mile networks as theycomprise the last segment connection from service providers’ central office(CO) to end users. They are also called first-mile networks in recent years asthey are the first segment of the broader network seen by users of telecommu-nication services. Example of access networks are twisted copper pairs connect-ing to each individual household (also called local loops) and residential coaxialcable drops from community antenna TV (CATV) service providers. Wi-Max isanother type of access technology which uses radio waves for last-mile connect-ivity. Traditionally, optical fibers have been widely used in backbone networksbecause of their huge available bandwidth and very low loss. Although fiber hasalso been touted as the next-generation access technology for a long time, it isnot until the beginning of this century that fiber has finally seen its growingcommercial importance as the technology of last-mile connection.Traditional telecommunication networks were developed for analog voiceservices. For a long time, 4 kHz was the bandwidth required to connect to end
1
users for voice services. A ubiquitous twisted copper network has been deployedby telephone companies (the Bell System in the United States and PTTs in othercountries) in industrialized countries for decades. It is not difficult to imaginethat such networks were optimized for analog voice frequency transmissions. Asa matter of fact, in order to achieve better economy and allow longer local loopdrops, inductors called loading coils have been installed in many old twistedcopper pair plants to enhance the voice frequency band performance. Loadingcoils, however, significantly attenuate high frequency signals outside the voicefrequency band and make them unsuitable for broadband digital subscriber line(DSL) services.Although voice signal transmission has been digitized into 64 kbps digitalchannel (DS0) for TDM switching long time ago, digital voice signals have beenconverted back to analog format to be backward-compatible with analog tele-phone sets before they are delivered to end users. The Internet is the driving forcefor digital local loops, also called DSLs [1]. The Internet was first invented in the1960s. For a long time after its invention, the Internet was mainly used byresearch and academia for data sharing. The first popular Internet applicationwas e-mail, which was invented in the early 1970s. It was not until the early1990s, when the World Wide Web and its graphical user interface MOSAICcame out, that the Internet started to become an important part of people’s lives.Because of the voice bandwidth limitation and transmission line noise, the bestdata rate available from an analog modem working on voice grade twistedcopper lines is 56 kbps.
Translation - Serbian Prvo Poglavlje
Uvod
Cedric F. Lam
OpVista Inc.
Nedavni porast zahteva povećanja propusnog opsega, podstaknut uslugama videa na zahtev (VOD – video-on-demand) i aplikacijama koje su iz dana u dan brojnije poput igranja igrica putem Interneta i uzajamnog skidanja podataka, oživeo je industriju optičke komunikacije. Nakon više od 20 godina aktivnog istraživanja, sistemi širokopojasnog optičkog pristupa zasnovani na PON-u (PON – passive optical network, pasivna optička mreža) konačno započinju svoju naširoku primenu duž Azije i Sjedinjenih američkih država. Evropski telekomunikacioni operateri i provajderi se podjednako interesuju za PON, kao napredno rešenje problema širokopojasnog pristupa.
1.1 Istorija širokopojasnih pristupnih mreža i PON-a
Pristupne mreže se oduvek nazivaju krajnjim delom mreže jer predstavljaju poslednji segment konekcije, koji potiče iz centrale provajdera (CO – central office), sa krajnjim korisnikom. Odnedavno se nazivaju i prvim delom mreže iz perspektive korisnika telekomunikacionih usluga koji ih doživljavaju kao prvi segment mnogo šire mreže. Klasični primeri elemenata pristupne mreže su upredene bakarne parice koje se povezuju sa svakim korisničkim domaćinstvom (takođe se zovu i lokalne linije) i stambeni koaksijalni kablovi koji se spuštaju od zajedničkih antena provajdera televizijskih usluga (CATV – community antenna television). Wi-Max je još jedan tip pristupne tehnologije koji se služi radio talasima u krajnjim delovima konekcije. Po pravilu, optička vlakna se uvek koriste za strukturu mreže okosnice zbog svog ogromnog propusnog opsega i minimalnih gubitaka. Iako se već duže vremena govori o vlaknu kao o pristupnoj tehnologiji nove generacije, tek početkom veka je ono doživelo porast u mogućnostima primene u domenu tehnologije krajnjeg dela konekcije.
Tradicionalna telekomunikaciona mreža je uspostavljena u cilju pružanja analognih glasovnih usluga. Dugo vremena je propusni opseg od samo 4 kHz bio dovoljan za povezivanje s krajnjim korisnicima zarad glasovnih usluga. Sveprisutna mreža od upredenih bakarnih parica se već decenijama koristi u telefonskim kompanijama (Bel sistem u Sjedinjenim američkim državama, PTT u drugim državama) svih industrijskih zemalja. Stoga nije nezamislivo što je takva mreža usklađena sa potrebama prenosa analogne glasovne frekvencije. Zapravo, kako bi se postigla veća ekonomičnost i produžili vodovi lokalnih linija, uvedeni su Pupinovi kalemovi koji su umetnuti u bakarne parice kako bi povećali rad opsega glasovne frekvencije. Ovi kalemovi, međutim, u značajnoj meri slabe visokofrekvencijske signale, van opsega glasovne frekvencije, zbog čega se ne mogu primeniti kod usluga širokopojasnih digitalnih pretplatničkih linija (DSL usluga).
Mada je prenos glasovnog signala odavno pretočen u digitalni kanal od 64 kb/s (DS0) zarad TDM svičevanja, digitalni glasovni signali se konvertuju u analogni format kako bi bili povratno-kompatibilni sa analognim telefonima pre nego što se dostave krajnjim korisnicima. Internet je taj koji podstiče digitalne pretplatničke linije, koje se još zovu i DSL (digital subscriber line), da se razvijaju. Internet je izumljen 60-ih godina dvadesetog veka. Dugo godina potom je korišćen isključivo radi razmene podataka u naučne i akademske svrhe. Elektronska pošta (e-mail), koja je nastala početkom 70-ih godina, bila je prva popularna aplikacija za Internet. Međutim, Internet je dobio ključnu ulogu u svakodnevnom životu tek kada su Svetska mreža (World Wide Web) i njen grafički korisnički interfejs, Mozaik, nastali početkom 90-ih godina. Zbog ograničenja glasovnog opsega i šuma prenosne linije, najbolja brzina prenosa podataka koja se mogla izvući iz analognog modema koji funkcioniše na bazi upredenih parica unapređenih za prenos glasa je 56 kb/s.
Serbian to English: Zašto Engleska nema pisani ustav? Detailed field: Government / Politics
Source text - Serbian Zašto Engleska nema pisani ustav?
Da bi Engleska dobila nov ustav dovoljno je promeniti „samo“ jednu odredbu – onu koja se odnosi na suverenost i suprematiju parlamenta. Da je britanski ustav bio napisan odmah na početku XVIII veka, bilo bi dovoljno da sadrži samo jednu odredbu: Postojaće parlament u UK, i on može da uradi šta god poželi. Ova tvrdnja, u osnovi, i dalje važi. Svaka promena u ustavu, bez obzira na obim i sadržaj samo je promena u okviru postojećeg ustava. Da bi stari ustav bio zamenjen novim, bilo je potrebno ograničiti svemoć parlamenta, ili ukinuti parlament. U oba slučaja, radi se o revoluciji. A Englezi su oduvek prezirali revolucije. Reforme koje znače postepenu promenu stvarnosti, „popravljanje“ postojećih institucija tako da odgovaraju zahtevima novih vremena, oduvek su odnosile prevagu nad radikalnim raskidima s prošlošću. Stoga bi usvajanje novog, pisanog ustava značilo revoluciju daleko veću i od „Slavne revolucije“. Englezi poslednjih decenija o tome mnogo govore, raspravljaju i pišu, ali i dalje ostaje pitanje na koje treba odgovoriti: Da li su spremni da se odreknu starog ustava?
Translation - English Why doesn’t England have a written constitution?
For England to have a new constitution, it is sufficient to alter only a single provision – that referring to the sovereignty and supremacy of the Parliament. If the British constitution had been written right at the beginning of the 18th century, it would have been sufficient for it to contain but a single provision: There shall be a Parliament and it can do whatever it desires. Basically, this claim is still valid. Every alteration in the constitution, regardless of its scope or content, is only an alteration within the existing constitution. In order to replace the old constitution with a new one, it was necessary to limit the omnipotency of the Parliament or abolish it. In both cases, a revolution would be inevitable. And the English have always despised revolutions. Reforms, denoting gradual changing of reality and ˝repairing˝ existing institutions so that they conform to the demands of the new age, have always taken precedence over radical braking away from the past. Therefore, adopting a new, written constitution would envolve a revolution far greater than the Glorious Revolution. The English have been discussing, debating and writing about this for many decades, yet a question to be answered remains: Are they ready to forsake the old constitution?
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