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All about SDH:A pictorial perspective……

Standards 1 Min Read

Dear Friends,

Sometime we require something that help us to understand SDH in quick mode.For this I have collected some snapshots that will help you crack your interviews as well as make you loaded with the know hows of the same..

1.SDH frame:-

 

 2.Mapping structure:-

3.Overheads:-

 

 

 

4.Path Overheads:-

 

 

 

 

 

5.Concatenation:-

6.Alarms:-

7.Alarm Flow:-

 

Your concerns and queries will be highly appreciated……….
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Optical Networks Communication System Design Considerations

Standards 10 Mins Read

Fiber Optic Communication System Design Considerations

When designing a fiber optic communication system some of the following factors must be taken into consideration:

  • Which modulation and multiplexing technique is best suited for the particular application?
  • Is enough power available at the receiver (power budget)?
  • Rise-time and bandwidth characteristics
  • Noise effects on system bandwidth, data rate, and bit error rate
  • Are erbium-doped fiber amplifiers required?
  • What type of fiber is best suited for the application?
  • Cost
  1. Power Budget

The power arriving at the detector must be sufficient to allow clean detection with few errors. Clearly, the signal at the receiver must be larger than the noise. The power at the detector, Pr, must be above the threshold level or receiver sensitivity Ps.

Pr >= Ps

The receiver sensitivity Ps is the signal power, in dBm, at the receiver that results in a particular bit error rate (BER). Typically the BER is chosen to be one error in 109 bits or 10–9.

The received power at the detector is a function of:

  1. Power emanating from the light source (laser diode or LED)—(PL)
  2. Source to fiber loss (Lsf)
  3. Fiber loss per km (FL) for a length of fiber (L)
  4. Connector or splice losses (Lconn)
  5. Fiber to detector loss (Lfd)

The allocation of power loss among system components is the power budget. The power margin is the difference between the received power Pr and the receiver sensitivity Ps by some margin Lm.

Lm = Pr – Ps

where  Lm is the loss margin in dB, Pr is the received power, Ps is the receiver sensitivity in dBm.

If all of the loss mechanisms in the system are taken into consideration, the loss margin can be expressed as the following equation. All units are dB and dBm.

Lm = PL – Lsf – (FL × L) – Lconn – Lfd – Ps

 

  1. Bandwidth and Riser Time Budgets

The transmission data rate of a digital fiber optic communication system is limited by the rise time of the various components, such as amplifiers and LEDs, and the dispersion of the fiber. The cumulative effect of all the components should not limit the bandwidth of the system. The rise time tr and bandwidth BW are related by

BW = 0.35/tr

This equation is used to determine the required system rise time. The appropriate components are then selected to meet the system rise time requirements. The relationship between total system rise time and component rise time is given by the following equation

where ts is the total system rise time and tr1, tr2, … are the rise times associated with the various components.

To simplify matters, divide the system into five groups:

  1. Transmitting circuits (ttc)
  2. LED or laser (tL)
  3. Fiber dispersion (tf)
  4. Photodiode (tph)
  5. Receiver circuits (trc)

The system rise time can then be expressed as

The system bandwidth can then be calculated using the following equation from the total rise time ts as given in the above equation

BW = 0.35/ts

Electrical and Optical Bandwidth

  • Electrical bandwidth (BWel) is defined as the frequency at which the ratio current out/current in (Iout/Iin) drops to 0.707. (Analog systems are usually specified in terms of electrical bandwidth.)
  • Optical bandwidth (BWopt) is the frequency at which the ratio power out/power in (Pout/Pin) drops to 0.5.

Because Pin and Pout are directly proportional to Iin and Iout (not I2in and I2out), the half-power point is equivalent to the half-current point. This results in a BWopt that is larger than the BWel as given in the following equation

BWel = 0.707 × BWopt

  1. Fiber Connectors

Many types of connectors are available for fiber optics, depending on the application. The most popular are:

  • SC—snap-in single-fiber connector
  • ST and FC—twist-on single-fiber connector
  • FDDI—fiber distributed data interface connector

In the 1980s, there were many different types and manufacturers of connectors. Today, the industry has shifted to standardized connector types, with details specified by organizations such as the Telecommunications Industry Association(TIA), the International Electrotechnical Commission, and the Electronic Industry Association (EIA).

Snap-in connector (SC)—developed by Nippon Telegraph and Telephone of Japan. Like most fiber connectors, it is built around a cylindrical ferrule that holds the fiber, and it mates with an interconnection adapter or coupling receptacle. A push on the connector latches it into place, with no need to turn it in a tight space, so a simple tug will not unplug it. It has a square cross section that allows high packing density on patch panels and makes it easy to package in a polarized duplex form that ensures the fibers are matched to the proper fibers in the mated connector.

Twist-on single-fiber connectors (ST and FC)—long used in data communication; one of several fiber connectors that evolved from designs originally used for copper coaxial cables.

Duplex connectors—A duplex connector includes a pair of fibers and generally has an internal key so it can be mated in only one orientation. Polarizing the connector in this way is important because most systems use separate fibers to carry signals in each direction, so it matters which fibers are connected. One simple type of duplex connector is a pair of SC connectors, mounted side by side in a single case. This takes advantage of their plug-in-lock design.

Other duplex connectors have been developed for specific types of networks, as part of comprehensive standards. One example is the fixed-shroud duplex (FSD) connector specified by the fiber distributed data interface (FDDI) standard.

  1. Fiber Optic Couplers

A fiber optic coupler is a device used to connect a single (or multiple) fiber to many other separate fibers. There are two general categories of couplers:

  • Star couplers
  • T-couplers
  1. Star Couplers

Transmissive type

Optical signals sent into a mixing block are available at all output fibers. Power is distributed evenly. For an n × n star coupler (n-inputs and n-outputs), the power available at each output fiber is 1/n the power of any input fiber.

The output power from a star coupler is simply

Po = Pin/n

where n = number of output fibers.

An important characteristic of transmissive star couplers is cross talk or the amount of input information coupled into another input. Cross coupling is given in decibels and is typically greater than 40 dB.

The reflective star coupler has the same power division as the transmissive type, but cross talk is not an issue because power from any fiber is distributed to all others.

  1. T-Couplers

In the following figure, power is launched into port 1 and is split between ports 2 and 3. The power split does not have to be equal. The power division is given in decibels or in percent. For example, and 80/20 split means 80% to port 2, 20% to port 3. In decibels, this corresponds to 0.97 dB for port 2 and 6.9 dB for port 3.

Directivity describes the transmission between the ports. For example, if P3/P1 = 0.5, P3/P2 does not necessarily equal 0.5. For a highly directive T-coupler, P3/P2 is very small. Typically, no power is expected to be transferred between any two ports on the same side of the coupler.

Another type of T-coupler uses a graded-index (GRIN) lens and a partially reflective surface to accomplish the coupling. The power division is a function of the reflecting mirror. This coupler is often used to monitor optical power in a fiber optic line.

  1. Wavelength-Division Multiplexers (WDM)

The couplers used for wavelength-division multiplexing (WDM) are designed specifically to make the coupling between ports a function of wavelength. The purpose of these couplers is to separate (or combine) signals transmitted at different wavelengths. Essentially, the transmitting coupler is a mixer and the receiving coupler is a wavelength filter. Wavelength-division multiplexers use several methods to separate different wavelengths depending on the spacing between the wavelengths. Separation of 1310 nm and 1550 nm is a simple operation and can be achieved with WDMs using bulk optical diffraction gratings. Wavelengths in the 1550-nm range that are spaced at greater than 1 to 2 nm can be resolved using WDMs that incorporate interference filters. An example of an 8-channel WDM using interference filters is given in the following figure. Fiber Bragg gratings are typically used to separate very closely spaced wavelengths in a DWDM system (< 0.8 nm).

  1. Erbium-Doped Fiber Amplifiers (EDFA)

Erbium-doped fiber amplifiers (EDFA)—The EDFA is an optical amplifier used to boost the signal level in the 1530-nm to 1570-nm region of the spectrum. When it is pumped by an external laser source of either 980 nm or 1480 nm, signal gain can be as high as 30 dB (1000 times). Because EDFAs allow signals to be regenerated without having to be converted back to electrical signals, systems are faster and more reliable. When used in conjunction with wavelength-division multiplexing, fiber optic systems can transmit enormous amounts of information over long distances with very high reliability.

  1. Fiber Bragg Gratings (FBG)

Fiber Bragg gratings—Fiber Bragg gratings are devices that are used for separating wavelengths through diffraction, similar to a diffraction grating (see the following figure). They are of critical importance in DWDM systems in which multiple closely spaced wavelengths require separation. Light entering the fiber Bragg grating is diffracted by the induced period variations in the index of refraction. By spacing the periodic variations at multiples of the half-wavelength of the desired signal, each variation reflects light with a 360° phase shift causing a constructive interference of a very specific wavelength while allowing others to pass. Fiber Bragg gratings are available with bandwidths ranging from 0.05 nm to >20 nm.

Fiber Bragg grating are typically used in conjunction with circulators, which are used to drop single or multiple narrowband WDM channels and to pass other “express” channels. Fiber Bragg
gratings have emerged as a major factor, along with EDFAs, in increasing the capacity of next generation high-bandwidth fiber optic systems.

The following figure depicts a typical scenario in which DWDM and EDFA technology is used to transmit a number of different channels of high-bandwidth information over a single fiber. As shown, n-individual wavelengths of light operating in accordance with the ITU grid are multiplexed together using a multichannel coupler/splitter or wavelength-division multiplexer. An optical isolator is used with each optical source to minimize troublesome back reflections. A tap coupler then removes 3% of the transmitted signal for wavelength and power monitoring. Upon traveling through a substantial length of fiber (50-100 Km), an EDFA is used to boost the signal strength. After a couple of stages of amplifications, an add/drop channel consisting of a fiber Bragg grating and circulator is introduced to extract and then reinject the signal operating at the λ3 wavelength. After another stage of amplification via EDFA, a broadband WDM is used to combine a 1310-nm signal with the 1550-nm window signals. At the receiver end, another broadband WDM extracts the 1310-nm signal, leaving the 1550-nm window signals. The 1550-nm window signals are finally separated using a DWDM that employs an array of fiber Bragg gratings, each tuned to the specific transmission wavelength. This system represents the current state of the art in high-bandwidth fiber optic data transmission.

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Some of the interesting facts

Standards 15 Mins Read
1. The English once took it to be an alphabet. The Chinese affectionately term it ‘the little mouse’. The Dutch call it an ‘elephant’s trunk’, the Germans a spider monkey, the Italians as a snail. It is ‘&amp;’ (ampersand).
2. The inspiration for the brand name Yahoo! Came from a word made up by Jonathan Swift in his book Gulliver’s Travels. A Yahoo was a person who was ugly and not a human in appearance.
3. The prime reason the Google home page is so bare, is due to the fact that the founders didn’t know the HTML and just wanted a quick interface. In fact, the submit button was a later addition and initially, hitting the RETURN key was the only way to burst Google into life.
4. Sweden has the highest percentage of its population i.e. 76.9 per cent hooked on to the Internet. In contrast, the world average is 11.9 per cent and India has a poor 7.2 per cent.
5. The Dilbert Zone was the first comic website on the Internet.
6. A resident of Tonga could have the rights to register domains ending in .to as Tongo’s Internet code is .to. Such possibilities are fun to consider: travel.to or go.to.
7. The day after Internet Explorer 4 was released, a few Microsoft employees left a 10 by 12-foot Internet Explorer logo on Netscape’s front lawn with a message that said “We love you” at the height of the browser wars in the late 90’s.
8. The world ‘e-mail’ has been banned by the French Ministry of culture. They are required to use the word ‘Courriel’ instead, which is the French equivalent of Internet. This move became the subject of ridicule from the cyber community in general.
9. Did you know that www.symbolics.com was the first ever domain name registered online?
10. According to a University of Minnesota report, researchers estimate the volume of Internet traffic is growing at an annual rate of 50 to 60 per cent.
11. The term Internet and World Wide Web are often used in every-day speech without much distinction. However, the Internet and the World Wide Web are not one and the same. The Internet is a global data communications system. It is a hardware and software infrastructure that provides connectivity between computers. In contrast, the Web is one of the services communicated via the Internet. It is a collection of interconnected documents and other resources, linked by hyperlinks and URLs.
12. In February 2009, Twitter had a monthly growth (of users) of over 1300 per cent several times more than Facebook.
13. The first graphical Web browser to become truly popular was Marc Andresen and Jamie Zawinski’s NCSA Mosaic. It was the first browser made available for Window’s, Mac and Unix X windows System with the first version appearing in MARCH 1993.
14. The cost of transmitting information has fallen dramatically. A trillion bits of information from Boston to Los Angeles from $150,000 in 1970 to 12 cents today. E-mailing a 40 page document from Chile to Kenya costs less than 10 cents, faxing it about $10, sending it by courier $50.
15. The typical Internet user worldwide is young, male and wealthy – a member of an elite minority.
16. The average total cost of using a local dialup Internet account for 20 hours a month and USD 60 a month in the US. The average African monthly salary is less than USD 60.
17. Before they can read, almost one in four children in nursery school are learning a skill that even some adults have yet to master: using the Internet, about 23per cent of children in nursery school – kids age 3,4 or 5 – have gone online.
18. at the end of the 20th century, 90 per cent of data on Africa was stored in Europe and the United States.
19. Facebook now has 24 million users who spend an average of 14 minutes on the site every time they visit. This is up from 8 minutes last September, according to Hit wise, a traffic measuring service.
20. MySpace has 67 million numbers – nearly 3 times as many as Facebook! MySpace users spend an average of 30 minutes on the site each time they visit.
21. if you want to sell your book on amazon.com you can set the price, but then they will take 55 per cent cut and leave you with only 45 per cent.
22. R Tomlinson was the first person on records to have sent an email. His email address was: <a href=”mailto:tom-linson@bbn.tenexa”>tom-linson@bbn.tenexa</a>. He had invented this software that allowed messages to be sent between computers. He is also credited with the use of the @ in email addresses.
23. Counting only domain name sites with content, Netcraft has tracked the growth of the internet since 1995 and says of the 100 million; around 48 million are active sites that are updated regularly. When it began observing sites through the domain name system in 1995, there were 18,000 web sites in existence.
24. On the internet, a ‘bastion host’ is the only host computer that a company allows to be addressed directly from the public network.
25. Around 1 per cent of the world’s 650 million corporate e-mail accounts are plugged into hardware and software that forwards incoming messages to a mobile device. And about 3.65 million of them us a Blackberry.
26. Almost half of people online have at least three e-mail accounts. In addition the average consumer has maintained the same e-mail address for four to six years.
27. Spam accounts for over 60 per cent of all email, according to Message Labs. Google says at least one third of all Gmail servers are filled with spam.
28. Yahoo started out as “Jerry and David’s guide to the world Wide Web”. Jerry Yang and David Filo were PhD candidates at Stanford in 1994 when they started the site.
29. The first Web browser was already capable of downloading and displaying movies, sounds and any file type supported by the operating system.
30. ‘Carnivore’ is the Internet surveillance system developed by the US Federal Bureau of Investigation (FBI), who developed it to monitor the electronic transmissions of criminal suspects.
31. Anthony Greco, aged 18, became the first person arrested for spam (unsolicited instant messages) on February 21, 2005.
32. A NeXT computer used by Tim Berners-Lee was the world’s first web server.
33. The first web site was built at CERN. CERN is the French acronym for European Council for Nuclear Research and is located at Geneva, Switzerland.
34. The World Wide Web is the most extensive implementation of the hypertext but it is not the only one. A computer help file is actually a hypertext document.
35. The concept of style sheets was already in place when the first browser was released.
36. Worldwide Web was programmed with Objective C.
37. Hypertext is implemented in the web as links in the browser window. Links are references to text that the user wants to access. When a link is clicked the referenced text is displayed or brought into focus.
38. The address of the world’s first web server is <a href=”http://info.cern.ch/”>http://info.cern.ch/</a> The URL of the first web page was <a href=”http://nxoc01.cern.ch/hypertext/WWW/TheProject.html”>http://nxoc01.cern.ch/hypertext/WWW/TheProject.html</a>. Although this page is not hosted anymore at CERN, a later version of the page is posted at <a href=”http://www.w3.org/History/199921103hypertext/hypertext/WWW/TheProject.html”>http://www.w3.org/History/199921103hypertext/hypertext/WWW/TheProject.html</a>.
39. In December 1991, the first institution in the US to adopt the web was the Stanford Linear Accelerator center (SLAC). True to the Berners-Lee vision, it was used to display an online catalog of SLAC’s documents.
40. Marc Andreessen started Netscape and released Netscape Navigator in 1994. during the height of its popularity, Netscape Navigator accounted for almost 90 per cent of all web use.
41. The first browser that made the web available to PC and Mac users was Mosaic. It was developed by National Center for Supercomputing (NCSA) led by Marc Andreessen in February, 1993. Mosaic was one of the first graphical web browsers and led to an explosion in web use.
42. April 30, 1993 is an important date for the Web because on that day, CERN announced that anyone may use WWW technology freely.
43. Microsoft released Internet Explorer on 1995. This event initiated the browser wars. By bundling internet explorer with the Windows operating system, by 2002, Internet Explorer became the most dominant web browser with a market share over 95 per cent.
44. It was in the Conference Dinner in May 26, 1994 where the first Best of WWW awards were given. It was by pure coincidence that the jazz band that played during the awards was called “Wolfgang and the Were Wolves”.
45. Only 4 per cent of Arab women use the Internet. Moroccan women represent almost a third of that figure.
46. As of July 2009, Microsoft Internet Explorer accounted for 67.68 per cent of all browsers used Mozilla Firefox was used by 22.47 per cent of all users.
47. The development of standards for the World Wide Web is managed by the W3C or the World Wide Web consortium. The W3C was founded in October, 1994 and headed by Tim Berners-Lee.
48. The first White House website was launched during the Clinton-Gore administration on October 21, 1994. Coincidentally, the site www.whitehouse.com linked to a pornography web site.
49. Open source technology dominates the web. The most common software used for web serving is called LAMP standing for the Linux operating system, apache web server, MySql database and PHP scripting language.
50. The “www” part of a web site (www.google.com) is optional and is not required by any web policy or standard.
51. Despite IPv4’s 4.3 billion unique addresses, it is forecasted that by 2011, the address space will be consumed. A newer scheme called IPv6 is slowly replacing IPv4 in some countries. IPv6 has the capability to address 2128 computers. to give perspective to this very big number, the world’s population of 6.5 billion people as of 2006 can be given 295 unique addresses.
52. YouTube’s bandwidth requirements to upload and view all those videos cost as much as 1 million dollars a day and drawing. The revenues generated by YouTube cannot pay for its upkeep.
53. The blue colored links on a web page is just a browser default because way back on the days when monitors only had 16 colours, blue was the darkest colour that did not affect text legibility.
54. All three letter word combinations from aaa.com to zzz.com are already registered as domain names.
55. Around 75 per cent of the music that is available for download has never been purchased and it is costing money just to be on the server.
56. One million domain names are registered every month.
57. According to AT&amp;T vice president Jim Cicconi, 8 hours of video is uploaded into YouTube every minute. This was on April 2008. On May 21, 2009, YouTube received 20 hours of video content per minute.
58. Of the 13 million music files available on the web, 52,000 tunes accounted for 80 per cent of download.
59. By 2012 it has been said that there will be 17 billion devices connected to the internet. In most of Asia, mobile phones are leading the way to internet connectivity.
60. The term Deep Web is used to refer to a wealth of information that is at least 400 to 550 times larger than the searchable Internet. This content consisting of most of the information on today’s active websites is stored in databases which are invisible to search engines. this information contains data such as prices of items, airfares and other stuff that will never surface unless somebody queries for that information. The Deep Web and all that hidden information is what prevents search engines from giving us a definitive answer to simple questions like “How much is the cheapest airfare from New York to London next Thursday?”
61. In a recent survey conducted by security specialist Symantec of the 100 most unsafe and malware infested web sites, 48 per cent of them feature adult content.
62. Naked women make up 80 per cent of all the pictures on the internet.
63. The online population of Facebook, 250 million users worldwide, and MySpace, which had 100 million accounts by 2007, are bigger than the populations of many nations worldwide. On April 2008, Facebook overtook MySpace in terms of monthly visits.
64. It took the web only 4 years to reach 50 million users. Radio took 38 years while TV made it in 13 years.
65. Amazon.com was formerly known as Cadabra.com
66. A blogger Kyle MacDonald, made history in 2006 by trading his way to glory. Starting out with a paper clip, he traded his way to increasingly costlier items and of value including a year’s rent and an afternoon with the Alice Cooper. He eventually traded a film role for a two-storey farmhouse Kipling, Saskatchewan.
67. Bit torrents, depending on location, are estimated to consume 27 to 55 per cent of all internet bandwidth as of February, 2009.
68. Domain registration was free until the National Science foundation decided to change this on September 14th, 1995.
69. It is estimated that one of every eight married couples started by meeting online.
70. Lee Stein invented the first online electronic bank in 1994 entitled, “First Virtual Holdings”.
71. The Internet is roughly 35% English with the Chinese at 14%. Yet only 13% of world’s population i.e. 812 million are Internet users as of December 2004. North America has the highest continental concentration with 70 per cent of the populace using the Internet.
72. Official statistics in the UK say that 29 per cent of women have never used the internet, but only 20 per cent of men.
73. In 1995, Bob Metcalfe coined the phrase ‘The Web might be better than sex’.
74. Iceland has the highest percentage of the Internet users at 68 per cent. The United States stands at 56%. 34% of all Malaysians us the Internet while only eight per cent of Jordanians are connected, 4% of Palestinians; 0.6% of Nigerians and 0.1% of Tajikistanis.
75. Employees at Google are encouraged to use 20 per cent of their time working on their own projects. Google News, Orkut are both examples of projects that grew from this working model.
76. Afghanistan has a combined telephone penetration of 3.4 per cent.
77. Someone is a victim of a cybercrime every 10 seconds and it is on the rise.
78. The first search engine for Gopher files was called Veronica, created by the University of Nevada System Computing Services group.
79. The Electrohippies Collective (Ehippies) is an international group of internet activists based in Oxfordshire, England, whose purpose is to express disapproval of governmental policies of mass media censorship and control of the Internet “in order to provide a ‘safe environment’ for corporations to do their deals.”
80. Luking is to read through mailing lists or news groups and get a feel of the topic before posting one’s own message.
81. The Internet was called the ‘Galactic Network’ in memos written by MIT’s JCR Licklider in 1962.
82. The first internet worm was created by Robert Morris, Jr, and attacked more than 6,000 Internet hosts.
83. SRS stands for Shared Registry Server which is the central system for all accredited registrars to access, register and control domain names.
84. The search engine Lycos is named after Lycosidae which is a Latin name for the wolf spider family.
85. It is believed that Subhash Ghai’s film Taal was the first bollywood movie to be widely promoted on the internet.
86. Rob Glasser’s company Progressive Networks launched the RealAudio system on April 10, 1995.
87. Butter Jeeves of the internet site AskJeeves.com made its debut as a large helium balloon in the Macy’s Thanksgiving Day parade in 2000.
88. In Beijing, the internet community has coined the word ‘Chortal’ as a shortened version of ‘Chinese’ Portal.
89. Satyam Online became the first private ISP in December 1998 to offer internet connection in India.
90. In 1946, the Merriam Webster defined a computer as a person who tabulates numbers, accountant, actuary, book keeper.
91. In 1969, advanced Research Projects Agency (ARPA) went online connecting four major US universities. The idea was to have a backup in case a military attack destroyed conventional communication system.
92. The first ever ISP was CompuServe which still exists under AOL, Timer Warner.
93. Jeff Bezos while starting his business could not name his website Cadabra due to copyright issues. He later named it amazon.com.
94. The longest phone cable is a submarine cable called FLAG (Fiber-Optic Link Around the Globe). It spans 16,800 miles from Japan to the United Kingdom and can carry 600,000 calls at a time.
95. The first coin operated machine ever designed was a holy-water dispenser that required a five-drachma piece to operate. It was the brainchild of the Greek scientist Hero in first century A.D.
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