Optical transmission technique


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Optical transmission technique

  2. 2. What is SONET1.Introduction to SONET Synchronous optical network (SONET) is a standard for optical telecommunications transport. The comprehensive SONET/synchronous digital hierarchy (SDH) standard is expected to provide the transport infrastructure for worldwide telecommunications for at least the next two or three decades. The increased configuration flexibility and bandwidth availability of SONET provides significant advantages over the older telecommunications system.
  3. 3. Background Before SONET, the first generations of fiber-optic systems inthe public telephone network used proprietary architectures,equipment, line codes, multiplexing formats, and maintenanceprocedures.The users of this equipment regional Bell operating companiesand interexchange carriers (IXCs) in the United States,Canada, Korea, Taiwan, and Hong Kong standards so thatthey could mix and match equipment from different suppliers.The task of creating such a standard was taken up in 1984 bythe ECSA (Exchange Carriers Standards Association) to establish astandard for connecting one fiber system to another. Thisstandard is called SONET.
  4. 4. SONET Network Elements
  5. 5. • Regenerator A regenerator is needed when, due to the long distance between multiplexers, the signal level in the fiber becomes too low.• Add/Drop Multiplexer (ADM) A single-stage multiplexer/demultiplexer can multiplex various inputs into an OC signal. At an add/drop site, only those signals that need to be accessed are dropped or inserted. The remaining traffic continues through the network element without requiring special pass-through units or other signal processing.
  6. 6. Synchronous & Asynchronous Communication1. Synchronous Transformations A synchronous transformation processes incoming rows and passes them on in the data flow one row at a time. Output is synchronous with input, meaning that it occurs at the same time. Therefore, to process a given row, the transformation does not need information about other rows in the data set. In the actual implementation, rows are grouped into buffers as they pass from one component to the next, but these buffers are transparent to the user, and you can assume that each row is processed separately.
  7. 7. Synchronous & Asynchronous CommunicationAsynchronous transmission Primarily when the data to be transmitted is generated at random intervals – the user keys in each character at an indeterminate rate – with possibly long random time intervals between each successive typed character Start bit and one or more stop bits – each transmitted character or byte is encapsulatedSONET In a synchronous system such as SONET, the average frequency of all clocks in the system will be the same (synchronous) or nearly the same (Every clock can be traced back to a highly stable reference supply.
  8. 8. What Are the Benefits of SONET?• Reduction in equipment requirements and an increase in network reliability• Definition of a synchronous multiplexing format for carrying lower level digital signals and a synchronous structure that greatly simplifies the interface to digital switches, digital cross-connect switches, and add-drop multiplexers
  9. 9. What Are the Benefits of SONET?• Availability of a set of generic standards that enable products from different vendors to be connected• Definition of a flexible architecture capable of accommodating future applications, with a variety of transmission rates
  10. 10. Wavelength-division multiplexing• In fiber-optic communications, wavelength-divisionmultiplexing (WDM) is a technology which multiplexesmultiple optical carrier signals on a single optical fiber byusing different wavelengths (colours) of laser light to carrydifferent signals.•This allows for a multiplication in capacity, in addition toenabling bidirectional communications over one strand offiber.•This is a form of frequency division multiplexing (FDM)but is commonly called wavelength division multiplexing.
  11. 11. How the Technology Works• The highway principle and the ~25 THz optical fiber .transmitting several different independent wavelengths simultaneously.
  12. 12. Basic Concept1. laser must emit light at a different wavelength.2. all the lasers light multiplexed together onto a single optical fiber.
  13. 13. Basic Concept3. Transmitted through a high-bandwidth optical fiber .
  14. 14. Basic Concept4. Signals must be demultiplexed at the receiving end( by distributing the total optical power to each output port and then requiring that each receiver selectively recover only one wavelength by using a tunable optical filter