ASSIGNMENT COMPUTER NETWORKSSubmitted To: - Submitted By: -Mr. Yogesh Soumya Subhadarshi BeheraCSE Lecturer 1826 B.Tech 6th Sem
Synchronous optical networking/Synchronous Digital HierarchySynchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH) arestandardized multiplexing protocols that transfer multiple digital bit streams over opticalfiber using lasers or highly coherent light from light-emitting diodes (LEDs). At low transmission ratesdata can also be transferred via an electrical interface. The method was developed to replacethe Plesiochronous Digital Hierarchy (PDH) system for transporting large amounts of telephone callsand data traffic over the same fiber without synchronization problems.SONET and SDH, which are essentially the same, were originally designed to transport circuit modecommunications (e.g., DS1, DS3) from a variety of different sources, but they were primarily designedto support real-time, uncompressed, circuit-switched voice encoded in PCM format. The primarydifficulty in doing this prior to SONET/SDH was that the synchronization sources of these variouscircuits were different. This meant that each circuit was actually operating at a slightly different rateand with different phase. SONET/SDH allowed for the simultaneous transport of many differentcircuits of differing origin within a single framing protocol. SONET/SDH is not itself a communicationsprotocol per se, but a transport protocol.Due to SONET/SDHs essential protocol neutrality and transport-oriented features, SONET/SDH wasthe obvious choice for transporting the fixed length Asynchronous Transfer Mode (ATM) frames alsoknown as cells. It quickly evolved mapping structures and concatenated payload containers totransport ATM connections. In other words, for ATM (and eventually other protocols such asEthernet), the internal complex structure previously used to transport circuit-oriented connections wasremoved and replaced with a large and concatenated frame (such as OC-3c) into which ATM cells, IPpackets, or Ethernet frames are placed.The SDH standard was originally defined by the European Telecommunications Standards Institute(ETSI), and is formalized as International Telecommunication Union (ITU) standards G.707,G.783, G.784, and G.803. The SONET standard was defined by Telcordia and AmericanNational Standards Institute (ANSI) standard T1.105.FEATURES OF SONET/SDH :-High transmission ratesTransmission rates of up to 40 Gb/s can be achieved in modern SONET systems making it the mostsuitable technology for backbones - the superhighways in todays telecommunications networks.Simplified add and drop functionCompared to the older DSn system, low bit rate channels can be easily extracted from and insertedinto the high-speed bit streams in SONET. It is now no longer necessary to apply the complex andcostly procedure of demultiplexing then remultiplexing the plesiochronous structure.
High availability and capacity matchingWith SONET, network providers can react quickly and easily to the requirements of their customers.For example, leased lines can be switched in a matter of minutes. The network provider can usestandardized network elements (NE) that can be controlled and monitored from a central location viaa telecommunications management network (TMN) system.ReliabilityModern SONET networks include various automatic back-up circuit and repair mechanisms which aredesigned to cope with system faults and are monitored by management. As a result, failure of a linkor an NE does not lead to failure of the entire network.Future-proof platform for new servicesSONET is the ideal platform for a wide range of services including POTS, ISDN, mobile radio, anddata communications (LAN, WAN, etc.). It is also able to handle more recent services such as videoon demand and digital video broadcasting via ATM.InterconnectionSONET makes it much easier to set up gateways between different network providers and to SDHsystems. The SONET interfaces are globally standardized, making it possible to combine NEs fromdifferent manufacturers into a single network thus reducing equipment costs. The trend in transportnetworks is toward ever-higher bit rates, such as OC768 (time division multiplex, TDM). The currenthigh costs of such NEs however are a restricting factor. The alternative lies in dense wavelengthdivision multiplexing (DWDM), a technology enabling the multiple use of single-mode optical fibers.As a result, a number of wavelengths can be used as carriers for the digital signals and transmittedsimultaneously through the fibers.Main goals of SONET/SDH: Fault tolerance of telecom providers requirement (99.999% - five nines - availability) Interoperability among different manufacturers Flexibility of upper layer formats to adapt to different source (not only voice) Complex monitoring capabilities of performance and of traffic (50 ms of recovery time)
Layering Model of SONETPath layer (close to OSI layer 3 - Network) Manages end-to-end connection Monitoring and management of user connectionLine Layer Multiplexing of several path-layer connection among nodes Protection and Fault ManagementSection Layer Define regenerator functions SONETs Line and Section layers are almost equivalent to 2 (Data Link) OSI layer
Photonic Layer (same as OSI layer 1) Defines all the transmission requirements of signals.The differences between SDH and SONETSDH stands for synchronous digital hierarchy. SDH is the synchronous technology usedeverywhere except the US, Canada and Japan. Development of this internationalcounterpart to SONET began a few years after SONET.The differences between SONET and SDH are based primarily on the differentsynchronous bit rates that must be mapped into them. In developing these twotechnologies, there was a need to integrate existing transmission techniques in order toenable network operators to gradually introduce SONET and SDH.Because the highest-order commonly used multiplex signal in N.A. is 45 Mb/s,51 Mb/swas a sufficient synchronous primary rate for virtually any SONET application. Howeverin the rest of the world, where 140 Mb/s mux signals are very common, 155 Mb/s (STM-1) was chosen as the primary synchronous mux rate. This bit rate is exactly the sameas the STS-3 or OC-3 bit rate.