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Abstract
This paper explains about SONET –Synchronous Digital Network, that has been greeted with unparalleled enthusiasm throughout the world. It also explains how it came into existence and in which way it differs from others. What does synchronous mean?” Bits from one telephone call are always in the same location inside a digital transmission frame”.
This material is assumed to be comfortable to the reader as the basic concepts of a public telecommunications network, with its separate functions of transmission and switching, and is assumed to be aware of the context for the growth of broadband traffic.
In the early 1970’s digital transmission systems began to appear, utilizing a method known as Pulse Code Modulation (PCM), first proposed by STC in 1937. As demand for voice telephony increased, and levels of traffic in the network grew ever higher, it became clear that standard 2 Mbit/s signal was not sufficient. To cope with the traffic loads occurring in the trunk network. As the need arose, further levels multiplexing were added to the standard at much higher speed and thus SONET came into existence. For the first time in telecommunications history there will be a worldwide, uniform and seamless transmission standard for service delivery. SONET provides the capability to send data at multi-gigabit rate over today’s single-mode fiber-optic links
As end-users become ever more dependent on effective communications, there has been an explosion in the demand for sophisticated telecom services. Services such as videoconferencing remote database access, and multimedia file transfer require a flexible network with the availability of virtually unlimited bandwidth. The complexity of the network, means that network operators are unable to meet this demand. At present SONET is being implemented for long-haul traffic, but there is no reason it cannot be used for short distances.
SYNCHRONOUS OPTICAL NETWORK (SONET)
Definition:
Synchronous optical network (SONET) is a standard for optical telecommunications transport formulated by the Exchange Carriers Standards Association (ECSA) for the American National Standards Institute (ANSI), which sets industry standards in the U.S. for telecommunications and other industries. The comprehensive SONET standard is expected to provide the transport infrastructure for worldwide telecommunications for at least the next two or three decades.
Introduction to SONET:
Synchronous optical network (SONET) is a standard for optical telecommunications transport. It was formulated by the ECSA for ANSI, which sets industry standards in the United States for telecommunications and other industries. 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. These advantages include the following:
• Reduction in equipment requirements and an increase in network reliability.
• Provision of overhead and payload bytes-the overhead bytes permit management of the payload bytes on an individual basis and facilitate centralized fault sectionalization
• Definition of a synchronous multiplexing format for carrying lower level digital signals (such as DS-1,DS-3) and a synchronous structure that greatly simplifies the interface to digital switches, digital cross-connect switches, and add-drop multiplexers
• 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
In brief, SONET defines optical carrier (OC) levels and electrically equivalent synchronous transport signals (STSs) for the fiber-optic-based transmission hierarchy.
SONET Layers
SONET has four optical interface layers. They are:
• Path Layer,
• Line Layer,
• Section Layer,
• Photonic Layer.
Path Layer : The Path Layer deals with the transport of services between the PTE. The main function of the Path Layer is to map the signals into a format required by the line layer . Its main functions are :
• Reads ,
• Interprets ,
• Modifies the path overhead for the performance and automatic protection switching.
Line Layer : The line layer deals with the transport of the path layer payload and its overhead across the physical medium. The main function of the line layer is to provide synchronization and to perform multiplexing for the path layer . Its main functions are :
• Protecting Switching ,
• Synchronization ,
• Multiplexing ,
• Line maintenance ,
• Error Monitoring .
Section Layer : The section layer deals with the transport of an STS-N frame across the physical medium. Its main functions are :
• Framing ,
• Scrambling ,
• Error Monitoring ,
• Section Maintenance.
Photonic Layer : The Photonic layers mainly deals with the transport of bits across the physical medium. Its main functions are :
• Wavelength ,
• Pulse Shape ,
• Power Levels.