Synchronous Optical Networking Introduction

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Synchronous Optical Networking is usually called SONET for short. The SONET standards were coded in the mid-1980s to consider benefit of low-cost fiber optic transmission. It defines a hierarchy of data rates, formats for framing and multiplexing the payload data, as well as optical signal specifications (wavelength and dispersion), allowing multi-vendor interoperability.

SONET may also be referred to as “T-1 on steroids”. Can you explain that? As you may know, the digital hierarchy (DS-0, DS-1, DS-2, DS-3 and much more) was created to provide cost-effective multiplexed transport for voice and data traffic from one location inside a network to a separate.

SONET and SDH (Synchronous Digital Hierarchy) are two equivalent multiplexing protocols for transferring multiple digital bit streams using lasers or LEDs (light-emitting diodes) over the same optical fiber. They were made to replace PDH (Plesiochronous Digital Hierarchy) system to get rid of the synchronization issues that PDH Multiplexer had. SONET is synchronous, which means that each connection achieves a continuing bit rate and delay. For example, SDH or SONET might be utilized to allow several Internet Service Providers to talk about exactly the same optical fiber, without being affected by each others traffic load, and without having to be able to temporarily borrow released capacity from one another. SONET and SDH are considered to become physical layer protocols since they offer permanent connections and do not involve packet mode communication. Only certain integer multiples of 64kbits/s are possible bit rates.

SONET is really TDM(time division multiplexing) based and this causes it to be readily supported fixed-rate services such as telephony. Its synchronous nature is designed to accept traffic at fixed multiples of the basic rate (64kbit/s), without requiring variable stuff bits or complex rate adaptation.

The SONET data transmission format is based on a 125us frame composed of 810 octets, of which 36 are overhead and 774 are payload data. The fundamental SONET signal, whose electrical and optical versions are referred to as STS-1 and OC-1, respectively, is thus a 51.84Mb/s data streams that readily accommodate TDM channels in multiples of 8 kb/s.

It is important in fiber optic network that SONET can be used to encapsulate PDH and other earlier digital transmission standards. It is also used directly to support either an ATM (Asynchronous Transfer Mode) or packet over SONET/SDH (POS) networking. So SONET/SDH is actually a generic all-purpose transport container for moving both voice and knowledge traffic. They in themselves aren’t communications protocols.

SONET brings by using it a subset of benefits that make it differentiate themselves from competitive technologies. These include mid-span meet, improved operations, administration, maintenance, and provisioning (OAM&P), support for multipoint circuit configurations, non-intrusive facility monitoring, and the capability to deploy a variety of new releases.

Improved OAM&P is among the greatest contributions that SONET brings to the networking field. Element and network monitoring, management, and maintenance has always been something of the catch-as-catch-can effort due to the complexity and diversity of elements inside a typical service provider’s network. SONET overhead includes error-checking ability, bytes for network survivability, and a diverse set of clearly defined management messages.

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