A sample text widget

Etiam pulvinar consectetur dolor sed malesuada. Ut convallis euismod dolor nec pretium. Nunc ut tristique massa.

Nam sodales mi vitae dolor ullamcorper et vulputate enim accumsan. Morbi orci magna, tincidunt vitae molestie nec, molestie at mi. Nulla nulla lorem, suscipit in posuere in, interdum non magna.

Explain SONET/SDH – a communication protocol?

Today we have two standardized protocols to govern the transfer of a number of digital bit streams namely:
1. SONET or synchronous optical networking
2. SDH or synchronous digital hierarchy

– The bit stream is transferred over the optical fibers using either light emitting diodes (LEDs) or lasers i.e., the sources that emit highly coherent light.
– However, an electrical interface can also serve as a transmission medium at low level of the transmission rates.
– This method eventually replaced the PDH (plesiochronous digital hierarchy) system that was once used for the transmission of large amounts of data traffic and phone calls over a single fiber avoiding the problems with synchronization.
– SONET and SDH are actually the same and have been designed for circuit mode communications.
– However, their primary purpose is to support the uncompressed and real time circuit – switched voice.
– Earlier when the SONET/ SDH did not exist, the main problem was posed by the different synchronization sources of the various circuits; also this was the reason why the rate of operation as well as the phase of operation of every circuit was different.
– This problem was easily overcome using SONET/ SDH since it made possible to simultaneously transport the different circuits having different synchronization sources lying in the same framing protocol.
– Thus SONET/SDH is not just a communication protocol but also a transport protocol.
– Due to its two essential qualities it became the much favored option for the transport of fixed length cells:
1. Transport – oriented features and
2. Protocol neutrality
– These cells are nothing but the ATM (asynchronous transfer mode) frames.
– It saw quick evolution of the concatenated payload containers and mapping structures to make ATM connection transportation possible.
– SONET/ SDH are used all over the world.
– While SDH has found its use all over the world, SONET is confined to United States and Canada.
– Even though the SONET came in to existence before SDH, still SONET is considered to be a varied form of SDH.
– This is so because the SDH has got a great share of the world market.
– ETSI or the European telecommunications standards institute holds the credit for initially defining the SDH standard known as the ITU (international telecommunication union) standards.
– However ANSI (American national standards institute) and Telecordia together defined the SONET standards.
– The same functions are defined using different terms in SONET and SDH.
– This sometimes causes confusion and exaggerates the differences between them.
– So after setting out few exceptions, SONET began to be considered as a subset of SDH.
– SONET consists of a number of transport containers for delivering a number of things such as:
1. Variety of protocols
2. Telephony
3. Ethernet
4. ATM
5. TCP/ IP traffic

– SONET is not ideally connection – oriented and so is not a native communications protocol.
– However, the HTTP traffic void of connection is indeed transported within its frames.
– Both these protocols by structure are heavy in nature.
– The way in which the header is interleaved between data is quite complex but this only provides a unique data rate to data and ability to float around relative to the frame structure as well as rate.
– However, this causes the protocol to have very low latency.
– Data passing may experience a delay of 32 microseconds.
– Protocol standards allow for extra padding at various stages of the structure.
– Even though this increases the complexity further, it is still recommended since it improves the overall performance.
– Basic unit of transmission for both the protocols are as follows:
1. For SDH it is Synchronous transport module, level 1 (STM – 1). Operating speed is 155.520 MBPS.
2. For SONET the same unit is referred to as OC – 3c (if the signal is carried optically) or STS – 3c (if the signal is carried electronically.). Operating speed is same as that of the SDH.

Leave a Reply

You can use these HTML tags

<a href="" title=""> <abbr title=""> <acronym title=""> <b> <blockquote cite=""> <cite> <code> <del datetime=""> <em> <i> <q cite=""> <s> <strike> <strong>