Computer Network Unit 1 q what are the topologies in computer n/w ?

Q15. Gine comparison between SONET and SDH.
Ans:

SDH/SONET technology is the main manner of information transport. With the increasingly mature related technologies, the combination of data and optical networks become closer. At the same time, the tremendous success and rise of data traffic have put the focus on the protocols and framing technologies for mapping data over SDH/SONET in fiber optical networks. A first attempt at a more efficient high-speed WAN protocol is packet over SDH/SONET, in which IP data packets are conveyed through using the link-layer point-to-point protocol and being encapsulated into byte-stuffed HDLC-like frames. LAPS also using byte-stuffed HDLC offers a simple method of providing Ethernet LAN extension over a public WAN. A generic framing procedure provides an efficient and protocol-agnostic frame delineation and encapsulation mechanism for transporting a variety of protocols over SDH/SONET tributaries. Protocol signals may be PDU-oriented, block-coded, or a constant bit stream. In this paper, we review several emerging technologies for the transport of packet services, and compare these framing technologies known as POS, LAPS and GFP. Finally we present several applications of these technologies.
Difference ;

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  Together they are a set of global standards that interface equipment from different vendors. SDH is basically the international version of SONET, and SONET can be thought of as the North American version of SDH.
  
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  There are some slight differences between SONET and SDH.
  
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  The main differences are in the basic SDH and SONET frame formats, but SDH and SONET are essentially identical beyond the STS-3 signal level. The base signal for SONET is STS-1 and the base signal for SDH is STM-1. STS-3c is equivalent to STM-1 and the lower tributaries can be mapped interchangeably between the two formats from that point on.
  
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  In SDH, both electrical and optical signals are referred to as STM signals.
  
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  In SONET, however, electrical signals are called STS and optical signals are referred to as OC.