VHDL Simulation of Tu-11/Tu-12 in Synchronous Digital Hierarchy

One of important transmission technologies in the broadband ISDN is the synchronous transmission technology based on SDH, a key concept of SONET/SDH is the pointer-based access to the encapsulated payloads in the SONET/SDH signal. The Synchronous Digital Hierarchy (SDH) and the Synchronous Optical NETwork (SONET) are hierarchies used in Europe/South-America and North-America/Japan, respectively. Both systems employ synchronous time division multiplexing techniques to transmit different tributaries (EI, Ethernet, ATM, etc) through the same physical channel. A primary goal in the development of the SDH/SONET formats is to define a synchronous optical hierarchy with sufficient flexibility to carry payloads of different types. SONET and SDH are based on transmission at rates that are integer multiples of 51.840 Mbps. SONET basic frame structure is called synchronous transport signal level one (STS-l). SDH basic modular signal is called synchronous transport module level one (STM-I). The STM-I rate is an extension of the basic STS-I (for this reason also called STM-O) and operates at 155.52 Mbps, carrying three interleaved STS-l frames.