•Plesiochronous Digital Hierarchy (PDH) is the original standard for telephone network, now abandoned in favor of SONET/SDH • Exploits Time Division Multiplexing
• Designed to support digital voice channels at 64kb/s
•No store and forward: imposes strict synchronization between TX and RX. A "plesio-synchronous" (almost synchronous) solution is adopted
• Different standards in US/Europe/Japan
SONET:
•Synchronous optical networking is a method for communicating digital information using lasers or light emitting diodes (LEDs) over optical fiber.
•SONET was introduced to handle large amount of telephone calls and interoperability between equipments of different vendors.
•Synchronous networking differs from PDH in that exact rates that are used to transport the data are highly synchronized across the entire network, made possible by atomic clocks.
The SDH is an international standard that is highly popular and used for its high speed data transfer of the telecommunication and digital signals. This synchronous system has been specially designed in order to provide a simple and flexible network infrastructure. This system has brought a considerable amount of change in the telecommunication networks that were based on the optical fibers as far as performance and cost were concerned.
The weaknesses that PDH faced paved way for the introduction and use of the SDH systems. Although the PDH proved to be a breakthrough in the field of digital transmission, the weaknesses that made it less demanded includes:
But if we compare the PDH system with that of the SDH system, the latter one has a large number of advantages. Some of the most common advantages enjoyed by the usage of SDH include:
Synchronous optical network (SONET)
A Well-defined infrastructure.
advantage 1. Effective in Recognition and correction of errors.
reduced fraud
The Tea Act.
Pyruvate dehydrogenase (PDH) are regulated by pyruvate dehydrogenase kinase (PDH-K) and PDH phosphatase. PDH-K effect on PDH is that it will inactivate PDH and PDH phosphatase will reactivate PDH. PDH-K is regulated by energy surpluses (ATP, NADH) and energy deficits (ADP, NAD). So when there is an energy surplus, PDH-K will inhibit PDH, and vice versa. PDH phosphatase will activate PDH and is upregulated by magnesium and calcium.
1)Small equipment . 2)less cost 3)point to point communications.
The PDH interface standard is not uniform,there is 1.5Mbps and 2Mbps. The PDH system have not strong management function.
A SONET is a type of network technology layer that is physical. It is used for transporting a lot of traffic over fiber optic cabling.
- Bit justification is needed in PDH - No would standards available at optical interface in PDH - line rates are not standard - Interfacing problem at multivendor equipment - PDH supports 16E1s and SDH supports 63E1s
PDH stands for Plesiochronous Digital Hierarchy. It is a technology that is used in telecommunications networks to send large quantities of data over digital transport equipment, like fiber optic and microwave radio systems.
Sonet Film was created in 1984.
Ishraq Sonet was born in 1987.
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SDH = 3 times of SONET
SONET (Synchronous Optical Network) is a physical layer network technology designed to carry large volumes of traffic over relatively long distances on fiber optic cabling.
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