plesiochronous การใช้

• Some systems may be only approximately synchronized, or plesiochronous.
• Three major types of timing are used on networks : synchronous, and plesiochronous.
• Plesiochronous digital hierarchy ( PDH ) was developed as a standard for multiplexing higher order frames.
• The most common example of a plesiochronous system design is the plesiochronous digital hierarchy networking standard.
• The most common example of a plesiochronous system design is the plesiochronous digital hierarchy networking standard.
• The asynchronous serial communication protocol is asynchronous on the byte level, but plesiochronous on the bit level.
• The signals thus formed are almost synchronous, except for differences within the permitted margins of tolerance, and for this reason they are called plesiochronous.
• The target was to supply the requested availability for the whole block ( Plesiochronous digital hierarchy, PDH, or Synchronous Digital Hierarchy, SDH ).
• Although originally deployed systems ( 1990s ) used plesiochronous digital hierarchy ( PDH ) links such as E1 / T1 links, more recent systems use Ethernet cabling.
• Based on the E1 signal, the ITU defined a hierarchy of plesiochronous signals that enables signals to be transported at rates of up to 140 Mbit / s.
• This allows the receiving multiplexer to correctly reconstruct the original data for each of the four 2 Mbit / s data streams, and at the correct, different, plesiochronous rates.
• A few years before a new standard for optical transmission systems called Synchronous Digital Hierarchy ( SDH ) had been developed and ratified as a global standard as a replacement for existing Plesiochronous Digital Hierarchy ( PDH ) equipment.
• In general, plesiochronous systems behave similarly to synchronous systems, except they must employ some means in order to cope with " sync slips ", which will happen at intervals due to the plesiochronous nature of the system.
• In general, plesiochronous systems behave similarly to synchronous systems, except they must employ some means in order to cope with " sync slips ", which will happen at intervals due to the plesiochronous nature of the system.
• The "'plesiochronous digital hierarchy "'( "'PDH "') is a technology used in telecommunications networks to transport large quantities of data over digital transport equipment such as fibre optic and microwave radio systems.
• In previous sections we have looked at an example in which a 140 Mbit / s signal was mapped into a VC-4, but the multiplexing map lets the STM-1 signal transport other types of Plesiochronous signals and even combinations of signals.
• Then the receiver samples at predefined intervals to determine the values of the bits in the byte; this is plesiochronous since it depends on the transmitter to transmit at roughly the same rate the receiver expects, without coordination of the rate while the bits are being transmitted.
• The term " plesiochronous " is derived from Greek " pl
  sios ", meaning near, and " chronos ", time, and refers to the fact that PDH networks run in a state where different parts of the network are nearly, but not quite perfectly, synchronized.
• As is the case with level 1 of the plesiochronous digital hierarchy ( 2 Mbit / s ), the higher levels of multiplexing are carried out bit by bit ( unlike the multiplexing of 64 kbit / s channels in a 2 Mbit / s signal, which is byte by byte ), thus making it impossible to identify the lower level frames inside a higher level frame.
• At the time of the design of ATM, 155 Mbit / s Synchronous Digital Hierarchy ( SDH ) with 135 Mbit / s payload was considered a fast optical network link, and many plesiochronous digital hierarchy ( PDH ) links in the digital network were considerably slower, ranging from 1.544 to 45 Mbit / s in the USA, and 2 to 34 Mbit / s in Europe.