PDH/SDH - Plesiochronous Digital Hierarchy/Synchronous Digital Hierarchy:

The Plesiochronous Digital Hierarchy or PDH is the technology in telecommunication networks for the transport of big data quantities through digital transport means like optical fibers and microwave radio systems. The term Plesiochronous derives from the Greek words plesio, meaning nearby, and from chromos, meaning time; referring to the fact that the different parts from PDH networks, even if working on the same nominal frequency, in reality are not synchronic between themselves. This terminology has been introduced following the conception and the development of synchronous transmission technologies (SDH and SONET).

The PDH technology allows the transmission of data with the same nominal rate but in reality the rate is slightly different. One of the most important features of the PDH systems is the bit interleaving multiplexing based on time division: the multiplexed stream is formed taking the bits from each contribution in sequence, organizing them in the relative time slot of the resulting stream. This operation is effectuated by an equipment called multiplexer. In a plesichronous system it is necessary to build in a compensation system due to the fact that each bit contribution has its own effective rate, similar but independent from the others. In transmission phase the multiplexer thus inserts additional slots to compensate the early or late arrival of the bits compared to the nominal multiplexing frequency, in order to allow the decoding in the receiving phase. These slots are called justification or stuffing bits.

The Synchronous Digital Hierarchy, or SDH, is a protocol used for telephone and data transmission in geographical networks through optical fibers o electrical cable.

The task of SDH is to aggregate data streams into different bit rates and retransmit them all together on long distances. Different as for the PDH, the SDH protocol is based on the fact that all elements of the network are synchronized between themselves with the same clock. Together with this, the definition of a particular structure, adding overhead service information, allows not only the extraction of each original bit contribution without having to effectuate the entire de-multiplexation of the complete stream, but it allows also the transferring of important information regarding the correct network management and signaling of failures and/or anomalous conditions or deterioration.

To maintain the compatibility with existing structures on the territory, next to broadcast applications for the transport of A/V signals, Elber diversifies its proper product range with radio link solutions of the telecom type. In this way the digital Elber modem, and consequently the radio link, is equipped with the most common interfaces belonging to the PDH/SDH hierarchies, i.e.:

Particularly the E3 interface can be suitable for the Ethernet stream transport at 34 Mbps. The goal is to realize extensive LAN networks on long distances using radio links as alternative or back-up for fiber (especially there where not available).

In this context the highly configurable and customized Digital Modem DDM310, is fundamental.

The data interface I/O E3 (34.368 Mb/s) is internally processed and digitally modulated/demodulated on the intermediate frequency of 70 MHz.

The Slim Line series realizes the IF-RF frequency conversions, and vice versa, in the 2 ÷ 15 GHz range.

The Slim Line transmitter (T-SL) and receiver (R-SL) have a compact design (rack 1U standard 19") not compromising though the performances of the equipment.

The outstanding characteristics are the low delay (less than 10 ns), the excellent noise figure of the receiver (less than 5dB) and the double IF signal frequency conversion, allowing up to 500 MHz of agility.