Notes on data communication and network-wide area network SONET/SDH

Notes on data communication and network-wide area network SONET/SDH
The high bandwidth of optical fiber is suitable for carrying large amounts of data at the same time in today's high data rates and low rates. For this reason, optical fiber and the need for data rate or high-bandwidth transmission technology to develop together, and then there is a need for standardization, so the US organization (ANSI) and the European organization (ITU-T) the corresponding standards are defined. Although the two standards are independent, the basic functions are intended and eventually compatible. ANSI standard is synchronous optical network, SONET, ITU-T standard is synchronous digital hierarchy, SDH)
SONET and SDH are synchronous networks that use synchronous TDM multiplexing. They are both in the OSI physical layer.

Signal
SONET defines a level system called synchronous transport signal (STS) for synchronous transmission signals. Each STS level (STS-1 to STS-192) supports a specific data rate. The corresponding optical signals are called optical carriers (optical carrier, OC). SDH also specifies a similar system, called a synchronous transmission block (sychronous transport module, STM ), STM is used for compatibility with existing European systems and STS levels.


In the figure, the rate of the STS-3 is exactly three times that of the STS-1, the rate of the STS-9 is exactly half of the STS-18, which means that 18 STS-1 channels can be reused into a STS-18 channel, 6 STS-3 channels can be reused into a STS-18 channel, and so on.
SONET Device
Is a simple link using SONET.


Sts mux: STS multiplexing, which combines signals from multiple electronic sources and generates corresponding OC signals.
Sts demux: an STS splitter that splits the optical OC signal into corresponding electronic signals.
R: regenerators, which convert the optical signal (OC-n) into the corresponding electrical signal (STS-n), generate the electrical signal, and finally convert the electrical signal into the corresponding OC-n signal.
ADM: a plug-in Multiplexing that adds STS from multiple sources to a given path or redirects the desired signal from a specific path without the need to break down the entire signal.
T: The device that uses the SONET network service. The terminal can be a vro.

Connection
Segment: connects the optical links of two adjacent devices.
Line: The network section between two musters (STS musters to plug-in musters, two plug-in musters or two STS musters.
Path: the end-to-end network between two STS multiplexing. SONET Layer
The SONET standard consists of four functional layers: photon layer, segment layer, line layer, and path layer.
The relationship between devices and layers is as follows:
SONET Frame
Each synchronous transmission signal, STS-n, consists of 8000 frames, each frame is a two-dimensional matrix of 90 * n columns and 9 rows. Each STS-n signal is transmitted at a fixed rate of 8000 frames per second. For each frame, bytes are transmitted from left to right, from top to bottom.

STS frame format
Is the frame format of the STS-1:

STS multiplexing
In the normal working mode of SONET, the STS-n signal is composed of n multiplexing STS-1 signals, sometimes we have a signal higher than the STS-1 data rate, in this case, SONET allows the generation of an STS-n signal, which is not considered to be n STS-1 signals, he is an STS-n signal that cannot be broken down into STS-1 signals, to illustrate this, the suffix c is added after the signal name, for example, STS-3c is a signal that cannot be decomposed into three STS-1 signals. (In an ATM network, the SPE of A STS-3c signal can be the bearer of an ATM Cell)