SONET（Synchronous Fiber Optical Network）
Introduction to SONET
A digital transmission standard first introduced by the United States in 1988. The clocks of the entire synchronous network come from a very accurate master clock (using an expensive cesium atomic clock with an accuracy better than plus or minus 10 to the power of -11).
The SONET fiber transmission system defines a line rate level structure for synchronous transmission. The transmission rate is based on 51.84 Mb/s, which corresponds to the transmission rate of T3/E3. This rate is called the first level synchronous transmission signal, ie STS. -1; The optical signal becomes the first-order optical carrier (OC), that is, OC-1. Standards from OC-1 - 51.84 Mb/s up to OC-3072 - about 160 Gbit/s have been defined. Usually expressed as OC-n.
We sometimes see in the literature that "the POS port transmission rate supports STM-1/OC-3 (155.52 Mbit/s)...". For STM (Synchronous Transmission Module, applied to SDH: Synchronous Digital Hierarchy, Synchronous Digital Series), there are different levels of synchronous transmission modules, and STM-1 is the first level synchronization module, which corresponds to the basic rate of STM. 155.52Mb/s. OC-3 is the third-order optical carrier rate of SONET, 51.83*3=155.49Mb/s. Therefore, the rates of STM-1 and SONET OC-3 are considered to be comparable, and appear earlier.
It is the standard for connecting fiber-optic transmission systems and was developed by the American National Standards Institute in the mid-1980s. It is a global physical network, much like an Ethernet twisted pair cable in a LAN. SONET can send data at speeds above 1 Gbps and can send data, voice and images.
Currently Defined Standard
OC: Optical Carrier Optical Carrier
Optical carrier (OC) is a set of signal bandwidths in a SONET fiber network with many defined levels. It is usually expressed as OC-n, where n is a multiple factor indicating how many times the base rate is 51.84 Mbit/s. The currently defined standards are:
OC-1 — 51.8 4Mbit/s
OC-3 — 155.52 Mbit/s
OC-12 — 622.08 Mbit/s
OC-24 — 1.244 Gbit/s
OC-48 — 2.488 Gbit/s
OC-96 — 4.976 Gbit/s
OC-192 — 9.953 Gbit/s
OC-256 — about 13 Gbit/s
OC-384 — about 20 Gbit/s
OC-768 — about 40 Gbit/s
OC-1536 — about 80 Gbit/s
OC-3072 — about 160 Gbit/s
The SONET standard defines four optical interface layers, as shown in the figure.
Although this is conceptually a bit like the OSI reference model, SONET itself only corresponds to the physical layer of OSI. The level of SONET is from top to bottom:
The Photonic Layer handles bit transfer across the fiber optic cable and is responsible for the conversion between the electrical signal of the synchronous transmission signal STS and the optical signal of the optical carrier OC. At this layer, the electro-optical converter communicates.
The Section Layer transmits STS-N frames over the fiber optic cable with framing and error detection.
The above two layers are necessary, but the following two layers are available.
The Line Layer is responsible for the synchronization and multiplexing of the path layer and the automatic protection of the exchange.
The Path Layer handles the transmission of traffic between Path Terminating Elements (PTEs), where the PET is a SONET capable switch. The path layer also has an interface to a non-SONET network.
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