SONET vs SDH
SONET/SDH is the dominant technology deployed in most metro and long distance networks. It refers to a group of fiber optic transmission rates that can transport digital signals with different capacities. The differences between SONET and SDH are below:
1. SONET is developed by ANSI (American National Standards Institute) and is primarily utilized in the United States. SDH was created by ITU-T (International Telecommunication Union - Telecommunication Standardization Sector) and is utilized worldwide.
2. The basic unit of SDH is synchronous transmission module level-1 (STM-1). The basic unit of SONET is Optical Carrier level-1 (OC-1).
3. SONET has 27 bytes of total transport overheads, while SDH has 81 bytes.
4. SONET offers lower transmission rates compared to SDH due to the absence of high-order multiplexing for signal transfer.
5. SONET can only transmit data synchronously. SDH can only transmit data both synchronously and asynchronously.
DWDM (Dense Wavelength Division Multiplexing) is a premier technology for increasing bandwidth over existing fiber infrastructure by creating multiple "virtual fibers" through the transmission of different wavelengths of light over a single physical fiber. Initially adopted by long-distance carriers to reduce costs associated with amplification, dispersion compensation, and regeneration in regional and national SONET networks, DWDM has since gained popularity in metro networks due to fiber exhaustion and increasing traffic volumes.
DWDM operates within the 1530 to 1565 nm range, known as the C-band, which aligns with the low-loss window of optical fiber and is compatible with Erbium-Doped Fiber Amplifiers (EDFA). The ITU-T standard specifies a grid of allowable wavelengths centered at 193.1 THz (1553.3 nm) with channels spaced at multiples of 25 GHz (0.2 nm). Commercial DWDM systems typically feature channels at 2.5 Gbps, 10 Gbps, and 40 Gbps, with higher bit rates requiring improved signal-to-noise ratios, closer amplifier spacing, and higher amplification, often using two DWDM optical amplifier in series. A standard 64-channel DWDM system at 10 Gbps can reach up to 1,500 km with amplifier spacing around 100 km. Advanced systems can extend the range up to 4,500 km but at a significantly higher cost.
