What is SONET?
SONET (Synchronous Optical Network) is a standard for optical telecommunications transport. It was formulated by the Exchange Carriers Standards Association (ECSA) for the American National Standards Institute (ANSI), which sets standards for North America.
Its international counterpart is SDH (Synchronous Digital Hierarchy), standardized by ITU. SONET defines optical carrier (OC) levels and electrically equivalent synchronous transport signals (STSs) for the fiber-optic based transmission hierarchy.
Key Advantages
- Direct optical interface (eliminates DCE).
- Worldwide standard compatibility (SDH).
- Network management capabilities (OAM&P).
- Support for high-speed data services.
Optical Pulse Transmission
SONET Network Elements
STS Multiplexer
Combines multiple low-speed signals (DS1, DS3) into a single high-speed STS-N signal.
Add-Drop Multiplexer (ADM)
The most common element. Allows adding or dropping lower-speed signals from a high-speed line without demultiplexing the entire signal.
Regenerator
Receives weakened signals, clocks itself off the received signal, replaces Section Overhead bytes, and retransmits the signal.
STS-1 Frame Structure
Matrix Visualization: 90 Columns x 9 Rows
Total: 810 Bytes (6480 bits)Section Overhead (SOH)
First 3 columns. Used for communication between regenerators and multiplexers.
Line Overhead (LOH)
Columns 4-9. Used for communication between multiplexers.
Synchronous Payload Envelope (SPE)
Columns 1-87 (after transport overhead). Carries the actual data payload.
SONET/SDH Hierarchy
Data Rates Comparison
| Optical Carrier | Electrical Signal | Line Rate (Mbps) | Payload Rate (Mbps) |
|---|---|---|---|
| OC-1 | STS-1 | 51.840 | 50.112 |
| OC-3 | STS-3 | 155.520 | 150.336 |
| OC-12 | STS-12 | 622.080 | 601.344 |
| OC-48 | STS-48 | 2488.320 | 2405.376 |
| OC-192 | STS-192 | 9953.280 | 9621.504 |
Payload Calculator
Approx. capacity
Virtual Lab: SONET Multiplexing
Visualize how low-speed tributaries are mapped into the STS-1 frame.