Chapter 17 SONET/SDH
Chapter 17 of Data Communications and Networking by Behrouz A. Forouzan, titled "SONET/SDH", focuses on Synchronous Optical Networking (SONET) and Synchronous Digital Hierarchy (SDH), two related standards for high-speed data transmission over optical fiber networks. Below are detailed notes on the chapter:
1. Introduction to SONET/SDH
SONET and SDH are standardized protocols that allow high-speed transmission of data over optical fiber networks.
SONET is the American standard, while SDH is its European counterpart, but both are functionally equivalent and interoperable.
2. SONET/SDH Architecture
SONET and SDH provide a framework for the transportation of various types of digital signals through a network. They use a structure of multiplexing and synchronous transmission to enable data transfer.
The basic unit of transmission in SONET is the STS-1 (Synchronous Transport Signal level 1), which operates at 51.84 Mbps. Higher transmission rates are multiples of STS-1, such as STS-3 and STS-12.
In SDH, the base transmission unit is STM-1 (Synchronous Transport Module level 1), which is equivalent to SONET's STS-3.
3. SONET Layers
SONET is organized into four layers:
Path Layer: Provides end-to-end data transfer between network devices.
Line Layer: Deals with the reliable transfer of data across a line, ensuring that information is transmitted correctly between multiplexers.
Section Layer: Handles the transmission of data over individual fiber-optic links.
Photonic Layer: The physical layer responsible for the transmission of light pulses over optical fiber.
4. SONET Frames
SONET uses a frame structure to transmit data. Each frame is composed of 90 columns and 9 rows, for a total of 810 bytes. An STS-1 frame is transmitted every 125 microseconds.
Each frame contains sections dedicated to different types of overhead:
Section Overhead: Manages the communication between devices in a network section.
Line Overhead: Provides error detection and correction for communication between multiplexers.
Path Overhead: Handles end-to-end communication between network endpoints.
5. STS Multiplexing
SONET uses byte-interleaving to multiplex multiple STS-1 signals into higher-level signals like STS-3 and STS-12. For example, three STS-1 signals can be combined to create an STS-3 signal.
Add/Drop Multiplexer (ADM): A device used to add or remove lower-level signals from a higher-level SONET signal without demultiplexing the entire signal.
6. SONET Networks
SONET supports three types of network topologies:
Linear Networks: Devices are connected in a straight line. Data can be transmitted in either direction, providing redundancy in case of a failure.
Ring Networks: Data is transmitted in a ring, with two transmission paths (clockwise and counterclockwise) for redundancy.
Mesh Networks: Devices are interconnected in a non-hierarchical structure, allowing for multiple transmission paths between any two points.
7. Virtual Tributaries
SONET allows for the transmission of lower-speed signals using virtual tributaries (VTs), which are sub-STS-1 units. VTs can be used to multiplex data from devices operating at slower speeds into the SONET network.
8. Summary
SONET and SDH are critical for high-speed optical networks, providing a standardized method for data transmission across long distances. They support various topologies and offer robust error detection and correction mechanisms.
These notes provide a detailed understanding of the key concepts and components of SONET and SDH as described in Chapter 17【7:9†source】【7:5†source】【7:10†source】【7:14†source】.
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