SDH frame structure

 # SDH Frame Structure

Synchronous Digital Hierarchy (SDH) is a standardized multiplexing protocol that transfers multiple digital bit streams over optical fiber. Here's an overview of the SDH frame structure:

## Basic STM-1 Frame Structure

The fundamental SDH frame is called STM-1 (Synchronous Transport Module level 1):

- **Frame duration**: 125 microseconds (8000 frames per second)

- **Frame size**: 2430 bytes (19440 bits)

- **Structure**: 9 rows × 270 columns of bytes

## Frame Composition

The SDH frame consists of three main parts:

1. **Section Overhead (SOH)**

   - 9 rows × 9 columns (81 bytes)

   - Divided into:

     - Regenerator Section Overhead (RSOH): rows 1-3

     - Multiplexer Section Overhead (MSOH): rows 5-9

2. **Payload (including Pointer)**

   - Administrative Unit Pointer (AU PTR): row 4, columns 1-9 (9 bytes)

   - Payload area: 9 rows × 261 columns (2349 bytes)

3. **Virtual Containers (VCs)**

   - The payload area carries Virtual Containers which contain the actual user data

   - Common VCs: VC-12 (2.048 Mbps), VC-3 (34.368 Mbps), VC-4 (139.264 Mbps)


## Higher Order SDH Frames


Higher capacity frames are created by byte-interleaving multiple STM-1 frames:


- STM-4: 4 × STM-1 = 9 rows × 1080 columns (38,880 bytes)

- STM-16: 16 × STM-1 = 9 rows × 4320 columns (155,520 bytes)

- STM-64: 64 × STM-1 = 9 rows × 17280 columns (622,080 bytes)

- STM-256: 256 × STM-1 = 9 rows × 69120 columns (2,488,320 bytes)

## Key Features

**Synchronization**: All network elements are synchronized to a common clock

**Pointer mechanism**: Allows flexible alignment of payload within frame

**Rich overhead**: Provides extensive OAM (Operations, Administration, and Maintenance) capabilities

**Multiplexing**: Efficiently combines lower-rate signals into higher-rate signals

SDH's rigid frame structure provides excellent network management capabilities and fault detection mechanisms, making it widely used in telecommunications networks.

Comments

Post a Comment

Popular posts from this blog

Alarms in OTN system and explanations

Optical Transport Network (OTN) systems have several alarms to monitor network health and detect issues that could impact performance. These alarms are categorized based on layers (OTU, ODU, and client signals) and types of failures. Here are the key OTN alarms and their explanations: 1. Optical Channel (OTU) Alarms These alarms occur at the Optical Transport Unit (OTU) layer, which ensures error correction and transport. LOF (Loss of Frame): The OTU cannot detect a valid frame alignment. This happens due to signal corruption. LOS (Loss of Signal): No optical signal is detected, often due to fiber cuts or transceiver issues. LOM (Loss of Multiframe): The multiframe alignment is lost, affecting higher-layer multiplexing. OTUk-BDI (Backward Defect Indication): The remote end reports a defect at the OTUk layer, signaling back to the sender. OTUk-SF (Signal Fail): Severe degradation in the signal, triggering protection switching. OTUk-SD (Signal Degrade): The signal is degra...
Read more

OTN frame structure with details

 The **Optical Transport Network (OTN)** framework is defined by the ITU-T G.709 standard, which specifies the structure and functionality of the OTN. OTN is designed to provide a standardized way to transport and manage high-speed data over optical networks. Below is an overview of the OTN frame structure:  **OTN Frame Structure** The OTN frame consists of several layers and overheads, which are organized into a hierarchical structure. The key components of the OTN frame include: 1. **OTUk (Optical Transport Unit, level k):**    - The OTUk is the basic frame structure used for transporting client signals.    - It includes:      - **Payload Area:** Carries the client data.      - **OTUk Overhead:** Provides management and monitoring functions.      - **OTUk FEC (Forward Error Correction):** Used for error detection and correction. 2. **ODUk (Optical Data Unit, level k):**    - The ODUk is a sub-layer wi...
Read more

OTN related alarms

In OTN (Optical Transport Network) technology, several alarms and indicators are used to monitor and troubleshoot network performance. Here are some common OTN-related alarms: ### **1. Loss of Signal (LOS)**    - Triggered when there is a complete loss of optical signal.    - Possible causes: Fiber cut, transmitter failure, or disconnected cable. ### **2. Loss of Frame (LOF)**    - Indicates that the OTN frame synchronization is lost.    - Possible causes: High bit errors, signal degradation, or equipment malfunction. ### **3. Loss of MultiFrame (LOM)**    - Occurs when the OTN multiframe alignment is lost.    - Possible causes: Synchronization issues or signal impairments. ### **4. Signal Degrade (SD)**    - Indicates degraded signal quality (BER exceeds threshold).    - Possible causes: Optical power issues, dispersion, or interference. ### **5. Signal Fail (SF)**    - Triggered when signal quali...
Read more