SONET vs SDH: Key Differences and Similarities

Here’s a breakdown of the similarities and differences between SONET (Synchronous Optical Network) and SDH (Synchronous Digital Hierarchy) technologies. Both are crucial for high-speed data transmission over fiber optic cables. Let’s dive in!

What are SONET and SDH?

Both SONET and SDH are techniques for transmitting information over fiber optic cables. They share the following core functions:

• Framing: They structure the data for transmission using the HDLC (High-Level Data Link Control) standard frame format.
• Error Checking: They provide mechanisms to detect and correct errors that might occur during transmission.
• Link Management: They handle the establishment, maintenance, and termination of the communication link.

The Key Difference: Origins

• SONET: Developed in the United States by the ANSI T1X1.5 committee.
• SDH: Developed internationally by the ITU (International Telecommunication Union).

Essentially, SONET can be considered a subset of SDH.

• SDH Basic Unit: Synchronous Transmission Module level-1 (STM-1)
• SONET Basic Unit: Optical Carrier level-1 (OC-1)

Higher rates like OC-3, OC-12, OC-18, OC-24, OC-36, OC-48, OC-96, and OC-192 are all derived from the basic OC-1 rate.

North American Digital Telephone System Rates

Here’s a table summarizing the data rates and voice channel capacities for the North American digital telephone system:

SONET Rates

The following table shows the data rates and voice channel capacities supported by the SONET system:

SDH Rates

Here’s a table outlining the data rates and voice channel capacities supported by the SDH system:

Data Rate Advancements

While OC-192 in SONET and SDH initially supported a maximum data rate of approximately 9953.28 Mbps, advancements in SDH have pushed data rates up to 40 Gbps and beyond.