SONET / SDH Technical Summary

What is SONET & SDH?

SONET and SDH are a set of related standards for synchronous data transmission over fiber optic networks. SONET is short for Synchronous Optical NETwork and SDH is an acronym for Synchronous Digital Hierarchy. SONET is the United States version of the standard published by the American National Standards Institute (ANSI). SDH is the international version of the standard published by theInternational Telecommunications Union (ITU).

SONET/SDH Digital Hierarchy

Optical Level

Electrical Level

Line Rate (Mbps)

Payload Rate (Mbps)

Overhead Rate (Mbps)

SDH Equivalent


STS-1 51.840 50.112 1.728


STS-3 155.520 150.336 5.184 STM-1


STS-9 466.560 451.008 15.552 STM-3


STS-12 622.080 601.344 20.736 STM-4


STS-18 933.120 902.016 31.104 STM-6


STS-24 1244.160 1202.688 41.472 STM-8


STS-36 1866.240 1804.032 62.208 STM-13


STS-48 2488.320 2405.376 82.944 STM-16


STS-96 4976.640 4810.752 165.888 STM-32


STS-192 9953.280 9621.504 331.776 STM-64

ANSI SONET Standards

The American National Standards Institute (ANSI) coordinates and approves SONET standards. The standards are actually developed by Committee T1 which is sponsored by the Alliance for Telecommunications Industry Solutions (ATIS) and accredited by ANSI to create network interconnection and interoperability standards for the United States. T1X1 and T1M1 are the primary T1 Technical Subcommittees responsible for SONET. T1X1 deals with “digital hierarchy and synchronization”. T1M1 deals with “internetworking operations, administration, maintenance, and provisioning (OAM&P). Listed below are some of the most commonly cited SONET standards available from ANSI. Refer to the ANSI web site at for a complete list of SONET standards along with information on purchasing the documents.


Basic Description including Multiplex Structure, Rates and Formats

ANSI T1.105.01: SONET

Automatic Protection Switching

ANSI T1.105.02: SONET

Payload Mappings

ANSI T1.105.03: SONET

Jitter at Network Interfaces

ANSI T1.105.03b: SONET

Jitter at Network Interfaces – DS1 Supplement

ANSI T1.105.04: SONET

Jitter at Network Interfaces – DS3 Wander Supplement

ANSI T1.105.05: SONET

Data Communication Channel Protocol and Architectures

ANSI T1.105.06: SONET

Tandem Connection Maintenance

ANSI T1.105.07: SONET

Physical Layer Specifications

ANSI T1.105.09: SONET

Sub-STS-1 Interface Rates and Formats Specification


Network Element Timing and Synchronization

ANSI T1.119.01: SONET

Operations, Administration, Maintenance, and Provisioning (OAM&P) – Communications: OAM&P Communications Protection Switching Fragment

ITU-T SDH Standards

The International Telecommunications Union (ITU) coordinates the development of SDH standards. ITU was formerly known as the CCITT. It is sponsored by the United Nations and coordinates the development of telecommunications standards for the entire world. Listed below are some of the most commonly cited SDH standards available from ITU. Refer to the ITU web site at for a complete list of SONET standards along with information on purchasing the documents. 

ITU-T G.707

Network Node Interface for the Synchronous Digital Hierarchy (SDH)

ITU-T G.781

Structure of Recommendations on Equipment for the Synchronous Digital Hierarchy (SDH)

ITU-T G.782

Types and Characteristics of Synchronous Digital Hierarchy (SDH) Equipment

ITU-T G.783

Characteristics of Synchronous Digital Hierarchy (SDH) Equipment Functional Blocks

ITU-T G.803

Architecture of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)

SONET Interoperability Forum (SIF)

The SONET Interoperability Form (SIF) was formed in 1994 to identify SONET interoperability issues. As solutions are defined, reviewed, and approved they are published as SIF Approved Documents.


The following standard from ITU defines the mapping of an ATM cell stream into an SDH frame structure.

ITU-T I.432: B-ISDN User-Network Interface – Physical Layer Specification

Similar specifications are available from the ATM Forum with the following being one example:

622.08 Mb/s Physical Layer Specification


Packet Over SONET (POS)

The Internet Engineering Task Force (IETF) has released RFCs that describe the use of Point-to-Point Protocol for transferring IP traffic natively over SONET and SDH circuits. These RFCs were developed by the PPP Extensions Working Group of IETF.IETF RFC2615: PPP over SONET/SDH

IETF RFC1661: The Point-to-Point Protocol (PPP)

IETF RFC1662: PPP in HDLC-like FramingPMC-Sierra, Inc. has proposed what they call a “POS-PHY” interface specification for attaching chips that implement the Packet Over Sonet protocol. See this press release for more information.

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