SONET and SDH

Synchronous Optical NETwork  (North America) -  Synchronous Digital Network (Rest of World)

First we will show some comparison tables from RFC2615 :

like-for-ike SONET and SDH entities

the only currently supported SONET/SDH SPE/VCs 
(SPE's = Synchronous Payload Envelopes, which are the same thing as VC's = Virtual Containers)

SONET and SDH primary Standards (there are many more than these)

** also see the SONET/SDH References page

Today, ANSI coordinates and approves the SONET standards, while the ITU-T takes care of the SDH standards. The standards are developed by the T1 committee. T1X1 and T1M1 are the primary T1 Technical Subcommittees responsible for SONET. T1X1 deals with the digital hierarchy (shown in Figure 1–5) 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.

ANSI SONET Standards ( http://www.ansi.org ) 

• ANSI T1.105: SONET—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 T1.105.03a: SONET—Jitter at Network Interfaces – DS1 Supplement
• ANSI T1.105.03b: SONET—Jitter at Network Interfaces – DS3 Wander Supplement
• ANSI T1.105.04: SONET—Data Communication Channel Protocol and Architectures
• ANSI T1.105.05: SONET—Tandem Connection Maintenance
• ANSI T1.105.06: SONET—Physical Layer Specifications
• ANSI T1.105.07: SONET—Sub-STS-1 Interface Rates and Formats Specification
• ANSI T1.105.09: SONET—Network Element Timing and Synchronization
• ANSI T1.119: SONET—OAM&P, Communications
• ANSI T1.119.01: SONET: OAM&P, Communications, and Protection Switching Fragment
  
  
  ITU SDH Standards ( www.itu.org ) 
  

• ITU-T G.803 Architecture of transport networks based on the synchronous digital hierarchy (SDH) 

• ITU-T G.707 Network Node Interface for the Synchronous Digital Hierarchy (SDH)

• G.708, "Network Node Interface for SDH," 1990
• G.709, "Synchronous Multiplexing Structure," 1990

• G.780, "Vocabulary of Terms for SDH Networks and Equipment," 11/94.

• 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

• G.784, "SDH Management," 1/94

• ITU-T G.803: Architecture of Transport Networks Based on the Synchronous Digital Hierarchy (SDH)

• G.832, "Transport of SDH Elements on PDH Networks: Frame and Multiplexing Structures," 11/93.
  

Telcordia (formerly Bellcore - http://telecom-info.telcordia.com  NOT www.telcordia.com !!!)

Over 50 documents that relate to SONET - they are very expensive - for example, the following document listed for US $2250 (at last check).

• GR 253 CORE: SONET Transport Systems: Common Generic Criteria

ETSI (European Telecommunications Standards Institute - www.etsi.org )

• ETSI EN 300 417-9-1 Transmission and Multiplexing (TM) Generic requirements of transport functionality of equipment Part 9: Synchronous Digital Hierarchy (SDH) concatenated path layer functions. Subpart 1: Requirements

NSIF (Network and Services Integration Forum) and ATIS () 

NSIF (Network and Services Integration Forum) is an industry group that was established to define and resolve SONET (synchronous optical network) implementation issues.  It was formed in 1994 by ATIS (Alliance for Telecommunications Industry) to identify SONET interoperability issues. As solutions are defined, reviewed, and approved they are published as SIF Approved Documents. 

IETF (Internet Engineering Task Force) - the IETF manages thousands of RFC's on SONET and SDH

 

Number	Title	Author or Ed.	Date	Format	More Info (Obs&Upd)	Status
RFC3946	Generalized Multi-Protocol Label Switching (GMPLS) Extensions for Synchronous Optical Network (SONET) and Synchronous Digital Hierarchy (SDH) Control	E. Mannie, D. Papadimitriou	October 2004	ASCII		PROPOSED STANDARD
RFC3592	Definitions of Managed Objects for the Synchronous Optical Network/Synchronous Digital Hierarchy (SONET/SDH) Interface Type	K. Tesink	September 2003	ASCII	Obsoletes RFC2558	DRAFT STANDARD
RFC3572	Internet Protocol Version 6 over MAPOS (Multiple Access Protocol Over SONET/SDH)	T. Ogura, M. Maruyama, T. Yoshida	July 2003	ASCII		INFORMATIONAL
RFC3474	Documentation of IANA assignments for Generalized MultiProtocol Label Switching (GMPLS) Resource Reservation Protocol - Traffic Engineering (RSVP-TE) Usage and Extensions for Automatically Switched Optical Network (ASON)	Z. Lin, D. Pendarakis	March 2003	ASCII		INFORMATIONAL
RFC3473	Generalized Multi-Protocol Label Switching (GMPLS) Signaling Resource ReserVation Protocol-Traffic Engineering (RSVP-TE) Extensions	L. Berger, Ed.	January 2003	ASCII	Updated by RFC4003 Errata	PROPOSED STANDARD
RFC3472	Generalized Multi-Protocol Label Switching (GMPLS) Signaling Constraint-based Routed Label Distribution Protocol (CR-LDP) Extensions	P. Ashwood-Smith, Ed., L. Berger, Ed.	January 2003	ASCII	Updated by RFC3468	PROPOSED STANDARD
RFC3471	Generalized Multi-Protocol Label Switching (GMPLS) Signaling Functional Description	L. Berger, Ed.	January 2003	ASCII		PROPOSED STANDARD
RFC3255	Extending Point-to-Point Protocol (PPP) over Synchronous Optical NETwork/Synchronous Digital Hierarchy (SONET/SDH) with virtual concatenation, high order and low order payloads	N. Jones, C. Murton	April 2002	ASCII		PROPOSED STANDARD
RFC3186	MAPOS/PPP Tunneling mode	S. Shimizu, T. Kawano, K. Murakami, E. Beier	December 2001	ASCII		INFORMATIONAL
RFC2823	PPP over Simple Data Link (SDL) using SONET/SDH with ATM-like framing	J. Carlson, P. Langner, E. Hernandez-Valencia, J. Manchester	May 2000	ASCII		EXPERIMENTAL
RFC2615	PPP over SONET/SDH	A. Malis, W. Simpson	June 1999	ASCII	Obsoletes RFC1619	PROPOSED STANDARD
RFC2558	Definitions of Managed Objects for the SONET/SDH Interface Type	K. Tesink	March 1999	ASCII	Obsoletes RFC1595, Obsoleted by RFC3592	PROPOSED STANDARD
RFC2175	MAPOS 16 - Multiple Access Protocol over SONET/SDH with 16 Bit Addressing	K. Murakami, M. Maruyama	June 1997	ASCII		INFORMATIONAL
RFC2171	MAPOS - Multiple Access Protocol over SONET/SDH Version 1	K. Murakami, M. Maruyama	June 1997	ASCII		INFORMATIONAL
RFC1619	PPP over SONET/SDH	W. Simpson	May 1994	ASCII	Obsoleted by RFC2615	PROPOSED STANDARD
RFC1595	Definitions of Managed Objects for the SONET/SDH Interface Type	T. Brown, K. Tesink	March 1994	ASCII	Obsoleted by RFC2558	PROPOSED STANDARD

SONET 

A standard for communicating digital information over optical fiber. It was originally developed by Bellcore to replace the older plesiochronous systems for transporting large amounts of telephone and data traffic.  Synchronous networking data rates are tightly synchronized to network based clocks. Thus the entire network operates synchronously. SDH was made possible by the existence of atomic clocks.

SDH (Synchronous Digital Hierarchy)

Before SONET, the Telecom systems were all PDH (Plesiochronous Digital Hierarchy), since the basic T-carrier system was not truly synchronous.  SONET allows true SDH system (Synchronous Digital Hierarchy) to be constructed, because it is clocked and synchronized by Atomic Clocks.

SONET Encapsulation

SONET can be used to encapsulate digital transmission standards, such as the T-carrier systems, ATM or POS (Packet over SONET).

SONET STS speeds

STS (Synchronous Transport Signal) and OC (Optical Carrier)

Earlier PDH (Plesiochronous Digital Hierarchy) systems defined speeds for North America at DS levels, or for the higher speeds, OC levels.  SONET defined new speed levels called STS (Synchronous Transport Signal), which is worldwide

STS-1 (Synchronous Transport Signal 1)  -  51.84 Mbps

Fortunately, the STS-1 was defined at the exact same speed as the OC-1 .

The basic SONET signal operates at 51.840 Mbit/s and is designated STS-1 (synchronous transport signal one). The STS-1 frame is the basic unit of transmission in SONET.

The STS-1 Frame used for SONET, is 810 Bytes, with 36 bytes of overhead.  The STS-1 frame is transmitted in exactly 125 microseconds on a fiber-optic circuit designated OC-1 (optical carrier one). In practice the terms STS-1 and OC-1 are used interchangeably.  The two major components of the STS-1 frame are :

1) SPE (Synchronous Payload Envelope) - 783 bytes - this includes the payload overhead (9 bytes, used for end to end signalling and error measurement) and the payload of 774 bytes

2) Transport Overhead - 27 bytes - this includes the section overhead and line overhead. These bytes are used for signalling and measuring transmission error rates.

The STS-1 payload throughput (about 50 Mbps) can to carry a full DS-3 frame (44.736 Mbps).

STM-1 (Synchronous Transmission Module 1) = OC-3  -  155.52 Mbps

- same as STS-3, which is the same as OC-3)

The STS-3 signal is also used as a basis for the SDH hierarchy, where it is designated STM-1 (synchronous transmission module one).

Three OC-1 (STS-1) signals are multiplexed by time-division multiplexing to form the next level of the SONET hierarchy, the OC-3 (STS-3), running at 155.52 Mbit/s. The multiplexing is performed by interleaving the bytes of the three STS-1 frames to form the STS-3 frame, containing 2430 bytes and transmitted in 125 microseconds.

STM-4 = OC-12  -  622.08 Mbps

Higher speed circuits are formed by successively aggregating multiples of slower circuits, their speed always being immediately apparent from their designation. For example, four OC-3 or STM-1 circuits can be agregated to form a 622.08 Mbit/s circuit designated as OC-12 or STM-4.

STM-64 = OC-192  -  9.95 Gbps

The current state of the art is the OC-192 or STM-64 circuit, which operates at rate of just under 10 Gbit/s. Speeds beyond 10 Gbit/s are not currently technically viable; however multiple OC-192 circuits can be carried over a single fiber pair by means of Dense Wave Division Multiplexing (DWDM). Such circuits are the basis for all modern transatlantic cable systems and other long-haul circuits.

Due to the fortuitous similarity in bit rates, 10 Gigabit Ethernet has been designed with a capability to interoperate with OC-192/STM-64 equipment

.

Virtual Tributaries and Virtual Containers

SPE (Synchronous Payload Envelope) = AU (Administrative Unit) = VT (Virtual Tributary - North America) = VC (Virtual Container - ROW)

TU = Tributary Unit (used in RoW)

SONET is designed to support a wide variety of payloads. The SONET node accepts these payloads and multiplexes them into a SONET envelope called an SPE (Synchronous Payload Envelope). These payloads are called virtual tributaries (VTs) in North America and virtual containers (VCs) in SDH. 

SDH/SONET defines a way or packaging capacity into Virtual Containers (VCs) which may be Higher Order Virtual Container (HVC) or Lower Order Virtual Containers (LVC). The term Tributary Unit (TU - used in RoW) or Virtual Tributary (VT - North America) describes a method of mapping PDH (e.g. T1) carriers onto SDH/SONET.