SONET SDH Tutorial

This page of SDH tutorial from wireless tutorials section covers SDH/SONET basics, HDLC frame, SDH terminologies, SDH rates, SONET STS-1 SDH Frame.

SONET and SDH are used for the same purpose i.e. communication over optical fibre links. They are physical layer standards designed to provide reliable transmission of information from source to the destination over optical fibre cables. SONET stands for Synchronous Optical Network developed by ANSI and SDH stands for Synchronous Digital Hierarchy developed by ITU.

SONET/SDH are needed to take care of following objectives in communication.
•  to carry multiple T or E carrier lines between two switching centers to take care of increased communication lines.
•  Data framing which is taken care by adopting HDLC frame format.
•  Managing information transfer between optical fibre nodes.
•  Multiplexing and de-multiplexing
•  Error checking
•  Take care of clock rate variation
•  Plesiochronous voice and data traffic mapping
•  Signalling required to perform automatic switching in failure events of fibre cable or optical nodes.

SDH/SONET Terminologies

SDH network terminologies

As shown in the figure.1 end to end connection between SDH/SONET networks is referred as path. Connection between major ADM nodes is referred as line. ADM stands for Add/Drop multiplexer. Connection between ADM and regenerator and also between regenerators is referred as section. Based on this following abbreviations are derived and are popularly used in SDH.

•   PTE -Path Terminating Equipment
•   LTE -Line terminating Equipment
•   STE -Section Terminating Equipment
•   ADM -Add/Drop Multiplexer

HDLC Frame

HDLC frame format

All the communication over SONET/SDH optical links follow HDLC frame format as defined in the figure. HDLC frame composed of flags at the beginning and at the end, address field, control field, information fields and CRC.

Character 0x7E is used as flag, which is also referred as framing character. This is very important and used to identify beginning as well as end of the frame. This is required as HDLC frame is of varying length due to variation in the information field part. CRC is used for error detection purpose. This field is about 2 or 4 bytes (octets).

Address- This field defines type of transmission mode i.e. unicast(0x0F) or multicast(0x8F). Control- This field defines type of frame transmission viz. Information data frame(I),Supervisory frame(S) or unnumbered frame(U).

Frame structure of wireless standards, technologies

Frame structure of various wireless standards/technologies are mentioned below. It include WiMAX, WLAN, Zigbee, GSM, GPRS, UMTS, LTE, TD-SCDMA, GPS, SDH, 11ac WLAN, AMPS, Ethernet, VLAN etc.

WiMAX physical layer Frame Structure as per 802.16d and 802.16e standards
WiMAX MAC layer Frame Structure as per OFDM 802.16d standard
Zigbee RF4CE Frame Structure
Zigbee physical layer Frame Structure
Zigbee MAC layer Frame Structure
GPRS Frame Structure
GPS Frame Structure
LTE Frame Structure
TD-SCDMA Frame Structure
UMTS Frame Structure
SONET Frame Structure
SDH Frame Structure
802.11ac PHY Frame Structure
802.11ac MAC layer Frame Structure
WLAN Frame Structure as per 802.11a,11b,11n,11ac standards
AMPS Frame Structure
Ethernet Frame Structure
VLAN Frame Structure
GSM Frame Structure


PDH versus SDH
SDH Frame structure
DWDM system basics
Fibre optic communication
Types of WDM
SONET versus SDH
What is PDMA?
What is WDM?
SDH Networks
SDH Modulation
PDH Frame structure