SDH

SDH
Name	SDH
Developer	International Telecommunication Union; British Telecom researchers; European Telecommunications Standards Institute
Introduced	1980s
Type	synchronous optical networking standard

SDH Synchronous Digital Hierarchy is a standardized protocol for transmitting digital signals over optical fiber and electrical media, designed to interconnect equipment from manufacturers such as Nokia, Huawei, Ericsson, Cisco Systems, and Alcatel-Lucent. It provides a framework adopted by carriers including Deutsche Telekom, BT Group, France Télécom, NTT, and AT&T to transport traffic between switches and routers built by vendors like Juniper Networks, Siemens, Motorola, and Fujitsu. SDH enables high-capacity links used in backbone networks that interwork with systems deployed by operators such as Verizon Communications, Orange S.A., Telefónica, Vodafone, and China Mobile.

Definition and Overview

SDH defines a hierarchy of synchronous signals and frame structures used by network operators such as British Telecom and Deutsche Telekom to multiplex plesiochronous signals from systems by Alcatel-Lucent and Ericsson. The technology specifies transmission rates, framing, and overhead bytes for management by equipment vendors like Siemens and Nokia Siemens Networks, and for interconnects at facilities operated by Level 3 Communications and Telia Company. SDH frames carry payloads including streams originated by switches from Cisco Systems and Juniper Networks and are monitored using tools developed by Tektronix and EXFO.

History and Development

Development began in the 1980s with contributions from entities such as British Telecom and the International Telecommunication Union, influenced by prior hierarchies developed by Bell Labs and regional initiatives by European Telecommunications Standards Institute. Standardization work involved committees of the ITU-T and industry consortia including participants from Nokia, Siemens, Alcatel, and NEC. Deployment accelerated during the 1990s across incumbents like France Télécom and NTT and was integrated into backbone upgrades by carriers such as AT&T and Verizon Communications, enabling intercontinental links via submarine cables supplied by contractors like Tyco International and Fujitsu.

Technical Architecture and Operation

SDH uses a synchronous frame structure defined by the ITU-T to carry payloads in containers and multiplexing hierarchies; implementations are produced by Nokia and Huawei. The architecture comprises synchronous transport modules, path overhead, and section overhead used for operations by network management systems from IBM and Hewlett-Packard Enterprise. Physical layers are realized on optical platforms from Ciena, Alcatel-Lucent, and Cisco Systems and integrate with transponders from Infinera and Fujitsu; synchronization sources include atomic clock references from Symmetricom and GPS receivers by Trimble. Protection mechanisms (e.g., rings) are deployed in topologies used by BT Group and Deutsche Telekom and interoperate with management protocols developed by Ericsson and Siemens.

Applications and Use Cases

Carriers such as Orange S.A. and Vodafone use SDH for backbone transport of voice and leased-line services originating on switches from Avaya or Alcatel-Lucent. Enterprises connected via managed services from Telia Company and Level 3 Communications rely on SDH to deliver private lines and enterprise WAN circuits. SDH is used in mobile backhaul deployed by T-Mobile, Vodafone, and China Mobile to connect radio access network equipment by Ericsson and Huawei. It is also employed in broadcast contribution links for broadcasters like BBC and CNN and in financial trading networks operated by institutions such as Goldman Sachs and JPMorgan Chase.

Standards and Regulatory Framework

The principal standards body for SDH is the ITU-T, with regional inputs from ETSI and international coordination involving operators like BT Group, Deutsche Telekom, and vendors such as Nokia and Alcatel-Lucent. National regulators including the Federal Communications Commission and the European Commission influence deployment via spectrum and interconnection rules affecting carriers like AT&T and Verizon Communications. Interoperability testing is performed in laboratories run by ETSI and industry testbeds hosted by organizations such as IETF working groups and vendor consortia including Multi-Protocol Label Switching testers and certification programs run by Broadband Forum.

Comparison with Alternative Technologies

SDH is compared to technologies like Plesiochronous Digital Hierarchy systems standardized by Bell Labs vendors, and to packet-based alternatives from Cisco Systems and Juniper Networks such as MPLS and Ethernet services promoted by IEEE 802.3ad. Optical transport alternatives from Infinera and Ciena include Dense Wavelength Division Multiplexing systems used by submarine cable operators like Prysmian Group; mobile backhaul increasingly uses microwave radios from Huawei and packet solutions from Cisco Systems adopted by T-Mobile and Verizon Wireless.

Implementation and Deployment Considerations

Operators such as NTT, France Télécom, and BT Group plan migration paths involving equipment from Nokia, Huawei, and Ericsson while coordinating with regulators including the Federal Communications Commission. Key considerations include interoperability testing with vendors like Ciena and Alcatel-Lucent, synchronization sourcing from Trimble and Symmetricom, protection schemes used by Deutsche Telekom and Level 3 Communications, and phased migration to packet technologies from Cisco Systems and Juniper Networks to support service offerings managed by IBM and systems integrators such as Accenture.

Category:Telecommunications standards