SONET/SDH Synchronization (SETS)

Foremost in any SONET/SDH transmission system is network synchronization performing to domestic and international standards for SONET (Bellcore GR-1244) and SDH (ITU-T G.812/813) at Stratum 3, 3E or 4 levels in dual-redundant, protection switched equipment. Semtech's SETS (Station Equipment Timing Synchronization) family of synchronization devices meets this challenge – and in the process sets a new standard of integration, performance, and system complexity reduced to simplicity of design.

Semtech's SETS devices each replace a dozen or more complex hardware ICs, plus DSP software, plus temperature calibration in a typical layout-sensitive, time consuming, large footprint custom design. The SETS solution is easily replicatible on each timing and line card, and the complete SETS solution consists of only two devices: a single SETS IC, plus a local crystal oscillator (XO).

The SETS family comprises the full-featured, ACS8510 Master/Slave SETS, accompanied by the line-card optimized ACS8515 Protection Switch SETS.

The ideal synchronization solution consists of a Master and Slave pair of ACS8510 devices, on a central/main synchronization card; each generating a group of intermediate frequency SEC clocks (typically 19.44MHz), plus frame sync clocks (8kHz), distributed along the backplane. Each of the ACS8510 devices thus feed their clocks downstream to a supporting cast of ACS8515 ICs on each line card, optimized to follow the upstream ACS8510's PLLs. The ACS8515 devices on each line card in turn implement intelligent, hitless protection switching for each optical or copper line card.

In Semtech's SETS Interchangeable XO Architecture, Holdover performance is isolated to the external 12.8MHz XO. In this way, the quality of the XO used need only match the Holdover requirements – one design fits all. For example, a 0.37ppm TCXO is used to satisfy Stratum 3; a 0.011ppm OCXO for Stratum 3E; a 20ppm TCXO for SMC; and an 80ppm cheap XO can be used for Stratum 4/no Holdover. Semtech has been working closely with two highly regarded XO supplier partners – Vectron and C-MAC – to ensure a supply of all these 12.8MHz XOs that have been optimized for Semtech's SETS solution.

Semtech Corporation, 652 Mitchell Road, Newbury Park, CA 91320. Tel: 805-498-2111; Fax: 805-498-4803.