جهاز SDH

بجهاز SDH في الواقع لا يوجد جهاز اسمه (Synchronous Digital Hierarchy (SDH ولكنه اسم بروتوكول يستخدم في اجهزة ال Transmission



- SDH (Synchronous Digital Hierarchy) is a standard technology for synchronous data transmission on optical media. It is the international equivalent of Synchronous Optical Network. Both technologies provide faster and less expensive network interconnection than traditional PDH (Plesiochronous Digital Hierarchy) equipment.
In digital telephone transmission, "synchronous" means the bits from one call are carried within one transmission frame. "Plesiochronous" means "almost (but not) synchronous," or a call that must be extracted from more than one transmission frame.

SDH uses the following Synchronous Transport Modules (STM) and rates: STM-1 (155 megabits per second), STM-4 (622 Mbps), STM-16 (2.5 gigabits per second), and STM-64 (10 Gbps.

حيث يقوم البروتوكول STM بحجز CHANNELs سواءً يوجد Traffic ام لا وبشكل متزامن.
وقد اتت تقنية Asynchronous Transport Modules (ATM)لتحل هذه المشكله اي تستخدم CHANNELS عند وجود Traffic فقط اي Service On Demand وبشكل متزامن ايظا.