SONET and SDH overview

Giới thiệu về công nghệ SONET và SDH trong truyền dẫn quang

SONET Overview

• SONET is a physical layer standard

• A synchronous frame structure for multiplexing digital traffic

• Frame structure: 9 rows of 90 columns of 8-bit bytes

• Bytes are transmitted one row at a time, from left to right

• First three columns of STS-1 frame are for section overhead and line overhead

• Remaining 87 columns are for the Synchronous Payload Envelope

(SPE)

STS-1 frame overheads

STS-1 frame: section overhead

Section overhead is recalculated for each SONET device

(regenerators and multiplexers).

STS-1 frame: line overhead

STS-1 frame: path overhead

Path overhead is only calculated for end-to-end (at STS multiplexers).

SONET Structure

SONET ARCHITECTURE

• Path Layer: Mapping of DS0, DS1, DS3, FDDI to Payload

• Line Layer: Frame synchronization and data multiplexing into a SONET frame

• Section Layer: Framing, error monitoring and bit-scrambling

• Photonic Layer: Fiber characteristics, encoding, transmitter and

receiver types

In a simple SONET linear network

• PTE (path-terminating equipment) sits at each end, takes sub-rate signals and multiplexes them into a SONET frame

• Between PTE devices are several LTE (line-terminating equipment) devices:

an ADM (add/drop multiplexer)

– Instead of de-multiplexing entire signal, as PTE does, it pulls out only sub-rate services it needs and inserts different signals

• If network is long enough, STE (section-terminating equipment) will be in fiber These repeaters take incoming signal from one side and rebroadcast it out on other side

– Placement of STE in the network depends on strength of signal being

transmitted down the fiber

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