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Sonet/SDH Rings & Network BY DARSINI S M
Introduction: • Synchronous optical network is the evaluation of digital TDM scheme. • It allows different types of signal formats to be transmitted over the fiber optic cable. • SONET Synchronous optical network in North America • SDH Synchronous Digital Hierarchy in other parts of the world. Definition: • It defines a Synchronous frame structure for transmitting TDM signals in the optical network. • It is a high speed network which encodes bit stream into optical signals.
Transmission Formats: • Synchronous Transport Signals STS • Synchronous Transport Module STM [SDH] Synchronous Transport Signals (STS): • It defines a hierarchy of signaling levels. • Each level Supports certain bit rates in Mbps. • Optical carriers are the physical links used to carry STS. • Optical carriers describes the conceptual and physical specifications of STS. [SONET]
Synchronous Transport Module (STM) • SDH defines a hierarchy of signaling levels. • STM – 1 is equivalent to STS – 3 Sonet/SDH transmission rates:
SONET FRAME: Synchronous Payload envelope(SPE) Transport Over head Path Over head
Transport over head(TOH): • First 3 columns comprise the TOH bytes that carry the network management information. • Section over head (SOH) • Line over head (LOH) • Section connects adjacent network elements like regenerators. • Line connects 2 sonnet devices. • LOH is used for communication between STS – N signals. Synchronous pay load envelope (SPE) • The remaining 87 columns : SPE • It carries user data + 9 bytes of path over head
Path Overhead (POH): • A path is a complete end-to-end connection. • POH is ‘9' by be data in a single column which can be located anywhere in SPE. • It supports the performance monitoring by the end equipment, signal labeling and a user channel. Transmission bit rate of SONET (i.e) STS-1: = (90 bytes / row) (9 rows/frame) (8 bits/byte) (125 US / frame) STS – 1 = 51.84 Mbps STS – N = n*51.84 mbps
SDH FRAME: Transport Over head Path Over head Synchronous Payload envelope(SPE) Transmission bit rate of SDH-1: = (270 bytes / row) (9 rows/frame) (8 bits/byte) (125 US / frame)
Optical interfaces: • To ensure the interconnection compatibility between the equipmnts. • The details are the optical source characteristics, the receiver sensitivity and distances for various types of fibers. Three categories & optical: Graded Index multimode : 1310nm - O band Conventional non-dispersion single mode 1310 nm 1550 nm [0-band & C-band] Dispersion-shifted single mode fiber 1550 nm Ge) C-band.
Optical sources:(based on attenuation & dispersion characteristics) • Light-emitting diodes (LEDs) • Multimode laser • Single mode laser RECEIVER SENSITIVITY: • Minimum acceptable average received power Rise and fall times • Optical returns loss TRANSMISSION DISTANCES: • Longer transmission distance required higher power LASERs Application of sonet/SDH • Basic architecture for b- ISDN and ATM • Very high speed transmission of voice & data signals using fiber - optic networks. • Widely used in telecommunication system.
Sonet/SDH Ring Architecture: • It is also called as self healing rings • In sonet/SDH , the traffic along a certain path can be switched to an alternate (or) standby path automatically in case of failure (or) degradation of the link.
Features of Ring Configuration: • There can be either two or four fibers running between the nodes on a ring. • Signals can travel either in clockwise only (unidirectional ring) or in both directions around the ring (Bidirectional ring). • Protection switching can be done in either • line switching • path switching • Two importance Ring Configuration: • UPSR (unidirectional path switched ring) • BLSR (bidirectional line switched ring)
unidirectional path-switched ring: • The signal is fed into both the primary and Protection fibers for Protection purpose. • The receiver continuously compares the fidelity of each signal. • In case of failure, it chooses the alternate path, Based on the quality of the received signal.
bidirectional line switched ring: • It consists of wo Primary paths and two secondary paths. • Primary: normal bidirectional Communication. • Secondary paths are used for protection purpose.
Transmitter or receiver card in the primary ring fails (or) break only in primary fiber: • When the affected nodes detect a loss of signal, it can switch both primary fibers to Secondary protection fiber pairs. (i.e) protection path becomes part of the primary. 2. Node (or) fiber- cable failure: In this situation, The nodes on either side & failed node, can switch the Primary to protection path as loopbacks
Sonet/SDH network configuration: • The general commercial configuration a large SONET/SDH network consists of Point-to-point links, Linear chairs, UPSR, BLSR and Interconneted rings.