SONET/SDH. By Iqtidar Ali

Transcription

1 SONET/SDH By Iqtidar Ali

2 SONET/SDH SONET/SDH means Synchronous Optical Network (SONET) was developed by ANSI. Synchronous Digital Hierarchy (SDH) was developed by ITU-T. The high bandwidth of fiber optic cable are suitable for today s highest data-rate technologies (such as video conferencing) and for carrying large numbers of lower-rate technologies at the same time. Without standards, internetworking among the existing proprietary systems is impossible.

3 Concern About SONET/SDH Among the concerns addressed by the designer of SONET and SDH, Three are particular interest to us. First, SONET/SDH is a synchronous network. A single clock is used to handle the timing of transmissions and equipment across the entire network. Second, SONET/SDH contains recommendations for the standardization of Fiber Optic Transmission System (FOTS) equipment sold by different manufacturers. Third, SONET/SDH physical specification and frame design include mechanisms that allow it to carry signals from incompatible tributary systems (particularly asynchronous services such as DS-0, DS-1). It is this flexibility that gives SONET a reputation for universal connectivity.

4 Synchronous Transport Signal As the first step in its flexibility, SONET defines a hierarchy of signaling levels called Synchronous Transport Signals (STSs). Each STS level (STS-1 to STS-192) supports a certain data rate, specified in megabits per second. The physical links defined to carry each level of STS are called Optical Carrier (OCs). OC levels describe the conceptual and physical specification of the links required to support each level of signaling. The most popular implementation are OC-1, OC-3, OC-12, OC-48, and OC-192.

5 Physical Configuration The devices used in SONET transmission system and some possible ways of arranging and linking those devices. SONET transmission relies on three basic devices: STS Multiplexers Regenerators and Add/Drop Multiplexer 10

6 Physical Configuration (Cont--) STS Multiplexer:- An STS multiplexer/demultiplexer either multiplexes signals from multiple sources into STS signal or demultiplexes an STS signal into different destination signals. Regenerator:- A SONET regenerator replaces some of the existing overhead information (header information) with new information. These devices function at the data link layer. Add/Drop Multiplexer: - It can add signals coming from different sources into a given path or remove a desired signal from a path and redirect it without demultiplexing the entire signal. Instead of relying on timing and bit positions, add/drop multiplexers use header information such as addresses and pointers

7 Sections, Lines, and Paths A Section is the optical link connecting two neighbor devices: multiplexer to multiplexer, multiplexer to regenerator, or regenerator to regenerator. A Line is the portion of the network between two multiplexer: STS multiplexer to add/drop multiplexer, two add/drop multiplexer or two STS multiplexers. A Path is the end to end portion of the network between two STS multiplexers. In a simple SONET of two STS multiplexers linked directly to each other, the section, line, and path are the same.

8 SONET Layers SONET defines four layers. The Photonic layer is the lowest layer and performs physical layer activities. The Section, Line, and Path layers correspond to the OSI model's data link layer. 13

9 Cont d Photonic Layer:- This layer is correspond to the physical layer of the OSI model. It includes physical specification for the optical fiber channel, the sensitivity of the receiver, multiplexing function, and so on. SONET uses NRZ encoding with the presence of light representing 1 and the absence of light representing 0. Section Layer:- This layer is responsible for the movement of a signal across a physical section. It handles framing, scrambling, and error control. Section layer overhead is added to the frame at this layer.

10 Cont d Line Layer This layer is responsible for the movement of a signal across a physical line. Line layer overhead is added to the frame at this layer. STS multiplexers and add/drop multiplexers provides line layer functions. Path Layer This layer is responsible for the movement of a signal from its optical source to its optical destination. At the optical source, the signal is changed from an electronic form into an optical form, multiplexed with other signals, and encapsulated in a frame. At the optical destination, the received frame is demultiplexed, and the individual optical signals are changed back into their electronic form. STS multiplexer provides path layer function.

11 Device-Layer Relationship Devices used in SONET transmission and the four layers of the standard. STS-Multiplexer is four layer, Add/drop Multiplexer is three layer, and Regenerator is two layer device. 16

12 SONET Frame Data received from electronic interface, such as a T-l line, encapsulated in a frame at the Path layer and overhead is added. Additional overhead is added, first at the Line layer and then at the Section layer. Finally, the frame is passed to the Photonic layer, where it is transformed into an optical signal. SONET overhead is not added as headers and trailers as we have seen in other protocols. Instead, SONET insert overhead at a variety of locations in the middle of the frame. 17

13 Applications SONET is designed to provide a backbone network for WANs. With a data rate of more than three gigabits per second. It can find applications in many area's. Some of these application are, SONET can replace existing T-l or T-3 lines. A T-l load can easily be carried in a VT l.5 tributary and a T-3 load can easily be carried in a full SPE of an STS-l frame. A lot of fiber-optic cables have already been laid without a common protocols. These can be combined into a network or networks using the SONET protocol. Most of these cables are not being used to their full capacity because of the lack of a protocol. SONET can be the carrier for ISDN and B-ISDN. SONET can be the carrier for ATM cells. SONET can replace the fiber optic cables used in cable TV networks. SONET can be used as the backbone. 35

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