SONET hardware / role:

• SONET stands for Synchronous Optical Networking (SONET), is a fiber optics-based network for use by telephone companies. It provides an open standard optical interface for transmission at the broadband user network and between network nodes.
• It defines optical signals and a synchronous frame structure for multiplexed digital traffic. Synchronous multiplexing of signals is the key feature of SONET / SDH. In synchronous multiplexing, the position of a tributary is fixed in the higher order multiplexed signal.
• SONET offers seamless interconnection among carriers without depending on their proprietary capabilities.
• Regardliess of carriers, bandwidth can be managed to provide maximum control and support for bandwidth on-demand services.
• SONET interconnects with a variety of current and emerging carrier service including FDDI, DQDB, frame relay, SMDS and ATM.
• SONET offers a transmission rate from 51.84 Mbps to 2.488 Gbps and can extend to mcuh higher rates. It is a layer 1 physical technology with a scalable network.
• SONET standard emphasizes the need for operations, administration and maintenance (OAM) of an end-to-end system. OAM refers to monitoring, managing and repairing of a SONET system.
• SONET has 4 layers: Photonic layer, Section Layer, Line Layer and path layer. In SONET, the basic unit of transport is the synchronous transport signal level 1 (STS-1) frame, which has a bit rate of 51.84 Mbps and repeats every 125 micro sec.
• The key features of the STS01 framing included: Frame repetition of 8000 frames / sec, frame duration of 125 micro sec and support for sub-STS-1 signals such as DS-1s.

SONET / SDH Hardware:

• The hardware aspects of SONET are difficult to describe in discrete terms because many of the functional elements overlap. The following is a description of the discrete functional elements of hardware devices:
• Terminal multiplexers are Path-Terminating Equipment (PTE) that provide access to the SONET network, operating in a manner similar to a T3/E-3 time division multiplexer. Multiple DS-0s, for example, can be multiplexed to form a VT1.5, several of which would then form a VTG and an STS-1 frame. Terminal multiplexers also accomplish the conversion from electrical STS-N signals into Optical Carrier (OC-N) signals.
• Concentrators perform the equivalent function as traditional electrical concentrators and hubs. SONET concentrators combine OC-3, and OC-12 interfaces into higher OC-N levels of transmission.
• Add/Drop Multiplexers (ADM) do not have exact equivalents in the electrical (Digital Signal, or DS), although they perform roughly the same functions as T-carrier TDMs. It is found in the Central Office Exchange (COE), they provide the capability to insert or drop individuals DS-1, DS-2 or DS-3 channels into a SONET transmission pipe.
• ADMs offer great advantage over traditional DS-N MUXs. ADMs perform the additional functions of dynamic bandwidth allocation, providing operation and protection channels, optical hubbing and ring protection.
• Digital Cross-Connects (DXC) perform approximately the same function as their electrical equivalents (DACs/DCCSs), providing switching and circuit grroming down to the DS-1 level.
• They provide a means of cross-connecting SONET/SDH channels through a software-driven, electronic common control cross-connect panel with a PC user interface. The routing of traffic through a DXC is accomplished through the use of payload pointers, which point to the payload in the OC-N frams and provide synchronization.
• DXCs also serve to connect thr fiber rings, which might take the form of a backbone ring and multiple subtended rings. DXCs perform the additional functions of monitoring and testing, network provisioning, maintenance and network restoral.
• Regenerators perform the same functions as their traditional electrical equivalents. It found under the skin of other SONET equipment, they are opto-electric devices that adjust the amplitude, timing and shape of the signal.

The advantages of SONET are as follows:

1. It offers the benefits of interconnectivity and interoperability between equipment of different manufacturers. The standardization translates into freedom of vendor choice and yields lower costs through competition.
2. SONET/SDH is extendable to the premises on a fully interoperable basis.
3. The increasingly availability of SONET local loops provide end-to-end advantages of enhanced bandwidth, error performance, dynamic allocation and network management.
4. It is a synchronous network and hence allows single-stage multiplexing and demultiplexing.
5. It is an integrated network on which all types of network can be tranported.
6. SONET/SDH offers the advantage of network resiliency through its inherent redundancy and self-healing capabilities.
7. The management features that are built into the SONET frame structure will help to maintain the circuits.
8. SONET offers tremendous security, as with fiber-optic transmission systems. Protection and fault tolerance are built into the SONET network design will translate into additional revenue for service providers.
9. It is a universal standard, non-proprietary, and employs a digital tranmission scheme. It is backward and forward compatible and can handle both current and future services.