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Features of SONET and T1

This section explains why SONET differs from other digital transport systems. First, SONET is an optical-based carrier (transport) network utilizing synchronous operations between the network components/nodes, such as multiplexers, terminals, and switches. SONET's high speeds (some systems operate at the gigabit rate) rely on high-capacity fiber. Much of the T1 technology is geared toward the use of copper (twisted pairs) media and operates at more modest transmission rates.

As just stated, the SONET network nodes are synchronized with each other through very accurate clocking operations, ensuring that traffic is not "damaged," or lost due to clocking inaccuracies. T1 clocking systems are very accurate, but are not as reliable as SONET systems. Later discussions explain how synchronous networks experience fewer errors than the older asynchronous networks and provide much better techniques for managing payloads.

SONET is quite robust and provides high availability with self-healing topologies. In the event a SONET link is lost due to node or fiber failure, SONET can recover by diverting the traffic to back-up facilities. Most T1 systems can be configured for backup, but "robustness" is not an inherent part of the original design of the T1 architecture.

SONET and its ITU-T counterpart SDH are international standards. As such, SONET paves the way for heterogeneous, multivendor systems to operate without conversions between them (with some exceptions).5

SONET uses powerful, yet simple, multiplexing and demultiplexing capabilities. Unlike T1, SONET gives the network node a direct access to low-rate multiplexed signals, without the need to demultiplex the signals back to the original form. In other words, the payloads residing inside a SONET signal are directly available to a SONET node.

Because of these capabilities, SONET efficiently combines, consolidates, and segregates traffic from different locations through one machine. This concept, known as grooming, eliminates back hauling6 and other inefficient techniques currently being used in transport networks. In older transport network configurations, grooming can eliminate back hauling, but it requires expensive configurations (such as back-to-back multiplexers that are connected with cables, panels, or electronic cross-connect equipment).

SONET provides extensive operations, administration, maintenance, and provisioning (OAM&P) services to the network user and administrator. Indeed, about 4% of the bandwidth in a SONET network is reserved for OAM&P. A T1 system only allows one bit per 193 bits for OAM&P. With this comparison in mind, it is easy to conclude that SONET has the capability for more extensive and powerful network management operations than T1.

Finally, like T1, SONET employs digital transmission schemes. Thus, the traffic is relatively immune to noise and other impairments on the communications channel. Of course, with the use of optical fibers, random errors on the channel are very rare.

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