SONET was created to solve a specfic problem that occured in the early days of the development of fiber networks. During the early days of the development of fiber network, there was issue with the fact that different carriers used different equipment and rate. Thus, if two network required a connection to one another, custom engineering of the network were required to permit the two carriers to establish a connection between their networks.
SONET created a common set of rate and a common frame structure that all network and carrier could use. Thus, a signal could travel from one network to another across multiple SONET carrier without requiring any additional engineering effort at the boundary between the network. The chart displays the relationship of the various rate of SONET to one another.
SONET: A Simple Way to Connect Networks
The chart display the rates in a hierarchy from the smallest to the largest rate. While it is not necessary for engineer and network designer to memorize the rates on the chart, it is important for engineer to understand that each rate on the chart is an even multiple of the rate listing immediately above it. This predictability in the setup of the rate allows for the addition of new capacity to a network while leaving intact the framing and protection function of the SONET data frame.
The SONET rate on the chart also display the relationship between the rate that are used in North America and the equivalent rate in other country that use the SDH (Synchronous Digital Hierarchy) system. Different bodies created the SONET and SDH system during different time period. As a result of the two system being built different, rate within the SONET system are not the same as those within the SDH system.
For instance, the OC-3 rate in the SONET system is the same as the STM-1 rate in the SDH system. As a result, SONET and SDH data can travel across ocean and continent to its destination without having the data being divided into smaller data unit along the way. SONET also include a protection system for its data network.
SONET ring use automatic protection switching to move data to an alternative path in the network in less than fifty millisecond. Because voice data, financial data, and utility service cannot permit for interruptions in the data movement between their originating network and destination network, data must be transferred at a rate of less than fifty millisecond. Thus, the overhead byte of its data frame provides protection for SONET network.
These overhead byte contain the information necessary to establish the automatic protection switch of the network. Another important use of SONET is that T-carrier and E-carrier signal can be contained within a SONET container. For instance, a T1 signal that used copper telephone line can be contained within SONET transmission path, and the individual receiving that signal wont be aware of the fact that the signal is contained within a SONET path.
This kind of containment allows for the old carrier to continue to use the same circuit for their customer. Additionally, the ability to contain the T-carrier and E-carrier signal within SONET container also permits those network to carry both voice and data signal. The SONET data frame contain 8,000 frame every second.
Each data frame contain a certain amount of overhead data, as well as payload data. The payload data is allowed to “float” within the data frame, which mean that certain byte within the frame contain information regarding where the payload data begin within that frame. These byte are critical to enabling SONET to incorporate add-drop multiplexer into its system.
These add-drop multiplexer are essential for allowing the insertion of data into a data frame without having to interrupt the remainder of the data transmission. SONET is now largely obsolete as a system for transmitting data. Instead, packet-based and optical transport system are the main technology that are used for data communication.
These new system offer more data capacity and bandwidth than SONET ever did. Nonetheless, many SONET system are still active and in use. For instance, the protection system and operation channel are already in place for these system.
Thus, any effort to eliminate SONET would of have to prove to the SONET network that the new system has the same restoration time as SONET has, as well as that the new system has the same visibility into the data frame that SONET is capable of providing. Thus, it is likely that SONET will continue to be used as long as the physical SONET fiber that contain the data are still in use. The hierarchy for the rate within SONET also serve two different category of individuals who work within the SONET network.
Engineer can use the SONET hierarchy to determine the data rate that will best accommodate the traffic that is to be carried along that network. Thus, engineer can determine the data rate required to meet the demand of the customer that are to be served by that network. Additionally, those SONET operator that are responsible for maintaining the SONET network can use the hierarchy to determine which type of legacy signal are still traveling along those network.
Both engineer and operator, therefore, benefit from the same rule set for the SONET system. The main concept illustrating by the main chart in this SONET system is that there is a base rate for SONET that can be multiplied to create the remaining rate within the system. Additionally, the base rate of SONET also can be protected in the same fashion as the other rate within the system.
Thus, SONET was able to develop system for metropolitan area as well as transoceanic data communication link. While the system and technology that are installed within SONET network may have changed over time, the requirements for restoration of data to each SONET network is the same as it was when SONET was initially created.