OTN and SONET
Posted by Paul on March 22, 2006
Can you expalin to me the difference between SONET and Optical Transport Network? I was thinking the OTN is just the upper layer (transport layer)of SONET. However, I read somewhere, it says the OTN wraps the SONET frames. This sounds like GFP. I am totally confused.
I will appreciate you can help me to understand these two items.
Paul Jean
SONET and Optical Transport Network (OTN) are both framing formats designed for optical networks. They both consist of an information payload and overhead information. The overhead information of both standards provides a rich set of management functions, including performance management, fault notification, fault localization, and management communications. Both include a multiplexing hierarchy, although the SONET hierarchy has a finer granularity than the OTN hierarchy. The rates specified by the OTN were chosen to allow it to carry specific SONET signals as a payload. These are the 2.5G, 10G and 40G SONET signals. When OTN carries SONET it does so transparently, without changing any of the SONET overhead information. This is particularly useful in wholesale network applications, where one carrier operating a SONET network procures a transmission segment from another carrier. Here transparency to management information and timing are critical to avoid SONET interoperability problems. There are three OTN rate signals defined so far, each somewhat higher than the corresponding 2.5G, 10G and 40G SONET signals. Additionally the OTN framing format includes Forward Error Correction, a feature that helps improve reach and reliability of optical transmission at high rates -- rates of 10G and beyond.
While the OTN conveniently accommodates SONET, it also can be used to carry other signals, including Ethernet and storage to name a few. The increasing interest in OTN today is driven by an application where it is used to carry a native 10 Gigabit Ethernet signal. The use of OTN to encapsulate 10 GE results in a transmission solution with the management benefits of SONET at the price points of Ethernet.
Further, though your question is about SONET, an ANSI (North American) standard, it is important to note that OTN is a global standard that has been accepted by both ANSI and ETSI (European standard). This means that no longer will SONET and SDH networks compete and require translation when the circuits cross the ocean. Instead, a circuit that is terminated in Europe and Asia will be the same format as North & South America -- a feature that will benefit everyone.
