Editing Synchronous optical networking (section)

==Next-generation SONET/SDH==
SONET/SDH development was originally driven by the need to transport multiple PDH signals—like DS1, E1, DS3, and E3—along with other groups of multiplexed 64&nbsp;kbit/s [[pulse-code modulated]] voice traffic. The ability to transport ATM traffic was another early application. In order to support large ATM bandwidths, concatenation was developed, whereby smaller multiplexing containers (e.g., STS-1) are inversely multiplexed to build up a larger container (e.g., STS-3c) to support large data-oriented pipes.

One problem with traditional concatenation, however, is inflexibility. Depending on the data and voice traffic mix that must be carried, there can be a large amount of unused bandwidth left over, due to the fixed sizes of concatenated containers. For example, fitting a 100&nbsp;Mbit/s [[Fast Ethernet]] connection inside a 155&nbsp;Mbit/s STS-3c container leads to considerable waste. More important is the need for all intermediate network elements to support newly introduced concatenation sizes. This problem was overcome with the introduction of Virtual Concatenation.

[[Virtual concatenation]] (VCAT) allows for a more arbitrary assembly of lower-order multiplexing containers, building larger containers of fairly arbitrary size (e.g., 100&nbsp;Mbit/s) without the need for intermediate network elements to support this particular form of concatenation. Virtual concatenation leverages the [[X.86]] or [[Generic Framing Procedure]] (GFP) protocols in order to map payloads of arbitrary bandwidth into the virtually concatenated container.

The [[Link Capacity Adjustment Scheme]] (LCAS) allows for dynamically changing the bandwidth via dynamic virtual concatenation, multiplexing containers based on the short-term bandwidth needs in the network.

The set of next-generation SONET/SDH protocols that enable Ethernet transport is referred to as [[Ethernet over SDH|Ethernet over SONET/SDH]] (EoS).