Ethernet frames which are to be sent on the SDH link are sent through an "encapsulation" block (typically Generic Framing Procedure or GFP) to create a synchronous stream of data from the asynchronous Ethernet packets.
The synchronous stream of encapsulated data is then passed through a mapping block which typically uses virtual concatenation (VCAT) to route the stream of bits over one or more SDH paths.
As this is byte interleaved, it provides a better level of security compared to other mechanisms for Ethernet transport.
[citation needed] After traversing SDH paths, the traffic is processed in the reverse fashion: virtual concatenation path processing to recreate the original synchronous byte stream, followed by decapsulation to converting the synchronous data stream to an asynchronous stream of Ethernet frames.
Hence this provide a better throughput compared to native Ethernet transport.