The optical fiber as medium for data transmission has enabled the possibility of a very elevated data rate up to 10 or 40Gbps per fiber. However the stack of protocols architecture throughout the OSI layers prevents the full use of the bandwidth in practice.
The different protocols in the stack are necessary to provide required functionalities related to the control plane, protection/restoration, packet delineation and synchronization.
Originally between the IP layer and the SDH layer there was an ATM layer that would provide most of those functions but presented two main drawbacks: 25% overhead per frame and the assembling and disassembling function requires processing resource limiting the actual bandwidth to 642Mbps.
The alternative and adopted possibility was to use IP layer directly over SDH. However with this new technology basic and required functionalities of the layer 2 were lost. The use of the PPP (point-to-point Protocol) and the HDLC (RFC 1662) were required for packet delineation and synchronization. In this architecture the packet delineation is performed by the use of flags, in order to protect the flag byte in SDH virtual container, byte stuffing is performed. The resource required to process byte stuffing limits the real bandwidth to up to 2.4 Gbps.
The current alternative is to migrate to WDM where the multiplexing is done in the wavelength sphere and not time based as it is in the SDH. To prevent the need for byte stuffing the adoption of Generic Framing Procedure (GFP), which can be easily implemented in an heterogeneous network.
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