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Next-Generation SDH/SONET
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Legacy SDH has always been a circuit-oriented technology, and as such was not optimized for data transport. Owing to the shortcomings of legacy SDH/SONET, and the rapid increase
in demand for data services, there were number of cries to replace SDH/SONET with 'superior' packet-friendly technology. However, it was soon realized that evolving SDH/SONET to
be more packet-friendly was a much better option that replacing it. The reasons behind this line of thinking were as follows:
- For one thing, SDH/SONET's installed base is too large for carriers to simply walk away from. Though arguments have been made for "cap-and-grow" strategies that favor
all-optical or native Ethernet transport, most operators cannot associate enough predicted revenue with that new overlay to justify capping growth altogether on their profitable
SDH/SONET networks.
- Another factor is the tremendous growth in data transport and services. Nearly all of this data remains transported within SDH/SONET (Frame Relay, ATM, Packet over Sonet,
Ethernet over Sonet, etc.), and it is this very multiplicity of data formats that is driving carriers to standardize on a unified method of transport. Though services may begin
as IP, Ethernet, Fiber Channel, Frame Relay, or ATM, a carrier's capex and opex can be greatly improved with a common transmission solution that has some degree of data
intelligence.
The efforts to evolve SDH/SONET to become more data-friendly resulted in the Next-Generation SDH/SONET. Next-generation SDH/SONET allowed the service providers to enhance their portfolio by including Ethernet Leased Lines along with TDM leased lines. Apart from increasing packet-awareness of SDH/SONET, these changes also added dynamism and ease of provisioning to the legacy SDH/SONET. Next-generation SDH/SONET, which came into existence around 2002, had 3 important components: Virtual Concatenation (VCAT) (ITU-T G.707/Y.1322 and G.783), Link Capacity Adjustment Scheme (LCAS) (ITU-T G.7042/Y.1305) and Generic Framing Procedure (GFP) (ITU-T G.7041 (2001) & ANSI T1.105.02 (2002)).
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