Why not just use TCP? Well you probably are but TCP is just a protocol that has to run on some sort of network transport. SONET is a network transport that carries TCP-based traffic. Ethernet, InfiniBand and Fibre Channel (FC) are all interfaces. Telephone carrier-based networks have been built for many years on SONET technology that typically employs optical fiber -- particularly for spanning great distances.
So, to summarize, you have optical fiber (maybe copper) at the lowest level. The cabling then supports a network like SONET with Ethernet, FC or InfiniBand mapped directly onto it. You increase bandwidth using some form of multiplexing. On a SONET network, you can also allocate bandwidth into OCx, such as OC3, OC12 or other subdivisions, and those, in turn, can carry different traffic. While TCP (or TCP/IP) is your virtual network, you still need the physical network -- what's inside that "cloud" -- to support the protocols.
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Go back to the beginning of the Storage Area Network FAQ Guide.
This was first published in January 2007