As the picture show above, it is the high level architecture which requires to run the entire UCS solution from Cisco. Not necessary every environment will require Nexus 7000, it is meant for large scale networking environment. You may go with various different switches to replace the Nexus 7000 in the picture depend on your requirement. In the current UCS release, the UCS 6100 interconnect fabric will integrate with the MDS 9000 series Fiber Channel environment or others compatible FC switches. This allow UCS blade I/O to be consolidated with CNA with 10Gbps per connection as FCoE.  This had significant reduce the physical cabling requirement per blade chassis.