Despite the evidence of the previous post, it wasn't all shopping today.
Still in revision for my OU Electromagnetism exam (SMT359) on October 15th, this morning I was working through the D field. I realised I had never properly understood it: the key is to realise that it's a kind of invariant as electric fields penetrate dielectrics and get reduced by the resulting polarisation effects.
At each point, the sum of the local field ε0E dielectric and the polarisation field Pdielectric equals the D field. Handy for calculation even if it doesn't seem to physically mean too much.
Some client work found me reviewing the current state of SDH technology. I knew about VCAT and LCAS and it was interesting that the standards guys are currently contemplating 160 Gbps (STM-1024). When I was working on SDH network design at Nortel about 15 years ago, the engineers were sceptical that 40 Gbps could ever be made to work.
SDH as a multiplexing technology is pointless unless the link speeds are a lot faster than the tributary rates. As these continue their inexorable rise - 100 Mbps, 1 Gbps - the signature SDH rates just have to get faster for those operators who still need it.