It has been at least eight years since transport equipment vendors started talking publicly about 40g solutions. Yet 40g has made little progress achieving acceptance in the market. Why in all this time has 40g not been able to displace 10g in the market ? The answer is simple : to date, 40g solutions offered by industry equipment vendors are not economically sensible. Given this, other than a number of feasibility experiments, 40g deployments have been limited.
Let's look at the basic market requirements for 40G that would make a 40G solution economically sound.