What are the typical speeds used on fibre links between COs in North American and elsewhere ? I realise that there are special cases, such as Shaw using WDM to reach 400gigabits/sec in a link in Western Canada. But what are the most common speeds ? Is WDM in common use to multiplex multiple 10gbps, 40gbps links ? Or is that used mostly for intercity trunks and intra-city trunks tend to not bother with WDM because of ample supply of fibre ? Do telcos typically quickly upgrade fibre strands to newer speeds, or are there still many strands handling only 100mbps or 1gbps between COs because telcos never got around to upgrading legacy equipment/services (such as ATM etc) ? Also in terms of costing WDM, would one typically have a card that has the multiple colours in the card and outputs a single multi-colour signal or would one typically have separate cards for each colour and then use a WDM "filter" to combine/separate colours onto the single strand ?