As 400 Gbps wide area network systems now are touted, one thinks back about 20 years to another time when service providers were weighing different solutions for their WANs.
Back then, when the WAN standard for long-haul optical transmission was 2.5 Gbps, WAN operators were pondering the cost and value of upgrading to either 10 Gbps or 40 Gbps.
As I recall, back around 2000 the cost of upgrading to 10 Gbps was about 2.5 times the cost of greenfield 2.5 Gbps networks.
Again, as I recall, 40 Gbps networks cost more than four times the cost of 10 Gbps. That made the decisions in favor of 10 Gbps--especially given the amount of dark fiber availability--logical.
Assuming the same pattern holds, WAN operators needing to add more capacity will opt for 100 Gbps networks once the price premium over 40 Gbps is about 2.5 times.
How long it will take for the economics of 400 Gbps to reach levels where it makes more sense, for most service providers, rather than a 100 Gbps upgrade is the issue.
As always, the economics are easier for metro networks and within data centers. But long haul upgrade economics are more difficult.
As always, “how long can we afford to wait?” affects the decision. Recalling the huge amount of dark fiber put into place around the turn of the century, the other issue is whether it makes more sense to continue using 10 Gbps on multiple fibers rather than upgrading either to 40 Gbps or 100 Gbps in the WAN.
Unlike baseband standards, which tend to increase by an order of magnitude each major generation, optical transport systems often do not, in part because of the technical issues for optical waveguides such as chromatic dispersion and cost issues such as port density.
That was an issue 20 years ago when network operators were looking to upgrade capacity to 10 Gbps or further to 40 Gbps, for example. Typically, backwards compatibility tends to be a bigger issue for long-haul and access network operators than for operators of data centers.
And a jump from 1 Gbps to 10 Gbps was easier to finesse than a leap to 40 Gbps. The consideration often involves an upgrade over existing optical cabling networks that disturbs existing operations the least possible amount.
Often, an order of magnitude leap in bandwidth requires quite a lot of network element replacement, and therefore higher cost. Local networks in the past used multimode fiber, while long-haul networks use single mode fiber.
That has cost implications. The cost of using a four-by-10 Gbps solution is roughly four times as much as a 10 Gbps solution, for example, on multimode networks. On a multimode, short-range network, a 10X solution (10 Gbps upgrade to 100 Gbps) costs about 10X more.
On a single mode, long haul network, the cost of upgrading from 10 Gbps to 40 Gbps is 4X. But the cost of upgrading to 100 Gbps is far more than 20X.
The reason, at a high level, is that the upgrade by 4X generally uses some form of multiplexing the older existing standard, but using more fibers in a cable. A multimode fiber network upgrade might involve only a switch of line cards.
On such local networks, where a 10-Gbps uses two fibers, transmission on a 40-Gbps multimode fiber network uses as many as 12 fibers in a cable, for example. An upgrade from 10-Gbps to 100 Gbps means upgrading from a two-fiber cable to a 24-fiber cable.
A 10X upgrade tends to be less of an issue for local users such as data centers or even metro networking suppliers but a much-greater issue for connectivity providers with comparatively greater sunk investments in optical cabling infrastructure.
Cost issues always matter, which is why, at transition points, service providers often are asked to choose between one option generally available now and a higher-performance option expected in a few years.
At least, that is what I seem to recall from past evaluations made by WAN operators about core network upgrades.
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