Indeed,
maybe the situation (in many countries) when the Carrier
sells a lot of TDM services.
But
in general, packet services are enough these days for many
carriers/regions.
There aren't enough TDM services to warrant DWDM, nowadays.
The reason for DWDM is mainly being driven by Ethernet, and IP.
At any reasonable scale, it's actually pretty hard to buy a TDM
service, in most markets.
Additionally,
I am sure that in many countries/Metro it is cheaper to lay
down a new fiber than to provision DWDM, even if it is a
pizza box.
I disagree. Existing fibre may be cheap because it was laid down a
decade or more ago, en masse, by several operators. So the market
would be experiencing a glut, not because it is cheap to open up the
roads and plant more fibre, but because there is so much of it to
begin with.
At worst, there is still enough duct space that the operator can
blow more fibre. But when that duct gets full, and there are no more
free ducts available, or another route needs to get built for
whatever reason, it is a rather costly affair to open up the roads
and trunk some fibre, in any market.
So no, DWDM is not more expensive, if you are delivering services at
scale. It is actually cheaper. It is only more expensive if you are
small scale, because in some markets, the fibre glut means you can
buy dark fibre for cheaper than you can light it with DWDM. But this
is a situation unique to small operators, not large ones.
The colored interface is still very expensive.
This only matters for the line side.
For client-facing, it's not a drama. And you typically buy more
optics for the client side than you do the line side.
Of
course, there are some Cities (not “towns”) where it is very
expensive or maybe even impossible to lay down a new fiber.
Yes,
in the majority of cases, it is cheaper to lay down fiber.
I think what you mean to say is that in the majority of cases where
there is fibre glut, and dark fibre is a market option, buying fibre
is cheaper than lighting it with DWDM. This is true. But I think
that on a global scale, this is the exception, not the rule.
In general, you are not likely to be able to buy dark fibre, cheaply
or otherwise, if you look at all markets in the world.
Hence,
the importance of DWDM for the Metro is overestimated.
Again, only if you are small scale.
If you are a large scale operator with as many IP/Ethernet customers
as you have Transport, DWDM is essential.
Use
only routers. Provision enough fiber. Have always 1 router
hop to the aggregation (hub-spoke topology), no routers
chaining in the ring.
If
fiber is not enough – then use normal DWDM with an external
transponder. Routers would be still in hub-spoke topology.
Yeah, you sound like an equipment vendor whose main customers are
incumbent telco's in a few rich markets :-).
The life of the average operator, around the world, is far less
glamorous.