On 5/2/23 07:28, Vasilenko Eduard via NANOG wrote:
The incumbent carrier typically has enough fiber strands to avoid any
colored interfaces (that are 3x expensive compare to gray) in the Metro.
Metro ring typically has 8-10 nodes (or similar). 16-20 strands of
fiber were not possible to construct anyway – any cable is bigger.
It is the same cost to lay down fiber on 16 strands or 32.
Hence, PTT just does not need DWDM in Metro, not at all. Hence, the
DWDM optimization that you are talking about below is not needed too.
This may or may not always be the case. Especially for large carriers,
where there could be a requirement to sell some of those dark fibre
pairs to large customers (think the content folk coming into town,
e.t.c.), they may no longer have the priviledge of having plenty of free
fibre in the metro. Or if they did, the rate of traffic expansion means
they burn through those fibre pairs pretty quick.
10Gbps isn't a lot nowadays, and 100Gbps may start to push the limits
depending on the size of the operator, the scope of the Metro-E ring and
the level of service that needs to be maintained during a re-route (two
available paths in the ring could balance 100Gbps of traffic, but if one
half of that ring breaks, the remaining path may need to carry a lot
more than 100Gbps, and then packets start to fall flat on the floor).
At that scale, DWDM in the metro will make sense, at least more sense
than 400G-ZR, at the moment.
If you rent a single pair of fiber then you need colored interfaces to
multiplex 8-10 nodes into 1 pair on the ring.
Then the movement of transponders from DWDM into the router would
eliminate 2 gray interfaces on every node (4 per link): one on the
router side, and another on the DWDM side.
Overall, it is about a 25% cost cut of the whole “router+DWDM”.
Some operators would also be selling Transport services in or along the
metro, and customers paying for that may require that they do not cross
a router device.
It is still 2x more expensive compare to using additional fiber
strands on YOUR fiber.
There are plenty of DWDM pizza boxes that cost next to nothing. At
scale, the price of these is not a stumbling block. And certainly, the
price of these would be far lower than a router line card.
By the way, about “well-defined stack of technologies”:
NMS (polished by SDN our days) should be cross-layer: it should manage
at the same time: ROADM/OADM in DWDM and colored laser in Router.
It is a vendor lock up to now (no multi-vendor). Hence, 25% cost
savings would go to the vendor that has such NMS, not to the carrier.
Technology still does not make sense because no multivendor support
between the NMS of one vendor and the router or DWDM of another.
Looking at the NMS history, it would probably never be multi-vendor.
For that reason, I am pessimistic about the future of the colored
interfaces in routers (and alien lambdas in DWDM). Despite a potential
25% cost advantage in eliminating gray interfaces.
OpenROADM is a good initiative. But it seems it's to be to Transport
equipment vendors what IPv6 and DNSSEC is to the IP world :-).
Mark.
