Routed optical networks

Wed May 3 04:09:08 UTC 2023

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.
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