[802.3_100GNGOPTX] Emerging new reach space

[Jack Jewell <jack@xxxxxxxxxxxxxx>]

Following last week's meetings, I think the following is relevant to frame our discussions of satisfying data center needs for low-cost low-power interconnections over reaches in the roughly 150-1000m range. This is a "30,000ft view,"without getting overly specific. 

Throughout GbE, 10GbE, 100GbE and into our discussions of 100GbE NextGenOptics, there have been 3 distinct spaces, with solutions optimized for each: Copper, MMF, and SMF. With increasing data rates, both copper and MMF specs focused on maintaining minimal cost, and their reach lengths decreased. E.g. MMF reach was up to 550m in GbE, then 300m in 10GbE (even shorter reach defined outside of IEEE), then 100-150m in 100GbE. MMF reach for 100GbE NextGenOptics will be even shorter unless electronics like EQ or FEC are included. Concurrently, MMF solutions have become attractive over copper at shorter and shorter distances. Both copper and MMF spaces have "literally" shrunk. In contrast, SMF solutions have maintained a 10km reach (not worrying about the initial 5km spec in GbE, or 40km solutions). To maintain the 10km reach, SMF solutions evolved from FP lasers, to DFB lasers, to WDM with cooled DFB lasers. The 10km solutions increasingly resemble longer-haul telecom solutions. There is an increasing cost disparity between MMF and SMF solutions. This is an observation, not a questioning of the reasons behind these trends. The increasing cost disparity between MMF and SMF solutions is accompanied by rapidly-growing data center needs for links longer than MMF can accommodate, at costs less than 10km SMF can accommodate. This has the appearance of the emergence of a new "reach space," which warrants its own optimized solution. The emergence of the new reach space is the crux of this discussion.

Last week, a straw poll showed heavy support for "a PMD supporting a 500m reach at 25% the cost of 100GBASE-LR4" (heavily favored over targets of 75% or 50% the cost of 100GBASE-LR4). By heavily favoring the most aggressive low-cost target, this vote further supports the need for an "optimized solution" for this reach space. By "optimized solution" I mean one which is free from constraints, e.g. interoperability with other solutions. Though interoperability is desirable, an interoperable solution is unlikely to achieve the cost target. In the 3 reach spaces discussed so far, there is NO interoperability between copper/MMF, MMF/SMF, or copper/SMF. Copper, MMF and SMF are optimized solutions. It will likely take an optimized solution to satisfy this "mid-reach" space at the desired costs. To repeat: This has the appearance of the emergence of a new "reach space," which warrants its own optimized solution. Since the reach target lies between "short reach" and "long reach," "mid reach" is a reasonable term

Without discussing specific technical solutions, it is noteworthy that all 4 technical presentations last week for this "mid-reach" space involved parallel SMF, which would not interoperate with either 100GBASE-LR4, MMF, or copper. They would be optimized solutions, and interest in their further work received the highest support in straw polls. Given the high-density environment of datacenters, a solution for the mid-reach space would have most impact if its operating power was sufficiently low to be implemented in a form factor compatible with MMF and copper sockets.

Cheers, Jack