Re: [HSSG] 40G MAC Rate Discussion
I disagree with some of the assumptions made below, in
particular the difference between 40G (4x10G as one pipe) and 40G
LAG (4x10G independent streams) for parallel
implementation. As Scott Kipp said the cost of a 40G QSFP (which
does not include any CDR's) is likely to be somewhat more than the cost of 4 10G
SFP parts. The fiber interconnect for the SFP's are duplex LC
whereas the QSFP has an MTP (I'm not sure what the relative cost of 4 duplex LC
jumpers versus an MTP jumper is, but I doubt the difference is
significant.). For the link itself the fibers are likely to be
similar. In short I think that any significant cost differences are
related to the cost of the IC's that are required to mux/demux the signals for
either 40G transmission or whatever is needed for LAG. There is no
factor of two difference between these options and what difference there is may
be in the other direction.
On the relative costs of the 100G versus 40G for parallel
solutions I think you are fairly close although you may have over-estimated
the difference in cost between the solutions for the PMD's. Assuming
we are talking 10x10G and 4x10G parallel solutions I would expect that the costs
would be similar per 10G stream, with the 4x10G implementation being somewhat
higher on that metric. (There are complexities in having Tx and Rx in the
same package, and the total number of components for the two solutions is
smaller per 10G stream for the 100G). My estimate is that the
relative costs of the two PMD's would be between 2x and 2.5x larger for the
100G. (ie cost per bit is either equal or somewhat less for the 100G
solution which is what you assumed).
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I'm returning to an item in the
discussion from April 6, where Matt Traverso wrote:
> - I'd like to hear a comment / perspective from the
> manufacturers on the utilization rate of the ribbon fiber
> For a 4x10G MMF approach presumably 8 strands in the 12 ribbon
> be used 4 for TX and 4 for RX. For a 10x10G MMF approach it
> 2 @12 with 10 @ Tx and 10 @ RX. What does this do to the
> usage rate metrics of MMF cabling?
of my response to your inquiry are straight forward and easy to provide without
cause for concern. More in depth response on cost gets tricky and I do not
want to cross over the line our chair has reminded us of. So I have
modified it a few times. As this material developed, it appears that it
could be the basis for a presentation. Hopefully it is acceptable and
For parallel MMF
connectivity the cost of the cabling for 4x10G will be half that of 10x10G
simply because 12-fiber cabling is used for the former and 24-fiber cabling is
used for the latter. Also the patch panel density (circuits per unit area)
will be double for the former compared to the latter. This may also be the
case for active equipment panel density. They both use the same cabling
componentry, but the latter requires twice as much.
The effect of this difference on the total cost of the
system is commensurate with the projected cost difference between the 40G and
100G PMDs, as detailed below.
April 9 Scott Kip wrote:
> I have heard that
the cost of a 5 Gig QSFP are
> comparable to the cost of a single XFP or
approximately 10 4-Gig SFPs.
> If the QSFP rolls out in relatively high
volumes, the QSFPs are expected
> to approach the cost of 4 SFPs at
relationship is true and from what I know of such things, then the cost to the
end user of an installed, tested, warranted, typical-length, 12-fiber, MM
structured cabling link, consisting of a cable terminated at patch panels plus
array-terminated cords on each end, is in the neighborhood of today's cost of a
pair of 20G QSFPs to an OEM (e.g. server, switch, router maker). In the
analysis that follows I'll assume that the future 40G QSFPs are 2x the cost of
20G QSFPs (i.e. 2x XFP cost), and that 100G PMDs are 5x XFP cost (trying to be
consistent with jewell_01_0107.pdf where 100G cost = 4x XENPAK cost). In
order to compare cabling and PMD costs at the end user level, a PMD cost
adjustment factor to account for integration by the OEM must be applied.
The same factor is applied to all cases. The tabulations that follow
should help make the basic trends over time and between data rate choices
XFP cost to the OEM as the monetary unit, the basic end user projected cost
cable cost 1 2
total cost 7
Here cabling cost is ~1/7
(14%) to ~2/17 (12%) of total cost. 40G total cost is 41% of the 100G
In about three to four
years time (assuming both 40G and 100G MM PMDs have the same initial
availability date) the cost is:
rate 40G 100G
PMD cost 3 7.5
cable cost 1
Here cabling cost is ~1/4 (25%) to ~2/9.5 (21%) of total cost. 40G
total cost is 42% of the 100G total cost.
If the 40G PMD is available ahead of 100G PMD, then the 40G solution
should be relatively lower in cost.
With the caveats of the above assumptions, the conclusion is that the 40G
QSFP PMD should offer significant advantage in cost for the total channel
relative to the 100G PMD from both transceiver and cabling perspectives.
The relative total cost ratio appears to stay fairly constant, even while
the cabling costs become relatively more significant. This is because the
ratio of the cabling costs is similar to that of the corresponding PMD costs.
To illustrate, if dominated completely by PMD cost differences, the ratio
would be 40%, while if totally dominated by cabling cost differences, the ratio
would be 50%.
If your metric of
value is cost per gigabit, the two scenarios practically equate. But if
your metric is absolute cost, then one would not have to pay for more than one
needs with a 40G solution.
offer another perspective, comparing to a LAGed 10G scenario:
LAG factor 4
the 40G solution provides a very favorable cost
comparison, at a cost that is a bit more than half of the 4xLAG 10G
As far as the other part of
your question regarding usage rate metrics for the cabling, as you can see from
the above analysis, leaving four dark fibers per cable (8 out of 12 active with
40G) instead of 2 (10 out of 12 active with 100G) does not have significant
impact, since the user procures the array-terminated cabling on a modulo 12
basis. Utilization efficiency can make a difference if the modulo-12
cabling supports more than one application at a time. For example, it
makes a cost difference if there are unused fibers for applications where we
deploy 2-fiber circuits over a 12-fiber cable. The 12-fiber cabling gets
amortized over one to six circuits depending on utilization.
Both the 40G and 100G scenarios have
degraded capacity utilization in the cable compared to 10GbE. Today a
12-fiber cable supports six 10GbE circuits for a capacity of 60G. That
same cable will support only 40G or 50G capacities for the 40G PMD or 100G PMD
respectively. But in both scenarios there are far fewer patch cords and
port interfaces to manage than for 10G links aggregated to match the comparative
data rates, and the overall cost for either of the higher-rate solutions should
be very favorable compared their LAGed counterparts.
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