[c-nsp] 1G (SFP) single-mode aggregation

Peter Rathlev peter at rathlev.dk
Thu Dec 15 08:44:56 EST 2011

We've been asked to look at how one could best cram a fair amount of SFP
links into not too much space. They are downlinks to FTTO switches. When
going full scale we're talking about maybe 2500 FTTO switches.

So the question is: How many (1G) SFP switchports can one hope to
terminate in a standard rack? And what is the smartest/cheapest/easiet
way to do it?

We've been looking at the things described further down. Any better
ideas than those? If anybody has good experience with non-Cisco
equipment I'd also love to hear about it. And if the idea of aggregating
as much as possible in a single rack is stupid, please tell me. :-)

- One rack holds two 6513E (20RU), each with 12 WS-X6748-SFP cards and
one supervisor, probably Sup2T. That's 1152 ports per standard 42RU
rack. The supervisor uplinks ports would be configured as 2*10G
port-channel, resulting in 20G uplink bandwidth per unit and thus about
120:1 total oversubscription, since each FTTO switch has 4 downlink
ports. Power budget would seem to be around 8 kW per rack if the numbers
from "show power" are used. (Anyone know what the real consumption is?)

- One rack holds 8 6504E (5RU), each with 3 WS-X6748-SFP cards and one
supervisor. That's also 1152 ports per rack. Using just one uplink would
result in about 60:1 oversubscription. This is more expensive, both
capex and power consumption, and somewhat more complicated. And we don't
really think that 60:1 is needed. A similar power budget of 8 kW seems
like a reasonable guess.

- One rack holds 40 WS-C3750X-24S (1RU). That's 960 ports per rack. We
would use them as 5 stacks of 8 members, each with one 2*10G MC
etherchannel as uplink, resulting in a total 80:1 oversubscription. The
power budget would also be around 8 kW, though for the 3750X Cisco
supplies the actual expected consumption with 100% load as around 110 W,
resulting in an expected consumption of 4.4 kW.

- We've also tried looking at the 4500E series, which we don't know much
about. I cannot seem to find any E-model 48 port SFP cards, only the
WS-X4448-GB-SFP which must have just a 6 GB/s fabric connection. There's
the WS-X4640-CSFP-E, which combined with the BX SFPs could deliver 80
"ports" per slot. One might shoehorn three 4710R+E (14RU each) into a
42RU rack, resulting in 1920 ports per rack. Total oversubscription
would be around 128:1.

Thank you.


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