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prairiesky

join:2008-12-08
canada
kudos:2
reply to bemis

Re: Google Fiber and oversubscribing

google is using 10gpon for their networks. and can have a max of probably 32 subs per OLT (maybe 64 but doubtful). They probably can't go higher that 1 Gbit due to Ethernet adapter limitations. (don't know if the modems have integrated switches). So just on packages, they have a max over subscription ratio of 3.2:1. Which basically means they don't have to worry about it.

They could back haul each olt with 10 gig link and not have to worry because the olt can't handle over 10gig. Somewhere up the line, the 10G links will all come together, but like the end user situation, each one of them won't be full all the time. so the same ratios of the next level of over subscription would occur.

Gpon has 1.25 gig / 32 customers

cable has i think 128 /node and each channel is 55 mbits. So 8 channels is 440 mbit capacity. (may be wrong on max subs)

Bascially, the further back in the system you go, the higher the ratios get.



Killa200
Premium
join:2005-12-02
Southeast TN
Reviews:
·Charter

said by prairiesky:

google is using 10gpon for their networks. and can have a max of probably 32 subs per OLT (maybe 64 but doubtful). They probably can't go higher that 1 Gbit due to Ethernet adapter limitations. (don't know if the modems have integrated switches). So just on packages, they have a max over subscription ratio of 3.2:1. Which basically means they don't have to worry about it.

They could back haul each olt with 10 gig link and not have to worry because the olt can't handle over 10gig. Somewhere up the line, the 10G links will all come together, but like the end user situation, each one of them won't be full all the time. so the same ratios of the next level of over subscription would occur.

Gpon has 1.25 gig / 32 customers

cable has i think 128 /node and each channel is 55 mbits. So 8 channels is 440 mbit capacity. (may be wrong on max subs)

Bascially, the further back in the system you go, the higher the ratios get.

XG-PON1 (10g assym) has a split ratio of up to 128:1 on fiber, making gbit downstream at max 12.8:1 and upstream 51.2:1

GPon (2.5 / 1.25) has a maximum split of 64

Cable docsis is unlimited within reason of hardware. Average of reason is ~256 max. A QAM 256 channel in a 6mhz slot is 38Mbps of usable bandwidth.

prairiesky

join:2008-12-08
canada
kudos:2

said by Killa200:

XG-PON1 (10g assym) has a split ratio of up to 128:1 on fiber, making gbit downstream at max 12.8:1 and upstream 51.2:1

GPon (2.5 / 1.25) has a maximum split of 64

Cable docsis is unlimited within reason of hardware. Average of reason is ~256 max. A QAM 256 channel in a 6mhz slot is 38Mbps of usable bandwidth.

It highly varies, the numbers you're showing really aren't real world numbers. They're based on the receive sensitivities and theoretical splits that can happen and doesn't take into account insertion losses, cable losses, etc. So they're basing those claims on a 21 db spread between send/recieve sensitivities. A) it's not recommended to go right to the edges, B) it's highly improbable it would happen.

So if you get get it to 18 db, you'd get a max of 64 subs and withing 15, you'd get 32 which is much more likely and gives you some room for error.

as for cable, I was remembering the euro docsis specs which is 55 gross 50 usable.

b