06-08-2010, 13:34
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#31
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Inactive
Join Date: Sep 2008
Location: Lincoln
Age: 50
Services: 350Mb (Hub 3) | TV: 2x TiVo on XL | Phone
Posts: 1,051
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Re: 50MB - 10MB Upload ?
It has dropped back to 5MB upload now.
Just checked the modem config page.
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06-08-2010, 13:49
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#32
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Sad Doig Fan!
Join Date: Aug 2007
Location: Barry South Wales
Age: 70
Services: With VM for BB 250Mb service.(Deal)
Posts: 11,850
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Re: 50MB - 10MB Upload ?
Trial over then, bit of a bummer for you. 
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06-08-2010, 14:32
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#33
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Inactive
Join Date: May 2004
Location: St Albans
Services: Tivo, 50Mbps
Posts: 134
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Re: 50MB - 10MB Upload ?
Quote:
Originally Posted by Ignitionnet
There is no requirement to ack every single packet, I'm not sure where this comes from. TCP does, by default, do cumulative acknowledgement - an ack implicitly acknowledges every transmitted packet up until the sequence number the acknowledgement is supplied for.
The exception to this is misconfigured TCP stacks.
If one is acknowledging every single packet 100Mbit requires 3.6Mbit of upstream as a bare minimum, which would, yes, mean that 1.75Mbit is not enough for the 53Mbit downstream on the 50M.
HTH.
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TCP stacks *used* to acknowledge every packet. These days, almost all TCP stacks implement delayed ACK which will (as the name suggests) delay ACKs, but SHOULD send at least one for every two packets. You therefore need approximately 1.8Mbps (by your calculation) for a 100Mbps downstream. It's probably possible to configure delayed ACK to acknowledge less often, but the default is always one ACK per two packets received.
http://freesoft.org/CIE/RFC/1122/110.htm
That said, it's assuming you're downloading efficiently with a 1500 btye MTU. As an example, my firewall pegs the TCP MSS to 1300 for various reasons, so in my case I'd need a little more upstream for my ACKs.
I'd also quite like to use the downstream while backing up my computer to Mozy!
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06-08-2010, 15:31
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#34
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Inactive
Join Date: Jun 2008
Location: Leeds, West Yorkshire
Age: 47
Posts: 13,995
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Re: 50MB - 10MB Upload ?
RFC2581, amongst others, deals with stretch acks.
Virgin can also skimp by using TurboDOX. I believe it's being re-enabled once fixed in the firmware. This plays some games with TCP streams to the extent where considerably less than 1.8Mbps is required from the client to saturate 100Mbps, and Payload Header Suppression further reduces the amount of data going across the actual coax.
Academic anyway, it'll be 100:10 so no problems!
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07-08-2010, 09:04
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#35
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Inactive
Join Date: Jul 2005
Location: Plymouth
Age: 37
Services: Sky HD Multiroom, VM XL Phone, VM XXL BB
Posts: 654
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Re: 50MB - 10MB Upload ?
I would die for a 10:1 connection ratio
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07-08-2010, 09:44
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#36
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cf.mega poster
Join Date: Sep 2003
Posts: 12,048
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Re: 50MB - 10MB Upload ?
Quote:
Originally Posted by Ignitionnet
The standard upgrade for 100Mbit and 10:1 ratio is 2 resegmentations and a doubling of channel width on overlay network, increasing upstream bandwidth by a factor of 8 and quadrupling downstream.
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Good news, lets hope this is stuck to and not changed come commercial rollout.
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