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Luminary

QoS and the "Broadcom Cut Through Forwarding feature"

Hi,

 

I've got a r7000 which works well with the V1.0.5.60_1.1.86 firmware. I've a USB drive and a Buffalo NAS connected to it. I have been poking around the forums and came across a post which recommended to disable QoS since it impedes the "Broadcom Cut Through Forwarding feature". I can not find much about that feature so I was wondering why I need it to the extent that I should disable QoS? I have a 150 mbps down connection if that matters in this context. I'm not much of a gamer but I do stream media from the NAS all the time to computers and TVs, and then there's of course Netflix which runs on one or more devices at all times. Othewise the good 'ol Internet use on phones laptops and desktops. 

 

//C

//CD
Message 1 of 7

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Guru

Re: QoS and the "Broadcom Cut Through Forwarding feature"

Cut Through Forwarding (CTF) is fancy speak for a feature that forwards traffic through the router using the built-in Broadcom chip.  CTF enables the router to forward traffic in the most efficient manner possible.  It is true that enabling QoS disables CTF.  This forces traffic to be handled by the router's CPU, which cannot forward traffic as efficiently as the Broadcom chip.  This has the biggest impact on those with Gigabit Internet service.  Without CTF, the R7000 can only handle about 450 Mbps, give or take.

 

Since your Internet service is 150 Mbps, there may not be a noticeable difference without CTF.  But it could also be said that QoS may not benefit you much either.  QoS is generally more useful when Internet speeds are lower.  It works by managing Internet traffic flows and prioritizing the most important ones. With 150 Mbps, several Internet media streams can easily be accommodated with plenty of bandwidth to spare, so there's no need to prioritize traffic.  QoS offers no benefit at all for traffic streamed from a local NAS.

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Message 2 of 7

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Guru

Re: QoS and the "Broadcom Cut Through Forwarding feature"

Cut Through Forwarding (CTF) is fancy speak for a feature that forwards traffic through the router using the built-in Broadcom chip.  CTF enables the router to forward traffic in the most efficient manner possible.  It is true that enabling QoS disables CTF.  This forces traffic to be handled by the router's CPU, which cannot forward traffic as efficiently as the Broadcom chip.  This has the biggest impact on those with Gigabit Internet service.  Without CTF, the R7000 can only handle about 450 Mbps, give or take.

 

Since your Internet service is 150 Mbps, there may not be a noticeable difference without CTF.  But it could also be said that QoS may not benefit you much either.  QoS is generally more useful when Internet speeds are lower.  It works by managing Internet traffic flows and prioritizing the most important ones. With 150 Mbps, several Internet media streams can easily be accommodated with plenty of bandwidth to spare, so there's no need to prioritize traffic.  QoS offers no benefit at all for traffic streamed from a local NAS.

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Message 2 of 7
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Prodigy

Re: QoS and the "Broadcom Cut Through Forwarding feature"

Traffic Monitoring, QoS and PPPoE all affect CTF.
Message 3 of 7
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Luminary

Re: QoS and the "Broadcom Cut Through Forwarding feature"

Thanks! There's both up and downlink QoS and I have 20 up. Does that make a difference? Could there be a reason to use only uplink QoS?
//CD
Message 4 of 7
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Guru

Re: QoS and the "Broadcom Cut Through Forwarding feature"

If you do a lot of uploading, then uplink QoS could help.  But the majority of traffic is in the downstream direction, for obvious reasons.

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Luminary

Re: QoS and the "Broadcom Cut Through Forwarding feature"

What I do a lot of is VOIP like Viber and Skype which does include uploads of course. Otherwise not much upload.
//CD
Message 6 of 7
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Guru

Re: QoS and the "Broadcom Cut Through Forwarding feature"

Conferencing apps typically don't use much bandwidth, even with video.  Uploading files is the biggie.  If you seldom do that, then you may not need QoS.

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