Value of inbound QoS

lifespeed

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This thread drifted from router discussions:

Dan, you are correct. The only way you are going to get QOS from a provider is with a SLA.

TCP traffic just flows along the Internet until one of the routers that it hits can't deliver the traffic as quickly as it is coming in. This happens by design at the ISP's last hop before it hits your business. If you have a 10 mbps download speed, they have programmed their last hop to deliver that rate to you. The data you requested may be arriving at that router at 100 mbps. That router then sends congestion packets, a type of ICMP traffic I believe, back to the source to get it to slow down.

So, lets say you set the maximum rate that your router can receive to 9 mbps. Now, when you download pipe gets full, the congestion packets are issued from your router, instead of the ISP's last router, and tells the TCP traffic to slow down. None of this affects UDP traffic. Since UDP traffic is, by definition, best efforts delivery, there is no slowing it down. It is just going to come barreling right on it.

So, if you have throttled your router at about 10% less than the ISP provides, you have left a 1 mbps window for UDP traffic, which you cannot stop anyway.

I have no idea if this is the correct explanation why this works, but where I have implemented this using PFSense as my endpoint, it seems to work.

John,

I think your description of traffic congestion at the ISP level is essentially correct. And I also seriously doubt they honor DSCP; rather they use their rather large BW to deliver traffic at maximum speed up to your paid-for limit. Also your description of TCP vs UDP I think is correct.

In my limited experience, a good ISP will have enough internal BW that their network does not become a QOS issue, hence strict adherence to DSCP tags is generally not required at their level. It is left to the customer to properly manage their use of ISP BW, something that QOS in both directions helps a VoIP/data customer optimally implement.

Here is where I think inbound QOS helps: your router will send congestion packets upstream to your ISP if an incoming TCP connection is threatening to interfere with the prioritized packets. This relieves the user of trying to set a fixed limit of 90% available BW, instead letting the router dynamically use Internet Protocol to control traffic as intended, alloting full BW to all uses of the WAN and LAN as specified in the QOS list.

I have observed the behavior of VoIP calls with simultaneous large BW data useage, and observed the effects of QOS in my Draytek 2130 router. I can hear the effect on phone calls and see the BW priorities dynamically shift. In both directions, of course. When I had a DGL-4300 router I had to do what others have referred to as "redneck QoS", limiting incoming BW useage by all non-VoIP users to a percentage of the total so there was always some incoming BW available for VoIP. A static, rather than dynamic allocation that essentially reduces your BW all the time to assure VoIP performance during a phone call. Trouble is you give up BW all the time to allow for the occasional phone call(s).
 
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Linetux

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Here is where I think inbound QOS helps: your router will send congestion packets upstream to your ISP if an incoming TCP connection is threatening to interfere with the prioritized packets. This relieves the user of trying to set a fixed limit of 90% available BW, instead letting the router dynamically use Internet Protocol to control traffic as intended, alloting full BW to all uses of the WAN and LAN as specified in the QOS list.

I am unaware of any ISP that does anything with QoS packets, other than strip them off... I've had conversations with a lot of major carriers about this subject as well.

If anyone has contrary experience, I'd love to know about it. But so far as I've ever experienced, keeping your own networks in check is the best you can do unless you have some kind of specific agreement in place wherein the carrier is reading your QoS tags, and this generally only happens over MPLS. Keep in mind with the internet, even if you were to get a carrier to respect your QoS tags, it's only good on their network - the next carrier they peer with surely won't respect those tags, and so on.
 

jmullinix

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I will give this a try. I know my "Redneck QOS" seems to work. I have just never tried what you are suggesting. I will report back.
 

dswartz

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lifespeed, can you be more specific about what 'tcp congestion packets' means? Also, as far as redneck QoS, this is much less of an issue if you have a decent broadband connection. My verizon FIOS is 25mb down, 25mb up, so sacrificing a few mb down to allow redneck QoS to work is not a big deal for me :)
 

Linetux

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I believe he's referring to the normal process in which TCP handles traffic. Basically if there aren't enough ACK's coming back for a TCP session, it will throttle down due to the fact that it 'thinks' that there's too much traffic on the pipe. As the ACK's start coming back, it slowly throttles-up until there are problems again, etc.

That's why when you oversaturate your uplink (which is easy to do on a split DSL/Cable line), your entire pipe suffers horribly :) And since VoIP is UDP based, it keeps spewing the packets no matter what, which, well, you know!
 

dswartz

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yeah, i know (i work on this stuff for a living LOL). i wanted him to explain what he thought a congestion packet was, since i wasn't aware of any such beast, so i assumed we had a terminology disconnect. The closest thing I can think of is ECN, but that is piggybacked on other outgoing packets (AFAIK), and requires the remote host to grok that. I am running pfsense for my gateway, and have RED set for the traffic shaper and have it set about 90% of the usable BW.
 

lifespeed

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No doubt my terminology wasn't correct, I am not a network expert. My understanding of TCP is the recipient 'acknowledges' receipt of packets. If these acknowledgements slow it is an indication the recipient can't handle the traffic volume and the sender slows down transmissions.

I believe this is one of the mechanisms on which a router with inbound QOS works: slowing lower-priority TCP traffic through this mechanism.

I am certain it also prioritizes inbound packets according to the rules that are setup, ensuring low latency across the WAN/LAN NAT and within the LAN.

Note neither of these mechanisms require the ISP honor DSCP. I never claimed this was something that happened.
 

dswartz

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Dredging this thread back, I found something interesting WRT inbound QoS. I am playing (as seen in a different thread) with Astaro Security Gateway, which has an inbound QoS option (checkbox) called "Download Equalizer". If download usage hits the specificed limit, it will start using Stochastic Fairness Queuing and Random Early Detection to start dropping packets from the inbound data stream (e.g. "conversation") that is the biggest offender, which for TCP, will slow it down.
 

lifespeed

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Inbound QoS is starting to appear in the higher-end stuff. One of the issues is how it is implemented: DSCP, by port, or by IP address (ideally any of the above). Each implementation has strengths and weaknesses, and implementation issues in the real world we live in where inbound packets may not necessarily have QoS tags.
 

Linetux

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And yet I have a provider trying to get my business by selling me bandwidth at $4.50/MB.

Such a disconnect... we could be doing so much better in this country with bandwidth penetration than we are. Gee, thanks MaBell (and others). I see you have done a great job at getting my home speeds booted when left to your own devices.

On a truly related note, I'm glad to see so many other lower-end devices start picking up on various traffic-shaping devices. It's a complicated subject to put into the SOHO/SMB devices.
 

lifespeed

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On a truly related note, I'm glad to see so many other lower-end devices start picking up on various traffic-shaping devices. It's a complicated subject to put into the SOHO/SMB devices.

Invariably with bugs in the implementation. Already seen it on an admittedly new product.

As for Ma Bell, they are abominable. Simply trying to milk that puny twisted pair for all they can without investing anything in infrastructure. I refuse to do business with anybody who wants those corroded 40 year wires under my street to (attempt) to carry my data. I'm talking to you, U-verse and DSL.

Coax or fiber. And I can't have fiber . . . yet.
 

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