From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mail-ve0-f176.google.com (mail-ve0-f176.google.com [209.85.128.176]) (using TLSv1 with cipher RC4-SHA (128/128 bits)) (Client CN "smtp.gmail.com", Issuer "Google Internet Authority" (verified OK)) by huchra.bufferbloat.net (Postfix) with ESMTPS id 7B1F021F0E8; Fri, 1 Mar 2013 19:39:57 -0800 (PST) Received: by mail-ve0-f176.google.com with SMTP id cz10so3438468veb.21 for ; Fri, 01 Mar 2013 19:39:56 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20120113; h=mime-version:x-received:in-reply-to:references:date:message-id :subject:from:to:cc:content-type; bh=2xjtyJfcx1U1HwEXZuYNlQrkTFjI6GeN/Y3tf58WE9M=; b=WhRsnbSfJ3dwWBI+pYeuaqJsvkD1U+QhyAxgtlL6YCpWCTTT99p75Ng/2uavZMnlig +doCWf2VxoDm0Nzf00SXqo/r2uYR0p+OTo2LzDPjuBkVTKfa6vrkR7/VptFFE+EqBHDC 6ooT3w5LQ5CEAG9t2LwiTfbetpdxwc6O8r8GWThD7VoYzoLfhNMkpRyO2xo+9DwYGpln NCEYuQJIYTzqBsNZu4tTATofNq6okkuFbMkVSndYxDMEqSsO3VK8Kn6AuuxtcoJYJI99 hMJSbEK1QLfDPigcl8r4TNAtfDIeBxlf5COuqY7BsfNRMv4mAJ1uN4Q4KmBP/gOD/btp oqXA== MIME-Version: 1.0 X-Received: by 10.58.214.231 with SMTP id od7mr5068036vec.44.1362195595992; Fri, 01 Mar 2013 19:39:55 -0800 (PST) Received: by 10.58.106.42 with HTTP; Fri, 1 Mar 2013 19:39:55 -0800 (PST) In-Reply-To: <1362155228.00438500@apps.rackspace.com> References: <1362077845.101114942@apps.rackspace.com> <1362152412.065117928@apps.rackspace.com> <1362155228.00438500@apps.rackspace.com> Date: Sat, 2 Mar 2013 09:09:55 +0530 Message-ID: From: Ketan Kulkarni To: dpreed@reed.com Content-Type: multipart/alternative; boundary=089e011831989d248704d6e8e07f Cc: "cerowrt-devel@lists.bufferbloat.net" , bloat Subject: Re: [Cerowrt-devel] Google working on experimental 3.8 Linux kernel for Android X-BeenThere: cerowrt-devel@lists.bufferbloat.net X-Mailman-Version: 2.1.13 Precedence: list List-Id: Development issues regarding the cerowrt test router project List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sat, 02 Mar 2013 03:39:58 -0000 --089e011831989d248704d6e8e07f Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi David, While I tend to agree with most of the stuff, however the complexity and too many knobs in mobile networks do come with the added technology. Consider from end-user perspective, getting a voice call while surfing/downloading on 2G/3G interrupts all the download and it is annoying. So when LTE provides a spec to handle voip + internet both simultaneously, its great benefit to end user. While roaming around in LTE and moving to 2G/3G network or vice-versa, the handoff occurs seamlessly, the internet traffic is not interrupted. This was not the case in previous mobile generations. End-user is more satisfied as it relates to the daily usage of mobile phones. Similarly going ahead we might very well have handoff from wifi to LTE - why not? Now for (non-technical) mobile users, these are good and simple to have features. But from networks perspective, where and how will this complexity be handled? definitely some nodes in the network will have to worry about LTE, UMTS, CDMA, eHRPD and what not. This gives some idea of how really complex the network looks like - http://www.trilliumposter.com/lte.php >From mobile ISP perspective, they invest heavy amount in getting channel license from governments. It takes years to cover up the amount invested. Moreover, consider e.g. facebook embedding ads as per user's interest areas. The ads revenue benefit facebook. However, the mobile ISPs who carry the same data and has potentially (more relevant) information of the subscriber cannot gain from this. This is a real problem to solve for ISPs. Monetization is becoming more relevant to ISPs which again will definitely lead to more complexity in network. >From field engineers, I think many of them are bound by what they are "asked" to do. They have certain task to complete, with exactly what to test, and in what time. Not all field engineers will think beyond that. If their senior technical leads ask them to test packet drops they will test drops. Going ahead if they are asked to test latency they will do so with whatever available resources and knowledge they have. We can not expect an average engineer to think beyond a certain level and do what is not expected out of them from their seniors. Not all will think of the internet finally. Even the network vendors like Cisco, ALU or Ericsson will test the latency and all the other stuff when there is real push from customers like VzW and ATT. Definitely the vendors can very well invest, research and come up with the latest methods and techniques of measurement and they are doing so to some extent. Still there is some time to come to a really good picture here. I think the tests like RRUL is definitely a good start and is more relevant to the ISPs VzW and ATT because its finally they own the network. If these companies are convinced, it will become little easy to push the vendors to do the right stuff. It then puts the correct target for field engineers to accomplish. We have to accept the fact that no standard till now specifies what and how to test latencies. This is one of many of the reasons beating bloat has been a daunting task in the complex world. FWIK, every ISP has a latency and jitter budget already with every node in their network and these are well communicated to vendors. Now how do one measure, under what scenarios is still not very clearly defined nor understood. So every one interpret these to their knowledge and understanding and a common consensus internally is achieved. Who looks at e2e latency? Who looks at the complex interactions of these nodes and their effect? - I really dont know. Add to that the dynamic behavior of cell and radio access. All this really complicates the stuff at network. While we have the right step with RRUL, but its still a long way to go for a better picture on mobile networks. Sometimes "LTE =3D Long Term Employment" is an apt description. Thanks, Ketan On Fri, Mar 1, 2013 at 9:57 PM, wrote: > I don't doubt that they test. My point was different - there are too man= y > knobs and too big a parameter space to test efectively. And that's the > point. > > > > I realize that it's extremely fun to invent parameters in "standards > organizations" like 3GPP. Everybody has their own favorite knob, and a > great rationale for some unusual, but critically "important" customer > requirement that might come up some day. Hell, Linux has a gazillion (ye= s, > that's a technical term in mathematics!) parameters, almost none of which > are touched. This reflects the fact that nothing ever gets removed once > added. LTE is now going into release 12, and it's completely ramified in= to > "solutions" to problems that will never be fixed in the field with those > solutions. It's great for European Publically Funded Academic-Industry > research - lots for those "Professors" to claim they invented. > > > > I've worked with telco contractors in the field. They don't read > manuals, and they don't read specs. They have a job to do, and so much > money to spend, and time's a wasting. They don't even work for Verizon o= r > ATT. They follow "specs" handed down, and charge more if you tell them > that the specs have changed. > > > > This is not how brand-new systems get tuned. > > > > It's a Clown Circus out there, and more parameters don't help. > > > > This is why "more buffering is better" continues to be the law of the lan= d > - the spec is defined to be "no lost packets under load". I'm sure that > the primary measure under load for RRUL will be "no lost packets" by the > time it gets to field engineers in the form of "specs" - because that's > what they've *always* been told, and they will disregard any changes as > "typos". > > > > A system with more than two control parameters that interact in complex > ways is ungovernable - and no control parameters in LTE are "orthogonal", > much less "linear" in their interaction. > > > > > > > > -----Original Message----- > From: "Jim Gettys" > Sent: Friday, March 1, 2013 11:09am > To: "David P Reed" > Cc: "Ketan Kulkarni" , " > cerowrt-devel@lists.bufferbloat.net" > Subject: Re: [Cerowrt-devel] Google working on experimental 3.8 Linux > kernel for Android > > > > > On Fri, Mar 1, 2013 at 10:40 AM, wrote: > >> One wonders why all this complexity is necessary, and how likely it is t= o >> be "well tuned" by operators and their contract installers. >> >> >> >> I'm willing to bet $1000 that all the testing that is done is "Can you >> hear me now" and a "speed test". Not even something as simple and >> effective as RRUL. >> > Actually, at least some the the carriers do much more extensive testing; > but not with the test tools we would like to see used (yet). > An example is AT&T, where in research, KK Ramakrishnan has a van with 20 > or so laptops so he can go driving around and load up a cell in the middl= e > of the night and get data. And he's research; the operations guys do lo= ts > of testing I gather, but more at the radio level. > Next up, is to educate KK to run RRUL. > And in my own company, I've seen data, but it is too high level: e.g. > performance of "web" video: e.g. siverlight, flash, youtube, etc. > A common disease that has complicated all this is the propensity for > companies to use Windows XP internally for everything: since window scali= ng > is turned off, you can't saturate a LTE link the way you might like to do > with a single TCP connection. > - Jim > >> >> >> -----Original Message----- >> From: "Ketan Kulkarni" >> Sent: Friday, March 1, 2013 3:00am >> To: "Jim Gettys" >> Cc: "cerowrt-devel@lists.bufferbloat.net" < >> cerowrt-devel@lists.bufferbloat.net> >> Subject: Re: [Cerowrt-devel] Google working on experimental 3.8 Linux >> kernel for Android >> >> >> >> On Fri, Mar 1, 2013 at 1:33 AM, Jim Gettys wrote: >> >>> I've got a bit more insight into LTE than I did in the past, courtesy o= f >>> the last couple days. >>> To begin with, LTE runs with several classes of service (the call them >>> bearers). Your VOIP traffic goes into one of them. >>> And I think there is another as well that is for guaranteed bit rate >>> traffic. One transmit opportunity may have a bunch of chunks of data, = and >>> that data may be destined for more than one device (IIRC). It's >>> substantially different than WiFi. >>> >> Just thought to put more light on bearer stuff: >> >> There are two ways bearers are setup: >> 1. UE initiated - where User Equipment sets-up the "parameters" for >> bearer >> 2. Network initiated - where node like PCRF and PGW sets-up the >> "parameters". >> Parameters include the Guaranteed bit-rates, maximum bit-rates. Somethin= g >> called QCI is associated with bearers. The QCI parameters are authorized= at >> PCRF (policy control rule function) and there is certain mapping maintai= ned >> at either PCRF or PGW between QCI values and DSCP and MBRs. >> These parameters enforcing is done at PGW (in such case it is termed as >> PCEF - policy and rule enforcement function). So PGWs depending on beare= rs >> can certainly modify dscp bits. Though these can be modified by other no= des >> in the network. >> >> There are two types of bearers: 1. Dedicated bearers - to carry traffic >> which need "special" treatment 2. Default or general pupose bearers - to >> carry all general purpose data. >> So generally the voip, streaming videos are passed over dedicated bearer= s >> and apply (generally) higher GBRs, MBRs and correct dscp markings. >> And other non-latency sensitive traffic generally follows the default >> bearer. >> >> Theoretical limit on maximum bearers is 11 though practically most of th= e >> deployments use upto 3 bearers max. >> >> Note that these parameters may very well very based on the subscriber >> profiles. Premium/Corporate subscribers can well have more GBRs and MBRs= . >> ISPs are generally very much sensitive to the correct markings at >> gateways for obvious reasons. >> >> But most of what we think of as Internet stuff (web surfing, dns, etc) >>> all gets dumped into a single best effort ("BE"), class. >>> The BE class is definitely badly bloated; I can't say how much because = I >>> don't really know yet; the test my colleague ran wasn't run long enough= to >>> be confident it filled the buffers). But I will say worse than most ca= ble >>> modems I've seen. I expect this will be true to different degrees on >>> different hardware. The other traffic classes haven't been tested yet = for >>> bufferbloat, though I suspect they will have it too. I was told that t= hose >>> classes have much shorter queues, and when the grow, they dump the whol= e >>> queues (because delivering late real time traffic is useless). But tru= st >>> *and* verify.... Verification hasn't been done for anything but BE >>> traffic, and that hasn't been quantified. >>> But each device gets a "fair" shot at bandwidth in the cell (or sector >>> of a cell; they run 3 radios in each cell), where fair is basically tim= e >>> based; if you are at the edge of a cell, you'll get a lot less bandwidt= h >>> than someone near a tower; and this fairness is guaranteed by a schedul= er >>> than runs in the base station (called a b-nodeb, IIIRC). So the base >>> station guarantees some sort of "fairness" between devices (a place whe= re >>> Linux's wifi stack today fails utterly, since there is a single queue p= er >>> device, rather than one per station). >>> Whether there are bloat problems at the link level in LTE due to error >>> correction I don't know yet; but it wouldn't surprise me; I know there = was >>> in 3g. The people I talked to this morning aren't familiar with the HA= RQ >>> layer in the system. >>> The base stations are complicated beasts; they have both a linux system >>> in them as well as a real time operating system based device inside We >>> don't know where the bottle neck(s) are yet. I spent lunch upping thei= r >>> paranoia and getting them through some conceptual hurdles (e.g. multipl= e >>> bottlenecks that may move, and the like). They will try to get me some= of >>> the data so I can help them figure it out. I don't know if the data fl= ow >>> goes through the linux system in the bnodeb or not, for example. >>> Most carriers are now trying to ensure that their backhauls from the >>> base station are never congested, though that is another known source o= f >>> problems. And then there is the lack of AQM at peering point routers..= .. >>> You'd think they might run WRED there, but many/most do not. >>> - Jim >>> >>> >>> On Thu, Feb 28, 2013 at 2:08 PM, Dave Taht wrote: >>> >>>> >>>> >>>> On Thu, Feb 28, 2013 at 1:57 PM, wrote: >>>> >>>>> Doesn't fq_codel need an estimate of link capacity? >>>>> >>>> No, it just measures delay. Since so far as I know the outgoing >>>> portion of LTE is not soft-rate limited, but sensitive to the actual >>>> available link bandwidth, fq_codel should work pretty good (if the >>>> underlying interfaces weren't horribly overbuffired) in that direction= . >>>> I'm looking forward to some measurements of actual buffering at the >>>> device driver/device levels. >>>> I don't know how inbound to the handset is managed via LTE. >>>> Still quite a few assumptions left to smash in the above. >>>> ... >>>> in the home router case.... >>>> ... >>>> When there are artificial rate limits in play (in, for example, a cabl= e >>>> modem/CMTS, hooked up via gigE yet rate limiting to 24up/4mbit down), = then >>>> a rate limiter (tbf,htb,hfsc) needs to be applied locally to move that= rate >>>> limiter/queue management into the local device, se we can manage it be= tter. >>>> I'd like to be rid of the need to use htb and come up with a rate >>>> limiter that could be adjusted dynamically from a daemon in userspace, >>>> probing for short all bandwidth fluctuations while monitoring the load= . It >>>> needent send that much data very often, to come up with a stable resul= t.... >>>> You've described one soft-rate sensing scheme (piggybacking on TCP), >>>> and I've thought up a few others, that could feed back from a daemon s= ome >>>> samples into a a soft(er) rate limiter that would keep control of the >>>> queues in the home router. I am thinking it's going to take way too lo= ng to >>>> fix the CPE and far easier to fix the home router via this method, and >>>> certainly it's too painful and inaccurate to merely measure the bandwi= dth >>>> once, then set a hard rate, when >>>> So far as I know the gargoyle project was experimenting with this >>>> approach. >>>> A problem is in places that connect more than one device to the cable >>>> modem... then you end up with those needing to communicate their perce= ption >>>> of the actual bandwidth beyond the link. >>>> >>>>> Where will it get that from the 4G or 3G uplink? >>>>> >>>>> >>>>> >>>>> -----Original Message----- >>>>> From: "Maciej Soltysiak" >>>>> Sent: Thursday, February 28, 2013 1:03pm >>>>> To: cerowrt-devel@lists.bufferbloat.net >>>>> Subject: [Cerowrt-devel] Google working on experimental 3.8 Linux >>>>> kernel for Android >>>>> >>>>> Hiya, >>>>> Looks like Google's experimenting with 3.8 for Android: >>>>> https://android.googlesource.com/kernel/common/+/experimental/android= -3.8 >>>>> Sounds great if this means they will utilize fq_codel, TFO, BQL, etc. >>>>> Anyway my nexus 7 says it has 3.1.10 and this 3.8 will probably go to >>>>> Android 5.0 so I hope Nexus 7 will get it too some day or at least 3.= 3+ >>>>> Phoronix coverage: >>>>> http://www.phoronix.com/scan.php?page=3Dnews_item&px=3DMTMxMzc >>>>> Their 3.8 changelog: >>>>> https://android.googlesource.com/kernel/common/+log/experimental/andr= oid-3.8 >>>>> Regards, >>>>> Maciej >>>>> _______________________________________________ >>>>> Cerowrt-devel mailing list >>>>> Cerowrt-devel@lists.bufferbloat.net >>>>> https://lists.bufferbloat.net/listinfo/cerowrt-devel >>>>> >>>>> >>>> >>>> -- >>>> Dave T=E4ht >>>> >>>> Fixing bufferbloat with cerowrt: >>>> http://www.teklibre.com/cerowrt/subscribe.html >>>> _______________________________________________ >>>> Cerowrt-devel mailing list >>>> Cerowrt-devel@lists.bufferbloat.net >>>> https://lists.bufferbloat.net/listinfo/cerowrt-devel >>>> >>>> >>> _______________________________________________ >>> Cerowrt-devel mailing list >>> Cerowrt-devel@lists.bufferbloat.net >>> https://lists.bufferbloat.net/listinfo/cerowrt-devel >>> >>> --089e011831989d248704d6e8e07f Content-Type: text/html; charset=ISO-8859-1 Content-Transfer-Encoding: quoted-printable Hi David,

While I tend to agree with most of the stuff, however the = complexity and too many knobs in mobile networks do come with the added tec= hnology.

Consider from end-user perspective, getting a voice call wh= ile surfing/downloading on 2G/3G interrupts all the download and it is anno= ying.
So when LTE provides a spec to handle voip + internet both simultaneously, = its great benefit to end user.
While roaming around in LTE and moving to= 2G/3G network or vice-versa, the handoff occurs seamlessly, the internet t= raffic is not interrupted. This was not the case in previous mobile generat= ions. End-user is more satisfied as it relates to the daily usage of mobile= phones.
Similarly going ahead we might very well have handoff from wifi to LTE - wh= y not?

Now for (non-technical) mobile users, these are good and sim= ple to have features. But from networks perspective, where and how will thi= s complexity be handled? definitely some nodes in the network will have to = worry about LTE, UMTS, CDMA, eHRPD and what not.
This gives some idea of how really complex the network looks like -
http://www.trilliumposter.com= /lte.php

From mobile ISP perspective, they invest heavy amount i= n getting channel license from governments. It takes years to cover up the = amount invested. Moreover, consider e.g. facebook embedding ads as per user= 's interest areas. The ads revenue benefit facebook. However, the mobil= e ISPs who carry the same data and has potentially (more relevant) informat= ion of the subscriber cannot gain from this.
This is a real problem to solve for ISPs. Monetization is becoming more rel= evant to ISPs which again will definitely lead to more complexity in networ= k.

From field engineers, I think many of them are bound by what they= are "asked" to do. They have certain task to complete, with exac= tly what to test, and in what time. Not all field engineers will think beyo= nd that. If their senior technical leads ask them to test packet drops they= will test drops. Going ahead if they are asked to test latency they will d= o so with whatever available resources and knowledge they have. We can not = expect an average engineer to think beyond a certain level and do what is n= ot expected out of them from their seniors. Not all will think of the inter= net finally.

Even the network vendors like Cisco, ALU or Ericsson will test the late= ncy and all the other stuff when there is real push from customers like VzW= and ATT. Definitely the vendors can very well invest, research and come up= with the latest methods and techniques of measurement and they are doing s= o to some extent.=A0 Still there is some time to come to a really good pict= ure here.

I think the tests like RRUL is definitely a good start and is more rele= vant to the ISPs VzW and ATT because its finally they own the network. If t= hese companies are convinced, it will become little easy to push the vendor= s to do the right stuff. It then puts the correct target for field engineer= s to accomplish.
We have to accept the fact that no standard till now specifies what and how= to test latencies. This is one of many of the reasons beating bloat has be= en a daunting task in the complex world.

FWIK, every ISP has a laten= cy and jitter budget already with every node in their network and these are= well communicated to vendors. Now how do one measure, under what scenarios= is still not very clearly defined nor understood. So every one interpret t= hese to their knowledge and understanding and a common consensus internally= is achieved.
Who looks at e2e latency? Who looks at the complex interactions of these no= des and their effect? - I really dont know.
Add to that the dynamic beha= vior of cell and radio access. All this really complicates the stuff at net= work.

While we have the right step with RRUL, but its still a long way to go = for a better picture on mobile networks.

Sometimes "LTE =3D Lon= g Term Employment" is an apt description.

Thanks,
Ketan

On Fri, Mar 1, 2013 at 9:57 PM, <dpreed@re= ed.com> wrote:

I don't = doubt that they test.=A0 My point was different - there are too many knobs = and too big a parameter space to test efectively.=A0 And that's the poi= nt.

=A0

I realize that it's extremely fun to in= vent parameters in "standards organizations" like 3GPP.=A0 Everyb= ody has their own favorite knob, and a great rationale for some unusual, bu= t critically "important" customer requirement that might come up = some day.=A0 Hell, Linux has a gazillion (yes, that's a technical term = in mathematics!) parameters, almost none of which are touched.=A0 This refl= ects the fact that nothing ever gets removed once added.=A0 LTE is now goin= g into release 12, and it's completely ramified into "solutions&qu= ot; to problems that will never be fixed in the field with those solutions.= =A0 It's great for European Publically Funded Academic-Industry researc= h - lots for those "Professors" to claim they invented.

=A0

I've worked with telco contractors in t= he field.=A0=A0 They don't read manuals, and they don't read specs.= =A0 They have a job to do, and so much money to spend, and time's a was= ting.=A0 They don't even work for Verizon or ATT.=A0 They follow "= specs" handed down, and charge more if you tell them that the specs ha= ve changed.

=A0

This is not how brand-new systems get tuned= .

=A0

It's a Clown Circus out there, and more= parameters don't help.

=A0

This is why "more buffering is better&= quot; continues to be the law of the land - the spec is defined to be "= ;no lost packets under load".=A0=A0 I'm sure that the primary meas= ure under load for RRUL will be "no lost packets" by the time it = gets to field engineers in the form of "specs" - because that'= ;s what they've *always* been told, and they will disregard any changes= as "typos".

=A0

A system with more than two control paramet= ers that interact in complex ways is ungovernable - and no control paramete= rs in LTE are "orthogonal", much less "linear" in their= interaction.

=A0

=A0

=A0

-----Original Message= -----
From: "Jim Gettys" <jg@freedesktop.org>
Sent: Friday, March 1, 2013 11:09am
To: "David P Reed" <dpreed@reed.com>
Cc: &qu= ot;Ketan Kulkarni" <ketkulka@gmail.com>, "cerowrt-devel@lists.bufferbloat.ne= t" <cerowrt-devel@lists.bufferbloat.net>
Subject: Re: [Cerowrt-devel] Google working on experimental 3.8 Linux kerne= l for Android




On Fri, Mar 1, 2013 at 10:40 AM, <dpreed@reed.co= m> wrote:

One wonders why all this= complexity is necessary, and how likely it is to be "well tuned"= by operators and their contract installers.

=A0

I'm willing to bet $= 1000 that all the testing that is done is "Can you hear me now" a= nd a "speed test".=A0 Not even something as simple and effective = as RRUL.

Actually, at least some the the carriers do much more extensive testin= g; but not with the test tools we would like to see used (yet).
An example is AT&T, where in research, KK Ramakrishnan has a van w= ith 20 or so laptops so he can go driving around and load up a cell in the = middle of the night and get data. =A0 And he's research; the operations= guys do lots of testing I gather, but more at the radio level.
Next up, is to educate KK to run RRUL.
And in my own company, I've seen data, but it is too high level: e= .g. performance of "web" video: e.g. siverlight, flash, youtube, = etc.
A common disease that has complicated all this is the propensity for c= ompanies to use Windows XP internally for everything: since window scaling = is turned off, you can't saturate a LTE link the way you might like to = do with a single TCP connection.
- Jim

=A0

-----Original Message---= --
From: "Ketan Kulkarni" <ketkulka@gmail.com>
Sent: Friday, March 1= , 2013 3:00am
To: "Jim Gettys" <jg@freedesktop.org>
Cc: "cerowrt-devel@lists.buff= erbloat.net" <cerowrt-devel@lists.bufferbloat.net>
Subject: Re: [Cerowrt-devel] Google working on experimental 3.8 Linux kern= el for Android



On Fri, Mar 1, 2013 at 1:33 AM, Jim Gettys <jg= @freedesktop.org> wrote:
I've got a bit more insight into LTE than I did in the= past, courtesy of the last couple days.
To begin with, LTE runs with several classes of service (the call them= bearers). =A0Your VOIP traffic goes into one of them.
And I think there is another as well that is for guaranteed bit rate t= raffic. =A0One transmit opportunity may have a bunch of chunks of data, and= that data may be destined for more than one device (IIRC). =A0It's sub= stantially different than WiFi.
Just thought to put more light on bearer stuff:

There are two w= ays bearers are setup:
1. UE initiated - where User Equipment sets-up t= he "parameters" for bearer
2. Network initiated - where node= like PCRF and PGW sets-up the "parameters".
Parameters include the Guaranteed bit-rates, maximum bit-rates. Something = called QCI is associated with bearers. The QCI parameters are authorized at= PCRF (policy control rule function) and there is certain mapping maintaine= d at either PCRF or PGW between QCI values and DSCP and MBRs.
These parameters enforcing is done at PGW (in such case it is termed as PC= EF - policy and rule enforcement function). So PGWs depending on bearers ca= n certainly modify dscp bits. Though these can be modified by other nodes i= n the network.

There are two types of bearers: 1. Dedicated bearers - to carry traffic= which need "special" treatment 2. Default or general pupose bear= ers - to carry all general purpose data.
So generally the voip, streamin= g videos are passed over dedicated bearers and apply (generally) higher GBR= s, MBRs and correct dscp markings.
And other non-latency sensitive traffic generally follows the default bear= er.

Theoretical limit on maximum bearers is 11 though practically mo= st of the deployments use upto 3 bearers max.

Note that these parame= ters may very well very based on the subscriber profiles. Premium/Corporate= subscribers can well have more GBRs and MBRs.
ISPs are generally very much sensitive to the correct markings at gateways= for obvious reasons.

But most of what we think of as Internet stuff (web surfing, dns, etc)= all gets dumped into a single best effort ("BE"), class.
The BE class is=A0definitely=A0badly bloated; I can't say how much= because I don't really know yet; the test my colleague ran wasn't = run long enough to be confident it filled the buffers). =A0But I will say w= orse than most cable modems I've seen. =A0I expect this will be true to= different degrees on different hardware. =A0The other traffic classes have= n't been tested yet for bufferbloat, though I suspect they will have it= too. =A0I was told that those classes have much shorter queues, and when t= he grow, they dump the whole queues (because delivering late real time traf= fic is useless). =A0But trust *and* verify.... =A0Verification hasn't b= een done for anything but BE traffic, and that hasn't been quantified.<= /div>
But each device gets a "fair" shot at bandwidth in the cell = (or sector of a cell; they run 3 radios in each cell), where fair is basica= lly time based; if you are at the edge of a cell, you'll get a lot less= bandwidth than someone near a tower; and this fairness is guaranteed by a = scheduler than runs in the base station (called a b-nodeb, IIIRC). =A0So th= e base station guarantees some sort of "fairness" between devices= (a place where Linux's wifi stack today fails utterly, since there is = a single queue per device, rather than one per station).
Whether there are bloat problems at the link level in LTE due to error= correction I don't know yet; but it wouldn't surprise me; I know t= here was in 3g. =A0The people I talked to this morning aren't familiar = with the HARQ layer in the system.
The base stations are complicated beasts; they have both a linux syste= m in them as well as a real time operating system based device inside =A0We= don't know where the bottle neck(s) are yet. =A0I spent lunch upping t= heir paranoia and getting them through some conceptual hurdles (e.g. multip= le bottlenecks that may move, and the like). =A0They will try to get me som= e of the data so I can help them figure it out. =A0I don't know if the = data flow goes through the linux system in the bnodeb or not, for example.<= /div>
Most carriers are now trying to ensure that their backhauls from the b= ase station are never congested, though that is another known source of pro= blems. =A0And then there is the lack of AQM at peering point routers.... = =A0You'd think they might run WRED there, but many/most do not.
- Jim


On Thu, Feb 28, 2013 at 2:08 PM, Dave Taht <d= ave.taht@gmail.com> wrote:


On Thu, Feb 28, 2013 at 1:57 PM, <dpreed@reed.com> wrote= :

Doesn't fq_codel nee= d an estimate of link capacity?

No, it just measures delay. Since so far as I know the outgoing portio= n of LTE is not soft-rate limited, but sensitive to the actual available li= nk bandwidth, fq_codel should work pretty good (if the underlying interface= s weren't horribly overbuffired) in that direction.
I'm looking forward to some measurements of actual buffering at th= e device driver/device levels.
I don't know how inbound to the handset is managed via LTE.
Still quite a few assumptions left to smash in the above.
...
in the home router case....
...
When there are artificial rate limits in play (in, for example, a cabl= e modem/CMTS, hooked up via gigE yet rate limiting to 24up/4mbit down), the= n a rate limiter (tbf,htb,hfsc) needs to be applied locally to move that ra= te limiter/queue management into the local device, se we can manage it bett= er.
I'd like to be rid of the need to use htb and come up with a rate = limiter that could be adjusted dynamically from a daemon in userspace, prob= ing for short all bandwidth fluctuations while monitoring the load. It need= ent send that much data very often, to come up with a stable result....
You've described one soft-rate sensing scheme (piggybacking on TCP= ), and I've thought up a few others, that could feed back from a daemon= some samples into a a soft(er) rate limiter that would keep control of the= queues in the home router. I am thinking it's going to take way too lo= ng to fix the CPE and far easier to fix the home router via this method, an= d certainly it's too painful and inaccurate to merely measure the bandw= idth once, then set a hard rate, when
So far as I know the gargoyle project was experimenting with this appr= oach.
A problem is in places that connect more than one device to the cable = modem... then you end up with those needing to communicate their perception= of the actual bandwidth beyond the link.

Where will it get that f= rom the 4G or 3G uplink?

=A0

-----Original Message---= --
From: "Maciej Soltysiak" <maciej@soltysiak.com>
Sent: Thursday,= February 28, 2013 1:03pm
To: cerowrt-devel@lists.bufferbloat.net
Subject: [Cerowrt-devel] Goog= le working on experimental 3.8 Linux kernel for Android

Hiya,
Looks like Google's experimenting with 3.8 for Android: https://android.googlesource.com/kernel/common/+/experim= ental/android-3.8
Sounds great if this means they will utilize fq_codel, TFO, BQL, etc.<= /div>
Anyway my nexus 7 says it has 3.1.10 and this 3.8 will probably go to = Android 5.0 so I hope Nexus 7 will get it too some day=A0or at least 3.3+
Regards,
Maciej
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--
Dave T=E4ht

Fixin= g bufferbloat with cerowrt: http://www.teklibre.com/cerowrt/subscribe.htm= l
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