Re: [re-ECN] FW: ConEx BoF announcement text

[Richard Bennett <[e-mail]>]

Per the original design of the Internet protocols, the responsibility 
for managing congestion fell on IP, not on TCP. The function was moved 
to TCP by Jacobson because the IP/ICMP method was unreliable for a 
number of reasons. The TCP solution was meant to be a short-term fix 
that would be replaced by a longer-term, better placed congestion 
control function. The TCP solution was several shortcomings:

1. Leads to Global Synchronization.
2. Takes a long time to react to congestion events.
3. Fails to keep the pipe saturated.
4. Isn't fair on a per-user basis.
5. Wastes resources by discarding packets at some random point in their 
path.
6. Treats all applications the same regardless of their requirements.
7. Doesn't do diddly for UDP.

Congestion exposure enables the development of systems of congestion 
management that are more effective, faster, more fair, and more 
resource-efficient than TCP-based solutions can be.

RB

Leslie Daigle wrote:
>
> Hi Toby,
>
> Sorry for not calling this out in the earlier notes.
>
> I'm concerned that rephrasing is getting a bit circular in logic -- 
> "we need congestion exposure because TCP can't do adequate congestion 
> exposure".    That kind of collapses to "we need congestion exposure" 
> without providing a basis for it.
>
> Generally, to the whole list -- let's step back and look at the set of 
> sentences.
>
>
> The Internet is, in essence, about pooling resources. The ability to 
> share capacity has been paramount to its success and has traditionally 
> been managed through the voluntary use of TCP congestion control. 
> However, TCP alone is unable to prevent bandwidth intensive 
> applications, such as peer-to-peer or streaming video, from causing 
> enough congestion over time to severely limit the user-experience of 
> many other users.
>
>
>
>
> Maybe we need to unpack it a bit, and consider Bill's suggestion of 
> s/user/application/.
>
> How can we express the functional assumptions of TCP congestion 
> control that are violated by the nature of P2P and video 
> applications?  And, what is the objective description of the impact of 
> TCP congestion control on this different traffic type?
>
> It's not that TCP congestion control is broken or failing, it's not 
> that these applications are wrong or evil, TCP congestion control just 
> isn't applicable.
>
> How can we capture that?
>
> Leslie.
>
>
>
> [e-mail] wrote:
>> Leslie,
>>
>> I actually replied yesterday afternoon (UK time) with a possible
>> alternative wording for the snippet of text that both Bob and Phil felt
>> was wrong. Having read the new version I have had another go:
>>
>> Current version (after your changes):
>>
>> " However, TCP alone is unable to prevent bandwidth intensive
>> applications, such as peer-to-peer or streaming video, from causing
>> enough congestion over time to severely limit the user-experience of
>> many other users."
>>
>> My suggested alternative:
>>
>> "However TCP alone is unable to prevent some users from causing
>> sufficient congestion over time to significantly impair the quality of
>> experience of other users."
>>
>> OR
>>
>> "However TCP alone is unable to prevent some users from creating
>> excessive congestion over time leading other users to experience
>> severely reduced network performance."
>>
>> I tried to find different words for user experience but it is hard. The
>> problem with pinning it down too tightly is that the impact is different
>> on each user and covers things such as increased jitter, delays to
>> downloads, stuttering video, unresponsive websites, etc. There is no one
>> measure that sums up all those effects other than a vague feeling that
>> the overall experience is better or worse.
>>
>> Toby
>>
>>
>>> -----Original Message-----
>>> From: [e-mail] [mailto:[e-mail]] On
>>> Behalf Of Leslie Daigle
>>> Sent: 20 October 2009 02:55
>>> To: Briscoe,RJ,Bob,XVR9 BRISCORJ R
>>> Cc: [e-mail]
>>> Subject: Re: [re-ECN] FW: ConEx BoF announcement text
>>>
>>>
>>> Bob,
>>>
>>> First -- thanks for making the suggestions as marked up text:  it
>> makes
>>> it easier for all of us to track what is (and is not) changing in the
>>> text.
>>>
>>> Having seen no further discussion of the changes, I've made the
>> changes
>>> as follows.  I've also indicated where I've not made the changes, in
>>> case there is further discussion (in-line):
>>>
>>>
>>> [e-mail] wrote:
>>>> Bob
>>>> Some (personal) comments in-line
>>>> Best wishes,
>>>> phil
>>>>
>>>> -----Original Message-----
>>>> From: [e-mail] [mailto:[e-mail]] On
>>> Behalf
>>>> Of Bob Briscoe
>>>> Sent: 18 October 2009 19:47
>>>> To: Leslie Daigle
>>>> Cc: [e-mail]
>>>> Subject: Re: [re-ECN] FW: ConEx BoF announcement text
>>>>
>>>> Leslie,
>>>>
>>>> I like the announcement text now (it was pretty good already).
>>>>
>>>> I have a few suggestions that seem like nits, but they are important
>>> (to
>>>> me).
>>>>
>>>> I'm assuming you "hold the token" on the text at the mo. So I've
>>>> pasted it from the wiki below, and added my comments.
>>>>
>>>>
>> =======================================================================
>>> =
>>>> ====
>>>>> Congestion Exposure (ConEx?) is a proposed new IETF activity to
>>>>> enable congestion to be exposed along the forwarding path of the
>>>>> Internet. By revealing expected congestion in the IP header of
>> every
>>>> packet,
>>>>
>>>> s/every packet/packets/
>>> Done
>>>
>>>> [phil] agree with your change
>>>>
>>>> [[[Reasoning: We shouldn't imply we have ambitions to ever make all
>>>> Internet traffic expose congestion. I defined the re-ECN protocol so
>>>> re-ECN and non-re-ECN packets can be distinguished. Then different
>>>> apps can choose to use it or not. And different ISPs can choose to
>>>> separately account for these two main types of traffic (or not).
>> This
>>>> is what we should mean by permanent partial deployment.
>>>>
>>>> For example, Sally Floyd was much less concerned about re-ECN once I
>>>> had made this design goal clear.
>>>>
>>>> Anyway, on practicality grounds, an ISP can't force all IP traffic
>> to
>>>> use ConEx, particularly if we've only initially defined it for some
>>>> transports like TCP and not others like DNS/UDP. Obviously, if an
>> ISP
>>>> uses congestion exposure in the future to limit heavy sources of
>>>> congestion, then the ISP is likely to severely limit non-re-ECN
>>>> traffic. But we should leave that up to each ISP.
>>>> ]]]
>>>>
>>>>
>>>>>  congestion exposure provides a generic network capability which
>>>>> allows greater freedom over how capacity is shared. Such
>>>>> information could be used for many purposes, including congestion
>>>>> policing, accountability and inter-domain SLAs. It may also open
>>>>> new approaches to QoS and traffic engineering.
>>>>>
>>>>> The Internet is, in essence, about pooling resources. The ability
>> to
>>>>> share capacity has been paramount to its success and has
>>>>> traditionally been managed through the voluntary use of TCP
>>>>> congestion control. However, TCP alone is unable to prevent
>>>>> bandwidth intensive applications,
>>>> s/bandwidth intensive applications/applications transferring high
>>>> traffic volumes/
>>> Not done -- agree with Phil.
>>>
>>>> [phil] personally I don't find your version any more or less clear
>>> than
>>>> the current text. maybe a 3rd version is needed!
>>>>
>>>> [[[Reasoning: TCP *can* limit bandwidth, but it cannot arbitrate
>>>> continuously heavy use of bandwidth over time.
>>>> ]]]
>>>>
>>>>> such as peer-to-peer or streaming video, from causing enough
>>> congestion
>>>> i/over time /
>>> Done.
>>>
>>>>> to severely limit the user-experience of many other end-hosts.
>>>> s/user-experience of many other end-hosts/experience of many other
>>>> users/
>>>>
>>>> [phil] ok
>>> Done.  As a bit of a gripe:  "user experience" is not quantifiable.
>> It
>>> would be nicer if we could actually express this in terms of some
>> other
>>> quantifiable impact at the end hosts.  I am not inspired to
>> suggestion,
>>> however.  (So, I did the mod as described :-) ).
>>>
>>>> [[[hosts don't have user-experiences
>>>> ]]]
>>>>
>>>>> This has led ISPs to deploy ad-hoc solutions such as volume
>>>>> accounting, rate policing and deep packet inspection in an attempt
>>>>> to distribute capacity differently. The consequences of such
>>>>> practices are increasingly leading to calls for government
>>>>> regulations and stifling innovation at the transport and
>> application
>>>>> layer (see for example, the problem statement I-D (ref below) and
>>>> RFC5594).
>>>>> We believe these problems stem from the lack of a network-layer
>>>>> system for accountability -- among all parties -- for sending
>>>>> traffic which causes congestion.
>>>> s/sending/forwarding/
>>>>
>>>> [phil] maybe this depends whether you think forwarding is a subset
>> or
>>>> sending, sending is a subset of forwarding, or neither. Perhaps the
>>>> easiest solution is to say "sending or forwarding"
>>> Changed to sending or forwarding.
>>>
>>>> [[[Reasoning: applies equally to networks or senders
>>>> ]]]
>>>>
>>>>> We propose a metric where IP packets carry information about the
>>>>> expected rest-of-path congestion, so that any network node may
>>>>> estimate how much congestion it is likely to cause by forwarding
>>>>> traffic. A network operator can then count the volume of congestion
>>>>> about to be caused by an aggregate of traffic as easily as it can
>>>>> count the volume of bytes entering its network today. Once ISPs can
>>>>> see rest-of-path congestion, they can actively discourage
>>>> d/actively /
>>> Done.
>>>
>>>> [phil] ok
>>>>
>>>> [[[Reasoning: passively (e.g. pricing) or actively (e.g. policing)
>>>> ]]]
>>>>
>>>>> users from causing large volumes of congestion, discourage other
>>>>> networks from allowing their users to cause congestion, and more
>>>>> meaningfully differentiate between the qualities of services
>> offered
>>>> >from potential connectivity partners. Meanwhile end-hosts may be
>>>>> freed from rate restrictions where their traffic causes little
>>>> congestion.
>>>>
>>>> i/In this environment the self-imposed constraint of
>> TCP-friendliness
>>>> could be relaxed, allowing a richer variety of application
>> behaviours
>>>> to evolve that would still prevent congestion collapse./
>>>>
>>>> [phil] if this is inserted, there is no point having the last
>>> sentence
>>>> ["Meanwhile..."], as they say the same thing. I don't care much
>>> between
>>>> them.
>>>>
>>>> [[[Your original had wording around this idea that has got lost in
>>>> translation.]]]
>>> No change made -- I think positing TCP-friendliness could be relaxed
>> is
>>> probably overreaching (happy to be educated otherwise), and largely
>>> think the rest is covered in the "Meanwhile" sentence.
>>>
>>>>
>>>>> The purpose of the BoF is to explore the support for and viability
>>>>> of pursuing an IETF activity to define a basic protocol to expose
>>>>> the expected rest-of-path congestion in the IP header. Any such
>>>>> protocol should work with minimal changes to the existing network,
>>>>> in particular it should work with unmodified routers.
>>>> d/Any such protocol should work with minimal changes to the existing
>>>> network, in particular it should work with unmodified routers./
>>>>
>>>> [phil] I have no strong preference where this text appears
>>>>
>>>> [[[Reasoning: A BoF announcement shouldn't contain strong
>>>> requirements-text. A little lower down, I've introduced text that
>>>> conveys the same sentiment without making it a strong requirement.
>>>> ]]]
>>> Done -- I do think the BoF announcement should give some sense of
>>> boundaries that exists.  Having said that, I don't care where it is,
>>> and
>>> am happy to migrate it closer to the proposal text.
>>>
>>>>> There is already one existing proposal that builds on ECN to
>> provide
>>>>> rest-of-path congestion information in every IP header
>>>> s/every IP header/IP headers/
>>> Done.
>>>
>>>>> and other proposals may come forward.
>>>>>
>>>>> If supported, an eventual WG would focus on the development of that
>>>> protocol
>>>>
>>>> s/that protocol/its chosen congestion exposure protocol/
>>>>
>>>>> as its main work item.
>>>> i/The chosen protocol will need to be deployable with minimal
>> changes
>>>> to the existing Internet and compare well against the existing
>>>> proposal, which works with unmodified routers./
>>> I inserted:
>>>
>>> "The chosen protocol will need to be deployable with minimal changes
>> to
>>> the existing Internet, preferably working with unmodified routers."
>>>
>>> I deleted the competition with the existing proposal -- either that's
>>> obvious, or something else is at play from which the BoF/WG should not
>>> be constrained, so it seemed an unnecessary restriction in the text.
>>>
>>>>> Additional work items could include detailing the motivations for
>>>>> congestion exposure, a threat analysis of the subsequent protocol,
>>>>> providing feedback on experimental trials and describing deployment
>>>>> considerations.
>>>> s/providing feedback on/reporting on/
>>> Done.
>>>
>>>> [phil] ok
>>>>
>>>>> Importantly, the proposed WG would encourage experimentation but
>> not
>>>>> deliberate on how congestion exposure should be used: our concern
>>>>> would be how flexibly the resulting protocol can support differing
>>>>> needs at run-time, rather than dictating a particular usage at
>>> design
>>>> time.
>>>>
>>>
>>> Thanks,
>>> Leslie.
>>>
>>>>
>>>> Bob
>>>>
>>>> At 04:02 17/10/2009, Leslie Daigle wrote:
>>>>
>>>>> Hi,
>>>>>
>>>>> I've posted a description on the BoF wiki page:
>>>>>
>>>>> http://trac.tools.ietf.org/area/tsv/trac/wiki/re-ECN
>>>>>
>>>>> I think I mostly followed the structural edits, but not the wording
>>>>> changes within sentences, because I felt there were important (if
>>>>> subtle) changes that I wasn't convinced about/would want further
>>>>> input from the list for.   But -- it's a wiki.  We can change the
>>>>> text, if there's need to do so!
>>>>>
>>>>> Thanks,
>>>>> Leslie.
>>>>>
>>>>>> Suggested edited version (slightly shorter and it moves references
>>>>>> to re-ECN further towards the end. Also tries to tighten up the
>>> text a
>>>> bit):
>>>>>> Congestion Exposure (ConEx) is a proposed new IETF activity that
>>>>>> reveals congestion along the forwarding path of the Internet. By
>>>>>> revealing the expected congestion in the IP header of every
>> packet,
>>>>>> congestion exposure provides a new generic network capability. We
>>>>>> believe such information could be used for many purposes,
>> including
>>>>>> congestion policing, accountability and inter-domain SLAs. It may
>>>>>> also open new approaches to QoS and traffic engineering.
>>>>>>
>>>>>> The Internet is, in essence, about pooling and sharing resources.
>>>>>> This has been paramount to its success and has traditionally been
>>>>>> managed through the voluntary use of TCP congestion
>>>>>> control.  However, TCP alone is unable to prevent bandwidth
>>>>>> intensive applications, such as peer-to-peer or streaming video,
>>>>> >from causing enough congestion to severely limit the
>>>>>> user-experience of many other end-hosts.  This has led ISPs to
>>>>>> deploy ad-hoc solutions such as volume accounting, rate policing
>>>>>> and deep packet inspection in an attempt to distribute capacity
>>>>>> differently. Such practices are leading to calls for government
>>>>>> regulation as well as stifling innovation at the transport and
>>>>>> application layer (see for example, the problem statement I-D (ref
>>>>>> below) and RFC5594).
>>>>>>
>>>>>> We believe these problems stem from the lack of accountability for
>>>>>> causing congestion at the network layer. We propose a metric where
>>>>>> all IP packets carry information about the expected rest-of-path
>>>>>> congestion, so that any network node may estimate how much
>>>>>> congestion it will cause by forwarding traffic. This will allow
>>>>>> network operators to count the volume of congestion about to be
>>>>>> caused as easily as the volume of bytes in any aggregate of
>>>>>> traffic. Once ISPs can see rest-of-path congestion, they can
>>>>>> actively discourage users from causing excessive congestion,
>>>>>> encourage other networks to control the congestion their customers
>>>>>> cause, and more meaningfully differentiate between the qualities
>> of
>>>>>> services offered by potential connectivity partners. Meanwhile
>>>>>> end-hosts can be freed from rate restrictions so long as they
>>>>>> control the overall congestion they cause.
>>>>>>
>>>>>> The purpose of this BoF is to explore whether the IETF community
>>>>>> agrees this lack of congestion exposure is a problem and to gauge
>>>>>> the support for and viability of pursuing an IETF activity to
>>>>>> define a basic protocol to expose the expected rest-of-path
>>>>>> congestion in the IP header.  Any such protocol should work with
>>>>>> minimal changes to the existing network; in particular it should
>>>>>> work with unmodified routers. There is already one existing
>>>>>> proposal that builds on ECN to provide rest-of-path congestion
>>>>>> information in every IP header and other proposals may come
>>> forward.
>>>>>> If supported, an eventual WG would focus on developing such a
>>>>>> protocol as its main work item.  Additional work items could
>>>>>> include detailing the motivations for congestion exposure, a
>> threat
>>>>>> analysis of the protocol, providing feedback on experimental
>> trials
>>>>>> and describing deployment considerations. Importantly, the
>> proposed
>>>>>> WG would encourage experimentation but not deliberate on how
>>>>>> congestion exposure should be used: our concern would be how
>>>>>> flexibly the resulting protocol can support differing needs at
>>>>>> run-time, rather than dictating a particular usage at design time.
>>>>>>
>>>>>>
>>>>>> *From:* [e-mail] [mailto:[e-mail]]
>>>>>> *On Behalf Of *[e-mail]
>>>>>> *Sent:* 16 October 2009 11:28
>>>>>> *To:* [e-mail]
>>>>>> *Subject:* [re-ECN] ConEx BoF announcement text
>>>>>>
>>>>>> Here's a slightly revised version of the announcement text -
>> thanks
>>>>>> to Joao and everyone who worked on it.
>>>>>>
>>>>>> The main change was to re-write the last 2 paras from the
>>>>>> perspective of the BoF. I also deleted the claim that the work
>>>>>> should be transport-agnostic, as I find 'transport' an ambiguous
>>>>>> word & also think the substantive point is already made by saying
>>>>>> the congestion is revealed in the IP header.
>>>>>>
>>>>>> Please send any further suggestions asap, so we can circulate to
>>>>>> other mailing lists later today
>>>>>>
>>>>>> Thanks
>>>>>> Phil & Leslie
>>>>>>
>>>>>> ---
>>>>>>
>>>>>> Congestion Exposure (ConEx) is a proposed new IETF activity to
>>>>>> enable congestion to be exposed along the forwarding path of the
>>>>>> Internet. By revealing expected congestion in the IP header of
>>>>>> every packet, congestion exposure provides a generic network
>>>>>> capability which allows greater freedom over how capacity is
>>> shared.
>>>>>>
>>>>>>
>>>>>> An existing proposal, building on ECN to reveal "rest-of-path"
>>>>>> information into the IP header, has already demonstrated how
>>>>>> congestion exposure can give an incentive to control one's impact
>>>>>> on the network beside TCP congestion-control. We believe this
>>>>>> "congestion exposure" information may be used for many purposes,
>>>>>> including congestion policing, accountability and inter-domain
>>>>>> SLAs. It may also open new approaches to QoS and traffic
>>> engineering.
>>>>>> The Internet is, in essence, about pooling resources. The ability
>>>>>> to share capacity has been paramount to its success and has
>>>>>> traditionally been managed through the voluntary use of TCP
>>>>>> congestion control.
>>>>>> However, TCP alone is unable to prevent bandwidth intensive
>>>>>> applications, such as peer-to-peer or streaming video, from
>> causing
>>>>>> enough congestion to severely limit the user-experience of many
>>>>>> other end-hosts.  This has led ISPs to deploy ad-hoc solutions
>> such
>>>>>> as volume accounting, rate policing and deep packet inspection in
>>>>>> an attempt to distribute capacity differently. The consequences of
>>>>>> such practices are increasingly leading to calls for government
>>>>>> regulations and stifling innovation at the transport and
>>>>>> application layer (see for example, the problem statement I-D (ref
>>>>>> below) and RFC5594).
>>>>>>
>>>>>> We believe these problems stem from the lack of a network-layer
>>>>>> system for accountability -- among all parties -- for sending
>>>>>> traffic which causes congestion. We propose a metric where IP
>>>>>> packets carry information about the expected rest-of-path
>>>>>> congestion, so that any network node may estimate how much
>>>>>> congestion it is likely to cause by forwarding traffic. A network
>>>>>> operator can then count the volume of congestion about to be
>> caused
>>>>>> by an aggregate of traffic as easily as it can count the volume of
>>>>>> bytes entering its network today. Once ISPs can see rest-of-path
>>>>>> congestion, they can actively discourage users from causing large
>>>>>> volumes of congestion, discourage other networks from allowing
>>>>>> their users to cause congestion, and more meaningfully
>>>>>> differentiate between the qualities of services offered from
>>>>>> potential connectivity partners. Meanwhile end-hosts may be freed
>>>>> >from rate restrictions where their traffic causes little
>>> congestion.
>>>>>> The purpose of the BoF is to explore the support for and viability
>>>>>> of pursuing an IETF activity to define a basic protocol to expose
>>>>>> the expected rest-of-path congestion in the IP header.  Any such
>>>>>> protocol should work with minimal changes to the existing network,
>>>>>> in particular it should work with unmodified routers.
>>>>>>
>>>>>> If supported, an eventual WG would focus on the development of
>> that
>>>>>> protocol as its main work item.  Additional work items could
>>>>>> include detailing the motivations for congestion exposure, a
>> threat
>>>>>> analysis of the subsequent protocol, providing feedback on
>>>>>> experimental trials and describing deployment considerations.
>>>>>> Importantly, the proposed WG would encourage experimentation but
>>>>>> not deliberate on how congestion exposure should be used: our
>>>>>> concern would be how flexibly the resulting protocol can support
>>>>>> differing needs at run-time, rather than dictating a particular
>>>>>> usage at design time.
>>>>>>
>>>>>>
>> -------------------------------------------------------------------
>>> ---
>>>> -- 
>>>>>> _______________________________________________
>>>>>> re-ECN mailing list
>>>>>> [e-mail]
>>>>>> https://www.ietf.org/mailman/listinfo/re-ecn
>>>>> -- 
>>>>>
>>>>> -------------------------------------------------------------------
>>>>> "Reality:
>>>>>      Yours to discover."
>>>>>                                 -- ThinkingCat
>>>>> Leslie Daigle
>>>>> [e-mail]
>>>>> -------------------------------------------------------------------
>>>>> _______________________________________________
>>>>> re-ECN mailing list
>>>>> [e-mail]
>>>>> https://www.ietf.org/mailman/listinfo/re-ecn
>>>> ________________________________________________________________
>>>> Bob Briscoe,                                BT Innovate & Design
>>>>
>>>> _______________________________________________
>>>> re-ECN mailing list
>>>> [e-mail]
>>>> https://www.ietf.org/mailman/listinfo/re-ecn
>>>>
>>> -- 
>>>
>>> -------------------------------------------------------------------
>>> "Reality:
>>>       Yours to discover."
>>>                                  -- ThinkingCat
>>> Leslie Daigle
>>> [e-mail]
>>> -------------------------------------------------------------------
>>> _______________________________________________
>>> re-ECN mailing list
>>> [e-mail]
>>> https://www.ietf.org/mailman/listinfo/re-ecn
>>
>

-- 
Richard Bennett
Research Fellow
Information Technology and Innovation Foundation
Washington, DC