Re: [Tsvwg] A comment on "draft-briscoe-tsvwg-relax-fairness-00" re file-sharing

["Robb Topolski" <[e-mail]>]

Hello Bob, thanks for the reply!

> a) Could my scenario become common, even if it's not currently prevalent?

> c) Who is actually correct for the Internet today? (split out into
> next posting)

One problem with applications, as you are aware, is that some users often
don't follow configuration guidance or instructions.  So the answer to the
two questions above is possibly and partially.  

For the users that won't follow instructions, there will be users like your
friend (mentioned elsewhere), who was running about 40 torrent
simultaneously.  Using Azureus, presuming all 45 torrents had sufficient
"leechers," such a mis-configuration would create an instance of a user with
over a hundred active uploading TCP connections (unless he changed the
setting that also limits each task to 3-4 upload slots).  But there will
also be users that accept the reasonable installation defaults, and never go
into "Advanced mode" to break away from the parameters set at install time.


Please, though, if your statement is about some future possible condition, I
ask you to please write it up making that point clear.  Your statements
about the present condition are being relied upon in certain serious debates
in numerous circles -- including other WGs of the IETF.  

We ARE (hopefully) going to continue to transition to more symmetric
connection model.  I don't think I have any confidence in any particular
view of how things will look then.  

Personally, I've seen enough fads come and go, and I see part of the
behavior on today's P2P networks being a fad of "appropriation."  Some (or
many) of these kids are downloading media faster than they can possibly
consume it.  It's either a hoarding reaction (e.g. "someday it will go
away") or it's a bragging-rights thing (e.g. "he who dies with the biggest
DVD stack, wins").  I have no data, it's just a hunch.

> equality was the dominant sharing regime (e.g. if, as access speeds
> increased, most congestion moved further into the network where FQ is
> too unscalable, e.g. border links).

You're over my head at the "FQ is too unscalable" part, but since you
mentioned border links, as you consider this future issue, also consider
that there may be more borders than we all might assume.  This might offload
some of the danger, I don't know if you've included it in your
considerations.

Having never seen the topography on paper before, one thing that surprised
me was learning that the Cable MSOs cannot be modeled as a single network.
Instead, they are several smaller metro-area networks -- one in each area,
and each with its own border/gateways to upper-tier transit providers (one
of which may be a company-owned backbone to other metro-areas).  

> I don't mind altering the figures in the draft accordingly, or
> qualifying their applicability.

Thanks, that would definitely help.  Can I also suggest using something
other than the word, "trick?"  It's not like any of these P2P apps are
setting up redundant connections to the same host (such as "download
accelerators" do).  Knowing some of these P2P developers as I do, the last
thing they want to do is harm the network -- they just want to fill the
space available. 


Robert M. "Robb" Topolski <[e-mail]>
Hillsboro, Oregon USA

Variables won't; constants aren't.
Osborn 

> -----Original Message-----
> From: Bob Briscoe [mailto:[e-mail]]
> Sent: Monday, April 14, 2008 5:06 AM
> To: Robb Topolski
> Cc: 'IETF Transport Area working group mailing list'
> Subject: Re: [Tsvwg] A coment on "draft-briscoe-tsvwg-relax-fairness-00"
> re file-sharing
> 
> Robb,
> 
> There's three types of responses to this (expanded below):
> a) Could my scenario become common, even if it's not currently prevalent?
> b) The discussion is over what the correct fairness /goal/ should be
> c) Who is actually correct for the Internet today? (split out into
> next posting)
> 
> Anyway, TCP doesn't actually determine capacity sharing for
> residential backhaul links - operators generally use per-user fair
> queuing. This draft merely shows how bad things would be if rate
> equality was the dominant sharing regime (e.g. if, as access speeds
> increased, most congestion moved further into the network where FQ is
> too unscalable, e.g. border links).
> 
> a) Could my scenario become common, even if it's not currently prevalent?
> ---------------------------
> The discussion below shows that (as you say) the main reason
> swarmcasting like BitTorrent doesn't open many connections is
> asymmetric access. If you look at the situation in countries like
> Japan (the [Res_p2p] reference), where symmetric 100M FTTH has become
> very prevalent over the last few years, this constraint disappears.
> Campus & enterprise networks are already symmetric.
> 
> We're designing protocols today so they will be available in a couple
> of years. We have to look ahead.
> 
> b) The discussion is over what the correct fairness /goal/ should be
> ---------------------------
> The draft is about the /combination/ of multiple connections and high
> activity factors. It's designed to show that the /goal/ of equal flow
> rates is not the one we should be pursuing. Even if my figure of
> 500-5000 times more traffic intensity is an order of magnitude wrong
> for most of today's Internet, 50-500 times more intensity (or even
> 5-50) still shows the original goal of equal flow rates is inappropriate.
> 
> I don't mind altering the figures in the draft accordingly, or
> qualifying their applicability.
> 
> 
> 
> Bob
> 
> At 05:30 12/04/2008, Robb Topolski wrote:
> >Comment on
> >
> >Problem Statement: We Don't Have To Do Fairness Ourselves
> >draft-briscoe-tsvwg-relax-fairness-00
> >
> >
> >Dear Working Group members,
> >
> >Thank you for your time working on this committee and issues such as
> these.
> >
> >The above quoted paragraph requires a number of corrections.  This
> paragraph
> >is a basis for the problem statement that follows it -- so getting the
> basis
> >down right is key to analysing the issue and sizing up the problem.  The
> >corrections that I hope to effectively communicate seem to me to reduce
> the
> >stated size of the problem.
> >
> >--Quote--
> >Even though file-sharing generally uses TCP, it uses the
> >well-known trick of opening multiple connections--currently around
> >100 actively transferring over different paths is not uncommon. A
> >competing Web application might open a couple of flows at a time, but
> >perhaps only actively transfer data 1-10% of the time (its activity
> >factor). Combining 50x less flows and 10-100x lower activity factor
> >means the traffic intensity from the Web app can be 500-5,000x less.
> >However, despite being so much lighter on the network, it gets 50x
> >less bit rate through the bottleneck.
> >--EndQuote--
> >
> >I am relatively certain that the draft is talking about BitTorrent above,
> >and it unforunately misinterprets what it does.  BitTorrent is the #1 P2P
> >File Sharing protocol in use today.  Furthermore, neither #2 P2P file
> >sharing protocol ED2K (aka eDonkey, eDonkey2000, eMule, or MFTP) nor #3
> >Gnutella (aka G1, G2, or Gnutella2) work like BitTorrent, nor as
> Briscoe's
> >draft described above.
> >
> >In the case of BitTorrent, between 35-70 TCP connections are generated.
> >However, only three or four of these connections are actively
> transferring
> >data.  Therefore, any benefit to the "trick" is erased.  The reason the
> >remainder sit idle is described in the specification
> >(http://wiki.theory.org/BitTorrentSpecification#Choking_and_Optimistic_Un
> cho
> >king), chief of which is the desire that BitTorrent NOT interfere with
> TCP
> >congestion control.
> >
> >It is important to remember that P2P users are largely residential users,
> >most using connections that are configured with asymmetric connections
> where
> >the maximum download bandwidth allowance is several times that of their
> >upload allowance.  In all of the discussions about "fairness" that I've
> been
> >involved in, it has to do with sharing the tiny upload pipe.  Filling the
> >generously-configured download pipe is seldom a user fairness concern (it
> is
> >also very difficult to control at the receiving end).  A trend is barely
> >beginning toward more symmetrical residential accounts, but it is
> probably
> >too small to accurately determine changes in usage patterns created by
> it.
> >
> >That BitTorrent uses "hundreds of connections" that are simultaneously
> >active is a common misperception.  While the draft likely did not mean to
> >inject emotionalism, the label of "trick" is both inaccurate and
> >inflammatory.  The reason that BitTorrent makes these idle connections is
> to
> >allow for one connection to "hunt" for the best reciprocating peer, which
> >allows two efficiently located peers to detect and reciprocate with each
> >other.  If not interfered with by network operators, this pretty much
> >ensures that the lowest-latency peers will eventually find one another
> and
> >engage in a long-term exchange of data.  This is not only fast for the
> user,
> >choosing the most efficient (lowest latency) pairings is friendliest to
> the
> >local ISP network and the Internet as a whole.
> >
> >All three of the top P2P protocols do open multiple upload connections.
> >ED2K seems happiest with 3-4 KB/s upload flows, Gnutella with 10 KB/s
> upload
> >flows, and BitTorrent with anywhere from 3 KB/s to 7 KB/s flows.
> Therefore,
> >the number of upload flows that a single peer might generate (think
> >different archives being sent by the same client simultaneously) is a
> >function of dividing the configured upload bandwidth by the amounts
> >decribed.
> >
> >An example:
> >
> >BitTorrent:  Upload limit set to 20 KB/s, 3-6 upload TCP connections
> >(remainder are idle or downloading only)
> >ED2K:  Upload limit set to 20 KB/s, 5-6 uploading TCP connections
> (remainder
> >of connections are downloading only or performing light-bandwidth
> >housekeeping, such as queue placement requests or updates)
> >Gnutella:  Upload limit set to 20 KB/s, 1-2 uploading TCP connections
> >(remainder, same as for ED2K).
> >
> >All three of the above have a UDP component, which is used for searching
> or
> >other light network housekeeping.  There is an emerging use of UDP for
> "NAT
> >hole punching" but these "connections" are still quite rare.
> >
> >I am happy to answer any questions or further clarify anything that I
> can.
> >
> >Sincerely,
> >
> >Robert M. "Robb" Topolski
> >[e-mail]
> 
> __________________________________________________________________________
> __
> Notice: This contribution is the personal view of the author and does
> not necessarily reflect the technical nor commercial direction of BT plc.
> __________________________________________________________________________
> __
> Bob Briscoe,                           Networks Research Centre, BT
> Research
> B54/77 Adastral Park,Martlesham Heath,Ipswich,IP5 3RE,UK.    +44 1473
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>