Re: [p2pi] Content Identifiers sent to ALTO server?

[Laird Popkin <laird at pando.com>]

Yes, exactly. That's the case (IMO) for both normal peers and p2p caches.

- Laird Popkin, CTO, Pando Networks
  mobile: 646/465-0570

----- Original Message -----
From: "Richard Woundy" <Richard_Woundy at cable.comcast.com>
To: "Laird Popkin" <laird at pando.com>, "John Leslie" <john at jlc.net>
Cc: p2pi at ietf.org
Sent: Monday, July 21, 2008 5:53:44 PM (GMT-0500) America/New_York
Subject: RE: [p2pi] Content Identifiers sent to ALTO server?

>ALTO guidance: Tracker (updated periodically, asynchronously) receives
optimization rules from the ALTO server.

Just to make sure I understand: in this scenario, the tracker would be
the ALTO client. The ALTO client (tracker) could send ALTO requests with
content IDs, and ALTO servers could respond with P2P caching servers
that store that content. When peers request content from the tracker,
the tracker can refer the peer to specific P2P caching servers, without
additional ALTO requests. The ALTO server would be insulated from any
peer's request for that content.

-- Rich

-----Original Message-----
From: p2pi-bounces at ietf.org [mailto:p2pi-bounces at ietf.org] On Behalf Of
Laird Popkin
Sent: Monday, July 21, 2008 10:29 AM
To: John Leslie
Cc: p2pi at ietf.org
Subject: Re: [p2pi] Content Identifiers sent to ALTO server?

I don't think that either of the scenarios that you list is particularly
likely for p2p swarm file downloading. I'll explain why, they outline
the model of ALTO that seems most valuable for that application.

1. If the client has a list of IP addresses, the list is short enough
that it can test throughput with each of them all fairly quickly, so the
value of ALTO is low in terms of optimizing p2p performance. This
scenario makes sense for some other applications (e.g. finding a good
network relay, or optimizing small swarm downloads).

2) I think that it's safe to assume that p2p networks will never send a
list of all IP addresses associated with a particular content swarm to
an ISP's ALTO server. This raises obvious business, privacy and legal
issues, which are at best quite concerning.

In addition, putting the ALTO protocol in the middle of a peer request
creates unacceptable operational problems for the p2p network that would
be far worse than any optimization that ALTO could provide. Let's
compare a standard BitTorrent "tracker announce", a tracker announce
with ALTO IP lookup" and "tracker announce with ALTO guidance" for a
peer in a swarm of 10,000 peers.

standard: peer announces, Tracker responds from list in memory (one MTU
each way, UDP). Fast, reliable in-memory operation.

ALTO IP list: In this model, information sent into or out of ALTO is
lists of IP addresses. Peer announces. Tracker sends request, with the
peer address and a complete list of the 10,000 peers in the swarm, to
the ALTO server. ALTO server computes optimal list and returns 50 peers.
Tracker returns list to peer. Tracker does this (send swarm peer list,
receive ALTO peer list) 2,000 times per second. This makes the p2p
tracker slow and unreliable (by adding external communication to what is
now an in-memory operation), and places a huge operational burden on the
ISP's ALTO server. I suspect that ISPs would have problems with this as
well, because it would effectly make their ALTO server a p2p tracker,
with all that implies.

ALTO guidance: Tracker (updated periodically, asynchronously) receives
optimization rules from the ALTO server. Peer announces. Tracker picks
optimal list from known swarm peers based on the ISP's rules, and
returns 50 peers to announcing peer. This is slightly slower than a
standard announce, but it's all in memory in the Tracker, and only
imposes a low volume of ALTO communications. Communication is the same
as the first case (one MTU each way, UDP), plus one ALTO message every
hour (or day, etc.) to update the optimization rules.

- Laird Popkin, CTO, Pando Networks
  mobile: 646/465-0570

----- Original Message -----
From: "John Leslie" <john at jlc.net>
To: "Laird Popkin" <laird at pando.com>
Cc: "Stas Khirman" <stas at khirman.com>, p2pi at ietf.org
Sent: Saturday, July 19, 2008 10:32:40 AM (GMT-0500) America/New_York
Subject: Content Identifiers sent to ALTO server?

Laird Popkin <laird at pando.com> wrote:
> 
> Note that content optimization can also (potentially) be
> content-specific. For example, in P4P, the guidance to the p2p
> networks can be 'tuned' to reflect the specific distribution of
> content.

   This is (potentially) helpful when content is sufficiently static
to flood the distribution information to all ALTO servers. This is
not the general case, and might not even be the most common case in
future scenarios.

> Perhaps the way to phrase this is that the ALTO server MUST support
> operation with no content identifiers, but ALTO clients MAY send
> content identifiers?

   I think Stas was saying that even receiving and discarding content
Identifiers could cause undesirable legal exposure to large ISPs.
In any case, I agree it could.

   I see two very different use cases for what we're discussing here.

1. Client has a list of IP addresses, and wants to know which to
   try first;

2. Client doesn't have a list of IP addresses, but has a Content
   Identifier, and wants an ordered list of IP addresses to try.

   I frankly would much prefer to develop these separately. The
second might well have reason to call upon the first; but the first
never has any reason to make use of the second. Trying to combine
both into a single protocol complicates things unnecessarily (even
before the legal complications come into play).

   Also, the two cases deal in information best known by parties
with vastly different interests in limiting distribution of that
information -- up to and including a business decision to obscure
or even falsify the information passed to certain other parties.

   The technical problems of combining both into a single protocol
look easy enough, but yield no measurable benefit. The legal and
information-protection problem are much more serious.

--
John Leslie <john at jlc.net>
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