I am surprised to see that ALTO is being proposed for a WG after the last BoF
concluded with no consensus whatsoever. I think a second BoF is more
appropriate than a WG on the topic at this time. That said, I do see the need
for this work, although I have some comments on the current direction.
Overall, I think we should work with the notion of an ALTO "service" rather
than specifically an ALTO "server". The ALTO service may be provided by a
server, a cluster of distributed servers or as a service in an overlay.
Although some of the charter wording talks about a "service" rather than a
"server", there is enough mention of a "server" entity to imply a strict
As part of that, I think there are a couple of key things that need to be
- A protocol that allows peers (or ALTO clients) to publish information about
themselves as part of the ALTO service. An example of such information may be
the uplink/downlink bandwidth of the peer.
- The ability to register information types with IANA and extend these. The
request/response protocol should be a generic enough container for any
information that peers can provide and look for, plus what may be available
from service providers, etc. There may be some guidelines on how such
information types can be registered and we may start with default ones.
Some further comments/questions inline.
[mailto:ietf-announce-bounces(_at_)ietf(_dot_)org] On Behalf Of IESG Secretary
Sent: Monday, October 06, 2008 1:36 PM
To: IETF Announcement list
Subject: WG Review: Application-Layer Traffic Optimization (alto)
A new IETF working group has been proposed in the
Applications Area. The IESG has not made any determination
as yet. The following draft charter was submitted, and is
provided for informational purposes only. Please send your
comments to the IESG mailing list (iesg(_at_)ietf(_dot_)org) by Monday,
October 13, 2008.
Application-Layer Traffic Optimization (alto)
Last Modified: 2008-09-29
Current Status: Proposed Working Group
Applications Area Director(s):
Lisa Dusseault (lisa at osafoundation.org) Chris Newman
(Chris.Newman at sun.com)
Applications Area Advisor:
Lisa Dusseault (lisa at osafoundation.org)
General Discussion: p2pi at ietf.org
To Subscribe: https://www.ietf.org/mailman/listinfo/p2pi
Description of Working Group:
A significant part of the Internet traffic today is generated
by peer-to-peer (P2P) applications used for file sharing,
real-time communications, and live media streaming. P2P
applications exchange large amounts of data, often uploading
as much as downloading. In contrast to client/server
architectures, P2P applications often have a selection of
peers and must choose.
One of the advantages of P2P systems comes from redundancy in
resource availability. This requires choosing among download
locations, yet applications have at best incomplete
information about the topology of the network. Applications
can sometimes make empirical measurements of link
performance, but even when this is an option it takes time.
The application cannot always start out with an optimal
arrangement of peers, thus causing at least temporary reduced
performance and excessive cross-domain traffic. Providing
more information for use in peer selection can improve P2P
performance and lower ISP costs.
The Working Group will design and specify an
Application-Layer Traffic Optimization (ALTO) service that
will provide applications with information to perform
better-than-random initial peer selection.
ALTO services may take different approaches at balancing
factors including maximum bandwidth, minimum cross-domain
traffic, lowest cost to the user, etc. The WG will consider
the needs of BitTorrent, tracker-less P2P, and other
applications, such as content delivery networks (CDN) and
What does the above sentence mean? If we are putting such a list together, we
must also take into account needs from structured P2P overlays such as those
being specified in P2PSIP.
The WG will focus on the following items:
- A "problem statement" document providing a description of the
problem and a common terminology.
- A requirements document. This document will list
requirements for the ALTO service, identifying, for example,
what kind of information P2P applications will need for
optimizing their choices.
- A request/response protocol for querying the ALTO service
to obtain information useful for peer selection, and a format
for requests and
responses. The WG does not require intermediaries between the ALTO
server and the peer querying it. If the requirements
analysis identifies the need to allow clients to delegate
third-parties to query the ALTO service on their behalf, the
WG will ensure that the protocol provides a mechanism to
assert the consent of the delegating client.
Is this meant to allow for entities such as proxies to be in the path?
- A document defining core request and response formats and
semantics to communicate network preferences to applications.
Since ALTO services may be run by entities with different
level of knowledge about the underlying network, such
preferences may have different representations. Initially the
WG will consider: IP ranges to prefer and to avoid, ranked
lists of the peers requested by the client, information about
topological proximity and approximate geographic locations.
Other usages will be considered as extensions to the charter
once the work for the initial services has been completed.
Earlier, it is mentioned that the requirements document will determine the
types of information that are useful for P2P applications. Given that, it
seems premature to conclude that the WG should consider the above mentioned
parameters. Also, as I mentioned earlier, I think it is essential to keep the
protocol and message formats extensible and allow for exchange of any
registered information type.
Another question I have is about the assumptions around expected peer
addressing models. Some of the above seems to hint at IP addresses - is this
an assumption already?
- In order to query the ALTO server, clients must first know
one or more ALTO servers that might provide useful
information. The WG will look at service discovery
mechanisms that are in use, or defined elsewhere (e.g.
based on DNS SRV records or DHCP options). If such discovery
mechanisms can be reused, the WG will produce a document to
specify how they may be adopted for locating such servers.
However, a new, general-purpose service discovery mechanism
is not in scope.
Alternately, the clients may look for ALTO services within an overlay. This
can be modeled as service discovery within the overlay - I'm, however, not
suggesting that we take on solutions for that.
When the WG considers standardizing information that the ALTO
server could provide, the following criteria are important to
ensure real feasibility.
- Can the ALTO service technically provide that information?
- Is the ALTO service willing to obtain and divulge that information?
- Is it information that a client will find useful?
I'm not sure how useful it is for us to answer this question. The protocol we
develop simply needs to be a container for any information that has a
registered type and fits a certain format.
- Can a client get that information without excessive privacy concerns
(e.g. by sending large lists of peers)?
- Is it information that a client cannot find easily some other way?
After these criteria are met, the generality of the data will
be considered for prioritizing standardization work, for
example the number of operators and clients that are likely
to be able to provide or use that particular data.
If we can build an extensible protocol, we don't need to define all possible
kinds of information that get carried in it.
case, this WG will not propose standards on how congestion is
signaled, remediated, or avoided, and will not deal with
information representing instantaneous network state.
Such issues belong to other IETF areas and will be treated
accordingly by the specific area.
This WG will focus solely on the communication protocol
between applications and ALTO servers. Note that ALTO
services may be useful in client-server environments as well
as P2P environments, although P2P environments are the first
focus. If, in the future, the IETF considers changes to
other protocols for actually implementing ALTO servers (e.g.
application-layer protocols for Internet coordinate systems,
routing protocol extensions for ISP-based solutions), such
work will be done in strict coordination with the appropriate WGs.
I hope we can also look at the above from a generalized service perspective
rather than just a client-server perspective.
Issues related to the content exchanged in P2P systems are
also excluded from the WG's scope, as is the issue dealing
with enforcing the legality of the content.
Goals and Milestones (very tentative dates):
Apr 2009: Working Group Last Call for problem statement Jun
2009: Submit problem statement to IESG as Informational Aug
2009: Working Group Last Call for requirements document Oct
2009: Submit requirements document to IESG as Informational
Jan 2010: Working Group Last Call for request/response
protocol Jan 2010: Working Group Last Call for usage document
for communicating network preferences Mar 2010: Submit
request/response protocol to IESG as Proposed Standard Mar
2010: Submit usage document to IESG as Proposed Standard May
2010: Working Group Last Call of discovery mechanism Jul
2010: Submit discovery mechanism to IESG as Proposed Standard
Aug 2010: Dissolve or re-charter
Initial Drafts for Consideration
- draft-marocco-alto-problem-statement-02 --
Application-Layer Traffic Optimization (ALTO) Problem Statement
- draft-kiesel-alto-reqs-00 -- Application-Layer Traffic Optimization
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