Technical Summary
Applications using the Internet already have access to some topology
information of Internet Service Provider (ISP) networks. For
example, views to Internet routing tables at looking glass servers
are available and can be practically downloaded to many network
application clients. What is missing is knowledge of the underlying
network topologies from the point of view of ISPs. In other words,
what an ISP prefers in terms of traffic optimization -- and a way to
distribute it.
The Application-Layer Traffic Optimization (ALTO) Service provides
network information (e.g., basic network location structure and
preferences of network paths) with the goal of modifying network
resource consumption patterns while maintaining or improving
application performance. The basic information of ALTO is based on
abstract maps of a network. These maps provide a simplified view,
yet enough information about a network for applications to
effectively utilize them. Additional services are built on top of
the maps.
This document describes a protocol implementing the ALTO Service.
Although the ALTO Service would primarily be provided by ISPs, other
entities such as content service providers could also operate an ALTO
Service. Applications that could use this service are those that
have a choice to which end points to connect. Examples of such
applications are peer-to-peer (P2P) and content delivery networks.
Working Group Summary
The specification process has been particularly long and
articulated. The WG had to make many decisions -- the architectural
ones reflected in the related requirements document -- that took
time. However, quite broad consensus was reached on almost all of
them.
Document Quality
The document shepherd has followed the specification process
closely, implementing a proof-of-concept client application himself
(http://alto.tilab.com/alto-xkcd/). He has proofread the final
version of the document and believes it is ready for publication.
Implementations: three implementations with some interoperability
were demostrated during a "running code show" organized at
IETF80. Seven client and five server implementations were tested in
an "interoperability event" at IETF81, with pretty good results
(http://www.ietf.org/mail-archive/web/alto/current/msg01181.html). A
second interoperability event was arranged during IETF85, were four
server and two client implementations were tested against 21 test
cases, with again good success rates (last slide of
http://www.ietf.org/proceedings/85/slides/slides-85-alto-0.pdf).
Expert supervision: since the protocol, despite being developed in
TSV, is an application level protocol, based on HTTP and following a
REST-ful approach, Peter Saint-Andre (also former responsible AD for
ALTO, before the WG was moved to TSV) was appointed as APPS expert
and has supervised the specification process in its crucial phases
(Peter stepped back as Tech advisor at a later phase). Other experts
from APPS (Martin Thomson, Alexey Melnikov), SEC (Richard Barnes,
Hannes Tshofenig) and OPS (David Harrington, Benoit Claise) have at
some point been involved and provided feedback on various aspects.
Ted Hardie kindly provided a early apps-dir review
(http://www.ietf.org/mail-archive/web/apps-discuss/current/msg05406.html)
that helped in improving the document quality quite a lot.
A Media Type review was requested on media-types@ietf.org, but was
never formally performed. However, in some private exchages
triggered by the review request, no issues were raised.
Personnel
Enrico Marocco is the document shepherd, Spencer Dawkins is the
responsible AD.