Application-Layer Traffic Optimization

The information below is for an older approved charter
Document Charter Application-Layer Traffic Optimization WG (alto) Snapshot
Title Application-Layer Traffic Optimization
Last updated 2008-11-11
State Approved
WG State Active
IESG Responsible AD Martin Duke
Charter Edit AD (None)
Send notices to (None)


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 must
    choose one or more suitable candidates from a selection of peers
    offering the same resource or service.
    One of the advantages of P2P systems comes from redundancy in resource
    availability.  This requires choosing among a list of peers, yet
    applications have at best incomplete information to help the
    selection, e.g., topology of the network.
    Applications can sometimes obtain network information dynamically or
    measure link performance with respect to particular peers, but even
    when this is an option it takes time.  The application cannot always
    start out with an optimal arrangement of peers, thus risking at least
    temporary poor 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 such
    as 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 mirror selection.
    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, types of information P2P
    applications may 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.  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.
    - A specification of core request and response formats and semantics
    to communicate network preferences to applications.  Since ALTO
    services may be run by entities with different levels 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 charter additions once
    the work for the initial services has been completed.
    - 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.
    - An informational document discussing deployment related issues and
    documenting lessons learned from early implementation experiences.
    When the WG considers standardizing information that the ALTO server
    could provide, the following criteria are important to ensure real
    - Can the ALTO service realistically discover that information?
    - Is the distribution of that information allowed by the operators of
    that service?
    - Is it information that a client will find useful?
    - 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 importance 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.  In any 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
    services (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.
    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.