Application-Layer Traffic Optimization

The information below is for an old version of the document
Document Proposed charter Application-Layer Traffic Optimization WG (alto) Snapshot
Title Application-Layer Traffic Optimization
Last updated 2014-05-13
State Start Chartering/Rechartering (Internal IESG/IAB Review) Rechartering
WG State Active
IESG Responsible AD Mirja K├╝hlewind
Charter Edit AD Spencer Dawkins
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The ALTO working group was established in 2008 to devise a
request/response protocol for allowing a host to benefit from a server
that is more cognizant of the network infrastructure than the host
would be. The working group has developed an HTTP-based protocol
to allow hosts to benefit from the network infrastructure
by having access to a pair of maps: a topology map and a cost map.

The origins of the ALTO protocol lie in peer-to-peer (P2P)
applications, where the host is a peer in a P2P network and desires a
rendezvous with other peers for file sharing, real-time
communications, etc. It is a testament to the flexibility of the ALTO
protocol that it is now being considered as a solution for problems
outside the P2P domain, such as in datacenter networks and in content
distribution networks (CDN) where exposing abstract topologies helps

To support the emerging new uses of ALTO, certain extensions are being
sought. These extensions can be classified as follows:

   o Protocol extensions for reducing the volume of on-the-wire data
     exchange required to align the ALTO server and
     clients. Extensions under consideration are mechanisms for
     delivering server-initiated notifications and partial updates of
     maps.  Efforts developed in other working groups such as
     Websockets and JSON-patch will be considered, as well as bespoke
     mechanisms specific to the ALTO protocol.

   o Extensions to the base ALTO server discovery mechanism
     (RFC-to-be) for deployment in heterogeneous network environments.
     Mechanisms under consideration are extensions for third-party and
     anycast-based server discovery.  Because the issue of third-party
     server discovery is broad and not particular to ALTO, the WG will
     prefer to use server discovery mechanisms produced by other
     working groups especially chartered to do so.  In the absence of
     such existing work, the WG will develop an ALTO-specific
     third-party server discovery mechanism.

   o Protocol extensions to convey a richer set of attributes to allow
     applications to determine not only "where" to connect but also
     "when" to connect.  Such additional information will be related
     both to endpoints (e.g. conveying server load and cache
     geo-location information for CDN use cases) and to
     endpoint-to-endpoint costs (e.g. bandwidth calendaring to
     represent time-averaged cost values in datacenter networks).

     The working group will specify such extension in coordination
     with other working groups that have a focus on the related use
     cases.  The scope of extensions is not limited to those
     identified by the WGs.

   o A document specifying how a graph representation format
     (e.g. originating from a YANG data model) can be used in ALTO and
     optionally be exported by an ALTO server in addition to network
     and cost maps. The WG will only consider abstract representation
     of the network layer; it will not consider, nor will it model,
     raw network topology, routing protocols, or RIB data.

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?

   - Can a client get that information without excessive privacy
     concerns?  Extensions defining new endpoint properties should
     focus on exposing attributes of endpoints that are related to the
     goals of ALTO -- optimization of application-layer traffic -- as
     opposed to more general properties of endpoints. Privacy aspects
     of new endpoint properties will in any case be evaluated to the
     guidelines provided in the IANA considerations and Security
     Considerations of the ALTO protocol specification (RFC-to-be,
     sections 14.3 and 15.4 at IESG review time).

    - Is it information that a client cannot find easily some other

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

Issues related to the specific content exchanged in systems that make
use of ALTO are also excluded from the WG's scope, as is the issue
dealing with enforcing the legality of the content.