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TSV Area ALTO Working Group RFC Request for Comments I-D Internet-Draft ALTO Exposing network information to applications can be a basic function of computer networking. Such network information can be exposed to applications through either the data path or the control path. This informational document conducts a survey and analysis of existing capabilities and performance of protocols transporting network information to applications. The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 when, and only when, they appear in all capitals, as shown here.

Application-Layer Traffic Optimization (ALTO) provides a means for network applications to obtain network status information so that the applications can identify efficient application-layer traffic patterns using the networks. Recently, multiple extensions are proposed to the ALTO base protocol to extend the ability of ALTO to transport network information to applications. The objective of this document is to put ALTO transport in the general context of transporting network information to applications, and evaluate ALTO and related protocols in their transport capabilities and efficiencies.

There can be a large design space to transport network information to applications. Broadly, the designs can be classified into two types: data path transport and control path transport. An example of data path transport is TCP ECN options, which allows networks to convey network information to applications (i.e., endhosts). In a general data path design, as data packets traverse a network, the network elements update the field(s) of the data packets to provide network information. The recent development of in-network telemetry (INT) focuses on data path transport. This document focuses on TCP options based data path transport. ALTO base protocol, on the other hand, is a control path design. In a general control path design, the network information is collected by a service and exposed to applications. This document focuses on ALTO transport and 3GPP NEF.

The information model includes the following abilities: information availability, information selection, update control, etc.

There can be substantial security issues when transporting network information to applications.

This informational document does not have IANA consideration.

The author thanks many reviewers for their comments.