TAPS S. Gjessing
Internet-Draft M. Welzl
Intended status: Informational University of Oslo
Expires: September 19, 2016 March 18, 2016

A Minimal Set of Transport Services for TAPS Systems


This draft will eventually recommend a minimal set of IETF Transport Services offered by end systems supporting TAPS, and give guidance on choosing among the available mechanisms and protocols. It categorizes the set of transport services given in the TAPS document draft-ietf-taps-transports-usage-00, assuming that the eventual minimal set of transport services will be based on a similar form of categorization.

Status of This Memo

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This Internet-Draft will expire on September 19, 2016.

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Table of Contents

1. Introduction

An application has an intended usage and demands for transport services, and the task of any system that implements TAPS is to offer these services to its applications, i.e. the applications running on top of TAPS, without binding an application to a particular transport protocol.

The present draft is based on [TAPS1] and [TAPS2] and follows the same terminology (also listed below). The purpose of these two drafts is, according to the TAPS charter, to "Define a set of Transport Services, identifying the services provided by existing IETF protocols and congestion control mechanisms." This is item 1 in the list of working group tasks. Also according to the TAPS charter, the working group will then "Specify the subset of those Transport Services, as identified in item 1, that end systems supporting TAPS will provide, and give guidance on choosing among available mechanisms and protocols. Note that not all the capabilities of IETF Transport protocols need to be exposed as Transport Services." Hence it is necessary to minimize the number of services that are offered. We begin this by grouping the transport features.

Following [TAPS2], we divide the transport service features into two main groups as follows:

  1. Connection related transport service features
    - Establishment
    - Availability
    - Maintenance
    - Termination
  2. Data Transfer Related Transport Service Features
    - Sending Data
    - Receiving Data
    - Errors

Because QoS is out of scope of TAPS, this document assumes a "best effort" service model [RFC5290], [RFC7305]. Applications using a TAPS system can therefore not make any assumptions about e.g. the time it will take to send a message. There are however certain requirements that are strictly kept by transport protocols today, and these must also be kept by a TAPS system. Some of these requirements relate to features that we call "Functional".

Functional features provide functionality that cannot be used without the application knowing about them, or else they violate assumptions that might cause the application to break. For example, unordered message delivery is a functional feature: it cannot be used without the application knowing about it because the application's assumption could be that messages arrive in-order, and in this case unordered delivery could cause the application to break. Change DSCP and data bundling (Nagle in TCP) are optimizing features: if a TAPS system autonomously decides to enable or disable them, an application will not break, but a TAPS system may be able to communicate more efficiently if the application is in control of this optimizing feature. Change DSCP and data bundling are examples of features that require application-specific knowledge (about delay/bandwidth requirements and the length of future data blocks that are to be transmitted, respectively). Some features, however, do not always require application-specific knowledge, and could therefore sometimes be used by a TAPS system without exposing them to the application. We call these features potentially automatable.

To summarize, features offered to applications are divided into two groups as follows:

The Application-specific features are further divided into two groups:

In the following, some features are additionally marked as DELETED. These features are IETF Transport protocol features that are not exposed to the TAPS user because they include functionality that is automatable. A few features are marked as "ADDED". These provide non-automatable functionality of DELETED features.

2. Terminology (as defined by draft-ietf-taps-transports-10)

The following terms are used throughout this document, and in subsequent documents produced by TAPS that describe the composition and decomposition of transport services.

Transport Service Feature:
a specific end-to-end feature that the transport layer provides to an application. Examples include confidentiality, reliable delivery, ordered delivery, message-versus-stream orientation, etc.
Transport Service:
a set of Transport Features, without an association to any given framing protocol, which provides a complete service to an application.
Transport Protocol:
an implementation that provides one or more different transport services using a specific framing and header format on the wire.
Transport Service Instance:
an arrangement of transport protocols with a selected set of features and configuration parameters that implements a single transport service, e.g., a protocol stack (RTP over UDP).
an entity that uses the transport layer for end-to-end delivery data across the network (this may also be an upper layer protocol or tunnel encapsulation).

3. The superset of transport service features

This section is based on the classification of the transport service features in pass 3 of [TAPS2]. As noted earlier, whether the usage of potentially automatable features can be automatized in a TAPS system depends on how much network-specific information an application wants to manipulate (e.g., to directly expose to its user). Therefore, in the following, "application-specific knowledge" refers to knowledge that only applications have, as opposed to all knowledge that applications may want to have.

3.1. CONNECTION Related Transport Service Features





3.2. DATA Transfer Related Transport Service Features

3.2.1. Sending Data

3.2.2. Receiving Data

3.2.3. Errors

4. Conclusion

The eventual recommendations are:

Given that the intention of TAPS is to break the design-time binding between applications and transport protocols, the decision on which features a TAPS system provides should also depend on the protocols that support them. Features that are provided by only one particular transport protocol have the potential to tie applications to that protocol. They should either not be offered, or replaced by fall-back functionality that allows for semantically correct operation (for example, ordered data delivery is correct but potentially slower for an application that requests unordered data delivery. "Potentially slower" is not a hindrance to correct operation within the "best effort" service model).

5. Acknowledgements

This work has received funding from the European Union's Horizon 2020 research and innovation programme under grant agreement No. 644334 (NEAT). The views expressed are solely those of the author(s).

6. IANA Considerations


This memo includes no request to IANA.

7. Security Considerations

Security will be considered in future versions of this document.

8. Informative References

[RFC5290] Floyd, S. and M. Allman, "Comments on the Usefulness of Simple Best-Effort Traffic", RFC 5290, DOI 10.17487/RFC5290, July 2008.
[RFC7305] Lear, E., "Report from the IAB Workshop on Internet Technology Adoption and Transition (ITAT)", RFC 7305, DOI 10.17487/RFC7305, July 2014.
[TAPS1] Fairhurst, G., Trammell, B. and M. Kuehlewind, "Services provided by IETF transport protocols and congestion control mechanisms", Internet-draft draft-ietf-taps-transports-10, March 2016.
[TAPS2] Welzl, M., Tuexen, M. and N. Khademi, "An Approach to Identify Services Provided by IETF Transport Protocols and Congestion Control Mechanisms", Internet-draft draft-ietf-taps-transports-usage-00, June 2015.

Authors' Addresses

Stein Gjessing University of Oslo PO Box 1080 Blindern Oslo, N-0316 Norway Phone: +47 22 85 24 44 EMail: steing@ifi.uio.no
Michael Welzl University of Oslo PO Box 1080 Blindern Oslo, N-0316 Norway Phone: +47 22 85 24 20 EMail: michawe@ifi.uio.no