TAPS S. Gjessing
Internet-Draft M. Welzl
Intended status: Informational University of Oslo
Expires: December 24, 2015 June 22, 2015

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. As a starting point for discussion, it currently only gives an overview of some ways to categorize the set of transport services in the first TAPS document (version 4: draft-ietf-taps-transports-04), 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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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 follows the same terminology (also listed below). We include an "inversion" (in the database sense) of [TAPS1], in that, based on the lists of protocol components in [TAPS1] we list all protocol features, and for each feature, we list the Transport Protocols that support this feature (as a component). The resulting list is very long. If the list of Transport Services that a TAPS system offers to applications was a simple copy of this list, the resulting system would be very hard to use. It is therefore necessary to minimize the number of services that are offered. We begin this by grouping these transport features.

The groups of features offered to applications are divided as follows:

  1. functional vs. non-functional
  2. static vs. initialization vs. dynamic
  3. single-sided vs. both-sided

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 a TAPS system.

Functional features use components that cannot be used without the application knowing about them, or else they violate assumptions that might cause the application to break. Components implementing non-functional features may be used without involving the application. 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. Multihoming and data bundling (Nagle in TCP) are non-functional 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 feature).

If a transport protocol offers a feature that can not be changed or opted out, this feature is called static in this protocol. An application uses a static feature either because it has requested it (and TAPS decide to fulfill this request by a protocol that has a component that implements this feature as static), or the static feature is offered to the application implicitly because TAPS chooses a protocol that implements it. For example, if an application chooses byte-stream-oriented delivery, it automatically also gets reliable delivery.

Initialization features can be chosen when communication begins but not adjusted later; this assumes that a TAPS system does not change protocols during a communication session. Examples of initialization features are flow control and congestion control.

Dynamic features are changeable during runtime. An example of a dynamic feature is data bundling (Nagle in TCP).

Single-sided features can be provided via components that are implemented only on the side where they applications requests the Transport Service. An example of a single-sided feature is data bundling (Nagle in TCP). Both-sided features can only be provided via components that are implemented on both sides. An example is error detection (checksum). Possibly certain features could benefit from, but do not need to be, implemented on both sides. Since the point of categorization is to determine the minimal set of Transport Services that a TAPS system must provide, the essential property of such features is that they *can* be implemented on only one side.

2. Terminology (as defined by draft-ietf-taps-transports-04)

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

Transport Service Feature:
a specific end-to-end feature that a transport service provides to its clients. Examples include confidentiality, reliable delivery, ordered delivery, message-versus-stream orientation, etc.
Transport Service:
a set of transport service 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 Protocol Component:
an implementation of a transport service feature within a protocol.
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. A list of all features in the considered IETF Transport Protocols

[TAPS1] provides a list of known IETF transport protocols and transport protocols frameworks. Here all features from [TAPS1] are listed:

4. Grouping of the features

This section presents a grouping of the features from [TAPS1] according to the three categories: functional vs. non-functional; static vs. initialization vs. dynamic; one-sided vs. two-sided.

The current version only includes the functional vs. non-functional categorization. The other categories will be included in future versions.

4.1. Functional vs. non-functional

4.1.1. Functional features

What is delivered (delivery type):

Reliability of delivery:

Direction of communication:

Ordered or unordered delivery:

Unicast, anycast, multicast or broadcast:

4.1.2. Non-functional features

These are features that the application can optionally specify. If a feature is not specified by the application it is undefined, i.e. the TAPS system may choose an implementation of any of the features listed.

Congestion control:


Connection oriented (or not):

Message sizes and fragmentation:

Setup negotiation:

Flow control:


Transport layer mobility:

Error detection, protection, FEC and integrity (divided into more groups?):



4.2. Components from draft-ietf-taps-transports-04 that are not specified or seen by the applications



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. Normative References

[TAPS1] Fairhurst, G., Trammell, B. and M. Kuehlewind, "Services provided by IETF transport protocols and congestion control mechanisms", Internet-draft draft-ietf-taps-transports-04, May 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