| 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
draft-gjessing-taps-minset-00
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.
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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:
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.
The following terms are defined throughout this document, and in subsequent documents produced by TAPS describing the composition and decomposition of transport services.
[TAPS1] provides a list of known IETF transport protocols and transport protocols frameworks. Here all features from [TAPS1] are listed:
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.
What is delivered (delivery type):
Reliability of delivery:
Direction of communication:
Ordered or unordered delivery:
Unicast, anycast, multicast or broadcast:
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:
Resilience:
Connection oriented (or not):
Message sizes and fragmentation:
Setup negotiation:
Flow control:
Multiplexing:
Transport layer mobility:
Error detection, protection, FEC and integrity (divided into more groups?):
Streams:
Bundling:
Segmentation:
Timestamps:
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).
XX RFC ED - PLEASE REMOVE THIS SECTION XXX
This memo includes no request to IANA.
Security will be considered in future versions of this document.
| [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. |