On Wed, Aug 27, 2014 at 3:01 AM, Michael Welzl <[email protected]> wrote:
> Hi, > > Thanks from me too! I'm also fine with it, great job! > > > Here are a few SUPER small nits, and I think none of them is necessary or > "meaningful", it's just cosmetics, from carefully reading the whole thing > yet again: > > - par2: there's a double "and" - I'd replace "...and UDP-Lite and the > LEDBAT..." with "..., UDP-Lite and the LEDBAT..." > This is an english thing. We're adding a list of protocols ending in UDP-Lite to a congestion control mechanism (LEDBAT). I think it is correct as written. > - par 3: I think it would read better if "also" was inserted in the last > sentence, replacing "Layering decisions must be made" was replace with > "Layering decisions must also be made", but I'm not a native speaker... > Yup. Fixed. > - par 5: (starting with "Because even TCP and UDP"): isn't this paragraph > logically connected to the previous one? I think they could be merged. Also > (again, not a native speaker, so not sure) I'd replace "Because even TCP > and UDP" with "Since even TCP and UDP" just to avoid having two sentences > start with "Because..." so close to each other. But that's really not > important and just style. > Combined the paras. See below. Transport Services (taps) Most Internet applications make use of the Transport Services provided by TCP (a reliable, in-order stream protocol) or UDP (an unreliable datagram protocol). We use the term "Transport Service" to mean an end-to-end facility provided by the transport layer that can only be correctly provided with information from the application. This information may be provided at design time, compile time, or run time and may include guidance from the application on whether the facility in question is required or simply a preference by the application. Four examples of Transport Services are reliable delivery, no guarantee of order preservation, content privacy to in-path devices, and minimal latency. Transport protocols such as SCTP, DCCP, WebSockets, MPTCP, and UDP-Lite and the LEDBAT congestion control mechanism extend the set of available Transport Services beyond those provided to applications by TCP and UDP. For example, SCTP provides potentially faster (than TCP) reliable delivery for applications because it can accept blocks of data out of order, and LEDBAT provides low-priority "scavenger" communication. However, application programmers face difficulty when they use protocols other than TCP or UDP. Most network stacks ship with only TCP and UDP as transport protocols. Many firewalls only pass TCP and UDP and some only support HTTP over TCP. As a result, using other transport protocols or building a new protocol over raw sockets risks having an application not work in many environments. Applications, therefore, must always be able to fall back to TCP or UDP, or even HTTP in many cases, and once the application programmer has committed to making an application work on TCP or UDP or HTTP, there is little incentive to try other transport protocols before falling back. Further, different protocols can provide the same services in different ways. Layering decisions must also be made (for example, whether a protocol is used natively or tunneled through UDP). Because of these complications, programmers often resort to either using TCP or HTTP or implementing their own customized "transport services" over UDP. When application developers re-implement transport features already available elsewhere they open the door to problems that simply using TCP would have avoided and ensure that the applications can't benefit from other transport protocols as they become available. And, since even TCP and UDP are not guaranteed to work in all environments today, some programmers simply give up on using TCP or UDP directly, relying instead on "HTTP as a Substrate". BCP 56 identified many issues with this strategy, but assuming that if "any protocol is available on a given network path and on the hosts that will be communicating, that protocol will be HTTP" is a reasonable strategy for today's Internet. The IESG has agreed with this viewpoint enough to publish the WebSocket protocol on the standards track. The goal of the TAPS working group is to help application and network stack programmers by describing an (abstract) interface for applications to make use of Transport Services. The Working Group deliverables emphasize defining Transport Services that are important to applications followed by experimental mechanisms to a) determine if the protocols to provide the requested services are available on the end points and supported along the path in the network and b) fall back, i.e., select alternate, possibly less-preferred, protocols when desired protocols are not available. The Working Group will not define a richer set of Transport Services for applications, although the TAPS deliverables could inform proposals for future chartered work on Transport Services. The Working Group will: 1) Define a set of Transport Services, prioritizing those provided by existing IETF protocols and congestion control mechanisms. As a starting point, the working group will consider services used between two endpoints. 2) 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. 3) Specify experimental support mechanisms to provide the Transport Services identified in work item 2. This document will explain how to select and engage an appropriate protocol and how to discover which protocols are available for a given connection. Further, it will provide a basis for incremental deployment. Work on this document will begin when the TAPS Transport Services have been specified. The following topics are out of scope for this Working Group: - Signaling-based Quality-of-Service (QoS) mechanisms - Definition of new encapsulations and tunneling mechanisms - Extension, modification, or creation of transport protocols - Language-specific APIs TAPS is not chartered to perform detailed analysis of the security aspects of transport protocols, but TAPS is being chartered almost simultaneously with TCPINC, which is developing the TCP extensions to provide unauthenticated encryption and integrity protection of TCP streams, and TAPS will work with TCPINC to ensure that TAPS will be able to accommodate the protocol extensions that TCPINC defines. Milestones: M9: Submit an Informational document to the IESG defining a set of services provided by IETF transport protocols and congestion control mechanisms. M15: Submit an Informational document to the IESG recommending a minimal set of Transport Services that end systems should support. M18: Submit an Experimental document to the IESG specifying one or more methods to provide applications with the Transport Services identified by the WG. M18: Recharter or close.
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