Transport Services
charter-ietf-taps-00-01

In the TAPS charter, the term "Transport Service" means any
service provided by the transport layer that can only be
correctly implemented with information from the application.

The vast majority of Internet applications make use of the
Transport Services provided by TCP (a reliable, in-order
stream protocol) or UDP (an unreliable datagram protocol).

Other transport protocols such as SCTP, DCCP, MPTCP,
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 reliable delivery for applications that
can accept blocks of data out of order, and LEDBAT provides
low-priority "scavenger" communication.

Application programmers face difficulty when they use protocols
other than TCP or UDP. Most network stacks only support TCP
and UDP, and many firewalls only pass TCP and UDP, so using
other transport protocols risks having an application not
work in many environments. Applications, therefore, must
always be able to fall back to TCP or UDP, and once the
application programmer has committed to making an application
work on TCP or UDP, 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 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 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 TCP would
have avoided, and ensure that the applications can't
benefit from other transport protocols as they become
available.

Alternatively, programmers may simply give up on using
transport protocols direcly, 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 Websockets protocol
on the standards track.

The Working Group deliverables will help an application
programmers identify the important Transport Services for
applications and determine if those Transport Services are
available on the end points and along the path in the network.
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:

• Identify Transport Services provided by existing IETF
  protocols and congestion control mechanisms. The resulting
  document will provide guidance on making a choice among
  available mechanisms and protocols to obtain a certain
  Transport Service. As a starting point, the working group will
  consider: ordering/sequence preservation, degree of
  reliability, and latency vs throughput, but is not prohibited
  from considering others.

• 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.

• Specify experimental mechanisms to provide a given Transport
  Service. This document will explain how to select and engage
  an appropriate protocol and how to discover which protocols
  are available for a given connection. Futher, it will provide
  a basis for incremental deployment.

The following topics are out of scope for this Working Group:

• Quality-of-Service (QoS) and tunneling mechanisms and services

• Definition of new encapsulations and tunneling mechanisms

• Extension or modification 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 summary of the services provided by IETF transport
protocols and congestion control mechanisms to IESG.
M15: Submit end system transport services to IESG.
M18: Submit specification of how the transport services can be
provided to IESG.