Transport-Services                                       M.J. Montpetit
Internet Draft                                                      MIT
Intended status: Informational                          I. Zhovnirovsky
Expires: August 3, 2014                                         QFactor
                                                       February 3, 2014

                       Use Cases and Requirements

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   This document describes some of the services and application use
   cases that may require specific transport services over an Internet
   subnetwork. It also presents, when available, some derived
   requirements and conditions of utilization that will allow to
   choose the most appropriate transport service. The use cases assume
   that choice of transport service is fully based on the requirements.
   In all cases however, the fallback is considered to be TCP or UDP.

Table of Contents

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2. Conventions used in this document. . . . . . . . . . . . . . . . 3

3. Application Use Cases and Derived Requirements . . . . . . . . . 3

3.1. Web Surfing/Browsing . . . . . . . . . . . . . . . . . . . . . 3

3.2. Streaming Video. . . . . . . . . . . . . . . . . . . . . . . . 5

3.3. Real-time Communications . . . . . . . . . . . . . . . . . . . 6

3.4. Photo/video Sharing. . . . . . . . . . . . . . . . . . . . . . 7
3.5. Data centers/storage . . . . . . . . . . . . . . . . . . . . . 7

3.6. Internet of Things (IoT) . . . . . . . . . . . . . . . . . . . 7
3.7. Public Safety. . . . . . . . . . . . . . . . . . . . . . . . . 7
3.8. Information Centric Networks/Content Centric Networks. . . . . 8
4. Security Considerations. . . . . . . . . . . . . . . . . . . . . 8
5. IANA Considerations. . . . . . . . . . . . . . . . . . . . . . . 9
6. Conclusions. . . . . . . . . . . . . . . . . . . . . . . . . . . 9
7. References . . . . . . . . . . . . . . . . . . . . . . . . . . . 9
8. Acknowledgments. . . . . . . . . . . . . . . . . . . . . . . . .10

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1. Introduction
   Different transport services are now being developed in the Internet
   Community to address the changing nature of services or applications
   and of the an Internet subnetworks themselves. For example, a number
   of these transports services are used to address performance
   requirement that standards such as the TCP and UDP protocol meet
   only partially either because of impairments in wireless
   transmission or the need for added security. This document defines
   the use cases most likely to necessitate the use of one of those
   transport service and to list their derived requirements. It
   will help define which transport service is best suited for an
   application and which API(s) would enable the use of those
   In general, the applications will request a connection by specifying
   a set of requirements. The the API will connect it to the best-fit
   "transport", falling back to TCP/UDP if nothing is compliant. Hence
   the use cases will help define how to update applications or
   middleware to perform in a better way without requiring any changes
   to existing APIs. They also envision some futuristic situations
   where applications would use a newer enhanced and common API,
   to benefit from novel network services. In this document the
   actual underlying link layer is not specified but it is
   assumed that, for example, wireless transport services could
   be used in many instances.
2. Conventions used in this document
   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119[1].
   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.
3. Application Use Cases and Derived Requirements

   In this section we define the use cases for a number of
   applications that require one (1) or more transport service.
   The application should be able to use an API based on derived
   requirements such as bandwidth or delay or security, beyond
   the usual fallback of TCP and UDP.

3.1. Web Surfing/Browsing

   Web surfing and browsing has been identified as applications that
   will most likely profit from transport services will improve the
   capacity occupancy, reduce slow start due to dropped packets or
   multiple connections and other inefficiencies due to for example
   Head-of-Line blocking.

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3.1.1. Faster Browsing via multi-streaming for HTTP prior to 2.0 Description
   Using a new TCP connection for every HTTP request is known to be
   inefficient; it causes delay for connection setup and requires a TCP
   connection to spend most of its time in slow start, operating at a
   point that may be far from the capacity of the path between the
   sender and receiver. HTTP/1.1 allows persistently using the same TCP
   connection for multiple HTTP requests, but with a fixed sequence
   that is defined by the browser, thereby creating Head-Of-Line (HOL)
   blocking delay if e.g. the first of several such requests requires
   accessing a database. SPDY and HTTP/2.0 seek to improve upon the
   performance of HTTP/1.1 by asynchronously multiplexing multiple
   application-level (web) flows onto a single TCP connection. However,
   HOL blocking delay in the order of a Round-Trip Time (RTT) can still
   occur whenever a packet is dropped, as TCP only allows delivering
   data in the exact order in which they arrive. This problem is
   addressed by QUIC [9], a UDP-based transport protocol that
   operates under the SPDY protocol for browsing [2].
   The SPDY/QUIC solution is not without issues. UDP may sometimes be
   blocked; some middle-boxes rate-limit UDP more than TCP [5]. Running
   a transport protocol in user space may have issues in very-low-RTT
   environments due to less precise Operating System timing. Not all
   clients and servers support both protocols. It seems that being able
   to provide similar benefits without requiring changing the HTTP
   implementation could be beneficial for many web browsers and
3.1.2. Derived requirements
   It is possible to let applications that open the same set of
   (seemingly) TCP connections between the same pair of hosts benefit
   from for example the multi streaming features of the Stream Control
   Transport Protocol(SCTP) [10]. In [11], this was prototypically
   done with middle-boxes that terminated the TCP connections and
   mapped them onto streams of a single SCTP association. This did not
   require any change to the applications themselves. If a similar
   function was provided by the Operating System, directly underneath
   the socket interface, the same benefits could be attained with less
   overhead. This requires hiding the use of SCTP (or any other
   multi-streaming- capable transport, e.g. Minion [7]) from
   applications, and it may need signaling inside the protocol
   in use to tell the host on the receiving end that these streams
   must be mapped back onto what an application believes to be TCP

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3.1.3. Other HTTP acceleration mechanisms

<To be provided>

3.2. Streaming Video
   Streaming video is one of the dominant traffic types on the
   Internet. Hence the choice of an appropriate transport service for
   video may become essential in the future to minimize congestion
   especially in edge subnetworks and improve user experience.
3.2.1. Adaptive Video Streaming
   <To be provided>

3.2.2. Scavenger-Type Pre-Fetching Of Streaming Media Description
   Streaming media applications use a play-out buffer on the receiver
   (consumer) side to avoid playback interruptions when the network
   bandwidth temporarily drops below the bit-rate of the stream. As
   visualized with the playback bar in most popular streaming systems
   such as e.g. YouTube, this buffer is typically filled a number of
   seconds ahead of the play-out time. If the network's capacity
   could allow filling it much further ahead, this could have
   multiple benefits for the viewer:

   -  if congestion happens later, the play-out would stay
      uninterrupted for a longer period or the risk of interruptions
      would be reduced

   -  if a user decides to skip ahead within the length of the already
      buffered data, this request could be honored instantly as the
      data are already available in the receiving host
   This is, however, not typically done. One reason to avoid pre-
   fetching much more than users need most of the time is that this may
   be seen as a waste of network capacity that could otherwise be left
   up to other applications. If, however, this was done in a scavenger-
   like mode, using a congestion control that backs off as soon as
   other flows compete for network capacity, this problem would
   disappear, and it would probably be beneficial to pre-fetch
   as much as possible at any time.

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   A transport protocol that is used for streaming media should, upon
   request from the application, switch to a low-priority congestion
   control mechanism such as LEDBAT on the fly. Switching back from
   low-priority to "normal" congestion control must happen when e.g.
   the user moves the playback bar beyond the end of the playback
   buffer; this must therefore also be possible on the fly.
3.3. Real-time Communications

   Real time communications can be divided into three (3)
   categories, namely voice, video and gaming that may have
   very different transport requirements.
3.3.1. Voice over IP Description
   Voice over IP uses the real time transport protocol (RTP) over UDP
   transport. The transport requirements of VoIP have been defined and
   solutions implemented including when there are interactions with
   intermediate boxes including firewalls and NAT boxes. Derived Requirements
   In order for a transport service to provide VoIP services it
   requires minimal delay, in-order delivery and adequate error
   mitigation. And while UDP is the preferred protocol newer transports
   (such as Minion or others) could provide better performance.
3.3.2. IP based real-time video Description
   TV over the Internet Protocol (IPTV) requires multicast streaming
   as well as minimal caching, except for so called "trick plays"
   (rewind, pause and fast forward) over linear transmission. The now
   concluded reliable multicast working group (rmt) has defined a
   number of mechanisms to provide IPTV services using
   acknowledgements andforward error correction. Derived Requirements
   In order for a transport service to provide IPTV services it
   requires minimal delay, in-order delivery and very good error

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3.3.3. Gaming

   Online games require very low delay and they use very small
   packets to ensure this (small packet are also features of VoIP).
   It is also beneficial to think that games could use tunneling and
   other multiplexing mechanisms to ensure minimal delay and
   synchronization between players. Description

  <to come> Derived Requirements
   <to come>
3.4. Photo/video Sharing
  <to come>
3.5. Data centers/storage
   There is a lot of work being performed in TCP for data centers (DCs)
   and as such DCs require certain characteristics from the transport

3.5.1. Description
   <reviewing DCTCP-slides][4] for inputs>

3.5.2  Derived Requirements
   <to come>
3.6. Internet of Things (IoT)
   While the Internet of Things has yes to define specific requirements
   for transport services a number of protocols to collect sensor data
   have been proposed, such a IBM Machine to Machine communication
   protocol call Message Queuing Telemetry Transport (MQTT) which
   covers part of the IoT spectrum of application.
   <More to come>
3.7. Public Safety
   In the past few years there has been a push for public safety
   systems to use Internet based protocols and private and public
   networks to ensure availability and resiliency.

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3.7.1. Description
   Public safety services are similar to the ones already defined above
   (browsing, caching, real time services, streaming etc.). However,
   the nature of these services requires strong security, high
   reliability and 'always on' nature.
3.7.2. Derived Requirements
   In order for transport services to be used in public safety strong
   encryption like the one proposed by tcpcrypt [3] may be useful. In
   addition low delay is essential. Reliability the and always-on
   requirements can also be enhanced by mechanisms like FEC. Some
   requirements are shared with multipath TCP [8].
3.8. Information Centric Networks/Content Centric Networks
   Information Centric (ICN) and Content Centric (CCN) Networking
   are emerging interest area in the Internet and define
   new mechanisms to connect to resources. The IRTF has chartered an
   ICN working group [6] that will investigate the issues like
   scalability and naming conventions to ensure deployability.
3.8.1. Description

   An ICN does not require a different transport but will signal
   transport requirements in a different manner.

3.8.2. Derived Requirements
   In the ICN/CCN work the access to a specific resource via the
   transport mechanism will be in the form of a publish/subscribe.
   It is for the transport to derive what this means in terms of

   <To be completed>
4. Security Considerations
   None relating to the document. Specific use case security
   requirements to be detailed later.

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5. IANA Considerations
   This document makes no request of IANA.
   Note to RFC Editor: this section may be removed on publication as an
6. Conclusion

   This document presents a number of use cases for applications that
   could benefit from transport services other than the usual TCP and
   UDP protocols. While there is no underlying architecture to the
   document it is assumed that the transport services would be
   chosen based on specific requirements and using standard APIs.
   It is also assumed that APIs would not require major changes
   with potential changes applied to applications or middle-boxes.

7. References

7.1.  Normative References

   [1]   Bradner, S., "Key words for use in RFCs to Indicate
         Requirement Levels", BCP 14, RFC 2119, March 1997.

7.2.  Informative References
   [2]   Mike Belshe, Robert Peon, "SPDY Protocol", draft-mbelshe-
         httpbis-spdy-00, February 2012.
   [3]   A. Bittau, Dan Boneh, M. Hamburg, H. Handley, D. Mazieres,
         Q. Slack, "Cryptographic protection of TCP Streams",
         draft-bittau-tcp-crypt-03, September 3, 2012.
   [4]   DTCP Slide deck:
   [5]   Seppo Hatonen, Aki Nyrhinen, Lars Eggert, Stephen Strowes,
         Pasi Sarolahti and Markku Kojo. "An Experimental Study of Home
         Gateway Characteristics." Proc. ACM SIGCOMM Internet
         Measurement Conference (IMC), Melbourne, Australia, November
         1-3, 2010.
   [6]   Information Centric Network IRTF charter:

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   [7]   Jana Iyengar, Stuart Cheschire, Josh Graessley, "Minion -
         Service Model and Conceptual API", draft-iyengar-minion-
         concept-02, October 21 2013 (work in progress).
   [8]   Michael Scharf, Alan Ford, "Multipath TCP (MPTCP)
         Application Interface Considerations", RFC 6897, March 2013.
   [9]   QUIC Slide Deck at IETF88,

   [10]  R. Stewart, ed. "Stream Control Transport Protocol", RFC
         4960, September 2007.
   [11]  Michael Welzl, Florian Niederbacher, Stein Gjessing:
         "Beneficial Transparent Deployment of SCTP: the Missing
         Pieces",IEEE GlobeCom 2011, 5-9 February 2011,
         Houston, Texas.
   <others to come>
8.  Acknowledgments
   The author would like to thank Michael Welzl, Jose Saldana,
   Lars Eggert and Martin Sustrik for use case suggestions and
   technical discussions prior to and during the preparation of
   this draft.

   Copyright (c) 2014 IETF Trust and the persons identified
   as authors.
   All rights reserved.
Authors' Addresses
Marie-Jose Montpetit

Igor Zhovnirovsky
QFactor Communications

Changes between version 00 and version 01
Minor changes:Rewrote the Abstract, fixed the introduction,
corrected spelling and some sentences, added a conclusion
and a reference to SCTP.

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