RFC6077

Open Research Issues in Internet Congestion Control

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RFC 6077       Open Issues in Internet Congestion Control  February 2011


   should be implemented in the end-systems.  This principle ensures
   that the network provides a general service and that it remains as
   simple as possible (any additional complexity is placed above the IP
   layer, i.e., at the edges) so as to ensure evolvability, reliability,
   and robustness.  Furthermore, the fate-sharing principle ([Clark88],
   "Design Philosophy of the DARPA Internet Protocols") mandates that an
   end-to-end Internet protocol design should not rely on the
   maintenance of any per-flow state (i.e., information about the state
   of the end-to-end communication) inside the network and that the
   network state (e.g., routing state) maintained by the Internet shall
   minimize its interaction with the states maintained at the
   endpoints/hosts [RFC1958].

   However, as discussed in [Moors02] for instance, congestion control
   cannot be realized as a pure end-to-end function only.  Congestion is
   an inherent network phenomenon and can only be resolved efficiently
   by some cooperation of end-systems and the network.  Congestion
   control in today's Internet protocols follows the end-to-end design
   principle insofar as only minimal feedback from the network is used,
   e.g., packet loss and delay.  The end-systems only decide how to
   react and how to avoid congestion.  The crux is that on the one hand,
   there would be substantial benefit by further assistance from the
   network, but, on the other hand, such network support could lead to
   duplication of functions, which might even harmfully interact with
   end-to-end protocol mechanisms.  The different requirements of
   applications (cf. the fairness discussion in Section 2.3) call for a
   variety of different congestion control approaches, but putting such
   per-flow behavior inside the network should be avoided, as such a
   design would clearly be at odds with the end-to-end and fate-sharing
   design principles.

   The end-to-end and fate-sharing principles are generally regarded as
   the key ingredients for ensuring a scalable and survivable network
   design.  In order to ensure that new congestion control mechanisms
   are scalable, violating these principles must therefore be avoided.

   For instance, protocols like XCP and RCP seem not to require flow
   state in the network, but this is only the case if the network trusts
   i) the receiver not to lie when feeding back the network's delta to
   the requested rate; ii) the source not to lie when declaring its
   rate; and iii) the source not to cheat when setting its rate in
   response to the feedback [Katabi04].

Papadimitriou, et al.         Informational                    [Page 13]
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