One document matched: draft-ietf-conex-destopt-01.xml

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<rfc category="std" ipr="trust200902" docName="draft-ietf-conex-destopt-01">
<front>
<title abbrev="Conex Destination Option">IPv6 Destination Option for Conex</title>
<author initials="S.K." surname="Krishnan" fullname="Suresh Krishnan"><organization>Ericsson</organization><address>
<postal>
<street>8400 Blvd Decarie</street><city>Town of Mount Royal</city><region>Quebec</region><country>Canada</country></postal>
<email>suresh.krishnan@ericsson.com</email></address>
</author>
<author initials="M.K." surname="Kuehlewind" fullname="Mirja Kuehlewind"><organization>IKR University of Stuttgart</organization><address>
<email>mirja.kuehlewind@ikr.uni-stuttgart.de</email></address>
</author>

<author initials="C.R.U." surname="Ucendo" fullname="Carlos Ralli Ucendo"><organization>Telefonica</organization><address>
<email>ralli@tid.es</email></address>
</author>

<date month="October" year="2011"/><area>Transport</area><workgroup>conex Working Group</workgroup>
 <abstract><t>Conex is a mechanism by which senders inform the network about the congestion encountered by packets earlier in the same flow. This document specifies an IPv6 destination option that is capable of carrying conex markings in IPv6 datagrams.</t>
 </abstract>
</front>
<middle>
<section anchor="intro" title="Introduction">
<t>Conex <xref target="CAM"/> is a mechanism by which senders inform the network about the congestion encountered by packets earlier in the same flow. This document specifies an IPv6 destination option <xref target="RFC2460"/> that can be used for performing conex markings in IPv6 datagrams.</t>
</section>

<section title="Conventions used in this document">
<t>The key words "MUST", "MUST NOT", "REQUIRED", "SHALL","SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in <xref target='RFC2119' />.</t>
</section>

<section anchor="background" title="Background">
<t>The Conex working group came up with a list of requirements that had to be met by any marking mechanism. It then considered several alternative mechanisms and evaluated their suitability for conex marking. There were no mechanisms found that were completely suitable, but the only mechanism that came close to meeting the requirements was IPv6 destination options. The analysis of the different alternatives can be found in [draft-krishnan-conex-ipv6].
<vspace blankLines="1000"/>
</t>
</section>

<section title="Conex Destination Option (CDO)">
<t>The Conex Destination Option (CDO) is a destination option that can be included in IPv6 datagrams that are sent by conex-aware senders in order to inform conex-aware nodes on the path about the CDO has an alignment requirement of (none).
</t> 
<figure title="Conex Destination Option Layout" anchor="cdo_layout">
<artwork>
 0                   1                   2                   3
 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
                                +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
                                |  Option Type  | Option Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|X|L|E|C|                       Reserved                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
</artwork>
</figure>
<figure>
<artwork>
  Option Type

     8-bit identifier of the type of option. The option identifier
     for the conex destination option will be allocated by the IANA.

  Option Length

     8-bit unsigned integer.  The length of the option (excluding 
     the Option Type and Option Length fields). This field MUST be
     set to the value 4.

  X Bit
     When this bit is set, the transport sender is using ConEx with 
     this packet. If it is reset, the sender is not using ConEx.

  L Bit

     When this bit is set, the transport sender has experienced a loss. 
     If it is reset, the sender has not experienced a loss.

  E Bit

     When this bit is set, the transport sender has experienced 
     ECN-signaled congestion. If it is reset, the sender has not 
     experienced ECN-signaled congestion.

  C Bit

     When this bit is set, the transport sender is building up 
     congestion credit. Otherwise it is not.
</artwork>
</figure>
<t> All packets of a ConEx-capable connection MUST carry the CDO.</t>
<t> If the X bit is the zero all other three bits MUST be zero as well. 
	If the X bit is zero that means that the connection is ConEx-capable but this
	packet SHOULD NOT be accounted to determine ConEx information in an audit function.
	This can be the case for e.g. pure control packets not carrying any user data. As an example in TCP pure
	ACKs are usually not ECN-capable and TCP does not have an mechanism to announce the lost
	of a pure ACK to the sender. Thus congestion information about the ACKs are not available at
	the sender. An audit function MUST be aware of this possibility and SHOULD ensure that not a 
	large amount of data is sent as not-ConEx capable with a ConEx capable connection.
</t>

<t> If the X bit is set, all three other bit (L, E, C) MAY be set. When ever one if this bits is set, the 
	number of bytes carried by this IP packet (incl. IP header) SHOULD be accounted when determining
	congestion or credit information. In IPv6 the length ca easily
	be calculated by the value given in the Payload Length header field (payload length + option space) plus
	a fixed value of 40 Bytes for the IP header itself. 
</t>
<t> In principle all of these three bits (L, E, C) 
	MAY be set in the same packet. In this case the packet size MUST be accounted more than once 
	for each respective ConEx information counter. 
	In practice loss and ECN
	marks can not occur at the same time, so there should usually be a way to signal the respective ConEx
	information in different packets. In many cases if congestion occurs the sender will not sent additional
	credit bit, but if e.g. a sender assumes losses because of an audit function or needs to maintain a certain
	sending	rate to make an application layer service work, the occurrence of credit bits (c) in parallel to
	congestion exposure bit (L, E) is reasonable.
</t>
<t> If a network node extracts the ConEx information from a connection, this node is usually supposed to hold this
	information byte-wise, e.g. comparing the total number of bytes sent with the number of bytes sent with
	ConEx congestion mark (L, E) to determine the current whole path congestion level. 
	When equally sized packets can be assumed accounting the number of packets (and comparing the total number
	to marked once) should deliver the same result. 
	But a network node MUST be aware that this estimation can be
	quite wrong and thus is not reliable if e.g. different sized packed are send.
</t>
</section>


<section title="Acknowledgements">
<t>
The authors would like to thank Marcelo Bagnulo, Bob Briscoe, Ingemar Johansson, Joel Halpern and John Leslie for the discussions that led to this document.
</t>
</section>

<section anchor="security" title="Security Considerations">
<t>This document does not bring up any new security issues. </t>
</section>

<section title="IANA Considerations">
<t>
   This document defines a new IPv6 destination option for carrying conex
   markings.  IANA is requested to assign a new destination option
   type in the Destination Options registry maintained at

   http://www.iana.org/assignments/ipv6-parameters

   <TBA1> Conex Destination Option [RFCXXXX]

   The act bits for this option need to be 10 and the chg bit needs to
   be 0.
</t>
</section>

</middle>

<back>
<references title="Normative References">

&rfc2119;&rfc2460;

     <reference anchor="CAM">
   <front>
  <title>Congestion Exposure (ConEx) Concepts and Abstract Mechanism</title> 
  <author initials="B" surname="Briscoe" fullname="Bob Briscoe">
  <organization /> 
  </author>
  <date month="March" day="14" year="2011" /> 
 <abstract>
  <t>This document describes an abstract mechanism by which senders inform the network about the congestion 
  encountered by packets earlier in the same flow. Today, the network may signal congestion to the receiver
  by ECN markings or by dropping packets, and the receiver may pass this information back to the sender in 
  transport-layer feedback. The mechanism to be developed by the ConEx WG will enable the sender to also 
  relay this congestion information back into the network in- band at the IP layer, such that the total level 
  of congestion is visible to all IP devices along the path, from where it could, for example, be provided as 
  input to traffic management.</t> 
  </abstract>
  </front>
  <seriesInfo name="Internet-Draft" value="draft-ietf-conex-abstract-mech-01" /> 
  <format type="TXT" target="http://www.ietf.org/internet-drafts/draft-ietf-conex-abstract-mech-01.txt" /> 
     </reference>

</references>
</back>
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