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ICCRG                                                       Jaehwoon Lee
Internet-Draft                                        Dongguk University
Intended status: Informational                              Chongho Yoon
Expires: July 30, 2020                        Korea Aerospace University
                                                        January 31, 2020



           Gated Adaptive CoDel for Time-Sensitive Network
                     draft-jaehwoon-icc-gacodel-00


Abstract

   This draft proposes a gated adaptive CoDel algorithm that can operate
   in the Time-Sensitive Network (TSN) environment. Here, we define
   Virtual sojourn time, virtual Interval and virtaul Target that are
   only operate on non-blocking part of TSN.



Status of this Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on July 30, 2020.

Copyright Notice

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Table of Contents



   1.  Introduction.................................................2
   2.  Conventions and Terminology..................................3
     2.1.  Conventions used in this document........................3
     2.2.  Terminology  ............................................3
   3.  Gated adaptive Codel for TSN.................................3
   4.  Security Considerations......................................3
   5.  IANA Considerations..........................................3
   6. References....................................................4
   Author's Address.................................................4



1.  Introduction

   Bufferbloat means that there are excess number of packets stored in
   the buffer in the bottleneck part of the packet-switched network.
   End-to-end latency, therefore, increases sharply due to the
   bufferbloat[1]. CoDel AQM is one of the active queue management (AQM)
   technique used to resolve the bufferbloat problem[2]. When a packet
   enters the buffer, CoDel records the current time in the packet by
   using the timestamp and computes the sojourn time on dequeue. Sojourn
   time, together with the initial INTERVAL and TARGET values set by the
   user, is used to determine whether to discard the packet or not.

   Time-sensitive network (TSN) provides the deterministic arrival
   service without delay for time-sensitive control traffic based on the
   time triggered scheduling that is synchronized with the Time
   Triggered Ethernet (TTE)[3-4]. In TSN, time is considered to be
   slotted. Each slot is further divided into two minislots. The first
   minislot is used to transmit time-sensitive control traffic. The
   other is used to transmit asynchronous traffic. In other words, from
   the point of view of asynchronous traffic, the gate is periodically
   blocked at the time interval is assigned to the time-sensitive
   control traffic. TSN provides reasonable scheduling to asynchronous
   traffic through credit based shaper and strict priority algorithm[5].
   However, as the size of the first mini slot gets larger, the
   bandwidth for asynchronous traffic decreases, and bufferbloat
   phenomenon worsens . CoDel can resolve the bufferbloat problem that
   may occur when transmitting the asynchronous traffic in TSN
   environment. In this case, gated scheduler asks CoDel whether to
   transmit the packet based on timing and scheduling information. When
   the packet can be transmitted without being discarded, gated


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   scheduler can transmit the packet during the time slot assigned to
   the asynchronous traffic. Codel decides whether to discard the packet
   on dequeue. When the gate is blocked, packets can arrive and be
   stored in the buffer anytime. However, packet that is stored in the
   buffer cannot be transmitted during the first minislot.  It means
   that the codel algorithm will not work and stop running when the gate
   is blocked. Therefore when applying codel to TSN, it is necessary to
   consider the fact that gate is periodically blocked.

   In this draft, we propose gated adaptive codel aqm to resolve the
   bufferbloat problem arising from  asynchronous traffic transmitted
   during the non-blocking period in the TSN environment.


2.  Conventions and Terminology

2.1.  Conventions

   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 RFC 2119 [6].


2.2 Terminology

    TBD


3.  Gated Adaptive CoDel for TSN

   In this section, we define a virtual time that only operates on the
   non-blocking period. It is independent of actual time used in the
   CoDel packet discarding algorithm. Here, packets that arrive during a
   blocked period are regarded as having arrived at the same time, while
   the order of arrival is maintained. Virtual sojourn time is defined
   as the actual sojourn time minus the blocking period. Moreover, the
   Virtual TARGET and Virtual INTERVAL should be calculated as follows
   and used in the codel algorithm.

   VirtualTARGET = ActualTARGET - GatedBlockingPeriod
   VirtualINTERVAL = ActualINTERVAL * (1-Blocking Period)/Gated Period.


4.  Security Considerations

   TBD

5.  IANA Considerations

   TBD

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6.  References

   [1]  G. Jim and K. Nichols, "Bufferbloat: Dark buffers in the
        Internet", Queue9.11, pp. 40, 2011

   [2]  K. Nichols, V. Jacobson, A. McGregor and J. Iyengar, "Controlled
        Delay Active Queue Management, RFC 8289, Jan. 2018.

   [3]  Institute of Electrical and Electronices Engineers,
        Time-Sensitive Networking Task Group.
        http://www.ieee802.org/1/pages/tsn.html, 2016.

   [4]  K. Hermann and G. Grunsteidl,"TTP-A time-triggered
        protocol for fault-tolerant real-time systems",
        Fault-Tolerant Computing, 1993. FTCS-23. Digest of Papers,
        The Twenty-Third International Symposium on IEEE, 1993.

   [5] IEEE 802.1 AVB Task Group, "IEEE 802.1Qav - Virtual
       Bridged Local Area Networks - Amendment: Forwarding and
       Queuing Enhancements for Time-Sensitive Streams", 2009.

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


Author's Address

   Jaehwoon Lee
   Dongguk University
   26, 3-ga Pil-dong, Chung-gu
   Seoul 100-715, KOREA
   Email: jaehwoon@dongguk.edu


   Chongho Yoon
   Korea Aerospace University
   76, Hanggongdaehak-ro, Deogyang-gu, Goyang-si,
   Gyeonggi-do, 10540, KOREA
   Email: yoonch@kau.ac.kr












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