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
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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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