Network Working Group Z. Du
Internet-Draft P. Liu
Intended status: Standards Track L. Geng
Expires: September 10, 2020 China Mobile
March 9, 2020
Micro-burst Decreasing in Layer3 Network for Low-Latency Traffic
draft-du-detnet-layer3-low-latency-00
Abstract
This document introduces a method to decrease the micro-bursts in
Layer3 network for low-latency traffic.
Requirements Language
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 [RFC2119].
Status of This Memo
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This Internet-Draft will expire on September 10, 2020.
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Table of Contents
1. Problem Statement . . . . . . . . . . . . . . . . . . . . . . 2
2. Mechanism to Decrease Micro-bursts . . . . . . . . . . . . . 3
2.1. Process of Edge Node . . . . . . . . . . . . . . . . . . 3
2.2. Process of Forwarding Node . . . . . . . . . . . . . . . 4
3. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 4
4. Security Considerations . . . . . . . . . . . . . . . . . . . 4
5. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 4
6. References . . . . . . . . . . . . . . . . . . . . . . . . . 5
6.1. Normative References . . . . . . . . . . . . . . . . . . 5
6.2. Informative References . . . . . . . . . . . . . . . . . 5
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 5
1. Problem Statement
Currently, the DetNet architecture in RFC 8655 [RFC8655] is supposed
to work in campus-wide networks and private WANs, and hasn't covered
the large-scale ISP network scenario. However, the low-latency
requirement exists in both L2 and L3 networks, and in both small and
large networks.
As talked in [I-D.qiang-detnet-large-scale-detnet], deploying
deterministic services in a large-scale network brings a lot of new
challenges. A novel method called LDN is introduced in
[I-D.qiang-detnet-large-scale-detnet], which explores the
deterministic forwarding over a large-scale network.
According to RFC 8655 [RFC8655], DetNet operates at the IP layer and
delivers service over lower-layer technologies such as MPLS and IEEE
802.1 Time-Sensitive Networking (TSN). However, the TSN mechanisms
are designed for L2 network originally, and cannot be directly used
in the large-scale layer 3 network because of various reasons. For
example, some TSN mechanisms need synchronization of the network
equipments, which is easier in a small network, but hard in a large
network; some mechanisms need a per-flow state in the forwarding
plane, which is un-scalable; and some TSN mechanisms need a constant
and forecastable traffic characteristics, which is more complicated
in a large network where much more flows exist and the traffic
characteristics is more dynamic.
The current forwarding mechanism in an IP router is based on
statistical multiplexing, and cannot provide the deterministic
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service because of various reasons. Even be given a high priority, a
deterministic packet can experience a long congestion delay or be
lost in a relatively light-loaded network, which is called micro-
burst in the network.
Figure 1 show the problem of the current scheduling mechanism of an
IP network. Before the scheduling in an IP network, the critical
packets are well paced, but after the scheduling, the packets will be
gathered even the total traffic rate is unchanged. When an IP
outgoing interface receives multiple critical flows from several
incoming interfaces, the situation becomes more serious. However, an
IP router will try to send them as soon as possible, so occasionally,
in some later hops, micro-bursts will emerge.
_ _ _ _ _ _ _ _ _ _ _
| | | | | | | | | | | | | | | | | | | | | |
---------------------------------------------------------------------
Before scheduling in an IP network
_ _ _ _ _ _ _ _ _ _ _
| || || || || || | | || || || || |
---------------------------------------------------------------------
After scheduling in an IP network
Figure 1: Change of the traffic characteristics in an IP network
This document proposes a method to support the low latency traffic
bearing in an IP network by avoiding micro-bursts in the network as
much as possible.
2. Mechanism to Decrease Micro-bursts
The mechanism needs the cooperation of the edge node and the
forwarding node in an IP network.
2.1. Process of Edge Node
The edge node of the IP network can recognize each critical flows
just as in the TSN network, and then give them individually a good
shaping. In fact, in TSN mechanisms, no micro-busrt will emerge for
critical traffic, and each TSN mechanism is proved to be effective
under some conditions.
This document suggests the edge node to shape the critical traffic by
using the CBS method in IEEE 802.1Qav, or the shaping methods in IEEE
802.1Qcr. They can generate a paced traffic for each critical flow.
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The parameters of the shaper, such as the sending rate, can be
configured for each flow by some means.
2.2. Process of Forwarding Node
For the forwarding node, it is uneasy to recognize each critical flow
because of the high pressure of forwarding. It is suggested that no
per-flow state is maintained in the forwarding node. Hence, the
forwarding node needs to aggregate the critical flows and handle them
together.
This document suggests that the forwarding node can deploy a specific
queue at each outgoing interface. The queue will buffer all critical
traffic that need to go out through that interface, and will pace
them by using methods mentioned in Section 2.1.
The shaping method in TSN is used here instead of the original
forwarding method in an IP router, which can make the critical
traffic be forwarded orderly instead of as soon as possible.
Therefore, micro-bursts can be decreased in the network.
If all the forwarding nodes can do their jobs properly, i.e., they
can well pace the critical traffic, no or rare micro-bursts for the
critical traffic will emerge. In this way, the critical traffic will
have a relatively low average latency in the IP network.
As no per-flow state is maintained in the forwarding node, the
sending rate of the shaper is hard to decide. In this document, the
sending rate is suggested to be generated referring to the incoming
rate of the queue. The purpose is to maintain a proper buffer depth
for the queue.
3. IANA Considerations
TBD.
4. Security Considerations
TBD.
5. Acknowledgements
TBD.
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6. References
6.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
6.2. Informative References
[I-D.qiang-detnet-large-scale-detnet]
Qiang, L., Geng, X., Liu, B., Eckert, T., Geng, L., and G.
Li, "Large-Scale Deterministic IP Network", draft-qiang-
detnet-large-scale-detnet-05 (work in progress), September
2019.
[RFC8655] Finn, N., Thubert, P., Varga, B., and J. Farkas,
"Deterministic Networking Architecture", RFC 8655,
DOI 10.17487/RFC8655, October 2019,
<https://www.rfc-editor.org/info/rfc8655>.
Authors' Addresses
Zongpeng Du
China Mobile
No.32 XuanWuMen West Street
Beijing 100053
China
Email: duzongpeng@foxmail.com
Peng Liu
China Mobile
No.32 XuanWuMen West Street
Beijing 100053
China
Email: liupengyjy@chinamobile.com
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Liang Geng
China Mobile
No.32 XuanWuMen West Street
Beijing 100053
China
Email: gengliang@chinamobile.com
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