Internet DRAFT - draft-peng-detnet-policing-jitter-control
draft-peng-detnet-policing-jitter-control
DetNet Shaofu. Peng
Internet-Draft ZTE
Intended status: Standards Track Peng. Liu
Expires: 21 July 2024 China Mobile
Kashinath. Basu
Oxford Brookes University
18 January 2024
Policing Caused Jitter Control Mechanism
draft-peng-detnet-policing-jitter-control-00
Abstract
A mechanism to eliminate jitter caused by policing delay is
described. It needs to be used in combination with a scheduling
mechanism that provides low jitter for the transport path, and
ultimately provides a low jitter guarantee for the application flow.
Status of This Memo
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Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Requirements Language . . . . . . . . . . . . . . . . . . . . 3
3. Overview of the Solution . . . . . . . . . . . . . . . . . . 3
4. Set Edge Policing Delay Budget . . . . . . . . . . . . . . . 5
5. Multi-domain considerations . . . . . . . . . . . . . . . . . 5
6. Encoding Considerations . . . . . . . . . . . . . . . . . . . 6
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8. Security Considerations . . . . . . . . . . . . . . . . . . . 7
9. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 7
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
10.1. Normative References . . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8
1. Introduction
A policing function, as defined in RFC2216, differentiates those
packets in a traffic flow which conform to a particular token bucket
specification from those packets which do not. A Token Bucket is a
particular form of traffic specification consisting of a "token rate"
r and a "bucket size" b. More specifically, the traffic must obey
the rule that over all time periods, the amount of data sent cannot
exceed r*T+b, where T is the length of the time period. The common
treatment accorded nonconforming packets may be relegating the packet
to best effort service, discarding the packet, or marking the packet
in some fashion.
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A flow with conforming packets released to the network is the
condition that must be followed to obtain deterministic forwarding
services. This is also consitent with the problem statement of flow
characterization in [RFC8557]. We assume that there is enough buffer
space at the network entry to store nonconforming packets, that is
important for deterministic flows that expect zero packet loss. A
conforming packet may expierence zero policing delay, while a
nonconforming packet may expierence non-zero policing delay. After
policing on the network entry, the packet will be guaranteed a
bounded delay or jitter by the applied scheduling mechanisms in the
network. Generally, the scheduling mechanism guarantees the delay
performance provided by the transport path in the network, and does
not pay attention to the runtime policing delay at the network entry.
Although some application flows may declare in the contract with the
network service provider that they will accept the introduction of
policing delay for illegally arrived packets (i.e., nonconforming
packets), other application flows, especially those that are
extremely sensitive to jitter, hope not to get larger jitter due to
the policing delay.
This document describes a mechanism to eliminate jitter caused by
policing delay. It needs to be used in combination with a scheduling
mechanism that provides low jitter for the transport path, and
ultimately provides a low jitter guarantee for the application flow.
2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. Overview of the Solution
The end-to-end delay expierenced by the application flow can be
considered to consist of two parts: edge policing delay, and
transport path delay. According to flow's end-to-end delay
requirement and edge policing delay budget, a transport path with
expected delay performance (i.e., end-to-end delay requirement minus
edge policing delay budget) can be calculated and setup. A propriate
edge policing delay budget can be configured for the application flow
according to its TSpec and actual possible arrival pattern, and
generally be the maximum policing delay that may be possibly
experienced at the network entry.
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The edge policing delay budget is consumed by the headend and
endpoint of the transport path. Meet:
edge policing delay budget = headend policing delay + endpoint
damping delay
The headend policing delay is the actual policing delay experienced
at the network entry. The endpoint damping delay is obtained by
subtracting the headend policing delay from the edge policing delay
budget .
Figure 1 shows that the relationship between these delay elements.
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
(~ ~)
(~ ~)
+------+ +-------+ +--------+ +------+
|AppSrc|---|Headend| |Endpoint|---|AppDst|
+------+ +-------+ +--------+ +------+
(~ ~)
(~ ~)
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
|<---------- E2E Delay Reuirement ---------->|
| |
| |<--------- Path Delay ----------->| |
|<-->| |<-->|
headend endpoint
policing damping
delay delay
Figure 1: Relationship Between Delay Elements
When the headend of the transport path receives the packet from the
application source, it may carry the endpoint damping delay in the
encoded packet sent to the endpoint, and the endpoint damping delay
will be used as the holding time imposed on the endpoint before the
packet is delivered to the application destination.
Note that some scheduling mechanisms, such as
[I-D.peng-detnet-deadline-based-forwarding] and
[I-D.peng-detnet-packet-timeslot-mechanism], also provide the latency
deviation (E) information of the transport path. Depending on the
implementation, the endpoint can use different buffers to firstly
implement jitter control based on path latency deviation (E) and
secondly jitter control based on endpoint damping delay, or use the
same buffer to uniformly implement jitter control based on the sum of
path latency deviation (E) and endpoint damping delay.
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Therefore, a flow with possible nonconforming packets will be
regulated and changed to be conforming at the network entry, then get
deterministic forwarding service within the network, and finally
reverts to the nonconforming pattern at the network exit and deliver
to the application destination.
4. Set Edge Policing Delay Budget
The edge policing delay budget can be configured for the application
flow according to its TSpec and actual possible arrival pattern.
For example, an application flow has service burst interval (SBI) 100
us, and three packets P1, P2, P3 per SBI. Assuming the maximum
packet size is 1000 bits. It can be seen that the bandwidth required
by the application flow is 30 Mbps. The packet size 1000 bits and
required bandwidth 30 Mbps are also the leaky bucket policing
parameters at the network entry.
In the ideal case, a conforming pattern of the application flow is
that the three packets arrive evenly in the SBI at the network entry.
However, a extremely case of nonconforming pattern may be that P1,
P2, P3 are closely arrived together. After leaky bucket regulation,
P1, P2 and P3 will get different policing delays, of which P3 has the
largest policing delay which may be 2/3 of SBI and can be used as
edge policing delay budget.
There may be other settings of edge policing delay budget that are
not based on the above extreme case, such as sampling the most likely
actual arrival pattern of flow to set a smaller edge policing delay
budget. Especially, for the timeslot based scheduling mechanism, the
edge policing delay budget may be set based on the maximum deviation
between the actual arrival timeslot and ideal arrival timeslot.
The network entry should maintain the edge policing delay budget for
each application flow, and when it receives a packet from the
application source, it identifies the flow to which the packet
belongs and applies the corresponding edge policing delay budget. If
the edge policing delay budget is M, and the actual policing delay of
the packet is S, then the endpoint damping delay for that packet
equals to M - S.
5. Multi-domain considerations
In the case of multi-domain, each domain may apply different
scheduling machanisms. For each transit domain and egress domain,
the input traffic should be conforming and then get the deterministic
forwarding services. However, the output traffic from upstream
domain may not always be conforming.
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One option is to implement jitter control based on endpoint damping
delay in each domian independently. That is, for each domain entry,
it maintain the edge policing delay budget for each application flow,
identify the application flow, regulate the nonconforming arrived
packet and calculate the endpoint damping delay for the packet. In
this option, each domain contribute a edge policing delay budget
repeatedly, which may lead to a large end-to-end delay (but not
necessarily, such as selecting a transport path with a smaller delay
in each domain ). When the packet leaves the upstream domain, the
encapsulation metadata related to the scheduling mechanism of the
upstream domain and the endpoint damping delay information are
removed, and then the current domain entry will re-encapsulate the
scheduling metadata related to the scheduling mechanism of the
current domain and the endpoint damping delay information. The
limitation for this option is the states maintained at each domain
entry.
Another optoin is to implement jitter control based on endpoint
damping delay only once for the entire multi-domian. The key
operation in this option is to treat each transit domain entry (or
egress domain entry) as a transit node of the scheduling mechanism of
that domain, that means that the legacy parameters of the scheduling
mechanism of the upstream domain (such as path latency deviation,
scheduling sorting information) need to continue to be input and used
as basic parameters in the current domain. The upstream domain exit
should be aware that the scheduling mechanism has switched, and is
responsible for mapping the metadata of the old scheduling mechanism
to the metadata of the new scheduling mechanism, and especially, the
metadata of the new scheduling mechanism contains the legacy
scheduling results of the previous domain. The current domian entry
should be aware of the legacy scheduling result (which can be treated
as initial scheduling parameters) carried in the received packet.
When the packet leaves the upstream domain, the endpoint damping
delay information is always persisted and unchanged. This option
seems less cost than the first option, e.g, no states per application
flow maintained on each domain entry. However, the the mapping of
scheduling metadata and processing initial scheduling parameters
should be excecuted on several border nodes.
6. Encoding Considerations
A new IPv6 option for DOH Options header ([RFC8200]), or a new
ancillary data for MPLS MNA header ([I-D.ietf-mpls-mna-hdr]), can be
defined to carry endpoint damping delay. It is also possible to
carry endpoint damping delay in an IPv6 Routing Header, such as in
the segment field, to flexibly control which nodes (e.g, each domain
exit, or only egress domain exit) need to implement jitter control
based on endpoint damping delay.
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The related encoding format and its usage will be defined in separate
documents.
7. IANA Considerations
This document need not require IANA allocations.
8. Security Considerations
TBD.
9. Acknowledgements
TBD.
10. References
10.1. Normative References
[I-D.ietf-mpls-mna-hdr]
Rajamanickam, J., Gandhi, R., Zigler, R., Song, H., and K.
Kompella, "MPLS Network Action (MNA) Sub-Stack Solution",
Work in Progress, Internet-Draft, draft-ietf-mpls-mna-hdr-
04, 21 October 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-mpls-
mna-hdr-04>.
[I-D.peng-detnet-deadline-based-forwarding]
Peng, S., Du, Z., Basu, K., cheng, Yang, D., and C. Liu,
"Deadline Based Deterministic Forwarding", Work in
Progress, Internet-Draft, draft-peng-detnet-deadline-
based-forwarding-08, 14 December 2023,
<https://datatracker.ietf.org/doc/html/draft-peng-detnet-
deadline-based-forwarding-08>.
[I-D.peng-detnet-packet-timeslot-mechanism]
Peng, S., Liu, P., Basu, K., Liu, A., Yang, D., and G.
Peng, "Timeslot Queueing and Forwarding Mechanism", Work
in Progress, Internet-Draft, draft-peng-detnet-packet-
timeslot-mechanism-05, 14 December 2023,
<https://datatracker.ietf.org/doc/html/draft-peng-detnet-
packet-timeslot-mechanism-05>.
[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>.
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[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.
[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.
[RFC8557] Finn, N. and P. Thubert, "Deterministic Networking Problem
Statement", RFC 8557, DOI 10.17487/RFC8557, May 2019,
<https://www.rfc-editor.org/info/rfc8557>.
Authors' Addresses
Shaofu Peng
ZTE
China
Email: peng.shaofu@zte.com.cn
Peng Liu
China Mobile
China
Email: liupengyjy@chinamobile.com
Kashinath Basu
Oxford Brookes University
United Kingdom
Email: kbasu@brookes.ac.uk
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