Network Working Group Y. Li
Internet-Draft H. Yang
Intended status: Informational T. Sun
Expires: January 9, 2022 China Mobile
July 8, 2021
One-way Delay Measurement Based on Deterministic Networking
draft-li-ippm-deterministic-owd-measurement-00
Abstract
One-way delay is a key indicator to measure network quality. Some
applications are one-way transmission in the network, such as some
high-definition video services, and are very sensitive to one-way
delay. Excessive delay will affect user experience greatly. To some
extent, the network can't even be used, so it is very important to
accurately measure the network transmission delay. The current one-
way delay measurement method has problems such as high complexity and
low measurement accuracy. In order to solve the problem of high-
precision one-way delay measurement, a one-way delay measurement
method based on deterministic networking is proposed in this
document. The method takes advantage of the delay characteristics of
the deterministic networking and does not depend on precise time
synchronization.
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Copyright (c) 2021 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. One-way Delay Measurement Method Based on Deterministic
Networking . . . . . . . . . . . . . . . . . . . . . . . . . 4
4. Procedures of the One-way Delay Measurement Method . . . . . 6
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
One-way transmission delay is a key indicator to measure network
quality. Some applications are based on one-way transmission in the
network, such as some high-definition video services, and are very
sensitive to one-way delay. Excessive one-way delay will affect user
experience dramatically, so it is very important to accurately
measure the one-way transmission delay of the network.
There are several kinds of methods to measure one-way delay. The
first kind of methods is active measurement. A sender will send
measurement protocol messages, such as Two-Way Active Measurement
Protocol (TWAMP) [RFC8186]messages, to the network to measure the
one-way delay of the sender and receiver. The advantage of active
measurement is that it is flexible in application. The disadvantage
is that the measurement messages cannot measure the delay of real
services, and the measurement of one-way delay requires sender and
receiver to support time synchronization protocol, such as NTP
[RFC5905]and PTP [IEEE.1588.2008]. The first kind of methods is
passive measurement. The passive measurement devices will calculate
network delay by collecting actual business traffic. The advantage
of passive measurement is that it can measure the one-way delay of
real services. The disadvantage is that two passive measurement
devices need to be deployed, and the two devices require time
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synchronization, which is difficult to implement. The third kind of
methods is hybrid measurement. Hybrid measurement is a combination
of active and passive measurements, that is, inserting some fields or
flags in the service message to realize the delay measurement of the
actual service. The disadvantage is that the message format of the
actual service is changed, which will affect the forwarding behavior
of the service and have observer effect. The network element needs
to be able to recognize and forward the modified service message, and
time synchronization of the network element is also required.
The above-mentioned one-way delay measurement methods have the
following shortcomings. Firstly, if the measurement message is
injected into actual network, it will occupy network bandwidth
resources and interfere with the actual service flow, so the measured
delay is not the delay of the actual service. Secondly, the
measurement equipment or network elements need to support time
synchronization protocols, which is difficult to implement and
costly.
To address the following shortcomings of existing methods, this
document presents the following technical solution. A high-precision
one-way delay measurement method is proposed, which can be used to
measure the one-way delay of actual service packets, without sending
measurement messages, without changing the actual network status,
without changing service messages, and without the need for network
elements to support time synchronization protocols.
2. Conventions Used in This Document
2.1. Terminology
NTP Network Time Protocol
PTP Precision Time Protocol
TWAMP Two-Way Active Measurement Protocol
SLA Service Level Agreement
2.2. 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.
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3. One-way Delay Measurement Method Based on Deterministic Networking
+-----------------------------------------------------------+
| Centralized Control Node |
+----+-------------+---------------+---------+---------+----+
^ ^ ^ ^ ^
| | T4 | T3 | | Tn
| | | +----+----+ |
| | | | Network | |
T1 | T2 | +----------------->Element 3+-+ |
| | | | | | | |
| | | | +---------+ | |
| | | | | |
| | | | | |
| | | | | |
| | | | | |
+----+----+ +----+--+-+ +----+----+ +-v--+----+
| Network | | Network | | Network | | Network |
|Element 1+--->Element 2+----->Element 4+--------->Element n|
| | | | | | | |
+---------+ +---------+ +---------+ +---------+
Figure 1: A schematic diagram of the network topology structure
A schematic diagram of the network topology structure to describe the
proposed method is shown in Figure 1. The network may be a SDN
(Software Defined Network) or a traditional network. Whether it is
SDN or traditional network, there is a centralized control node (or
called a centralized management unit) for collecting network
information sent by network elements and sending control information
to the network. Taking SDN as an example, the centralized control
node can be a SDN controller. For traditional networks, the
centralized control node can be a network management system. The
information from the network element to the centralized control node
generally passes through the management network. In our solution,
the management network from each network element to the centralized
control node is required to use a delay deterministic network. As an
example, the delay deterministic network may be a time sensitive
network (TSN) or a deterministic Internet (Deterministic Internet
Network, DIP) [RFC8655], etc. Through the delay deterministic
network, the transmission delay of the network element information
from the network element to the centralized control node can be
guaranteed to be fixed. T1~Tn in Figure 1 represent the network
element information delay from the network element to the centralized
control node of network element 1 to n respectively.
As shown in Figure 1, suppose network traffic of a real service flow
passes through network element 1, network element 2, ..., network
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element n in turn, and the time when network traffic passes through
the network element is recorded as t1, t2, ..., tn. The timestamp
maybe the ingress timestamp of network traffic entering the network
element or the egress timestamp of network traffic flowing out of the
network element after the forwarding is completed. Each network
element transmits the flow information to the centralized control
node through the delay deterministic network when real traffic
passes, and the transmission delays of each network element to
transmit the flow information to the centralized control node through
the delay deterministic network are denoted as T1, T2, ..., Tn,
respectively. The timestamps when the centralized control node
receives the flow information of each network element are t1', t2',
..., tn'.
Taking the calculation of the one-way transmission delay of traffic
from network element 1 to network element 2 as an example, the one-
way transmission delay can be calculated in the following way.
Firstly, because the clocks of network element 1 and network element
2 are not synchronized, suppose the time deviation between the two is
delta_t. Then the one-way transmission delay of traffic from network
element 1 to network element 2 satisfies the following formula (1).
Among them, Delay represents the one-way transmission delay of
traffic from network element 1 to network element 2.
Formula (1): Delay = t2 - t1 - delta_t
Secondly, because the clocks between network element 1 and the
centralized control node are not synchronized, assuming that the time
deviation between the two is delta_t', the time for the traffic
information collected from the network element 1 to reach the
centralized control node through the delay deterministic network
satisfies the following formula (2).
Formula (2): t1' = t1 + T1 + delta_t'
Thirdly, the clocks between network element 2 and the centralized
control node are not synchronized, and the time deviation between
network element 2 and the centralized control node is delta_t'-
delta_t. The time t2' for the collected traffic to reach the
centralized control node satisfies the following formula (3).
Formula (3): t2' = t2 + T2 + delta_t' - delta_t
Forthly, subtracting the formula (2) from the above formula (3), we
can obtain the following formula (4).
Formula (4): t2 - t1 - delta_t = t2' - t1' + T1 - T2
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Fifthly, substituting the above formula (4) into the above formula
(1), the following formula (5) can be obtained.
Formula (5): Delay = t2' - t1' + T1 - T2
So far, the one-way transmission delay of traffic from network
element 1 to network element 2 is obtained. Taking the calculation
of one-way transmission delay of traffic from network element 1 to
network element 3 as an example, the one-way transmission delay can
be calculated in the following way: I) Referring to the above formula
(5), the one-way transmission delay of traffic from network element 1
to network element 2 is: Delay12 = t2' - t1' + T1 - T2. II)
Referring to the above formula (5), the one-way transmission delay of
traffic from network element 2 to network element 3 is: Delay23 = t3'
- t2' + T2 - T3. III) The one-way transmission delay of traffic from
network element 1 to network element 3 is: Delay13 = Delay12 +
Delay23 = t2' - t1' + T1 - T2 + t3' -t2' +T2 - T3 = t3' - t1' + T1 -
T3. It can be seen that the one-way transmission delay between any
two network elements can be calculated similarly to the above formula
(5). For example, taking network element m and network element n as
an example, the transmission delay of traffic from network element m
to network element n is: Delay = tn' - tm' + Tm - Tn, where tn' and
tm' are the time when the traffic information of network element m
and network n reaches the centralized control node, and Tm and Tn are
transmission delay of the traffic information from network element m
and network element n to the centralized control node respectively
through delay deterministic network.
4. Procedures of the One-way Delay Measurement Method
In this section, the procedures of the proposed one-way delay
measurement method will be elaborated. Assume there are two network
element. It is determined that the time when the centralized control
node receives the first flow information is the first time, and the
time when the second flow information is received by the centralized
control node is determined to be the second time. The first flow
information is sent to the centralized control node via delay
deterministic network, and the second flow information is also sent
to the centralized control node via delay deterministic network. The
procedures of the one-way delay measurement method is shown in
Figure 2.
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+-----------+ +-----------+ +---------------------+ +--------------+
| Network | | Network | | Delay Deterministic | | Centralized |
| Element m | | Element n | | Network | | Control Node |
+-----+-----+ +-----+-----+ +---------------------+ +-------+------+
| | |
| | |
| | |
| | The first transmission +-------+--------+
| | delay is Tm | tm' represents |
+----------------------------------------------> the first time |
| | +-------+--------+
| | |
| | |
| | The second transmission +-------+--------+
| | delay is Tn | tn' represents |
| +-------------------------------> the second time|
| | +-------+--------+
| | |
| | |
| | |
+ + +
Figure 2: Procedures of the one-way delay measurement method
The transmission delay of traffic from the first network element to
the second network element can be determined based on the first time,
the second time, the first transmission delay, and the second
transmission delay.
The first traffic information is sent by the first network element to
the centralized control node via a delay deterministic network at the
moment when the traffic passes through the first network element.
And the time when the traffic passes through the first network
element refers to the moment when traffic enters the first network
element or the time when traffic flows out of the first network
element.
The second traffic information is sent by the second network element
to the centralized control node via a delay deterministic network at
the moment when the traffic passes through the second network
element. And the time when the traffic passes through the second
network element refers to the moment when traffic enters the second
network element or the time when traffic flows out of the second
network element.
It is determined that the transmission delay of the first traffic
information from the first network element to the centralized control
node is the first transmission delay, and it is determined that the
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transmission delay of the second traffic information from the second
network element to the centralized control node is the second
transmission delay. The transmission delay of traffic from the first
network element to the second network element can be determined based
on the following formula: Delay=tn'-tm'+Tm-Tn. Wherein, tn'
represents the second time, tm' represents the first time, Tm
represents the first transmission delay, Tn represents the second
transmission delay, and Delay represents transmission delay of the
traffic from the first network element to the second network element.
In the above method, the delay deterministic network is used to
ensure that the first transmission delay and the second transmission
delay are fixed delays.
5. Security Considerations
TBD.
6. IANA Considerations
TBD.
7. Normative References
[IEEE.1588.2008]
IEEE, "IEEE Standard for a Precision Clock Synchronization
Protocol for Networked Measurement and Control Systems",
July 2008.
[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>.
[RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch,
"Network Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010,
<https://www.rfc-editor.org/info/rfc5905>.
[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>.
[RFC8186] Mirsky, G. and I. Meilik, "Support of the IEEE 1588
Timestamp Format in a Two-Way Active Measurement Protocol
(TWAMP)", RFC 8186, DOI 10.17487/RFC8186, June 2017,
<https://www.rfc-editor.org/info/rfc8186>.
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[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
Yang Li
China Mobile
Beijing 100053
China
Email: liyangzn@chinamobile.com
Hongwei Yang
China Mobile
Beijing 100053
China
Email: yanghongwei@chinamobile.com
Tao Sun
China Mobile
Beijing 100053
China
Email: suntao@chinamobile.com
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