Internet DRAFT - draft-li-ippm-ref-delay-measurement
draft-li-ippm-ref-delay-measurement
Network Working Group Y. Li
Internet-Draft T. Sun
Intended status: Standards Track H. Yang
Expires: 14 August 2022 D. Chen
China Mobile
Y. Wang
Huawei
10 February 2022
One-way Delay Measurement Based on Reference Delay
draft-li-ippm-ref-delay-measurement-02
Abstract
The end-to-end network one-way delay is an important performance
metric in the 5G network. For realizing the accurate one-way delay
measurement, existing methods requires the end-to-end deployment of
accurate clock synchronization mechanism, such as PTP or GPS, which
results in relatively high deployment cost. Another method can
derive the one-way delay from the round-trip delay. In this case,
since the delay of the downlink and uplink may be asymmetric, the
measurement accuracy is relatively low. Hence, this document
introduces a method to measure the end-to-end network one-way delay
based on a reference delay guaranteed by deterministic networking
without clock synchronization.The advantage of this solution is that
it has high measurement accuracy and can test any flow type.
Status of This Memo
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This Internet-Draft will expire on 14 August 2022.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
3. The method of One-way Delay Measurement Based on Reference
Delay . . . . . . . . . . . . . . . . . . . . . . . . . . 4
3.1. One-way Delay Measurement Method . . . . . . . . . . . . 5
3.2. Packet and Measurement Header Format . . . . . . . . . . 7
4. Acquisition of Reference Delay . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 8
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 8
7. Normative References . . . . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
With the gradual promotion of new-generation network technologies
(such as 5G networks) and their application in various industries,
SLA guarantees for network quality become more and more important.
For example, different 5G services have different requirements for
network performance indicators such as delay, jitter, packet loss,
and bandwidth. Among them, the 5G network delay is defined as end-
to-end one-way delay of the network. Real-time and accurate
measurement of the end-to-end one-way delay is very important for the
SLA guarantee of network services, and has become an urgent and
important requirement.
As shown in figure 1, 5G network HD video surveillance service is a
common scenario having requirement of end-to-end one-way delay
measurement. In this case, one end of the network is a high-
definition surveillance camera in the wireless access side, and the
other end of the network is a video server. The end-to-end one-way
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delay from the surveillance camera to the video server is the sum of
T1, T2, T3 and T4, which is composed of delay in wireless access
network, optical transmission network, 5G core network, and IP data
network.
+--------+ +-------+ +-------+ +-------+
+------+ |Wireless| |Optical| |5G Core| | IP | +------+
|Camera+<->+ Access +<->+ Trans +<->+Network+<->+ Data +<->+Server|
+------+ |Network | |Network| | | |Network| +------+
+--------+ +-------+ +-------+ +-------+
|<---- T1 ---->|<--- T2 -->|<--- T3 -->|<--- T4 ---->|
Figure 1: Figure 1:A Scenario for End-to-end One-way Delay
The existing one-way delay measurement solutions are divided into two
types. One type of mechanism to calculate one-way delay is based on
the measurement of round-trip delay. However, for example, because
upstream traffic and downstream traffic do not share the same path in
5G network, the accuracy of the end-to-end one-way delay calculated
from the round-trip delay is low. Another type of mechanism is in-
band OAM with accurate network time synchronization mechanism , such
as NTP[RFC5905] or PTP[IEEE.1588.2008].
The one-way delay measurement solution based on precise network time
synchronization requires the deployment of an end-to-end time
synchronization mechanism. The current time synchronization accuracy
based on the NTP protocol can only reach millisecond level, which
cannot fully meet the measurement accuracy requirements. The time
synchronization accuracy based on the GPS module or the PTP protocol
can meet the requirements. However, because many data centers are
actually located underground or in rooms without GPS signals, so GPS
clock information cannot be continuously obtained for time
synchronization. For time synchronization solutions based on the PTP
protocol, each device in the wireless access network, 5G transport
network, and 5G core network must support the PTP protocol, which is
unrealistic at the moment. So the one-way delay measurement solution
based on precise end-to-end time synchronization is expensive and
difficult to be deployed.
This document introduces a one-way delay measurement mechanism for
Deterministic Networking (DetNet) [RFC8655]. The one-way delay
measurement is based on a stable one-way delay of a reference DetNet
packet, named as reference delay, which is known in advance and has
extremely low jitter. We can use the reference delay provided by the
reference DetNet packet to derive the one-way delay of other common
service packets.
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2. Conventions Used in This Document
2.1. Terminology
NTP Network Time Protocol
PTP Precision Time 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.
3. The method of One-way Delay Measurement Based on Reference Delay
The end-to-end one-way delay of a reference packet with a stable
delay in the network can be used as a reference delay, denoted as
Dref, which is known in advance and has extremely low jitter. This
section will describe in detail the end-to-end one-way delay
measurement method based on reference delay of the reference packet.
Assume that the end-to-end one-way delay from the sender to the
receiver is measured, as shown in figure 2. The intermediate network
devices other than the sender and receiver are hidden in the figure.
+------------+ +------------+
| | Clock Offset | |
| Sender | +---------------> | Receiver |
| | | |
+------------+ +------------+
Reference +-----+ Dref +-----+
Packet: | Ts1 | +-------------------> | Tr1 |
+-----+ +-----+
Target +-----+ Dtarget +-----+
Packet: | Ts2 | +-------------------> | Tr2 |
+-----+ +-----+
Figure 2: Figure 2:Topology of One-way Delay Measurement
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3.1. One-way Delay Measurement Method
The measurement steps are shown in figure 3, which describe the
measurement steps at the sender side and receiver side respectively.
For the sender side, a reference packet is sent. In the first step,
the sender gets ready to send a reference packet; in the second step,
the sender marks an egress timestamp Ts1 for the reference packet; in
the third step, the sender encapsulates the egress timestamp of the
reference packet in the measurement header of the reference packet;
in the fourth step, the sender sends the reference packet. For the
target packet, the sender side procedures are the same,we omit it for
simplicity. The sending time of the target packet is according to
the traffic model of real applications. On the other hand, the
sender can send the reference packet according to a fixed frequency
or adjust the sending frequency according to the link usage rate, so
that the target packet can always find a nearby reference packet to
make sure that the sending time interval between the reference packet
and the target packet is small.
For the reference packet, the processing steps at the receiver are
shown in figure 3. In the first step, the reference packet arrives
at the receiver, and the receiver receives the reference packet; in
the second step, the receiver timestamps the reference packet at the
entrance, which is denoted as Tr1; in the third step, the receiver
decapsulates the measurement header of the reference packet to obtain
the sender side timestamp Ts1; in the fourth step, the receiver
records the timestamp information of Ts1 and Tr1; in the fifth step,
the receiver uses the source/destination pair obtained by
decapsulation in the third step as the search key, queries the
reference delay table and records the reference delay search result,
denoted as Dref.
For the target packet, the processing steps at the receiver are also
shown in figure 3. In the first step, the target packet arrives at
the receiver, and the receiver receives the target packet; in the
second step, the receiver timestamps the target packet at the
entrance, which is denoted as Tr2; in the third step, the receiver
decapsulates the measurement header of the target packet to obtain
the sender side timestamp Ts2; in the fourth step, the receiver
records the timestamp information of Ts2 and Tr2; in the fifth step,
the receiver calculates the target one-way delay, which we want to
measure, according to the recorded timestamp information Ts1, Ts2,
Tr1, Tr2 and reference delay information Dref. The target one-way
delay of the target packet is recorded as Dtarget.
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Sender Side Procedures for both Reference and Target Packet:
+-------+ +------------+ +-------------+ +-------+
|Sender | |Sender Side | |Sender Side | |Sending|
|Ready +-->+Timestamping+-->+Encapsulation+-->+ Packet|
| | | | | | | |
+-------+ +------------+ +-------------+ +-------+
Receiver Side Procedures for Reference Packet:
+---------+ +-------------+ +-------------+ +---------+ +---------+
|Reference| |Receiver Side| |Receiver Side| |Timestamp| |Query for|
|Packet +->+Timestamping +->+Decapsulation+->+Recorded +->+Reference|
|Arrival | | | | | | | | Delay |
+---------+ +-------------+ +-------------+ +---------+ +---------+
Receiver Side Procedures for Target Packet:
+-------+ +-------------+ +-------------+ +---------+ +-----------+
| Target| |Receiver Side| |Receiver Side| |Timestamp| | One-way |
| Packet+->+Timestamping +->+Decapsulation+->+Recorded +->+ Delay |
|Arrival| | | | | | | |Calculation|
+-------+ +-------------+ +-------------+ +---------+ +-----------+
Figure 3: Figure 3: Measurement steps for Sender and Receiver
Respectively
Now we describe the fifth step of the receiver procedures for the
target packet in figure 3, that is, calculating the one-way delay
Dtarget of the target packet based on the recorded timestamp
information Ts1, Ts2, Tr1, Tr2 and the reference delay information
Dref. The calculation method is the core of this solution. For the
reference packet, leveraging the receiver timestamp minus the sender
timestamp, we can get Equation 1.
Equation 1: Tr1 - Ts1 = Dref + Offset1
where Offset1 is the time offset between the sender and the receiver
when the reference packet transmission occurs. Similarly, for the
target packet, we can get Equation 2 using the same method.
Equation 2: Tr2 - Ts2 = Dtarget + Offset2
where Offset2 is the time offset between the sender and the receiver
when the target packet transmission occurs. Assuming that the
sending time interval between the reference packet and the target
packet is very small, we can get that Offset1 = Offset2. By
(Equation 2 - Equation 1), we can get Equation 3.
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Equation 3: Dtarget = (Tr2 + Ts1) - (Tr1 + Ts2) + Dref
So the one-way delay of the target packet can be calculated by
Equation 3.
3.2. Packet and Measurement Header Format
The sender encapsulates the timestamp information and sender-receiver
pair information in the measurement header of the sent packet, as
shown in figure 4. The position of measurement header is in the
option field of the TCP protocol header. The delay measurement
option format is defined in figure 5. The Length value is 8 octets,
which is in accordance with TCP option. The sender ID is one octet,
and the receiver ID is also one octet. The sender side timestamp is
4 octets, which can store accurate timestamp information.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Ethernet header (14 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| IP header (20 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| TCP header (20 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TCP Delay Measurement Option (8 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Data |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Figure 4: Format of Reference or Target Packet
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Kind=TBA | Length | Sender ID | Receiver ID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Side Timestamp (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Figure 5: TCP Delay Measurement Option Format
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4. Acquisition of Reference Delay
The end-to-end one-way delay includes three parts, namely the
transmission delay, the internal processing delay of the network
devices, and the internal queueing delay of the network devices.
Among them, fixed parts of the delay include transmission delay and
internal processing delay. The transmission delay is related to
transmission distance and transmission media. For example, in
optical fiber, it is about 5ns per meter. With transmission path and
media determined, it is basically a fixed value. The internal
processing delay of a network device includes processing delay of the
device's internal pipeline or processor and serial-to-parallel
conversion delay of the interface, which is related to in/out port
rate of the device, message length and forwarding behavior. The
magnitude of the internal processing delay is at microsecond level,
and it is basically a fixed value related to the chip design
specifications of a particular network device. Variable part of the
delay is the internal queueing delay. The queueing delay of the
device internal buffer is related to the queue depth, queue
scheduling algorithm, message priority and message length. For each
device along the end-to-end path, the queueing delay can reach
microsecond or even millisecond level, depending on values of the
above parameters and network congestion state.
With the continuous development of networking technologies and
application requirements, a series of new network technologies have
emerged which can guarantee bounded end-to-end delay and ultra small
jitter. For example, deterministic network[RFC8655], by leveraging
novel scheduling algorithms and packet priority settings, can
stabilize queuing delay of network device on the end-to-end path. As
a result, the end-to-end one-way delay is extremely low and bounded.
So packets transmitted by a deterministic network with delay
guarantee can be used as reference packets, and their end-to-end one-
way delay can be used as reference delays. The acquisition method of
reference delay is not limited to the above method based on
deterministic network technology.
5. Security Considerations
TBD.
6. IANA Considerations
This document requests IANA to assign a Kind Number in TCP Option to
indicate TCP Delay Measurement option.
7. Normative References
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[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>.
[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
Tao Sun
China Mobile
Beijing
100053
China
Email: suntao@chinamobile.com
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Hongwei Yang
China Mobile
Beijing
100053
China
Email: yanghongwei@chinamobile.com
Danyang Chen
China Mobile
Beijing
100053
China
Email: chendanyang@chinamobile.com
Yali Wang
Huawei
156 Beiqing Rd., Haidian District
Beijing
China
Email: wangyali11@huawei.com
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