IPPM Working Group X. Min
Internet-Draft D. Zhanwei
Intended status: Standards Track ZTE
Expires: April 15, 2018 October 12, 2017
TWAMP Extensions for Direct Loss Measurement
draft-xiao-ippm-twamp-ext-direct-loss-01
Abstract
This document describes an optional extension for Two-Way Active
Measurement Protocol (TWAMP) allowing direct loss measurement of IP
traffic with the TWAMP-Test protocol.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
1.1. Conventions Used in This Document . . . . . . . . . . . . 2
1.1.1. Terminology . . . . . . . . . . . . . . . . . . . . . 2
1.1.2. Requirements Language . . . . . . . . . . . . . . . . 3
2. TWAMP-Control Extension . . . . . . . . . . . . . . . . . . . 3
2.1. Connection Setup with Direct Loss Measurement Mode . . . 3
3. TWAMP-Test Extensions . . . . . . . . . . . . . . . . . . . . 3
3.1. Sender Test Packet Format and Content . . . . . . . . . . 4
3.2. Reflector Test Packet Format and Content . . . . . . . . 6
3.3. Traffic Loss Calculation . . . . . . . . . . . . . . . . 10
4. Operational Guide . . . . . . . . . . . . . . . . . . . . . . 11
5. Security Considerations . . . . . . . . . . . . . . . . . . . 11
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11
7. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 11
8. Normative References . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 12
1. Introduction
The Two-Way Active Measurement Protocol (TWAMP) [RFC5357] is an
extension of the One-Way Active Measurement Protocol (OWAMP)
[RFC4656]. The TWAMP is a well-defined protocol which is widely used
for measurement of two-way or round-trip metrics, in addition to the
one-way metrics of OWAMP.
When TWAMP or OWAMP is used for measurement of metric loss, it
actually measures the loss of test packets, so it's a kind of
"synthetic" loss measurement. In some cases, considering the IP
traffic loss characteristics of short-time burst loss, it's expected
to get more accurate loss measurement results when measuring the
direct loss of IP traffic instead of test packets.
To address this, this document describes an optional and simple
feature for TWAMP, which allows TWAMP-Test protocol to be used for
direct loss measurement of IP traffic.
1.1. Conventions Used in This Document
1.1.1. Terminology
DSCP: Differentiated Services Code Point
IPPM: IP Performance Metrics
TWAMP: Two-Way Active Measurement Protocol
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OWAMP: One-Way Active Measurement Protocol
UDP: User Datagram Protocol
1.1.2. 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.
2. TWAMP-Control Extension
TWAMP connection establishment follows the procedure defined in
Section 3.1 of [RFC4656] and Section 3.1 of [RFC5357] where the Modes
field is used to identify and select specific communication
capabilities. At the same time, the Modes field is recognized and
used as an extension mechanism [RFC6038]. The new feature requires a
new flag, Direct Loss Measurement flag, to identify the ability of
both Session-Sender and Session-Reflector to perform direct loss
measurement, and to support the new Session-Sender packet format and
the new Session-Reflector packet format in the TWAMP-Test protocol.
See Section 6 for details on the assigned bit position.
2.1. Connection Setup with Direct Loss Measurement Mode
The Server sets the Direct Loss Measurement flag in the Modes field
of the Server Greeting message to indicate its capability and
willingness to perform it. If the Control-Client agrees to perform
direct loss measurement on some or all test sessions invoked with
this control connection, it MUST set the Direct Loss Measurement flag
in the Modes field in the Setup Response message.
3. TWAMP-Test Extensions
The TWAMP-Test protocol is similar to the OWAMP [RFC4656] test
protocol with the exception that the Session-Reflector transmits test
packets to the Session-Sender in response to each test packet it
receives. TWAMP, see Section 4 of [RFC5357], defines two additional
test packet formats for packets transmitted by the Session-Reflector.
The appropriate format depends on the security mode chosen. The new
mode specified in this document adds counter(s) of IP traffic packets
into each test packet format.
When the Server and Control-Client have agreed to use the direct loss
measurement mode during control connection setup, then the Session-
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Sender and the Session-Reflector SHOULD all conform to the
requirements of that mode, as identified below.
3.1. Sender Test Packet Format and Content
Formats of the test packet transmitted by the Session-Sender in
unauthenticated, authenticated, and encrypted modes have been defined
in Section 4.1.2 of [RFC4656] (as indicated in Section 4.1.2 of
[RFC5357]). For the Session-Sender that supports direct loss
measurement, these formats are displayed in Figures 1 and 2.
For unauthenticated mode:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Tx Couter(S_TxC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. Packet Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Session-Sender Test Packet Format with direct loss
measurement in Unauthenticated Mode
For authenticated and encrypted modes:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MBZ (6 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Tx Counter(S_TxC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
. .
. Packet Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Session-Sender Test Packet Format with Direct Loss
Measurement in Authenticated and Encrypted Modes
The Sender Tx Counter (S_TxC) is set to the number of IP packets of
the particular monitored flow transmitted towards the Reflector.
Section 4 provides operational guide on how to determine the scope of
IP traffic packets that need to be counted. Note that the Sender
test packets are not counted.
In authenticated and encrypted modes, the S_TxC is followed by a new
12 octets MBZ (MUST be zero) field to make it 16-octet aligned, which
is required for authentication and encryption.
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The intention of embedding S_TxC in the Session-Sender test packets
is for the Session-Sender to calculate direct loss of IP traffic, and
the loss calculation algorithm is described in Section 3.3.
The new direct loss measurement mode defined in this document and the
two extended TWAMP modes defined in [RFC6038] can be selected
simultaneously.
When the Symmetrical Size mode defined in [RFC6038] is also selected,
S_TxC SHOULD be embedded in the Session-Sender Packet formatted in
Section 5.1.4 of [RFC6038], with the same position as depicted in
Figure 1.
When the Reflect Octets mode defined in [RFC6038] is also selected,
S_TxC SHOULD be embedded in the Session-Sender Packet formatted in
Section 5.1.2 of [RFC6038], with the same position as depicted in
Figure 1.
When both the Symmetrical Size mode and the Reflect Octets mode are
also selected, S_TxC SHOULD be embedded in the Session-Sender Packet
formatted in Section 5.1.5 of [RFC6038], with the same position as
depicted in Figure 1.
3.2. Reflector Test Packet Format and Content
Formats of the test packet transmitted by the Session-Reflector in
unauthenticated, authenticated, and encrypted modes have been defined
in Section 4.2.1 of [RFC5357]. For the Session-Reflector that
supports direct loss measurement, these formats are displayed in
Figures 3 and 4.
For unauthenticated mode:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender TTL | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Sender Tx couter(S_TxC ) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Reflector Rx couter(R_RxC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
| Reflector Tx couter(R_TxC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
. .
. Packet Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Session-Reflector Test Packet Format with direct loss
measurement in Unauthenticated Mode
For authenticated and encrypted modes:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (12 octets) |
| |
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| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MBZ (6 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (8 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (12 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Timestamp |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MBZ (6 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender TTL | |
+-+-+-+-+-+-+-+-+ +
| |
| |
| MBZ (15 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sender Tx Counter(S_TxC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reflector Rx Counter(R_RxC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reflector Tx Counter(R_TxC) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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| |
| MBZ (12 octets) |
| |
+++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++++
| HMAC (16 octets) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-|
. .
. Packet Padding .
. .
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Session-Reflector Test Packet Format with Direct Loss
Measurement in Authenticated and Encrypted Modes
The Sender Tx Counter (S_TxC) is copied from the received Sender Test
Packet.
The Reflector Rx Counter (R_RxC) is set to the number of IP traffic
packets received by the Reflector. Section 4 provides operational
guide on how to determine the scope of IP traffic packets that need
to be counted. Note that the Sender test packets are not counted.
The Reflector Tx Counter (R_TxC) is set to the number of IP traffic
packets transmitted towards the Sender. Section 4 provides
operational guide on how to determine the scope of IP traffic packets
that need to be counted. Note that the Reflector test packets are
not counted.
In authenticated and encrypted modes, the S_TxC, R_RxC and R_TxC are
respectively followed by a new 12 octets MBZ (MUST be zero) field to
make it 16-octet aligned, which is required for authentication and
encryption.
The intention of embedding S_TxC, R_RxC and R_TxC in the Session-
Reflector test packets is for the Session-Sender to calculate direct
loss of IP traffic, and the loss calculation algorithm is described
in Section 3.3.
When the Symmetrical Size mode defined in [RFC6038] is also selected,
basing on what's specified in Section 5.2.2 of [RFC6038], the
Session-Reflector packet format would follow Figure 3.
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When the Reflect Octets mode defined in [RFC6038] is also selected,
S_TxC, R_RxC and R_TxC SHOULD be embedded in the Session-Reflector
Packet formatted in Section 5.2.1 of [RFC6038], with the same
position as depicted in Figure 3.
When both the Symmetrical Size mode and the Reflect Octets mode are
also selected, S_TxC, R_RxC and R_TxC SHOULD be embedded in the
Session- Reflector Packet formatted in Section 5.2.1 of [RFC6038],
with the same position as depicted in Figure 3.
3.3. Traffic Loss Calculation
Upon receiving a Reflector Test Packet, the Session-Sender uses the
following values to make loss calculation:
o Received S_TxC, R_RxC and R_TxC values embedded in Reflector Test
Packet and local counter S_RxC value at the time this Reflector Test
Packet was received. These values are represented as S_TxC[n],
R_RxC[n], R_TxC[n], and S_RxC[n], where n is the reception time of
the current Reflector Test Packet.
o Previous Received S_TxC, R_RxC and R_TxC values embedded in
Reflector Test Packet and local counter S_RxC value at the time the
previous Reflector Test Packet was received. These values are
represented as S_TxC[n-1], R_RxC[n-1], R_TxC[n-1], and S_RxC[n-1],
where n-1 is the reception time of the previous Reflector Test
Packet.
The formulas for calculating the far-end loss, near-end loss, far-end
loss rate and near-end loss rate are as following:
o Far-end loss: F_Loss[n-1,n] = (S_TxC[n]-S_TxC[n-1])-(R_RxC[n]-
R_RxC[n-1])
o Near-end loss: N_Loss[n-1,n] = (R_TxC[n]-R_TxC[n-1])-(S_RxC[n]-
S_RxC[n-1])
o Far-end loss rate: F_LossRate[n-1,n] = F_Loss[n-1,n]/(S_TxC[n]-
S_TxC[n-1])
o Near-end loss rate: N_LossRate[n-1,n] = N_Loss[n-1,n]/(R_TxC[n]-
R_TxC[n-1])
Here far-end means the direction from the Session-Sender to the
Session-Reflector and near-end means the direction from the Session-
Reflector to the Session-Sender.
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4. Operational Guide
In order to make meaningful loss measurement, in general, the scope
of IP traffic packets that need to be counted, i.e. the IP traffic
packets counting rules, should be provisioned before starting Test
Sessions, and the provisioned arguments usually include ingress port,
source IP address, destination IP address, IP DSCP and UDP port
number. For the scenarios where the exact source/destination IP
address and IP DSCP of IP traffic can be known, such as mobile
backhaul, the Test Packets should use the same source/destination IP
address and IP DSCP as IP traffic, and it shall result in more
accurate measurements.
5. Security Considerations
Use of direct loss measurement in a test session does not appear to
introduce any additional security threat to hosts that communicate
with TWAMP as defined in [RFC5357]. The security considerations that
apply to any active measurement of live networks are relevant here as
well. See the Security Considerations sections in [RFC4656] and
[RFC5357].
6. IANA Considerations
In the TWAMP-Modes registry defined in [RFC5618], a new Direct Loss
Measurement Capability is requested from IANA as follows:
+--------+--------------------------+------------------+------------+
| Bit | Description | Semantics | Reference |
| Pos | | Definition | |
+--------+--------------------------+------------------+------------+
| 10 | Direct Loss Measurement | Section 2 | This |
| | Capability | | Document |
+--------+--------------------------+------------------+------------+
Table 1: New Direct Loss Measurement Capability
7. Acknowledgements
The authors would like to thank Greg Mirsky and Guo Jun for their
valuable comments.
8. 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>.
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[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006,
<https://www.rfc-editor.org/info/rfc4656>.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, DOI 10.17487/RFC5357, October 2008,
<https://www.rfc-editor.org/info/rfc5357>.
[RFC5618] Morton, A. and K. Hedayat, "Mixed Security Mode for the
Two-Way Active Measurement Protocol (TWAMP)", RFC 5618,
DOI 10.17487/RFC5618, August 2009,
<https://www.rfc-editor.org/info/rfc5618>.
[RFC6038] Morton, A. and L. Ciavattone, "Two-Way Active Measurement
Protocol (TWAMP) Reflect Octets and Symmetrical Size
Features", RFC 6038, DOI 10.17487/RFC6038, October 2010,
<https://www.rfc-editor.org/info/rfc6038>.
[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>.
Authors' Addresses
Xiao Min
ZTE
Nanjing
CN
Phone: +86 25 88016576
Email: xiao.min2@zte.com.cn
Dou Zhanwei
ZTE
Nanjing
CN
Phone: +86 25 52874656
Email: dou.zhanwei@zte.com.cn
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