Network Working Group H. Yang
Internet-Draft K. Yao
Intended status: Informational T. Sun
Expires: August 26, 2021 C. Zhou
China Mobile
W. Cheng
J. Wang
Centec networks
February 22, 2021
Precise Network Measurement Protocol
draft-yang-ippm-pnmp-00
Abstract
PNMP, precise network measurement protocol, is used for out-of-band
network measurement. As 5G is continuously evolving, there become
many more time sensitive services which require high precision of
measurements. In addition, in order to better simulate the
transmission of packets of monitored services, the length and
priorities of the measurement packets SHOULD be customized,
especially for some network that is inclined to get congested. PNMP
can not only support PTP, precise time protocol, but also allow some
customization on packet payload. It only introduces a little
overhead by adding an extendable header over IP header.
Status of This Memo
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This Internet-Draft will expire on August 26, 2021.
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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. PNMP Operations . . . . . . . . . . . . . . . . . . . . . . . 3
3.1. IP Header Update . . . . . . . . . . . . . . . . . . . . 4
3.2. PNMP Header Format . . . . . . . . . . . . . . . . . . . 5
3.3. Customization of Length and Priority . . . . . . . . . . 6
3.3.1. Length . . . . . . . . . . . . . . . . . . . . . . . 6
3.3.2. Priority . . . . . . . . . . . . . . . . . . . . . . 7
4. Measurement Procedures . . . . . . . . . . . . . . . . . . . 8
5. Security Considerations . . . . . . . . . . . . . . . . . . . 9
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
7. Normative References . . . . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
The precision of some conventional ways used to measure the one-way
or round-trip delay and jitter, including ICMP (ping command) and
Iperf, a measurement tool, is highly dependent on
NTP[RFC5905]precision which is between millisecond and second. As 5G
has arisen and it is still continuously evolving, many industrial
scenarios, such as internet of vehicles, and other time sensitive
services have new requirements for time precision which is in
microsecond and even in nanosecond. With the growing support of
Precision Time Protocol (PTP) [IEEE.1588.2008], in many industrial
scenarios, such as industrial control network and video transmission
network, devices can be synchronized in very high precision that is
in sub-microsecond.
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Although TWAMP has already supported PTP timestamp, as is stated
in[RFC8186] , the current protocol doesn't allow customizing the
length and priorities of packets. Since packets of actual services
have different length and priorities, which MAY lead to different
time delay, the measurement packets need to be designed to meet such
requirements. Moreover, when there are many different paths between
source and destination, ECMP, equal cost multi-path algorithm is used
to balance the load in different paths. In order to make measurement
packets transmitted in the same path as the packet of monitored
services, they MUST contain the same 5-tuple elements when computing
the hash algorithm. The document defines PNMP by introducing an
extendable header over IP header, which could make ECMP algorithm
treats the measurement packets and the monitored packets as the same.
2. Conventions Used in This Document
2.1. Terminology
NTP Network Time Protocol
PTP Precision Time Protocol
TWAMP Two-Way Active Measurement Protocol
DSCP Differentiated Services Code Point
ICMP Internet Control Message Protocol
ECMP Equal Cost Multi Path
PNMP Precise Network Measurement Protocol
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. PNMP Operations
PNMP needs to modify the IP header and adds an extendable layer
between layer 3 and layer 4. The added layer records the information
copied from the monitored packet in order to compute the hash
algorithm, and additionally, it serves as a sign to tell switches or
routers at each hop that the packet is used for network measurement.
The major purpose of the definition of PNMP is to ensure that the
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measurement packet can be treated as much likely the same as the
monitored packet. In this way, the out-of-band measurement can
approximate the in-band network measurement to a great extent.
3.1. IP Header Update
Before introducing the extendable PNMP header, some updates in the IP
header needs to be declared. Such updates have been shown in the
figures below in both IPv4 and IPv6 header format. The protocol
fields in both IPv4 and IPv6 headers are updated to represent that
the extendable PNMP header is added over layer 3.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL | DS | Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol=PNMP | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination IPv4 Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: IPV4 Header Format
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| Traffic Class | Flow Label |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Payload Length |Next Hdr = PNMP| Hop Limit |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Source IPv6 Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
+ +
| |
+ Destination IPv6 Address +
| |
+ +
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: IPV6 Header Format
3.2. PNMP Header Format
PNMP header format is shown in figure below. The extendable header
is a 64-bit header which contains several fields.
*Version. This field represents the version number of the protocol.
Since the protocol is first defined in this document, the version
number is 0 here.
*Next Header. Since PNMP header is inserted between layer 3 and
layer 4, the next header field needs to record the followed layer 4
header, UDP or TCP.
*Source Port. This source port MUST be clarified, because it is not
the source port copied from layer 4 of this packet, but from the
monitored packet. When using ECMP algorithm to compute the hash
value of the chosen 5-tuple elements that contains the source and
destination IP address, source and destination port, and the layer 4
protocol, UDP or TCP, PNMP MUST ensure that the measurement packet
has the same hash value as the monitored packet. According to this
principle, the source port field in PNMP header MUST be the same as
the source port in layer 4 header of the monitored packet.
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*Destination Port. Similarly, this field is the same as the
destination port of the monitored packet.
*Pre-allocated field. This field is used for some specific purposes.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Next Hdr | Source Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Port | Pre-allocated |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: PNMP Header Format
3.3. Customization of Length and Priority
Another feature of PNMP is that the length and priorities of packets
can be set manually in order to get close to the messages of
monitored services, and this is crucial for some time sensitive
services. Customization of message length and priority can be done
in adjustments below.
3.3.1. Length
The complete PTP event or general message is composed by three major
parts, header, body, and suffix, as described in PTPv2
[IEEE.1588.2008] . The specification allows the suffix to be zero
length if the message does not carry any information other than its
timestamp. To simulate the transmission of messages of monitored
services, the suffix can be filled with extra bytes, and in this way,
the total length of this PTP messages can be the same as the actual
ones. Thereby, in the figure below, the suffix is labeled as
'customized'.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| header (34 octets) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| Timestamp (10 octets) |
| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| suffix (customized) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: PTP Message Format
3.3.2. Priority
Priorities of packets are set in the DS field of IP header which is
defined in [RFC2474] . The format of IP header is shown in the figure
below where the DS field occupies the second octet. The first 6 bits
of the DS field is named as DSCP, differentiated services code point,
which are used to represent maximum 64 priorities.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Version| IHL | DS | Total Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identification |Flags| Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Time to Live | Protocol=PNMP | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: IP Header Format
The complete encapsulation of PTP messages by the UDP/TCP header,
PNMP header, IP header, and Mac header is shown in the figure below,
with their length and priorities customized.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| Ethernet header (14 octets) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| IP header (20 octets) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PNMP header |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| UDP/TCP header |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ ~
| PTP Message in Payload (more than 44 octets) |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FCS |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Format of PTP Message over UDP/TCP
4. Measurement Procedures
* First of all, the network to which both source and destination are
connected needs to be synchronized globally.
* Before measuring the time delay and jitter between source and
destination, measurement mode needs to be enabled and every switch or
router MUST support the ability to distinguish packets encapsulated
by PNMP header.
* At each hop, every monitored packet needs to know the next hop it
will go to, so as the measurement packet. Apart from updating the
source and destination address in IP header, the PNMP header should
be updated too. The source and destination port of monitored packets
MUST be recorded first and pasted on the source port and destination
port of PNMP header respectively. In this way, when there are
multiple paths between two consecutive hops, the measurement packets
can be transmitted together with the monitored packets.
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5. Security Considerations
TBD.
6. IANA Considerations
As is regularized in IANA, the source port or destination port 319
and 320 in UDP/TCP header are defined to represent PTP event message
and PTP general message respectively, the source port and destination
port in PNMP header MUST not cover 319 or 320.
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>.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
"Definition of the Differentiated Services Field (DS
Field) in the IPv4 and IPv6 Headers", RFC 2474,
DOI 10.17487/RFC2474, December 1998,
<https://www.rfc-editor.org/info/rfc2474>.
[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>.
Authors' Addresses
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Hongwei Yang
China Mobile
Beijing 100053
China
Email: yanghongwei@chinamobile.com
Kehan Yao
China Mobile
Beijing 100053
China
Email: yaokehan@chinamobile.com
Tao Sun
China Mobile
Beijing 100053
China
Email: suntao@chinamobile.com
Cheng Zhou
China Mobile
Beijing 100053
China
Email: zhouchengyjy@chinamobile.com
Wei Cheng
Centec networks
Suzhou 215000
China
Email: chengw@centecnetworks.com
Junjie Wang
Centec networks
Suzhou 215000
China
Email: wangjj@centecnetworks.com
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