draft-ietf-mpls-loss-delay-01.txt   draft-ietf-mpls-loss-delay-02.txt 
MPLS D. Frost MPLS D. Frost
Internet-Draft S. Bryant Internet-Draft S. Bryant
Intended status: Standards Track Cisco Systems Intended status: Standards Track Cisco Systems
Expires: August 8, 2011 February 4, 2011 Expires: October 22, 2011 April 20, 2011
Packet Loss and Delay Measurement for MPLS Networks Packet Loss and Delay Measurement for MPLS Networks
draft-ietf-mpls-loss-delay-01 draft-ietf-mpls-loss-delay-02
Abstract Abstract
Many service provider service level agreements (SLAs) depend on the Many service provider service level agreements (SLAs) depend on the
ability to measure and monitor performance metrics for packet loss ability to measure and monitor performance metrics for packet loss
and one-way and two-way delay, as well as related metrics such as and one-way and two-way delay, as well as related metrics such as
delay variation and channel throughput. This measurement capability delay variation and channel throughput. This measurement capability
also provides operators with greater visibility into the performance also provides operators with greater visibility into the performance
characteristics of their networks, thereby facilitating planning, characteristics of their networks, thereby facilitating planning,
troubleshooting, and evaluation. This document specifies protocol troubleshooting, and evaluation. This document specifies protocol
skipping to change at page 1, line 44 skipping to change at page 1, line 44
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet- working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/. Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 8, 2011. This Internet-Draft will expire on October 22, 2011.
Copyright Notice Copyright Notice
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 1.1. Applicability and Scope . . . . . . . . . . . . . . . . . 5
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6 2. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . . 6
2.1. Packet Loss Measurement . . . . . . . . . . . . . . . . . 7 2.1. Basic Bidirectional Measurement . . . . . . . . . . . . . 6
2.2. Throughput Measurement . . . . . . . . . . . . . . . . . . 9 2.2. Packet Loss Measurement . . . . . . . . . . . . . . . . . 7
2.3. Delay Measurement . . . . . . . . . . . . . . . . . . . . 9 2.3. Throughput Measurement . . . . . . . . . . . . . . . . . . 9
2.4. Delay Variation Measurement . . . . . . . . . . . . . . . 11 2.4. Delay Measurement . . . . . . . . . . . . . . . . . . . . 10
2.5. Unidirectional Measurement . . . . . . . . . . . . . . . . 11 2.5. Delay Variation Measurement . . . . . . . . . . . . . . . 11
2.6. Loopback Measurement . . . . . . . . . . . . . . . . . . . 12 2.6. Unidirectional Measurement . . . . . . . . . . . . . . . . 12
2.7. Measurement Considerations . . . . . . . . . . . . . . . . 12 2.7. Dyadic Measurement . . . . . . . . . . . . . . . . . . . . 12
2.7.1. Types of Channels . . . . . . . . . . . . . . . . . . 12 2.8. Loopback Measurement . . . . . . . . . . . . . . . . . . . 13
2.7.2. Quality of Service . . . . . . . . . . . . . . . . . . 12 2.9. Measurement Considerations . . . . . . . . . . . . . . . . 13
2.7.3. Equal Cost Multipath . . . . . . . . . . . . . . . . . 13 2.9.1. Types of Channels . . . . . . . . . . . . . . . . . . 13
2.7.4. Intermediate Nodes . . . . . . . . . . . . . . . . . . 13 2.9.2. Quality of Service . . . . . . . . . . . . . . . . . . 13
2.7.5. Different Transmit and Receive Interfaces . . . . . . 14 2.9.3. Measurement Point Location . . . . . . . . . . . . . . 14
2.7.6. Loss Measurement Modes . . . . . . . . . . . . . . . . 14 2.9.4. Equal Cost Multipath . . . . . . . . . . . . . . . . . 14
2.7.7. Loss Measurement Scope . . . . . . . . . . . . . . . . 16 2.9.5. Intermediate Nodes . . . . . . . . . . . . . . . . . . 14
2.7.8. Delay Measurement Accuracy . . . . . . . . . . . . . . 16 2.9.6. Different Transmit and Receive Interfaces . . . . . . 15
2.7.9. Delay Measurement Timestamp Format . . . . . . . . . . 16 2.9.7. External Post-Processing . . . . . . . . . . . . . . . 15
3. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 17 2.9.8. Loss Measurement Modes . . . . . . . . . . . . . . . . 16
3.1. Loss Measurement Message Format . . . . . . . . . . . . . 17 2.9.9. Loss Measurement Scope . . . . . . . . . . . . . . . . 17
3.2. Delay Measurement Message Format . . . . . . . . . . . . . 22 2.9.10. Delay Measurement Accuracy . . . . . . . . . . . . . . 17
3.3. Combined Loss/Delay Measurement Message Format . . . . . . 24 2.9.11. Delay Measurement Timestamp Format . . . . . . . . . . 17
3.4. Timestamp Field Formats . . . . . . . . . . . . . . . . . 25 3. Message Formats . . . . . . . . . . . . . . . . . . . . . . . 18
3.5. TLV Objects . . . . . . . . . . . . . . . . . . . . . . . 26 3.1. Loss Measurement Message Format . . . . . . . . . . . . . 19
3.5.1. Padding . . . . . . . . . . . . . . . . . . . . . . . 27 3.2. Delay Measurement Message Format . . . . . . . . . . . . . 24
3.5.2. Addressing . . . . . . . . . . . . . . . . . . . . . . 27 3.3. Combined Loss/Delay Measurement Message Format . . . . . . 26
3.5.3. Session Query Interval . . . . . . . . . . . . . . . . 28 3.4. Timestamp Field Formats . . . . . . . . . . . . . . . . . 27
4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 28 3.5. TLV Objects . . . . . . . . . . . . . . . . . . . . . . . 28
4.1. Loss Measurement Procedures . . . . . . . . . . . . . . . 28 3.5.1. Padding . . . . . . . . . . . . . . . . . . . . . . . 29
4.1.1. Initiating a Loss Measurement Operation . . . . . . . 28 3.5.2. Addressing . . . . . . . . . . . . . . . . . . . . . . 30
4.1.2. Transmitting a Loss Measurement Query . . . . . . . . 29 3.5.3. Loopback Request . . . . . . . . . . . . . . . . . . . 30
4.1.3. Receiving a Loss Measurement Query . . . . . . . . . . 30 3.5.4. Session Query Interval . . . . . . . . . . . . . . . . 31
4.1.4. Transmitting a Loss Measurement Response . . . . . . . 30 4. Operation . . . . . . . . . . . . . . . . . . . . . . . . . . 32
4.1.5. Receiving a Loss Measurement Response . . . . . . . . 31 4.1. Operational Overview . . . . . . . . . . . . . . . . . . . 32
4.1.6. Loss Calculation . . . . . . . . . . . . . . . . . . . 31 4.2. Loss Measurement Procedures . . . . . . . . . . . . . . . 33
4.1.7. Quality of Service . . . . . . . . . . . . . . . . . . 31 4.2.1. Initiating a Loss Measurement Operation . . . . . . . 33
4.1.8. G-ACh Packets . . . . . . . . . . . . . . . . . . . . 31 4.2.2. Transmitting a Loss Measurement Query . . . . . . . . 33
4.1.9. Test Messages . . . . . . . . . . . . . . . . . . . . 32 4.2.3. Receiving a Loss Measurement Query . . . . . . . . . . 34
4.1.10. Message Loss and Packet Misorder Conditions . . . . . 32 4.2.4. Transmitting a Loss Measurement Response . . . . . . . 34
4.2. Delay Measurement Procedures . . . . . . . . . . . . . . . 33 4.2.5. Receiving a Loss Measurement Response . . . . . . . . 35
4.2.1. Transmitting a Delay Measurement Query . . . . . . . . 33 4.2.6. Loss Calculation . . . . . . . . . . . . . . . . . . . 35
4.2.2. Receiving a Delay Measurement Query . . . . . . . . . 34 4.2.7. Quality of Service . . . . . . . . . . . . . . . . . . 36
4.2.3. Transmitting a Delay Measurement Response . . . . . . 34 4.2.8. G-ACh Packets . . . . . . . . . . . . . . . . . . . . 36
4.2.4. Receiving a Delay Measurement Response . . . . . . . . 35 4.2.9. Test Messages . . . . . . . . . . . . . . . . . . . . 36
4.2.5. Timestamp Format Negotiation . . . . . . . . . . . . . 35 4.2.10. Message Loss and Packet Misorder Conditions . . . . . 37
4.2.6. Quality of Service . . . . . . . . . . . . . . . . . . 36 4.3. Delay Measurement Procedures . . . . . . . . . . . . . . . 38
4.3. Combined Loss/Delay Measurement Procedures . . . . . . . . 36 4.3.1. Transmitting a Delay Measurement Query . . . . . . . . 38
5. Congestion Considerations . . . . . . . . . . . . . . . . . . 36 4.3.2. Receiving a Delay Measurement Query . . . . . . . . . 38
6. Security Considerations . . . . . . . . . . . . . . . . . . . 37 4.3.3. Transmitting a Delay Measurement Response . . . . . . 39
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 38 4.3.4. Receiving a Delay Measurement Response . . . . . . . . 40
7.1. Allocation of PW Associated Channel Types . . . . . . . . 38 4.3.5. Timestamp Format Negotiation . . . . . . . . . . . . . 40
7.2. Creation of Measurement Timestamp Type Registry . . . . . 39 4.3.6. Quality of Service . . . . . . . . . . . . . . . . . . 41
7.3. Creation of MPLS Loss/Delay Measurement Control Code 4.4. Combined Loss/Delay Measurement Procedures . . . . . . . . 41
Registry . . . . . . . . . . . . . . . . . . . . . . . . . 39 5. Implementation Disclosure Requirements . . . . . . . . . . . . 41
7.4. Creation of MPLS Loss/Delay Measurement TLV Object 6. Congestion Considerations . . . . . . . . . . . . . . . . . . 42
Registry . . . . . . . . . . . . . . . . . . . . . . . . . 40 7. Security Considerations . . . . . . . . . . . . . . . . . . . 43
8. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 41 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 44
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 41 8.1. Allocation of PW Associated Channel Types . . . . . . . . 44
9.1. Normative References . . . . . . . . . . . . . . . . . . . 41 8.2. Creation of Measurement Timestamp Type Registry . . . . . 44
9.2. Informative References . . . . . . . . . . . . . . . . . . 42 8.3. Creation of MPLS Loss/Delay Measurement Control Code
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 42 Registry . . . . . . . . . . . . . . . . . . . . . . . . . 45
8.4. Creation of MPLS Loss/Delay Measurement TLV Object
Registry . . . . . . . . . . . . . . . . . . . . . . . . . 46
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 47
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 47
10.1. Normative References . . . . . . . . . . . . . . . . . . . 47
10.2. Informative References . . . . . . . . . . . . . . . . . . 48
Appendix A. Default Timestamp Format Rationale . . . . . . . . . 49
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 49
1. Introduction 1. Introduction
Many service provider service level agreements (SLAs) depend on the Many service provider service level agreements (SLAs) depend on the
ability to measure and monitor performance metrics for packet loss ability to measure and monitor performance metrics for packet loss
and one-way and two-way delay, as well as related metrics such as and one-way and two-way delay, as well as related metrics such as
delay variation and channel throughput. This measurement capability delay variation and channel throughput. This measurement capability
also provides operators with greater visibility into the performance also provides operators with greater visibility into the performance
characteristics of their networks, thereby facilitating planning, characteristics of their networks, thereby facilitating planning,
troubleshooting, and evaluation. This document specifies protocol troubleshooting, and evaluation. This document specifies protocol
skipping to change at page 5, line 13 skipping to change at page 5, line 13
measurement. measurement.
o The DM protocol is stateless. o The DM protocol is stateless.
o The LM protocol is "almost" stateless: loss is computed as a delta o The LM protocol is "almost" stateless: loss is computed as a delta
between successive messages, and thus the data associated with the between successive messages, and thus the data associated with the
last message received must be retained. last message received must be retained.
o The LM protocol can perform two distinct kinds of loss o The LM protocol can perform two distinct kinds of loss
measurement: it can measure the loss of specially generated test measurement: it can measure the loss of specially generated test
packets in order to infer the approximate data-plane loss level messages in order to infer the approximate data-plane loss level
(inferred measurement); or it can directly measure data-plane (inferred measurement); or it can directly measure data-plane
packet loss (direct measurement). Direct measurement provides packet loss (direct measurement). Direct measurement provides
perfect loss accounting, but may require specialized hardware perfect loss accounting, but may require specialized hardware
support and is only applicable to some LSP types. Inferred support and is only applicable to some LSP types. Inferred
measurement provides only approximate loss accounting but is measurement provides only approximate loss accounting but is
generally applicable. generally applicable.
o The LM protocol supports both 32-bit and 64-bit packet counters. The direct LM method is also known as "frame-based" in the context
of Ethernet transport networks [Y.1731]. Inferred LM is a
generalization of the "synthetic" measurement approach currently
in development for Ethernet networks, in the sense that it allows
test messages to be decoupled from measurement messages.
o The LM protocol supports measurement in terms of both packet o The LM protocol supports measurement in terms of both packet
counts and octet counts. counts and octet counts.
o The LM protocol supports both 32-bit and 64-bit counters.
o The LM protocol can be used to measure channel throughput as well o The LM protocol can be used to measure channel throughput as well
as packet loss. as packet loss.
o The DM protocol supports multiple timestamp formats, and provides o The DM protocol supports multiple timestamp formats, and provides
a simple means for the two endpoints of a bidirectional connection a simple means for the two endpoints of a bidirectional connection
to agree on a preferred format. This procedure reduces to a to agree on a preferred format. This procedure reduces to a
triviality for implementations supporting only a single timestamp triviality for implementations supporting only a single timestamp
format. format.
o The DM protocol supports varying the measurement message size in o The DM protocol supports varying the measurement message size in
order to measure delays associated with different packet sizes. order to measure delays associated with different packet sizes.
1.1. Terminology 1.1. Applicability and Scope
This document specifies measurement procedures and protocol messages
that are intended to be applicable in a wide variety of
circumstances, and amenable to implementation by a wide range of
hardware- and software-based measurement systems. As such, it does
not attempt to mandate measurement quality levels or analyze specific
end-user applications.
Although the procedures in this document are presented in the context
of MPLS, they have no essential dependence on MPLS and generalize
easily to other types of packet networks. Such generalizations are,
however, outside the scope of this document.
1.2. Terminology
Term Definition Term Definition
----- ------------------------------------------- ----- -------------------------------------------
ACH Associated Channel Header ACH Associated Channel Header
DM Delay Measurement DM Delay Measurement
ECMP Equal Cost Multipath
G-ACh Generic Associated Channel G-ACh Generic Associated Channel
LM Loss Measurement LM Loss Measurement
LSE Label Stack Entry LSE Label Stack Entry
LSP Label Switched Path LSP Label Switched Path
LSR Label Switching Router
NTP Network Time Protocol NTP Network Time Protocol
OAM Operations, Administration, and Maintenance OAM Operations, Administration, and Maintenance
PTP Precision Time Protocol PTP Precision Time Protocol
PW Pseudowire
TC Traffic Class TC Traffic Class
2. Overview 2. Overview
This section begins with a summary of the basic methods used for the This section begins with a summary of the basic methods used for the
bidirectional measurement of packet loss and delay. These bidirectional measurement of packet loss and delay. These
measurement methods are then described in detail. Finally a list of measurement methods are then described in detail. Finally a list of
practical considerations are discussed that may come into play to practical considerations are discussed that may come into play to
inform or modify these simple procedures. inform or modify these simple procedures. This section is limited to
theoretical discussion; for protocol specifics the reader is referred
to Section 3 and Section 4.
2.1. Basic Bidirectional Measurement
The following figure shows the reference scenario. The following figure shows the reference scenario.
T1 T2 T1 T2
+-------+/ Query \+-------+ +-------+/ Query \+-------+
| | - - - - - - - - ->| | | | - - - - - - - - ->| |
| A |===================| B | | A |===================| B |
| |<- - - - - - - - - | | | |<- - - - - - - - - | |
+-------+\ Response /+-------+ +-------+\ Response /+-------+
T4 T3 T4 T3
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recording the instant at which it is transmitted, i.e. T1. When the recording the instant at which it is transmitted, i.e. T1. When the
message reaches B, a timestamp is added recording the instant at message reaches B, a timestamp is added recording the instant at
which it is received (T2). The message can now be reflected from B which it is received (T2). The message can now be reflected from B
to A, with B adding its transmit timestamp (T3) and A adding its to A, with B adding its transmit timestamp (T3) and A adding its
receive timestamp (T4). These four timestamps enable A to compute receive timestamp (T4). These four timestamps enable A to compute
the one-way delay in each direction, as well as the two-way delay for the one-way delay in each direction, as well as the two-way delay for
the channel. The one-way delay computations require that the clocks the channel. The one-way delay computations require that the clocks
of A and B be synchronized; mechanisms for clock synchronization are of A and B be synchronized; mechanisms for clock synchronization are
outside the scope of this document. outside the scope of this document.
2.1. Packet Loss Measurement 2.2. Packet Loss Measurement
Suppose a bidirectional channel exists between the nodes A and B. The Suppose a bidirectional channel exists between the nodes A and B. The
objective is to measure at A the following two quantities associated objective is to measure at A the following two quantities associated
with the channel: with the channel:
A_TxLoss (transmit loss): the number of packets transmitted by A A_TxLoss (transmit loss): the number of packets transmitted by A
over the channel but not received at B; over the channel but not received at B;
A_RxLoss (receive loss): the number of packets transmitted by B A_RxLoss (receive loss): the number of packets transmitted by B
over the channel but not received at A. over the channel but not received at A.
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A_TxP[n]: the total count of packets transmitted by A over the A_TxP[n]: the total count of packets transmitted by A over the
channel prior to the time this message is transmitted. channel prior to the time this message is transmitted.
When such a message is received at B, the following value is recorded When such a message is received at B, the following value is recorded
in the message: in the message:
B_RxP[n]: the total count of packets received by B over the B_RxP[n]: the total count of packets received by B over the
channel at the time this message is received (excluding the channel at the time this message is received (excluding the
message itself). message itself).
At this point, B inserts an appropriate response code into the At this point, B transmits the message back to A, recording within it
message and transmits it back to A, recording within it the following the following value:
value:
B_TxP[n]: the total count of packets transmitted by B over the B_TxP[n]: the total count of packets transmitted by B over the
channel prior to the time this response is transmitted. channel prior to the time this response is transmitted.
When the message response is received back at A, the following value When the message response is received back at A, the following value
is recorded in the message: is recorded in the message:
A_RxP[n]: the total count of packets received by A over the A_RxP[n]: the total count of packets received by A over the
channel at the time this response is received (excluding the channel at the time this response is received (excluding the
message itself). message itself).
The transmit loss A_TxLoss[n-1,n] and receive loss A_RxLoss[n-1,n] The transmit loss A_TxLoss[n-1,n] and receive loss A_RxLoss[n-1,n]
within the measurement interval marked by the messages LM[n-1] and within the measurement interval marked by the messages LM[n-1] and
LM[n] are computed by A as follows: LM[n] are computed by A as follows:
A_TxLoss[n-1,n] = (A_TxP[n] - A_TxP[n-1]) - (B_RxP[n] - B_RxP[n-1]) A_TxLoss[n-1,n] = (A_TxP[n] - A_TxP[n-1]) - (B_RxP[n] - B_RxP[n-1])
A_RxLoss[n-1,n] = (B_TxP[n] - B_TxP[n-1]) - (A_RxP[n] - A_RxP[n-1]) A_RxLoss[n-1,n] = (B_TxP[n] - B_TxP[n-1]) - (A_RxP[n] - A_RxP[n-1])
where the arithmetic is modulo the counter size. where the arithmetic is modulo the counter size.
(Strictly speaking, it is not necessary that the fourth count,
A_RxP[n], actually be written in the message, but this is convenient
for some implementations and useful if the message is to be forwarded
on to an external measurement system.)
The derived values The derived values
A_TxLoss = A_TxLoss[1,2] + A_TxLoss[2,3] + ... A_TxLoss = A_TxLoss[1,2] + A_TxLoss[2,3] + ...
A_RxLoss = A_RxLoss[1,2] + A_RxLoss[2,3] + ... A_RxLoss = A_RxLoss[1,2] + A_RxLoss[2,3] + ...
are updated each time a response to an LM message is received and are updated each time a response to an LM message is received and
processed, and represent the total transmit and receive loss over the processed, and represent the total transmit and receive loss over the
channel since the LM operation was initiated. channel since the LM operation was initiated.
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response arrives. This data MAY be discarded, and MUST NOT be used response arrives. This data MAY be discarded, and MUST NOT be used
as a basis for measurement, if MaxLMInterval elapses before the next as a basis for measurement, if MaxLMInterval elapses before the next
response arrives, because in this case an unambiguous measurement response arrives, because in this case an unambiguous measurement
cannot be made. cannot be made.
The foregoing discussion has assumed the counted objects are packets, The foregoing discussion has assumed the counted objects are packets,
but this need not be the case. In particular, octets may be counted but this need not be the case. In particular, octets may be counted
instead. This will, of course, reduce the MaxLMInterval instead. This will, of course, reduce the MaxLMInterval
proportionately. proportionately.
2.2. Throughput Measurement In addition to absolute aggregate loss counts, the individual loss
counts yield additional metrics such as the average loss rate over
any multiple of the measurement interval. An accurate loss rate can
be determined over time even in the presence of anomalies affecting
individual measurements, such as those due to packet misordering
(Section 4.2.10).
2.3. Throughput Measurement
If LM query messages contain a timestamp recording their time of If LM query messages contain a timestamp recording their time of
transmission, this data can be combined with the packet or octet transmission, this data can be combined with the packet or octet
counts to yield a measurement of the throughput sustained over the counts to yield measurements of the throughput offered and delivered
channel during the interval. This metric can be called the delivered over the channel during the interval. Just as for loss measurement,
throughput. As for loss measurement, the interval counts can be the interval counts can be accumulated to arrive at the throughput of
accumulated to arrive at the delivered throughput of the channel the channel since the start of the measurement operation, or used to
since the start of the measurement operation. This procedure also derive related metrics such as the average throughput rate. This
enables out-of-service throughput testing when combined with a simple procedure also enables out-of-service throughput testing when
packet generator. combined with a simple packet generator.
2.3. Delay Measurement 2.4. Delay Measurement
Suppose a bidirectional channel exists between the nodes A and B. The Suppose a bidirectional channel exists between the nodes A and B. The
objective is to measure at A one or more of the following quantities objective is to measure at A one or more of the following quantities
associated with the channel: associated with the channel:
o The one-way delay associated with the forward (A to B) direction o The one-way delay associated with the forward (A to B) direction
of the channel; of the channel;
o The one-way delay associated with the reverse (B to A) direction o The one-way delay associated with the reverse (B to A) direction
of the channel; of the channel;
o The two-way delay (A to B to A) associated with the channel. o The two-way delay (A to B to A) associated with the channel.
The one-way delay metric for packet networks is described in The one-way delay metric for packet networks is described in
[RFC2679]. Measurement of the one-way delay quantities requires that [RFC2679]. In the case of two-way delay, there are actually two
the clocks of A and B be synchronized, whereas the two-way delay can possible metrics of interest. The "two-way channel delay" is the sum
be measured directly even when this is not the case (provided A and B of the one-way delays in each direction and reflects the delay of the
have stable clocks). channel itself, irrespective of processing delays within the remote
endpoint B. The "round-trip delay" is described in [RFC2681] and
includes in addition any delay associated with remote endpoint
processing.
In the case of two-way delay, there are actually two possible metrics Measurement of the one-way delay quantities requires that the clocks
of interest. The "two-way channel delay" is the sum of the one-way of A and B be synchronized, whereas the two-way delay metrics can be
delays in each direction and reflects the delay of the channel measured directly even when this is not the case (provided A and B
itself, irrespective of processing delays within the remote endpoint have stable clocks).
B. The "round-trip delay" is described in [RFC2681] and includes in
addition any delay associated with remote endpoint processing.
A measurement is accomplished by sending a Delay Measurement (DM) A measurement is accomplished by sending a Delay Measurement (DM)
query message over the channel to B which contains the following query message over the channel to B which contains the following
timestamp: timestamp:
T1: the time the DM query message is transmitted from A. T1: the time the DM query message is transmitted from A.
When the message arrives at B, the following timestamp is recorded in When the message arrives at B, the following timestamp is recorded in
the message: the message:
T2: the time the DM query message is received at B. T2: the time the DM query message is received at B.
At this point B inserts an appropriate response code into the message At this point B transmits the message back to A, recording within it
and transmits it back to A, recording within it the following the following timestamp:
timestamp:
T3: the time the DM response message is transmitted from B. T3: the time the DM response message is transmitted from B.
When the message arrives back at A, the following timestamp is When the message arrives back at A, the following timestamp is
recorded in the message: recorded in the message:
T4: the time the DM response message is received back at A. T4: the time the DM response message is received back at A.
(Strictly speaking, it is not necessary that the fourth timestamp,
T4, actually be written in the message, but this is convenient for
some implementations and useful if the message is to be forwarded on
to an external measurement system.)
At this point, A can compute the two-way channel delay associated At this point, A can compute the two-way channel delay associated
with the channel as with the channel as
two-way channel delay = (T4 - T1) - (T3 - T2) two-way channel delay = (T4 - T1) - (T3 - T2)
and the round-trip delay as and the round-trip delay as
round-trip delay = T4 - T1. round-trip delay = T4 - T1.
If the clocks of A and B are known at A to be synchronized, then both If the clocks of A and B are known at A to be synchronized, then both
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two-way channel delay = (T4 - T1) - (T3 - T2) two-way channel delay = (T4 - T1) - (T3 - T2)
and the round-trip delay as and the round-trip delay as
round-trip delay = T4 - T1. round-trip delay = T4 - T1.
If the clocks of A and B are known at A to be synchronized, then both If the clocks of A and B are known at A to be synchronized, then both
one-way delay values, as well as the two-way channel delay, can be one-way delay values, as well as the two-way channel delay, can be
computed at A as computed at A as
forward one-way delay = T2 - T1 forward one-way delay = T2 - T1
reverse one-way delay = T4 - T3 reverse one-way delay = T4 - T3
two-way channel delay = forward delay + reverse delay. two-way channel delay = forward delay + reverse delay.
2.4. Delay Variation Measurement 2.5. Delay Variation Measurement
Packet Delay Variation (PDV) [RFC3393] is another performance metric Packet Delay Variation (PDV) [RFC3393] is another performance metric
important in some applications. The PDV of a pair of packets within important in some applications. The PDV of a pair of packets within
a stream of packets is defined for a selected pair of packets in the a stream of packets is defined for a selected pair of packets in the
stream going from measurement point 1 to measurement point 2. The stream going from measurement point 1 to measurement point 2. The
PDV is the difference between the one-way delay of the selected PDV is the difference between the one-way delay of the selected
packets. packets.
A PDV measurement can therefore be derived from successive delay A PDV measurement can therefore be derived from successive delay
measurements obtained through the procedures in Section 2.3. An measurements obtained through the procedures in Section 2.4. An
important point regarding PDV measurement, however, is that it can be important point regarding PDV measurement, however, is that it can be
carried out based on one-way delay measurements even when the clocks carried out based on one-way delay measurements even when the clocks
of the two systems involved in those measurements are not of the two systems involved in those measurements are not
synchronized. synchronized.
2.5. Unidirectional Measurement 2.6. Unidirectional Measurement
In the case that the channel from A to (B1, ..., Bk) is In the case that the channel from A to (B1, ..., Bk) is
unidirectional, i.e. is a unidirectional LSP, LM and DM measurements unidirectional, i.e. is a unidirectional LSP, LM and DM measurements
can be carried out at B1, ..., Bk instead of at A. can be carried out at B1, ..., Bk instead of at A.
For LM this is accomplished by initiating an LM operation at A and For LM this is accomplished by initiating an LM operation at A and
carrying out the same procedures as for bidirectional channels, carrying out the same procedures as for bidirectional channels,
except that no responses from B1, ..., Bk to A are generated. except that no responses from B1, ..., Bk to A are generated.
Instead, each terminal node B uses the A_TxP and B_RxP values in the Instead, each terminal node B uses the A_TxP and B_RxP values in the
LM messages it receives to compute the receive loss associated with LM messages it receives to compute the receive loss associated with
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B_RxLoss[n-1,n] = (A_TxP[n] - A_TxP[n-1]) - (B_RxP[n] - B_RxP[n-1]) B_RxLoss[n-1,n] = (A_TxP[n] - A_TxP[n-1]) - (B_RxP[n] - B_RxP[n-1])
For DM, of course, only the forward one-way delay can be measured and For DM, of course, only the forward one-way delay can be measured and
the clock synchronization requirement applies. the clock synchronization requirement applies.
Alternatively, if an out-of-band channel from a terminal node B back Alternatively, if an out-of-band channel from a terminal node B back
to A is available, the LM and DM message responses can be to A is available, the LM and DM message responses can be
communicated to A via this channel so that the measurements can be communicated to A via this channel so that the measurements can be
carried out at A. carried out at A.
2.6. Loopback Measurement 2.7. Dyadic Measurement
The basic procedures for bidirectional measurement assume that the
measurement process is conducted by and for the querier node A. It is
possible instead, with only minor variation of these procedures, to
conduct a dyadic or "dual-ended" measurement process in which both
nodes A and B perform loss or delay measurement based on the same
message flow. This is achieved by stipulating that A copy the third
and fourth counter or timestamp values from a response message into
the third and fourth slots of the next query, which are otherwise
unused, thereby providing B with equivalent information to that
learned by A.
The dyadic procedure has the advantage of halving the number of
messages required for both A and B to perform a given kind of
measurement, but comes at the expense of each node's ability to
control its own measurement process independently, and introduces
additional operational complexity into the measurement protocols.
The quantity of measurement traffic is also expected to be low
relative to that of user traffic, particularly when 64-bit counters
are used for LM. Consequently this document does not attempt to
specify a dyadic operational mode. It is however still possible, and
may be useful, for A to perform the extra copy, thereby providing
additional information to B even when its participation in the
measurement process is passive.
2.8. Loopback Measurement
Some bidirectional channels may be placed into a loopback state such Some bidirectional channels may be placed into a loopback state such
that query messages are looped back to the querier without that messages are looped back to the sender without modification. In
modification. In this situation, LM and DM procedures can be used to this situation, LM and DM procedures can be used to carry out
carry out measurements associated with the circular path. measurements associated with the circular path. This is done by
generating "queries" with the Response flag set to 1.
For LM, the loss computation in this case is: For LM, the loss computation in this case is:
A_Loss[n-1,n] = (A_TxP[n] - A_TxP[n-1]) - (A_RxP[n] - A_RxP[n-1]) A_Loss[n-1,n] = (A_TxP[n] - A_TxP[n-1]) - (A_RxP[n] - A_RxP[n-1])
For DM, the round-trip delay is computed. In this case, however, the For DM, the round-trip delay is computed. In this case, however, the
remote endpoint processing time component reflects only the time remote endpoint processing time component reflects only the time
required to loop the message from channel input to channel output. required to loop the message from channel input to channel output.
Query messages must include some form of source identifier in order 2.9. Measurement Considerations
for looped-back queries to be differentiated from queries initiated
by the far end.
2.7. Measurement Considerations
A number of additional considerations apply in practice to the A number of additional considerations apply in practice to the
measurement methods summarized above. measurement methods summarized above.
2.7.1. Types of Channels 2.9.1. Types of Channels
There are several types of channels in MPLS networks over which loss There are several types of channels in MPLS networks over which loss
and delay measurement may be conducted. The channel type may and delay measurement may be conducted. The channel type may
restrict the kinds of measurement that can be performed. In all restrict the kinds of measurement that can be performed. In all
cases, LM and DM messages flow over the MPLS Generic Associated cases, LM and DM messages flow over the MPLS Generic Associated
Channel (G-ACh), which is described in detail in [RFC5586]. Channel (G-ACh), which is described in detail in [RFC5586].
Broadly, a channel in an MPLS network may be either a link, a Label Broadly, a channel in an MPLS network may be either a link, a Label
Switched Path (LSP) [RFC3031], or a pseudowire [RFC3985]. Links are Switched Path (LSP) [RFC3031], or a pseudowire [RFC3985]. Links are
bidirectional and are also referred to as MPLS sections; see bidirectional and are also referred to as MPLS sections; see
[RFC5586] and [RFC5960]. Pseudowires are bidirectional. Label [RFC5586] and [RFC5960]. Pseudowires are bidirectional. Label
Switched Paths may be either unidirectional or bidirectional. Switched Paths may be either unidirectional or bidirectional.
The LM and DM protocols discussed in this document are initiated from The LM and DM protocols discussed in this document are initiated from
a single node, the querier. A query message may be received either a single node, the querier. A query message may be received either
by a single node or by multiple nodes, depending on the nature of the by a single node or by multiple nodes, depending on the nature of the
channel. In the latter case these protocols provide point-to- channel. In the latter case these protocols provide point-to-
multipoint measurement capabilities. multipoint measurement capabilities.
2.7.2. Quality of Service 2.9.2. Quality of Service
Quality of Service (QoS) capabilities, in the form of the Quality of Service (QoS) capabilities, in the form of the
Differentiated Services architecture, apply to MPLS as specified in Differentiated Services architecture, apply to MPLS as specified in
[RFC3270] and [RFC5462]. Different classes of traffic are [RFC3270] and [RFC5462]. Different classes of traffic are
distinguished by the three-bit Traffic Class (TC) field of an MPLS distinguished by the three-bit Traffic Class (TC) field of an MPLS
Label Stack Entry (LSE). Delay measurement therefore applies on a Label Stack Entry (LSE). Delay measurement therefore applies on a
per-traffic-class basis, and the TC values of LSEs above the G-ACh per-traffic-class basis, and the TC values of LSEs above the G-ACh
Label (GAL) that precedes a DM message are significant. Packet loss Label (GAL) that precedes a DM message are significant. Packet loss
can be measured with respect either to the channel as a whole or to a can be measured with respect either to the channel as a whole or to a
specific traffic class. specific traffic class.
Another aspect of packet processing which often arises in the context 2.9.3. Measurement Point Location
of QoS concerns the location of the measurement points for loss and
delay within the sending and receiving nodes, which is
implementation-dependent. For example, a sending implementation may
or may not consider a packet to be "lost", for LM purposes, that was
discarded prior to transmission for queuing-related reasons;
conversely, a receiving implementation may or may not consider a
packet to be "lost", for LM purposes, if it was physically received
but discarded during receive-path processing. The location of delay
measurement points similarly impacts what, precisely, is being
measured. The principal consideration here is that the behavior of
an implementation in these respects SHOULD be made clear to the user.
2.7.3. Equal Cost Multipath The location of the measurement points for loss and delay within the
sending and receiving nodes is implementation-dependent but directly
affects the nature of the measurements. For example, a sending
implementation may or may not consider a packet to be "lost", for LM
purposes, that was discarded prior to transmission for queuing-
related reasons; conversely, a receiving implementation may or may
not consider a packet to be "lost", for LM purposes, if it was
physically received but discarded during receive-path processing.
The location of delay measurement points similarly determines what,
precisely, is being measured. The principal consideration here is
that the behavior of an implementation in these respects MUST be made
clear to the user.
2.9.4. Equal Cost Multipath
Equal Cost Multipath (ECMP) is the behavior of distributing packets Equal Cost Multipath (ECMP) is the behavior of distributing packets
across multiple alternate paths toward a destination. The use of across multiple alternate paths toward a destination. The use of
ECMP in MPLS networks is described in BCP 128 [RFC4928]. The typical ECMP in MPLS networks is described in BCP 128 [RFC4928]. The typical
result of ECMP being performed on an LSP which is subject to delay result of ECMP being performed on an LSP which is subject to delay
measurement will be that only the delay of one of the available paths measurement will be that only the delay of one of the available paths
is and can be measured. is and can be measured.
The effects of ECMP on loss measurement will depend on the LM mode. The effects of ECMP on loss measurement will depend on the LM mode.
In the case of direct LM, the measurement will account for any In the case of direct LM, the measurement will account for any
skipping to change at page 13, line 48 skipping to change at page 14, line 46
many paths exist between them. However, the presence of ECMP many paths exist between them. However, the presence of ECMP
increases the likelihood of misordering both of LM messages relative increases the likelihood of misordering both of LM messages relative
to data packets, and of the LM messages themselves. Such to data packets, and of the LM messages themselves. Such
misorderings tend to create unmeasurable intervals and thus degrade misorderings tend to create unmeasurable intervals and thus degrade
the accuracy of loss measurement. The effects of ECMP are similar the accuracy of loss measurement. The effects of ECMP are similar
for inferred LM, with the additional caveat that, unless the test for inferred LM, with the additional caveat that, unless the test
packets are specially constructed so as to probe all available paths, packets are specially constructed so as to probe all available paths,
the loss characteristics of one or more of the alternate paths cannot the loss characteristics of one or more of the alternate paths cannot
be accounted for. be accounted for.
2.7.4. Intermediate Nodes 2.9.5. Intermediate Nodes
In the case of an LSP, it may be desirable to measure the loss or In the case of an LSP, it may be desirable to measure the loss or
delay to or from an intermediate node as well as between LSP delay to or from an intermediate node as well as between LSP
endpoints. This can be done in principle by setting the Time to Live endpoints. This can be done in principle by setting the Time to Live
(TTL) field in the outer LSE appropriately when targeting a (TTL) field in the outer LSE appropriately when targeting a
measurement message to an intermediate node. This procedure may measurement message to an intermediate node. This procedure may
fail, however, if hardware-assisted measurement is in use, because fail, however, if hardware-assisted measurement is in use, because
the processing of the packet by the intermediate node occurs only as the processing of the packet by the intermediate node occurs only as
the result of TTL expiry, and the handling of TTL expiry may occur at the result of TTL expiry, and the handling of TTL expiry may occur at
a later processing stage in the implementation than the hardware- a later processing stage in the implementation than the hardware-
assisted measurement function. Often the motivation for conducting assisted measurement function. Often the motivation for conducting
measurements to intermediate nodes is an attempt to localize a measurements to intermediate nodes is an attempt to localize a
problem that has been detected on the LSP. In this case, if problem that has been detected on the LSP. In this case, if
intermediate nodes are not capable of performing hardware-assisted intermediate nodes are not capable of performing hardware-assisted
measurement, a less accurate - but usually sufficient - software- measurement, a less accurate - but usually sufficient - software-
based measurement can be conducted instead. based measurement can be conducted instead.
2.7.5. Different Transmit and Receive Interfaces 2.9.6. Different Transmit and Receive Interfaces
The overview of the bidirectional measurement process presented in The overview of the bidirectional measurement process presented in
Section 2 is also applicable when the transmit and receive interfaces Section 2 is also applicable when the transmit and receive interfaces
at A or B differ from one another. Some additional considerations, at A or B differ from one another. Some additional considerations,
however, do apply in this case: however, do apply in this case:
o If different clocks are associated with transmit and receive o If different clocks are associated with transmit and receive
processing, these clocks must be synchronized in order to compute processing, these clocks must be synchronized in order to compute
the two-way delay. the two-way delay.
o The DM protocol specified in this document requires that the o The DM protocol specified in this document requires that the
timestamp formats used by the interfaces that receive a DM query timestamp formats used by the interfaces that receive a DM query
and transmit a DM response agree. and transmit a DM response agree.
o The LM protocol specified in this document supports both 32-bit o The LM protocol specified in this document supports both 32-bit
and 64-bit counter sizes, but the use of 32-bit counters at any of and 64-bit counter sizes, but the use of 32-bit counters at any of
the up to four interfaces involved in an LM operation will result the up to four interfaces involved in an LM operation will result
in 32-bit LM calculations for both directions of the channel. in 32-bit LM calculations for both directions of the channel.
[Editor's note: The last two restrictions could be relaxed if 2.9.7. External Post-Processing
desired, at the expense of some additional protocol complexity.]
2.7.6. Loss Measurement Modes In some circumstances it may be desirable to carry out the final
measurement computation at an external post-processing device
dedicated to the purpose. This can be achieved in supporting
implementations by, for example, configuring the querier, in the case
of a bidirectional measurement session, to forward each response it
receives to the post-processor via any convenient protocol. The
unidirectional case can be handled similarly through configuration of
the receiver, or by including an instruction in query messages for
the receiver to respond out-of-band to the appropriate return
address.
Post-processing devices may have the ability to store measurement
data for an extended period and to generate a variety of useful
statistics from them. External post-processing also allows the
measurement process to be completely stateless at the querier and
responder.
2.9.8. Loss Measurement Modes
The summary of loss measurement at the beginning of Section 2 above The summary of loss measurement at the beginning of Section 2 above
made reference to the "count of packets" transmitted and received made reference to the "count of packets" transmitted and received
over a channel. If the counted packets are the packets flowing over over a channel. If the counted packets are the packets flowing over
the channel in the data plane, the loss measurement is said to the channel in the data plane, the loss measurement is said to
operate in "direct mode". If, on the other hand, the counted packets operate in "direct mode". If, on the other hand, the counted packets
are selected control packets from which the approximate loss are selected control packets from which the approximate loss
characteristics of the channel are being inferred, the loss characteristics of the channel are being inferred, the loss
measurement is said to operate in "inferred mode". measurement is said to operate in "inferred mode".
Direct LM has the advantage of being able to provide perfect loss Direct LM has the advantage of being able to provide perfect loss
accounting when it is available. There are, however, several accounting when it is available. There are, however, several
limitations associated with direct LM. constraints associated with direct LM.
For accurate direct LM to occur, packets must not be sent between the For accurate direct LM to occur, packets must not be sent between the
time the transmit count for an outbound LM message is determined and time the transmit count for an outbound LM message is determined and
the time the message is actually transmitted. Similarly, packets the time the message is actually transmitted. Similarly, packets
must not be received and processed between the time an LM message is must not be received and processed between the time an LM message is
received and the time the receive count for the message is received and the time the receive count for the message is
determined. If these "synchronization conditions" do not hold, the determined. If these "synchronization conditions" do not hold, the
LM message counters will not reflect the true state of the data LM message counters will not reflect the true state of the data
plane, with the result that, for example, the receive count of B may plane, with the result that, for example, the receive count of B may
be greater than the transmit count of A, and attempts to compute loss be greater than the transmit count of A, and attempts to compute loss
by taking the difference will yield an invalid result. This by taking the difference will yield an invalid result. This
requirement for synchronization between LM message counters and the requirement for synchronization between LM message counters and the
data plane may require special support from hardware-based forwarding data plane may require special support from hardware-based forwarding
implementations. implementations.
Another limitation of direct LM is that it may be difficult or A limitation of direct LM is that it may be difficult or impossible
impossible to apply in cases where the channel is an LSP and the LSP to apply in cases where the channel is an LSP and the LSP label at
label at the receiver is either nonexistent or fails to identify a the receiver is either nonexistent or fails to identify a unique
unique sending node. The first case happens when Penultimate Hop sending node. The first case happens when Penultimate Hop Popping
Popping (PHP) is used on the LSP, and the second case generally holds (PHP) is used on the LSP, and the second case generally holds for
for LSPs based on the Label Distribution Protocol (LDP) [RFC5036] as LSPs based on the Label Distribution Protocol (LDP) [RFC5036] as
opposed to, for example, those based on Traffic Engineering opposed to, for example, those based on Traffic Engineering
extensions to the Resource Reservation Protocol (RSVP-TE) [RFC3209]. extensions to the Resource Reservation Protocol (RSVP-TE) [RFC3209].
These conditions may make it infeasible for the receiver to identify These conditions may make it infeasible for the receiver to identify
the data-plane packets associated with a particular source and LSP in the data-plane packets associated with a particular source and LSP in
order to count them, or to infer the source and LSP context order to count them, or to infer the source and LSP context
associated with an LM message. associated with an LM message. Direct LM is also vulnerable to
disruption in the event that the ingress or egress interface
associated with an LSP changes during the LSP's lifetime.
Inferred LM works in the same manner as direct LM except that the Inferred LM works in the same manner as direct LM except that the
counted packets are special control packets, called test messages, counted packets are special control packets, called test messages,
generated by the sender. Test messages may be either packets generated by the sender. Test messages may be either packets
explicitly constructed and used for LM or packets with a different explicitly constructed and used for LM or packets with a different
primary purpose, such as those associated with a Bidirectional primary purpose, such as those associated with a Bidirectional
Forwarding Detection (BFD) [RFC5884] session. Forwarding Detection (BFD) [RFC5884] session.
The synchronization conditions discussed above for direct LM also The synchronization conditions discussed above for direct LM also
apply to inferred LM, the only difference being that the required apply to inferred LM, the only difference being that the required
synchronization is now between the LM counters and the test message synchronization is now between the LM counters and the test message
generation process. Protocol and application designers MUST take generation process. Protocol and application designers MUST take
these synchronization requirements into account when developing tools these synchronization requirements into account when developing tools
for inferred LM, and make their behavior in this regard clear to the for inferred LM, and make their behavior in this regard clear to the
user. user.
Inferred LM provides only an approximate view of the loss level Inferred LM provides only an approximate view of the loss level
associated with a channel, but is typically applicable even in cases associated with a channel, but is typically applicable even in cases
where direct LM is not. where direct LM is not.
2.7.7. Loss Measurement Scope 2.9.9. Loss Measurement Scope
In the case of direct LM, where data-plane packets are counted, there In the case of direct LM, where data-plane packets are counted, there
are different possibilities for which kinds of packets are included are different possibilities for which kinds of packets are included
in the count and which are excluded. The set of packets counted for in the count and which are excluded. The set of packets counted for
LM is called the loss measurement scope. As noted above, one factor LM is called the loss measurement scope. As noted above, one factor
affecting the LM scope is whether all data packets are counted or affecting the LM scope is whether all data packets are counted or
only those belonging to a particular traffic class. Another is only those belonging to a particular traffic class. Another is
whether various "auxiliary" flows associated with a data channel are whether various "auxiliary" flows associated with a data channel are
counted, such as packets flowing over the G-ACh. Implementations counted, such as packets flowing over the G-ACh. Implementations
SHOULD make their supported LM scopes clear to the user, and care MUST make their supported LM scopes clear to the user, and care must
must be taken to ensure that the scopes of the channel endpoints be taken to ensure that the scopes of the channel endpoints agree.
agree.
2.7.8. Delay Measurement Accuracy 2.9.10. Delay Measurement Accuracy
The delay measurement procedures described in this document are The delay measurement procedures described in this document are
designed to facilitate hardware-assisted measurement and to function designed to facilitate hardware-assisted measurement and to function
in the same way whether or not such hardware assistance is used. The in the same way whether or not such hardware assistance is used. The
main difference in the two cases is one of measurement accuracy. main difference in the two cases is one of measurement accuracy.
Implementations SHOULD make their delay measurement accuracy levels Implementations MUST make their delay measurement accuracy levels
clear to the user. clear to the user.
2.7.9. Delay Measurement Timestamp Format 2.9.11. Delay Measurement Timestamp Format
There are two significant timestamp formats in common use: the There are two significant timestamp formats in common use: the
timestamp format of the Internet standard Network Time Protocol timestamp format of the Internet standard Network Time Protocol
(NTP), described in [RFC5905], and the timestamp format used in the (NTP), described in [RFC5905], and the timestamp format used in the
IEEE 1588 Precision Time Protocol (PTP) [IEEE1588]. IEEE 1588 Precision Time Protocol (PTP) [IEEE1588].
The NTP format has the advantages of wide use and long deployment in The NTP format has the advantages of wide use and long deployment in
the Internet, and was specifically designed to make the computation the Internet, and was specifically designed to make the computation
of timestamp differences as simple and efficient as possible. On the of timestamp differences as simple and efficient as possible. On the
other hand, there is also now a significant deployment of equipment other hand, there is also now a significant deployment of equipment
designed to support the PTP format. designed to support the PTP format.
The approach taken in this document is therefore to include in DM The approach taken in this document is therefore to include in DM
messages fields which identify the timestamp formats used by the two messages fields which identify the timestamp formats used by the two
devices involved in a DM operation. This implies that a node devices involved in a DM operation. This implies that a node
attempting to carry out a DM operation may be faced with the problem attempting to carry out a DM operation may be faced with the problem
of computing with and possibly reconciling different timestamp of computing with and possibly reconciling different timestamp
formats. Support for multiple timestamp formats is OPTIONAL. An formats. Timestamp format support requirements are specified in
implementation SHOULD, however, make clear which timestamp formats it Section 3.4.
supports and the extent of its support for computation with and
reconciliation of different formats for purposes of delay
measurement.
In recognition of the wide deployment, particularly in hardware-based
timing implementations, of IEEE 1588 PTP, the PTP timestamp format is
the default format used in DM messages. This format MUST be
supported.
3. Message Formats 3. Message Formats
Loss Measurement and Delay Measurement messages flow over the MPLS Loss Measurement and Delay Measurement messages flow over the MPLS
Generic Associated Channel (G-ACh) [RFC5586]. Thus, a packet Generic Associated Channel (G-ACh) [RFC5586]. Thus, a packet
containing an LM or DM message contains an MPLS label stack, with the containing an LM or DM message contains an MPLS label stack, with the
G-ACh Label (GAL) at the bottom of the stack. The GAL is followed by G-ACh Label (GAL) at the bottom of the stack. The GAL is followed by
an Associated Channel Header (ACH) which identifies the message type, an Associated Channel Header (ACH) which identifies the message type,
and the message body follows the ACH. and the message body follows the ACH.
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the formats for the DLM+DM and ILM+DM messages. the formats for the DLM+DM and ILM+DM messages.
For these channel types, the ACH SHALL NOT be followed by the ACH TLV For these channel types, the ACH SHALL NOT be followed by the ACH TLV
Header defined in [RFC5586]. Header defined in [RFC5586].
The fixed-format portion of a message MAY be followed by a block of The fixed-format portion of a message MAY be followed by a block of
Type-Length-Value (TLV) fields. The TLV block provides an extensible Type-Length-Value (TLV) fields. The TLV block provides an extensible
way of attaching subsidiary information to LM and DM messages. way of attaching subsidiary information to LM and DM messages.
Several such TLV fields are defined below. Several such TLV fields are defined below.
All integer values for fields defined in this document SHALL be
encoded in network byte order.
3.1. Loss Measurement Message Format 3.1. Loss Measurement Message Format
The format of a Loss Measurement message, which follows the The format of a Loss Measurement message, which follows the
Associated Channel Header (ACH), is as follows: Associated Channel Header (ACH), is as follows:
0 1 2 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 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| Flags | Control Code | Message Length | |Version| Flags | Control Code | Message Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 18, line 51 skipping to change at page 20, line 21
Data Format Flags Flags specifying the format of message data Data Format Flags Flags specifying the format of message data
(DFlags) (DFlags)
Origin Timestamp Format of the Origin Timestamp field Origin Timestamp Format of the Origin Timestamp field
Format (OTF) Format (OTF)
Reserved Reserved for future specification Reserved Reserved for future specification
Session Identifier Set arbitrarily by the querier Session Identifier Set arbitrarily by the querier
Differentiated Differentiated Services Code Point (DSCP) being Differentiated Differentiated Services Code Point (DSCP) being
Services (DS) Field measured Services (DS) Field measured
Origin Timestamp Query message transmission timestamp Origin Timestamp Query message transmission timestamp
Counter 1-4 Packet counter values in network byte order Counter 1-4 LM counter values
TLV Block Optional block of Type-Length-Value fields TLV Block Optional block of Type-Length-Value fields
The possible values for these fields are as follows. The possible values for these fields are as follows.
Version: Currently set to 0. Version: Currently set to 0.
Flags: The format of the Flags field is shown below. Flags: The format of the Flags field is shown below.
+-+-+-+-+ +-+-+-+-+
|R|T|0|0| |R|T|0|0|
+-+-+-+-+ +-+-+-+-+
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For a Query: For a Query:
0x0: In-band Response Requested. Indicates that this query has 0x0: In-band Response Requested. Indicates that this query has
been sent over a bidirectional channel and the response is been sent over a bidirectional channel and the response is
expected over the same channel. expected over the same channel.
0x1: Out-of-band Response Requested. Indicates that the 0x1: Out-of-band Response Requested. Indicates that the
response should be sent via an out-of-band channel. response should be sent via an out-of-band channel.
0x2: No Response Requested. Indicates that no response to the 0x2: No Response Requested. Indicates that no response to the
query should be sent. query should be sent. This mode can be used, for example, if
all nodes involved are being controlled by a Network Management
System.
For a Response: For a Response:
Codes 0x0-0xF are reserved for non-error responses. Codes 0x0-0xF are reserved for non-error responses.
0x1: Success. Indicates that the operation was successful. 0x1: Success. Indicates that the operation was successful.
0x2: Notification - Data Format Invalid. Indicates that the 0x2: Notification - Data Format Invalid. Indicates that the
query was processed but the format of the data fields in this query was processed but the format of the data fields in this
response may be inconsistent. Consequently these data fields response may be inconsistent. Consequently these data fields
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0x3: Notification - Initialization In Progress. Indicates that 0x3: Notification - Initialization In Progress. Indicates that
the query was processed but this response does not contain the query was processed but this response does not contain
valid measurement data because the responder's initialization valid measurement data because the responder's initialization
process has not completed. process has not completed.
0x4: Notification - Data Reset Occurred. Indicates that the 0x4: Notification - Data Reset Occurred. Indicates that the
query was processed but a reset has recently occurred which may query was processed but a reset has recently occurred which may
render the data in this response inconsistent relative to render the data in this response inconsistent relative to
earlier responses. earlier responses.
0x5: Notification - Resource Temporarily Unavailable.
Indicates that the query was processed but resources were
unavailable to complete the requested measurement, and that
consequently this response does not contain valid measurement
data.
0x10: Error - Unspecified Error. Indicates that the operation 0x10: Error - Unspecified Error. Indicates that the operation
failed for an unspecified reason. failed for an unspecified reason.
0x11: Error - Unsupported Version. Indicates that the 0x11: Error - Unsupported Version. Indicates that the
operation failed because the protocol version supplied in the operation failed because the protocol version supplied in the
query message is not supported. query message is not supported.
0x12: Error - Unsupported Control Code. Indicates that the 0x12: Error - Unsupported Control Code. Indicates that the
operation failed because the Control Code requested an operation failed because the Control Code requested an
operation that is not available for this channel. operation that is not available for this channel.
skipping to change at page 21, line 9 skipping to change at page 22, line 36
and marked as mandatory is not supported. and marked as mandatory is not supported.
0x18: Error - Unsupported Query Interval. Indicates that the 0x18: Error - Unsupported Query Interval. Indicates that the
operation failed because the query message rate exceeded the operation failed because the query message rate exceeded the
configured threshold. configured threshold.
0x19: Error - Administrative Block. Indicates that the 0x19: Error - Administrative Block. Indicates that the
operation failed because it has been administratively operation failed because it has been administratively
disallowed. disallowed.
0x1A: Error - Temporary Resource Exhaustion. Indicates that 0x1A: Error - Resource Unavailable. Indicates that the
the operation failed because node resources were not available. operation failed because node resources were not available.
0x1B: Error - Resource Released. Indicates that the operation
failed because node resources for this measurement session were
administratively released.
0x1C: Error - Invalid Message. Indicates that the operation
failed because the received query message was malformed.
0x1D: Error - Protocol Error. Indicates that the operation
failed because a protocol error was found in the received query
message.
Message Length: Set to the total length of this message in bytes. Message Length: Set to the total length of this message in bytes.
DFlags: The format of the DFlags field is shown below. DFlags: The format of the DFlags field is shown below.
+-+-+-+-+ +-+-+-+-+
|X|B|0|0| |X|B|0|0|
+-+-+-+-+ +-+-+-+-+
Loss Measurement Message Flags Loss Measurement Message Flags
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B: Octet (byte) count. When set to 1, indicates that the Counter B: Octet (byte) count. When set to 1, indicates that the Counter
1-4 fields represent octet counts. When set to 0, indicates that 1-4 fields represent octet counts. When set to 0, indicates that
the Counter 1-4 fields represent packet counts. the Counter 1-4 fields represent packet counts.
0: Set to 0. 0: Set to 0.
Origin Timestamp Format: The format of the Origin Timestamp field, as Origin Timestamp Format: The format of the Origin Timestamp field, as
specified in Section 3.4. specified in Section 3.4.
Session Identifier: Set arbitrarily in a query and copied in the Session Identifier: Set arbitrarily in a query and copied in the
response, if any. response, if any. This field uniquely identifies a measurement
operation (also called a session) that consists of a sequence of
messages. All messages in the sequence have the same Session
Identifier.
DS: When the T flag is set to 1, this field is set to the DSCP value DS: When the T flag is set to 1, this field is set to the DSCP value
[RFC3260] that corresponds to the traffic class being measured. For [RFC3260] that corresponds to the traffic class being measured. For
MPLS, where the traffic class of a channel is identified by the MPLS, where the traffic class of a channel is identified by the
three-bit Traffic Class in the channel's LSE [RFC5462], this field three-bit Traffic Class in the channel's LSE [RFC5462], this field
SHOULD be set to the Class Selector Codepoint [RFC2474] that SHOULD be set to the Class Selector Codepoint [RFC2474] that
corresponds to that Traffic Class. When the T flag is set to 0, the corresponds to that Traffic Class. When the T flag is set to 0, the
value of this field is arbitrary, and the field can be considered value of this field is arbitrary, and the field can be considered
part of the Session Identifier. part of the Session Identifier.
Origin Timestamp: Timestamp recording the transmit time of the query Origin Timestamp: Timestamp recording the transmit time of the query
message. message.
Counter 1-4: Referring to Section 2.1, when a query is sent from A, Counter 1-4: Referring to Section 2.2, when a query is sent from A,
Counter 1 is set to A_TxP and the other counter fields are set to 0. Counter 1 is set to A_TxP and the other counter fields are set to 0.
When the query is received at B, Counter 2 is set to B_RxP. At this When the query is received at B, Counter 2 is set to B_RxP. At this
point, B copies Counter 1 to Counter 3 and Counter 2 to Counter 4, point, B copies Counter 1 to Counter 3 and Counter 2 to Counter 4,
and re-initializes Counter 1 and Counter 2 to 0. When B transmits and re-initializes Counter 1 and Counter 2 to 0. When B transmits
the response, Counter 1 is set to B_TxP. When the response is the response, Counter 1 is set to B_TxP. When the response is
received at A, Counter 2 is set to A_RxP. received at A, Counter 2 is set to A_RxP.
The mapping of counter types such as A_TxP to the counter fields 1-4 The mapping of counter types such as A_TxP to the counter fields 1-4
is designed to ensure that transmit counter values are always written is designed to ensure that transmit counter values are always written
at the same fixed offset in the packet, and likewise for receive at the same fixed offset in the packet, and likewise for receive
counters. This property is important for hardware processing. counters. This property may be important for hardware processing.
All counter values MUST be in network byte order. When a 32-bit When a 32-bit counter value is written to one of the counter fields,
counter value is written to one of the counter fields, that value that value SHALL be written to the low-order 32 bits of the field;
SHALL be written to the low-order 32 bits of the field; the high- the high-order 32 bits of the field MUST, in this case, be set to 0.
order 32 bits of the field MUST, in this case, be set to 0.
TLV Block: Zero or more TLV fields. TLV Block: Zero or more TLV fields.
3.2. Delay Measurement Message Format 3.2. Delay Measurement Message Format
The format of a Delay Measurement message, which follows the The format of a Delay Measurement message, which follows the
Associated Channel Header (ACH), is as follows: Associated Channel Header (ACH), is as follows:
0 1 2 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 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
skipping to change at page 24, line 5 skipping to change at page 25, line 29
Services (DS) Field measured Services (DS) Field measured
Timestamp 1-4 64-bit timestamp values Timestamp 1-4 64-bit timestamp values
TLV Block Optional block of Type-Length-Value fields TLV Block Optional block of Type-Length-Value fields
Reserved fields MUST be set to 0 and ignored upon receipt. The Reserved fields MUST be set to 0 and ignored upon receipt. The
possible values for the remaining fields are as follows. possible values for the remaining fields are as follows.
Version: Currently set to 0. Version: Currently set to 0.
Flags: As specified in Section 3.1, except for the X flag, which is Flags: As specified in Section 3.1. The T flag in a DM message is
set to 0, and the T flag, which is set to 1. set to 1.
Control Code: As specified in Section 3.1. Control Code: As specified in Section 3.1.
Message Length: Set to the total length of this message in bytes. Message Length: Set to the total length of this message in bytes.
Querier Timestamp Format: The format of the timestamp values written Querier Timestamp Format: The format of the timestamp values written
by the querier, as specified in Section 3.4. by the querier, as specified in Section 3.4.
Responder Timestamp Format: The format of the timestamp values Responder Timestamp Format: The format of the timestamp values
written by the responder, as specified in Section 3.4. written by the responder, as specified in Section 3.4.
Responder's Preferred Timestamp Format: The timestamp format Responder's Preferred Timestamp Format: The timestamp format
preferred by the responder, as specified in Section 3.4. preferred by the responder, as specified in Section 3.4.
Session Identifier: As specified in Section 3.1. Session Identifier: As specified in Section 3.1.
DS: As specified in Section 3.1. DS: As specified in Section 3.1.
Timestamp 1-4: Referring to Section 2.3, when a query is sent from A, Timestamp 1-4: Referring to Section 2.4, when a query is sent from A,
Timestamp 1 is set to T1 and the other timestamp fields are set to 0. Timestamp 1 is set to T1 and the other timestamp fields are set to 0.
When the query is received at B, Timestamp 2 is set to T2. At this When the query is received at B, Timestamp 2 is set to T2. At this
point, B copies Timestamp 1 to Timestamp 3 and Timestamp 2 to point, B copies Timestamp 1 to Timestamp 3 and Timestamp 2 to
Timestamp 4, and re-initializes Timestamp 1 and Timestamp 2 to 0. Timestamp 4, and re-initializes Timestamp 1 and Timestamp 2 to 0.
When B transmits the response, Timestamp 1 is set to T3. When the When B transmits the response, Timestamp 1 is set to T3. When the
response is received at A, Timestamp 2 is set to T4. The actual response is received at A, Timestamp 2 is set to T4. The actual
formats of the timestamp fields written by A and B are indicated by formats of the timestamp fields written by A and B are indicated by
the Querier Timestamp Format and Responder Timestamp Format fields the Querier Timestamp Format and Responder Timestamp Format fields
respectively. respectively.
skipping to change at page 25, line 39 skipping to change at page 27, line 39
. . . .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Counter 4 | | Counter 4 |
| | | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ TLV Block ~ ~ TLV Block ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Loss/Delay Measurement Message Format Figure 4: Loss/Delay Measurement Message Format
The LM/DM message fields have the same meanings as the corresponding The fields of this message have the same meanings as the
fields in the LM and DM message formats. corresponding fields in the LM and DM message formats, except that
the roles of the OTF and Origin Timestamp fields for LM are here
played by the QTF and Timestamp 1 fields, respectively.
3.4. Timestamp Field Formats 3.4. Timestamp Field Formats
The following timestamp format field values are specified in this The following timestamp format field values are specified in this
document: document:
0: Null timestamp format. This value is a placeholder indicating 0: Null timestamp format. This value is a placeholder indicating
that the timestamp field does not contain a meaningful timestamp. that the timestamp field does not contain a meaningful timestamp.
1: Sequence number. This value indicates that the timestamp field 1: Sequence number. This value indicates that the timestamp field
is to be viewed as a simple 64-bit sequence number. is to be viewed as a simple 64-bit sequence number. This provides
a simple solution for applications that do not require a real
absolute timestamp, but only an indication of message ordering; an
example is LM exception detection.
2: Network Time Protocol version 4 64-bit timestamp format 2: Network Time Protocol version 4 64-bit timestamp format
[RFC5905]. This format consists of a 32-bit seconds field [RFC5905]. This format consists of a 32-bit seconds field
followed by a 32-bit fractional seconds field, so that it can be followed by a 32-bit fractional seconds field, so that it can be
regarded as a fixed-point 64-bit quantity. regarded as a fixed-point 64-bit quantity.
3: IEEE 1588-2002 (1588v1) Precision Time Protocol timestamp 3: IEEE 1588-2002 (1588v1) Precision Time Protocol timestamp
format [IEEE1588]. This format consists of a 32-bit seconds field format [IEEE1588]. This format consists of a 32-bit seconds field
followed by a 32-bit nanoseconds field. followed by a 32-bit nanoseconds field.
In recognition of the wide deployment, particularly in hardware-based
timing implementations, of IEEE 1588 PTP, the PTP timestamp format is
the default format used in Delay Measurement messages. This format
MUST be supported. Support for other timestamp formats is OPTIONAL.
Timestamp formats of n < 64 bits in size SHALL be encoded in the 64- Timestamp formats of n < 64 bits in size SHALL be encoded in the 64-
bit timestamp fields specified in this document using the n high- bit timestamp fields specified in this document using the n high-
order bits of the field. The remaining 64 - n low-order bits in the order bits of the field. The remaining 64 - n low-order bits in the
field SHOULD be set to 0 and MUST be ignored when reading the field. field SHOULD be set to 0 and MUST be ignored when reading the field.
To ensure that it is possible to find an interoperable mode between
implementations it is necessary to select one timestamp format as the
default. The timestamp format chosen as the default is IEEE 1588v1
PTP; this format MUST be supported. The rationale for this choice is
discussed in Appendix A. Implementations SHOULD also be capable of
reading timestamps written in NTPv4 64-bit format and reconciling
them internally with PTP timestamps for measurement purposes.
Support for other timestamp formats is OPTIONAL.
The implementation MUST make clear which timestamp formats it
supports and the extent of its support for computation with and
reconciliation of different formats for measurement purposes.
3.5. TLV Objects 3.5. TLV Objects
The TLV Block in LM and DM messages consists of zero or more objects The TLV Block in LM and DM messages consists of zero or more objects
with the following format: with the following format:
0 1 2 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Value ~ | Type | Length | Value ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
skipping to change at page 26, line 49 skipping to change at page 29, line 14
be up to 255 bytes long. be up to 255 bytes long.
The Type space is divided into Mandatory and Optional subspaces: The Type space is divided into Mandatory and Optional subspaces:
Type Range Semantics Type Range Semantics
-------------- --------- -------------- ---------
0-127 Mandatory 0-127 Mandatory
128-255 Optional 128-255 Optional
Upon receipt of a query message including an unrecognized mandatory Upon receipt of a query message including an unrecognized mandatory
TLV object, the recipient MUST discard the message or respond with an TLV object, the recipient MUST respond with an Unsupported Mandatory
appropriate error code. TLV Object error code.
The types defined are as follows: The types defined are as follows:
Type Definition Type Definition
-------------- --------------------------------- -------------- ---------------------------------
Mandatory Mandatory
0 Padding - copy in response 0 Padding - copy in response
1 Return Address 1 Return Address
2 Session Query Interval 2 Session Query Interval
3-119 Reserved 3 Loopback Request
4-119 Reserved
120-127 Implementation-specific usage 120-127 Implementation-specific usage
Optional Optional
128 Padding - do not copy in response 128 Padding - do not copy in response
129 Destination Address 129 Destination Address
130 Source Address 130 Source Address
131-247 Reserved 131-247 Reserved
248-255 Implementation-specific usage 248-255 Implementation-specific usage
3.5.1. Padding 3.5.1. Padding
The two padding objects permit the augmentation of packet size; this The two padding objects permit the augmentation of packet size; this
is mainly useful for delay measurement. The type of padding is mainly useful for delay measurement. The type of padding
indicates whether the padding supplied by the querier is to be copied indicates whether the padding supplied by the querier is to be copied
to, or omitted from, the response. More than one padding object MAY to, or omitted from, the response. Asymmetrical padding may be
be present, in which case they SHOULD be continguous. Padding useful when responses are delivered out-of-band or when different
objects SHOULD occur at the end of the TLV Block. The Value field of maximum transmission unit sizes apply to the two components of a
a padding object is arbitrary. bidirectional channel.
More than one padding object MAY be present, in which case they
SHOULD be continguous. Padding objects SHOULD occur at the end of
the TLV Block. The Value field of a padding object is arbitrary.
3.5.2. Addressing 3.5.2. Addressing
The addressing objects have the following format: The addressing objects have the following format:
0 1 2 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | Address Family | | Type | Length | Address Family |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Addressing Object Format Addressing Object Format
The Address Family field indicates the type of the address, and SHALL The Address Family field indicates the type of the address, and SHALL
be set to one of the assigned values in the IANA Address Family be set to one of the assigned values in the IANA Address Family
Numbers registry. Numbers registry.
The Source and Destination address objects indicate the addresses of The Source and Destination address objects indicate the addresses of
the sender and the intended recipient of the message, respectively. the sender and the intended recipient of the message, respectively.
The Source Address of a query message SHOULD be used as the The Source Address of a query message SHOULD be used as the
destination for an out-of-band response unless some other out-of-band destination for an out-of-band response unless some other out-of-band
response mechanism has been configured, and unless a Return Address response mechanism has been configured, and unless a Return Address
object is present, in which case the Return Address specifies the object is present, in which case the Return Address specifies the
target of the response. The Return Address object MUST NOT appear in target of the response. The Return Address object MUST NOT appear in
a response. a response.
3.5.3. Session Query Interval 3.5.3. Loopback Request
The Loopback Request object, when included in a query, indicates a
request that the query message be returned to the sender unmodified.
This object has a Length of 0.
Upon receiving the reflected query message back from the responder,
the querier MUST NOT retransmit the message. Information that
uniquely identifies the original query source, such as a Source
Address object, can be included to enable the querier to
differentiate one of its own loopback queries from a loopback query
initiated by the far end.
This object may be useful, for example, when the querier is
interested only in the round-trip delay metric. In this case no
support for delay measurement is required at the responder at all,
other than the ability to recognize a DM query that includes this
object and return it unmodified.
3.5.4. Session Query Interval
The Value field of the Session Query Interval object is a 32-bit The Value field of the Session Query Interval object is a 32-bit
unsigned positive (nonzero) integer in network byte order that unsigned integer that specifies a time interval in milliseconds:
specifies a time interval in milliseconds. When attached to a query
message, this time interval indicates the interval between successive
query messages in this measurement session. When attached to a
response, this time interval indicates the minimum query interval
supported by the responder for the measurement type indicated by the
query.
When initiating a new measurement session, the querier SHOULD include 0 1 2 3
this object to inform the responder of the rate at which it intends 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
to send query messages in this session. Upon receiving a non-error +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
response, the querier MAY then stop including this object in | Type | Length | Session Query >
subsequent messages in the session for as long as its query +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
transmission rate remains the same. When a query is received with a < Interval (ms) |
Session Query Interval that is too low for the receiver to support, +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
the receiver SHOULD include this object when it generates an error
response.
Lower query intervals (i.e. higher query rates) provide finer Session Query Interval Object Format
This time interval indicates the interval between successive query
messages in a specific measurement session. The purpose of the
Session Query Interval (SQI) object is to enable the querier and
responder of a measurement session to agree on a query rate. The
procedures for handling this object SHALL be as follows:
1. The querier notifies the responder that it wishes to be informed
of the responder's minimum query interval for this session by
including the SQI object in its query messages, with a Value of
0.
2. When the responder receives a query that includes an SQI object
with a Value of 0, the responder includes an SQI object in the
response with the Value set to the minimum query interval it
supports for this session.
3. When the querier receives a response that includes an SQI object,
it selects a query interval for the session that is greater than
or equal to the Value specified in the SQI object and adjusts its
query transmission rate accordingly, including in each subsequent
query an SQI object with a Value equal to the selected query
interval. Once a response to one of these subsequent queries has
been received, the querier infers that the responder has been
apprised of the selected query interval and MAY then stop
including the SQI object in queries associated with this session.
Similar procedures allow the query rate to be changed during the
course of the session by either the querier or the responder. For
example, to inform the querier of a change in the minimum supported
query interval, the responder begins including a corresponding SQI
object in its responses, and the querier adjusts its query rate if
necessary and includes a corresponding SQI object in its queries
until a response is received.
Shorter query intervals (i.e. higher query rates) provide finer
measurement granularity at the expense of additional load on measurement granularity at the expense of additional load on
measurement endpoints and the network; see Section 5 for further measurement endpoints and the network; see Section 6 for further
discussion. discussion.
4. Operation 4. Operation
4.1. Loss Measurement Procedures 4.1. Operational Overview
4.1.1. Initiating a Loss Measurement Operation A loss or delay measurement operation, also called a session, is
controlled by the querier and consists of a sequence of query
messages associated with a particular channel and a common set of
measurement parameters. If the session parameters include a response
request, then the receiving node or nodes will (under normal
conditions) generate a response message for each query message
received, and these responses are also considered part of the
session. All query and response messages in a session carry a common
session identifier.
Measurement sessions are initiated at the discretion of the network
operator and are terminated either at the operator's request or as
the result of an error condition. A session may be as brief as a
single message exchange, for example when a DM query is used by the
operator to "ping" a remote node, or may extend throughout the
lifetime of the channel.
When a session is initiated for which responses are requested, the
querier SHOULD initialize a timer, called the SessionResponseTimeout,
that indicates how long the querier will wait for a response before
abandoning the session and notifying the user that a timeout has
occurred. This timer persists for the lifetime of the session and is
reset each time a response message for the session is received.
When a query message is received that requests a response, a variety
of exceptional conditions may arise that prevent the responder from
generating a response that contains valid measurement data. Such
conditions fall broadly into two classes: transient exceptions from
which recovery is possible, and fatal exceptions that require
termination of the session. When an exception arises, the responder
SHOULD generate a response with an appropriate Notification or Error
control code according as the exception is, respectively, transient
or fatal. When the querier receives an Error response, the session
MUST be terminated and the user informed.
A common example of a transient exception occurs when a new session
is initiated and the responder requires a period of time to become
ready before it can begin providing useful responses. The response
control code corresponding to this situation is Notification -
Initialization In Progress. Typical examples of fatal exceptions are
cases where the querier has requested a type of measurement that the
responder does not support, or where a query message is malformed.
When initiating a session the querier SHOULD employ the Session Query
Interval mechanism (Section 3.5.4) to establish a mutually agreeable
query rate with the responder. Responders SHOULD employ rate-
limiting mechanisms to guard against the possibility of receiving an
excessive quantity of query messages.
4.2. Loss Measurement Procedures
4.2.1. Initiating a Loss Measurement Operation
An LM operation for a particular channel consists of sending a An LM operation for a particular channel consists of sending a
sequence (LM[1], LM[2], ...) of LM query messages over the channel at sequence (LM[1], LM[2], ...) of LM query messages over the channel at
a specific rate and processing the responses received, if any. As a specific rate and processing the responses received, if any. As
described in Section 2.1, the packet loss associated with the channel described in Section 2.2, the packet loss associated with the channel
during the operation is computed as a delta between successive during the operation is computed as a delta between successive
messages; these deltas can be accumulated to obtain a running total messages; these deltas can be accumulated to obtain a running total
of the packet loss for the channel. of the packet loss for the channel, or used to derive related metrics
such as the average loss rate.
The query message transmission rate MUST be sufficiently high, given The query message transmission rate MUST be sufficiently high, given
the LM message counter size (which can be either 32 or 64 bits) and the LM message counter size (which can be either 32 or 64 bits) and
the speed and minimum packet size of the underlying channel, that the the speed and minimum packet size of the underlying channel, that the
ambiguity condition noted in Section 2.1 cannot arise. The ambiguity condition noted in Section 2.2 cannot arise. The
implementation SHOULD assume, in evaluating this rate, that the implementation SHOULD assume, in evaluating this rate, that the
counter size is 32 bits unless explicitly configured otherwise, or counter size is 32 bits unless explicitly configured otherwise, or
unless (in the case of a bidirectional channel) all local and remote unless (in the case of a bidirectional channel) all local and remote
interfaces involved in the LM operation are known to be 64-bit- interfaces involved in the LM operation are known to be 64-bit-
capable, which can be inferred from the value of the X flag in an LM capable, which can be inferred from the value of the X flag in an LM
response. response.
When initiating an LM operation, the far end may require a period of 4.2.2. Transmitting a Loss Measurement Query
time to become ready for the requested measurement operation. During
this period, LM queries MAY simply be discarded, and the querier
expecting a response SHOULD be prepared for this situation, for
example by setting a timer to differentiate between an acceptable
initialization delay and a permanent unavailability condition at the
far end. Alternatively, the receiver MAY respond, possibly in a
rate-limited manner, to queries received during this period with an
appropriate notification code.
4.1.2. Transmitting a Loss Measurement Query
When transmitting an LM Query over a channel, the Version field MUST When transmitting an LM Query over a channel, the Version field MUST
be set to 0. The R flag MUST be set to 0. The T flag SHALL be set be set to 0. The R flag MUST be set to 0. The T flag SHALL be set
to 1 if, and only if, the measurement is specific to a particular to 1 if, and only if, the measurement is specific to a particular
traffic class, in which case the DS field SHALL identify that traffic traffic class, in which case the DS field SHALL identify that traffic
class. class.
The X flag MUST be set to 1 if the transmitting interface writes 64- The X flag MUST be set to 1 if the transmitting interface writes 64-
bit LM counters, and otherwise MUST be set to 0 to indicate that 32- bit LM counters, and otherwise MUST be set to 0 to indicate that 32-
bit counters are written. The B flag SHALL be set to 1 to indicate bit counters are written. The B flag SHALL be set to 1 to indicate
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requested). requested).
The Session Identifier field can be set arbitrarily. The Session Identifier field can be set arbitrarily.
The Origin Timestamp field SHOULD be set to the time at which this The Origin Timestamp field SHOULD be set to the time at which this
message is transmitted, and the Origin Timestamp Format field MUST be message is transmitted, and the Origin Timestamp Format field MUST be
set to indicate its format, according to Section 3.4. set to indicate its format, according to Section 3.4.
The Counter 1 field SHOULD be set to the total count of units The Counter 1 field SHOULD be set to the total count of units
(packets or octets, according to the B flag) transmitted over the (packets or octets, according to the B flag) transmitted over the
channel prior to this LM Query. The remaining Counter fields MUST be channel prior to this LM Query, or to 0 if this is the beginning of a
set to 0. measurement session for which counter data is not yet available. The
Counter 2 field MUST be set to 0. If a response was previously
received in this measurement session, the Counter 1 and Counter 2
fields of the most recent such response MAY be copied to the Counter
3 and Counter 4 fields, respectively, of this query; otherwise, the
Counter 3 and Counter 4 fields MUST be set to 0.
4.1.3. Receiving a Loss Measurement Query 4.2.3. Receiving a Loss Measurement Query
Upon receipt of an LM Query message, the Counter 2 field SHOULD be Upon receipt of an LM Query message, the Counter 2 field SHOULD be
set to the total count of units (packets or octets, according to the set to the total count of units (packets or octets, according to the
B flag) received over the channel prior to this LM Query. If the B flag) received over the channel prior to this LM Query. If the
receiving interface writes 32-bit LM counters, the X flag MUST be set receiving interface writes 32-bit LM counters, the X flag MUST be set
to 0. to 0.
At this point the LM Query message must be inspected. If the Control At this point the LM Query message must be inspected. If the Control
Code field is set to 0x2 (no response requested), an LM Response Code field is set to 0x2 (no response requested), an LM Response
message MUST NOT be transmitted. If the Control Code field is set to message MUST NOT be transmitted. If the Control Code field is set to
0x0 (in-band response requested) or 0x1 (out-of-band response 0x0 (in-band response requested) or 0x1 (out-of-band response
requested), then an in-band or out-of-band response, respectively, requested), then an in-band or out-of-band response, respectively,
SHOULD be transmitted unless this has been prevented by an SHOULD be transmitted unless this has been prevented by an
administrative, security or congestion control mechanism. administrative, security or congestion control mechanism.
4.1.4. Transmitting a Loss Measurement Response In the case of a fatal exception that prevents the requested
measurement from being made, the error SHOULD be reported, either via
a response if one was requested or else as a notification to the
user.
4.2.4. Transmitting a Loss Measurement Response
When constructing a Response to an LM Query, the Version field MUST When constructing a Response to an LM Query, the Version field MUST
be set to 0. The R flag MUST be set to 1. The value of the T flag be set to 0. The R flag MUST be set to 1. The value of the T flag
MUST be copied from the LM Query. MUST be copied from the LM Query.
The X flag MUST be set to 0 if the transmitting interface writes 32- The X flag MUST be set to 0 if the transmitting interface writes 32-
bit LM counters; otherwise its value MUST be copied from the LM bit LM counters; otherwise its value MUST be copied from the LM
Query. The B flag MUST be copied from the LM Query. Query. The B flag MUST be copied from the LM Query.
The Session Identifier, Origin Timestamp, and Origin Timestamp Format The Session Identifier, Origin Timestamp, and Origin Timestamp Format
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messages listed in Section 3.1. The value 0x10 (Unspecified Error) messages listed in Section 3.1. The value 0x10 (Unspecified Error)
SHOULD NOT be used if one of the other more specific error codes is SHOULD NOT be used if one of the other more specific error codes is
applicable. applicable.
If the response is transmitted in-band, the Counter 1 field SHOULD be If the response is transmitted in-band, the Counter 1 field SHOULD be
set to the total count of units transmitted over the channel prior to set to the total count of units transmitted over the channel prior to
this LM Response. If the response is transmitted out-of-band, the this LM Response. If the response is transmitted out-of-band, the
Counter 1 field MUST be set to 0. In either case, the Counter 2 Counter 1 field MUST be set to 0. In either case, the Counter 2
field MUST be set to 0. field MUST be set to 0.
4.1.5. Receiving a Loss Measurement Response 4.2.5. Receiving a Loss Measurement Response
Upon in-band receipt of an LM Response message, the Counter 2 field Upon in-band receipt of an LM Response message, the Counter 2 field
SHOULD be set to the total count of units received over the channel is set to the total count of units received over the channel prior to
prior to this LM Response. If the receiving interface writes 32-bit this LM Response. If the receiving interface writes 32-bit LM
LM counters, the X flag MUST be set to 0. counters, the X flag is set to 0. (Since the life of the LM message
in the network has ended at this point, it is up to the receiver
whether these final modifications are made to the packet. If the
message is to be forwarded on for external post-processing
(Section 2.9.7) then these modifications MUST be made.)
Upon out-of-band receipt of an LM Response message, the Counter 1 and Upon out-of-band receipt of an LM Response message, the Counter 1 and
Counter 2 fields MUST NOT be used for purposes of loss measurement. Counter 2 fields MUST NOT be used for purposes of loss measurement.
If the Control Code in an LM Response is anything other than 0x1 If the Control Code in an LM Response is anything other than 0x1
(Success), the counter values in the response MUST NOT be used for (Success), the counter values in the response MUST NOT be used for
purposes of loss measurement. When the Control Code indicates an purposes of loss measurement. If the Control Code indicates an error
error condition, the LM operation SHOULD be suspended and an condition, or if the response message is invalid, the LM operation
appropriate notification to the user generated. If a temporary error MUST be terminated and an appropriate notification to the user
condition is indicated, the LM operation MAY be restarted generated.
automatically.
4.1.6. Loss Calculation 4.2.6. Loss Calculation
Calculation of packet loss is carried out according to the procedures Calculation of packet loss is carried out according to the procedures
in Section 2.1. The X flag in an LM message informs the device in Section 2.2. The X flag in an LM message informs the device
performing the calculation whether to perform 32-bit or 64-bit performing the calculation whether to perform 32-bit or 64-bit
arithmetic. If the flag value is equal to 1, all interfaces involved arithmetic. If the flag value is equal to 1, all interfaces involved
in the LM operation have written 64-bit counter values, and 64-bit in the LM operation have written 64-bit counter values, and 64-bit
arithmetic can be used. If the flag value is equal to 0, at least arithmetic can be used. If the flag value is equal to 0, at least
one interface involved in the operation has written a 32-bit counter one interface involved in the operation has written a 32-bit counter
value, and 32-bit arithmetic is carried out using the low-order 32 value, and 32-bit arithmetic is carried out using the low-order 32
bits of each counter value. bits of each counter value.
Note that the semantics of the X flag allow all devices to Note that the semantics of the X flag allow all devices to
interoperate regardless of their counter size support. Thus, an interoperate regardless of their counter size support. Thus, an
implementation MUST NOT generate an error response based on the value implementation MUST NOT generate an error response based on the value
of this flag. of this flag.
4.1.7. Quality of Service 4.2.7. Quality of Service
The TC field of the LSE corresponding to the channel (e.g. LSP) The TC field of the LSE corresponding to the channel (e.g. LSP)
being measured SHOULD be set to a traffic class equal to or better being measured SHOULD be set to a traffic class equal to or better
than the best TC within the measurement scope to minimize the chance than the best TC within the measurement scope to minimize the chance
of out-of-order conditions. of out-of-order conditions.
4.1.8. G-ACh Packets 4.2.8. G-ACh Packets
By default, direct LM MUST exclude packets transmitted and received By default, direct LM MUST exclude packets transmitted and received
over the Generic Associated Channel (G-ACh). An implementation MAY over the Generic Associated Channel (G-ACh). An implementation MAY
provide the means to alter the direct LM scope to include some or all provide the means to alter the direct LM scope to include some or all
G-ACh messages. Care must be taken when altering the LM scope to G-ACh messages. Care must be taken when altering the LM scope to
ensure that both endpoints are in agreement. ensure that both endpoints are in agreement.
4.1.9. Test Messages 4.2.9. Test Messages
In the case of inferred LM, the packets counted for LM consist of In the case of inferred LM, the packets counted for LM consist of
test messages generated for this purpose, or of some other class of test messages generated for this purpose, or of some other class of
packets deemed to provide a good proxy for data packets flowing over packets deemed to provide a good proxy for data packets flowing over
the channel. The specification of test protocols and proxy packets the channel. The specification of test protocols and proxy packets
is outside the scope of this document. is outside the scope of this document, but some guidelines are
discussed below.
An identifier common to both the test or proxy messages and the LM An identifier common to both the test or proxy messages and the LM
messages may be required to make correlation possible. The combined messages may be required to make correlation possible. The combined
value of the Session Identifier and DS fields SHOULD be used for this value of the Session Identifier and DS fields SHOULD be used for this
purpose when possible. That is, test messages in this case will purpose when possible. That is, test messages in this case will
include a 32-bit field which can carry the value of the combined include a 32-bit field which can carry the value of the combined
Session Identifier + DS field present in LM messages. When TC- Session Identifier + DS field present in LM messages. When TC-
specific LM is conducted, the DS field of the LSE in the label stack specific LM is conducted, the DS field of the LSE in the label stack
of a test message corresponding to the channel (e.g. LSP) over which of a test message corresponding to the channel (e.g. LSP) over which
the message is sent MUST correspond to the DS value in the associated the message is sent MUST correspond to the DS value in the associated
LM messages. LM messages.
4.1.10. Message Loss and Packet Misorder Conditions A separate test message protocol SHOULD include a timeout value in
its messages that informs the responder when to discard any state
associated with a specific test.
4.2.10. Message Loss and Packet Misorder Conditions
Because an LM operation consists of a message sequence with state Because an LM operation consists of a message sequence with state
maintained from one message to the next, LM is subject to the effects maintained from one message to the next, LM is subject to the effects
of lost messages and misordered packets in a way that DM is not. of lost messages and misordered packets in a way that DM is not.
Because this state exists only on the querier, the handling of these Because this state exists only on the querier, the handling of these
conditions is, strictly speaking, a local matter. This section, conditions is, strictly speaking, a local matter. This section,
however, presents recommended procedures for handling such however, presents recommended procedures for handling such
conditions. conditions. Note that in the absence of ECMP, packet misordering
within a traffic class is a relatively rare event.
The first kind of anomaly that may occur is that one or more LM The first kind of anomaly that may occur is that one or more LM
messages may be lost in transit. The effect of such loss is that messages may be lost in transit. The effect of such loss is that
when an LM Response is next received at the querier, an unambiguous when an LM Response is next received at the querier, an unambiguous
interpretation of the counter values it contains may be impossible, interpretation of the counter values it contains may be impossible,
for the reasons described at the end of Section 2.1. Whether this is for the reasons described at the end of Section 2.2. Whether this is
so depends on the number of messages lost and the other variables so depends on the number of messages lost and the other variables
mentioned in that section, such as the LM message rate and the mentioned in that section, such as the LM message rate and the
channel parameters. channel parameters.
Another possibility is that LM messages are misordered in transit, so Another possibility is that LM messages are misordered in transit, so
that for instance the response to LM[n] is received prior to the that for instance the response to LM[n] is received prior to the
response to LM[n-1]. A typical implementation will discard the late response to LM[n-1]. A typical implementation will discard the late
response to LM[n-1], so that the effect is the same as the case of a response to LM[n-1], so that the effect is the same as the case of a
lost message. lost message.
Finally, LM is subject to the possibility that data packets are Finally, LM is subject to the possibility that data packets are
misordered relative to LM messages. This condition can result, for misordered relative to LM messages. This condition can result, for
example, in a transmit count of 100 and a corresponding receive count example, in a transmit count of 100 and a corresponding receive count
of 101. The effect here is that the A_TxLoss[n-1,n] value (for of 101. The effect here is that the A_TxLoss[n-1,n] value (for
example) for a given measurement interval will appear to be extremely example) for a given measurement interval will appear to be extremely
(if not impossibly) large. The other case, where an LM message (if not impossibly) large. The other case, where an LM message
arrives earlier than some of the packets, simply results in those arrives earlier than some of the packets, simply results in those
packets being counted as lost, which is usually what is desired. packets being counted as lost.
An implementation SHOULD identify a threshold value that indicates An implementation SHOULD identify a threshold value that indicates
the upper bound of lost packets measured in a single computation the upper bound of lost packets measured in a single computation
beyond which the interval is considered unmeasurable. This is called beyond which the interval is considered unmeasurable. This is called
the MaxLMIntervalLoss threshold. It is clear that this threshold the MaxLMIntervalLoss threshold. It is clear that this threshold
should be no higher than the maximum number of packets (or bytes) the should be no higher than the maximum number of packets (or bytes) the
channel is capable of transmitting over the interval, but it may be channel is capable of transmitting over the interval, but it may be
lower. Upon encountering an unmeasurable interval, the LM state lower. Upon encountering an unmeasurable interval, the LM state
(i.e. data values from the last LM message received) SHOULD be (i.e. data values from the last LM message received) SHOULD be
discarded. discarded.
With regard to lost LM messages, the MaxLMInterval (see Section 2.1) With regard to lost LM messages, the MaxLMInterval (see Section 2.2)
indicates the maximum amount of time that can elapse before the LM indicates the maximum amount of time that can elapse before the LM
state is discarded. If some messages are lost, but a message is state is discarded. If some messages are lost, but a message is
subsequently received within MaxLMInterval, its timestamp or sequence subsequently received within MaxLMInterval, its timestamp or sequence
number will quantify the loss, and it MAY still be used for number will quantify the loss, and it MAY still be used for
measurement, although the measurement interval will in this case be measurement, although the measurement interval will in this case be
longer than usual. longer than usual.
If an LM message is received that has a timestamp less than or equal If an LM message is received that has a timestamp less than or equal
to the timestamp of the last LM message received, this indicates that to the timestamp of the last LM message received, this indicates that
an exception has occurred, and the current interval SHOULD be an exception has occurred, and the current interval SHOULD be
considered unmeasurable unless the implementation has some other way considered unmeasurable unless the implementation has some other way
of handling this condition. of handling this condition.
4.2. Delay Measurement Procedures 4.3. Delay Measurement Procedures
4.2.1. Transmitting a Delay Measurement Query 4.3.1. Transmitting a Delay Measurement Query
When transmitting a DM Query over a channel, the Version and Reserved When transmitting a DM Query over a channel, the Version and Reserved
fields MUST be set to 0. The R flag MUST be set to 0, the T flag fields MUST be set to 0. The R flag MUST be set to 0, the T flag
MUST be set to 1, and the remaining flag bits MUST be set to 0. MUST be set to 1, and the remaining flag bits MUST be set to 0.
The Control Code field MUST be set to one of the values for Query The Control Code field MUST be set to one of the values for Query
messages listed in Section 3.1; if the channel is unidirectional, messages listed in Section 3.1; if the channel is unidirectional,
this field MUST NOT be set to 0x0 (Query: in-band response this field MUST NOT be set to 0x0 (Query: in-band response
requested). requested).
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format used by the querier when writing timestamp fields in this format used by the querier when writing timestamp fields in this
message; the possible values for this field are listed in message; the possible values for this field are listed in
Section 3.4. The Responder Timestamp Format and Responder's Section 3.4. The Responder Timestamp Format and Responder's
Preferred Timestamp Format fields MUST be set to 0. Preferred Timestamp Format fields MUST be set to 0.
The Session Identifier field can be set arbitrarily. The DS field The Session Identifier field can be set arbitrarily. The DS field
MUST be set to the traffic class being measured. MUST be set to the traffic class being measured.
The Timestamp 1 field SHOULD be set to the time at which this DM The Timestamp 1 field SHOULD be set to the time at which this DM
Query is transmitted, in the format indicated by the Querier Query is transmitted, in the format indicated by the Querier
Timestamp Format field. The other timestamp fields MUST be set to 0. Timestamp Format field. The Timestamp 2 field MUST be set to 0. If
a response was previously received in this measurement session, the
Timestamp 1 and Timestamp 2 fields of the most recent such response
MAY be copied to the Timestamp 3 and Timestamp 4 fields,
respectively, of this query; otherwise, the Timestamp 3 and Timestamp
4 fields MUST be set to 0.
4.2.2. Receiving a Delay Measurement Query 4.3.2. Receiving a Delay Measurement Query
Upon receipt of a DM Query message, the Timestamp 2 field SHOULD be Upon receipt of a DM Query message, the Timestamp 2 field SHOULD be
set to the time at which this DM Query is received. set to the time at which this DM Query is received.
At this point the DM Query message must be inspected. If the Control At this point the DM Query message must be inspected. If the Control
Code field is set to 0x2 (no response requested), a DM Response Code field is set to 0x2 (no response requested), a DM Response
message MUST NOT be transmitted. If the Control Code field is set to message MUST NOT be transmitted. If the Control Code field is set to
0x0 (in-band response requested) or 0x1 (out-of-band response 0x0 (in-band response requested) or 0x1 (out-of-band response
requested), then an in-band or out-of-band response, respectively, requested), then an in-band or out-of-band response, respectively,
SHOULD be transmitted unless this has been prevented by an SHOULD be transmitted unless this has been prevented by an
administrative, security or congestion control mechanism. administrative, security or congestion control mechanism.
4.2.3. Transmitting a Delay Measurement Response In the case of a fatal exception that prevents the requested
measurement from being made, the error SHOULD be reported, either via
a response if one was requested or else as a notification to the
user.
4.3.3. Transmitting a Delay Measurement Response
When constructing a Response to a DM Query, the Version and Reserved When constructing a Response to a DM Query, the Version and Reserved
fields MUST be set to 0. The R flag MUST be set to 1, the T flag fields MUST be set to 0. The R flag MUST be set to 1, the T flag
MUST be set to 1, and the remaining flag bits MUST be set to 0. MUST be set to 1, and the remaining flag bits MUST be set to 0.
The Session Identifier and Querier Timestamp Format (QTF) fields MUST The Session Identifier and Querier Timestamp Format (QTF) fields MUST
be copied from the DM Query. The Timestamp 1 and Timestamp 2 fields be copied from the DM Query. The Timestamp 1 and Timestamp 2 fields
from the DM Query MUST be copied to the Timestamp 3 and Timestamp 4 from the DM Query MUST be copied to the Timestamp 3 and Timestamp 4
fields, respectively, of the DM Response. fields, respectively, of the DM Response.
The Responder Timestamp Format (RTF) field MUST be set to the The Responder Timestamp Format (RTF) field MUST be set to the
timestamp format used by the responder when writing timestamp fields timestamp format used by the responder when writing timestamp fields
in this message, i.e. Timestamp 4 and (if applicable) Timestamp 1; in this message, i.e. Timestamp 4 and (if applicable) Timestamp 1;
the possible values for this field are listed in Section 3.4. the possible values for this field are listed in Section 3.4.
Furthermore, the RTF field MUST be set equal either to the QTF or the Furthermore, the RTF field MUST be set equal either to the QTF or the
RPTF field. See Section 4.2.5 for guidelines on selection of the RPTF field. See Section 4.3.5 for guidelines on selection of the
value for this field. value for this field.
The Responder's Preferred Timestamp Format (RPTF) field MUST be set The Responder's Preferred Timestamp Format (RPTF) field MUST be set
to one of the values listed in Section 3.4 and SHOULD be set to to one of the values listed in Section 3.4 and SHOULD be set to
indicate the timestamp format with which the responder can provide indicate the timestamp format with which the responder can provide
the best accuracy for purposes of delay measurement. the best accuracy for purposes of delay measurement.
The Control Code field MUST be set to one of the values for Response The Control Code field MUST be set to one of the values for Response
messages listed in Section 3.1. The value 0x10 (Unspecified Error) messages listed in Section 3.1. The value 0x10 (Unspecified Error)
SHOULD NOT be used if one of the other more specific error codes is SHOULD NOT be used if one of the other more specific error codes is
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If the response is transmitted in-band, the Timestamp 1 field SHOULD If the response is transmitted in-band, the Timestamp 1 field SHOULD
be set to the time at which this DM Response is transmitted. If the be set to the time at which this DM Response is transmitted. If the
response is transmitted out-of-band, the Timestamp 1 field MUST be response is transmitted out-of-band, the Timestamp 1 field MUST be
set to 0. In either case, the Timestamp 2 field MUST be set to 0. set to 0. In either case, the Timestamp 2 field MUST be set to 0.
If the response is transmitted in-band and the Control Code in the If the response is transmitted in-band and the Control Code in the
message is 0x1 (Success), then the Timestamp 1 and Timestamp 4 fields message is 0x1 (Success), then the Timestamp 1 and Timestamp 4 fields
MUST have the same format, which will be the format indicated in the MUST have the same format, which will be the format indicated in the
Responder Timestamp Format field. Responder Timestamp Format field.
4.2.4. Receiving a Delay Measurement Response 4.3.4. Receiving a Delay Measurement Response
Upon in-band receipt of a DM Response message, the Timestamp 2 field Upon in-band receipt of a DM Response message, the Timestamp 2 field
SHOULD be set to the time at which this DM Response is received. is set to the time at which this DM Response is received. (Since the
life of the DM message in the network has ended at this point, it is
up to the receiver whether this final modification is made to the
packet. If the message is to be forwarded on for external post-
processing (Section 2.9.7) then these modifications MUST be made.)
Upon out-of-band receipt of a DM Response message, the Timestamp 1 Upon out-of-band receipt of a DM Response message, the Timestamp 1
and Timestamp 2 fields MUST NOT be used for purposes of delay and Timestamp 2 fields MUST NOT be used for purposes of delay
measurement. measurement.
If the Control Code in a DM Response is anything other than 0x1 If the Control Code in a DM Response is anything other than 0x1
(Success), the timestamp values in the response MUST NOT be used for (Success), the timestamp values in the response MUST NOT be used for
purposes of delay measurement. When the Control Code indicates an purposes of delay measurement. If the Control Code indicates an
error condition, an appropriate notification to the user SHOULD be error condition, or if the response message is invalid, the DM
generated. operation MUST be terminated and an appropriate notification to the
user generated.
4.2.5. Timestamp Format Negotiation 4.3.5. Timestamp Format Negotiation
In case either the querier or the responder in a DM transaction is In case either the querier or the responder in a DM transaction is
capable of supporting multiple timestamp formats, it is desirable to capable of supporting multiple timestamp formats, it is desirable to
determine the optimal format for purposes of delay measurement on a determine the optimal format for purposes of delay measurement on a
particular channel. The procedures for making this determination particular channel. The procedures for making this determination
SHALL be as follows. SHALL be as follows.
Upon sending an initial DM Query over a channel, the querier sets the Upon sending an initial DM Query over a channel, the querier sets the
Querier Timestamp Format (QTF) field to its preferred timestamp Querier Timestamp Format (QTF) field to its preferred timestamp
format. format.
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to 0x2 (Notification - Data Format Invalid). to 0x2 (Notification - Data Format Invalid).
Upon receiving a DM Response, the querier knows from the RTF field in Upon receiving a DM Response, the querier knows from the RTF field in
the message whether the responder is capable of supporting its the message whether the responder is capable of supporting its
preferred timestamp format: if it is, the RTF will be equal to the preferred timestamp format: if it is, the RTF will be equal to the
QTF. The querier also knows the responder's preferred timestamp QTF. The querier also knows the responder's preferred timestamp
format from the RPTF field. The querier can then decide whether to format from the RPTF field. The querier can then decide whether to
retain its current QTF or to change it and repeat the negotiation retain its current QTF or to change it and repeat the negotiation
procedures. procedures.
4.2.5.1. Single-Format Procedures 4.3.5.1. Single-Format Procedures
When an implementation supports only one timestamp format, the When an implementation supports only one timestamp format, the
procedures above reduce to the following simple behavior: procedures above reduce to the following simple behavior:
o All DM Queries are transmitted with the same QTF; o All DM Queries are transmitted with the same QTF;
o All DM Responses are transmitted with the same RTF, and the RPTF o All DM Responses are transmitted with the same RTF, and the RPTF
is always set equal to the RTF; is always set equal to the RTF;
o All DM Responses received with RTF not equal to QTF are discarded; o All DM Responses received with RTF not equal to QTF are discarded;
o On a unidirectional channel, all DM Queries received with QTF not o On a unidirectional channel, all DM Queries received with QTF not
equal to the supported format are discarded. equal to the supported format are discarded.
4.2.6. Quality of Service 4.3.6. Quality of Service
The TC field of the LSE corresponding to the channel (e.g. LSP) The TC field of the LSE corresponding to the channel (e.g. LSP)
being measured MUST be set to the value that corresponds to the DS being measured MUST be set to the value that corresponds to the DS
field in the DM message. field in the DM message.
4.3. Combined Loss/Delay Measurement Procedures 4.4. Combined Loss/Delay Measurement Procedures
The combined LM/DM message defined in Section 3.3 allows loss and The combined LM/DM message defined in Section 3.3 allows loss and
delay measurement to be carried out simultaneously. This message delay measurement to be carried out simultaneously. This message
SHOULD be treated as an LM message which happens to carry additional SHOULD be treated as an LM message which happens to carry additional
timestamp data, with the timestamp fields processed as per delay timestamp data, with the timestamp fields processed as per delay
measurement procedures. measurement procedures.
5. Congestion Considerations 5. Implementation Disclosure Requirements
This section summarizes the requirements placed on implementations
for capabilities disclosure. The purpose of these requirements is to
ensure that end users have a clear understanding of implementation
capabilities and characteristics that have a direct impact on how
loss and delay measurement mechanisms function in specific
situations. Implementations are REQUIRED to state:
o METRICS: Which of the following metrics are supported: packet
loss, packet throughput, octet loss, octet throughput, average
loss rate, one-way delay, round-trip delay, two-way channel delay,
packet delay variation.
o MP-LOCATION: The location of loss and delay measurement points
with respect to other stages of packet processing, such as
queuing.
o CHANNEL-TYPES: The types of channels for which LM and DM are
supported, including LSP types, pseudowires, and sections (links).
o QUERY-RATE: The minimum supported query intervals for LM and DM
sessions, both in the querier and responder roles.
o LOOP: Whether loopback measurement (Section 2.8) is supported.
o LM-TYPES: Whether direct or inferred LM is supported, and for the
latter, which test protocols or proxy message types are supported.
o LM-COUNTERS: Whether 64-bit counters are supported.
o LM-ACCURACY: The expected measurement accuracy levels for the
supported forms of LM, and the expected impact of exception
conditions such as lost and misordered messages.
o LM-SYNC: The implementation's behavior in regard to the
synchronization conditions discussed in Section 2.9.8.
o LM-SCOPE: The supported LM scopes (Section 2.9.9 and
Section 4.2.8).
o DM-ACCURACY: The expected measurement accuracy levels for the
supported forms of DM.
o DM-TS-FORMATS: The supported timestamp formats and the extent of
support for computation with and reconciliation of different
formats.
6. Congestion Considerations
An MPLS network may be traffic-engineered in such a way that the An MPLS network may be traffic-engineered in such a way that the
bandwidth required both for client traffic and for control, bandwidth required both for client traffic and for control,
management and OAM traffic is always available. The following management and OAM traffic is always available. The following
congestion considerations therefore apply only when this is not the congestion considerations therefore apply only when this is not the
case. case.
The proactive generation of Loss Measurement and Delay Measurement The proactive generation of Loss Measurement and Delay Measurement
messages for purposes of monitoring the performance of an MPLS messages for purposes of monitoring the performance of an MPLS
channel naturally results in a degree of additional load placed on channel naturally results in a degree of additional load placed on
both the network and the terminal nodes of the channel. When both the network and the terminal nodes of the channel. When
configuring such monitoring, operators should be mindful of the configuring such monitoring, operators should be mindful of the
overhead involved and should choose transmit rates that do not stress overhead involved and should choose transmit rates that do not stress
network resources unduly; such choices must be informed by the network resources unduly; such choices must be informed by the
deployment context. In case of slower links or lower-speed devices, deployment context. In case of slower links or lower-speed devices,
for example, lower Loss Measurement message rates can be chosen, up for example, lower Loss Measurement message rates can be chosen, up
to the limits noted at the end of Section 2.1. to the limits noted at the end of Section 2.2.
In general, lower measurement message rates place less load on the In general, lower measurement message rates place less load on the
network at the expense of reduced granularity. For delay measurement network at the expense of reduced granularity. For delay measurement
this reduced granularity translates to a greater possibility that the this reduced granularity translates to a greater possibility that the
delay associated with a channel temporarily exceeds the expected delay associated with a channel temporarily exceeds the expected
threshold without detection. For loss measurement, it translates to threshold without detection. For loss measurement, it translates to
a larger gap in loss information in case of exceptional circumstances a larger gap in loss information in case of exceptional circumstances
such as lost LM messages or misordered packets. such as lost LM messages or misordered packets.
When carrying out a sustained measurement operation such as an LM When carrying out a sustained measurement operation such as an LM
skipping to change at page 37, line 43 skipping to change at page 43, line 41
accompanied by an appropriate notification to the user so that the accompanied by an appropriate notification to the user so that the
condition can be investigated and corrected. condition can be investigated and corrected.
From the receiver perspective, the main consideration is the From the receiver perspective, the main consideration is the
possibility of receiving an excessive quantity of measurement possibility of receiving an excessive quantity of measurement
messages. An implementation SHOULD employ a mechanism such as rate- messages. An implementation SHOULD employ a mechanism such as rate-
limiting to guard against the effects of this case. Authentication limiting to guard against the effects of this case. Authentication
procedures can also be used to ensure that only queries from procedures can also be used to ensure that only queries from
authorized devices are processed. authorized devices are processed.
6. Security Considerations 7. Security Considerations
There are three main types of security considerations associated with There are three main types of security considerations associated with
the exchange of performance monitoring messages such as those the exchange of performance monitoring messages such as those
described in this document: the possibility of a malicious or described in this document: the possibility of a malicious or
misconfigured device generating an excessive quantity of messages, misconfigured device generating an excessive quantity of messages,
causing service impairment; the possibility of unauthorized causing service impairment; the possibility of unauthorized
alteration of messages in transit; and the possibility of an alteration of messages in transit; and the possibility of an
unauthorized device learning the data contained in or implied by such unauthorized device learning the data contained in or implied by such
messages. messages.
The first consideration is discussed in Section 5. If reception or The first consideration is discussed in Section 6. If reception or
alteration of performance-related data by unauthorized devices is an alteration of performance-related data by unauthorized devices is an
operational concern, authentication and/or encryption procedures operational concern, authentication and/or encryption procedures
should be used to ensure message integrity and confidentiality. Such should be used to ensure message integrity and confidentiality. Such
procedures are outside the scope of this document, but have general procedures are outside the scope of this document, but have general
applicability to OAM protocols in MPLS networks. applicability to OAM protocols in MPLS networks.
7. IANA Considerations 8. IANA Considerations
This document makes the following requests of IANA: This document makes the following requests of IANA:
o Allocation of Channel Types in the PW Associated Channel Type o Allocation of Channel Types in the PW Associated Channel Type
registry registry
o Creation of a Measurement Timestamp Type registry o Creation of a Measurement Timestamp Type registry
o Creation of an MPLS Loss/Delay Measurement Control Code registry o Creation of an MPLS Loss/Delay Measurement Control Code registry
o Creation of an MPLS Loss/Delay Measurement Type-Length-Value (TLV) o Creation of an MPLS Loss/Delay Measurement Type-Length-Value (TLV)
Object registry Object registry
7.1. Allocation of PW Associated Channel Types 8.1. Allocation of PW Associated Channel Types
As per the IANA considerations in [RFC5586], IANA is requested to As per the IANA considerations in [RFC5586], IANA is requested to
allocate the following Channel Types in the PW Associated Channel allocate the following Channel Types in the PW Associated Channel
Type registry: Type registry:
Value Description TLV Follows Reference Value Description TLV Follows Reference
----- -------------------------------------- ----------- ------------ ----- -------------------------------------- ----------- ------------
TBD MPLS Direct Packet Loss Measurement No (this draft) TBD MPLS Direct Packet Loss Measurement No (this draft)
(DLM) (DLM)
TBD MPLS Inferred Packet Loss Measurement No (this draft) TBD MPLS Inferred Packet Loss Measurement No (this draft)
(ILM) (ILM)
TBD MPLS Packet Delay Measurement (DM) No (this draft) TBD MPLS Packet Delay Measurement (DM) No (this draft)
TBD MPLS Direct Packet Loss and Delay No (this draft) TBD MPLS Direct Packet Loss and Delay No (this draft)
Measurement (DLM+DM) Measurement (DLM+DM)
TBD MPLS Inferred Packet Loss and Delay No (this draft) TBD MPLS Inferred Packet Loss and Delay No (this draft)
Measurement (ILM+DM) Measurement (ILM+DM)
The values marked TBD are to be allocated by IANA as appropriate. The values marked TBD are to be allocated by IANA as appropriate.
7.2. Creation of Measurement Timestamp Type Registry 8.2. Creation of Measurement Timestamp Type Registry
IANA is requested to create a new Measurement Timestamp Type IANA is requested to create a new Measurement Timestamp Type
registry, with format and initial allocations as follows: registry, with format and initial allocations as follows:
Type Description Size in bits Reference Type Description Size in bits Reference
---- -------------------------------------- ------------ ------------ ---- -------------------------------------- ------------ ------------
0 Null Timestamp 64 (this draft) 0 Null Timestamp 64 (this draft)
1 Sequence Number 64 (this draft) 1 Sequence Number 64 (this draft)
2 Network Time Protocol version 4 64-bit 64 (this draft) 2 Network Time Protocol version 4 64-bit 64 (this draft)
Timestamp Timestamp
3 IEEE 1588 version 1 Timestamp 64 (this draft) 3 IEEE 1588 version 1 Timestamp 64 (this draft)
The range of the Type field is 0-15. The range of the Type field is 0-15.
7.3. Creation of MPLS Loss/Delay Measurement Control Code Registry The allocation policy for this registry is IETF Review.
8.3. Creation of MPLS Loss/Delay Measurement Control Code Registry
IANA is requested to create a new MPLS Loss/Delay Measurement Control IANA is requested to create a new MPLS Loss/Delay Measurement Control
Code registry. This registry is divided into two separate parts, one Code registry. This registry is divided into two separate parts, one
for Query Codes and the other for Response Codes, with formats and for Query Codes and the other for Response Codes, with formats and
initial allocations as follows: initial allocations as follows:
Query Codes Query Codes
Code Description Reference Code Description Reference
---- ------------------------------ ------------ ---- ------------------------------ ------------
0x0 In-band Response Requested (this draft) 0x0 In-band Response Requested (this draft)
0x1 Out-of-band Response Requested (this draft) 0x1 Out-of-band Response Requested (this draft)
0x2 No Response Requested (this draft) 0x2 No Response Requested (this draft)
Response Codes Response Codes
Code Description Reference Code Description Reference
---- ----------------------------------- ------------ ---- ----------------------------------- ------------
0x0 Reserved (this draft)
0x1 Success (this draft) 0x1 Success (this draft)
0x2 Data Format Invalid (this draft) 0x2 Data Format Invalid (this draft)
0x3 Initialization In Progress (this draft) 0x3 Initialization In Progress (this draft)
0x4 Data Reset Occurred (this draft) 0x4 Data Reset Occurred (this draft)
0x5 Resource Temporarily Unavailable (this draft)
0x10 Unspecified Error (this draft) 0x10 Unspecified Error (this draft)
0x11 Unsupported Version (this draft) 0x11 Unsupported Version (this draft)
0x12 Unsupported Control Code (this draft) 0x12 Unsupported Control Code (this draft)
0x13 Unsupported Data Format (this draft) 0x13 Unsupported Data Format (this draft)
0x14 Authentication Failure (this draft) 0x14 Authentication Failure (this draft)
0x15 Invalid Destination Node Identifier (this draft) 0x15 Invalid Destination Node Identifier (this draft)
0x16 Connection Mismatch (this draft) 0x16 Connection Mismatch (this draft)
0x17 Unsupported Mandatory TLV Object (this draft) 0x17 Unsupported Mandatory TLV Object (this draft)
0x18 Unsupported Query Interval (this draft) 0x18 Unsupported Query Interval (this draft)
0x19 Administrative Block (this draft) 0x19 Administrative Block (this draft)
0x1A Temporary Resource Exhaustion (this draft) 0x1A Resource Unavailable (this draft)
0x1B Resource Released (this draft)
0x1C Invalid Message (this draft)
0x1D Protocol Error (this draft)
IANA is also requested to indicate that the values 0x0 - 0xF in the IANA is also requested to indicate that the values 0x0 - 0xF in the
Response Code section are reserved for non-error response codes. Response Code section are reserved for non-error response codes.
The range of the Code field is 0 - 255. The range of the Code field is 0 - 255.
7.4. Creation of MPLS Loss/Delay Measurement TLV Object Registry The allocation policy for this registry is IETF Review.
8.4. Creation of MPLS Loss/Delay Measurement TLV Object Registry
IANA is requested to create a new MPLS Loss/Delay Measurement TLV IANA is requested to create a new MPLS Loss/Delay Measurement TLV
Object registry, with format and initial allocations as follows: Object registry, with format and initial allocations as follows:
Type Description Reference Type Description Reference
------- --------------------------------- ------------ ------- --------------------------------- ------------
0 Padding - copy in response (this draft) 0 Padding - copy in response (this draft)
1 Return Address (this draft) 1 Return Address (this draft)
2 Session Query Interval (this draft) 2 Session Query Interval (this draft)
3 Loopback Request (this draft)
120-127 Implementation-specific usage (this draft) 120-127 Implementation-specific usage (this draft)
128 Padding - do not copy in response (this draft) 128 Padding - do not copy in response (this draft)
129 Destination Address (this draft) 129 Destination Address (this draft)
130 Source Address (this draft) 130 Source Address (this draft)
248-255 Implementation-specific usage (this draft) 248-255 Implementation-specific usage (this draft)
IANA is also requested to indicate that Types 0-127 are classified as IANA is also requested to indicate that Types 0-127 are classified as
Mandatory, and that Types 128-255 are classified as Optional. Mandatory, and that Types 128-255 are classified as Optional.
The range of the Type field is 0 - 255. The range of the Type field is 0 - 255.
8. Acknowledgments The allocation policy for this registry is IETF Review, except for
the ranges marked "Implementation-specific usage", for which the
policy is Private Use.
9. Acknowledgments
The authors wish to thank the many participants of the MPLS working The authors wish to thank the many participants of the MPLS working
group who provided detailed review and feedback on this document. group who provided detailed review and feedback on this document.
The authors offer special thanks to Alexander Vainshtein, Loa The authors offer special thanks to Alexander Vainshtein, Loa
Andersson, and Hiroyuki Takagi for many helpful thoughts and Andersson, and Hiroyuki Takagi for many helpful thoughts and
discussions, and to Linda Dunbar for the idea of using LM messages discussions, to Linda Dunbar for the idea of using LM messages for
for throughput measurement. throughput measurement, and to Ben Niven-Jenkins, Marc Lasserre, and
Ben Mack-Crane for their valuable comments.
9. References 10. References
9.1. Normative References 10.1. Normative References
[IEEE1588] [IEEE1588]
IEEE, "1588-2008 IEEE Standard for a Precision Clock IEEE, "1588-2008 IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and Synchronization Protocol for Networked Measurement and
Control Systems", March 2008. Control Systems", March 2008.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997. Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black, [RFC2474] Nichols, K., Blake, S., Baker, F., and D. Black,
skipping to change at page 42, line 5 skipping to change at page 48, line 25
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, February 2009. Class" Field", RFC 5462, February 2009.
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic [RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009. Associated Channel", RFC 5586, June 2009.
[RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network [RFC5905] Mills, D., Martin, J., Burbank, J., and W. Kasch, "Network
Time Protocol Version 4: Protocol and Algorithms Time Protocol Version 4: Protocol and Algorithms
Specification", RFC 5905, June 2010. Specification", RFC 5905, June 2010.
9.2. Informative References 10.2. Informative References
[RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way [RFC2679] Almes, G., Kalidindi, S., and M. Zekauskas, "A One-way
Delay Metric for IPPM", RFC 2679, September 1999. Delay Metric for IPPM", RFC 2679, September 1999.
[RFC2681] Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip [RFC2681] Almes, G., Kalidindi, S., and M. Zekauskas, "A Round-trip
Delay Metric for IPPM", RFC 2681, September 1999. Delay Metric for IPPM", RFC 2681, September 1999.
[RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V., [RFC3209] Awduche, D., Berger, L., Gan, D., Li, T., Srinivasan, V.,
and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP and G. Swallow, "RSVP-TE: Extensions to RSVP for LSP
Tunnels", RFC 3209, December 2001. Tunnels", RFC 3209, December 2001.
skipping to change at page 42, line 45 skipping to change at page 49, line 17
"Bidirectional Forwarding Detection (BFD) for MPLS Label "Bidirectional Forwarding Detection (BFD) for MPLS Label
Switched Paths (LSPs)", RFC 5884, June 2010. Switched Paths (LSPs)", RFC 5884, June 2010.
[RFC5921] Bocci, M., Bryant, S., Frost, D., Levrau, L., and L. [RFC5921] Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
Berger, "A Framework for MPLS in Transport Networks", Berger, "A Framework for MPLS in Transport Networks",
RFC 5921, July 2010. RFC 5921, July 2010.
[RFC5960] Frost, D., Bryant, S., and M. Bocci, "MPLS Transport [RFC5960] Frost, D., Bryant, S., and M. Bocci, "MPLS Transport
Profile Data Plane Architecture", RFC 5960, August 2010. Profile Data Plane Architecture", RFC 5960, August 2010.
[Y.1731] ITU-T Recommendation Y.1731, "OAM Functions and Mechanisms
for Ethernet based Networks", February 2008.
Appendix A. Default Timestamp Format Rationale
This document initially proposed the Network Time Protocol (NTP)
timestamp format as the mandatory default, as this is the normal
default timestamp in IETF protocols and thus would seem the "natural"
choice. However a number of considerations have led instead to the
specification of the truncated IEEE1588 Precision Time Protocol (PTP)
timestamp as the default. NTP has not gained traction in industry as
the protocol of choice for high quality timing infrastructure, whilst
IEEE1588 PTP has become the de facto time transfer protocol in
networks which are specially engineered to provide high accuracy time
distribution service. The PTP timestamp format is also the ITU-T
format of choice for packet transport networks, which may rely on
MPLS protocols. Applications such as one-way delay measurement need
the best time service available, and converting between the NTP and
PTP timestamp formats is not a trivial transformation, particularly
when it is required that this be done in real time without loss of
accuracy.
The truncated IEEE1588 PTP format specified in this document is
considered to provide a more than adequate wrap time and greater time
resolution than it is expected will be needed for the operational
lifetime of this protocol. By truncating the timestamp at both the
high and low order bits, the protocol achieves a worthwhile reduction
in system resources.
Authors' Addresses Authors' Addresses
Dan Frost Dan Frost
Cisco Systems Cisco Systems
Email: danfrost@cisco.com Email: danfrost@cisco.com
Stewart Bryant Stewart Bryant
Cisco Systems Cisco Systems
Email: stbryant@cisco.com Email: stbryant@cisco.com
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