SFC Working Group G. Mirsky
Internet-Draft ZTE Corp.
Intended status: Standards Track G. Fioccola
Expires: October 25, 2017 Telecom Italia
April 23, 2017
Performance Measurement (PM) with Alternate Marking Method in Service
Function Chaining (SFC) Domain
draft-mirsky-sfc-pmamm-00
Abstract
This document describes how the alternate marking method be used as
the passive performance measurement method in a Service Function
Chaining (SFC) domain.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 2
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 2
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. Mark Field in NSH Base Header . . . . . . . . . . . . . . . . 3
4. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 4
4.1. Single Mark Enabled Measurement . . . . . . . . . . . . . 4
4.2. Double Mark Enabled Measurement . . . . . . . . . . . . . 5
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 5
6. Security Considerations . . . . . . . . . . . . . . . . . . . 6
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 6
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 6
8.1. Normative References . . . . . . . . . . . . . . . . . . 6
8.2. Informative References . . . . . . . . . . . . . . . . . 6
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
[RFC7665] introduced architecture of a Service Function Chain (SFC)
in the network and defined its components as classifier, Sevice
Function Forwarder (SFF), and Service Function (SF).
[I-D.ietf-ippm-alt-mark] describes passive performance measurement
method, which can be used to measure packet loss, latency and jitter
on live traffic. Because this method is based on marking consecutive
batches of packets the method often referred as Alternate Marking
Method (AMM).
This document defines how the alternate marking method can be used to
measure packet loss and delay metrics of a service flow over e2e or
any segment of the SFC.
2. Conventions used in this document
2.1. Terminology
MM: Marking Method
OAM: Operations, Administration and Maintenance
SFC: Service Function Chain
SF: Service Function
SFF: Service Function Forwarder
SFP: Service Function Path
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2.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in
[RFC2119].
3. Mark Field in NSH Base Header
[I-D.ietf-sfc-nsh] defines format of the Network Service Header
(NSH). The format of NSH Base is presented in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Ver|O|R| TTL | Length |R|R|R|R|MD Type| Proto |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: NSH Base format
This document defines two bit long field, referred as Mark field, as
part of NSH Base and designated for the alternate marking performance
measurement method [I-D.ietf-ippm-alt-mark]. The Mark field MUST NOT
be used in defining forwarding and/or quality of service treatment of
a SFC packet. The Mark field MUST be used only for the performance
measurement of data traffic in SFC layer. Because setting of the
field to any value does not affect forwarding and/or quality of
service treatment of a packet, the alternate marking method in SFC
layer can be viewed as true example of passive performance
measurement method.
The Figure 2 displays format of the Mark field.
0
0 1
+-+-+-+-+
| S | D |
+-+-+-+-+
Figure 2: Mark field format
where:
o S- Single mark method;
o D - Double mark method.
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4. Theory of Operation
The marking method can be successfully used in the SFC. Without
limiting any generality consider SFC presented in Figure 3. Any
combination of markings, Loss and/or Delay, can be applied to a
service flow by any component of the SFC at either ingress or egress
point to perform node, link, segment or end-to-end measurement to
detect performance degradation defect and localize it efficiently.
+---+ +---+ +---+ +---+ +---+ +---+
|SF1| |SF2| |SF3| |SF4| |SF5| |SF6|
+---+ +---+ +---+ +---+ +---+ +---+
\ / \ / \ /
+----------+ +----+ +----+ +----+
|Classifier|---|SFF1|---------|SFF2|---------|SFF3|
+----------+ +----+ +----+ +----+
Figure 3: SFC network
Using the marking method a component of the SFC creates distinct sub-
flows in the particular service traffic over SFC. Each sub-flow
consists of consecutive blocks that are unambiguously recognizable by
a monitoring point at any component of the SFC and can be measured to
calculate packet loss and/or packet delay metrics.
4.1. Single Mark Enabled Measurement
As explained in the [I-D.ietf-ippm-alt-mark], marking can be applied
to delineate blocks of packets based either on equal number of
packets in a block or based on equal time interval. The latter
method offers better control as it allows better account for
capabilities of downstream nodes to report statistics related to
batches of packets and, at the same time, time resolution that
affects defect detection interval.
If the Single Mark measurement used, then the D flag MUST be set to
zero on transmit and ignored by monitoring point.
The S flag is used to create alternate flows to measure the packet
loss by switching value of the S flag every N-th packet or at certain
time intervals. Delay metrics MAY be calculated with the alternate
flow using any of the following methods:
o First/Last Packet Delay calculation: whenever the marking, i.e.
value of S flag, changes a component of the SFC can store the
timestamp of the first/last packet of the block. The timestamp
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can be compared with the timestamp of the packet that arrived in
the same order through a monitoring point at downstream component
of the SFC to compute packet delay. Because timestamps collected
based on order of arrival this method is sensitive to packet loss
and re-ordering of packets
o Average Packet Delay calculation: an average delay is calculated
by considering the average arrival time of the packets within a
single block. A component of the SFC may collect timestamps for
each packet received within a single block. Average of the
timestamp is the sum of all the timestamps divided by the total
number of packets received. Then difference between averages
calculated at two monitoring points is the average packet delay on
that segment. This method is robust to out of order packets and
also to packet loss (only a small error is introduced). This
method only provides single metric for the duration of the block
and it doesn't give the minimum and maximum delay values. This
limitation could be overcome by reducing the duration of the block
by means of an highly optimized implementation of the method.
4.2. Double Mark Enabled Measurement
Double Mark method allows measurement of minimum and maximum delays
for the monitored flow but it requires more nodal and network
resources. If the Double Mark method used, then the S flag MUST be
used to create the alternate flow, i.e. mark larger batches of
packets. The D flag MUST be used to mark single packets to measure
delay jitter.
The first marking (S flag alternation) is needed for packet loss and
also for average delay measurement. The second marking (D flag is
put to one) creates a new set of marked packets that are fully
identified over the SFC, so that a componenet can store the
timestamps of these packets; these timestamps can be compared with
the timestamps of the same packets on another component of the SFC to
compute packet delay values for each packet. The number of
measurements can be easily increased by changing the frequency of the
second marking. But the frequency of the second marking must be not
too high in order to avoid out of order issues. This method is
useful to have not only the average delay but also the minimum and
maximum delay values and, in wider terms, to know more about the
statistic distribution of delay values.
5. IANA Considerations
This document requests IANA to register format of the OAM field of
NSH as the following:
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+--------------+---------+--------------------------+---------------+
| Bit Position | Marking | Description | Reference |
+--------------+---------+--------------------------+---------------+
| 0 | S | Single Mark Measurement | This document |
| 1 | D | Double Mark Measurement | This document |
+--------------+---------+--------------------------+---------------+
Table 1: OAM field of BIER Header
6. Security Considerations
This document lists the OAM requirement for SFC domain and does not
raise any security concerns or issues in addition to ones common to
networking and SFC.
7. Acknowledgement
TBD
8. References
8.1. Normative References
[I-D.ietf-sfc-nsh]
Quinn, P. and U. Elzur, "Network Service Header", draft-
ietf-sfc-nsh-12 (work in progress), February 2017.
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<http://www.rfc-editor.org/info/rfc7665>.
8.2. Informative References
[I-D.ietf-ippm-alt-mark]
Fioccola, G., Capello, A., Cociglio, M., Castaldelli, L.,
Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi,
"Alternate Marking method for passive performance
monitoring", draft-ietf-ippm-alt-mark-04 (work in
progress), March 2017.
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Authors' Addresses
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
Giuseppe Fioccola
Telecom Italia
Email: giuseppe.fioccola@telecomitalia.it
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