SFC Working Group G. Mirsky
Internet-Draft ZTE Corp.
Intended status: Standards Track G. Fioccola
Expires: December 24, 2018 Telecom Italia
T. Mizrahi
June 22, 2018

Performance Measurement (PM) with Alternate Marking Method in Service Function Chaining (SFC) Domain


This document describes how the alternate marking method be used as the passive performance measurement method in a Service Function Chaining (SFC) domain.

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Table of Contents

1. Introduction

[RFC7665] introduced architecture of a Service Function Chain (SFC) in the network and defined its components as classifier, Service Function Forwarder (SFF), and Service Function (SF). [RFC8321] 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 to 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

NSH: Network Service Header

2.2. Requirements Language

The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in BCP 14 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.

3. Mark Field in NSH Base Header

   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  | M |R|R|MD Type|     Proto     |

Figure 1: NSH Base format

[RFC8300] defines the format of the Network Service Header (NSH). Figure 1, as part of NSH Base and designated for the alternate marking performance measurement method [RFC8321]. The Mark field MUST NOT be used in defining forwarding and/or quality of service treatment of an SFC packet. The Mark field MUST be used only for the performance measurement of data traffic in SFC layer. Because the 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 a true example of passive performance measurement method.

The Figure 2 displays format of the Mark field.

 0   1 
| L | D |

Figure 2: Mark field format

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|
                +---+  +---+   +---+  +---+   +---+  +---+
                   \   /          \  /           \  /    
   +----------+   +----+         +----+         +----+    
   +----------+   +----+         +----+         +----+           

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 [RFC8321], marking can be applied to delineate blocks of packets based either on the 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 Delay flag Figure 2 MUST be set to zero on transmit and ignored on reception by monitoring point.

The Loss flag is used to create alternate flows to measure the packet loss by switching the value of the Loss 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:

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 Loss flag MUST be used to create the alternate flow, i.e. mark larger batches of packets. The Delay flag MUST be used to mark single packets to measure delay jitter.

The first marking (Loss flag alternation) is needed for packet loss and also for average delay measurement. The second marking (Delay flag is put to one) creates a new set of marked packets that are fully identified over the SFC, so that a component 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 supports calculation of 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.

4.3. Residence Time Measurement with the Alternate Marking Method

Residence time is the variable part of the propagation delay that a packet experiences traversing a network, e.g. SFC. Residence Time over an SFC is the sum of the nodal residence times, i.e. periods that the packet spent in each of SFFs that compose the SFC. The nodal residence time in SFC itself is the sum of sub-nodal residence times that the packet spent in each of SFs that are part of the given SFC and are mapped to the SFF. The residence time and deviation of the residence time metrics may include any combination of minimum, maximum, values over measurement period, as well as mean, median, percentile. These metrics may be used to evaluate the performance of the SFC and its elements before and during its operation.

Use of the specially marked packets simplifies residence time measurement and correlation of the measured metrics over the SFC end-to-end. For example, the alternate marking method may be used as described in Section 4.2 to identify packets in the data flow to be used to measure the residence time. The nodal and sub-nodal residence time metrics can be locally calculated and then collected using either in-band or out-band OAM mechanisms.

5. IANA Considerations

5.1. Mark Field in NSH Base Header

This document requests IANA to allocate Mark field as two bits-long field from NSH Base Header Reserved Bits [RFC8300].

This document requests IANA to register values of the Mark field of NSH as the following:

Mark field of SFC NSH
Bit Position Marking Description Reference
Single Mark Measurement  This document
Double Mark Measurement  This document

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. Acknowledgment


8. References

8.1. Normative References

[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[RFC8300] Quinn, P., Elzur, U. and C. Pignataro, "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, January 2018.

8.2. Informative References

[RFC7665] Halpern, J. and C. Pignataro, "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015.
[RFC8321] Fioccola, G., Capello, A., Cociglio, M., Castaldelli, L., Chen, M., Zheng, L., Mirsky, G. and T. Mizrahi, "Alternate-Marking Method for Passive and Hybrid Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321, January 2018.

Authors' Addresses

Greg Mirsky ZTE Corp. EMail: gregimirsky@gmail.com
Giuseppe Fioccola Telecom Italia EMail: giuseppe.fioccola@telecomitalia.it
Tal Mizrahi Marvell 6 Hamada St. Yokneam, Israel EMail: talmi@marvell.com