Performance Measurement (PM) with Alternate Marking Method in Service Function Chaining (SFC) Network Service Header (NSH) DomainEricssongregimirsky@gmail.comHuawei Technologiesgiuseppe.fioccola@huawei.comHuawei Network.IO Innovation LabIsraeltal.mizrahi.phd@gmail.com
Routing
IPPM Working GroupInternet-DraftSFCNSHOAMPerformance Measurement
This document describes how the alternate marking method can be used
as the efficient performance measurement method taking advantage of the actual data flows
in a Service Function Chaining domain using Network Service Header encapsulation.
Introduction introduced the architecture of a Service Function
Chain (SFC) in the network and defined its components. These include Classifier,
Service Function Forwarder (SFF), Service Function (SF), and Service Function proxy.
provides a reference framework for Operations,
Administration and Maintenance (OAM) for SFC.
describes the hybrid 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 procedure is often referred to as Alternate Marking Method (AMM).
This document defines how packet loss and delay metrics
of a service flow over end-to-end (E2E) Service Function Path (SFP) or any SFP segment can be measured using AMM.
This document is aligned with the SFC OAM Performance Measurement
requirements defined in . It states that any SFC-aware network device
must have the ability to perform loss and delay measurements over the service function chain as a unit,
i.e., E2E, or to a specific segment of service function through the SFC. Besides, AMM
can be used in combination with complementing it in achieving the
SFC performance measurement objective with Network Service Header data plane.
Conventions used in this documentAcronymsAMM: Alternate Marking Method OAM: Operations, Administration and MaintenanceSFC: Service Function ChainSFP: Service Function PathSF: Service FunctionSFF: Service Function ForwarderSPI: Service Path IdentifierNSH: Network Service HeaderE2E end-to-endRequirements 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
when, and only when, they appear in all capitals, as shown here.
Mark Field in NSH Base Header defines the format of the Network Service Header (NSH).
This document defines the one-bit long field, referred to as Mark field (M in ,
as part of NSH Base and designated
for the alternate marking performance measurement method . The Mark field MUST be set to
0 at initialization of NSH and ignored on the receipt when the method is not in use.
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 the SFC layer. Though the setting of the field to any value likely not affect
forwarding and/or quality of service treatment of a packet, the alternate marking method in the SFC layer is characterized as
an example of a hybrid performance measurement method according to .
Theory of Operation
The marking method can be successfully used in the SFC.
Without limiting any generality consider SFC presented in .
Any combination of markings, Loss and/or Delay, can be applied to a service flow by
any SFC component at either ingress or egress point
to perform node, link, segment, or E2E measurement to detect
performance degradation defects and localize them efficiently.
An SFP might include a Re-classifier. Processing of an SFC packet by the Re-classifier might result in
that packet being directed to a different SFP identified, for example, by Service Path Identifier's (SPI) value A'.
In that case, the Re-classifier MUST set the value of the Mark field
according to the local AMM policy defined for the SPI's value A'. Note that the default
AMM policy is to set the value of the Mark field to 0.
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.
Single Mark Enabled Measurement
As explained in the , marking can be
applied to delineate blocks of packets
based either on the equal number of packets in a block or based on the same time interval.
The latter method offers better control
as it allows a 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.
The Mark flag is used to create distinctive flows to measure the packet loss by
switching the value of the Mark flag every N-th packet or at specified time intervals.
Delay metrics MAY be calculated with the alternate flow using any of the
following methods:
First/Last Packet Delay calculation: whenever the marking, i.e., the value
of Mark flag changes a component of the SFC can store the timestamp of the first/last
packet of the block. The timestamp can be compared with the timestamp of the
packet that arrived in the same order through a monitoring
point at a downstream component of the SFC to compute packet delay. Because
timestamps collected based on the order of arrival, this method is sensitive to packet
loss and re-ordering of packets
Average Packet Delay calculation: an average delay is calculated by
considering the packets' average arrival time within a single block.
A component of the SFC may collect timestamps for each packet received within
a single block. The timestamp average is the sum of all the timestamps
divided by the total number of packets received. Then the 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
packet loss (only a small error is introduced). This method only provides
a single metric for the duration of the block, and it doesn't give the minimum
and maximum delay values. Highly optimized implementation of the method
can reduce the duration of the block and thus overcome the limitation.
Multiplexed Mark Enabled Measurement
There is also a scheme that method allows measurement of minimum and maximum delays for the monitored flow
using a single marking flag. This methodology is
described in . The
concept is that in the middle of each block of packets with a certain
value of the M flag, a single packet has the M flag inverted. By
examining the stream, the packets with the inverted bit can be easily
identified and employed for delay measurement. This variation of AMM
is advantageous because it requires only one bit
from each packet, and such bits are always in short supply.
Residence Time Measurement with the Alternate Marking Method
Residence time is the variable part of the propagation delay that a packet experiences while 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 SFF that
composes 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 the measurement period.
It also may include mean, median, and percentiles calculated values. 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 E2E SFC. For example,
AMM may be used as described in 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.
IANA ConsiderationsMark Field in NSH Base HeaderThis document requests IANA to allocate the one-bit field from NSH Base Header Bits as the Mark field of NSH as the following:
Mark field of SFC NSH
Bit Position
Description
Reference
TBA
Mark field
This document
Security Considerations
This document defines the use of AMM in an SFC domain and thus all security considerations
specific to SFC discussed in and are applicable.
By introducing AMM into the SFC environment, it inherits all security considerations discussed in .
A new Mark flag is defined in this specification to be used by AMM. Processing of
AMM does require additional computational resources and creates a certain amount
of state information per AMM flow performance metrics. An implementation MUST provide control over the number
of concurrent AMM flows that a node process.
Acknowledgment
TBD
ReferencesNormative ReferencesInformative References