Performance Measurement (PM) with Marking Method in Bit Index Explicit Replication (BIER) LayerZTE Corp.gregimirsky@gmail.comHuawei Technologiesvero.zheng@huawei.comHuawei Technologiesmach.chen@huawei.comTelecom Italiagiuseppe.fioccola@telecomitalia.it
Routing
BIER Working GroupInternet-DraftBIEROAMPerformance Measurement
This document describes a hybrid performance measurement method
for multicast service over Bit Index Explicit Replication (BIER) domain.
introduces and explains Bit Index Explicit Replication (BIER)
architecture and how it supports forwarding of multicast data packets.
specified that in
case of BIER encapsulation in MPLS network a BIER-MPLS label, label that is at the bottom of the label stack,
uniquely identifies the multicast flow.
describes hybrid performance measurement method, per
classification of measurement methods.
Packet Network Performance Monitoring (PNPM), 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 Marking Method (MM).
This document defines how marking method can be used on BIER layer to measure packet loss and delay metrics
of a multicast flow in MPLS network.
BFR: Bit-Forwarding Router BFER: Bit-Forwarding Egress RouterBFIR: Bit-Forwarding Ingress RouterBIER: Bit Index Explicit ReplicationMM: Marking Method OAM: Operations, Administration and Maintenance
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.
defined two bit long field, referred as OAM, designated
for the marking performance measurement method. The OAM field MUST NOT be used in defining forwarding
and/or quality of service treatment of a BIER packet. The OAM field MUST be used only for the
performance measurement of data traffic in BIER layer. Because setting of the field to any value does not affect
forwarding and/or quality of service treatment of a packet, the marking method in BIER layer can be viewed as
example of hybrid performance measurement method.
The displays format of the OAM field
where:
L - Loss flag;
D - Delay flag.
The marking method can be successfully used in the multicast environment supported by BIER layer.
Without limiting any generality consider multicast network presented in .
Any combination of markings, Loss and/or Delay, can be applied to a multicast flow by
any Bit Forwarding Router (BFR) 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.
Using the marking method a BFR creates distinct sub-flows in the particular multicast traffic
over BIER layer. Each sub-flow consists of consecutive blocks that are unambiguously
recognizable by a monitoring point at any BFR and can be measured to calculate packet loss
and/or packet delay metrics.
As explained in the , 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 to measure pcket loss, then the D flag MUST be set to zero on transmit and ignored
by monitoring point.
The L flag is used to create alternate flows to measure the packet loss by switching value
of the L 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:
First/Last Packet Delay calculation: whenever the marking, i.e. value of L flag, changes
a BFR 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 downstream BFR to compute packet delay.
Because timestamps collected based on 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 average
arrival time of the packets within a single block. A BFR 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.
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 L 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 (L 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 BIER network, so that a BFR can store the timestamps of these
packets; these timestamps can be compared with the timestamps of the
same packets on a second BFR 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.
This document requests IANA to register format of the OAM field of BIER Header as the following:
Bit PositionMarkingDescriptionReference0 S Single Mark Measurement This document1 D Double Mark Measurement This document
This document list the OAM requirement for BIER-enabled domain
and does not raise any security concerns or issues in addition to ones common to networking.
TBD