Dominik Schneuwly discussed the value of in-service synchronization monitoring and probing, as well as the increasingly important role of network functions virtualization at ITSF 2016.

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In-Service Monitoring of PTP
Performance
Dominik Schneuwly, 24th October 2016

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Outline
•
Introduction
•
Sampling the Network Sites
•
Probing Techniques
•
Reduction of Data Quantity
•
Easy-to-Use Representation of Results
•
Conclusion and Outlook

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What Are We Talking About?
• Purpose: Monitor the performance of network in real
time, raise an alarm when an action for preserving the
performance is required
• Means:
• Permanent installation of sync probes in selected sites
• Continous collection of measurement results
• Anaysis and consolidation of the results into a form
which is useful to the network operator (operations

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Sync Probing Infrastructure
NENENENENENE GM
GNSS
NE
Probe
GNSS
Probe
GNSS
Probe
GNSS
eNode B
Probe
GNSS
Data Base
Analysis
Presentation
Data collection
channel

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Sync Probing Infrastructure
•
Probe: Tool located in the network for the acquisition of measured
data
• Challenge: Density of probes vs cost
•
Data collection channel:
• Challenge: Limitation of used traffic data rate (bandwidth)
•
Data base: Storage of measured data
• Challenge: Limitation of stored data quantity
•
Analysis: Processing of the measured data and automatic
interpretation
•

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Sampling the Network Sites
•
Sampling: Choosing a reasonable number of probe installation
sites
•
Two questions:
• How many? Depends on gain/cost ratio - see upcoming slides
• Where? Adopt a sampling strategy!
•
Sampling strategies:
• Random
• Worst case sites, i.e. cell sites
• Impact-based: privilege sites where bad performance has strong impact
• Witness path: take a representative path and probe on all sites along
the path

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Sampling Strategy: Cell Sites
S
S S
S
S
S
S
S
S
S
S
S
S
S S
S
S S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
GM
GNSS
Probe
GNSS
Probe
GNSS
Pro be
GNSS
Probe
GNSS
Probe
GNSS
Probe
GNSS

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Sampling Strategy: BC / APTSC Sites
S
S S
S
S
S
S
S
S
S
S
S
S
S S
S
S S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
GM
GNSS
Probe
GNSS
Pro be
GNSS
Pro be
GNSS
Probe
GNSS
Probe
GNSS

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Sampling Strategy: Along a Path
N
max│TE│
eNode BNENENENENENENE
Probe
GNSS
Probe
GNSS
Probe
GNSS
Probe
GNSS
1.1 μs
At different times of the day, i.e. with different traffic loads
GM
GNSS
NE

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Probing a Slave Clock – Physical Output
4
Slave’s physical output signal can be monitored vs. GNSS
GNSS
Slave Clock
(DUT)
T1
T4 T3
10 MHz/BITS/SyncE
T1
T4 T3
1PPS
T-GM
Network
CLK TIE and 1PPS Time
Error
CLK and 1PPS MTIE
Sync Probe

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T1
T4
Probing a Slave Clock – Passive Probing
GNSS
Slave Clock
(DUT)
T3
T1
T4
T3
T3
Packet MTIE
Packet Time Error
T-GM
Network
Sync Probe
•
The sync probe is placed at a calibrated distance from the slave clock
•
The sync probe functions as a passive PTP probe (fiber tapping or mirroring switch)
•
Probing is based on T3 embedded in the PTP delay request messages

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Probing a Boundary Clock – Active Probing
• The sync probe is placed at a calibrated distance from the master port of the
boundary clock
•
The sync probe functions as slave clock and performs measurements at the same
time (active PTP probe)
• Probing is based on T1 & T4 embedded in the PTP sync messages
Boundary
Clock
(DUT)
Slave Clock
T1
T4 T3
T1 T4
T3
T1
T4
Packet MTIE
Time Error
T3
T-GM
GNSS
Sync Probe

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T1
T4
Probing a Boundary Clock – Passive Probing
Boundary
Clock
(DUT)
Slave Clock
T3
T1
T4
T3
T1
Packet MTIE
Packet Time Error
T-GM
GNSS
Sync Probe
•
The sync probe is placed at a calibrated distance from the master port of the
boundary clock
•
The sync probe functions as passive PTP probe (fiber tapping or mirroring switch)
•
Probing is based on T1 & T4 embedded in the PTP sync messages

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Distribution of Data Processing
•
How much data processing in the probe?
•
How much data processing in the analyzer?
•
Has an impact on:
• Total cost of N probes
• Cost of analyzer
• Quantity of data to be transfered (from probes to data base) and stored
(in data base)
Metric
calculation
InterpretationPre-processing
2way
TE
calculation
TEFWD
TEREV
e.g.:
peak-to-peak
MTIE
etc.
e.g.:
comparing with
mask
e.g.:
packet selection

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Distribution of Data Processing
•
System cost (CAPEX)
vs cost of traffic
bandwith (OPEX)
•
Typical optimization
problem seen in
network function
virtualization (NFV)
•
General tendency in
NFV: centralizing
processing functions
•
Sync probing is getting
more accessible
All in
Probe
All in
Analyzer
Traffic
bandwidth
Equipment
Cost
CostofnProbes
CostofAnalyzer

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Presentation of the Results
•
An easy-to-use presentation is key!
•
Must help in deciding corrective actions
•
Examples:

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What to Do With the Results
Presentation of the results is action-oriented; two action fields:
•
Operations and maintenance:
• Act upon configurable parameters, software, etc.
• E.g., traffic engineering, QoS, load balancing, adapting packet rates,
adapting flow networking, etc.
• Repairs
• Short term (minutes, hours)
• OPEX related
•
Network expansion:

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Conclusion and Outlook
•
In-service monitoring of sync complements the supply of sync
•
In-service monitoring of sync is as necessary as ever
•
Miniaturization and advanced data processing make sync probing
more accessible
•
Network function virtualization (NFV) will play an increasingly
important role

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Thank You
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