Evolution of IP/OL Performance
Management
Robert Doverspike, Jennifer Yates, Jorge Pastor,
Martin Birk – AT&T Labs Research
AT&T Labs Research
Outline
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Key Takeaways
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•
Performance Management – must consider interlayer
(focus IP)
Evolution story for IP/OL
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Architecture for Long Haul Networks
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Example problems
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Next chapter in evolution
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Page 2
Let’s get it right this time
AT&T Labs Research
Title
Key Takeaways
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Optical PM goals should focus on use in IP layer
– Links in the IP layer form connections in the optical layer
– Virtually all high rate connections are IP links (between
either routers or Ethernet switches)
Perfect optical layer detection is a lofty goal, but
– will fall short if architected in isolation
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E.g., need to have strong inter-layer coordination
Why do we stress this for OL?
– Inter-layer fault management has many flaws in practice,
even after 15 years of SONET perfecting
– Need adequate mechanisms across layers to handle
scenarios when things go wrong or confusion reigns
Page 3
AT&T Labs Research
Title
Evolution Story for Long Haul Networks
IP Layer
1st Generation
SONET Ring
Layer
Pt-Pt WDM Layer
Router
DCS/Intelligent Optical Switch
ADM
Degree-n OADM/WXC
Page 4
WDM Terminal
AT&T Labs Research
Title
Evolution Story for Long Haul Networks
IP Layer
1st Generation
SONET Ring
Layer
DCS Layer
Pt-Pt WDM Layer
Router
DCS/Intelligent Optical Switch
ADM
Degree-n OADM/WXC
Page 5
WDM Terminal
AT&T Labs Research
Title
Evolution Story for Long Haul Networks
IP Layer
2nd Generation
1st Generation
SONET Ring
Layer
ULH/WXC Layer
Pt-Pt WDM Layer
Router
DCS/Intelligent Optical Switch
ADM
Degree-n OADM/WXC
Page 6
WDM Terminal
AT&T Labs Research
Title
Evolution Story for Long Haul Networks
IP Layer
1st
Generation
3rd Generation
2nd Generation
SONET Ring
Layer
ULH/WXC Layer
Pt-Pt WDM Layer
Router
DCS/Intelligent Optical Switch
ADM
Degree-n OADM/WXC
Page 7
WDM Terminal
AT&T Labs Research
Title
Some of the problems we’ve encountered
IP Layer
X
SONET Ring
Layer
Ring switching impact on higher layers
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Upper layer has timer – waits for lower layer to restore – Done!
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Wrong! – not a simple decision on when to take IP link up and down
Page 8
AT&T Labs Research
Title
Some of the problems we’ve encountered
1st Generation of IP/OL
IP Layer
PPP ACK; OSPF ping 
AIS-P
BER-P
CLR
SONET Ring
Layer
•
 AIS-P
X LOS-L 
AIS-P
BER-P
CLR
 LOS-L
SONET alarms received by upper layer are ambiguous and conflicting
•
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Many error types in SONET: BER, AIS, P-LOS, clear during protection
switching
Arrive at different times
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Software bugs – routers don’t behave as expected
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Inconsistencies in calculation of BER and IP layer holddown timer
Page 9
AT&T Labs Research
Title
What is the source of these problems?
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No standards for inter-layer interaction
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Physical layer: testers need requirement scripts to test – no
standard, no script
No industry requirement often means no testing, no sharing
of behavior
Historically, L1 and L3 labs have been separate
•
–
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Some members of Telecom community have integrated their
labs
Software bugs – routers don’t behave as expected
No specification of common parameters and metric
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•
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Example: Router measures BER in fixed timer intervals
Router takes link down upon TCA (threshold exceeded)
Protection switching results in VERY short but high burst of
error  Crosses router threshold even though it is << 10 ms!
Page 10
AT&T Labs Research
Title
What is the source of these problems?
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Shared Risk Groups still not well modeled
– Single failure at lower layer results in multiple, scattered link failures at
higher layer – network unprepared to restore
– Example: portions of dual IP access links routed over same ring – both
links taken down due to previous confusion
LA
NY
SF
Washington
IP (logical) layer
Physical (fibre) layer
LA
NY
SF
Washington
Common SRLG
Page 11
AT&T Labs Research
Title
Identity Crisis
2nd Generation of IP/OL
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High speed (2.5/10/40Gbs) IP links skip SONET ring/xconnect
layer and instead route over long sequences of Point-to-point WDM
systems, interconnected by O/E/O optical transponders
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Should the Optical Path pretend to be a transparent (like dark
fiber)
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•
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OR: Should it display characteristics of SONET Section/Line/Path
Fault Management Architecture?
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E.g., No AIS/BER TCA – re-transmit all LOS/LOP to Path Termination
Points
How does one isolate faults for repair (OTs, Amplifiers, WDM Terms)?
However: then similar 1st Gen IP/SONET Ring confusion occurs
Practicality dictated that industry implemented a combination of
both approaches
Page 12
AT&T Labs Research
Title
ULH/WSC: The Final Solution?
3rd Generation of IP/OL
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Use long-term model of all-optical path to IP layer link
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Two major issues to resolve
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–
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What if intermediate OEO exists in near-term?
How do we model restoration at OL and how does IP layer interact?
IP layer responsible for deciding link health
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Fast link layer detection (LOS)
GIGE and other signal are going to be transported over the 3rd Gen
OL
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Page 13
Is the set of PM alarms and TCAs we inherit from SONET appropriate for 3rd Gen
OL?
If not, which ones or new ones should we define?
AT&T Labs Research
Title
Some potential approaches
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OL only passes simple alarms to the upper layer, e.g., LOS.
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–
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Upper layer makes its assessments of BER, packet coding
violations, ACK failures
OL still does fault isolation for OEO components or
amplifiers (e.g., to WDM Term or EMS or Fault OSS), but
NOT passed up to IP layer
Where/how do we do this? Standards, Fora, vendor
interactions, carrier requirements?
Repair process:
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Need to correlate what fails in the OL with what fails in the
IP layer (1 to many map)
Network discovery of IP/OL relationships (e.g., SRLG)
across layers would facilitate fault correlation process
Page 14
AT&T Labs Research
Title