1 outside plant code:(9454). lesson declared fault localization of telecommunication cable 2
TRANSCRIPT
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Outside plant Code:(9454)
Lesson declared
Fault localization of telecommunication cable
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Layering in the current Internet
IP
Optics
Fiber
MPLS
OVERLAYS
Ethernet
Fiber-spans
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Layering is a mixed blessingLayering allows us to contain complexity
Each layer evolves independently without affecting any other layer
Allows us to focus on one layer at a time
There are associated challenges too… Routine operational tasks need associations
across layers Example: mapping an IP link to optical circuit,
overlay link to an IP path Lack of accurate cross-layer associations can
affect the reliability of the network
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Intended planned maintenance
Los Angeles
San Francisco
Seattle
Denver
Dallas
St Louis
Chicago
Boston
New York
Orlando
Planned maintenance
on optics
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Intended planned maintenance Optical component is
on circuit id A Lookup database to
map circuit id A to IP link
Due to mis-association, incorrectly maps it to LA to Dallas
Increase OSPF weight on LA to Dallas link
Disconnect component Causes failure
Los Angeles
San Francisco
Denver
Traffic from LA to Dallas is rerouted
via Denver
Dallas
X
LA to San Francisco link is
congested
High OSPF weight
Planned maintenance can induce faults if
accurate associations are not maintained
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Customer Fault Tolerance
Customer in NJ
New York
Philadelphia
InternetInternet Shared optical element
INTRA-CARRIERDIVERSITY
Customer in NJ
New York
InternetInternet
Sprint
Level 3
INTER-CARRIERDIVERSITY
Going through same conduit or Holland tunnel ?
Customer diversity information requiresaccurate cross-layer
associations, sometimes across domains
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Fault diagnosis
Los Angeles
San Francisco
Seattle
Denver
Dallas
St Louis
Chicago
Boston
New York
Orlando
What happened
?!!
X
Because of a bug, IP forwarding path changed, but MPLS
did not !
MPLS circuit between LA and
New York
Diagnosing faults requiresaccurate cross-layer
associations
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Why is it hard ?Can’t the operators maintain associations in
a centralized fashion ? Maintain database as links are provisioned Update as and when interfaces are re-homed
Hard due to flux in topology Churn because of dynamic topology changes Human errors during re-homing interfaces Operational realities – separation of concerns
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How it is done today ?A combination of non-standard databases
Human-generated inventory data Measurement data obtained from probes Configuration state from network elements
Policies implemented in network elements Higher complexity and overhead
No compatibility across ASes Difficult to evolve a network Difficult to integrate two networks after acquisition Difficult to incorporate third-party tools
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Why not concentrate on restoration?Advantages of lower-layer restoration
Hides lower-layer failures from impacting upper layers
Obviates to some extent need for cross-layer visibility
Cross-layer visibility still important Lower-layer restoration more expensive than IP
restoration Subtle performance changes (e.g., RTT) need
diagnosis
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Why not fatten the interfaces ? Fattening interfaces to make layers aware of
the entire topologies above and below Layers discover and propagate mappings
automatically Management system can query the network to
obtain mappings
Fattening results in high complexity Interoperability is a big challenge – long
design and test cyclesWider interfaces impact security
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Cross-layerPolicyServer
Architecture for cross-layer visibility
Ping
Trace-route
Backboneplanning
Customer diversity
Backbonemaintenance
FaultdiagnosisDB
MANAGEMENTAPPLICATIONS
BOW-TIE
IP
Optics
Fiber
MPLS
OVERLAYS
IP HOUR-GLASS
Ethernet
Fiberspans
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IP
Optics
FIBER, FIBERSPAN
MPLS
OVERLAYS
Standardize what goes in !
IP
Optics
FIBER, FIBERSPAN
MPLS
OVERLAYS Standardize what goes in(e.g. IP topologies)
AS1Facilitates interactionbetween ISP policy servers
AS2
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Advantages of the bow-tieTopology, routing information and other
associations can be queried for maintenance, diversity, and fault diagnosis
Cooperation across ASes to present better visibility across domains
Policies easily enforced through the serverLower overhead on network elements
Caching of common queries possible Historical questions can be answered
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Evolution path to improve accuracyA lot of room for improvementArchitecture accommodates evolution so that
accuracy can be improved over timeEvolution path for individual layers
Fiber & Fiber-spans Optical components IP links MPLS and overlay paths
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Fiber & Fiberspans Automated mechanisms
[sebos02] Inject labels through
fibers or use RFID GPS to determine the
location of fibers Transmit this information
to the DB More coverage results in
better accuracy but expensive
FIBER
DB
GPSOPTICALTAPS / RFID
FIBER
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Optical componentsManual mechanisms
Basic consistency checks Automatic correlation mechanisms such as
[kompella05nsdi] to output errors
Automatic mechanisms Neighbor discovery for active optical devices Configuration state from “intelligent” optical
networks (that support dynamic restoration)
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Optical components
Neighbor discoverythrough periodic
broadcasts at opticallayer
DB
Configuration state during restoration
Intelligent Optical
Network
Intelligent Optical
Network
ROUTER A ROUTER B
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Other layers IP layer
Periodically obtain configuration information to construct topology
Automatically collect up/down messages to provide up-to-date view
MPLS and overlay paths Static paths obtained from configuration Dynamic paths obtained by monitoring signaling
messages
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SummaryAccurate associations critical to many
operational tasksA bow-tie architecture for cross-layer visibility
Provides the cross-layer associations as a service to various applications
Allows better cooperation among ASes through standardizing what goes into the database
Policy controlled export of these associations Lower overhead on network elements Allows for innovation while containing complexity
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Future research directionsDesign automated mechanisms at each layer
to improve cross-layer visibility What frequency should information be obtained? How do we resolve conflicts (minimal edits) in the
database?
Identify higher-level models that we need to standardize
Devise incentives for cooperation among ASes
Define a language to specify policies
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Questions ?