Lecture: 6 Network Survivability and Robustness Ajmal Muhammad, Robert Forchheimer Information Coding Group ISY Department
Jan 03, 2016
Lecture: 6 Network Survivability and Robustness
Ajmal Muhammad, Robert ForchheimerInformation Coding Group
ISY Department
Outline
Introduction to Network Survivability Protection Techniques Classification
Link failure, equipment failure Path protection, link protection Dedicated resources, shared resources
Physical Layer Attacks Optical Network Component Vulnerabilities
Fibers, switches, amplifiers Protection and Prevention of Attacks
Network Survivability
A very important aspect of modern networks Optical fibers with extremely large capacity has becomes dominant
transport medium. Interruption for even short period of time may have disastrous
consequences. No service provider is willing to accept unprotected networks anymore.
Restoration = function of rerouting failed connections
Survivability = property of a network to be resilient to failure
Requires physical redundancy and restoration protocols.
Optics in the Internet
SONET
DataCenter SONET
SONET
SONET
DWDM DWD
M
Access
Long HaulAccess
MetroMetro
Protection and Restoration in Internet
A well defined set of restoration techniques already exists in the upper electronic layers:
ATM/MPLS IP TCP
Restoration speeds in different layers: BGP-4: 15 – 30 minutes OSPF: 10 seconds to minutes SONET: 50 milliseconds Optical Mesh: currently hundred milliseconds to minutes
Why Optical Layer Protection?
Advantages: Speed Efficiency
Limitations Detection of all faults not possible (3R). Protects traffic in units of lightpaths. Race conditions when optical and client layer both try
to protect against same failure.
Protection Techniques Classification
Restoration techniques can protect the network against: Link failures
Fiber-cables cuts and link devices failures (amplifiers) Equipment failures
OXCs, OADMs, electro-optical interface
Protection can be implemented in: Optical channel sub-layer (path protection) Optical multiplex sub-layer (link protection)
Different protection techniques for: Ring networks Mesh networks
Protection in Ring Network
1+1 Path Protection
Used in access rings for traffic aggregation into
central office
1:1 Link Protection
Used for inter-office rings
1:1 Span and Link Protection
Used in metropolitan or long- haul rings
Unidirectional Path Switched Ring Bidirectional Link Switched Ring Bidirectional Link Switched Ring
Unidirectional Path Switched Ring (UPSR)
Signal sent on both working and
protected path
Best quality signal selected
Receiving Traffic
N1 send data to N2
N1N2
Outside Ring = WorkingInside Ring = Protection
Sending Traffic
N4
N3
1+1 Protection
Traffic is sent over two parallel paths, and the destination selects a better one.
In case of failure, the destination switch onto the other path.
Pros: simple for implementation and fast restoration
Cons: waste of bandwidth
Bidirectional Link Switched Ring (2-Fiber BLSRs)
Sending/ReceivingTraffic
Sending/ReceivingTraffic
N1 send data to N2 & N2 replies to N1
Both Rings = Working & Protection
N1N2
N4
N3
1:1 Protection
During normal operation, no traffic or low priority traffic is sent across the backup path.
In case failure both the source and destination switch onto the protection path.
Pros: better network utilization. Cons: required signaling overhead, slower restoration.
Protection in Mesh Networks
Working Path
Backup Path
Network planning and survivability design Disjoint path idea: service working route and its backup
route are topologically diverse Lightpaths of a logical topology can withstand physical
link failures
Reactive A search is initiated to find a
new lightpath which does not use the failed components after the failure happens.
It can not guarantee successful recovery,
Longer restoration time
Proactive Backup lightpaths are
identified and resources are reserved at the time of establishing the primary lightpath itself.
100 percent restoration Faster recovery
Reactive / Proactive
Taxonomy
Path Protection
Dedicated Path Protection Shared Path Protection
• Backup resources are used for protection of multiple links• Assume independent failure and handle single failure• The capacity reserved for protection is greatly reduced
Path Switching: restoration is handled by the source and the destination.
Normal Operation
Link Switching: restoration is handled by the nodes adjacent to the failure.
Span Protection: if additional fiber is available.
Link Switching: restoration is handled by the nodes adjacent to the failure.
Link Protection
Path Protection / Link Protection
Outline
Introduction to Network Survivability Protection Techniques Classification
Link failure, equipment failure Path protection, link protection Dedicated resources, shared resources
Physical Layer Attacks Optical Network Component Vulnerabilities
Fibers, switches, amplifiers Protection and Prevention of Attacks
Physical Layer Attacks
Attack: Intentional action against the ideal and secure functioning of the network
Attacks are much more hazardous than component failures as the damage they cause is more difficult to prevent:
Attacks Classification
Service disruption: prevents communication or degrades the quality of service (QoS)All connections and components appear to be functioning well in the optical domain, but the electrical bit error rates (BERs) of the legitimate channels are already impaired
Tapping: compromises privacy by providing unauthorized users access to data, which can then be used for eavesdropping or traffic analyses
Component Vulnerabilities: FibersBending the fiber violates the total internal reflection and causes light to leak outside the fiber
Exploiting fiber nonlinearities: cross-phase modulation and Raman effects may cause a signal on one wavelength to amplify or attenuate a signal on another wavelengthCo-propagate a malicious signal on a fiber and decrease QoS or tap legitimate signals
Commercial tapping devices introduce losses less than 0.5 dB and some even below 0.1 dB
Photodetector can pick up such leakage anddeliver the transmitted content to the intruder
Optical SwitchesOptical switches are prone to signal leakage, giving rise to crosstalk
Inter-channel crosstalk: occurs between signals on adjacent channels. Can be eliminated by using narrow pass-band receivers.
Intra-channel crosstalk: occurs among signals on the same wavelengths, or signals whose wavelengths fall within each other’s receiver pass-band.
Crosstalk levels of optical switches range from -35 dB (SOA, liquid crystal, electro-optical, thermo-optical) to -55 dB for MEMS.
Malicious users can take advantage ofthis to cause service degradation and/or perform eavesdropping
ExamplesTapping attack exploiting intra-channel crosstalk in an optical switch
Jamming attack exploiting intra-channel crosstalk in an optical switch
If a tapper gains access to upper output port, part of the signal at lambda 2 is delivered straight into his hands
Attacker injects a high-powered signal on the sameWavelength (in-band jamming) as other legitimate data signals.
Components of the high-power signal will leak onto adjacent channels, impairing the quality of thetransmission on those signals
Optical AmplifiersErbium-doped fiber amplifiers (EDFAs) are the most commonly used amplifier in today’s WDM networks.
An optical amplifier is characterized by its gain, gain bandwidth, gain saturation, polarization sensitivity and amplifier noise.
The distribution of excited electrons is not uniformat various levels within a band
The gain of an EDFA depends on the wavelength of the incoming signal with a peak around 1532 nm
Can be compensated by employing passive or dynamicgain equalization
Gain Competition in EDFAThe limited number of available upper-state photons necessary for signal amplification must be divided among all incoming signals.
Each of the signals is granted photons proportional to its power level, which can lead to gain competition.
Stronger incoming signals receive more gain, while weaker signals receive less
Gain competition can be exploited to create service disruptionA malicious user can inject a powerful signal on a wavelength different from those of other legitimate signals (out-of-band jamming), but still within the pass-band of the amplifier.
The stronger malicious signal will get more gain than weaker legitimate signals, robbing them of power.
Qos level of the legitimate signals will deteriorate, potentially leading to service denial.
Equip amplifiers with input and output power monitoring capability
Low Power QoS AttackOptical splitter is attached at the head of link AB to attenuate the propagation power by a certain amount (7 dB).
Link AB OSNR degradation for LP1 & LP3 exacerbate to 18.5 dB.
Attack is able to propagate by taking advantage of the OXC equalizations.
Equalizer in node B will attenuate LP2
to ensure the flat power spectrum on link
BC
7 dB attenuation
The amplifier (with gain control of 15 dB) are placed such that each can exactly compensate the loss introduced by the preceding fiber spans
75 km
Performance metrics of each channel measured at different places of the network
Make the network moresensitive to the abnormalchanges
Performance monitoring at the amps & OXCs shouldbe aware of the real-timeLP configuration and varythe alarming thresholdsaccordingly
Protection and Prevention of AttacksAchieving complete protection requires large investments by the network operator.
Hardware measures- shielding the fiber, additional equipment capable of limiting excessive power (e.g., optical limiting amplifiers, variable optical attenuators or optical fuses). Use components with lower crosstalk levels.
Transmission schemes- applying different modulation and coding techniques, limiting the bandwidth and power of certain signals.
Architecture and protocol design- identifying and avoiding risky links or assigning different routes and wavelengths to separate trusted from untrusted users.
Optical encryption- protect communication confidentiality by making it incomprehensible to an eavesdropper.