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Lecture Note on Survivability

Lecture Note on Survivability. Impact of Outages. Service Outage Impact. FCC Reportable. Social/ Business Impacts. Packet (X.25) Disconnect. Call- Dropping Private Line Disconnect. 6th Range. 5th Range. Trigger Change- over of CCS Links. May Drop Voiceband Calls. 4th

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Lecture Note on Survivability

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  1. Lecture Note on Survivability

  2. Impact of Outages Service Outage Impact FCC Reportable Social/ Business Impacts Packet (X.25) Disconnect Call- Dropping Private Line Disconnect 6th Range 5th Range Trigger Change- over of CCS Links May Drop Voiceband Calls 4th Range 3rd Range 2nd Range "Hit" 1st Range APS 5 min 0 50 msec 200 msec 2 sec 10 sec 30 min

  3. Market Drivers for Survivability • Customer Relations • Competitive Advantage • Revenue • Negative - Tariff Rebates • Positive - Premium Services • Business Customers • Medical Institutions • Government Agencies • Impact on Operations • Minimize Liability

  4. Network Survivability • Availability: 99.999% (5 nines) => less than 5 min downtime per year • Since a network is made up of several components, the only way to reach 5-nines is to add survivability • Survivability = continued services in the presence of failures • Protection switching or restoration: mechanisms used to ensure survivability • Add redundant capacity, detect faults and automatically re-route traffic around the failure • Restoration: related term, but slower time-scale • Protection: fast time-scale: 10s-100s of ms… • implemented in a distributed manner to ensure fast restoration

  5. Failure Types • Types of failure: • Components: links, nodes, channels in WDM, active components, software… • Human error: backhoe fiber cut • Systems: Entire COs can fail due to catastrophic events • Single failure vs multiple concurrent failures • Goal: mean repair time << mean time between failures… • Protection depends upon applications • SONET/SDH: 60 ms (legacy drop calls threshold) • Survivability provided at several layers

  6. Network Survivability Architectures Linear Protection Architectures Ring Protection Architectures Mesh Restoration Architectures

  7. Network Availability & Survivability Availability is the probability that a system is able to perform its designed functions when called upon to do so. Availability = Reliability Reliability + Recovery

  8. Quantification of Availability

  9. PSTN End-to-End Availability 99.94% PSTN • Individual elements have an availability of 99.99% • One cut off call in 8000 calls (3 min for average call). Five ineffective calls in every 10,000 calls. NI NI 0.005 % 0.005 % AN 0.01 % AN 0.01 % LE LE Facility Entrance Facility Entrance NI : Network Interface LE : Local Exchange LD : Long Distance AN : Access Network LD 0.005 % 0.005 % 0.02 %

  10. Service Requirements Vs Network Availability

  11. IP Network Expectations L : Low M : Medium H : High

  12. Measuring Availability: Port Method • Based on Port Count in Network • Does not take into account the bandwidth of ports (e.g. OC-192 and 64k are both ports) • Good for dedicated access service because ports are tied to customers. (Total # of Ports X Sample Period) - (number of impacted port x outage duration) x 100 (Total number of Ports x sample period)

  13. Port Method Example • 10,000 active access ports Network • Access router with 100 access ports fails for 30 minutes. • Total Available Port-Hours = 10,000*24 = 240,000 • Total Down Port-Hours = 100*.5 = 50 • Availability for a Single Day = (240000-50/240,000)*100 = 99.979166 %

  14. Bandwidth Method • Based on Amount of Bandwidth available in Network • Takes into account the bandwidth of ports • Good for core routers (Total amount of BW X Sample Period) - (Amount of BW impacted x outage duration) x 100 (Total amount of BW in network x sample period)

  15. Bandwidth Method Example • Total capacity of network 100 Gigabits/sec • Access Router with 1 Gigabits/sec BW fails for 30 minutes. • Total BW available in network for a day = 100*24 = 2400 Gigabits/sec • Total BW lost in outage = 1*.5 = 0.5 • Availability for a Single Day = ((2400-0.5)/2,400)*100 = 99.979166 %

  16. (number of impacted customers x outage duration) ] x 10-6 DPM = [ (total number of customers x sample period) Defects Per Million Method • Used in PSTN networks, defined as number of blocked calls per one million calls averaged over one year.

  17. Defects Per Million Example • 10,000 active access ports Network • Access Router with 100 access ports fails for 30 minutes. • Total Available Port-Hours = 10,000*24 = 240,000 • Total Down Port-Hours = 100*.5 = 50 • Daily DPM = (50/240,000)*1,000,000 = 208

  18. Working and Protect Fibers

  19. Protection Topologies - Linear • Two nodes connected to each other with two or more sets of links Protect Protect Working Working (1+1) (1:n)

  20. Protection Topologies - Ring • Two or more nodes connected to each other with a ring of links • Line vs. Drop interfaces • East vs. West interfaces W E D L E L W Working Protect W E E W

  21. Protection Topologies - Mesh • Three or more nodes connected to each other • Can be sparse or complete meshes • Spans may be individually protected with linear protection • Overall edge-to-edge connectivity is protected through multiple paths Working Protect

  22. Ring Topologies ADM ADM 2 Fiber Ring 4 Fiber Ring DCC ADM DCC ADM Each Line Is Full Duplex Each Line Is Full Duplex ADM ADM ADM ADM DCC ADM DCC ADM ADM ADM Uni- vs. Bi- Directional All Traffic Runs Clockwise, vs Either Way

  23. Automatic Protection Switching (APS) ADM ADM ADM ADM ADM ADM Line Protection Switching Path Protection Switching Uses TOH Trunk Application Backup Capacity Is Idle Supports 1:n, where n=1-14 Uses POH Access Line Applications Duplicate Traffic Sent On Protect 1+1 • Automatic Protection Switching • Line Or Path Based • Restoration Times ~ 50 ms • K1, K2 Bytes Signal Change

  24. Protection Switching Terminology • 1+1 architectures - permanent bridge at the source - select at sink • m:n architectures - m entities provide protection for n working entities where m is less than or equal to n • allows unprotected extra traffic • most common - SONET linear 1:1 and 1:n • Coordination Protocol - provides coordination between controllers in source and sink • Required for all m:n architectures • Not required for 1+1 architectures unless they employ bi-directional protection switching

  25. 1+1 vs 1:n Protect Protect Working Working (1+1) (1:n)

  26. Linear 1+1 APS BR = Bridge SW = Switch TX = Transmitter RX = Receiver Working BR TX RX SW Protection RX TX Working SW RX TX BR RX TX Protection

  27. Protection Switching • Dedicated vs Shared: working connection assigned dedicated or shared protection bandwidth • 1+1 is dedicated, 1:n is shared • Revertive vs Non-revertive: after failure is fixed, traffic is automatically or manually switched back • Shared protection schemes are usually revertive • Uni-directional or bi-directional protection: • Uni: each direction of traffic is handled independent of the other. Fiber cut => only one direction switched over to protection . Usually done with dedicated protection; no signaling required. • Bi-directional transmission on fiber (full duplex) => requires bi-directional switching & signaling required

  28. Ring Protection Today: multiple “stacked” rings over DWDM (different s)

  29. Unidirectional Path Switched Ring (UPSR) A-B B-A Bridge Failure-free State Path Selection W B fiber 1 Bridge P A-B C A B-A Path Selection fiber 2 D * One fiber is “working” and the other is “protecting” at all nodes… * Traffic sent simultaneously on working and protect paths… * Protection done at path layer (like 1+1)…

  30. Unidirectional Path Switched Ring (UPSR) Bridge Path Selection Failure State W fiber 1 B Bridge P A-B C A B-A Path Selection fiber 2 D

  31. UPSR Discussion • Easily handles failures of links, transmitters, receivers or nodes • Simple to implement: no signaling protocol or communication needed between nodes • Drawback: does not spatially re-use the fiber capacity because it is similar to 1+1 linear protection model • No sharing of protection (like m:n model) • BLSRs can support aggregate traffic capacities higher than transmission rate • UPSR is popular in lower-speed local exchange and access networks • No specified limit on number of nodes or ring length of UPSR, only limited by difference in delays of paths

  32. C D Bidirectional Line Switched Ring (BLSR/2) Protection Working 2-Fiber BLSR B AC A C C A A C A

  33. Bi-directional Line Switched Ring (BLSR/2) Protection Working Ring Switch 2-Fiber BLSR B A A C A C C C A C A Ring Switch D

  34. B C Bi-directional Line Switched Ring (BLSR/2) Protection Working Node Failure 2-Fiber BLSR A A C A C C A C A Ring Switch Ring Switch D

  35. B C Node Failures => “Squelching” Customer 1 Customer 2 2-Fiber BLSR Node Failure Customer 1 Customer 2 A A C A C C A C A Ring Switch Ring Switch D

  36. B A C D Bi-directional Line Switched Ring (BLSR/4) 4-Fiber BLSR Working Protection A C A C C A C A

  37. B C D Bidirectional Line Switched Ring 4-Fiber BLSR Span Switch A C A C C A A C A Protection Working

  38. B C D Bidirectional Line Switched Ring Node Failure 4-Fiber BLSR Ring Switch A C A A C C A C A Ring Switch Protection Also Need to Squelch any Misconnected Traffic Working

  39. BLSR Discussion • BLSR/2 can be thought of as BLSR/4 with protection fibers embedded in the same fiber • One half of the capacity is used for protection purposes in each fiber • Span switching and ring switching is possible only in BLSR, not in UPSR • 1:n and m:n capabilities possible in BLSR • More efficient in protecting distributed traffic patterns due to the sharing • Ring management more complex in BLSR/4 • K1/K2 bytes of SONET overhead is used to accomplish this

  40. Deployment of UPSR and BLSR Regional Ring (BLSR) Intra-Regional Ring (BLSR) Intra-Regional Ring (BLSR) Access Rings (UPSR)

  41. Mesh Restoration Central Controller DC DCS DCS DC DC DCS DCS DCS DCS DC DCS DCS Self Healing Restoration Architecture Reconfigurable (or Rerouting) Restoration Architecture DC = Distributed Controller

  42. Mesh Restoration Working Path DCS DCS Line or Link Restoration DCS DCS DCS DCS Path Restoration • Control: Centralized or Distributed • Route Calculation: Preplanned or Dynamic • Type of Alternate Routing: Line or Path

  43. Mesh Restoration vs Ring/Linear Protection

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