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Telecommunication network reliability Dr. Chidung LAC

Telecommunication network reliability Dr. Chidung LAC. Outline. Dependability and survivability Availability assessment Recovery mechanisms Physical layer ATM network IP level From random non-intentional to provocated failures. Dependability and survivability (1/2).

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Telecommunication network reliability Dr. Chidung LAC

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  1. Telecommunication network reliability Dr.Chidung LAC

  2. Outline • Dependability and survivability • Availability assessment • Recovery mechanisms • Physical layer • ATM network • IP level • From random non-intentional to provocated failures

  3. Dependability and survivability (1/2) Quality of Service Service Accessibility Security Ease of use Billing continuity Availability Performances Survivability Nominal Degraded state state

  4. Dependability and survivability (2/2) Unavailability Failures Congestion Reliability Traffic engineering Network System Offered Grade of Maintenance elements Maintainability capacity traffic service support Abnormal situations Man-made events Natural disasters (Security) Dependability (Safety)

  5. Availability assessment methodology • Identification of elements contributing to the service’s unavailability (equipments, cable infrastructure, OAM errors, …) • Block diagram representation (series, parallel) of these elements taking into account network architecture (redundancy, …) • Allocation of a failure rate l and a repair time MTTR to each element • Estimated values from equipments vendors (l) • Use of field data (l, MTTR) • Service unavailability and failure rate assessment

  6. Availability assessment : example (1/2) ADM WDM WDM WDM WDM ADM ADM WDM WDM Amplifier Optical distribution frame Optical fiber

  7. Availability assessment : example (2/2) • ADM block diagram representation • Unavailability and failure rate calculation UBoard i = lBoard i * MTTRBoard i USerial system = S UBoard j UParallel system = P UBoard k  UADM • lSerial system = Sli • lParallel system = l1U2+ l2 U1  lADM

  8. Pre-WDM networks protection Automatic protection switching

  9. Pre-WDM self-healing rings (1/2) Unidirectional rings

  10. Pre-WDM self-healing rings (2/2) Bidirectional rings

  11. Pre-WDM meshed networks restoration 2 1 3 2 1 3 Failure 4 5 6 4 5 6 8 7 9 8 7 9 Around the failure 2 1 3 2 1 3 Failure Failure 4 5 6 4 5 6 8 7 9 8 7 9 Local-destination End-to-end

  12. WDM rings protection 2-fiber bidirectional rings

  13. WDM meshed networks (1/2) 1 ® 2 1 ® 2 (l ) l ® l ) (l 1 2 1 Failure 1 l ® l 1 2 2 1 3 l 2 l 1 4 5 6 Failure 5 ® 6 5 ® 6 (l ) (l ) 1 1 Link protection Dedicated approach 1 ® 2 1 ® 2 1 ® 2 1 ® 2 (l ) (l ) (l ) (l ) 1 1 1 1 l Failure 1 2 2 1 1 3 3 l 1 or l 1 l 1 4 4 5 5 6 6 Failure 5 ® 6 5 ® 6 5 ® 6 5 ® 6 (l ) (l ) (l ) 1 1 1 (l ) 1 Shared approach

  14. WDM meshed networks (2/2) Path protection

  15. ATM network (1/2) • ATM v/s SDH-SONET • Bandwidth on-demand v/s no dynamic bandwidth control • Bursty traffic v/s switched services, private lines • Logical v/s physical path structure • Variations of VPs and VCs’ capabilities (from 0 to the physical link rate) v/s fixed capacities • Non-hierarchy v/s hierarchy path capacity • Separation of capacity allocation and physical route assignment for VPs and VCs • OAM bandwidth with allocation on demand  delay reduction for restoration message exchange, quicker detection of system degradation • Faster detection of soft failure

  16. ATM network (2/2) • Automatic protection switching  VPs or VCs used as links (protection units) • 1+1 : connection switching by the receiver side node (from working to backup link) • 1:1 : switching done both by the transmitter side and the receiver side nodes • Self-healing network • Distributed control restoration scheme • More effective resource utilization • Dynamic planned scheme : flooding algorithm to locate restoration routes • Preplanned scheme : predetermination of the optimal alternate route and pre-assignement of a backup VP to each VP

  17. IP level • Recovery mechanisms proposed for MultiProtocol Label Switching • Architecture used : • Integrated Services with Resource Reservation Protocol (signaling protocol) • Differentiated Services • Main recovery modes : • Link protection 1+1 and 1:1 • Path protection • Restoration/rerouting : on-demand establishment of Label Switched Paths

  18. From random non-intentional to provocated failures • Telcos’ poor experience in the domain • Example of assessment difficulty : how to apply mathematical failure rate distribution ? • Possible directions : • Infrastructure’s protection : security reinforcement • Logical intrusion : main challenge with actual’s networks interfunctioning (operators’ networks, Internet, …) • Behavior modelling : human factors applied to volontary acts • Some initiatives : • Critical Infrastructure Protection  cascading effects due to interdependencies among different domains • IEEE DIREN’02, New York, June 2002

  19. To probe further • IEEE Communications – Issue on Survivable communication networks, August 1999 • IEEE Communications – Issue on Resilience in communication networks, January 2002 • IEEE Network – Issue on Network and service security, Nov/Dec 2002 • ITU-T, Rec. E.800, Terms and definitions related to QoS and network performance including dependability • Network reliability steering committee, Alliance for telecommunications industry solutions, http://www.atis.org • T1A1.2 WG on Network Survivability Performance, Reliability/availability framework for IP-based networks and services, Draft technical report, July 2001

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