ITU-T Workshop on Security Seoul (Korea), 13-14 May 2002 Telecommunication network reliability Dr. Chidung LAC

ITU-T Workshop on SecuritySeoul (Korea), 13-14 May 2002

Telecommunication network reliability

Dr. Chidung LAC

france telecom R&D 2ITU-T Workshop on Security

Seoul (Korea), 13-14 May 2002

Outline

Dependability and survivabilityAvailability assessment Recovery mechanisms

Physical layer ATM network IP level

From random non-intentional to provocated failures



Dependability and survivability (1/2)

Quality of Service

AccessibilityService

continuitySecurity Ease of use Billing

Availability Performances

Degradedstate

Nominalstate

Survivability



Dependability and survivability (2/2)

Unavailability

Reliability

MaintenancesupportMaintainability

Traffic engineering

Systemcapacity

Offeredtraffic

Grade ofservice

FailuresCongestion

Abnormalsituations

Natural disasters(Safety)

Man-made events(Security)Dependability

Networkelements



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 and a repair time MTTR to each element

Estimated values from equipments vendors () Use of field data (, MTTR)

Service unavailability and failure rate assessment



Availability assessment : example (1/2)

Optical distribution frame

Amplifier

ADM

ADM

Optical fiber

WDM

WDM WDM

WDM

WDM

WDM

ADM



Availability assessment : example (2/2)

Powersupply

Powersupply

Backplane

Tributaryunit

Opticalaggregate

Clock

Clock

ADM block diagram representation

Unavailability and failure rate calculation

UBoard i = Board i * MTTRBoard i

USerial system = UBoard j

UParallel system = UBoard k UADM

Serial system = i

Parallel system = U2U1 ADM

Board i Failurerate

i (h-1)

MTTRi

(h)

Unavailability

Ui

Tributary unit 3 10-5 1,5 4,5 10-5

Backplane 1 10-5 1,5 1,5 10-5

… … … …



Pre-WDM networks protection

Automatic protection switching

Link 1

Link 2

Source

Working link

Backuplink

1+1 1:1

Destination

1:n

...

n working links

m:n

...

...

Source

Source

Source

Destination

Destination

Destination

m backup links

Backuplink

n working links



Pre-WDM self-healing rings (1/2)

Unidirectional rings

Backupring

Workingring

A

B

A

B

Link protection (1:1)

Path 1

Path 2

B

A

B

Failure

Path protection (1+1)

Failure

A



Pre-WDM self-healing rings (2/2)

Bidirectional rings

2-fiber ring

B

A

A

B

...

Unused backup bandwidth

...

4-fiber ring

A

Backuprings

B

A

Failure

Backup bandwidth used

Failure

...

Workingrings

B



Pre-WDM meshed networks restoration

1 2 3

4

7

5

8 9

6

1 2 3

4

7

5

8 9

6

Failure

Around the failure

1 2 3

4

7

5

8 9

6

Failure

End-to-end

Failure

1 2 3

4

7

5

8 9

6

Local-destination



WDM rings protection

2-fiber bidirectional

rings

Shared wavelenght

Failure

C

D

C

D

C D

C D

C D

C D

C D

C D

C D

C

D

C

D

Failure

C D

C D

C D

C D



WDM meshed networks (1/2)

Link protection

1 2 3

4 5 6

Dedicated approach

1 2 3

4 5 6

Shared approach

Failure1 2 3

4 5 6

or

Failure

Failure

Failure



WDM meshed networks (2/2)

Path protection

1 2 3

4 5 6

Dedicated approach

1 2 3

4 5 6

Failure

1 2 3

4 5 6

Shared approach

or

Failure

Failure

Failure



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



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



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



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



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

Documents

ITU-T Workshop on Security Seoul (Korea), 13-14 May 2002 Telecommunication network reliability Dr. Chidung LAC