Relative Hop*OChRelative #Switch Ports

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NOC’2003 Vienna 1

Resilience with Tailored

Recovery Time in Switched Optical Networks

T. Jakab, Zs. Lakatos, jakab@hit.bme.hu

Department of Telecommunications,

Budapest University of Technology and Economics Budapest, Hungary

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NOC’2003 Vienna 2

Outline

• Motivations

• Optical Channel Based Services in Switched Intelligent Optical Networks

• Potential Resilience Options for Permanent Optical Channel Based Services

• Resilience with Tailored Recovery Time

• Summary and Conclusions

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NOC’2003 Vienna 3

Motivations

• Intelligent flexibility is required in optical networks

– to cope with traffic uncertainties,

– to enable fast optical channel provisioning, – to support complex shared capacity based

resilience.

• Efficient resilience schemes are of increased importance in optical networks carrying highly concentrated traffic.

• Service differentiation is a crucial point to

support different client services and improve service profitability.

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NOC’2003 Vienna 4

Optical Channel Based Services

• Transport Services

– Permanent optical channel service,

– Soft-permanent optical channel service, – Lambda trunking service,

– OVPN service.

• Service Requirements – Fast provisioning,

– Differentiated services,

– Enhanced service resilience.

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NOC’2003 Vienna 5

Network Resilience

• Dynamic application of extra network resources to limit the impact of failures

• Based on dedicated or shared network resources

• Requires intelligent switching function to be supported in nodes

• Basic schemes:

– 1+1 dedicated protection, – n:m shared protection,

– restoration (failure state dependent dynamic configuration of shared capacities).

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NOC’2003 Vienna 6

Illustrative numerical results

• Analysis of different resilience options – Full flexibility implies restoration

• Resilience of switched OCh based services

– Service oriented considerations – restoration with tailored recovery time

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NOC’2003 Vienna 7

Illustrative examples (1)

Resilience in Full Flexible Networks

0%

50%

100%

150%

200%

250%

300%

not prot.

optimal path rest.

1+1 Resilience Cases

Relative Hop*OCh

Extra for resilience Working

0%

50%

100%

150%

200%

250%

300%

not prot.

full flex.

1+1 term.

switch.

1+1 full flex.

optimal path rest.

full flex.

Resilience Cases

Relative #Switch Ports

Extra due to resilience Working

• Full flexible network: each capacity unit terminates on switching-capable node equipment (e.g. flex. OADM or OXC)

Comparison of link capacities Comparison of switch capacities

Extra for dedicated resilience

Savings on capacity

sharing Switches

not used for resilience

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NOC’2003 Vienna 8

Illustrative examples (1a - Link capacities)

Resilience in Full Flexible Networks

0%

50%

100%

150%

200%

250%

300%

not prot.

optimal path rest.

0%

50%

100%

150%

200%

250%

300%

not prot.

full flex.

1+1 term.

switch.

1+1 full flex.

optimal path rest.

full flex.

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NOC’2003 Vienna 9

Illustrative examples (1a)

Link capacities for Resilience in Full Flexible Networks

• Full flexible network: each capacity unit terminates on

switching-capable node equipment (e.g. flex. OADM or OXC) Comparison of link capacities

0%

50%

100%

150%

200%

250%

300%

not prot.

optimal path rest.

1+1

Relative Hop*OCh

Extra for resilience

Working Savings on

capacity sharing Extra for

dedicated resilience

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NOC’2003 Vienna 10

Illustrative examples (1b - Switch capacities)

Resilience in Full Flexible Networks

0%

50%

100%

150%

200%

250%

300%

not prot.

optimal path rest.

0%

50%

100%

150%

200%

250%

300%

not prot.

full flex.

1+1 term.

switch.

1+1 full flex.

optimal path rest.

full flex.

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Illustrative examples (1b)

Switch capacities for Resilience in Full Flexible Networks

• Full flexible network: each capacity unit terminates on

switching-capable node equipment (e.g. flex. OADM or OXC)

0%

50%

100%

150%

200%

250%

300%

not prot.

full flex.

1+1 term.

switch.

1+1 full flex.

optimal path rest.

full flex.

Extra due to resilience Working

Comparison of switch capacitiesSwitches not used for resilience purposes

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Network Resilience Service Considerations

• Different applications may need resilience with different characteristics, such as

– recovery speed, or

– rate of recovered capacity (partial/entire).

• Different resilient classes can be specified according to the different needs

• Aim: meet different resilience requirements on the same technical basis and lowest cost

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Restoration with Tailored Recovery Time

• Recovery time is assumed to be proportional with the

number of active switching nodes involved in the process, and with the processing load of each active switch

• Some switches can be pre-set and fixed to speed up the recovery process

• Reduced flexibility results in less efficient capacity sharing, therefore the amount of extra resources for restoration is increasing

• The joint optimisation of different classes may reduce the penalty

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Restoration with Tailored Recovery Time

Working path 1

Working path 2 Single

Failure 1

Single Failure 2

Recovery path 2 Recovery path 1

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Restoration with Tailored Recovery Time

Working path 1

Failure 1

Recovery path 2 Recovery path 1 Pre-set

switches

Capacity sharing

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Restoration with Tailored Recovery Time

Working path 1

Failure 1

Recovery path 2 Recovery path 1 Pre-set

switches

No capacity sharing

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Restoration with Tailored Recovery Time

Traditional restoration 1+1

dedicated protection

Resource needs for networks with different resilience options

0%

20%

40%

60%

80%

100%

120%

1+1 path prot.

single hop path rest.

min. path rest.

double hop path

rest.

double and triple

hop path rest.

capac.

opt. path rest.

Resilience options

OCh*hop

Recovery path statistics for different resilience options

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

1+1 path prot.

rest.

hop path rest.

capac.

Resilience options Average logical hop count

spare for resilience working

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Illustrative examples (2a - Average Logical Hop Count)

Restoration with Tailored Recovery Time

0%

20%

40%

60%

80%

100%

120%

1+1 path prot.

rest.

hop path rest.

capac.

OCh*hop

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

1+1 path prot.

rest.

capac.

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NOC’2003 Vienna 19 Recovery path statistics for different resilience

options

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

1+1 path prot.

rest.

capac.

Illustrative examples (2a)

Restoration with Tailored Recovery Time

Average Logical Hop Count

1+1 dedicated protection

Traditional restoration Single logical

hop, receiver end switching only

Fastest

Multiple logical hops, switching in each node via

the path

Slowest

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Illustrative examples (2b - Resource Needs)

Restoration with Tailored Recovery Time

0%

20%

40%

60%

80%

100%

120%

1+1 path prot.

rest.

hop path rest.

capac.

OCh*hop

0.00 0.50 1.00 1.50 2.00 2.50 3.00 3.50

1+1 path prot.

rest.

capac.

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NOC’2003 Vienna 21 Resource needs for networks with different

resilience options

0%

20%

40%

60%

80%

100%

120%

1+1 path prot.

rest.

capac.

OCh*hop

Illustrative examples (2b)

Restoration with Tailored Recovery Time

Resource Needs

Highest extra for resilience

(No sharing - 1+1 dedicated protection

only)

Capacity optimal restoration without

recovery time specifications

Same routing without effective capacity constraints

(simplified case)

From faster to slower

Demand classes with different recovery time

requirements,

different classifications

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Summary on Restoration with Tailored Recovery Time

• Different clients and applications require different recovery times

• Applying restoration, to shorten the the recovery time some switches can be pre-set via the restoration paths

• Pre-set switches decrease de resilience capacity sharing efficiency, therefore the resilience related extra capacity increases

• Joint optimisation of multiple recovery time classes decreases this penalty

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Conclusions

• Intelligent switching introduced in optical networks enables enhanced resilience schemes

• Shared capacity oriented restoration is the cost effective solution for the resilience in full flexible networks

• Demand classes of different recovery times enables service differentiation, however the joint optimisation of these classes results in low capacity penalty