Internet-2 Fall Meeting Optical PanelTuesday September 20th 2005

brian.smith@meriton.com

Electrical vs Optical Switching in R&E Networks

Capabilities

Economics

Reliability

Capabilities

Functionality OEO OOO

Transparency(bit rate and protocol)

Yes- wide range of signals

Yes

Low Latency Yes Yes

Single wavelength granularity(I.e. no wavelength stranding)

Yes Yes

Mesh Support (multi-degree) Yes Yes- Blocking issues

Wavelength Translation Yes Yes – extra components

- Available (at a cost)

Grid Conversion(e.g. CWDM to DWDM)

Yes No

Protocol Performance Monitoring

Easy + optical power/OSNR

Optical power/OSNR only

Wavelength Protection & Hitless Maintenance

Easy Ring – Easy

Mesh – More difficult

Economics

The most cost effective solution is dependent on

The architecture of the node (East-West / Mesh)

How much traffic is required to add/drop at the node

How much traffic is Pass-through at the node

OEO and OOO available in same node for most cost effective solution over network lifespan.

Economics

2-Degree - 100% add/drop node

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# add/drop w avelengths

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OEO OOO

Example 1: All traffic is ‘available’ for add/drop at the node but

can be pass-through if necessary – assumes 10GigE traffic

OEO is more cost effective at all capacities

Economics

2-Degree Node- 32 wavelength Capacity

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% add/drop traffic

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OOO OEO

Example 2: Fixed capacity of 32 wavelengths – %age of traffic

available at the node is variable – Assumes 10GigE traffic

OOO more cost effective with increasing pass-through traffic

Economics

Example 3: QUILT Network Model (October 2004) : Metro 2-1 node.

Mix of 2.5G(50%) and 10G(50%) traffic. 25% pass-through traffic (10G)

Quilt Node Metro 2-1 Example

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Network Capacity (wavelengths)

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OEO OOO

OOO / OEO equally cost effective at Day-1 :OEO

becomes more attractive as more capacity is added

Reliability Factor (32 availability, 8 add/drop)

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Year (20xx)

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Reliability

OPTICAL

ELECTRONIC

Electronic switching is a well proven, field deployed technology.

With increase in market volumes (2008) Optical ROADM reliability

will be on a par with electrical reliability

Questions

Are there performance issues related to OOO vs OEO ? With OOO, the express (pass-thru) wavelengths will traverse a longer

optical path, though more optical amplifiers and filters than the equivalent OEO solution so . . The required OSNR for the OOO case will be higher than OEO due to the

build up of non-linear impairments and a reduction in the dispersion window. OOO will experience more pass-band narrowing through the cascaded optical

ROADM – therefore more signal distortion effects must be managed within the link engineering.

OOO does however provide dynamic gain flattening and power equalization. Optical amplifiers with advanced transient suppression and monitoring

features are required for OOO. The number of OEO nodes traversed will eventually be limited by jitter

accumulation along the path. If design is within link budget limitations, both will perform equally well

Questions

What are the advantages/disadvantages of OOO vs OEO related to monitoring ? An Electronic switch fabric has access to layer 0, 1 and higher

Performance Monitoring which provides for remote network troubleshooting and for fast, effective protection switching.

OOO has access to optical power/OSNR measurement only.

Electronic switching fabrics allow loop-backs to be set remotely which cuts the cost and time required for network troubleshooting – there is no equivalent in an OOO system.

Questions

What are the advantages/disadvantages of OOO vs OEO related to switching especially in providing dynamic capabilities ? OEO is by definition non-blocking and so multi-degree ring

interconnection and mesh networking are simple compared to OOO from an engineering and control perspective. Where the number of pass-through wavelengths is small, OEO provides a more cost effective solution.

In the cases where significant pass-through traffic is required (in east west or multi-degree networks), OOO provides a more cost effective solution than OEO.

For cases where the traffic is a mix of 2.5G and 10G, add/drop and pass-through at a node, the cost differential is less well defined (as was discussed re the Quilt network model !)

In large rings and multi-degree cases OOO requires complex path dispersion management which is fiber type dependent.

Questions

Which is better suited beyond 10G and what are the advantages/disadvantages of each ? From a cost perspective, OOO is better suited to 40G traffic when pass-

through wavelengths are required at a node.

For 40G pass-through, OEO would cost a minimum of 4 times that of an equivalent 10G port – switching electrically at native 40G rates is not on the development radar

For OOO and depending on the 40Gbps+ technology used, there will be a limit on the number of cascaded OOO hops in a chain (ring or mesh) before pass-band narrowing starts to cause significant ISI.

40Gbps+ will require more strict control of dispersion in OOO systems and will have a reduced OSNR tolerance compared to 10G systems.