Internet-2 Fall Meeting Optical Panel Tuesday September 20 th 2005

Electrical vs Optical Switching in R&E Networks  Capabilities  Economics  Reliability

Capabilities FunctionalityOEOOOO Transparency (bit rate and protocol) Yes - wide range of signals Yes Low LatencyYes Single wavelength granularity (I.e. no wavelength stranding) Yes Mesh Support (multi-degree)Yes Yes - Blocking issues Wavelength TranslationYes Yes – extra components - Available (at a cost) Grid Conversion (e.g. CWDM to DWDM) YesNo Protocol Performance Monitoring Easy + optical power/OSNR Optical power/OSNR only Wavelength Protection & Hitless Maintenance EasyRing – 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 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 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) OOO / OEO equally cost effective at Day-1 :OEO becomes more attractive as more capacity is added

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.