WDM Network Elements - Electrical and Computer Engineering - Lecture Slides, Slides of Electrical Engineering

Download WDM Network Elements - Electrical and Computer Engineering - Lecture Slides and more Slides Electrical Engineering in PDF only on Docsity! WDM Network Elements Docsity.com Architectural Aspects of Network Elements ! Optical Line Terminals (OLT) – widely deployed today ! Optical Add-Drop Multiplexers (OADM) – some deployment has been done ! Optical Crossconnects (OXC) – deployment just starting Docsity.com Important Features of WDM Architecture ! Each link can support a number of wavelengths (physical limitations!) ! Wavelength Reuse: Multiple lightpaths can use the same wavelength in the network as long as they do not overlap on the same link. ! Wavelength conversion: lightpaths may undergo conversion along the lightpath for better utilization/adaptation of signals. ! Transparency: optical layer is protocol insensitive. ! Circuit Switching: lightpath establishment on demand. (no packet switching at the optical layer!) ! Survivability: in event of link/node failures lightpaths can be rerouted (resiliency!) ! Lightpath topology: graph representation of nodes and links/lightpaths between them (the view of the higher layer) Docsity.com fon Optical Line Terminals (OLTS) Docsity.com Elements inside OLTs ! Transponders ! Wavelength multiplexers (demultiplexers) ! (Optical amplifiers) λ1 , IP router SONET SONET O/E/O O/E/O Laser Receiver Non ITU λ Non ITU λ ITU λ3 ITU λ2 ITU λ1 λ1 λ2 λ3 λOSC λOSC Optical line terminal Transponder Mux/demux Docsity.com Optical Multiplexers ! Any multiplexing technology can be used ! Optical amplifiers may be used to boost signals in both directions (for reception as well as transmission). Docsity.com Supervisory Channel in OLTs ! Optical Supervisory Channel (OSC) is carried on a separate wavelength ! OSC is used to monitor the performance of amps on the links as well as for management functions (performance, fault, configuration, security, accounting) . Docsity.com fio Optical Line Amplifiers Docsity.com io Optical Add/Drop Multiplexers (OADM) Docsity.com OADMs ! May be used in OLAs (seen previously). ! Can be used as stand alone network elements. ! OADMs can save on costs significantly, by reducing the number of point-to-point connections (terminations), thus reducing the number of OLTs (and transponders, that generate most of the cost). ! In the first of the following pictures - at node B six out of eight transponders are connected back-to-back – what a waste! Docsity.com OADM vs. OLT Note, that transponders can be skipped in the first picture, if those OLTs Are engineered in that way. (remember power levels and required SNR!) Optical passthrough Add/Drop Add/Drop Transponder OLT OADM Node A Node A Node B Node B Node C Node C (a) (b) Docsity.com Modular Parallel OADM Architecture ! Implies constraints on what λ-s can be adropped. ! Cost effective also if adropping small number of λ-s. ! The tolerance of lasers/filters can be higher ! Loss is fixed (adropping additional channels is easy). ! Modular multistage approaches are also used today ! Loss is not uniform for all λ-s. λ1, λ2,…, λW λ1, λ2,…, λW Band 4 Drop Add Demux Mux Band 3 Band 2 Band 1 λ1,λ2 Docsity.com Serial OADM Architecture ! A single channel is adropped (SC-OADM). To drop multiple channels, SC-OADMs can be cascaded. ! Adding additional SC-OADMs disrupts existing channels for a short while, thus planning is needed ahead of time. ! Highly modular (cost is low for less λ-s). ! Loss increases with λ-s to be adropped which may require additional OLAs. λ1, λ2,…, λW λ1, λ2,…, λW Drop Add λ1 λ2 Docsity.com Engineering Problems with ni SC-OADMS — X+3dB 28 dB LS. ATA, v TC x va Fi Fà VÀ A B E D (b) A +6dB AA ii zed ZE Lan A B Cc D Docsity.com Reconfigurable OADMS ly Optical switch TS i Mux Docsity.com Reconfigurable OADMS [TIR va Tunable transponders ta (d) Docsity.com A a Optical Crossconnects (OXC) Docsity.com Key Functions of OXCs ! Software controlled service provisioning ! Protection of lightpaths against defects ! Bit rate transparency is a desirable attribute ! Performance monitoring capabilities (testing, non-intrusive troubleshooting) ! Wavelength conversion may be incorporated ! Multiplexing and grooming of STS signals can be incorporated (electrical domain) Docsity.com OXC Main Parts ! Switch core – the switch that actually performs the crossconnect function ! Port complex – port cards or interfaces to other equipment ! OXCs and OLTs can be interconnected in different ways: ! Opaque configurations: the signal is converted in the E domain ! All-optical: signal remains in the optical domain Docsity.com Optical vs. Electrical Core ! Electrical core has a total switch capacity e.g., 2.56Tbps. This can be used to switch e.g., 1024 OC- 48 or 256 OC-192 signals. ! Optical core cannot offer grooming or switching at lower signal speeds ! Optical core is bit-rate independent (and transparent) the cost is the same no matter what signal it is switching (unlike electrical ports). ! Optical core is more scalable thus future proof and may allow to switch groups of wavelengths inexpensively. Docsity.com Comparison of Architectures LowMediumHighHighFootprint LowMediumHighHighPower cons. LowMediumHighMediumCost/port Optical PowerOptical PowerBERBERSwitching NoYesYesYesλ conversion HighestHighHighLowCapacity NoNoNoYesGrooming d)c)b)a)Figure OpticalOpticalOpticalElectricalSwitch-core All-OpticalOpaqueOpaqueOpaqueAttribute Docsity.com All-Optical OXCs ! The bottom architecture of the last picture. ! No: ! Low speed grooming ! Wavelength conversion ! Signal regeneration ! One solution is to combine the optical core (groups of wavelengths or entire fibres can be switched at once) with an electronic core. ! Since there is no wavelength conversion, architecture can be simplified – wavelength planes. Docsity.com Combined Optical — Electrical Core Pda A dda d5 4 OLT |A ta) OLT Wavelength or se ol Ta Local add/drop waveband switching E E Low-speed grooming, ___ wavelength conversion, regeneration E E Q O wol Fromf/to clients Docsity.com