Adapt TransportPCE code to Sulfur
[transportpce.git] / pce / src / main / java / org / opendaylight / transportpce / pce / graph / PostAlgoPathValidator.java
index 55ea21b5fe418fadb2606753cec25edf5ed3350c..ba4eee7d692ddd6b69f9f04baa2ee4345a92b152 100644 (file)
 
 package org.opendaylight.transportpce.pce.graph;
 
+import edu.umd.cs.findbugs.annotations.SuppressFBWarnings;
+import java.math.RoundingMode;
+import java.util.ArrayList;
+import java.util.Arrays;
+import java.util.BitSet;
+import java.util.Collections;
+import java.util.HashMap;
+import java.util.List;
 import java.util.Map;
-
 import org.jgrapht.GraphPath;
 import org.opendaylight.transportpce.common.ResponseCodes;
+import org.opendaylight.transportpce.common.StringConstants;
+import org.opendaylight.transportpce.common.fixedflex.GridConstant;
+import org.opendaylight.transportpce.common.fixedflex.GridUtils;
+import org.opendaylight.transportpce.pce.constraints.PceConstraints;
+import org.opendaylight.transportpce.pce.constraints.PceConstraints.ResourcePair;
 import org.opendaylight.transportpce.pce.networkanalyzer.PceNode;
 import org.opendaylight.transportpce.pce.networkanalyzer.PceResult;
+import org.opendaylight.yang.gen.v1.http.org.opendaylight.transportpce.pce.rev220615.SpectrumAssignment;
+import org.opendaylight.yang.gen.v1.http.org.opendaylight.transportpce.pce.rev220615.SpectrumAssignmentBuilder;
+import org.opendaylight.yang.gen.v1.http.org.openroadm.network.types.rev211210.OpenroadmLinkType;
+import org.opendaylight.yang.gen.v1.http.org.openroadm.otn.common.types.rev181130.OpucnTribSlotDef;
 import org.opendaylight.yang.gen.v1.urn.ietf.params.xml.ns.yang.ietf.network.rev180226.NodeId;
+import org.opendaylight.yangtools.yang.common.Uint16;
 import org.slf4j.Logger;
 import org.slf4j.LoggerFactory;
 
 public class PostAlgoPathValidator {
     /* Logging. */
-    private static final Logger LOG = LoggerFactory.getLogger(PceGraph.class);
+    private static final Logger LOG = LoggerFactory.getLogger(PostAlgoPathValidator.class);
 
-    // TODO hard-coded 96
-    private static final int MAX_WAWELENGTH = 96;
+    private static final double MIN_OSNR_W100G = 17;
+    private static final double TRX_OSNR = 33;
+    private static final double ADD_OSNR = 30;
+    public static final Long CONST_OSNR = 1L;
+    public static final double SYS_MARGIN = 0;
 
-    public PceResult checkPath(GraphPath<String, PceGraphEdge> path,
-            Map<NodeId, PceNode> allPceNodes, PceResult pceResult) {
+    @SuppressWarnings("fallthrough")
+    @SuppressFBWarnings(
+        value = "SF_SWITCH_FALLTHROUGH",
+        justification = "intentional fallthrough")
+    public PceResult checkPath(GraphPath<String, PceGraphEdge> path, Map<NodeId, PceNode> allPceNodes,
+        PceResult pceResult, PceConstraints pceHardConstraints, String serviceType) {
 
-        if (path.getEdgeList().size() == 0) {
+        // check if the path is empty
+        if (path.getEdgeList().isEmpty()) {
             pceResult.setRC(ResponseCodes.RESPONSE_FAILED);
             return pceResult;
         }
+        int spectralWidthSlotNumber = GridConstant.SPECTRAL_WIDTH_SLOT_NUMBER_MAP
+            .getOrDefault(serviceType, GridConstant.NB_SLOTS_100G);
+        SpectrumAssignment spectrumAssignment = null;
+        //variable to deal with 1GE (Nb=1) and 10GE (Nb=10) cases
+        switch (serviceType) {
+            case StringConstants.SERVICE_TYPE_OTUC2:
+            case StringConstants.SERVICE_TYPE_OTUC3:
+            case StringConstants.SERVICE_TYPE_OTUC4:
+            case StringConstants.SERVICE_TYPE_400GE:
+                spectralWidthSlotNumber = GridConstant.SPECTRAL_WIDTH_SLOT_NUMBER_MAP
+                    .getOrDefault(serviceType, GridConstant.NB_SLOTS_400G);
+            //fallthrough
+            case StringConstants.SERVICE_TYPE_100GE_T:
+            case StringConstants.SERVICE_TYPE_OTU4:
+                spectrumAssignment = getSpectrumAssignment(path, allPceNodes, spectralWidthSlotNumber);
+                pceResult.setServiceType(serviceType);
+                if (spectrumAssignment.getBeginIndex().equals(Uint16.valueOf(0))
+                        && spectrumAssignment.getStopIndex().equals(Uint16.valueOf(0))) {
+                    pceResult.setRC(ResponseCodes.RESPONSE_FAILED);
+                    pceResult.setLocalCause(PceResult.LocalCause.NO_PATH_EXISTS);
+                    return pceResult;
+                }
+                if (spectrumAssignment.getFlexGrid()) {
+                    LOG.info("Spectrum assignment flexgrid mode");
+                    pceResult.setResultWavelength(GridConstant.IRRELEVANT_WAVELENGTH_NUMBER);
+                } else {
+                    LOG.info("Spectrum assignment fixedgrid mode");
+                    pceResult.setResultWavelength(
+                            GridUtils.getWaveLengthIndexFromSpectrumAssigment(spectrumAssignment.getBeginIndex()
+                                .toJava()));
+                }
+                pceResult.setMinFreq(GridUtils.getStartFrequencyFromIndex(spectrumAssignment.getBeginIndex().toJava()));
+                pceResult.setMaxFreq(GridUtils.getStopFrequencyFromIndex(spectrumAssignment.getStopIndex().toJava()));
+                LOG.info("In PostAlgoPathValidator: spectrum assignment found {} {}", spectrumAssignment, path);
 
-        // choose wavelength available in all nodes of the path
-        pceResult.setRC(ResponseCodes.RESPONSE_FAILED);
-        Long waveL = chooseWavelength(path, allPceNodes);
-        if (waveL > 0) {
-            pceResult.setResultWavelength(waveL);
-            pceResult.setRC(ResponseCodes.RESPONSE_OK);
-            LOG.info("In PostAlgoPathValidator: chooseWavelength WL found {} {}", waveL, path.toString());
-        }
+                // Check the OSNR
+                if (!checkOSNR(path)) {
+                    pceResult.setRC(ResponseCodes.RESPONSE_FAILED);
+                    pceResult.setLocalCause(PceResult.LocalCause.OUT_OF_SPEC_OSNR);
+                    return pceResult;
+                }
 
-        // TODO here other post algo validations can be added
-        // more data can be sent to PceGraph module via PceResult structure if
-        // required
-        stubCheckOSNR(path);
+                // Check if MaxLatency is defined in the hard constraints
+                if ((pceHardConstraints.getMaxLatency() != -1)
+                        && (!checkLatency(pceHardConstraints.getMaxLatency(), path))) {
+                    pceResult.setRC(ResponseCodes.RESPONSE_FAILED);
+                    pceResult.setLocalCause(PceResult.LocalCause.TOO_HIGH_LATENCY);
+                    return pceResult;
+                }
+
+                // Check if nodes are included in the hard constraints
+                if (!checkInclude(path, pceHardConstraints)) {
+                    pceResult.setRC(ResponseCodes.RESPONSE_FAILED);
+                    pceResult.setLocalCause(PceResult.LocalCause.HD_NODE_INCLUDE);
+                    return pceResult;
+                }
+
+                // TODO here other post algo validations can be added
+                // more data can be sent to PceGraph module via PceResult structure if required
+
+                pceResult.setRC(ResponseCodes.RESPONSE_OK);
+                pceResult.setLocalCause(PceResult.LocalCause.NONE);
+                break;
+            case StringConstants.SERVICE_TYPE_100GE_M:
+            case StringConstants.SERVICE_TYPE_10GE:
+            case StringConstants.SERVICE_TYPE_1GE:
+                Map<String, Integer> tribSlotNbMap = Map.of(
+                    StringConstants.SERVICE_TYPE_100GE_M, 20,
+                    StringConstants.SERVICE_TYPE_10GE, 8,
+                    StringConstants.SERVICE_TYPE_1GE, 1);
+                int tribSlotNb = tribSlotNbMap.get(serviceType);
+                pceResult.setRC(ResponseCodes.RESPONSE_FAILED);
+                pceResult.setServiceType(serviceType);
+                Map<String, List<Uint16>> tribSlot = chooseTribSlot(path, allPceNodes, tribSlotNb);
+                Map<String, Uint16> tribPort = chooseTribPort(path, allPceNodes, tribSlot, tribSlotNb);
+                List<OpucnTribSlotDef> resultTribPortTribSlot = getMinMaxTpTs(tribPort, tribSlot);
 
+                if (resultTribPortTribSlot.get(0) != null && resultTribPortTribSlot.get(1) != null) {
+                    pceResult.setResultTribPortTribSlot(resultTribPortTribSlot);
+                    pceResult.setRC(ResponseCodes.RESPONSE_OK);
+                    LOG.info("In PostAlgoPathValidator: found TribPort {} - tribSlot {} - tribSlotNb {}",
+                        tribPort, tribSlot, tribSlotNb);
+                }
+                break;
+            case StringConstants.SERVICE_TYPE_ODU4:
+            case StringConstants.SERVICE_TYPE_ODUC2:
+            case StringConstants.SERVICE_TYPE_ODUC3:
+            case StringConstants.SERVICE_TYPE_ODUC4:
+            case StringConstants.SERVICE_TYPE_100GE_S:
+                pceResult.setRC(ResponseCodes.RESPONSE_OK);
+                pceResult.setServiceType(serviceType);
+                LOG.info("In PostAlgoPathValidator: ODU4/ODUCn path found {}", path);
+                break;
+            default:
+                pceResult.setRC(ResponseCodes.RESPONSE_FAILED);
+                LOG.warn("In PostAlgoPathValidator checkPath: unsupported serviceType {} found {}",
+                    serviceType, path);
+                break;
+        }
         return pceResult;
     }
 
-    private Long chooseWavelength(GraphPath<String, PceGraphEdge> path, Map<NodeId, PceNode> allPceNodes) {
-        Long wavelength = -1L;
+    // Check the latency
+    private boolean checkLatency(Long maxLatency, GraphPath<String, PceGraphEdge> path) {
+        double latency = 0;
 
-        for (long i = 1; i <= MAX_WAWELENGTH; i++) {
-            boolean completed = true;
-            LOG.debug("In chooseWavelength: {} {}", path.getLength(), path.toString());
-            for (PceGraphEdge edge : path.getEdgeList()) {
-                LOG.debug("In chooseWavelength: source {} ", edge.link().getSourceId().toString());
-                PceNode pceNode = allPceNodes.get(edge.link().getSourceId());
-                if (!pceNode.checkWL(i)) {
-                    completed = false;
+        for (PceGraphEdge edge : path.getEdgeList()) {
+            if (edge.link() == null || edge.link().getLatency() == null) {
+                LOG.warn("- In checkLatency: the link {} does not contain latency field",
+                    edge.link().getLinkId().getValue());
+                return false;
+            }
+            latency += edge.link().getLatency();
+            LOG.debug("- In checkLatency: latency of {} = {} units", edge.link().getLinkId().getValue(), latency);
+        }
+        return (latency < maxLatency);
+    }
+
+    // Check the inclusion if it is defined in the hard constraints
+    private boolean checkInclude(GraphPath<String, PceGraphEdge> path, PceConstraints pceHardConstraintsInput) {
+        List<ResourcePair> listToInclude = pceHardConstraintsInput.getListToInclude();
+        if (listToInclude.isEmpty()) {
+            return true;
+        }
+
+        List<PceGraphEdge> pathEdges = path.getEdgeList();
+        LOG.debug(" in checkInclude vertex list: [{}]", path.getVertexList());
+
+        List<String> listOfElementsSubNode = new ArrayList<>();
+        listOfElementsSubNode.add(pathEdges.get(0).link().getsourceNetworkSupNodeId());
+        listOfElementsSubNode.addAll(listOfElementsBuild(pathEdges, PceConstraints.ResourceType.NODE,
+            pceHardConstraintsInput));
+
+        List<String> listOfElementsCLLI = new ArrayList<>();
+        listOfElementsCLLI.add(pathEdges.get(0).link().getsourceCLLI());
+        listOfElementsCLLI.addAll(listOfElementsBuild(pathEdges, PceConstraints.ResourceType.CLLI,
+            pceHardConstraintsInput));
+
+        List<String> listOfElementsSRLG = new ArrayList<>();
+        // first link is XPONDEROUTPUT, no SRLG for it
+        listOfElementsSRLG.add("NONE");
+        listOfElementsSRLG.addAll(listOfElementsBuild(pathEdges, PceConstraints.ResourceType.SRLG,
+            pceHardConstraintsInput));
+
+        // validation: check each type for each element
+        for (ResourcePair next : listToInclude) {
+            int indx = -1;
+            switch (next.getType()) {
+                case NODE:
+                    if (listOfElementsSubNode.contains(next.getName())) {
+                        indx = listOfElementsSubNode.indexOf(next.getName());
+                    }
+                    break;
+                case SRLG:
+                    if (listOfElementsSRLG.contains(next.getName())) {
+                        indx = listOfElementsSRLG.indexOf(next.getName());
+                    }
+                    break;
+                case CLLI:
+                    if (listOfElementsCLLI.contains(next.getName())) {
+                        indx = listOfElementsCLLI.indexOf(next.getName());
+                    }
+                    break;
+                default:
+                    LOG.warn(" in checkInclude vertex list unsupported resource type: [{}]", next.getType());
+            }
+
+            if (indx < 0) {
+                LOG.debug(" in checkInclude stopped : {} ", next.getName());
+                return false;
+            }
+
+            LOG.debug(" in checkInclude next found {} in {}", next.getName(), path.getVertexList());
+
+            listOfElementsSubNode.subList(0, indx).clear();
+            listOfElementsCLLI.subList(0, indx).clear();
+            listOfElementsSRLG.subList(0, indx).clear();
+        }
+
+        LOG.info(" in checkInclude passed : {} ", path.getVertexList());
+        return true;
+    }
+
+    private List<String> listOfElementsBuild(List<PceGraphEdge> pathEdges, PceConstraints.ResourceType type,
+        PceConstraints pceHardConstraints) {
+
+        List<String> listOfElements = new ArrayList<>();
+        for (PceGraphEdge link : pathEdges) {
+            switch (type) {
+                case NODE:
+                    listOfElements.add(link.link().getdestNetworkSupNodeId());
+                    break;
+                case CLLI:
+                    listOfElements.add(link.link().getdestCLLI());
+                    break;
+                case SRLG:
+                    if (link.link().getlinkType() != OpenroadmLinkType.ROADMTOROADM) {
+                        listOfElements.add("NONE");
+                        break;
+                    }
+                    // srlg of link is List<Long>. But in this algo we need string representation of
+                    // one SRLG
+                    // this should be any SRLG mentioned in include constraints if any of them if
+                    // mentioned
+                    boolean found = false;
+                    for (Long srlg : link.link().getsrlgList()) {
+                        String srlgStr = String.valueOf(srlg);
+                        if (pceHardConstraints.getSRLGnames().contains(srlgStr)) {
+                            listOfElements.add(srlgStr);
+                            LOG.info("listOfElementsBuild. FOUND SRLG {} in link {}", srlgStr, link.link());
+                            found = true;
+                        }
+                    }
+                    if (!found) {
+                        // there is no specific srlg to include. thus add to list just the first one
+                        listOfElements.add("NONE");
+                    }
                     break;
+                default:
+                    LOG.debug("listOfElementsBuild unsupported resource type");
+            }
+        }
+        return listOfElements;
+    }
+
+    private Map<String, Uint16> chooseTribPort(GraphPath<String,
+        PceGraphEdge> path, Map<NodeId, PceNode> allPceNodes, Map<String, List<Uint16>> tribSlotMap, int nbSlot) {
+        LOG.info("In choosetribPort: edgeList = {} ", path.getEdgeList());
+        Map<String, Uint16> tribPortMap = new HashMap<>();
+
+        for (PceGraphEdge edge : path.getEdgeList()) {
+            NodeId linkSrcNode = edge.link().getSourceId();
+            String linkSrcTp = edge.link().getSourceTP().getValue();
+            NodeId linkDestNode = edge.link().getDestId();
+            String linkDestTp = edge.link().getDestTP().getValue();
+            PceNode pceOtnNodeSrc = allPceNodes.get(linkSrcNode);
+            PceNode pceOtnNodeDest = allPceNodes.get(linkDestNode);
+            List<Uint16> srcTpnPool = pceOtnNodeSrc.getAvailableTribPorts().get(linkSrcTp);
+            List<Uint16> destTpnPool = pceOtnNodeDest.getAvailableTribPorts().get(linkDestTp);
+            List<Uint16> commonEdgeTpnPool = new ArrayList<>();
+            for (Uint16 srcTpn : srcTpnPool) {
+                if (destTpnPool.contains(srcTpn)) {
+                    commonEdgeTpnPool.add(srcTpn);
                 }
             }
-            if (completed) {
-                wavelength = i;
-                break;
+
+            if (!commonEdgeTpnPool.isEmpty()) {
+                Integer startTribSlot = tribSlotMap.values().stream().findFirst().get().get(0).toJava();
+                Integer tribPort = (int) Math.ceil((double)startTribSlot / nbSlot);
+                for (Uint16 commonTribPort : commonEdgeTpnPool) {
+                    if (tribPort.equals(commonTribPort.toJava())) {
+                        tribPortMap.put(edge.link().getLinkId().getValue(), commonTribPort);
+                    }
+                }
             }
         }
-        return wavelength;
+        tribPortMap.forEach((k,v) -> LOG.info("TribPortMap : k = {}, v = {}", k, v));
+        return tribPortMap;
     }
 
-    private boolean stubCheckOSNR(GraphPath<String, PceGraphEdge> path) {
-        double localOsnr = 0L;
+    private Map<String, List<Uint16>> chooseTribSlot(GraphPath<String,
+        PceGraphEdge> path, Map<NodeId, PceNode> allPceNodes, int nbSlot) {
+        LOG.info("In choosetribSlot: edgeList = {} ", path.getEdgeList());
+        Map<String, List<Uint16>> tribSlotMap = new HashMap<>();
+
         for (PceGraphEdge edge : path.getEdgeList()) {
-            localOsnr = localOsnr + edge.link().getosnr();
+            NodeId linkSrcNode = edge.link().getSourceId();
+            String linkSrcTp = edge.link().getSourceTP().getValue();
+            NodeId linkDestNode = edge.link().getDestId();
+            String linkDestTp = edge.link().getDestTP().getValue();
+            PceNode pceOtnNodeSrc = allPceNodes.get(linkSrcNode);
+            PceNode pceOtnNodeDest = allPceNodes.get(linkDestNode);
+            List<Uint16> srcTsPool = pceOtnNodeSrc.getAvailableTribSlots().get(linkSrcTp);
+            List<Uint16> destTsPool = pceOtnNodeDest.getAvailableTribSlots().get(linkDestTp);
+            List<Uint16> commonEdgeTsPoolList = new ArrayList<>();
+            List<Uint16> tribSlotList = new ArrayList<>();
+            for (Uint16 integer : srcTsPool) {
+                if (destTsPool.contains(integer)) {
+                    commonEdgeTsPoolList.add(integer);
+                }
+            }
+            Collections.sort(commonEdgeTsPoolList);
+            List<Uint16> commonGoodStartEdgeTsPoolList = new ArrayList<>();
+            for (Uint16 startEdgeTsPool : commonEdgeTsPoolList) {
+                if (Integer.valueOf(1).equals(startEdgeTsPool.toJava() % nbSlot)
+                        || nbSlot == 1) {
+                    commonGoodStartEdgeTsPoolList.add(startEdgeTsPool);
+                }
+            }
+            Collections.sort(commonGoodStartEdgeTsPoolList);
+            boolean goodTsList = false;
+            for (Uint16 goodStartTsPool : commonGoodStartEdgeTsPoolList) {
+                int goodStartIndex = commonEdgeTsPoolList.indexOf(Uint16.valueOf(goodStartTsPool.intValue()));
+                if (!goodTsList && commonEdgeTsPoolList.size() - goodStartIndex >= nbSlot) {
+                    for (int i = 0; i < nbSlot; i++) {
+                        if (!commonEdgeTsPoolList.get(goodStartIndex + i)
+                                .equals(Uint16.valueOf(goodStartTsPool.toJava() + i))) {
+                            goodTsList = false;
+                            tribSlotList.clear();
+                            break;
+                        }
+                        tribSlotList.add(commonEdgeTsPoolList.get(goodStartIndex + i));
+                        goodTsList = true;
+                    }
+                }
+            }
+            tribSlotMap.put(edge.link().getLinkId().getValue(), tribSlotList);
         }
-        LOG.info("In OSNR Stub: {}", localOsnr);
-        return true;
+        tribSlotMap.forEach((k,v) -> LOG.info("TribSlotMap : k = {}, v = {}", k, v));
+        return tribSlotMap;
+    }
+
+    private List<OpucnTribSlotDef> getMinMaxTpTs(Map<String, Uint16> tribPort, Map<String, List<Uint16>> tribSlot) {
+        String tribport = tribPort.values().toArray()[0].toString();
+        @SuppressWarnings("unchecked")
+        List<Uint16> tsList = (List<Uint16>) tribSlot.values().toArray()[0];
+        OpucnTribSlotDef minOpucnTs = OpucnTribSlotDef
+            .getDefaultInstance(String.join(".", tribport, tsList.get(0).toString()));
+        OpucnTribSlotDef maxOpucnTs = OpucnTribSlotDef
+            .getDefaultInstance(String.join(".", tribport, tsList.get(tsList.size() - 1).toString()));
+        List<OpucnTribSlotDef> minmaxTpTsList = new ArrayList<>();
+        minmaxTpTsList.add(minOpucnTs);
+        minmaxTpTsList.add(maxOpucnTs);
+        return minmaxTpTsList;
+    }
+
+    // Check the path OSNR
+    private boolean checkOSNR(GraphPath<String, PceGraphEdge> path) {
+        double linkOsnrDb;
+        double osnrDb = 0;
+        LOG.info("- In checkOSNR: OSNR of the transmitter = {} dB", TRX_OSNR);
+        LOG.info("- In checkOSNR: add-path incremental OSNR = {} dB", ADD_OSNR);
+        double inverseLocalOsnr = getInverseOsnrLinkLu(TRX_OSNR) + getInverseOsnrLinkLu(ADD_OSNR);
+        for (PceGraphEdge edge : path.getEdgeList()) {
+            if (edge.link().getlinkType() == OpenroadmLinkType.ROADMTOROADM) {
+                // link OSNR in dB
+                linkOsnrDb = edge.link().getosnr();
+                LOG.info("- In checkOSNR: OSNR of {} = {} dB", edge.link().getLinkId().getValue(), linkOsnrDb);
+                // 1 over the local OSNR, in linear units
+                inverseLocalOsnr += getInverseOsnrLinkLu(linkOsnrDb);
+            }
+        }
+        try {
+            osnrDb = getOsnrDb(1 / inverseLocalOsnr);
+        } catch (ArithmeticException e) {
+            LOG.debug("In checkOSNR: OSNR is equal to 0 and the number of links is: {}", path.getEdgeList().size());
+            return false;
+        }
+        LOG.info("In checkOSNR: OSNR of the path is {} dB", osnrDb);
+        return ((osnrDb + SYS_MARGIN) > MIN_OSNR_W100G);
+    }
+
+    private double getOsnrDb(double osnrLu) {
+        return (10 * Math.log10(osnrLu));
+    }
+
+    private double getInverseOsnrLinkLu(double linkOsnrDb) {
+        // 1 over the link OSNR, in linear units
+        double linkOsnrLu = Math.pow(10, (linkOsnrDb / 10.0));
+        LOG.debug("In retrieveosnr: the inverse of link osnr is {} (Linear Unit)", linkOsnrLu);
+        return (CONST_OSNR / linkOsnrLu);
+    }
+
+    /**
+     * Get spectrum assignment for path.
+     *
+     * @param path                    the path for which we get spectrum assignment.
+     * @param allPceNodes             all optical nodes.
+     * @param spectralWidthSlotNumber number of slot for spectral width. Depends on
+     *                                service type.
+     * @return a spectrum assignment object which contains begin and end index. If
+     *         no spectrum assignment found, beginIndex = stopIndex = 0
+     */
+    private SpectrumAssignment getSpectrumAssignment(GraphPath<String, PceGraphEdge> path,
+            Map<NodeId, PceNode> allPceNodes, int spectralWidthSlotNumber) {
+        byte[] freqMap = new byte[GridConstant.NB_OCTECTS];
+        Arrays.fill(freqMap, (byte) GridConstant.AVAILABLE_SLOT_VALUE);
+        BitSet result = BitSet.valueOf(freqMap);
+        boolean isFlexGrid = true;
+        LOG.info("Processing path {} with length {}", path, path.getLength());
+        BitSet pceNodeFreqMap;
+        for (PceGraphEdge edge : path.getEdgeList()) {
+            LOG.info("Processing source {} ", edge.link().getSourceId());
+            if (allPceNodes.containsKey(edge.link().getSourceId())) {
+                PceNode pceNode = allPceNodes.get(edge.link().getSourceId());
+                LOG.info("Processing PCE node {}", pceNode);
+                if (StringConstants.OPENROADM_DEVICE_VERSION_1_2_1.equals(pceNode.getVersion())) {
+                    LOG.info("Node {}: version is {} and slot width granularity is {} -> fixed grid mode",
+                        pceNode.getNodeId(), pceNode.getVersion(), pceNode.getSlotWidthGranularity());
+                    isFlexGrid = false;
+                }
+                if ((pceNode.getSlotWidthGranularity().setScale(0, RoundingMode.CEILING)
+                        .equals(GridConstant.SLOT_WIDTH_50))
+                        && (pceNode.getCentralFreqGranularity().setScale(0, RoundingMode.CEILING)
+                        .equals(GridConstant.SLOT_WIDTH_50))) {
+                    LOG.info("Node {}: version is {} with slot width granularity  {} and central "
+                            + "frequency granularity is {} -> fixed grid mode",
+                        pceNode.getNodeId(), pceNode.getVersion(), pceNode.getSlotWidthGranularity(),
+                        pceNode.getCentralFreqGranularity());
+                    isFlexGrid = false;
+                }
+                pceNodeFreqMap = pceNode.getBitSetData();
+                LOG.debug("Pce node bitset {}", pceNodeFreqMap);
+                if (pceNodeFreqMap != null) {
+                    result.and(pceNodeFreqMap);
+                    LOG.debug("intermediate bitset {}", result);
+                }
+            }
+        }
+        LOG.debug("Bitset result {}", result);
+        return computeBestSpectrumAssignment(result, spectralWidthSlotNumber, isFlexGrid);
+    }
+
+    /**
+     * Compute spectrum assignment from spectrum occupation for spectral width.
+     *
+     * @param spectrumOccupation      the spectrum occupation BitSet.
+     * @param spectralWidthSlotNumber the nb slots for spectral width.
+     * @param isFlexGrid              true if flexible grid, false otherwise.
+     * @return a spectrum assignment object which contains begin and stop index. If
+     *         no spectrum assignment found, beginIndex = stopIndex = 0
+     */
+    private SpectrumAssignment computeBestSpectrumAssignment(BitSet spectrumOccupation, int spectralWidthSlotNumber,
+            boolean isFlexGrid) {
+        SpectrumAssignmentBuilder spectrumAssignmentBldr = new SpectrumAssignmentBuilder()
+            .setBeginIndex(Uint16.valueOf(0))
+            .setStopIndex(Uint16.valueOf(0))
+            .setFlexGrid(isFlexGrid);
+        BitSet referenceBitSet = new BitSet(spectralWidthSlotNumber);
+        referenceBitSet.set(0, spectralWidthSlotNumber);
+        int nbSteps = isFlexGrid ? spectralWidthSlotNumber : 1;
+        //higher is the frequency, smallest is the wavelength number
+        //in operational, the allocation is done through wavelength starting from the smallest
+        //so we have to loop from the last element of the spectrum occupation
+        for (int i = spectrumOccupation.size(); i >= spectralWidthSlotNumber; i -= nbSteps) {
+            if (spectrumOccupation.get(i - spectralWidthSlotNumber, i).equals(referenceBitSet)) {
+                spectrumAssignmentBldr.setBeginIndex(Uint16.valueOf(i - spectralWidthSlotNumber));
+                spectrumAssignmentBldr.setStopIndex(Uint16.valueOf(i - 1));
+                break;
+            }
+        }
+        return spectrumAssignmentBldr.build();
     }
 }