Re-assembled the topology subsystem.

@@ -16,7 +16,7 @@ public class DefaultLink extends AbstractModel implements Link {
     private final Type type;
 
     /**
-     * Creates a link description using the supplied information.
+     * Creates an infrastructure link using the supplied information.
      *
      * @param providerId provider identity
      * @param src        link source

+package org.onlab.onos.net;
+
+import com.google.common.collect.ImmutableList;
+import org.onlab.onos.net.provider.ProviderId;
+
+import java.util.List;
+import java.util.Objects;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static com.google.common.base.Preconditions.checkNotNull;
+
+/**
+ * Default implementation of a network path.
+ */
+public class DefaultPath extends DefaultLink implements Path {
+
+    private final List<Link> links;
+    private final double cost;
+
+    /**
+     * Creates a path from the specified source and destination using the
+     * supplied list of links.
+     *
+     * @param providerId provider identity
+     * @param links      contiguous links that comprise the path
+     * @param cost       unit-less path cost
+     */
+    public DefaultPath(ProviderId providerId, List<Link> links, double cost) {
+        super(providerId, source(links), destination(links), Type.INDIRECT);
+        this.links = ImmutableList.copyOf(links);
+        this.cost = cost;
+    }
+
+    @Override
+    public List<Link> links() {
+        return links;
+    }
+
+    @Override
+    public double cost() {
+        return cost;
+    }
+
+    // Returns the source of the first link.
+    private static ConnectPoint source(List<Link> links) {
+        checkNotNull(links, "List of path links cannot be null");
+        checkArgument(!links.isEmpty(), "List of path links cannot be empty");
+        return links.get(0).src();
+    }
+
+    // Returns the destination of the last link.
+    private static ConnectPoint destination(List<Link> links) {
+        checkNotNull(links, "List of path links cannot be null");
+        checkArgument(!links.isEmpty(), "List of path links cannot be empty");
+        return links.get(links.size() - 1).dst();
+    }
+
+    @Override
+    public int hashCode() {
+        return 31 * super.hashCode() + Objects.hash(links);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj instanceof DefaultPath) {
+            final DefaultPath other = (DefaultPath) obj;
+            return Objects.equals(this.links, other.links);
+        }
+        return false;
+    }
+}

@@ -17,4 +17,11 @@ public interface Path extends Link {
      */
     List<Link> links();
 
+    /**
+     * Returns the path cost as a unit-less value.
+     *
+     * @return unit-less path cost
+     */
+    double cost();
+
 }

@@ -27,6 +27,15 @@ public final class ClusterId {
         return new ClusterId(id);
     }
 
+    /**
+     * Returns the backing integer index.
+     *
+     * @return backing integer index
+     */
+    public int index() {
+        return id;
+    }
+
     @Override
     public int hashCode() {
         return Objects.hash(id);

+package org.onlab.onos.net.topology;
+
+import com.google.common.collect.ImmutableSet;
+import org.onlab.onos.net.Description;
+
+/**
+ * Describes attribute(s) of a network graph.
+ */
+public interface GraphDescription extends Description {
+
+    /**
+     * Returns the creation timestamp of the graph description. This is
+     * expressed in system nanos to allow proper sequencing.
+     *
+     * @return graph description creation timestamp
+     */
+    long timestamp();
+
+    /**
+     * Returns the set of topology graph vertexes.
+     *
+     * @return set of graph vertexes
+     */
+    ImmutableSet<TopologyVertex> vertexes();
+
+    /**
+     * Returns the set of topology graph edges.
+     *
+     * @return set of graph edges
+     */
+    ImmutableSet<TopologyEdge> edges();
+
+}
+

@@ -6,5 +6,5 @@ import org.onlab.graph.EdgeWeight;
  * Entity capable of determining cost or weight of a specified topology
  * graph edge.
  */
-public interface LinkWeight extends EdgeWeight<TopoVertex, TopoEdge> {
+public interface LinkWeight extends EdgeWeight<TopologyVertex, TopologyEdge> {
 }

-package org.onlab.onos.net.topology;
-
-import com.google.common.collect.ImmutableMap;
-import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.ImmutableSetMultimap;
-import org.onlab.graph.Graph;
-import org.onlab.onos.net.Description;
-import org.onlab.onos.net.DeviceId;
-import org.onlab.onos.net.Link;
-
-import static org.onlab.graph.GraphPathSearch.Result;
-
-/**
- * Describes attribute(s) of a network topology.
- */
-public interface TopologyDescription extends Description {
-
-    /**
-     * Returns the creation timestamp of the topology description. This is
-     * expressed in system nanos to allow proper sequencing.
-     *
-     * @return topology description creation timestamp
-     */
-    long timestamp();
-
-    /**
-     * Returns the topology graph in immutable form.
-     *
-     * @return network graph
-     */
-    Graph<TopoVertex, TopoEdge> graph();
-
-    /**
-     * Returns an immutable map of path search results for each source device.
-     *
-     * @return map of path search result for each source node
-     */
-    ImmutableMap<DeviceId, Result<TopoVertex, TopoEdge>> pathsBySource();
-
-    /**
-     * Returns the set of topology SCC clusters.
-     *
-     * @return set of SCC clusters
-     */
-    ImmutableSet<TopologyCluster> clusters();
-
-    /**
-     * Returns an immutable set multi-map of devices for each cluster.
-     *
-     * @return set multi-map of devices that belong to each cluster
-     */
-    ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster();
-
-    /**
-     * Returns an immutable set multi-map of links for each cluster.
-     *
-     * @return set multi-map of links that belong to each cluster
-     */
-    ImmutableSetMultimap<TopologyCluster, Link> linksByCluster();
-
-}
-

@@ -6,7 +6,7 @@ import org.onlab.onos.net.Link;
 /**
  * Represents an edge in the topology graph.
  */
-public interface TopoEdge extends Edge<TopoVertex> {
+public interface TopologyEdge extends Edge<TopologyVertex> {
 
     /**
      * Returns the associated infrastructure link.

+package org.onlab.onos.net.topology;
+
+import org.onlab.graph.Graph;
+
+/**
+ * Represents an immutable topology graph.
+ */
+public interface TopologyGraph extends Graph<TopologyVertex, TopologyEdge> {
+
+}

@@ -10,16 +10,13 @@ import java.util.List;
  */
 public interface TopologyProviderService extends ProviderService<TopologyProvider> {
 
-    // What can be conveyed in a topology that isn't by individual
-    // providers?
-
     /**
      * Signals the core that some aspect of the topology has changed.
      *
-     * @param topoDescription information about topology
+     * @param graphDescription information about the network graph
      * @param reasons          events that triggered topology change
      */
-    void topologyChanged(TopologyDescription topoDescription,
+    void topologyChanged(GraphDescription graphDescription,
                          List<Event> reasons);
 
 }

 package org.onlab.onos.net.topology;
 
-import org.onlab.graph.Graph;
 import org.onlab.onos.net.ConnectPoint;
 import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.Path;
@@ -41,7 +40,7 @@ public interface TopologyService {
      * @param topology topology descriptor
      * @return topology graph view
      */
-    Graph<TopoVertex, TopoEdge> getGraph(Topology topology);
+    TopologyGraph getGraph(Topology topology);
 
     /**
      * Returns the set of all shortest paths, precomputed in terms of hop-count,

@@ -6,7 +6,7 @@ import org.onlab.onos.net.DeviceId;
 /**
  * Represents a vertex in the topology graph.
  */
-public interface TopoVertex extends Vertex {
+public interface TopologyVertex extends Vertex {
 
     /**
      * Returns the associated infrastructure device identification.

+package org.onlab.onos.net.trivial.topology.impl;
+
+import com.google.common.collect.ImmutableSet;
+import com.google.common.collect.Maps;
+import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.Device;
+import org.onlab.onos.net.DeviceId;
+import org.onlab.onos.net.Link;
+import org.onlab.onos.net.topology.GraphDescription;
+import org.onlab.onos.net.topology.TopologyEdge;
+import org.onlab.onos.net.topology.TopologyVertex;
+
+import java.util.Map;
+
+/**
+ * Default implementation of an immutable topology graph data carrier.
+ */
+class DefaultGraphDescription implements GraphDescription {
+
+    private final long nanos;
+    private final ImmutableSet<TopologyVertex> vertexes;
+    private final ImmutableSet<TopologyEdge> edges;
+
+    private final Map<DeviceId, TopologyVertex> vertexesById = Maps.newHashMap();
+
+
+    /**
+     * Creates a minimal topology graph description to allow core to construct
+     * and process the topology graph.
+     *
+     * @param nanos   time in nanos of when the topology description was created
+     * @param devices collection of infrastructure devices
+     * @param links   collection of infrastructure links
+     */
+    DefaultGraphDescription(long nanos, Iterable<Device> devices, Iterable<Link> links) {
+        this.nanos = nanos;
+        this.vertexes = buildVertexes(devices);
+        this.edges = buildEdges(links);
+        vertexesById.clear();
+    }
+
+    @Override
+    public long timestamp() {
+        return nanos;
+    }
+
+    @Override
+    public ImmutableSet<TopologyVertex> vertexes() {
+        return vertexes;
+    }
+
+    @Override
+    public ImmutableSet<TopologyEdge> edges() {
+        return edges;
+    }
+
+    // Builds a set of topology vertexes from the specified list of devices
+    private ImmutableSet<TopologyVertex> buildVertexes(Iterable<Device> devices) {
+        ImmutableSet.Builder<TopologyVertex> vertexes = ImmutableSet.builder();
+        for (Device device : devices) {
+            TopologyVertex vertex = new DefaultTopologyVertex(device.id());
+            vertexes.add(vertex);
+            vertexesById.put(vertex.deviceId(), vertex);
+        }
+        return vertexes.build();
+    }
+
+    // Builds a set of topology vertexes from the specified list of links
+    private ImmutableSet<TopologyEdge> buildEdges(Iterable<Link> links) {
+        ImmutableSet.Builder<TopologyEdge> edges = ImmutableSet.builder();
+        for (Link link : links) {
+            edges.add(new DefaultTopologyEdge(vertexOf(link.src()),
+                                              vertexOf(link.dst()), link));
+        }
+        return edges.build();
+    }
+
+    // Fetches a vertex corresponding to the given connection point device.
+    private TopologyVertex vertexOf(ConnectPoint connectPoint) {
+        DeviceId id = connectPoint.deviceId();
+        TopologyVertex vertex = vertexesById.get(id);
+        if (vertex == null) {
+            // If vertex does not exist, create one and register it.
+            vertex = new DefaultTopologyVertex(id);
+            vertexesById.put(id, vertex);
+        }
+        return vertex;
+    }
+
+}

@@ -3,38 +3,65 @@ package org.onlab.onos.net.trivial.topology.impl;
 import com.google.common.collect.ImmutableMap;
 import com.google.common.collect.ImmutableSet;
 import com.google.common.collect.ImmutableSetMultimap;
-import org.onlab.graph.Graph;
+import org.onlab.graph.DijkstraGraphSearch;
 import org.onlab.graph.GraphPathSearch;
+import org.onlab.graph.TarjanGraphSearch;
 import org.onlab.onos.net.AbstractModel;
 import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.DefaultPath;
 import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.Link;
 import org.onlab.onos.net.Path;
 import org.onlab.onos.net.provider.ProviderId;
-import org.onlab.onos.net.topology.TopoEdge;
-import org.onlab.onos.net.topology.TopoVertex;
+import org.onlab.onos.net.topology.ClusterId;
+import org.onlab.onos.net.topology.DefaultTopologyCluster;
+import org.onlab.onos.net.topology.GraphDescription;
+import org.onlab.onos.net.topology.LinkWeight;
 import org.onlab.onos.net.topology.Topology;
 import org.onlab.onos.net.topology.TopologyCluster;
-import org.onlab.onos.net.topology.TopologyDescription;
+import org.onlab.onos.net.topology.TopologyEdge;
+import org.onlab.onos.net.topology.TopologyGraph;
+import org.onlab.onos.net.topology.TopologyVertex;
 
+import java.util.ArrayList;
+import java.util.List;
+import java.util.Map;
 import java.util.Set;
 
+import static com.google.common.base.MoreObjects.toStringHelper;
+import static com.google.common.collect.ImmutableSetMultimap.Builder;
+import static org.onlab.graph.GraphPathSearch.Result;
+import static org.onlab.graph.TarjanGraphSearch.SCCResult;
+import static org.onlab.onos.net.Link.Type.INDIRECT;
+
 /**
  * Default implementation of the topology descriptor. This carries the
  * backing topology data.
  */
 public class DefaultTopology extends AbstractModel implements Topology {
 
+    private static final DijkstraGraphSearch<TopologyVertex, TopologyEdge> DIJKSTRA =
+            new DijkstraGraphSearch<>();
+    private static final TarjanGraphSearch<TopologyVertex, TopologyEdge> TARJAN =
+            new TarjanGraphSearch<>();
+
+    private static final ProviderId PID = new ProviderId("org.onlab.onos.net");
+
     private final long time;
-    private final int pathCount;
+    private final TopologyGraph graph;
+
+    private final SCCResult<TopologyVertex, TopologyEdge> clusterResults;
+    private final ImmutableMap<DeviceId, Result<TopologyVertex, TopologyEdge>> results;
+    private final ImmutableSetMultimap<PathKey, Path> paths;
 
-    private final Graph<TopoVertex, TopoEdge> graph;
-    private final ImmutableMap<DeviceId, GraphPathSearch.Result<TopoVertex, TopoEdge>> results;
+    private final ImmutableMap<ClusterId, TopologyCluster> clusters;
+    private final ImmutableSet<ConnectPoint> infrastructurePoints;
+    private final ImmutableSetMultimap<ClusterId, ConnectPoint> broadcastSets;
+
+    private ImmutableMap<DeviceId, TopologyCluster> clustersByDevice;
+    private ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster;
+    private ImmutableSetMultimap<TopologyCluster, Link> linksByCluster;
 
-    private final ImmutableSet<TopologyCluster> clusters;
-    private final ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster;
-    private final ImmutableSetMultimap<TopologyCluster, Link> linksByCluster;
-    private final ImmutableSet connectPoints;
 
     /**
      * Creates a topology descriptor attributed to the specified provider.
@@ -42,17 +69,24 @@ public class DefaultTopology extends AbstractModel implements Topology {
      * @param providerId  identity of the provider
      * @param description data describing the new topology
      */
-    DefaultTopology(ProviderId providerId, TopologyDescription description) {
+    DefaultTopology(ProviderId providerId, GraphDescription description) {
         super(providerId);
         this.time = description.timestamp();
-        this.graph = description.graph();
-        this.results = description.pathsBySource();
-        this.clusters = description.clusters();
-        this.devicesByCluster = description.devicesByCluster();
-        this.linksByCluster = description.linksByCluster();
 
-        this.connectPoints = ImmutableSet.of();
-        this.pathCount = 0;
+        // Build the graph
+        this.graph = new DefaultTopologyGraph(description.vertexes(),
+                                              description.edges());
+
+        this.results = searchForShortestPaths();
+        this.paths = buildPaths();
+
+        this.clusterResults = searchForClusters();
+        this.clusters = buildTopologyClusters();
+
+        buildIndexes();
+
+        this.broadcastSets = buildBroadcastSets();
+        this.infrastructurePoints = findInfrastructurePoints();
     }
 
     @Override
@@ -77,26 +111,303 @@ public class DefaultTopology extends AbstractModel implements Topology {
 
     @Override
     public int pathCount() {
-        return pathCount;
+        return paths.size();
     }
 
+    /**
+     * Returns the backing topology graph.
+     *
+     * @return topology graph
+     */
+    TopologyGraph getGraph() {
+        return graph;
+    }
+
+    /**
+     * Returns the set of topology clusters.
+     *
+     * @return set of clusters
+     */
     Set<TopologyCluster> getClusters() {
-        return clusters;
+        return ImmutableSet.copyOf(clusters.values());
     }
 
-    Graph<TopoVertex, TopoEdge> getGraph() {
-        return graph;
+    /**
+     * Returns the set of cluster devices.
+     *
+     * @param cluster topology cluster
+     * @return cluster devices
+     */
+    Set<DeviceId> getClusterDevices(TopologyCluster cluster) {
+        return devicesByCluster.get(cluster);
+    }
+
+    /**
+     * Returns the set of cluster links.
+     *
+     * @param cluster topology cluster
+     * @return cluster links
+     */
+    Set<Link> getClusterLinks(TopologyCluster cluster) {
+        return linksByCluster.get(cluster);
     }
 
+    /**
+     * Indicates whether the given point is an infrastructure link end-point.
+     *
+     * @param connectPoint connection point
+     * @return true if infrastructure
+     */
     boolean isInfrastructure(ConnectPoint connectPoint) {
-        return connectPoints.contains(connectPoint);
+        return infrastructurePoints.contains(connectPoint);
     }
 
+    /**
+     * Indicates whether the given point is part of a broadcast tree.
+     *
+     * @param connectPoint connection point
+     * @return true if in broadcast tree
+     */
     boolean isInBroadcastTree(ConnectPoint connectPoint) {
-        return false;
+        // Any non-infrastructure, i.e. edge points are assumed to be OK
+        if (!isInfrastructure(connectPoint)) {
+            return true;
+        }
+
+        // Find the cluster to which the device belongs.
+        TopologyCluster cluster = clustersByDevice.get(connectPoint.deviceId());
+        if (cluster == null) {
+            throw new IllegalArgumentException("No cluster found for device " + connectPoint.deviceId());
+        }
+
+        // If the broadcast tree is null or empty, or if the point explicitly
+        // belongs to the broadcast tree points, return true;
+        Set<ConnectPoint> points = broadcastSets.get(cluster.id());
+        return points == null || points.isEmpty() || points.contains(connectPoint);
     }
 
+    /**
+     * Returns the set of pre-computed shortest paths between source and
+     * destination devices.
+     *
+     * @param src source device
+     * @param dst destination device
+     * @return set of shortest paths
+     */
     Set<Path> getPaths(DeviceId src, DeviceId dst) {
-        return null; // pointToPointPaths.get(key(src, dst));
+        return paths.get(new PathKey(src, dst));
+    }
+
+    /**
+     * Computes on-demand the set of shortest paths between source and
+     * destination devices.
+     *
+     * @param src source device
+     * @param dst destination device
+     * @return set of shortest paths
+     */
+    Set<Path> getPaths(DeviceId src, DeviceId dst, LinkWeight weight) {
+        GraphPathSearch.Result<TopologyVertex, TopologyEdge> result =
+                DIJKSTRA.search(graph, new DefaultTopologyVertex(src),
+                                new DefaultTopologyVertex(dst), weight);
+        ImmutableSet.Builder<Path> builder = ImmutableSet.builder();
+        for (org.onlab.graph.Path<TopologyVertex, TopologyEdge> path : result.paths()) {
+            builder.add(networkPath(path));
+        }
+        return builder.build();
+    }
+
+
+    // Searches the graph for all shortest paths and returns the search results.
+    private ImmutableMap<DeviceId, Result<TopologyVertex, TopologyEdge>> searchForShortestPaths() {
+        ImmutableMap.Builder<DeviceId, Result<TopologyVertex, TopologyEdge>> builder = ImmutableMap.builder();
+
+        // Search graph paths for each source to all destinations.
+        LinkWeight weight = new HopCountLinkWeight(graph.getVertexes().size());
+        for (TopologyVertex src : graph.getVertexes()) {
+            builder.put(src.deviceId(), DIJKSTRA.search(graph, src, null, weight));
+        }
+        return builder.build();
+    }
+
+    // Builds network paths from the graph path search results
+    private ImmutableSetMultimap<PathKey, Path> buildPaths() {
+        Builder<PathKey, Path> builder = ImmutableSetMultimap.builder();
+        for (DeviceId deviceId : results.keySet()) {
+            Result<TopologyVertex, TopologyEdge> result = results.get(deviceId);
+            for (org.onlab.graph.Path<TopologyVertex, TopologyEdge> path : result.paths()) {
+                builder.put(new PathKey(path.src().deviceId(), path.dst().deviceId()),
+                            networkPath(path));
+            }
+        }
+        return builder.build();
+    }
+
+    // Converts graph path to a network path with the same cost.
+    private Path networkPath(org.onlab.graph.Path<TopologyVertex, TopologyEdge> path) {
+        List<Link> links = new ArrayList<>();
+        for (TopologyEdge edge : path.edges()) {
+            links.add(edge.link());
+        }
+        return new DefaultPath(PID, links, path.cost());
+    }
+
+
+    // Searches for SCC clusters in the network topology graph using Tarjan
+    // algorithm.
+    private SCCResult<TopologyVertex, TopologyEdge> searchForClusters() {
+        return TARJAN.search(graph, new NoIndirectLinksWeight());
+    }
+
+    // Builds the topology clusters and returns the id-cluster bindings.
+    private ImmutableMap<ClusterId, TopologyCluster> buildTopologyClusters() {
+        ImmutableMap.Builder<ClusterId, TopologyCluster> clusterBuilder = ImmutableMap.builder();
+        SCCResult<TopologyVertex, TopologyEdge> result =
+                TARJAN.search(graph, new NoIndirectLinksWeight());
+
+        // Extract both vertexes and edges from the results; the lists form
+        // pairs along the same index.
+        List<Set<TopologyVertex>> clusterVertexes = result.clusterVertexes();
+        List<Set<TopologyEdge>> clusterEdges = result.clusterEdges();
+
+        // Scan over the lists and create a cluster from the results.
+        for (int i = 0, n = result.clusterCount(); i < n; i++) {
+            Set<TopologyVertex> vertexSet = clusterVertexes.get(i);
+            Set<TopologyEdge> edgeSet = clusterEdges.get(i);
+
+            ClusterId cid = ClusterId.clusterId(i);
+            DefaultTopologyCluster cluster =
+                    new DefaultTopologyCluster(cid, vertexSet.size(), edgeSet.size(),
+                                               findRoot(vertexSet).deviceId());
+            clusterBuilder.put(cid, cluster);
+        }
+        return clusterBuilder.build();
+    }
+
+    // Finds the vertex whose device id is the lexicographical minimum in the
+    // specified set.
+    private TopologyVertex findRoot(Set<TopologyVertex> vertexSet) {
+        TopologyVertex minVertex = null;
+        for (TopologyVertex vertex : vertexSet) {
+            if (minVertex == null ||
+                    minVertex.deviceId().toString()
+                            .compareTo(minVertex.deviceId().toString()) < 0) {
+                minVertex = vertex;
+            }
+        }
+        return minVertex;
+    }
+
+    // Processes a map of broadcast sets for each cluster.
+    private ImmutableSetMultimap<ClusterId, ConnectPoint> buildBroadcastSets() {
+        Builder<ClusterId, ConnectPoint> builder = ImmutableSetMultimap.builder();
+        for (TopologyCluster cluster : clusters.values()) {
+            addClusterBroadcastSet(cluster, builder);
+        }
+        return builder.build();
+    }
+
+    // Finds all broadcast points for the cluster. These are those connection
+    // points which lie along the shortest paths between the cluster root and
+    // all other devices within the cluster.
+    private void addClusterBroadcastSet(TopologyCluster cluster,
+                                        Builder<ClusterId, ConnectPoint> builder) {
+        // Use the graph root search results to build the broadcast set.
+        Result<TopologyVertex, TopologyEdge> result = results.get(cluster.root());
+        for (Map.Entry<TopologyVertex, Set<TopologyEdge>> entry : result.parents().entrySet()) {
+            TopologyVertex vertex = entry.getKey();
+
+            // Ignore any parents that lead outside the cluster.
+            if (clustersByDevice.get(vertex.deviceId()) != cluster) {
+                continue;
+            }
+
+            // Ignore any back-link sets that are empty.
+            Set<TopologyEdge> parents = entry.getValue();
+            if (parents.isEmpty()) {
+                continue;
+            }
+
+            // Use the first back-link source and destinations to add to the
+            // broadcast set.
+            Link link = parents.iterator().next().link();
+            builder.put(cluster.id(), link.src());
+            builder.put(cluster.id(), link.dst());
+        }
+    }
+
+    // Collects and returns an set of all infrastructure link end-points.
+    private ImmutableSet<ConnectPoint> findInfrastructurePoints() {
+        ImmutableSet.Builder<ConnectPoint> builder = ImmutableSet.builder();
+        for (TopologyEdge edge : graph.getEdges()) {
+            builder.add(edge.link().src());
+            builder.add(edge.link().dst());
+        }
+        return builder.build();
+    }
+
+    // Builds cluster-devices, cluster-links and device-cluster indexes.
+    private void buildIndexes() {
+        // Prepare the index builders
+        ImmutableMap.Builder<DeviceId, TopologyCluster> clusterBuilder = ImmutableMap.builder();
+        ImmutableSetMultimap.Builder<TopologyCluster, DeviceId> devicesBuilder = ImmutableSetMultimap.builder();
+        ImmutableSetMultimap.Builder<TopologyCluster, Link> linksBuilder = ImmutableSetMultimap.builder();
+
+        // Now scan through all the clusters
+        for (TopologyCluster cluster : clusters.values()) {
+            int i = cluster.id().index();
+
+            // Scan through all the cluster vertexes.
+            for (TopologyVertex vertex : clusterResults.clusterVertexes().get(i)) {
+                devicesBuilder.put(cluster, vertex.deviceId());
+                clusterBuilder.put(vertex.deviceId(), cluster);
+            }
+
+            // Scan through all the cluster edges.
+            for (TopologyEdge edge : clusterResults.clusterEdges().get(i)) {
+                linksBuilder.put(cluster, edge.link());
+            }
+        }
+
+        // Finalize all indexes.
+        clustersByDevice = clusterBuilder.build();
+        devicesByCluster = devicesBuilder.build();
+        linksByCluster = linksBuilder.build();
+    }
+
+    // Link weight for measuring link cost as hop count with indirect links
+    // being as expensive as traversing the entire graph to assume the worst.
+    private static class HopCountLinkWeight implements LinkWeight {
+        private final int indirectLinkCost;
+
+        HopCountLinkWeight(int indirectLinkCost) {
+            this.indirectLinkCost = indirectLinkCost;
+        }
+
+        @Override
+        public double weight(TopologyEdge edge) {
+            // To force preference to use direct paths first, make indirect
+            // links as expensive as the linear vertex traversal.
+            return edge.link().type() == INDIRECT ? indirectLinkCost : 1;
+        }
+    }
+
+    // Link weight for preventing traversal over indirect links.
+    private static class NoIndirectLinksWeight implements LinkWeight {
+        @Override
+        public double weight(TopologyEdge edge) {
+            return edge.link().type() == INDIRECT ? -1 : 1;
+        }
+    }
+
+    @Override
+    public String toString() {
+        return toStringHelper(this)
+                .add("time", time)
+                .add("clusters", clusterCount())
+                .add("devices", deviceCount())
+                .add("links", linkCount())
+                .add("pathCount", pathCount())
+                .toString();
     }
 }

-package org.onlab.onos.net.trivial.topology.provider.impl;
+package org.onlab.onos.net.trivial.topology.impl;
 
 import org.onlab.onos.net.Link;
-import org.onlab.onos.net.topology.TopoEdge;
-import org.onlab.onos.net.topology.TopoVertex;
+import org.onlab.onos.net.topology.TopologyEdge;
+import org.onlab.onos.net.topology.TopologyVertex;
 
 import java.util.Objects;
 
@@ -11,11 +11,11 @@ import static com.google.common.base.MoreObjects.toStringHelper;
 /**
  * Implementation of the topology edge backed by a link.
  */
-class DefaultTopoEdge implements TopoEdge {
+class DefaultTopologyEdge implements TopologyEdge {
 
     private final Link link;
-    private final TopoVertex src;
-    private final TopoVertex dst;
+    private final TopologyVertex src;
+    private final TopologyVertex dst;
 
     /**
      * Creates a new topology edge.
@@ -24,7 +24,7 @@ class DefaultTopoEdge implements TopoEdge {
      * @param dst  destination vertex
      * @param link infrastructure link
      */
-    DefaultTopoEdge(TopoVertex src, TopoVertex dst, Link link) {
+    DefaultTopologyEdge(TopologyVertex src, TopologyVertex dst, Link link) {
         this.src = src;
         this.dst = dst;
         this.link = link;
@@ -36,12 +36,12 @@ class DefaultTopoEdge implements TopoEdge {
     }
 
     @Override
-    public TopoVertex src() {
+    public TopologyVertex src() {
         return src;
     }
 
     @Override
-    public TopoVertex dst() {
+    public TopologyVertex dst() {
         return dst;
     }
 
@@ -52,8 +52,8 @@ class DefaultTopoEdge implements TopoEdge {
 
     @Override
     public boolean equals(Object obj) {
-        if (obj instanceof DefaultTopoEdge) {
-            final DefaultTopoEdge other = (DefaultTopoEdge) obj;
+        if (obj instanceof DefaultTopologyEdge) {
+            final DefaultTopologyEdge other = (DefaultTopologyEdge) obj;
             return Objects.equals(this.link, other.link);
         }
         return false;

+package org.onlab.onos.net.trivial.topology.impl;
+
+import org.onlab.graph.AdjacencyListsGraph;
+import org.onlab.onos.net.topology.TopologyEdge;
+import org.onlab.onos.net.topology.TopologyGraph;
+import org.onlab.onos.net.topology.TopologyVertex;
+
+import java.util.Set;
+
+/**
+ * Default implementation of an immutable topology graph based on a generic
+ * implementation of adjacency lists graph.
+ */
+public class DefaultTopologyGraph
+        extends AdjacencyListsGraph<TopologyVertex, TopologyEdge>
+        implements TopologyGraph {
+
+    /**
+     * Creates a topology graph comprising of the specified vertexes and edges.
+     *
+     * @param vertexes set of graph vertexes
+     * @param edges    set of graph edges
+     */
+    public DefaultTopologyGraph(Set<TopologyVertex> vertexes, Set<TopologyEdge> edges) {
+        super(vertexes, edges);
+    }
+
+}

-package org.onlab.onos.net.trivial.topology.provider.impl;
+package org.onlab.onos.net.trivial.topology.impl;
 
 import org.apache.felix.scr.annotations.Activate;
 import org.apache.felix.scr.annotations.Component;
@@ -16,7 +16,7 @@ import org.onlab.onos.net.link.LinkListener;
 import org.onlab.onos.net.link.LinkService;
 import org.onlab.onos.net.provider.AbstractProvider;
 import org.onlab.onos.net.provider.ProviderId;
-import org.onlab.onos.net.topology.TopologyDescription;
+import org.onlab.onos.net.topology.GraphDescription;
 import org.onlab.onos.net.topology.TopologyProvider;
 import org.onlab.onos.net.topology.TopologyProviderRegistry;
 import org.onlab.onos.net.topology.TopologyProviderService;
@@ -35,7 +35,7 @@ import static org.slf4j.LoggerFactory.getLogger;
  * Simple implementation of a network topology provider/computor.
  */
 @Component(immediate = true)
-public class SimpleTopologyProvider extends AbstractProvider
+public class DefaultTopologyProvider extends AbstractProvider
         implements TopologyProvider {
 
     // TODO: make these configurable
@@ -70,7 +70,7 @@ public class SimpleTopologyProvider extends AbstractProvider
     /**
      * Creates a provider with the supplier identifier.
      */
-    public SimpleTopologyProvider() {
+    public DefaultTopologyProvider() {
         super(new ProviderId("org.onlab.onos.provider.topology"));
     }
 
@@ -110,15 +110,17 @@ public class SimpleTopologyProvider extends AbstractProvider
      * @param reasons events which triggered the topology change
      */
     private synchronized void triggerTopologyBuild(List<Event> reasons) {
+        if (executor != null) {
             executor.execute(new TopologyBuilderTask(reasons));
         }
+    }
 
     // Builds the topology using the latest device and link information
     // and citing the specified events as reasons for the change.
     private void buildTopology(List<Event> reasons) {
         if (isStarted) {
-            TopologyDescription desc =
-                    new DefaultTopologyDescription(System.nanoTime(),
+            GraphDescription desc =
+                    new DefaultGraphDescription(System.nanoTime(),
                                                 deviceService.getDevices(),
                                                 linkService.getLinks());
             providerService.topologyChanged(desc, reasons);

-package org.onlab.onos.net.trivial.topology.provider.impl;
+package org.onlab.onos.net.trivial.topology.impl;
 
 import org.onlab.onos.net.DeviceId;
-import org.onlab.onos.net.topology.TopoVertex;
+import org.onlab.onos.net.topology.TopologyVertex;
 
 import java.util.Objects;
 
 /**
  * Implementation of the topology vertex backed by a device id.
  */
-class DefaultTopoVertex implements TopoVertex {
+class DefaultTopologyVertex implements TopologyVertex {
 
     private final DeviceId deviceId;
 
@@ -17,7 +17,7 @@ class DefaultTopoVertex implements TopoVertex {
      *
      * @param deviceId backing infrastructure device identifier
      */
-    DefaultTopoVertex(DeviceId deviceId) {
+    DefaultTopologyVertex(DeviceId deviceId) {
         this.deviceId = deviceId;
     }
 
@@ -33,8 +33,8 @@ class DefaultTopoVertex implements TopoVertex {
 
     @Override
     public boolean equals(Object obj) {
-        if (obj instanceof DefaultTopoVertex) {
-            final DefaultTopoVertex other = (DefaultTopoVertex) obj;
+        if (obj instanceof DefaultTopologyVertex) {
+            final DefaultTopologyVertex other = (DefaultTopologyVertex) obj;
             return Objects.equals(this.deviceId, other.deviceId);
         }
         return false;

+package org.onlab.onos.net.trivial.topology.impl;
+
+import org.onlab.onos.net.DeviceId;
+
+import java.util.Objects;
+
+/**
+ * Key for filing src/dst paths.
+ */
+class PathKey {
+    private final DeviceId src;
+    private final DeviceId dst;
+
+    /**
+     * Creates a path key from the given source/dest pair.
+     * @param src source device
+     * @param dst destination device
+     */
+    PathKey(DeviceId src, DeviceId dst) {
+        this.src = src;
+        this.dst = dst;
+    }
+
+    @Override
+    public int hashCode() {
+        return Objects.hash(src, dst);
+    }
+
+    @Override
+    public boolean equals(Object obj) {
+        if (obj instanceof PathKey) {
+            final PathKey other = (PathKey) obj;
+            return Objects.equals(this.src, other.src) && Objects.equals(this.dst, other.dst);
+        }
+        return false;
+    }
+}

@@ -6,7 +6,6 @@ import org.apache.felix.scr.annotations.Deactivate;
 import org.apache.felix.scr.annotations.Reference;
 import org.apache.felix.scr.annotations.ReferenceCardinality;
 import org.apache.felix.scr.annotations.Service;
-import org.onlab.graph.Graph;
 import org.onlab.onos.event.AbstractListenerRegistry;
 import org.onlab.onos.event.Event;
 import org.onlab.onos.event.EventDeliveryService;
@@ -15,13 +14,12 @@ import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.Path;
 import org.onlab.onos.net.provider.AbstractProviderRegistry;
 import org.onlab.onos.net.provider.AbstractProviderService;
+import org.onlab.onos.net.topology.GraphDescription;
 import org.onlab.onos.net.topology.LinkWeight;
-import org.onlab.onos.net.topology.TopoEdge;
-import org.onlab.onos.net.topology.TopoVertex;
 import org.onlab.onos.net.topology.Topology;
 import org.onlab.onos.net.topology.TopologyCluster;
-import org.onlab.onos.net.topology.TopologyDescription;
 import org.onlab.onos.net.topology.TopologyEvent;
+import org.onlab.onos.net.topology.TopologyGraph;
 import org.onlab.onos.net.topology.TopologyListener;
 import org.onlab.onos.net.topology.TopologyProvider;
 import org.onlab.onos.net.topology.TopologyProviderRegistry;
@@ -98,7 +96,7 @@ public class SimpleTopologyManager
     }
 
     @Override
-    public Graph<TopoVertex, TopoEdge> getGraph(Topology topology) {
+    public TopologyGraph getGraph(Topology topology) {
         checkNotNull(topology, TOPOLOGY_NULL);
         return store.getGraph(defaultTopology(topology));
     }
@@ -159,16 +157,14 @@ public class SimpleTopologyManager
         }
 
         @Override
-        public void topologyChanged(TopologyDescription topoDescription,
+        public void topologyChanged(GraphDescription topoDescription,
                                     List<Event> reasons) {
             checkNotNull(topoDescription, "Topology description cannot be null");
 
-            log.info("Topology changed due to: {}", // to be removed soon
-                     reasons == null ? "initial compute" : reasons);
             TopologyEvent event = store.updateTopology(provider().id(),
                                                        topoDescription, reasons);
             if (event != null) {
-                log.info("Topology changed due to: {}",
+                log.info("Topology {} changed due to: {}", event.subject(),
                          reasons == null ? "initial compute" : reasons);
                 eventDispatcher.post(event);
             }

 package org.onlab.onos.net.trivial.topology.impl;
 
-import org.onlab.graph.Graph;
 import org.onlab.onos.event.Event;
 import org.onlab.onos.net.ConnectPoint;
 import org.onlab.onos.net.DeviceId;
 import org.onlab.onos.net.Path;
 import org.onlab.onos.net.provider.ProviderId;
+import org.onlab.onos.net.topology.GraphDescription;
 import org.onlab.onos.net.topology.LinkWeight;
-import org.onlab.onos.net.topology.TopoEdge;
-import org.onlab.onos.net.topology.TopoVertex;
 import org.onlab.onos.net.topology.Topology;
 import org.onlab.onos.net.topology.TopologyCluster;
-import org.onlab.onos.net.topology.TopologyDescription;
 import org.onlab.onos.net.topology.TopologyEvent;
+import org.onlab.onos.net.topology.TopologyGraph;
 
 import java.util.List;
 import java.util.Set;
@@ -61,7 +59,7 @@ class SimpleTopologyStore {
      * @param topology topology descriptor
      * @return graph view
      */
-    Graph<TopoVertex, TopoEdge> getGraph(DefaultTopology topology) {
+    TopologyGraph getGraph(DefaultTopology topology) {
         return topology.getGraph();
     }
 
@@ -88,7 +86,7 @@ class SimpleTopologyStore {
      */
     Set<Path> getPaths(DefaultTopology topology, DeviceId src, DeviceId dst,
                        LinkWeight weight) {
-        return null;
+        return topology.getPaths(src, dst, weight);
     }
 
     /**
@@ -117,26 +115,28 @@ class SimpleTopologyStore {
      * Generates a new topology snapshot from the specified description.
      *
      * @param providerId       provider identification
-     * @param topoDescription topology description
+     * @param graphDescription topology graph description
      * @param reasons          list of events that triggered the update
      * @return topology update event or null if the description is old
      */
     TopologyEvent updateTopology(ProviderId providerId,
-                                 TopologyDescription topoDescription,
+                                 GraphDescription graphDescription,
                                  List<Event> reasons) {
         // First off, make sure that what we're given is indeed newer than
         // what we already have.
-        if (current != null && topoDescription.timestamp() < current.time()) {
+        if (current != null && graphDescription.timestamp() < current.time()) {
             return null;
         }
 
         // Have the default topology construct self from the description data.
         DefaultTopology newTopology =
-                new DefaultTopology(providerId, topoDescription);
+                new DefaultTopology(providerId, graphDescription);
 
         // Promote the new topology to current and return a ready-to-send event.
+        synchronized (this) {
             current = newTopology;
             return new TopologyEvent(TopologyEvent.Type.TOPOLOGY_CHANGED, current);
         }
+    }
 
 }

-package org.onlab.onos.net.trivial.topology.provider.impl;
-
-import com.google.common.collect.ImmutableMap;
-import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.ImmutableSetMultimap;
-import com.google.common.collect.Maps;
-import com.google.common.collect.Sets;
-import org.onlab.graph.AdjacencyListsGraph;
-import org.onlab.graph.DijkstraGraphSearch;
-import org.onlab.graph.Graph;
-import org.onlab.graph.GraphPathSearch;
-import org.onlab.graph.TarjanGraphSearch;
-import org.onlab.onos.net.ConnectPoint;
-import org.onlab.onos.net.Device;
-import org.onlab.onos.net.DeviceId;
-import org.onlab.onos.net.Link;
-import org.onlab.onos.net.topology.ClusterId;
-import org.onlab.onos.net.topology.DefaultTopologyCluster;
-import org.onlab.onos.net.topology.LinkWeight;
-import org.onlab.onos.net.topology.TopoEdge;
-import org.onlab.onos.net.topology.TopoVertex;
-import org.onlab.onos.net.topology.TopologyCluster;
-import org.onlab.onos.net.topology.TopologyDescription;
-
-import java.util.List;
-import java.util.Map;
-import java.util.Set;
-
-import static com.google.common.collect.ImmutableSetMultimap.Builder;
-import static com.google.common.collect.ImmutableSetMultimap.builder;
-import static org.onlab.graph.GraphPathSearch.Result;
-import static org.onlab.graph.TarjanGraphSearch.SCCResult;
-import static org.onlab.onos.net.Link.Type.INDIRECT;
-
-/**
- * Default implementation of an immutable topology data carrier.
- */
-class DefaultTopologyDescription implements TopologyDescription {
-
-    private static final GraphPathSearch<TopoVertex, TopoEdge> DIJKSTRA =
-            new DijkstraGraphSearch<>();
-    private static final TarjanGraphSearch<TopoVertex, TopoEdge> TARJAN =
-            new TarjanGraphSearch<>();
-
-    private final long nanos;
-    private final Map<DeviceId, TopoVertex> vertexesById = Maps.newHashMap();
-    private final Graph<TopoVertex, TopoEdge> graph;
-    private final ImmutableMap<DeviceId, Result<TopoVertex, TopoEdge>> results;
-
-    // Cluster-related structures
-    private final ImmutableSet<TopologyCluster> clusters;
-    private ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster;
-    private ImmutableSetMultimap<TopologyCluster, Link> linksByCluster;
-
-    /**
-     * Creates a topology description to carry topology vitals to the core.
-     *
-     * @param nanos   time in nanos of when the topology description was created
-     * @param devices collection of infrastructure devices
-     * @param links   collection of infrastructure links
-     */
-    DefaultTopologyDescription(long nanos, Iterable<Device> devices, Iterable<Link> links) {
-        this.nanos = nanos;
-        this.graph = buildGraph(devices, links);
-        this.results = computeDefaultPaths();
-        this.clusters = computeClusters();
-    }
-
-    @Override
-    public long timestamp() {
-        return nanos;
-    }
-
-    @Override
-    public Graph<TopoVertex, TopoEdge> graph() {
-        return graph;
-    }
-
-    @Override
-    public ImmutableMap<DeviceId, Result<TopoVertex, TopoEdge>> pathsBySource() {
-        return results;
-    }
-
-    @Override
-    public ImmutableSet<TopologyCluster> clusters() {
-        return clusters;
-    }
-
-    @Override
-    public ImmutableSetMultimap<TopologyCluster, DeviceId> devicesByCluster() {
-        return devicesByCluster;
-    }
-
-    @Override
-    public ImmutableSetMultimap<TopologyCluster, Link> linksByCluster() {
-        return linksByCluster;
-    }
-
-    // Link weight for measuring link cost as hop count with indirect links
-    // being as expensive as traversing the entire graph to assume the worst.
-    private static class HopCountLinkWeight implements LinkWeight {
-        private final int indirectLinkCost;
-
-        HopCountLinkWeight(int indirectLinkCost) {
-            this.indirectLinkCost = indirectLinkCost;
-        }
-
-        @Override
-        public double weight(TopoEdge edge) {
-            // To force preference to use direct paths first, make indirect
-            // links as expensive as the linear vertex traversal.
-            return edge.link().type() == INDIRECT ? indirectLinkCost : 1;
-        }
-    }
-
-    // Link weight for preventing traversal over indirect links.
-    private static class NoIndirectLinksWeight implements LinkWeight {
-        @Override
-        public double weight(TopoEdge edge) {
-            return edge.link().type() == INDIRECT ? -1 : 1;
-        }
-    }
-
-    // Constructs the topology graph using the supplied devices and links.
-    private Graph<TopoVertex, TopoEdge> buildGraph(Iterable<Device> devices,
-                                                   Iterable<Link> links) {
-        return new AdjacencyListsGraph<>(buildVertexes(devices),
-                                         buildEdges(links));
-    }
-
-    // Builds a set of topology vertexes from the specified list of devices
-    private Set<TopoVertex> buildVertexes(Iterable<Device> devices) {
-        Set<TopoVertex> vertexes = Sets.newHashSet();
-        for (Device device : devices) {
-            TopoVertex vertex = new DefaultTopoVertex(device.id());
-            vertexes.add(vertex);
-            vertexesById.put(vertex.deviceId(), vertex);
-        }
-        return vertexes;
-    }
-
-    // Builds a set of topology vertexes from the specified list of links
-    private Set<TopoEdge> buildEdges(Iterable<Link> links) {
-        Set<TopoEdge> edges = Sets.newHashSet();
-        for (Link link : links) {
-            edges.add(new DefaultTopoEdge(vertexOf(link.src()),
-                                          vertexOf(link.dst()), link));
-        }
-        return edges;
-    }
-
-    // Computes the default shortest paths for all source/dest pairs using
-    // the multi-path Dijkstra and hop-count as path cost.
-    private ImmutableMap<DeviceId, Result<TopoVertex, TopoEdge>> computeDefaultPaths() {
-        LinkWeight weight = new HopCountLinkWeight(graph.getVertexes().size());
-        ImmutableMap.Builder<DeviceId, Result<TopoVertex, TopoEdge>> results =
-                ImmutableMap.builder();
-
-        // Search graph paths for each source to all destinations.
-        for (TopoVertex src : vertexesById.values()) {
-            results.put(src.deviceId(), DIJKSTRA.search(graph, src, null, weight));
-        }
-        return results.build();
-    }
-
-    // Computes topology SCC clusters using Tarjan algorithm.
-    private ImmutableSet<TopologyCluster> computeClusters() {
-        ImmutableSet.Builder<TopologyCluster> clusterBuilder = ImmutableSet.builder();
-        SCCResult<TopoVertex, TopoEdge> result =
-                TARJAN.search(graph, new NoIndirectLinksWeight());
-
-        // Extract both vertexes and edges from the results; the lists form
-        // pairs along the same index.
-        List<Set<TopoVertex>> clusterVertexes = result.clusterVertexes();
-        List<Set<TopoEdge>> clusterEdges = result.clusterEdges();
-
-        Builder<TopologyCluster, DeviceId> devicesBuilder = ImmutableSetMultimap.builder();
-        Builder<TopologyCluster, Link> linksBuilder = ImmutableSetMultimap.builder();
-
-        // Scan over the lists and create a cluster from the results.
-        for (int i = 0, n = result.clusterCount(); i < n; i++) {
-            Set<TopoVertex> vertexSet = clusterVertexes.get(i);
-            Set<TopoEdge> edgeSet = clusterEdges.get(i);
-
-            DefaultTopologyCluster cluster =
-                    new DefaultTopologyCluster(ClusterId.clusterId(i),
-                                               vertexSet.size(), edgeSet.size(),
-                                               findRoot(vertexSet).deviceId());
-            clusterBuilder.add(cluster);
-            findClusterDevices(vertexSet, cluster, devicesBuilder);
-            findClusterLinks(edgeSet, cluster, linksBuilder);
-        }
-        return clusterBuilder.build();
-    }
-
-    // Scans through the set of cluster vertexes and puts their devices in a
-    // multi-map associated with the cluster. It also binds the devices to
-    // the cluster.
-    private void findClusterDevices(Set<TopoVertex> vertexSet,
-                                    DefaultTopologyCluster cluster,
-                                    Builder<TopologyCluster, DeviceId> builder) {
-        for (TopoVertex vertex : vertexSet) {
-            DeviceId deviceId = vertex.deviceId();
-            builder.put(cluster, deviceId);
-        }
-    }
-
-    // Scans through the set of cluster edges and puts their links in a
-    // multi-map associated with the cluster.
-    private void findClusterLinks(Set<TopoEdge> edgeSet,
-                                  DefaultTopologyCluster cluster,
-                                  Builder<TopologyCluster, Link> builder) {
-        for (TopoEdge edge : edgeSet) {
-            builder.put(cluster, edge.link());
-        }
-    }
-
-    // Finds the vertex whose device id is the lexicographical minimum in the
-    // specified set.
-    private TopoVertex findRoot(Set<TopoVertex> vertexSet) {
-        TopoVertex minVertex = null;
-        for (TopoVertex vertex : vertexSet) {
-            if (minVertex == null ||
-                    minVertex.deviceId().toString()
-                            .compareTo(minVertex.deviceId().toString()) < 0) {
-                minVertex = vertex;
-            }
-        }
-        return minVertex;
-    }
-
-    // Fetches a vertex corresponding to the given connection point device.
-    private TopoVertex vertexOf(ConnectPoint connectPoint) {
-        DeviceId id = connectPoint.deviceId();
-        TopoVertex vertex = vertexesById.get(id);
-        if (vertex == null) {
-            // If vertex does not exist, create one and register it.
-            vertex = new DefaultTopoVertex(id);
-            vertexesById.put(id, vertex);
-        }
-        return vertex;
-    }
-
-}

-<body>
-Built-in protocol-agnostic topology builder &amp; provider.
-</body>
\ No newline at end of file