Added GossipLinkStore with basic replication for link state.

+package org.onlab.onos.store.link.impl;
+
+import com.google.common.base.Function;
+import com.google.common.base.Predicate;
+import com.google.common.collect.FluentIterable;
+import com.google.common.collect.HashMultimap;
+import com.google.common.collect.Maps;
+import com.google.common.collect.SetMultimap;
+
+import org.apache.commons.lang3.concurrent.ConcurrentUtils;
+import org.apache.felix.scr.annotations.Activate;
+import org.apache.felix.scr.annotations.Component;
+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.onos.cluster.ClusterService;
+import org.onlab.onos.net.AnnotationsUtil;
+import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.DefaultAnnotations;
+import org.onlab.onos.net.DefaultLink;
+import org.onlab.onos.net.DeviceId;
+import org.onlab.onos.net.Link;
+import org.onlab.onos.net.SparseAnnotations;
+import org.onlab.onos.net.Link.Type;
+import org.onlab.onos.net.LinkKey;
+import org.onlab.onos.net.Provided;
+import org.onlab.onos.net.link.DefaultLinkDescription;
+import org.onlab.onos.net.link.LinkDescription;
+import org.onlab.onos.net.link.LinkEvent;
+import org.onlab.onos.net.link.LinkStore;
+import org.onlab.onos.net.link.LinkStoreDelegate;
+import org.onlab.onos.net.provider.ProviderId;
+import org.onlab.onos.store.AbstractStore;
+import org.onlab.onos.store.ClockService;
+import org.onlab.onos.store.Timestamp;
+import org.onlab.onos.store.cluster.messaging.ClusterCommunicationService;
+import org.onlab.onos.store.cluster.messaging.ClusterMessage;
+import org.onlab.onos.store.cluster.messaging.ClusterMessageHandler;
+import org.onlab.onos.store.cluster.messaging.MessageSubject;
+import org.onlab.onos.store.common.impl.Timestamped;
+import org.onlab.onos.store.serializers.DistributedStoreSerializers;
+import org.onlab.onos.store.serializers.KryoSerializer;
+import org.onlab.util.KryoPool;
+import org.onlab.util.NewConcurrentHashMap;
+import org.slf4j.Logger;
+
+import java.io.IOException;
+import java.util.Collections;
+import java.util.HashSet;
+import java.util.Map;
+import java.util.Set;
+import java.util.Map.Entry;
+import java.util.concurrent.ConcurrentHashMap;
+import java.util.concurrent.ConcurrentMap;
+
+import static org.onlab.onos.net.DefaultAnnotations.union;
+import static org.onlab.onos.net.DefaultAnnotations.merge;
+import static org.onlab.onos.net.Link.Type.DIRECT;
+import static org.onlab.onos.net.Link.Type.INDIRECT;
+import static org.onlab.onos.net.link.LinkEvent.Type.*;
+import static org.slf4j.LoggerFactory.getLogger;
+import static com.google.common.collect.Multimaps.synchronizedSetMultimap;
+import static com.google.common.base.Predicates.notNull;
+
+/**
+ * Manages inventory of infrastructure links in distributed data store
+ * that uses optimistic replication and gossip based techniques.
+ */
+@Component(immediate = true)
+@Service
+public class GossipLinkStore
+        extends AbstractStore<LinkEvent, LinkStoreDelegate>
+        implements LinkStore {
+
+    private final Logger log = getLogger(getClass());
+
+    // Link inventory
+    private final ConcurrentMap<LinkKey, ConcurrentMap<ProviderId, Timestamped<LinkDescription>>> linkDescs =
+        new ConcurrentHashMap<>();
+
+    // Link instance cache
+    private final ConcurrentMap<LinkKey, Link> links = new ConcurrentHashMap<>();
+
+    // Egress and ingress link sets
+    private final SetMultimap<DeviceId, LinkKey> srcLinks = createSynchronizedHashMultiMap();
+    private final SetMultimap<DeviceId, LinkKey> dstLinks = createSynchronizedHashMultiMap();
+
+    // Remove links
+    private final Map<LinkKey, Timestamp> removedLinks = Maps.newHashMap();
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected ClockService clockService;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected ClusterCommunicationService clusterCommunicator;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected ClusterService clusterService;
+
+    private static final KryoSerializer SERIALIZER = new KryoSerializer() {
+        @Override
+        protected void setupKryoPool() {
+            serializerPool = KryoPool.newBuilder()
+                    .register(DistributedStoreSerializers.COMMON)
+                    .register(InternalLinkEvent.class)
+                    .register(InternalLinkRemovedEvent.class)
+                    .build()
+                    .populate(1);
+        }
+    };
+
+    @Activate
+    public void activate() {
+
+        clusterCommunicator.addSubscriber(
+                GossipLinkStoreMessageSubjects.LINK_UPDATE, new InternalLinkEventListener());
+        clusterCommunicator.addSubscriber(
+                GossipLinkStoreMessageSubjects.LINK_REMOVED, new InternalLinkRemovedEventListener());
+
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        linkDescs.clear();
+        links.clear();
+        srcLinks.clear();
+        dstLinks.clear();
+        log.info("Stopped");
+    }
+
+    @Override
+    public int getLinkCount() {
+        return links.size();
+    }
+
+    @Override
+    public Iterable<Link> getLinks() {
+        return Collections.unmodifiableCollection(links.values());
+    }
+
+    @Override
+    public Set<Link> getDeviceEgressLinks(DeviceId deviceId) {
+        // lock for iteration
+        synchronized (srcLinks) {
+            return FluentIterable.from(srcLinks.get(deviceId))
+            .transform(lookupLink())
+            .filter(notNull())
+            .toSet();
+        }
+    }
+
+    @Override
+    public Set<Link> getDeviceIngressLinks(DeviceId deviceId) {
+        // lock for iteration
+        synchronized (dstLinks) {
+            return FluentIterable.from(dstLinks.get(deviceId))
+            .transform(lookupLink())
+            .filter(notNull())
+            .toSet();
+        }
+    }
+
+    @Override
+    public Link getLink(ConnectPoint src, ConnectPoint dst) {
+        return links.get(new LinkKey(src, dst));
+    }
+
+    @Override
+    public Set<Link> getEgressLinks(ConnectPoint src) {
+        Set<Link> egress = new HashSet<>();
+        for (LinkKey linkKey : srcLinks.get(src.deviceId())) {
+            if (linkKey.src().equals(src)) {
+                egress.add(links.get(linkKey));
+            }
+        }
+        return egress;
+    }
+
+    @Override
+    public Set<Link> getIngressLinks(ConnectPoint dst) {
+        Set<Link> ingress = new HashSet<>();
+        for (LinkKey linkKey : dstLinks.get(dst.deviceId())) {
+            if (linkKey.dst().equals(dst)) {
+                ingress.add(links.get(linkKey));
+            }
+        }
+        return ingress;
+    }
+
+    @Override
+    public LinkEvent createOrUpdateLink(ProviderId providerId,
+                                        LinkDescription linkDescription) {
+
+        DeviceId dstDeviceId = linkDescription.dst().deviceId();
+        Timestamp newTimestamp = clockService.getTimestamp(dstDeviceId);
+
+        final Timestamped<LinkDescription> deltaDesc = new Timestamped<>(linkDescription, newTimestamp);
+
+        LinkEvent event = createOrUpdateLinkInternal(providerId, deltaDesc);
+
+        if (event != null) {
+            log.info("Notifying peers of a link update topology event from providerId: "
+                    + "{}  between src: {} and dst: {}",
+                    providerId, linkDescription.src(), linkDescription.dst());
+            try {
+                notifyPeers(new InternalLinkEvent(providerId, deltaDesc));
+            } catch (IOException e) {
+                log.info("Failed to notify peers of a link update topology event from providerId: "
+                        + "{}  between src: {} and dst: {}",
+                        providerId, linkDescription.src(), linkDescription.dst());
+            }
+        }
+        return event;
+    }
+
+    private LinkEvent createOrUpdateLinkInternal(
+            ProviderId providerId,
+            Timestamped<LinkDescription> linkDescription) {
+
+        LinkKey key = new LinkKey(linkDescription.value().src(), linkDescription.value().dst());
+        ConcurrentMap<ProviderId, Timestamped<LinkDescription>> descs = getLinkDescriptions(key);
+
+        synchronized (descs) {
+            // if the link was previously removed, we should proceed if and
+            // only if this request is more recent.
+            Timestamp linkRemovedTimestamp = removedLinks.get(key);
+            if (linkRemovedTimestamp != null) {
+                if (linkDescription.isNewer(linkRemovedTimestamp)) {
+                    removedLinks.remove(key);
+                } else {
+                    return null;
+                }
+            }
+
+            final Link oldLink = links.get(key);
+            // update description
+            createOrUpdateLinkDescription(descs, providerId, linkDescription);
+            final Link newLink = composeLink(descs);
+            if (oldLink == null) {
+                return createLink(key, newLink);
+            }
+            return updateLink(key, oldLink, newLink);
+        }
+    }
+
+    // Guarded by linkDescs value (=locking each Link)
+    private Timestamped<LinkDescription> createOrUpdateLinkDescription(
+            ConcurrentMap<ProviderId, Timestamped<LinkDescription>> existingLinkDescriptions,
+            ProviderId providerId,
+            Timestamped<LinkDescription> linkDescription) {
+
+        // merge existing attributes and merge
+        Timestamped<LinkDescription> existingLinkDescription = existingLinkDescriptions.get(providerId);
+        if (existingLinkDescription != null && existingLinkDescription.isNewer(linkDescription)) {
+            return null;
+        }
+        Timestamped<LinkDescription> newLinkDescription = linkDescription;
+        if (existingLinkDescription != null) {
+            SparseAnnotations merged = union(existingLinkDescription.value().annotations(),
+                    linkDescription.value().annotations());
+            newLinkDescription = new Timestamped<LinkDescription>(
+                    new DefaultLinkDescription(
+                        linkDescription.value().src(),
+                        linkDescription.value().dst(),
+                        linkDescription.value().type(), merged),
+                    linkDescription.timestamp());
+        }
+        return existingLinkDescriptions.put(providerId, newLinkDescription);
+    }
+
+    // Creates and stores the link and returns the appropriate event.
+    // Guarded by linkDescs value (=locking each Link)
+    private LinkEvent createLink(LinkKey key, Link newLink) {
+
+        if (newLink.providerId().isAncillary()) {
+            // TODO: revisit ancillary only Link handling
+
+            // currently treating ancillary only as down (not visible outside)
+            return null;
+        }
+
+        links.put(key, newLink);
+        srcLinks.put(newLink.src().deviceId(), key);
+        dstLinks.put(newLink.dst().deviceId(), key);
+        return new LinkEvent(LINK_ADDED, newLink);
+    }
+
+    // Updates, if necessary the specified link and returns the appropriate event.
+    // Guarded by linkDescs value (=locking each Link)
+    private LinkEvent updateLink(LinkKey key, Link oldLink, Link newLink) {
+
+        if (newLink.providerId().isAncillary()) {
+            // TODO: revisit ancillary only Link handling
+
+            // currently treating ancillary only as down (not visible outside)
+            return null;
+        }
+
+        if ((oldLink.type() == INDIRECT && newLink.type() == DIRECT) ||
+            !AnnotationsUtil.isEqual(oldLink.annotations(), newLink.annotations())) {
+
+            links.put(key, newLink);
+            // strictly speaking following can be ommitted
+            srcLinks.put(oldLink.src().deviceId(), key);
+            dstLinks.put(oldLink.dst().deviceId(), key);
+            return new LinkEvent(LINK_UPDATED, newLink);
+        }
+        return null;
+    }
+
+    @Override
+    public LinkEvent removeLink(ConnectPoint src, ConnectPoint dst) {
+        final LinkKey key = new LinkKey(src, dst);
+
+        DeviceId dstDeviceId = dst.deviceId();
+        Timestamp timestamp = clockService.getTimestamp(dstDeviceId);
+
+        LinkEvent event = removeLinkInternal(key, timestamp);
+
+        if (event != null) {
+            log.info("Notifying peers of a link removed topology event for a link "
+                    + "between src: {} and dst: {}", src, dst);
+            try {
+                notifyPeers(new InternalLinkRemovedEvent(key, timestamp));
+            } catch (IOException e) {
+                log.error("Failed to notify peers of a link removed topology event for a link "
+                        + "between src: {} and dst: {}", src, dst);
+            }
+        }
+        return event;
+    }
+
+    private LinkEvent removeLinkInternal(LinkKey key, Timestamp timestamp) {
+        ConcurrentMap<ProviderId, Timestamped<LinkDescription>> linkDescriptions =
+                getLinkDescriptions(key);
+        synchronized (linkDescriptions) {
+            // accept removal request if given timestamp is newer than
+            // the latest Timestamp from Primary provider
+            ProviderId primaryProviderId = pickPrimaryProviderId(linkDescriptions);
+            if (linkDescriptions.get(primaryProviderId).isNewer(timestamp)) {
+                return null;
+            }
+            removedLinks.put(key, timestamp);
+            Link link = links.remove(key);
+            linkDescriptions.clear();
+            if (link != null) {
+                srcLinks.remove(link.src().deviceId(), key);
+                dstLinks.remove(link.dst().deviceId(), key);
+                return new LinkEvent(LINK_REMOVED, link);
+            }
+            return null;
+        }
+    }
+
+    private static <K, V> SetMultimap<K, V> createSynchronizedHashMultiMap() {
+        return synchronizedSetMultimap(HashMultimap.<K, V>create());
+    }
+
+    /**
+     * @return primary ProviderID, or randomly chosen one if none exists
+     */
+    private ProviderId pickPrimaryProviderId(
+            ConcurrentMap<ProviderId, Timestamped<LinkDescription>> providerDescs) {
+
+        ProviderId fallBackPrimary = null;
+        for (Entry<ProviderId, Timestamped<LinkDescription>> e : providerDescs.entrySet()) {
+            if (!e.getKey().isAncillary()) {
+                return e.getKey();
+            } else if (fallBackPrimary == null) {
+                // pick randomly as a fallback in case there is no primary
+                fallBackPrimary = e.getKey();
+            }
+        }
+        return fallBackPrimary;
+    }
+
+    private Link composeLink(ConcurrentMap<ProviderId, Timestamped<LinkDescription>> linkDescriptions) {
+        ProviderId primaryProviderId = pickPrimaryProviderId(linkDescriptions);
+        Timestamped<LinkDescription> base = linkDescriptions.get(primaryProviderId);
+
+        ConnectPoint src = base.value().src();
+        ConnectPoint dst = base.value().dst();
+        Type type = base.value().type();
+        DefaultAnnotations annotations = DefaultAnnotations.builder().build();
+        annotations = merge(annotations, base.value().annotations());
+
+        for (Entry<ProviderId, Timestamped<LinkDescription>> e : linkDescriptions.entrySet()) {
+            if (primaryProviderId.equals(e.getKey())) {
+                continue;
+            }
+
+            // TODO: should keep track of Description timestamp
+            // and only merge conflicting keys when timestamp is newer
+            // Currently assuming there will never be a key conflict between
+            // providers
+
+            // annotation merging. not so efficient, should revisit later
+            annotations = merge(annotations, e.getValue().value().annotations());
+        }
+
+        return new DefaultLink(primaryProviderId , src, dst, type, annotations);
+    }
+
+    private ConcurrentMap<ProviderId, Timestamped<LinkDescription>> getLinkDescriptions(LinkKey key) {
+        return ConcurrentUtils.createIfAbsentUnchecked(linkDescs, key,
+                NewConcurrentHashMap.<ProviderId, Timestamped<LinkDescription>>ifNeeded());
+    }
+
+    private final Function<LinkKey, Link> lookupLink = new LookupLink();
+    private Function<LinkKey, Link> lookupLink() {
+        return lookupLink;
+    }
+
+    private final class LookupLink implements Function<LinkKey, Link> {
+        @Override
+        public Link apply(LinkKey input) {
+            return links.get(input);
+        }
+    }
+
+    private static final Predicate<Provided> IS_PRIMARY = new IsPrimary();
+    private static final Predicate<Provided> isPrimary() {
+        return IS_PRIMARY;
+    }
+
+    private static final class IsPrimary implements Predicate<Provided> {
+
+        @Override
+        public boolean apply(Provided input) {
+            return !input.providerId().isAncillary();
+        }
+    }
+
+    private void notifyDelegateIfNotNull(LinkEvent event) {
+        if (event != null) {
+            notifyDelegate(event);
+        }
+    }
+
+    // TODO: should we be throwing exception?
+    private void broadcastMessage(MessageSubject subject, Object event) throws IOException {
+        ClusterMessage message = new ClusterMessage(
+                clusterService.getLocalNode().id(),
+                subject,
+                SERIALIZER.encode(event));
+        clusterCommunicator.broadcast(message);
+    }
+
+    private void notifyPeers(InternalLinkEvent event) throws IOException {
+        broadcastMessage(GossipLinkStoreMessageSubjects.LINK_UPDATE, event);
+    }
+
+    private void notifyPeers(InternalLinkRemovedEvent event) throws IOException {
+        broadcastMessage(GossipLinkStoreMessageSubjects.LINK_REMOVED, event);
+    }
+
+    private class InternalLinkEventListener implements ClusterMessageHandler {
+        @Override
+        public void handle(ClusterMessage message) {
+
+            log.info("Received link event from peer: {}", message.sender());
+            InternalLinkEvent event = (InternalLinkEvent) SERIALIZER.decode(message.payload());
+
+            ProviderId providerId = event.providerId();
+            Timestamped<LinkDescription> linkDescription = event.linkDescription();
+
+            notifyDelegateIfNotNull(createOrUpdateLinkInternal(providerId, linkDescription));
+        }
+    }
+
+    private class InternalLinkRemovedEventListener implements ClusterMessageHandler {
+        @Override
+        public void handle(ClusterMessage message) {
+
+            log.info("Received link removed event from peer: {}", message.sender());
+            InternalLinkRemovedEvent event = (InternalLinkRemovedEvent) SERIALIZER.decode(message.payload());
+
+            LinkKey linkKey = event.linkKey();
+            Timestamp timestamp = event.timestamp();
+
+            notifyDelegateIfNotNull(removeLinkInternal(linkKey, timestamp));
+        }
+    }
+}

+package org.onlab.onos.store.link.impl;
+
+import org.onlab.onos.store.cluster.messaging.MessageSubject;
+
+/**
+ * MessageSubjects used by GossipLinkStore peer-peer communication.
+ */
+public final class GossipLinkStoreMessageSubjects {
+
+    private GossipLinkStoreMessageSubjects() {}
+
+    public static final MessageSubject LINK_UPDATE = new MessageSubject("peer-link-update");
+    public static final MessageSubject LINK_REMOVED = new MessageSubject("peer-link-removed");
+}

+package org.onlab.onos.store.link.impl;
+
+import com.google.common.base.MoreObjects;
+
+import org.onlab.onos.net.link.LinkDescription;
+import org.onlab.onos.net.provider.ProviderId;
+import org.onlab.onos.store.common.impl.Timestamped;
+
+/**
+ * Information published by GossipDeviceStore to notify peers of a device
+ * change event.
+ */
+public class InternalLinkEvent {
+
+    private final ProviderId providerId;
+    private final Timestamped<LinkDescription> linkDescription;
+
+    protected InternalLinkEvent(
+            ProviderId providerId,
+            Timestamped<LinkDescription> linkDescription) {
+        this.providerId = providerId;
+        this.linkDescription = linkDescription;
+    }
+
+    public ProviderId providerId() {
+        return providerId;
+    }
+
+    public Timestamped<LinkDescription> linkDescription() {
+        return linkDescription;
+    }
+
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(getClass())
+                .add("providerId", providerId)
+                .add("linkDescription", linkDescription)
+                .toString();
+    }
+
+    // for serializer
+    protected InternalLinkEvent() {
+        this.providerId = null;
+        this.linkDescription = null;
+    }
+}

+package org.onlab.onos.store.link.impl;
+
+import org.onlab.onos.net.LinkKey;
+import org.onlab.onos.store.Timestamp;
+
+import com.google.common.base.MoreObjects;
+
+/**
+ * Information published by GossipLinkStore to notify peers of a link
+ * being removed.
+ */
+public class InternalLinkRemovedEvent {
+
+    private final LinkKey linkKey;
+    private final Timestamp timestamp;
+
+    /**
+     * Creates a InternalLinkRemovedEvent.
+     * @param linkKey identifier of the removed link.
+     * @param timestamp timestamp of when the link was removed.
+     */
+    public InternalLinkRemovedEvent(LinkKey linkKey, Timestamp timestamp) {
+        this.linkKey = linkKey;
+        this.timestamp = timestamp;
+    }
+
+    public LinkKey linkKey() {
+        return linkKey;
+    }
+
+    public Timestamp timestamp() {
+        return timestamp;
+    }
+
+    @Override
+    public String toString() {
+        return MoreObjects.toStringHelper(getClass())
+                .add("linkKey", linkKey)
+                .add("timestamp", timestamp)
+                .toString();
+    }
+
+    // for serializer
+    @SuppressWarnings("unused")
+    private InternalLinkRemovedEvent() {
+        linkKey = null;
+        timestamp = null;
+    }
+}
\ No newline at end of file

-package org.onlab.onos.store.link.impl;
-
-import static org.onlab.onos.net.Link.Type.DIRECT;
-import static org.onlab.onos.net.Link.Type.INDIRECT;
-import static org.onlab.onos.net.link.LinkEvent.Type.LINK_ADDED;
-import static org.onlab.onos.net.link.LinkEvent.Type.LINK_REMOVED;
-import static org.onlab.onos.net.link.LinkEvent.Type.LINK_UPDATED;
-import static org.slf4j.LoggerFactory.getLogger;
-
-import java.util.HashSet;
-import java.util.Set;
-import java.util.concurrent.ConcurrentHashMap;
-import java.util.concurrent.ConcurrentMap;
-
-import org.apache.felix.scr.annotations.Activate;
-import org.apache.felix.scr.annotations.Component;
-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.onos.net.ConnectPoint;
-import org.onlab.onos.net.DefaultLink;
-import org.onlab.onos.net.DeviceId;
-import org.onlab.onos.net.Link;
-import org.onlab.onos.net.LinkKey;
-import org.onlab.onos.net.link.LinkDescription;
-import org.onlab.onos.net.link.LinkEvent;
-import org.onlab.onos.net.link.LinkStore;
-import org.onlab.onos.net.link.LinkStoreDelegate;
-import org.onlab.onos.net.provider.ProviderId;
-import org.onlab.onos.store.AbstractStore;
-import org.onlab.onos.store.ClockService;
-import org.onlab.onos.store.Timestamp;
-import org.slf4j.Logger;
-
-import com.google.common.collect.HashMultimap;
-import com.google.common.collect.ImmutableSet;
-import com.google.common.collect.Multimap;
-import com.google.common.collect.ImmutableSet.Builder;
-
-import static com.google.common.base.Preconditions.checkArgument;
-import static com.google.common.base.Preconditions.checkState;
-
-//TODO: Add support for multiple provider and annotations
-/**
- * Manages inventory of infrastructure links using a protocol that takes into consideration
- * the order in which events occur.
- */
-// FIXME: This does not yet implement the full protocol.
-// The full protocol requires the sender of LLDP message to include the
-// version information of src device/port and the receiver to
-// take that into account when figuring out if a more recent src
-// device/port down event renders the link discovery obsolete.
-@Component(immediate = true)
-@Service
-public class OnosDistributedLinkStore
-    extends AbstractStore<LinkEvent, LinkStoreDelegate>
-    implements LinkStore {
-
-    private final Logger log = getLogger(getClass());
-
-    // Link inventory
-    private ConcurrentMap<LinkKey, VersionedValue<Link>> links;
-
-    public static final String LINK_NOT_FOUND = "Link between %s and %s not found";
-
-    // TODO synchronize?
-    // Egress and ingress link sets
-    private final Multimap<DeviceId, VersionedValue<Link>> srcLinks = HashMultimap.create();
-    private final Multimap<DeviceId, VersionedValue<Link>> dstLinks = HashMultimap.create();
-
-    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
-    protected ClockService clockService;
-
-    @Activate
-    public void activate() {
-
-        links = new ConcurrentHashMap<>();
-
-        log.info("Started");
-    }
-
-    @Deactivate
-    public void deactivate() {
-        log.info("Stopped");
-    }
-
-    @Override
-    public int getLinkCount() {
-        return links.size();
-    }
-
-    @Override
-    public Iterable<Link> getLinks() {
-        Builder<Link> builder = ImmutableSet.builder();
-        synchronized (this) {
-            for (VersionedValue<Link> link : links.values()) {
-                builder.add(link.entity());
-            }
-            return builder.build();
-        }
-    }
-
-    @Override
-    public Set<Link> getDeviceEgressLinks(DeviceId deviceId) {
-        Set<VersionedValue<Link>> egressLinks = ImmutableSet.copyOf(srcLinks.get(deviceId));
-        Set<Link> rawEgressLinks = new HashSet<>();
-        for (VersionedValue<Link> link : egressLinks) {
-            rawEgressLinks.add(link.entity());
-        }
-        return rawEgressLinks;
-    }
-
-    @Override
-    public Set<Link> getDeviceIngressLinks(DeviceId deviceId) {
-        Set<VersionedValue<Link>> ingressLinks = ImmutableSet.copyOf(dstLinks.get(deviceId));
-        Set<Link> rawIngressLinks = new HashSet<>();
-        for (VersionedValue<Link> link : ingressLinks) {
-            rawIngressLinks.add(link.entity());
-        }
-        return rawIngressLinks;
-    }
-
-    @Override
-    public Link getLink(ConnectPoint src, ConnectPoint dst) {
-        VersionedValue<Link> link = links.get(new LinkKey(src, dst));
-        checkArgument(link != null, "LINK_NOT_FOUND", src, dst);
-        return link.entity();
-    }
-
-    @Override
-    public Set<Link> getEgressLinks(ConnectPoint src) {
-        Set<Link> egressLinks = new HashSet<>();
-        for (VersionedValue<Link> link : srcLinks.get(src.deviceId())) {
-            if (link.entity().src().equals(src)) {
-                egressLinks.add(link.entity());
-            }
-        }
-        return egressLinks;
-    }
-
-    @Override
-    public Set<Link> getIngressLinks(ConnectPoint dst) {
-        Set<Link> ingressLinks = new HashSet<>();
-        for (VersionedValue<Link> link : dstLinks.get(dst.deviceId())) {
-            if (link.entity().dst().equals(dst)) {
-                ingressLinks.add(link.entity());
-            }
-        }
-        return ingressLinks;
-    }
-
-    @Override
-    public LinkEvent createOrUpdateLink(ProviderId providerId,
-                                        LinkDescription linkDescription) {
-
-        final DeviceId destinationDeviceId = linkDescription.dst().deviceId();
-        final Timestamp newTimestamp = clockService.getTimestamp(destinationDeviceId);
-
-        LinkKey key = new LinkKey(linkDescription.src(), linkDescription.dst());
-        VersionedValue<Link> link = links.get(key);
-        if (link == null) {
-            return createLink(providerId, key, linkDescription, newTimestamp);
-        }
-
-        checkState(newTimestamp.compareTo(link.timestamp()) > 0,
-                "Existing Link has a timestamp in the future!");
-
-        return updateLink(providerId, link, key, linkDescription, newTimestamp);
-    }
-
-    // Creates and stores the link and returns the appropriate event.
-    private LinkEvent createLink(ProviderId providerId, LinkKey key,
-            LinkDescription linkDescription, Timestamp timestamp) {
-        VersionedValue<Link> link = new VersionedValue<Link>(new DefaultLink(providerId, key.src(), key.dst(),
-                linkDescription.type()), true, timestamp);
-        synchronized (this) {
-            links.put(key, link);
-            addNewLink(link, timestamp);
-        }
-        // FIXME: notify peers.
-        return new LinkEvent(LINK_ADDED, link.entity());
-    }
-
-    // update Egress and ingress link sets
-    private void addNewLink(VersionedValue<Link> link, Timestamp timestamp) {
-        Link rawLink = link.entity();
-        synchronized (this) {
-            srcLinks.put(rawLink.src().deviceId(), link);
-            dstLinks.put(rawLink.dst().deviceId(), link);
-        }
-    }
-
-    // Updates, if necessary the specified link and returns the appropriate event.
-    private LinkEvent updateLink(ProviderId providerId, VersionedValue<Link> existingLink,
-                                 LinkKey key, LinkDescription linkDescription, Timestamp timestamp) {
-        // FIXME confirm Link update condition is OK
-        if (existingLink.entity().type() == INDIRECT && linkDescription.type() == DIRECT) {
-            synchronized (this) {
-
-                VersionedValue<Link> updatedLink = new VersionedValue<Link>(
-                        new DefaultLink(providerId, existingLink.entity().src(), existingLink.entity().dst(),
-                                        linkDescription.type()), true, timestamp);
-                links.replace(key, existingLink, updatedLink);
-
-                replaceLink(existingLink, updatedLink);
-                // FIXME: notify peers.
-                return new LinkEvent(LINK_UPDATED, updatedLink.entity());
-            }
-        }
-        return null;
-    }
-
-    // update Egress and ingress link sets
-    private void replaceLink(VersionedValue<Link> current, VersionedValue<Link> updated) {
-        synchronized (this) {
-            srcLinks.remove(current.entity().src().deviceId(), current);
-            dstLinks.remove(current.entity().dst().deviceId(), current);
-
-            srcLinks.put(current.entity().src().deviceId(), updated);
-            dstLinks.put(current.entity().dst().deviceId(), updated);
-        }
-    }
-
-    @Override
-    public LinkEvent removeLink(ConnectPoint src, ConnectPoint dst) {
-        synchronized (this) {
-            LinkKey key = new LinkKey(src, dst);
-            VersionedValue<Link> link = links.remove(key);
-            if (link != null) {
-                removeLink(link);
-                // notify peers
-                return new LinkEvent(LINK_REMOVED, link.entity());
-            }
-            return null;
-        }
-    }
-
-    // update Egress and ingress link sets
-    private void removeLink(VersionedValue<Link> link) {
-        synchronized (this) {
-            srcLinks.remove(link.entity().src().deviceId(), link);
-            dstLinks.remove(link.entity().dst().deviceId(), link);
-        }
-    }
-}

@@ -24,6 +24,7 @@ import org.onlab.onos.net.Port;
 import org.onlab.onos.net.PortNumber;
 import org.onlab.onos.net.device.DefaultDeviceDescription;
 import org.onlab.onos.net.device.DefaultPortDescription;
+import org.onlab.onos.net.link.DefaultLinkDescription;
 import org.onlab.onos.net.provider.ProviderId;
 import org.onlab.onos.store.Timestamp;
 import org.onlab.packet.IpAddress;
@@ -58,6 +59,7 @@ public final class KryoPoolUtil {
                     DefaultControllerNode.class,
                     DefaultDevice.class,
                     DefaultDeviceDescription.class,
+                    DefaultLinkDescription.class,
                     MastershipRole.class,
                     Port.class,
                     DefaultPortDescription.class,