diff --git a/core/net/src/main/java/org/onlab/onos/event/impl/SimpleEventDispatcher.java b/core/net/src/main/java/org/onlab/onos/event/impl/SimpleEventDispatcher.java
new file mode 100644
index 0000000..3834676
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/event/impl/SimpleEventDispatcher.java
@@ -0,0 +1,93 @@
+package org.onlab.onos.event.impl;
+
+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.Service;
+import org.onlab.onos.event.AbstractEvent;
+import org.onlab.onos.event.DefaultEventSinkRegistry;
+import org.onlab.onos.event.Event;
+import org.onlab.onos.event.EventDeliveryService;
+import org.onlab.onos.event.EventSink;
+import org.slf4j.Logger;
+
+import java.util.concurrent.BlockingQueue;
+import java.util.concurrent.ExecutorService;
+import java.util.concurrent.LinkedBlockingQueue;
+
+import static java.util.concurrent.Executors.newSingleThreadExecutor;
+import static org.onlab.util.Tools.namedThreads;
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Simple implementation of an event dispatching service.
+ */
+@Component(immediate = true)
+@Service
+public class SimpleEventDispatcher extends DefaultEventSinkRegistry
+        implements EventDeliveryService {
+
+    private final Logger log = getLogger(getClass());
+
+    private final ExecutorService executor =
+            newSingleThreadExecutor(namedThreads("event-dispatch-%d"));
+
+    @SuppressWarnings("unchecked")
+    private static final Event KILL_PILL = new AbstractEvent(null, 0) {
+    };
+
+    private final BlockingQueue<Event> events = new LinkedBlockingQueue<>();
+
+    private volatile boolean stopped = false;
+
+    @Override
+    public void post(Event event) {
+        events.add(event);
+    }
+
+    @Activate
+    public void activate() {
+        stopped = false;
+        executor.execute(new DispatchLoop());
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        stopped = true;
+        post(KILL_PILL);
+        log.info("Stopped");
+    }
+
+    // Auxiliary event dispatching loop that feeds off the events queue.
+    private class DispatchLoop implements Runnable {
+        @Override
+        @SuppressWarnings("unchecked")
+        public void run() {
+            log.info("Dispatch loop initiated");
+            while (!stopped) {
+                try {
+                    // Fetch the next event and if it is the kill-pill, bail
+                    Event event = events.take();
+                    if (event == KILL_PILL) {
+                        break;
+                    }
+
+                    // Locate the sink for the event class and use it to
+                    // process the event
+                    EventSink sink = getSink(event.getClass());
+                    if (sink != null) {
+                        sink.process(event);
+                    } else {
+                        log.warn("No sink registered for event class {}",
+                                 event.getClass());
+                    }
+                } catch (Exception e) {
+                    log.warn("Error encountered while dispatching event:", e);
+                }
+            }
+            log.info("Dispatch loop terminated");
+        }
+    }
+
+}
diff --git a/core/net/src/main/java/org/onlab/onos/event/impl/package-info.java b/core/net/src/main/java/org/onlab/onos/event/impl/package-info.java
new file mode 100644
index 0000000..46722ad
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/event/impl/package-info.java
@@ -0,0 +1,4 @@
+/**
+ * Local event dispatching mechanism.
+ */
+package org.onlab.onos.event.impl;
diff --git a/core/net/src/main/java/org/onlab/onos/net/device/impl/DeviceManager.java b/core/net/src/main/java/org/onlab/onos/net/device/impl/DeviceManager.java
new file mode 100644
index 0000000..5964c08
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/device/impl/DeviceManager.java
@@ -0,0 +1,223 @@
+package org.onlab.onos.net.device.impl;
+
+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.event.AbstractListenerRegistry;
+import org.onlab.onos.event.EventDeliveryService;
+import org.onlab.onos.net.Device;
+import org.onlab.onos.net.DeviceId;
+import org.onlab.onos.net.MastershipRole;
+import org.onlab.onos.net.Port;
+import org.onlab.onos.net.PortNumber;
+import org.onlab.onos.net.device.DeviceAdminService;
+import org.onlab.onos.net.device.DeviceDescription;
+import org.onlab.onos.net.device.DeviceEvent;
+import org.onlab.onos.net.device.DeviceListener;
+import org.onlab.onos.net.device.DeviceProvider;
+import org.onlab.onos.net.device.DeviceProviderRegistry;
+import org.onlab.onos.net.device.DeviceProviderService;
+import org.onlab.onos.net.device.DeviceService;
+import org.onlab.onos.net.device.DeviceStore;
+import org.onlab.onos.net.device.PortDescription;
+import org.onlab.onos.net.provider.AbstractProviderRegistry;
+import org.onlab.onos.net.provider.AbstractProviderService;
+import org.slf4j.Logger;
+
+import java.util.List;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Provides basic implementation of the device SB &amp; NB APIs.
+ */
+@Component(immediate = true)
+@Service
+public class DeviceManager
+        extends AbstractProviderRegistry<DeviceProvider, DeviceProviderService>
+        implements DeviceService, DeviceAdminService, DeviceProviderRegistry {
+
+    private static final String DEVICE_ID_NULL = "Device ID cannot be null";
+    private static final String PORT_NUMBER_NULL = "Port number cannot be null";
+    private static final String DEVICE_DESCRIPTION_NULL = "Device description cannot be null";
+    private static final String PORT_DESCRIPTION_NULL = "Port description cannot be null";
+    private static final String ROLE_NULL = "Role cannot be null";
+
+    private final Logger log = getLogger(getClass());
+
+    protected final AbstractListenerRegistry<DeviceEvent, DeviceListener>
+            listenerRegistry = new AbstractListenerRegistry<>();
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected DeviceStore store;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected EventDeliveryService eventDispatcher;
+
+    @Activate
+    public void activate() {
+        eventDispatcher.addSink(DeviceEvent.class, listenerRegistry);
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        eventDispatcher.removeSink(DeviceEvent.class);
+        log.info("Stopped");
+    }
+
+    @Override
+    public int getDeviceCount() {
+        return store.getDeviceCount();
+    }
+
+    @Override
+    public Iterable<Device> getDevices() {
+        return store.getDevices();
+    }
+
+    @Override
+    public Device getDevice(DeviceId deviceId) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        return store.getDevice(deviceId);
+    }
+
+    @Override
+    public MastershipRole getRole(DeviceId deviceId) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        return store.getRole(deviceId);
+    }
+
+    @Override
+    public List<Port> getPorts(DeviceId deviceId) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        return store.getPorts(deviceId);
+    }
+
+    @Override
+    public Port getPort(DeviceId deviceId, PortNumber portNumber) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        checkNotNull(portNumber, PORT_NUMBER_NULL);
+        return store.getPort(deviceId, portNumber);
+    }
+
+    @Override
+    public boolean isAvailable(DeviceId deviceId) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        return store.isAvailable(deviceId);
+    }
+
+    @Override
+    public void setRole(DeviceId deviceId, MastershipRole newRole) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        checkNotNull(newRole, ROLE_NULL);
+        DeviceEvent event = store.setRole(deviceId, newRole);
+        if (event != null) {
+            Device device = event.subject();
+            DeviceProvider provider = getProvider(device.providerId());
+            if (provider != null) {
+                provider.roleChanged(device, newRole);
+            }
+            post(event);
+        }
+    }
+
+    @Override
+    public void removeDevice(DeviceId deviceId) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        DeviceEvent event = store.removeDevice(deviceId);
+        if (event != null) {
+            log.info("Device {} administratively removed", deviceId);
+            post(event);
+        }
+    }
+
+    @Override
+    public void addListener(DeviceListener listener) {
+        listenerRegistry.addListener(listener);
+    }
+
+    @Override
+    public void removeListener(DeviceListener listener) {
+        listenerRegistry.removeListener(listener);
+    }
+
+    @Override
+    protected DeviceProviderService createProviderService(DeviceProvider provider) {
+        return new InternalDeviceProviderService(provider);
+    }
+
+    // Personalized device provider service issued to the supplied provider.
+    private class InternalDeviceProviderService
+            extends AbstractProviderService<DeviceProvider>
+            implements DeviceProviderService {
+
+        InternalDeviceProviderService(DeviceProvider provider) {
+            super(provider);
+        }
+
+        @Override
+        public void deviceConnected(DeviceId deviceId, DeviceDescription deviceDescription) {
+            checkNotNull(deviceId, DEVICE_ID_NULL);
+            checkNotNull(deviceDescription, DEVICE_DESCRIPTION_NULL);
+            checkValidity();
+            DeviceEvent event = store.createOrUpdateDevice(provider().id(),
+                                                           deviceId, deviceDescription);
+
+            // If there was a change of any kind, trigger role selection process.
+            if (event != null) {
+                log.info("Device {} connected", deviceId);
+                Device device = event.subject();
+                provider().roleChanged(device, store.getRole(device.id()));
+                post(event);
+            }
+        }
+
+        @Override
+        public void deviceDisconnected(DeviceId deviceId) {
+            checkNotNull(deviceId, DEVICE_ID_NULL);
+            checkValidity();
+            DeviceEvent event = store.markOffline(deviceId);
+            if (event != null) {
+                log.info("Device {} disconnected", deviceId);
+                post(event);
+            }
+        }
+
+        @Override
+        public void updatePorts(DeviceId deviceId, List<PortDescription> portDescriptions) {
+            checkNotNull(deviceId, DEVICE_ID_NULL);
+            checkNotNull(portDescriptions, "Port descriptions list cannot be null");
+            checkValidity();
+            List<DeviceEvent> events = store.updatePorts(deviceId, portDescriptions);
+            for (DeviceEvent event : events) {
+                post(event);
+            }
+        }
+
+        @Override
+        public void portStatusChanged(DeviceId deviceId, PortDescription portDescription) {
+            checkNotNull(deviceId, DEVICE_ID_NULL);
+            checkNotNull(portDescription, PORT_DESCRIPTION_NULL);
+            checkValidity();
+            DeviceEvent event = store.updatePortStatus(deviceId, portDescription);
+            if (event != null) {
+                log.info("Device {} port {} status changed", deviceId,
+                         event.port().number());
+                post(event);
+            }
+        }
+    }
+
+    // Posts the specified event to the local event dispatcher.
+    private void post(DeviceEvent event) {
+        if (event != null && eventDispatcher != null) {
+            eventDispatcher.post(event);
+        }
+    }
+
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/flow/impl/SimpleFlowRuleManager.java b/core/net/src/main/java/org/onlab/onos/net/flow/impl/SimpleFlowRuleManager.java
new file mode 100644
index 0000000..4a1cd3b
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/flow/impl/SimpleFlowRuleManager.java
@@ -0,0 +1,169 @@
+package org.onlab.onos.net.flow.impl;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.slf4j.LoggerFactory.getLogger;
+
+import java.util.ArrayList;
+import java.util.List;
+
+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.event.AbstractListenerRegistry;
+import org.onlab.onos.event.EventDeliveryService;
+import org.onlab.onos.net.Device;
+import org.onlab.onos.net.DeviceId;
+import org.onlab.onos.net.device.DeviceService;
+import org.onlab.onos.net.flow.FlowRule;
+import org.onlab.onos.net.flow.FlowRuleEvent;
+import org.onlab.onos.net.flow.FlowRuleListener;
+import org.onlab.onos.net.flow.FlowRuleProvider;
+import org.onlab.onos.net.flow.FlowRuleProviderRegistry;
+import org.onlab.onos.net.flow.FlowRuleProviderService;
+import org.onlab.onos.net.flow.FlowRuleService;
+import org.onlab.onos.net.flow.FlowRuleStore;
+import org.onlab.onos.net.provider.AbstractProviderRegistry;
+import org.onlab.onos.net.provider.AbstractProviderService;
+import org.slf4j.Logger;
+
+@Component(immediate = true)
+@Service
+public class SimpleFlowRuleManager
+        extends AbstractProviderRegistry<FlowRuleProvider, FlowRuleProviderService>
+        implements FlowRuleService, FlowRuleProviderRegistry {
+
+    public static final String FLOW_RULE_NULL = "FlowRule cannot be null";
+    private final Logger log = getLogger(getClass());
+
+    private final AbstractListenerRegistry<FlowRuleEvent, FlowRuleListener>
+            listenerRegistry = new AbstractListenerRegistry<>();
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected FlowRuleStore store;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected EventDeliveryService eventDispatcher;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected DeviceService deviceService;
+
+    @Activate
+    public void activate() {
+        eventDispatcher.addSink(FlowRuleEvent.class, listenerRegistry);
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        eventDispatcher.removeSink(FlowRuleEvent.class);
+        log.info("Stopped");
+    }
+
+    @Override
+    public Iterable<FlowRule> getFlowEntries(DeviceId deviceId) {
+        return store.getFlowEntries(deviceId);
+    }
+
+    @Override
+    public List<FlowRule> applyFlowRules(FlowRule... flowRules) {
+        List<FlowRule> entries = new ArrayList<FlowRule>();
+
+        for (int i = 0; i < flowRules.length; i++) {
+            FlowRule f = flowRules[i];
+            final Device device = deviceService.getDevice(f.deviceId());
+            final FlowRuleProvider frp = getProvider(device.providerId());
+            entries.add(store.storeFlowRule(f));
+            frp.applyFlowRule(f);
+        }
+
+        return entries;
+    }
+
+    @Override
+    public void removeFlowRules(FlowRule... flowRules) {
+        for (int i = 0; i < flowRules.length; i++) {
+            FlowRule f = flowRules[i];
+            final Device device = deviceService.getDevice(f.deviceId());
+            final FlowRuleProvider frp = getProvider(device.providerId());
+            store.removeFlowRule(f);
+            frp.removeFlowRule(f);
+        }
+
+    }
+
+    @Override
+    public void addListener(FlowRuleListener listener) {
+        listenerRegistry.addListener(listener);
+    }
+
+    @Override
+    public void removeListener(FlowRuleListener listener) {
+        listenerRegistry.removeListener(listener);
+    }
+
+    @Override
+    protected FlowRuleProviderService createProviderService(
+            FlowRuleProvider provider) {
+        return new InternalFlowRuleProviderService(provider);
+    }
+
+    private class InternalFlowRuleProviderService
+            extends AbstractProviderService<FlowRuleProvider>
+            implements FlowRuleProviderService {
+
+        protected InternalFlowRuleProviderService(FlowRuleProvider provider) {
+            super(provider);
+        }
+
+        @Override
+        public void flowRemoved(FlowRule flowRule) {
+            checkNotNull(flowRule, FLOW_RULE_NULL);
+            checkValidity();
+            FlowRuleEvent event = store.removeFlowRule(flowRule);
+
+            if (event != null) {
+                log.debug("Flow {} removed", flowRule);
+                post(event);
+            }
+        }
+
+        @Override
+        public void flowMissing(FlowRule flowRule) {
+            checkNotNull(flowRule, FLOW_RULE_NULL);
+            checkValidity();
+            // TODO Auto-generated method stub
+
+        }
+
+        @Override
+        public void flowAdded(FlowRule flowRule) {
+            checkNotNull(flowRule, FLOW_RULE_NULL);
+            checkValidity();
+
+            FlowRuleEvent event = store.addOrUpdateFlowRule(flowRule);
+            if (event == null) {
+                log.debug("Flow {} updated", flowRule);
+            } else {
+                log.debug("Flow {} added", flowRule);
+                post(event);
+            }
+        }
+
+        // Posts the specified event to the local event dispatcher.
+        private void post(FlowRuleEvent event) {
+            if (event != null) {
+                eventDispatcher.post(event);
+            }
+        }
+
+        @Override
+        public void pushFlowMetrics(Iterable<FlowRule> flowEntries) {
+            // TODO Auto-generated method stub
+
+        }
+    }
+
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/flow/impl/package-info.java b/core/net/src/main/java/org/onlab/onos/net/flow/impl/package-info.java
new file mode 100644
index 0000000..0d05cb2
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/flow/impl/package-info.java
@@ -0,0 +1,4 @@
+/**
+ * Core subsystem for tracking and manipulating global flow state.
+ */
+package org.onlab.onos.net.flow.impl;
diff --git a/core/net/src/main/java/org/onlab/onos/net/host/impl/SimpleHostManager.java b/core/net/src/main/java/org/onlab/onos/net/host/impl/SimpleHostManager.java
new file mode 100644
index 0000000..bc9312d
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/host/impl/SimpleHostManager.java
@@ -0,0 +1,190 @@
+package org.onlab.onos.net.host.impl;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.slf4j.LoggerFactory.getLogger;
+
+import java.util.Set;
+
+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.event.AbstractListenerRegistry;
+import org.onlab.onos.event.EventDeliveryService;
+import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.DeviceId;
+import org.onlab.onos.net.Host;
+import org.onlab.onos.net.HostId;
+import org.onlab.onos.net.host.HostAdminService;
+import org.onlab.onos.net.host.HostDescription;
+import org.onlab.onos.net.host.HostEvent;
+import org.onlab.onos.net.host.HostListener;
+import org.onlab.onos.net.host.HostProvider;
+import org.onlab.onos.net.host.HostProviderRegistry;
+import org.onlab.onos.net.host.HostProviderService;
+import org.onlab.onos.net.host.HostService;
+import org.onlab.onos.net.host.HostStore;
+import org.onlab.onos.net.provider.AbstractProviderRegistry;
+import org.onlab.onos.net.provider.AbstractProviderService;
+import org.onlab.packet.IpPrefix;
+import org.onlab.packet.MacAddress;
+import org.onlab.packet.VlanId;
+import org.slf4j.Logger;
+
+/**
+ * Provides basic implementation of the host SB &amp; NB APIs.
+ */
+@Component(immediate = true)
+@Service
+public class SimpleHostManager
+        extends AbstractProviderRegistry<HostProvider, HostProviderService>
+        implements HostService, HostAdminService, HostProviderRegistry {
+
+    public static final String HOST_ID_NULL = "Host ID cannot be null";
+    private final Logger log = getLogger(getClass());
+
+    private final AbstractListenerRegistry<HostEvent, HostListener>
+            listenerRegistry = new AbstractListenerRegistry<>();
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected HostStore store;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected EventDeliveryService eventDispatcher;
+
+
+    @Activate
+    public void activate() {
+        eventDispatcher.addSink(HostEvent.class, listenerRegistry);
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        eventDispatcher.removeSink(HostEvent.class);
+        log.info("Stopped");
+    }
+
+    @Override
+    protected HostProviderService createProviderService(HostProvider provider) {
+        return new InternalHostProviderService(provider);
+    }
+
+    @Override
+    public int getHostCount() {
+        return store.getHostCount();
+    }
+
+    @Override
+    public Iterable<Host> getHosts() {
+        return store.getHosts();
+    }
+
+    @Override
+    public Host getHost(HostId hostId) {
+        checkNotNull(hostId, HOST_ID_NULL);
+        return store.getHost(hostId);
+    }
+
+    @Override
+    public Set<Host> getHostsByVlan(VlanId vlanId) {
+        return store.getHosts(vlanId);
+    }
+
+    @Override
+    public Set<Host> getHostsByMac(MacAddress mac) {
+        checkNotNull(mac, "MAC address cannot be null");
+        return store.getHosts(mac);
+    }
+
+    @Override
+    public Set<Host> getHostsByIp(IpPrefix ip) {
+        checkNotNull(ip, "IP address cannot be null");
+        return store.getHosts(ip);
+    }
+
+    @Override
+    public Set<Host> getConnectedHosts(ConnectPoint connectPoint) {
+        checkNotNull(connectPoint, "Connection point cannot be null");
+        return store.getConnectedHosts(connectPoint);
+    }
+
+    @Override
+    public Set<Host> getConnectedHosts(DeviceId deviceId) {
+        checkNotNull(deviceId, "Device ID cannot be null");
+        return store.getConnectedHosts(deviceId);
+    }
+
+    @Override
+    public void monitorIp(IpPrefix ip) {
+        // TODO pass through to SimpleHostMonitor
+    }
+
+    @Override
+    public void stopMonitoringIp(IpPrefix ip) {
+        // TODO pass through to SimpleHostMonitor
+    }
+
+    @Override
+    public void addListener(HostListener listener) {
+        listenerRegistry.addListener(listener);
+    }
+
+    @Override
+    public void removeListener(HostListener listener) {
+        listenerRegistry.removeListener(listener);
+    }
+
+    @Override
+    public void removeHost(HostId hostId) {
+        checkNotNull(hostId, HOST_ID_NULL);
+        HostEvent event = store.removeHost(hostId);
+        if (event != null) {
+            log.info("Host {} administratively removed", hostId);
+            post(event);
+        }
+    }
+
+    // Personalized host provider service issued to the supplied provider.
+    private class InternalHostProviderService
+            extends AbstractProviderService<HostProvider>
+            implements HostProviderService {
+
+        InternalHostProviderService(HostProvider provider) {
+            super(provider);
+        }
+
+        @Override
+        public void hostDetected(HostId hostId, HostDescription hostDescription) {
+            checkNotNull(hostId, HOST_ID_NULL);
+            checkValidity();
+            HostEvent event = store.createOrUpdateHost(provider().id(), hostId,
+                                                       hostDescription);
+            if (event != null) {
+                log.debug("Host {} detected", hostId);
+                post(event);
+            }
+        }
+
+        @Override
+        public void hostVanished(HostId hostId) {
+            checkNotNull(hostId, HOST_ID_NULL);
+            checkValidity();
+            HostEvent event = store.removeHost(hostId);
+            if (event != null) {
+                log.debug("Host {} vanished", hostId);
+                post(event);
+            }
+        }
+    }
+
+    // Posts the specified event to the local event dispatcher.
+    private void post(HostEvent event) {
+        if (event != null) {
+            eventDispatcher.post(event);
+        }
+    }
+
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/host/impl/SimpleHostMonitor.java b/core/net/src/main/java/org/onlab/onos/net/host/impl/SimpleHostMonitor.java
new file mode 100644
index 0000000..4849466
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/host/impl/SimpleHostMonitor.java
@@ -0,0 +1,108 @@
+package org.onlab.onos.net.host.impl;
+
+import java.util.HashSet;
+import java.util.Set;
+import java.util.concurrent.TimeUnit;
+
+import org.jboss.netty.util.Timeout;
+import org.jboss.netty.util.TimerTask;
+import org.onlab.onos.net.Device;
+import org.onlab.onos.net.Host;
+import org.onlab.onos.net.Port;
+import org.onlab.onos.net.device.DeviceService;
+import org.onlab.onos.net.host.HostProvider;
+import org.onlab.onos.net.host.HostService;
+import org.onlab.onos.net.packet.PacketProvider;
+import org.onlab.onos.net.topology.TopologyService;
+import org.onlab.packet.IpPrefix;
+import org.onlab.util.Timer;
+
+public class SimpleHostMonitor implements TimerTask {
+
+    private final HostService hostService;
+    private final TopologyService topologyService;
+    private final DeviceService deviceService;
+    private final HostProvider hostProvider;
+    private final PacketProvider packetProvider;
+
+    private final Set<IpPrefix> monitoredAddresses;
+
+    private final long probeRate;
+
+    private Timeout timeout;
+
+    public SimpleHostMonitor(HostService hostService, TopologyService topologyService,
+            DeviceService deviceService,
+            HostProvider hostProvider, PacketProvider packetProvider) {
+        this.hostService = hostService;
+        this.topologyService = topologyService;
+        this.deviceService = deviceService;
+        this.hostProvider = hostProvider;
+        this.packetProvider = packetProvider;
+
+        monitoredAddresses = new HashSet<>();
+
+        probeRate = 30000; // milliseconds
+
+        timeout = Timer.getTimer().newTimeout(this, 0, TimeUnit.MILLISECONDS);
+    }
+
+    public void addMonitoringFor(IpPrefix ip) {
+        monitoredAddresses.add(ip);
+    }
+
+    public void stopMonitoring(IpPrefix ip) {
+        monitoredAddresses.remove(ip);
+    }
+
+    public void shutdown() {
+        timeout.cancel();
+    }
+
+    @Override
+    public void run(Timeout timeout) throws Exception {
+        for (IpPrefix ip : monitoredAddresses) {
+            Set<Host> hosts = hostService.getHostsByIp(ip);
+
+            if (hosts.isEmpty()) {
+                sendArpRequest(ip);
+            } else {
+                for (Host host : hosts) {
+                    hostProvider.triggerProbe(host);
+                }
+            }
+        }
+
+        timeout = Timer.getTimer().newTimeout(this, probeRate, TimeUnit.MILLISECONDS);
+    }
+
+    /**
+     * Sends an ARP request for the given IP address.
+     *
+     * @param targetIp IP address to ARP for
+     */
+    private void sendArpRequest(IpPrefix targetIp) {
+        // emit ARP packet out appropriate ports
+
+        // if ip in one of the configured (external) subnets
+        //   sent out that port
+        // else (ip isn't in any configured subnet)
+        //   send out all non-external edge ports
+
+        for (Device device : deviceService.getDevices()) {
+            for (Port port : deviceService.getPorts(device.id())) {
+                for (IpPrefix ip : port.ipAddresses()) {
+                    if (ip.contains(targetIp)) {
+                        sendProbe(port, targetIp);
+                        continue;
+                    }
+                }
+            }
+        }
+
+    }
+
+    private void sendProbe(Port port, IpPrefix targetIp) {
+
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/host/impl/package-info.java b/core/net/src/main/java/org/onlab/onos/net/host/impl/package-info.java
new file mode 100644
index 0000000..55370d3
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/host/impl/package-info.java
@@ -0,0 +1,4 @@
+/**
+ * Core subsystem for tracking global inventory of end-station hosts.
+ */
+package org.onlab.onos.net.host.impl;
diff --git a/core/net/src/main/java/org/onlab/onos/net/link/impl/LinkManager.java b/core/net/src/main/java/org/onlab/onos/net/link/impl/LinkManager.java
new file mode 100644
index 0000000..9ac5e80
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/link/impl/LinkManager.java
@@ -0,0 +1,239 @@
+package org.onlab.onos.net.link.impl;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.slf4j.LoggerFactory.getLogger;
+
+import java.util.Set;
+
+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.event.AbstractListenerRegistry;
+import org.onlab.onos.event.EventDeliveryService;
+import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.DeviceId;
+import org.onlab.onos.net.Link;
+import org.onlab.onos.net.device.DeviceEvent;
+import org.onlab.onos.net.device.DeviceListener;
+import org.onlab.onos.net.device.DeviceService;
+import org.onlab.onos.net.link.LinkAdminService;
+import org.onlab.onos.net.link.LinkDescription;
+import org.onlab.onos.net.link.LinkEvent;
+import org.onlab.onos.net.link.LinkListener;
+import org.onlab.onos.net.link.LinkProvider;
+import org.onlab.onos.net.link.LinkProviderRegistry;
+import org.onlab.onos.net.link.LinkProviderService;
+import org.onlab.onos.net.link.LinkService;
+import org.onlab.onos.net.link.LinkStore;
+import org.onlab.onos.net.provider.AbstractProviderRegistry;
+import org.onlab.onos.net.provider.AbstractProviderService;
+import org.slf4j.Logger;
+
+import com.google.common.collect.Sets;
+
+/**
+ * Provides basic implementation of the link SB &amp; NB APIs.
+ */
+@Component(immediate = true)
+@Service
+public class LinkManager
+        extends AbstractProviderRegistry<LinkProvider, LinkProviderService>
+        implements LinkService, LinkAdminService, LinkProviderRegistry {
+
+    private static final String DEVICE_ID_NULL = "Device ID cannot be null";
+    private static final String LINK_DESC_NULL = "Link description cannot be null";
+    private static final String CONNECT_POINT_NULL = "Connection point cannot be null";
+
+    private final Logger log = getLogger(getClass());
+
+    protected final AbstractListenerRegistry<LinkEvent, LinkListener>
+            listenerRegistry = new AbstractListenerRegistry<>();
+
+    private final DeviceListener deviceListener = new InnerDeviceListener();
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected LinkStore store;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected DeviceService deviceService;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected EventDeliveryService eventDispatcher;
+
+    @Activate
+    public void activate() {
+        eventDispatcher.addSink(LinkEvent.class, listenerRegistry);
+        deviceService.addListener(deviceListener);
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        eventDispatcher.removeSink(LinkEvent.class);
+        deviceService.removeListener(deviceListener);
+        log.info("Stopped");
+    }
+
+    @Override
+    public int getLinkCount() {
+        return store.getLinkCount();
+    }
+
+    @Override
+    public Iterable<Link> getLinks() {
+        return store.getLinks();
+    }
+
+    @Override
+    public Set<Link> getDeviceLinks(DeviceId deviceId) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        return Sets.union(store.getDeviceEgressLinks(deviceId),
+                          store.getDeviceIngressLinks(deviceId));
+    }
+
+    @Override
+    public Set<Link> getDeviceEgressLinks(DeviceId deviceId) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        return store.getDeviceEgressLinks(deviceId);
+    }
+
+    @Override
+    public Set<Link> getDeviceIngressLinks(DeviceId deviceId) {
+        checkNotNull(deviceId, DEVICE_ID_NULL);
+        return store.getDeviceIngressLinks(deviceId);
+    }
+
+    @Override
+    public Set<Link> getLinks(ConnectPoint connectPoint) {
+        checkNotNull(connectPoint, CONNECT_POINT_NULL);
+        return Sets.union(store.getEgressLinks(connectPoint),
+                          store.getIngressLinks(connectPoint));
+    }
+
+    @Override
+    public Set<Link> getEgressLinks(ConnectPoint connectPoint) {
+        checkNotNull(connectPoint, CONNECT_POINT_NULL);
+        return store.getEgressLinks(connectPoint);
+    }
+
+    @Override
+    public Set<Link> getIngressLinks(ConnectPoint connectPoint) {
+        checkNotNull(connectPoint, CONNECT_POINT_NULL);
+        return store.getIngressLinks(connectPoint);
+    }
+
+    @Override
+    public Link getLink(ConnectPoint src, ConnectPoint dst) {
+        checkNotNull(src, CONNECT_POINT_NULL);
+        checkNotNull(dst, CONNECT_POINT_NULL);
+        return store.getLink(src, dst);
+    }
+
+    @Override
+    public void removeLinks(ConnectPoint connectPoint) {
+        removeLinks(getLinks(connectPoint));
+    }
+
+    @Override
+    public void removeLinks(DeviceId deviceId) {
+        removeLinks(getDeviceLinks(deviceId));
+    }
+
+    @Override
+    public void addListener(LinkListener listener) {
+        listenerRegistry.addListener(listener);
+    }
+
+    @Override
+    public void removeListener(LinkListener listener) {
+        listenerRegistry.removeListener(listener);
+    }
+
+    // Auxiliary interceptor for device remove events to prune links that
+    // are associated with the removed device or its port.
+    private class InnerDeviceListener implements DeviceListener {
+        @Override
+        public void event(DeviceEvent event) {
+            if (event.type() == DeviceEvent.Type.DEVICE_REMOVED) {
+                removeLinks(event.subject().id());
+            } else if (event.type() == DeviceEvent.Type.PORT_REMOVED) {
+                removeLinks(new ConnectPoint(event.subject().id(),
+                                             event.port().number()));
+            }
+        }
+    }
+
+    @Override
+    protected LinkProviderService createProviderService(LinkProvider provider) {
+        return new InternalLinkProviderService(provider);
+    }
+
+    // Personalized link provider service issued to the supplied provider.
+    private class InternalLinkProviderService
+            extends AbstractProviderService<LinkProvider>
+            implements LinkProviderService {
+
+        InternalLinkProviderService(LinkProvider provider) {
+            super(provider);
+        }
+
+        @Override
+        public void linkDetected(LinkDescription linkDescription) {
+            checkNotNull(linkDescription, LINK_DESC_NULL);
+            checkValidity();
+            LinkEvent event = store.createOrUpdateLink(provider().id(),
+                                                       linkDescription);
+            if (event != null) {
+                log.debug("Link {} detected", linkDescription);
+                post(event);
+            }
+        }
+
+        @Override
+        public void linkVanished(LinkDescription linkDescription) {
+            checkNotNull(linkDescription, LINK_DESC_NULL);
+            checkValidity();
+            LinkEvent event = store.removeLink(linkDescription.src(),
+                                               linkDescription.dst());
+            if (event != null) {
+                log.info("Link {} vanished", linkDescription);
+                post(event);
+            }
+        }
+
+        @Override
+        public void linksVanished(ConnectPoint connectPoint) {
+            checkNotNull(connectPoint, "Connect point cannot be null");
+            checkValidity();
+            log.info("Links for connection point {} vanished", connectPoint);
+            removeLinks(getLinks(connectPoint));
+        }
+
+        @Override
+        public void linksVanished(DeviceId deviceId) {
+            checkNotNull(deviceId, DEVICE_ID_NULL);
+            checkValidity();
+            log.info("Links for device {} vanished", deviceId);
+            removeLinks(getDeviceLinks(deviceId));
+        }
+    }
+
+    // Removes all links in the specified set and emits appropriate events.
+    private void removeLinks(Set<Link> links) {
+        for (Link link : links) {
+            LinkEvent event = store.removeLink(link.src(), link.dst());
+            post(event);
+        }
+    }
+
+    // Posts the specified event to the local event dispatcher.
+    private void post(LinkEvent event) {
+        if (event != null) {
+            eventDispatcher.post(event);
+        }
+    }
+
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/packet/impl/SimplePacketManager.java b/core/net/src/main/java/org/onlab/onos/net/packet/impl/SimplePacketManager.java
new file mode 100644
index 0000000..ee1b025
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/packet/impl/SimplePacketManager.java
@@ -0,0 +1,96 @@
+package org.onlab.onos.net.packet.impl;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.slf4j.LoggerFactory.getLogger;
+
+import java.util.Map;
+import java.util.TreeMap;
+
+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.Device;
+import org.onlab.onos.net.device.DeviceService;
+import org.onlab.onos.net.packet.OutboundPacket;
+import org.onlab.onos.net.packet.PacketContext;
+import org.onlab.onos.net.packet.PacketProcessor;
+import org.onlab.onos.net.packet.PacketProvider;
+import org.onlab.onos.net.packet.PacketProviderRegistry;
+import org.onlab.onos.net.packet.PacketProviderService;
+import org.onlab.onos.net.packet.PacketService;
+import org.onlab.onos.net.provider.AbstractProviderRegistry;
+import org.onlab.onos.net.provider.AbstractProviderService;
+import org.slf4j.Logger;
+
+/**
+ * Provides a basic implementation of the packet SB &amp; NB APIs.
+ */
+@Component(immediate = true)
+@Service
+public class SimplePacketManager
+extends AbstractProviderRegistry<PacketProvider, PacketProviderService>
+implements PacketService, PacketProviderRegistry {
+
+    private final Logger log = getLogger(getClass());
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    private DeviceService deviceService;
+
+    private final Map<Integer, PacketProcessor> processors = new TreeMap<>();
+
+    @Activate
+    public void activate() {
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        log.info("Stopped");
+    }
+
+    @Override
+    public void addProcessor(PacketProcessor processor, int priority) {
+        checkNotNull(processor, "Processor cannot be null");
+        processors.put(priority, processor);
+    }
+
+    @Override
+    public void removeProcessor(PacketProcessor processor) {
+        checkNotNull(processor, "Processor cannot be null");
+        processors.values().remove(processor);
+    }
+
+    @Override
+    public void emit(OutboundPacket packet) {
+        checkNotNull(packet, "Packet cannot be null");
+        final Device device = deviceService.getDevice(packet.sendThrough());
+        final PacketProvider packetProvider = getProvider(device.providerId());
+        packetProvider.emit(packet);
+    }
+
+    @Override
+    protected PacketProviderService createProviderService(PacketProvider provider) {
+        return new InternalPacketProviderService(provider);
+    }
+
+    // Personalized link provider service issued to the supplied provider.
+    private class InternalPacketProviderService
+    extends AbstractProviderService<PacketProvider>
+    implements PacketProviderService {
+
+        protected InternalPacketProviderService(PacketProvider provider) {
+            super(provider);
+        }
+
+        @Override
+        public void processPacket(PacketContext context) {
+            for (PacketProcessor processor : processors.values()) {
+                processor.process(context);
+            }
+        }
+
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/packet/impl/package-info.java b/core/net/src/main/java/org/onlab/onos/net/packet/impl/package-info.java
new file mode 100644
index 0000000..78dfeaa
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/packet/impl/package-info.java
@@ -0,0 +1,6 @@
+/**
+ * Core subsystem for processing inbound packets and emitting outbound packets.
+ * Processing of inbound packets is always in the local context only, but
+ * emitting outbound packets allows for cluster-wide operation.
+ */
+package org.onlab.onos.net.packet.impl;
diff --git a/core/net/src/main/java/org/onlab/onos/net/topology/impl/DefaultTopologyProvider.java b/core/net/src/main/java/org/onlab/onos/net/topology/impl/DefaultTopologyProvider.java
new file mode 100644
index 0000000..770f368
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/topology/impl/DefaultTopologyProvider.java
@@ -0,0 +1,183 @@
+package org.onlab.onos.net.topology.impl;
+
+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.onlab.onos.event.AbstractEventAccumulator;
+import org.onlab.onos.event.Event;
+import org.onlab.onos.event.EventAccumulator;
+import org.onlab.onos.net.device.DeviceEvent;
+import org.onlab.onos.net.device.DeviceListener;
+import org.onlab.onos.net.device.DeviceService;
+import org.onlab.onos.net.link.LinkEvent;
+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.DefaultGraphDescription;
+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;
+import org.slf4j.Logger;
+
+import java.util.List;
+import java.util.Timer;
+import java.util.concurrent.ExecutorService;
+
+import static java.util.concurrent.Executors.newFixedThreadPool;
+import static org.onlab.onos.net.device.DeviceEvent.Type.*;
+import static org.onlab.util.Tools.namedThreads;
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Default implementation of a network topology provider that feeds off
+ * device and link subsystem events to trigger assembly and computation of
+ * new topology snapshots.
+ */
+@Component(immediate = true)
+public class DefaultTopologyProvider extends AbstractProvider
+        implements TopologyProvider {
+
+    // TODO: make these configurable
+    private static final int MAX_EVENTS = 100;
+    private static final int MAX_IDLE_MS = 50;
+    private static final int MAX_BATCH_MS = 200;
+    private static final int MAX_THREADS = 8;
+
+    // FIXME: Replace with a system-wide timer instance;
+    // TODO: Convert to use HashedWheelTimer or produce a variant of that; then decide which we want to adopt
+    private static final Timer TIMER = new Timer();
+
+    private final Logger log = getLogger(getClass());
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected TopologyProviderRegistry providerRegistry;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected DeviceService deviceService;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected LinkService linkService;
+
+    private volatile boolean isStarted = false;
+
+    private TopologyProviderService providerService;
+    private DeviceListener deviceListener = new InnerDeviceListener();
+    private LinkListener linkListener = new InnerLinkListener();
+
+    private EventAccumulator accumulator;
+    private ExecutorService executor;
+
+    /**
+     * Creates a provider with the supplier identifier.
+     */
+    public DefaultTopologyProvider() {
+        super(new ProviderId("core", "org.onlab.onos.provider.topology"));
+    }
+
+    @Activate
+    public synchronized void activate() {
+        executor = newFixedThreadPool(MAX_THREADS, namedThreads("topo-build-%d"));
+        accumulator = new TopologyChangeAccumulator();
+
+        providerService = providerRegistry.register(this);
+        deviceService.addListener(deviceListener);
+        linkService.addListener(linkListener);
+
+        isStarted = true;
+        triggerTopologyBuild(null);
+        log.info("Started");
+    }
+
+    @Deactivate
+    public synchronized void deactivate() {
+        isStarted = false;
+
+        deviceService.removeListener(deviceListener);
+        linkService.removeListener(linkListener);
+        providerRegistry.unregister(this);
+        providerService = null;
+
+        executor.shutdownNow();
+        executor = null;
+
+        log.info("Stopped");
+    }
+
+    /**
+     * Triggers assembly of topology data citing the specified events as the
+     * reason.
+     *
+     * @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) {
+            GraphDescription desc =
+                    new DefaultGraphDescription(System.nanoTime(),
+                                                deviceService.getDevices(),
+                                                linkService.getLinks());
+            providerService.topologyChanged(desc, reasons);
+        }
+    }
+
+    // Callback for device events
+    private class InnerDeviceListener implements DeviceListener {
+        @Override
+        public void event(DeviceEvent event) {
+            DeviceEvent.Type type = event.type();
+            if (type == DEVICE_ADDED || type == DEVICE_REMOVED ||
+                    type == DEVICE_AVAILABILITY_CHANGED) {
+                accumulator.add(event);
+            }
+        }
+    }
+
+    // Callback for link events
+    private class InnerLinkListener implements LinkListener {
+        @Override
+        public void event(LinkEvent event) {
+            accumulator.add(event);
+        }
+    }
+
+    // Event accumulator for paced triggering of topology assembly.
+    private class TopologyChangeAccumulator
+            extends AbstractEventAccumulator implements EventAccumulator {
+
+        TopologyChangeAccumulator() {
+            super(TIMER, MAX_EVENTS, MAX_BATCH_MS, MAX_IDLE_MS);
+        }
+
+        @Override
+        public void processEvents(List<Event> events) {
+            triggerTopologyBuild(events);
+        }
+
+    }
+
+    // Task for building topology data in a separate thread.
+    private class TopologyBuilderTask implements Runnable {
+        private final List<Event> reasons;
+
+        public TopologyBuilderTask(List<Event> reasons) {
+            this.reasons = reasons;
+        }
+
+        @Override
+        public void run() {
+            buildTopology(reasons);
+        }
+    }
+
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/topology/impl/PathManager.java b/core/net/src/main/java/org/onlab/onos/net/topology/impl/PathManager.java
new file mode 100644
index 0000000..47cb376
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/topology/impl/PathManager.java
@@ -0,0 +1,170 @@
+package org.onlab.onos.net.topology.impl;
+
+import com.google.common.collect.Lists;
+import com.google.common.collect.Sets;
+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.DefaultEdgeLink;
+import org.onlab.onos.net.DefaultPath;
+import org.onlab.onos.net.DeviceId;
+import org.onlab.onos.net.EdgeLink;
+import org.onlab.onos.net.ElementId;
+import org.onlab.onos.net.Host;
+import org.onlab.onos.net.HostId;
+import org.onlab.onos.net.HostLocation;
+import org.onlab.onos.net.Link;
+import org.onlab.onos.net.Path;
+import org.onlab.onos.net.PortNumber;
+import org.onlab.onos.net.host.HostService;
+import org.onlab.onos.net.topology.PathService;
+import org.onlab.onos.net.provider.ProviderId;
+import org.onlab.onos.net.topology.LinkWeight;
+import org.onlab.onos.net.topology.Topology;
+import org.onlab.onos.net.topology.TopologyService;
+import org.slf4j.Logger;
+
+import java.util.List;
+import java.util.Set;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.onlab.onos.net.DeviceId.deviceId;
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Provides implementation of a path selection service atop the current
+ * topology and host services.
+ */
+@Component(immediate = true)
+@Service
+public class PathManager implements PathService {
+
+    private static final String ELEMENT_ID_NULL = "Element ID cannot be null";
+
+    private static final ProviderId PID = new ProviderId("core", "org.onlab.onos.core");
+    private static final PortNumber P0 = PortNumber.portNumber(0);
+
+    private static final EdgeLink NOT_HOST = new NotHost();
+
+    private final Logger log = getLogger(getClass());
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected TopologyService topologyService;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected HostService hostService;
+
+    @Activate
+    public void setUp() {
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void tearDown() {
+        log.info("Stopped");
+    }
+
+    @Override
+    public Set<Path> getPaths(ElementId src, ElementId dst) {
+        return getPaths(src, dst, null);
+    }
+
+    @Override
+    public Set<Path> getPaths(ElementId src, ElementId dst, LinkWeight weight) {
+        checkNotNull(src, ELEMENT_ID_NULL);
+        checkNotNull(dst, ELEMENT_ID_NULL);
+
+        // Get the source and destination edge locations
+        EdgeLink srcEdge = getEdgeLink(src, true);
+        EdgeLink dstEdge = getEdgeLink(dst, false);
+
+        DeviceId srcDevice = srcEdge != NOT_HOST ? srcEdge.dst().deviceId() : (DeviceId) src;
+        DeviceId dstDevice = dstEdge != NOT_HOST ? dstEdge.src().deviceId() : (DeviceId) dst;
+
+        // If the source and destination are on the same edge device, there
+        // is just one path, so build it and return it.
+        if (srcDevice.equals(dstDevice)) {
+            return edgeToEdgePaths(srcEdge, dstEdge);
+        }
+
+        // Otherwise get all paths between the source and destination edge
+        // devices.
+        Topology topology = topologyService.currentTopology();
+        Set<Path> paths = weight == null ?
+                topologyService.getPaths(topology, srcDevice, dstDevice) :
+                topologyService.getPaths(topology, srcDevice, dstDevice, weight);
+
+        return edgeToEdgePaths(srcEdge, dstEdge, paths);
+    }
+
+    // Finds the host edge link if the element ID is a host id of an existing
+    // host. Otherwise, if the host does not exist, it returns null and if
+    // the element ID is not a host ID, returns NOT_HOST edge link.
+    private EdgeLink getEdgeLink(ElementId elementId, boolean isIngress) {
+        if (elementId instanceof HostId) {
+            // Resolve the host, return null.
+            Host host = hostService.getHost((HostId) elementId);
+            if (host == null) {
+                return null;
+            }
+            return new DefaultEdgeLink(PID, new ConnectPoint(elementId, P0),
+                                       host.location(), isIngress);
+        }
+        return NOT_HOST;
+    }
+
+    // Produces a set of direct edge-to-edge paths.
+    private Set<Path> edgeToEdgePaths(EdgeLink srcLink, EdgeLink dstLink) {
+        Set<Path> endToEndPaths = Sets.newHashSetWithExpectedSize(1);
+        if (srcLink != NOT_HOST || dstLink != NOT_HOST) {
+            endToEndPaths.add(edgeToEdgePath(srcLink, dstLink));
+        }
+        return endToEndPaths;
+    }
+
+    // Produces a direct edge-to-edge path.
+    private Path edgeToEdgePath(EdgeLink srcLink, EdgeLink dstLink) {
+        List<Link> links = Lists.newArrayListWithCapacity(2);
+        // Add source and destination edge links only if they are real.
+        if (srcLink != NOT_HOST) {
+            links.add(srcLink);
+        }
+        if (dstLink != NOT_HOST) {
+            links.add(dstLink);
+        }
+        return new DefaultPath(PID, links, 2);
+    }
+
+    // Produces a set of edge-to-edge paths using the set of infrastructure
+    // paths and the given edge links.
+    private Set<Path> edgeToEdgePaths(EdgeLink srcLink, EdgeLink dstLink, Set<Path> paths) {
+        Set<Path> endToEndPaths = Sets.newHashSetWithExpectedSize(paths.size());
+        for (Path path : paths) {
+            endToEndPaths.add(edgeToEdgePath(srcLink, dstLink, path));
+        }
+        return endToEndPaths;
+    }
+
+    // Produces an edge-to-edge path using the specified infrastructure path
+    // and edge links.
+    private Path edgeToEdgePath(EdgeLink srcLink, EdgeLink dstLink, Path path) {
+        List<Link> links = Lists.newArrayListWithCapacity(path.links().size() + 2);
+        links.add(srcLink);
+        links.addAll(path.links());
+        links.add(dstLink);
+        return new DefaultPath(path.providerId(), links, path.cost() + 2);
+    }
+
+    // Special value for edge link to represent that this is really not an
+    // edge link since the src or dst are really an infrastructure device.
+    private static class NotHost extends DefaultEdgeLink implements EdgeLink {
+        NotHost() {
+            super(PID, new ConnectPoint(HostId.hostId("nic:none"), P0),
+                  new HostLocation(deviceId("none:none"), P0, 0L), false);
+        }
+    }
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/topology/impl/TopologyManager.java b/core/net/src/main/java/org/onlab/onos/net/topology/impl/TopologyManager.java
new file mode 100644
index 0000000..57e9fb7
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/topology/impl/TopologyManager.java
@@ -0,0 +1,191 @@
+package org.onlab.onos.net.topology.impl;
+
+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.event.AbstractListenerRegistry;
+import org.onlab.onos.event.Event;
+import org.onlab.onos.event.EventDeliveryService;
+import org.onlab.onos.net.ConnectPoint;
+import org.onlab.onos.net.DeviceId;
+import org.onlab.onos.net.Link;
+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.ClusterId;
+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.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;
+import org.onlab.onos.net.topology.TopologyProviderService;
+import org.onlab.onos.net.topology.TopologyService;
+import org.onlab.onos.net.topology.TopologyStore;
+import org.slf4j.Logger;
+
+import java.util.List;
+import java.util.Set;
+
+import static com.google.common.base.Preconditions.checkNotNull;
+import static org.slf4j.LoggerFactory.getLogger;
+
+/**
+ * Provides basic implementation of the topology SB &amp; NB APIs.
+ */
+@Component(immediate = true)
+@Service
+public class TopologyManager
+        extends AbstractProviderRegistry<TopologyProvider, TopologyProviderService>
+        implements TopologyService, TopologyProviderRegistry {
+
+    public static final String TOPOLOGY_NULL = "Topology cannot be null";
+    private static final String DEVICE_ID_NULL = "Device ID cannot be null";
+    private static final String CLUSTER_ID_NULL = "Cluster ID cannot be null";
+    private static final String CLUSTER_NULL = "Topology cluster cannot be null";
+    public static final String CONNECTION_POINT_NULL = "Connection point cannot be null";
+
+    private final Logger log = getLogger(getClass());
+
+    private final AbstractListenerRegistry<TopologyEvent, TopologyListener>
+            listenerRegistry = new AbstractListenerRegistry<>();
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected TopologyStore store;
+
+    @Reference(cardinality = ReferenceCardinality.MANDATORY_UNARY)
+    protected EventDeliveryService eventDispatcher;
+
+
+    @Activate
+    public void activate() {
+        eventDispatcher.addSink(TopologyEvent.class, listenerRegistry);
+        log.info("Started");
+    }
+
+    @Deactivate
+    public void deactivate() {
+        eventDispatcher.removeSink(TopologyEvent.class);
+        log.info("Stopped");
+    }
+
+    @Override
+    public Topology currentTopology() {
+        return store.currentTopology();
+    }
+
+    @Override
+    public boolean isLatest(Topology topology) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        return store.isLatest(topology);
+    }
+
+    @Override
+    public Set<TopologyCluster> getClusters(Topology topology) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        return store.getClusters(topology);
+    }
+
+    @Override
+    public TopologyCluster getCluster(Topology topology, ClusterId clusterId) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        checkNotNull(topology, CLUSTER_ID_NULL);
+        return store.getCluster(topology, clusterId);
+    }
+
+    @Override
+    public Set<DeviceId> getClusterDevices(Topology topology, TopologyCluster cluster) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        checkNotNull(topology, CLUSTER_NULL);
+        return store.getClusterDevices(topology, cluster);
+    }
+
+    @Override
+    public Set<Link> getClusterLinks(Topology topology, TopologyCluster cluster) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        checkNotNull(topology, CLUSTER_NULL);
+        return store.getClusterLinks(topology, cluster);
+    }
+
+    @Override
+    public TopologyGraph getGraph(Topology topology) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        return store.getGraph(topology);
+    }
+
+    @Override
+    public Set<Path> getPaths(Topology topology, DeviceId src, DeviceId dst) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        checkNotNull(src, DEVICE_ID_NULL);
+        checkNotNull(dst, DEVICE_ID_NULL);
+        return store.getPaths(topology, src, dst);
+    }
+
+    @Override
+    public Set<Path> getPaths(Topology topology, DeviceId src, DeviceId dst, LinkWeight weight) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        checkNotNull(src, DEVICE_ID_NULL);
+        checkNotNull(dst, DEVICE_ID_NULL);
+        checkNotNull(weight, "Link weight cannot be null");
+        return store.getPaths(topology, src, dst, weight);
+    }
+
+    @Override
+    public boolean isInfrastructure(Topology topology, ConnectPoint connectPoint) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        checkNotNull(connectPoint, CONNECTION_POINT_NULL);
+        return store.isInfrastructure(topology, connectPoint);
+    }
+
+    @Override
+    public boolean isBroadcastPoint(Topology topology, ConnectPoint connectPoint) {
+        checkNotNull(topology, TOPOLOGY_NULL);
+        checkNotNull(connectPoint, CONNECTION_POINT_NULL);
+        return store.isBroadcastPoint(topology, connectPoint);
+    }
+
+    @Override
+    public void addListener(TopologyListener listener) {
+        listenerRegistry.addListener(listener);
+    }
+
+    @Override
+    public void removeListener(TopologyListener listener) {
+        listenerRegistry.removeListener(listener);
+    }
+
+    // Personalized host provider service issued to the supplied provider.
+    @Override
+    protected TopologyProviderService createProviderService(TopologyProvider provider) {
+        return new InternalTopologyProviderService(provider);
+    }
+
+    private class InternalTopologyProviderService
+            extends AbstractProviderService<TopologyProvider>
+            implements TopologyProviderService {
+
+        InternalTopologyProviderService(TopologyProvider provider) {
+            super(provider);
+        }
+
+        @Override
+        public void topologyChanged(GraphDescription topoDescription,
+                                    List<Event> reasons) {
+            checkNotNull(topoDescription, "Topology description cannot be null");
+
+            TopologyEvent event = store.updateTopology(provider().id(),
+                                                       topoDescription, reasons);
+            if (event != null) {
+                log.info("Topology {} changed", event.subject());
+                eventDispatcher.post(event);
+            }
+        }
+    }
+
+}
diff --git a/core/net/src/main/java/org/onlab/onos/net/topology/impl/package-info.java b/core/net/src/main/java/org/onlab/onos/net/topology/impl/package-info.java
new file mode 100644
index 0000000..17c3644
--- /dev/null
+++ b/core/net/src/main/java/org/onlab/onos/net/topology/impl/package-info.java
@@ -0,0 +1,4 @@
+/**
+ * Core subsystem for tracking global &amp; consistent topology graph views.
+ */
+package org.onlab.onos.net.topology.impl;