diff --git a/les/balance.go b/les/balance.go
index 1eae56071c..1d3cbd143e 100644
--- a/les/balance.go
+++ b/les/balance.go
@@ -68,6 +68,7 @@ type balanceCallback struct {
 }
 
 // init initializes balanceTracker
+// Note: capacity should never be zero
 func (bt *balanceTracker) init(clock mclock.Clock, capacity uint64) {
 	bt.clock = clock
 	bt.initTime, bt.lastUpdate = clock.Now(), clock.Now() // Init timestamps
@@ -99,7 +100,7 @@ func (bt *balanceTracker) stop(now mclock.AbsTime) {
 // balance is zero then negative balance translates to a positive priority.
 func (bt *balanceTracker) balanceToPriority(b balance) int64 {
 	if b.pos > 0 {
-		return ^int64(b.pos / bt.capacity)
+		return -int64(b.pos / bt.capacity)
 	}
 	return int64(b.neg)
 }
@@ -107,7 +108,7 @@ func (bt *balanceTracker) balanceToPriority(b balance) int64 {
 func (bt *balanceTracker) posBalanceMissing(targetPriority int64, targetCapacity uint64, after time.Duration) uint64 {
 	if targetPriority > 0 {
 		negPrice := uint64(float64(after) * bt.negTimeFactor)
-		if negPrice+bt.balance.neg <= uint64(targetPriority) {
+		if negPrice+bt.balance.neg < uint64(targetPriority) {
 			return 0
 		}
 		if uint64(targetPriority) > bt.balance.neg && bt.negTimeFactor > 1e-100 {
@@ -119,7 +120,7 @@ func (bt *balanceTracker) posBalanceMissing(targetPriority int64, targetCapacity
 		}
 		targetPriority = 0
 	}
-	posRequired := uint64(float64(^targetPriority)*float64(targetCapacity) + float64(after)*bt.timeFactor)
+	posRequired := uint64(float64(-targetPriority)*float64(targetCapacity)+float64(after)*bt.timeFactor) + 1
 	if posRequired >= maxBalance {
 		return math.MaxUint64 // target not reachable
 	}
@@ -164,7 +165,7 @@ func (bt *balanceTracker) timeUntil(priority int64) (time.Duration, bool) {
 			return 0, false
 		}
 		if priority < 0 {
-			newBalance := uint64(^priority) * bt.capacity
+			newBalance := uint64(-priority) * bt.capacity
 			if newBalance > bt.balance.pos {
 				return 0, false
 			}
@@ -189,6 +190,7 @@ func (bt *balanceTracker) timeUntil(priority int64) (time.Duration, bool) {
 }
 
 // setCapacity updates the capacity value used for priority calculation
+// Note: capacity should never be zero
 func (bt *balanceTracker) setCapacity(capacity uint64) {
 	bt.lock.Lock()
 	defer bt.lock.Unlock()
diff --git a/les/balance_test.go b/les/balance_test.go
index b571c2cc5c..2cf4fcc730 100644
--- a/les/balance_test.go
+++ b/les/balance_test.go
@@ -141,8 +141,8 @@ func TestBalanceToPriority(t *testing.T) {
 		neg      uint64
 		priority int64
 	}{
-		{1000, 0, ^int64(1)},
-		{2000, 0, ^int64(2)}, // Higher balance, lower priority value
+		{1000, 0, -1},
+		{2000, 0, -2}, // Higher balance, lower priority value
 		{0, 0, 0},
 		{0, 1000, 1000},
 	}
@@ -172,16 +172,16 @@ func TestEstimatedPriority(t *testing.T) {
 		reqCost    uint64        // single request cost
 		priority   int64         // expected estimated priority
 	}{
-		{time.Second, time.Second, 0, ^int64(58)},
-		{0, time.Second, 0, ^int64(58)},
+		{time.Second, time.Second, 0, -58},
+		{0, time.Second, 0, -58},
 
 		// 2 seconds time cost, 1 second estimated time cost, 10^9 request cost,
 		// 10^9 estimated request cost per second.
-		{time.Second, time.Second, 1000000000, ^int64(55)},
+		{time.Second, time.Second, 1000000000, -55},
 
 		// 3 seconds time cost, 3 second estimated time cost, 10^9*2 request cost,
 		// 4*10^9 estimated request cost.
-		{time.Second, 3 * time.Second, 1000000000, ^int64(48)},
+		{time.Second, 3 * time.Second, 1000000000, -48},
 
 		// All positive balance is used up
 		{time.Second * 55, 0, 0, 0},
@@ -213,7 +213,7 @@ func TestCallbackChecking(t *testing.T) {
 		priority int64
 		expDiff  time.Duration
 	}{
-		{^int64(500), time.Millisecond * 500},
+		{-500, time.Millisecond * 500},
 		{0, time.Second},
 		{int64(time.Second), 2 * time.Second},
 	}
diff --git a/les/client_handler.go b/les/client_handler.go
index 7d167c33f7..485a1395b5 100644
--- a/les/client_handler.go
+++ b/les/client_handler.go
@@ -116,28 +116,48 @@ func (h *clientHandler) handle(p *peer) error {
 		p.Log().Debug("Light Ethereum handshake failed", "err", err)
 		return err
 	}
-	// Register the peer locally
-	if err := h.backend.peers.Register(p); err != nil {
-		p.Log().Error("Light Ethereum peer registration failed", "err", err)
-		return err
-	}
-	serverConnectionGauge.Update(int64(h.backend.peers.Len()))
 
-	connectedAt := mclock.Now()
-	defer func() {
-		h.backend.peers.Unregister(p.id)
+	var (
+		connectedAt mclock.AbsTime
+		lastActive  bool
+	)
+	activate := func() {
+		// Register the peer locally
+		if err := h.backend.peers.Register(p); err != nil {
+			p.Log().Error("Light Ethereum peer registration failed", "err", err)
+			return
+		}
+		serverConnectionGauge.Update(int64(h.backend.peers.Len()))
+		connectedAt = mclock.Now()
+		h.fetcher.announce(p, p.headInfo)
+		lastActive = true
+	}
+	deactivate := func() {
+		h.backend.peers.Unregister(p)
 		connectionTimer.Update(time.Duration(mclock.Now() - connectedAt))
 		serverConnectionGauge.Update(int64(h.backend.peers.Len()))
+		lastActive = false
+	}
+	defer func() {
+		if lastActive {
+			deactivate()
+		}
+		h.backend.peers.Disconnect(p.id)
 	}()
 
-	h.fetcher.announce(p, p.headInfo)
-
 	// pool entry can be nil during the unit test.
 	if p.poolEntry != nil {
 		h.backend.serverPool.registered(p.poolEntry)
 	}
+
 	// Spawn a main loop to handle all incoming messages.
 	for {
+		if p.active && !lastActive {
+			activate()
+		}
+		if !p.active && lastActive {
+			deactivate()
+		}
 		if err := h.handleMsg(p); err != nil {
 			p.Log().Debug("Light Ethereum message handling failed", "err", err)
 			p.fcServer.DumpLogs()
@@ -400,7 +420,7 @@ func (h *clientHandler) makeLespayCall(p *peer, cmd []byte, handler func([]byte)
 }
 
 func (h *clientHandler) removePeer(id string) {
-	h.backend.peers.Unregister(id)
+	h.backend.peers.Disconnect(id)
 }
 
 type peerConnection struct {
diff --git a/les/clientpool.go b/les/clientpool.go
index 89393d8e30..86d3f988f4 100644
--- a/les/clientpool.go
+++ b/les/clientpool.go
@@ -39,19 +39,20 @@ const (
 	negBalanceExpTC              = time.Hour        // time constant for exponentially reducing negative balance
 	fixedPointMultiplier         = 0x1000000        // constant to convert logarithms to fixed point format
 	lazyQueueRefresh             = time.Second * 10 // refresh period of the connected queue
+	tryActivatePeriod            = time.Second * 5  // periodically check whether inactive clients can be activated
 	persistCumulativeTimeRefresh = time.Minute * 5  // refresh period of the cumulative running time persistence
 	posBalanceCacheLimit         = 8192             // the maximum number of cached items in positive balance queue
 	negBalanceCacheLimit         = 8192             // the maximum number of cached items in negative balance queue
 	fullRatioTC                  = time.Hour
 
-	// connectedBias is applied to already connected clients So that
+	// activeBias is applied to already connected clients So that
 	// already connected client won't be kicked out very soon and we
 	// can ensure all connected clients can have enough time to request
 	// or sync some data.
 	//
 	// todo(rjl493456442) make it configurable. It can be the option of
 	// free trial time!
-	connectedBias = time.Minute * 3
+	activeBias = time.Minute * 3
 )
 
 // clientPool implements a client database that assigns a priority to each client
@@ -61,7 +62,7 @@ const (
 // then negative balance is accumulated.
 //
 // Balance tracking and priority calculation for connected clients is done by
-// balanceTracker. connectedQueue ensures that clients with the lowest positive or
+// balanceTracker. activeQueue ensures that clients with the lowest positive or
 // highest negative balance get evicted when the total capacity allowance is full
 // and new clients with a better balance want to connect.
 //
@@ -83,24 +84,25 @@ type clientPool struct {
 	closed     bool
 	removePeer func(enode.ID)
 
-	connectedMap   map[enode.ID]*clientInfo
-	connectedQueue *prque.LazyQueue
+	connectedMap  map[enode.ID]*clientInfo
+	activeQueue   *prque.LazyQueue
+	inactiveQueue *prque.Prque
 
-	connectedBalances, disconnectedBalances         uint64
+	activeBalances, inactiveBalances                uint64
 	lastConnectedBalanceUpdate, fullRatioLastUpdate mclock.AbsTime
 	fullRatio                                       float64
 
 	defaultPosFactors, defaultNegFactors priceFactors
 
-	connLimit         int            // The maximum number of connections that clientpool can support
-	capLimit          uint64         // The maximum cumulative capacity that clientpool can support
-	connectedCap      uint64         // The sum of the capacity of the current clientpool connected
-	priorityConnected uint64         // The sum of the capacity of currently connected priority clients
-	minCap            uint64         // The minimal capacity value allowed for any client
-	freeClientCap     uint64         // The capacity value of each free client
-	startTime         mclock.AbsTime // The timestamp at which the clientpool started running
-	cumulativeTime    int64          // The cumulative running time of clientpool at the start point.
-	disableBias       bool           // Disable connection bias(used in testing)
+	activeLimit    int            // The maximum number of connections that clientpool can support
+	capLimit       uint64         // The maximum cumulative capacity that clientpool can support
+	activeCap      uint64         // The sum of the capacity of the current clientpool connected
+	priorityActive uint64         // The sum of the capacity of currently connected priority clients
+	minCap         uint64         // The minimal capacity value allowed for any client
+	freeClientCap  uint64         // The capacity value of each free client
+	startTime      mclock.AbsTime // The timestamp at which the clientpool started running
+	cumulativeTime int64          // The cumulative running time of clientpool at the start point.
+	disableBias    bool           // Disable connection bias(used in testing)
 }
 
 // clientPeer represents a client in the pool.
@@ -120,36 +122,37 @@ type clientInfo struct {
 	address                string
 	id                     enode.ID
 	freeID                 string
+	active                 bool
 	connectedAt            mclock.AbsTime
 	capacity               uint64
 	priority               bool
 	pool                   *clientPool
 	peer                   clientPeer
-	queueIndex             int // position in connectedQueue
+	queueIndex             int // position in activeQueue
 	balanceTracker         balanceTracker
 	posFactors, negFactors priceFactors
 	balanceMetaInfo        string
 }
 
-// connSetIndex callback updates clientInfo item index in connectedQueue
+// connSetIndex callback updates clientInfo item index in activeQueue
 func connSetIndex(a interface{}, index int) {
 	a.(*clientInfo).queueIndex = index
 }
 
-// connPriority callback returns actual priority of clientInfo item in connectedQueue
+// connPriority callback returns actual priority of clientInfo item in activeQueue
 func connPriority(a interface{}, now mclock.AbsTime) int64 {
 	c := a.(*clientInfo)
 	return c.balanceTracker.getPriority(now)
 }
 
-// connMaxPriority callback returns estimated maximum priority of clientInfo item in connectedQueue
+// connMaxPriority callback returns estimated maximum priority of clientInfo item in activeQueue
 func connMaxPriority(a interface{}, until mclock.AbsTime) int64 {
 	c := a.(*clientInfo)
 	pri := c.balanceTracker.estimatedPriority(until, true)
 	c.balanceTracker.addCallback(balanceCallbackQueue, pri+1, func() {
 		c.pool.lock.Lock()
-		if c.queueIndex != -1 {
-			c.pool.connectedQueue.Update(c.queueIndex)
+		if c.active && c.queueIndex != -1 {
+			c.pool.activeQueue.Update(c.queueIndex)
 		}
 		c.pool.lock.Unlock()
 	})
@@ -172,7 +175,8 @@ func newClientPool(db ethdb.Database, minCap, freeClientCap uint64, clock mclock
 		ndb:            ndb,
 		clock:          clock,
 		connectedMap:   make(map[enode.ID]*clientInfo),
-		connectedQueue: prque.NewLazyQueue(connSetIndex, connPriority, connMaxPriority, clock, lazyQueueRefresh),
+		activeQueue:    prque.NewLazyQueue(connSetIndex, connPriority, connMaxPriority, clock, lazyQueueRefresh),
+		inactiveQueue:  prque.New(connSetIndex),
 		minCap:         minCap,
 		freeClientCap:  freeClientCap,
 		removePeer:     removePeer,
@@ -193,7 +197,7 @@ func newClientPool(db ethdb.Database, minCap, freeClientCap uint64, clock mclock
 			stop = true
 		}
 		for i := 0; i < l; i++ {
-			pool.disconnectedBalances += pool.ndb.getOrNewPB(ids[i]).value
+			pool.inactiveBalances += pool.ndb.getOrNewPB(ids[i]).value
 		}
 		if stop {
 			break
@@ -210,8 +214,16 @@ func newClientPool(db ethdb.Database, minCap, freeClientCap uint64, clock mclock
 			select {
 			case <-clock.After(lazyQueueRefresh):
 				pool.lock.Lock()
-				pool.connectedQueue.Refresh()
+				pool.activeQueue.Refresh()
 				pool.lock.Unlock()
+			case <-pool.stopCh:
+				return
+			}
+		}
+	}()
+	go func() {
+		for {
+			select {
 			case <-clock.After(persistCumulativeTimeRefresh):
 				pool.ndb.setCumulativeTime(pool.logOffset(clock.Now()))
 			case <-pool.stopCh:
@@ -219,6 +231,18 @@ func newClientPool(db ethdb.Database, minCap, freeClientCap uint64, clock mclock
 			}
 		}
 	}()
+	go func() {
+		for {
+			select {
+			case <-clock.After(tryActivatePeriod):
+				pool.lock.Lock()
+				pool.tryActivateClients()
+				pool.lock.Unlock()
+			case <-pool.stopCh:
+				return
+			}
+		}
+	}()
 	return pool
 }
 
@@ -234,8 +258,8 @@ func (f *clientPool) stop() {
 
 func (f *clientPool) updateFullRatio() {
 	full := float64(1)
-	if f.priorityConnected < f.capLimit {
-		freeCap := f.capLimit - f.priorityConnected
+	if f.priorityActive < f.capLimit {
+		freeCap := f.capLimit - f.priorityActive
 		if freeCap > f.freeClientCap {
 			freeCapThreshold := f.capLimit / 4
 			if freeCap > freeCapThreshold {
@@ -275,43 +299,37 @@ func (f *clientPool) totalTokenAmount() uint64 {
 
 	now := f.clock.Now()
 	if now > f.lastConnectedBalanceUpdate+mclock.AbsTime(time.Second) {
-		f.connectedBalances = 0
+		f.activeBalances = 0
 		for _, c := range f.connectedMap {
 			pos, _ := c.balanceTracker.getBalance(now)
-			f.connectedBalances += pos
+			f.activeBalances += pos
 		}
 		f.lastConnectedBalanceUpdate = now
 	}
-	return f.connectedBalances + f.disconnectedBalances
+	return f.activeBalances + f.inactiveBalances
 }
 
 // connect should be called after a successful handshake. If the connection was
 // rejected, there is no need to call disconnect.
-func (f *clientPool) connect(peer clientPeer, capacity uint64) bool {
+func (f *clientPool) connect(peer clientPeer, reqCapacity uint64) (uint64, error) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
 	// Short circuit if clientPool is already closed.
 	if f.closed {
-		return false
+		return 0, fmt.Errorf("Client pool is already closed")
 	}
 	// Dedup connected peers.
 	id, freeID := peer.ID(), peer.freeClientId()
 	if _, ok := f.connectedMap[id]; ok {
 		clientRejectedMeter.Mark(1)
 		log.Debug("Client already connected", "address", freeID, "id", peerIdToString(id))
-		return false
+		return 0, fmt.Errorf("Client already connected   address = %s  id = %s", freeID, peerIdToString(id))
 	}
-	var missing uint64
-	missing, capacity = f.capAvailable(id, freeID, capacity, 0, true)
-	if missing != 0 {
-		return false
-	}
-	// capacity is available, create and add client
 	pb := f.ndb.getOrNewPB(id)
 	nb := f.ndb.getOrNewNB(freeID)
 	e := &clientInfo{
-		capacity:        capacity,
+		capacity:        reqCapacity,
 		pool:            f,
 		peer:            peer,
 		address:         freeID,
@@ -324,33 +342,38 @@ func (f *clientPool) connect(peer clientPeer, capacity uint64) bool {
 		negFactors:      f.defaultNegFactors,
 		balanceMetaInfo: pb.meta,
 	}
-	f.initBalanceTracker(&e.balanceTracker, pb, nb, capacity)
-	// Register new client to connection queue.
-	f.disconnectedBalances -= pb.value
-	f.connectedBalances += pb.value
+	missing, capacity := f.capAvailable(id, freeID, reqCapacity, 0, true)
 	f.connectedMap[id] = e
-	f.connectedQueue.Push(e)
-	f.connectedCap += e.capacity
+	if missing != 0 {
+		// capacity is not available, add client to inactive queue
+		f.initBalanceTracker(&e.balanceTracker, pb, nb, capacity, false)
+		f.inactiveQueue.Push(e, -connPriority(e, f.clock.Now()))
+		return 0, nil
+	}
+	// capacity is available, add client
+	e.active = true
+	e.capacity = capacity
+	f.initBalanceTracker(&e.balanceTracker, pb, nb, capacity, true)
+	// Register new client to connection queue.
+	f.inactiveBalances -= pb.value
+	f.activeBalances += pb.value
+	f.activeQueue.Push(e)
+	f.activeCap += e.capacity
 
 	// If the current client is a paid client, monitor the status of client,
 	// downgrade it to normal client if positive balance is used up.
 	if e.priority {
 		f.updateFullRatio()
-		f.priorityConnected += capacity
+		f.priorityActive += capacity
 		e.balanceTracker.addCallback(balanceCallbackZero, 0, func() { f.balanceExhausted(id) })
 	}
-	// If the capacity of client is not the default value(free capacity), notify
-	// it to update capacity.
-	if e.capacity != f.freeClientCap {
-		e.peer.updateCapacity(e.capacity)
-	}
-	totalConnectedGauge.Update(int64(f.connectedCap))
+	totalConnectedGauge.Update(int64(f.activeCap))
 	clientConnectedMeter.Mark(1)
 	log.Debug("Client accepted", "address", freeID)
-	return true
+	return e.capacity, nil
 }
 
-func (f *clientPool) initBalanceTracker(bt *balanceTracker, pb posBalance, nb negBalance, capacity uint64) {
+func (f *clientPool) initBalanceTracker(bt *balanceTracker, pb posBalance, nb negBalance, capacity uint64, active bool) {
 	posBalance := pb.value
 	var negBalance uint64
 	if nb.logValue != 0 {
@@ -358,7 +381,11 @@ func (f *clientPool) initBalanceTracker(bt *balanceTracker, pb posBalance, nb ne
 	}
 	bt.init(f.clock, capacity)
 	bt.setBalance(posBalance, negBalance)
-	updatePriceFactors(bt, f.defaultPosFactors, f.defaultNegFactors, capacity)
+	if active {
+		updatePriceFactors(bt, f.defaultPosFactors, f.defaultNegFactors, capacity)
+	} else {
+		zeroPriceFactors(bt)
+	}
 }
 
 // disconnect should be called when a connection is terminated. If the disconnection
@@ -372,13 +399,20 @@ func (f *clientPool) disconnect(p clientPeer) {
 	if f.closed {
 		return
 	}
-	// Short circuit if the peer hasn't been registered.
-	e := f.connectedMap[p.ID()]
-	if e == nil {
+	e, ok := f.connectedMap[p.ID()]
+	if !ok {
 		log.Debug("Client not connected", "address", p.freeClientId(), "id", peerIdToString(p.ID()))
 		return
 	}
-	f.dropClient(e, f.clock.Now(), false)
+	if e.active {
+		f.deactivateClient(e)
+	}
+	f.finalizeBalance(e, f.clock.Now())
+	f.inactiveQueue.Remove(e.queueIndex)
+	delete(f.connectedMap, e.id)
+	clientDisconnectedMeter.Mark(1)
+	log.Debug("Client disconnected", "address", e.address)
+	f.tryActivateClients()
 }
 
 // capAvailable checks whether the current priority level of the given client is enough to
@@ -392,19 +426,19 @@ func (f *clientPool) capAvailable(id enode.ID, freeID string, capacity uint64, m
 	if capacity < f.minCap {
 		capacity = f.minCap
 	}
-	newCapacity := f.connectedCap + capacity
-	newCount := f.connectedQueue.Size() + 1
+	newCapacity := f.activeCap + capacity
+	newCount := f.activeQueue.Size() + 1
 	client := f.connectedMap[id]
-	if client != nil {
+	if client != nil && client.active {
 		newCapacity -= client.capacity
 		newCount--
 	}
-	if newCapacity > f.capLimit || newCount > f.connLimit {
+	if newCapacity > f.capLimit || newCount > f.activeLimit {
 		var (
 			popList        []*clientInfo
 			targetPriority int64
 		)
-		f.connectedQueue.MultiPop(func(data interface{}, priority int64) bool {
+		f.activeQueue.MultiPop(func(data interface{}, priority int64) bool {
 			c := data.(*clientInfo)
 			popList = append(popList, c)
 			if c != client {
@@ -412,9 +446,9 @@ func (f *clientPool) capAvailable(id enode.ID, freeID string, capacity uint64, m
 				newCapacity -= c.capacity
 				newCount--
 			}
-			return newCapacity > f.capLimit || newCount > f.connLimit
+			return newCapacity > f.capLimit || newCount > f.activeLimit
 		})
-		if newCapacity > f.capLimit || newCount > f.connLimit {
+		if newCapacity > f.capLimit || newCount > f.activeLimit {
 			missing = math.MaxUint64
 		} else {
 			var bt *balanceTracker
@@ -422,12 +456,12 @@ func (f *clientPool) capAvailable(id enode.ID, freeID string, capacity uint64, m
 				bt = &client.balanceTracker
 			} else {
 				bt = &balanceTracker{}
-				f.initBalanceTracker(bt, f.ndb.getOrNewPB(id), f.ndb.getOrNewNB(freeID), capacity)
+				f.initBalanceTracker(bt, f.ndb.getOrNewPB(id), f.ndb.getOrNewNB(freeID), capacity, true)
 			}
-			if capacity != f.freeClientCap && targetPriority >= -1 {
-				targetPriority = -2
+			if capacity != f.freeClientCap && targetPriority >= 0 {
+				targetPriority = -1
 			}
-			bias := connectedBias
+			bias := activeBias
 			if f.disableBias {
 				bias = 0
 			}
@@ -441,9 +475,9 @@ func (f *clientPool) capAvailable(id enode.ID, freeID string, capacity uint64, m
 		}
 		for _, c := range popList {
 			if kick && c != client {
-				f.dropClient(c, f.clock.Now(), true)
+				f.deactivateClient(c)
 			} else {
-				f.connectedQueue.Push(c)
+				f.activeQueue.Push(c)
 			}
 		}
 	}
@@ -482,28 +516,56 @@ func (f *clientPool) setDefaultFactors(posFactors, negFactors priceFactors) {
 	f.defaultNegFactors = negFactors
 }
 
-// dropClient removes a client from the connected queue and finalizes its balance.
-// If kick is true then it also initiates the disconnection.
-func (f *clientPool) dropClient(e *clientInfo, now mclock.AbsTime, kick bool) {
-	if _, ok := f.connectedMap[e.id]; !ok {
+func (f *clientPool) deactivateClient(e *clientInfo) {
+	if _, ok := f.connectedMap[e.id]; !ok || !e.active {
 		return
 	}
-	f.finalizeBalance(e, now)
-	f.connectedQueue.Remove(e.queueIndex)
-	delete(f.connectedMap, e.id)
-	f.connectedCap -= e.capacity
+	f.activeQueue.Remove(e.queueIndex)
+	f.activeCap -= e.capacity
 	if e.priority {
 		f.updateFullRatio()
-		f.priorityConnected -= e.capacity
+		f.priorityActive -= e.capacity
 	}
-	totalConnectedGauge.Update(int64(f.connectedCap))
-	if kick {
-		clientKickedMeter.Mark(1)
-		log.Debug("Client kicked out", "address", e.address)
-		f.removePeer(e.id)
-	} else {
-		clientDisconnectedMeter.Mark(1)
-		log.Debug("Client disconnected", "address", e.address)
+	e.active = false
+	e.peer.updateCapacity(0)
+	totalConnectedGauge.Update(int64(f.activeCap))
+	f.inactiveQueue.Push(e, -connPriority(e, f.clock.Now()))
+	//TODO start timer
+}
+
+func (f *clientPool) tryActivateClients() {
+	now := f.clock.Now()
+	for f.inactiveQueue.Size() != 0 {
+		e := f.inactiveQueue.PopItem().(*clientInfo)
+		missing, capacity := f.capAvailable(e.id, e.freeID, e.capacity, 0, true)
+		if missing != 0 {
+			f.inactiveQueue.Push(e, -connPriority(e, now))
+			return
+		}
+		// capacity is available, activate client
+		e.active = true
+		e.capacity = capacity
+		e.peer.updateCapacity(capacity)
+		balance, _ := e.balanceTracker.getBalance(now)
+		e.balanceTracker.setCapacity(capacity)
+		updatePriceFactors(&e.balanceTracker, f.defaultPosFactors, f.defaultNegFactors, capacity)
+		// Register activated client to connection queue.
+		f.inactiveBalances -= balance
+		f.activeBalances += balance
+		f.activeQueue.Push(e)
+		f.activeCap += e.capacity
+
+		// If the current client is a paid client, monitor the status of client,
+		// downgrade it to normal client if positive balance is used up.
+		if e.priority {
+			f.updateFullRatio()
+			f.priorityActive += capacity
+			e.balanceTracker.addCallback(balanceCallbackZero, 0, func() { f.balanceExhausted(e.id) })
+		}
+		e.peer.updateCapacity(e.capacity)
+		totalConnectedGauge.Update(int64(f.activeCap))
+		clientConnectedMeter.Mark(1)
+		log.Debug("Client activated", "address", e.freeID)
 	}
 }
 
@@ -513,7 +575,7 @@ func (f *clientPool) capacityInfo() (uint64, uint64, uint64) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
-	return f.capLimit, f.connectedCap, f.priorityConnected
+	return f.capLimit, f.activeCap, f.priorityActive
 }
 
 // finalizeBalance stops the balance tracker, retrieves the final balances and
@@ -521,8 +583,8 @@ func (f *clientPool) capacityInfo() (uint64, uint64, uint64) {
 func (f *clientPool) finalizeBalance(c *clientInfo, now mclock.AbsTime) {
 	c.balanceTracker.stop(now)
 	pos, neg := c.balanceTracker.getBalance(now)
-	f.disconnectedBalances += pos
-	f.connectedBalances -= pos
+	f.inactiveBalances += pos
+	f.activeBalances -= pos
 
 	pb, nb := f.ndb.getOrNewPB(c.id), f.ndb.getOrNewNB(c.address)
 	pb.value = pos
@@ -549,12 +611,12 @@ func (f *clientPool) balanceExhausted(id enode.ID) {
 	}
 	if c.priority {
 		f.updateFullRatio()
-		f.priorityConnected -= c.capacity
+		f.priorityActive -= c.capacity
 	}
 	c.priority = false
 	if c.capacity != f.freeClientCap {
-		f.connectedCap += f.freeClientCap - c.capacity
-		totalConnectedGauge.Update(int64(f.connectedCap))
+		f.activeCap += f.freeClientCap - c.capacity
+		totalConnectedGauge.Update(int64(f.activeCap))
 		c.capacity = f.freeClientCap
 		c.balanceTracker.setCapacity(c.capacity)
 		c.peer.updateCapacity(c.capacity)
@@ -564,20 +626,22 @@ func (f *clientPool) balanceExhausted(id enode.ID) {
 	f.ndb.setPB(id, pb)
 }
 
-// setConnLimit sets the maximum number and total capacity of connected clients,
+// setactiveLimit sets the maximum number and total capacity of connected clients,
 // dropping some of them if necessary.
 func (f *clientPool) setLimits(totalConn int, totalCap uint64) {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
 	f.updateFullRatio()
-	f.connLimit = totalConn
+	f.activeLimit = totalConn
 	f.capLimit = totalCap
-	if f.connectedCap > f.capLimit || f.connectedQueue.Size() > f.connLimit {
-		f.connectedQueue.MultiPop(func(data interface{}, priority int64) bool {
-			f.dropClient(data.(*clientInfo), mclock.Now(), true)
-			return f.connectedCap > f.capLimit || f.connectedQueue.Size() > f.connLimit
+	if f.activeCap > f.capLimit || f.activeQueue.Size() > f.activeLimit {
+		f.activeQueue.MultiPop(func(data interface{}, priority int64) bool {
+			f.deactivateClient(data.(*clientInfo))
+			return f.activeCap > f.capLimit || f.activeQueue.Size() > f.activeLimit
 		})
+	} else {
+		f.tryActivateClients()
 	}
 }
 
@@ -599,15 +663,16 @@ func (f *clientPool) setCapacity(id enode.ID, freeID string, capacity uint64, mi
 		if c == nil {
 			return 0, capacity, fmt.Errorf("client %064x is not connected", c.id[:])
 		}
-		f.connectedCap += capacity - c.capacity
+		f.activeCap += capacity - c.capacity
 		f.updateFullRatio()
-		f.priorityConnected += capacity - c.capacity
+		f.priorityActive += capacity - c.capacity
 		c.capacity = capacity
 		c.balanceTracker.setCapacity(capacity)
-		f.connectedQueue.Update(c.queueIndex)
-		totalConnectedGauge.Update(int64(f.connectedCap))
+		f.activeQueue.Update(c.queueIndex)
+		totalConnectedGauge.Update(int64(f.activeCap))
 		updatePriceFactors(&c.balanceTracker, c.posFactors, c.negFactors, c.capacity)
 		c.peer.updateCapacity(c.capacity)
+		f.tryActivateClients()
 	}
 	return 0, capacity, nil
 }
@@ -625,11 +690,11 @@ func (f *clientPool) requestCost(p *peer, cost uint64) uint64 {
 	f.lock.Lock()
 	defer f.lock.Unlock()
 
-	info, exist := f.connectedMap[p.ID()]
-	if !exist || f.closed {
+	c := f.connectedMap[p.ID()]
+	if c == nil || f.closed {
 		return 0
 	}
-	return info.balanceTracker.requestCost(cost)
+	return c.balanceTracker.requestCost(cost)
 }
 
 // logOffset calculates the time-dependent offset for the logarithmic
@@ -650,6 +715,11 @@ func updatePriceFactors(bt *balanceTracker, posFactors, negFactors priceFactors,
 	bt.setFactors(false, posFactors.timeFactor+float64(capacity)*posFactors.capacityFactor/1000000, posFactors.requestFactor)
 }
 
+func zeroPriceFactors(bt *balanceTracker) {
+	bt.setFactors(true, 0, 0)
+	bt.setFactors(false, 0, 0)
+}
+
 // getPosBalance retrieves a single positive balance entry from cache or the database
 func (f *clientPool) getPosBalance(id enode.ID) posBalance {
 	f.lock.Lock()
@@ -692,22 +762,32 @@ func (f *clientPool) addBalance(id enode.ID, amount int64, meta string) (uint64,
 	f.ndb.setPB(id, pb)
 	if c != nil {
 		c.balanceTracker.setBalance(pb.value, negBalance)
-		if !c.priority && pb.value > 0 {
-			// The capacity should be adjusted based on the requirement,
-			// but we have no idea about the new capacity, need a second
-			// call to udpate it.
-			f.updateFullRatio()
-			c.priority = true
-			f.priorityConnected += c.capacity
-			c.balanceTracker.addCallback(balanceCallbackZero, 0, func() { f.balanceExhausted(id) })
+		if c.active {
+			f.activeQueue.Update(c.queueIndex)
+			if !c.priority && pb.value > 0 {
+				// The capacity should be adjusted based on the requirement,
+				// but we have no idea about the new capacity, need a second
+				// call to udpate it.
+				f.updateFullRatio()
+				f.priorityActive += c.capacity
+				c.balanceTracker.addCallback(balanceCallbackZero, 0, func() { f.balanceExhausted(id) })
+			}
+			c.balanceMetaInfo = meta
+			f.activeBalances += pb.value - oldBalance
+		} else {
+			f.inactiveQueue.Remove(c.queueIndex)
+			f.inactiveQueue.Push(c, -connPriority(c, f.clock.Now()))
+			f.inactiveBalances += pb.value - oldBalance
+		}
+		if pb.value > 0 {
+			c.priority = true
+			// if balance is set to zero then reverting to non-priority status
+			// is handled by the balanceExhausted callback
 		}
-		// if balance is set to zero then reverting to non-priority status
-		// is handled by the balanceExhausted callback
-		c.balanceMetaInfo = meta
-		f.connectedBalances += pb.value - oldBalance
 	} else {
-		f.disconnectedBalances += pb.value - oldBalance
+		f.inactiveBalances += pb.value - oldBalance
 	}
+	f.tryActivateClients()
 	return oldBalance, pb.value, nil
 }
 
diff --git a/les/clientpool_test.go b/les/clientpool_test.go
index 23564d4052..5b4170ec00 100644
--- a/les/clientpool_test.go
+++ b/les/clientpool_test.go
@@ -56,29 +56,34 @@ func TestClientPoolL100C300P20(t *testing.T) {
 
 const testClientPoolTicks = 100000
 
-type poolTestPeer int
-
-func (i poolTestPeer) ID() enode.ID {
-	return enode.ID{byte(i % 256), byte(i >> 8)}
+type poolTestPeer struct {
+	index     int
+	disconnCh chan int
+	cap       uint64
 }
 
-func (i poolTestPeer) freeClientId() string {
+func newPoolTestPeer(i int, disconnCh chan int) *poolTestPeer {
+	return &poolTestPeer{index: i, disconnCh: disconnCh}
+}
+
+func (i *poolTestPeer) ID() enode.ID {
+	return enode.ID{byte(i.index % 256), byte(i.index >> 8)}
+}
+
+func (i *poolTestPeer) freeClientId() string {
 	return fmt.Sprintf("addr #%d", i)
 }
 
-func (i poolTestPeer) updateCapacity(uint64) {}
-
-type poolTestPeerWithCap struct {
-	poolTestPeer
-
-	cap uint64
+func (i *poolTestPeer) updateCapacity(cap uint64) {
+	i.cap = cap
+	if cap == 0 && i.disconnCh != nil {
+		i.disconnCh <- i.index
+	}
 }
 
-func (i *poolTestPeerWithCap) updateCapacity(cap uint64) { i.cap = cap }
+func (i *poolTestPeer) freezeClient() {}
 
-func (i poolTestPeer) freezeClient() {}
-
-func testClientPool(t *testing.T, connLimit, clientCount, paidCount int, randomDisconnect bool) {
+func testClientPool(t *testing.T, activeLimit, clientCount, paidCount int, randomDisconnect bool) {
 	rand.Seed(time.Now().UnixNano())
 	var (
 		clock     mclock.Simulated
@@ -91,13 +96,14 @@ func testClientPool(t *testing.T, connLimit, clientCount, paidCount int, randomD
 		}
 		pool = newClientPool(db, 1, 1, &clock, disconnFn)
 	)
+
 	pool.disableBias = true
-	pool.setLimits(connLimit, uint64(connLimit))
+	pool.setLimits(activeLimit, uint64(activeLimit))
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
 	// pool should accept new peers up to its connected limit
-	for i := 0; i < connLimit; i++ {
-		if pool.connect(poolTestPeer(i), 0) {
+	for i := 0; i < activeLimit; i++ {
+		if cap, _ := pool.connect(newPoolTestPeer(i, disconnCh), 0); cap != 0 {
 			connected[i] = true
 		} else {
 			t.Fatalf("Test peer #%d rejected", i)
@@ -111,28 +117,30 @@ func testClientPool(t *testing.T, connLimit, clientCount, paidCount int, randomD
 			// give a positive balance to some of the peers
 			amount := testClientPoolTicks / 2 * int64(time.Second) // enough for half of the simulation period
 			for i := 0; i < paidCount; i++ {
-				pool.addBalance(poolTestPeer(i).ID(), amount, "")
+				pool.addBalance(newPoolTestPeer(i, disconnCh).ID(), amount, "")
 			}
 		}
 
 		i := rand.Intn(clientCount)
 		if connected[i] {
 			if randomDisconnect {
-				pool.disconnect(poolTestPeer(i))
+				pool.disconnect(newPoolTestPeer(i, disconnCh))
 				connected[i] = false
 				connTicks[i] += tickCounter
 			}
 		} else {
-			if pool.connect(poolTestPeer(i), 0) {
+			if cap, _ := pool.connect(newPoolTestPeer(i, disconnCh), 0); cap != 0 {
 				connected[i] = true
 				connTicks[i] -= tickCounter
+			} else {
+				pool.disconnect(newPoolTestPeer(i, disconnCh))
 			}
 		}
 	pollDisconnects:
 		for {
 			select {
 			case i := <-disconnCh:
-				pool.disconnect(poolTestPeer(i))
+				pool.disconnect(newPoolTestPeer(i, disconnCh))
 				if connected[i] {
 					connTicks[i] += tickCounter
 					connected[i] = false
@@ -143,10 +151,10 @@ func testClientPool(t *testing.T, connLimit, clientCount, paidCount int, randomD
 		}
 	}
 
-	expTicks := testClientPoolTicks/2*connLimit/clientCount + testClientPoolTicks/2*(connLimit-paidCount)/(clientCount-paidCount)
+	expTicks := testClientPoolTicks/2*activeLimit/clientCount + testClientPoolTicks/2*(activeLimit-paidCount)/(clientCount-paidCount)
 	expMin := expTicks - expTicks/5
 	expMax := expTicks + expTicks/5
-	paidTicks := testClientPoolTicks/2*connLimit/clientCount + testClientPoolTicks/2
+	paidTicks := testClientPoolTicks/2*activeLimit/clientCount + testClientPoolTicks/2
 	paidMin := paidTicks - paidTicks/5
 	paidMax := paidTicks + paidTicks/5
 
@@ -178,9 +186,9 @@ func TestConnectPaidClient(t *testing.T) {
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
 	// Add balance for an external client and mark it as paid client
-	pool.addBalance(poolTestPeer(0).ID(), 1000, "")
+	pool.addBalance(newPoolTestPeer(0, nil).ID(), 1000, "")
 
-	if !pool.connect(poolTestPeer(0), 10) {
+	if cap, _ := pool.connect(newPoolTestPeer(0, nil), 10); cap == 0 {
 		t.Fatalf("Failed to connect paid client")
 	}
 }
@@ -196,10 +204,10 @@ func TestConnectPaidClientToSmallPool(t *testing.T) {
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
 	// Add balance for an external client and mark it as paid client
-	pool.addBalance(poolTestPeer(0).ID(), 1000, "")
+	pool.addBalance(newPoolTestPeer(0, nil).ID(), 1000, "")
 
 	// Connect a fat paid client to pool, should reject it.
-	if pool.connect(poolTestPeer(0), 100) {
+	if cap, _ := pool.connect(newPoolTestPeer(0, nil), 100); cap != 0 {
 		t.Fatalf("Connected fat paid client, should reject it")
 	}
 }
@@ -216,17 +224,17 @@ func TestConnectPaidClientToFullPool(t *testing.T) {
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
 	for i := 0; i < 10; i++ {
-		pool.addBalance(poolTestPeer(i).ID(), 1000000000, "")
-		pool.connect(poolTestPeer(i), 1)
+		pool.addBalance(newPoolTestPeer(i, nil).ID(), 1000000000, "")
+		pool.connect(newPoolTestPeer(i, nil), 1)
 	}
-	pool.addBalance(poolTestPeer(11).ID(), 1000, "") // Add low balance to new paid client
-	if pool.connect(poolTestPeer(11), 1) {
+	pool.addBalance(newPoolTestPeer(11, nil).ID(), 1000, "") // Add low balance to new paid client
+	if cap, _ := pool.connect(newPoolTestPeer(11, nil), 1); cap != 0 {
 		t.Fatalf("Low balance paid client should be rejected")
 	}
 	clock.Run(time.Second)
-	pool.addBalance(poolTestPeer(12).ID(), 1000000000*60*3, "") // Add high balance to new paid client
-	if !pool.connect(poolTestPeer(12), 1) {
-		t.Fatalf("High balance paid client should be accpected")
+	pool.addBalance(newPoolTestPeer(12, nil).ID(), 1000000000*60*3+1, "") // Add high balance to new paid client
+	if cap, _ := pool.connect(newPoolTestPeer(12, nil), 1); cap == 0 {
+		t.Fatalf("High balance paid client should be accepted")
 	}
 }
 
@@ -243,13 +251,13 @@ func TestPaidClientKickedOut(t *testing.T) {
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
 	for i := 0; i < 10; i++ {
-		pool.addBalance(poolTestPeer(i).ID(), 1000000000, "") // 1 second allowance
-		pool.connect(poolTestPeer(i), 1)
+		pool.addBalance(newPoolTestPeer(i, kickedCh).ID(), 1000000000, "") // 1 second allowance
+		pool.connect(newPoolTestPeer(i, kickedCh), 1)
 		clock.Run(time.Millisecond)
 	}
 	clock.Run(time.Second)
-	clock.Run(connectedBias)
-	if !pool.connect(poolTestPeer(11), 0) {
+	clock.Run(activeBias)
+	if cap, _ := pool.connect(newPoolTestPeer(11, kickedCh), 0); cap == 0 {
 		t.Fatalf("Free client should be accectped")
 	}
 	select {
@@ -271,7 +279,7 @@ func TestConnectFreeClient(t *testing.T) {
 	defer pool.stop()
 	pool.setLimits(10, uint64(10))
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
-	if !pool.connect(poolTestPeer(0), 10) {
+	if cap, _ := pool.connect(newPoolTestPeer(0, nil), 10); cap == 0 {
 		t.Fatalf("Failed to connect free client")
 	}
 }
@@ -288,18 +296,18 @@ func TestConnectFreeClientToFullPool(t *testing.T) {
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
 	for i := 0; i < 10; i++ {
-		pool.connect(poolTestPeer(i), 1)
+		pool.connect(newPoolTestPeer(i, nil), 1)
 	}
-	if pool.connect(poolTestPeer(11), 1) {
+	if cap, _ := pool.connect(newPoolTestPeer(11, nil), 1); cap != 0 {
 		t.Fatalf("New free client should be rejected")
 	}
 	clock.Run(time.Minute)
-	if pool.connect(poolTestPeer(12), 1) {
+	if cap, _ := pool.connect(newPoolTestPeer(12, nil), 1); cap != 0 {
 		t.Fatalf("New free client should be rejected")
 	}
 	clock.Run(time.Millisecond)
 	clock.Run(4 * time.Minute)
-	if !pool.connect(poolTestPeer(13), 1) {
+	if cap, _ := pool.connect(newPoolTestPeer(13, nil), 1); cap == 0 {
 		t.Fatalf("Old client connects more than 5min should be kicked")
 	}
 }
@@ -317,15 +325,16 @@ func TestFreeClientKickedOut(t *testing.T) {
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
 	for i := 0; i < 10; i++ {
-		pool.connect(poolTestPeer(i), 1)
+		pool.connect(newPoolTestPeer(i, kicked), 1)
 		clock.Run(time.Millisecond)
 	}
-	if pool.connect(poolTestPeer(10), 1) {
+	if cap, _ := pool.connect(newPoolTestPeer(10, kicked), 1); cap != 0 {
 		t.Fatalf("New free client should be rejected")
 	}
+	pool.disconnect(newPoolTestPeer(10, kicked))
 	clock.Run(5 * time.Minute)
 	for i := 0; i < 10; i++ {
-		pool.connect(poolTestPeer(i+10), 1)
+		pool.connect(newPoolTestPeer(i+10, kicked), 1)
 	}
 	for i := 0; i < 10; i++ {
 		select {
@@ -351,12 +360,12 @@ func TestPositiveBalanceCalculation(t *testing.T) {
 	pool.setLimits(10, uint64(10)) // Total capacity limit is 10
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
-	pool.addBalance(poolTestPeer(0).ID(), int64(time.Minute*3), "")
-	pool.connect(poolTestPeer(0), 10)
+	pool.addBalance(newPoolTestPeer(0, kicked).ID(), int64(time.Minute*3), "")
+	pool.connect(newPoolTestPeer(0, kicked), 10)
 	clock.Run(time.Minute)
 
-	pool.disconnect(poolTestPeer(0))
-	pb := pool.ndb.getOrNewPB(poolTestPeer(0).ID())
+	pool.disconnect(newPoolTestPeer(0, kicked))
+	pb := pool.ndb.getOrNewPB(newPoolTestPeer(0, kicked).ID())
 	if pb.value != uint64(time.Minute*2) {
 		t.Fatalf("Positive balance mismatch, want %v, got %v", uint64(time.Minute*2), pb.value)
 	}
@@ -374,11 +383,9 @@ func TestDowngradePriorityClient(t *testing.T) {
 	pool.setLimits(10, uint64(10)) // Total capacity limit is 10
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
-	p := &poolTestPeerWithCap{
-		poolTestPeer: poolTestPeer(0),
-	}
+	p := newPoolTestPeer(0, kicked)
 	pool.addBalance(p.ID(), int64(time.Minute), "")
-	pool.connect(p, 10)
+	p.cap, _ = pool.connect(p, 10)
 	if p.cap != 10 {
 		t.Fatalf("The capcacity of priority peer hasn't been updated, got: %d", p.cap)
 	}
@@ -388,13 +395,13 @@ func TestDowngradePriorityClient(t *testing.T) {
 	if p.cap != 1 {
 		t.Fatalf("The capcacity of peer should be downgraded, got: %d", p.cap)
 	}
-	pb := pool.ndb.getOrNewPB(poolTestPeer(0).ID())
+	pb := pool.ndb.getOrNewPB(newPoolTestPeer(0, kicked).ID())
 	if pb.value != 0 {
 		t.Fatalf("Positive balance mismatch, want %v, got %v", 0, pb.value)
 	}
 
-	pool.addBalance(poolTestPeer(0).ID(), int64(time.Minute), "")
-	pb = pool.ndb.getOrNewPB(poolTestPeer(0).ID())
+	pool.addBalance(newPoolTestPeer(0, kicked).ID(), int64(time.Minute), "")
+	pb = pool.ndb.getOrNewPB(newPoolTestPeer(0, kicked).ID())
 	if pb.value != uint64(time.Minute) {
 		t.Fatalf("Positive balance mismatch, want %v, got %v", uint64(time.Minute), pb.value)
 	}
@@ -402,36 +409,34 @@ func TestDowngradePriorityClient(t *testing.T) {
 
 func TestNegativeBalanceCalculation(t *testing.T) {
 	var (
-		clock  mclock.Simulated
-		db     = rawdb.NewMemoryDatabase()
-		kicked = make(chan int, 10)
+		clock mclock.Simulated
+		db    = rawdb.NewMemoryDatabase()
 	)
-	removeFn := func(id enode.ID) { kicked <- int(id[0]) } // Noop
-	pool := newClientPool(db, 1, 1, &clock, removeFn)
+	pool := newClientPool(db, 1, 1, &clock, nil)
 	defer pool.stop()
 	pool.setLimits(10, uint64(10)) // Total capacity limit is 10
 	pool.setDefaultFactors(priceFactors{1, 0, 1}, priceFactors{1, 0, 1})
 
 	for i := 0; i < 10; i++ {
-		pool.connect(poolTestPeer(i), 1)
+		pool.connect(newPoolTestPeer(i, nil), 1)
 	}
 	clock.Run(time.Second)
 
 	for i := 0; i < 10; i++ {
-		pool.disconnect(poolTestPeer(i))
-		nb := pool.ndb.getOrNewNB(poolTestPeer(i).freeClientId())
+		pool.disconnect(newPoolTestPeer(i, nil))
+		nb := pool.ndb.getOrNewNB(newPoolTestPeer(i, nil).freeClientId())
 		if nb.logValue != 0 {
 			t.Fatalf("Short connection shouldn't be recorded")
 		}
 	}
 
 	for i := 0; i < 10; i++ {
-		pool.connect(poolTestPeer(i), 1)
+		pool.connect(newPoolTestPeer(i, nil), 1)
 	}
 	clock.Run(time.Minute)
 	for i := 0; i < 10; i++ {
-		pool.disconnect(poolTestPeer(i))
-		nb := pool.ndb.getOrNewNB(poolTestPeer(i).freeClientId())
+		pool.disconnect(newPoolTestPeer(i, nil))
+		nb := pool.ndb.getOrNewNB(newPoolTestPeer(i, nil).freeClientId())
 		nb.logValue -= pool.logOffset(clock.Now())
 		nb.logValue /= fixedPointMultiplier
 		if nb.logValue != int64(math.Log(float64(time.Minute/time.Second))) {
@@ -541,3 +546,83 @@ func TestNodeDBExpiration(t *testing.T) {
 		t.Fatalf("Failed to evict useless negative balances, want %v, got %d", 4, iterated)
 	}
 }
+
+func TestInactiveClient(t *testing.T) {
+	var (
+		clock mclock.Simulated
+		db    = rawdb.NewMemoryDatabase()
+	)
+	pool := newClientPool(db, 1, 1, &clock, nil)
+	defer pool.stop()
+	pool.setLimits(2, uint64(2)) // Total capacity limit is 10
+
+	p1 := newPoolTestPeer(1, nil)
+	p2 := newPoolTestPeer(2, nil)
+	p3 := newPoolTestPeer(3, nil)
+	pool.addBalance(p1.ID(), 1000, "")
+	pool.addBalance(p3.ID(), 2000, "")
+	// p1: 1000  p2: 0  p3: 2000
+	p1.cap, _ = pool.connect(p1, 1)
+	if p1.cap != 1 {
+		t.Fatalf("Failed to connect peer #1")
+	}
+	p2.cap, _ = pool.connect(p2, 1)
+	if p2.cap != 1 {
+		t.Fatalf("Failed to connect peer #2")
+	}
+	p3.cap, _ = pool.connect(p3, 1)
+	if p3.cap != 1 {
+		t.Fatalf("Failed to connect peer #3")
+	}
+	if p2.cap != 0 {
+		t.Fatalf("Failed to deactivate peer #2")
+	}
+	pool.addBalance(p2.ID(), 3000, "")
+	// p1: 1000  p2: 3000  p3: 2000
+	if p2.cap != 1 {
+		t.Fatalf("Failed to activate peer #2")
+	}
+	if p1.cap != 0 {
+		t.Fatalf("Failed to deactivate peer #1")
+	}
+	pool.addBalance(p2.ID(), -2500, "")
+	// p1: 1000  p2: 500  p3: 2000
+	if p1.cap != 1 {
+		t.Fatalf("Failed to activate peer #1")
+	}
+	if p2.cap != 0 {
+		t.Fatalf("Failed to deactivate peer #2")
+	}
+	pool.setDefaultFactors(priceFactors{1e-9, 0, 0}, priceFactors{1e-9, 0, 0})
+	p4 := newPoolTestPeer(4, nil)
+	pool.addBalance(p4.ID(), 1500, "")
+	// p1: 1000  p2: 500  p3: 2000  p4: 1500
+	p4.cap, _ = pool.connect(p4, 1)
+	if p4.cap != 1 {
+		t.Fatalf("Failed to activate peer #4")
+	}
+	if p1.cap != 0 {
+		t.Fatalf("Failed to deactivate peer #1")
+	}
+	clock.Run(time.Second * 600)
+	// manually trigger a check to avoid a long real-time wait
+	pool.lock.Lock()
+	pool.tryActivateClients()
+	pool.lock.Unlock()
+	// p1: 1000  p2: 500  p3: 2000  p4: 900
+	if p1.cap != 1 {
+		t.Fatalf("Failed to activate peer #1")
+	}
+	if p4.cap != 0 {
+		t.Fatalf("Failed to deactivate peer #4")
+	}
+	pool.disconnect(p2)
+	pool.disconnect(p4)
+	pool.addBalance(p1.ID(), -1000, "")
+	if p1.cap != 1 {
+		t.Fatalf("Should not deactivate peer #1")
+	}
+	if p2.cap != 0 {
+		t.Fatalf("Should not activate peer #2")
+	}
+}
diff --git a/les/costtracker.go b/les/costtracker.go
index 81da045660..abf8618ffd 100644
--- a/les/costtracker.go
+++ b/les/costtracker.go
@@ -159,15 +159,9 @@ func newCostTracker(db ethdb.Database, config *eth.Config) (*costTracker, uint64
 	}
 	ct.gfLoop()
 	costList := ct.makeCostList(ct.globalFactor() * 1.25)
-	for _, c := range costList {
-		amount := minBufferReqAmount[c.MsgCode]
-		cost := c.BaseCost + amount*c.ReqCost
-		if cost > ct.minBufLimit {
-			ct.minBufLimit = cost
-		}
-	}
-	ct.minBufLimit *= uint64(minBufferMultiplier)
-	return ct, (ct.minBufLimit-1)/bufLimitRatio + 1
+	var minRecharge uint64
+	ct.minBufLimit, minRecharge = costList.decode(ProtocolLengths[ServerProtocolVersions[len(ServerProtocolVersions)-1]]).reqParams()
+	return ct, minRecharge
 }
 
 // stop stops the cost tracker and saves the cost factor statistics to the database
@@ -480,6 +474,22 @@ func (table requestCostTable) getMaxCost(code, amount uint64) uint64 {
 	return costs.baseCost + amount*costs.reqCost
 }
 
+func (table requestCostTable) reqParams() (minRecharge, minBufLimit uint64) {
+	for code, c := range table {
+		amount := minBufferReqAmount[code]
+		cost := c.baseCost + amount*c.reqCost
+		if cost > minBufLimit {
+			minBufLimit = cost
+		}
+	}
+	minBufLimit *= uint64(minBufferMultiplier)
+	if minBufLimit < 1 {
+		minBufLimit = 1
+	}
+	minRecharge = (minBufLimit-1)/bufLimitRatio + 1
+	return
+}
+
 // decode converts a cost list to a cost table
 func (list RequestCostList) decode(protocolLength uint64) requestCostTable {
 	table := make(requestCostTable)
diff --git a/les/handler_test.go b/les/handler_test.go
index 7293493d2a..08796b49e8 100644
--- a/les/handler_test.go
+++ b/les/handler_test.go
@@ -60,7 +60,7 @@ func TestGetBlockHeadersLes3(t *testing.T) { testGetBlockHeaders(t, 3) }
 func TestGetBlockHeadersLes4(t *testing.T) { testGetBlockHeaders(t, 4) }
 
 func testGetBlockHeaders(t *testing.T, protocol int) {
-	server, tearDown := newServerEnv(t, downloader.MaxHashFetch+15, protocol, nil, false, true, 0)
+	server, tearDown := newServerEnv(t, downloader.MaxHashFetch+15, protocol, nil, false, true, 0, true)
 	defer tearDown()
 
 	bc := server.handler.blockchain
@@ -190,7 +190,7 @@ func TestGetBlockBodiesLes3(t *testing.T) { testGetBlockBodies(t, 3) }
 func TestGetBlockBodiesLes4(t *testing.T) { testGetBlockBodies(t, 4) }
 
 func testGetBlockBodies(t *testing.T, protocol int) {
-	server, tearDown := newServerEnv(t, downloader.MaxBlockFetch+15, protocol, nil, false, true, 0)
+	server, tearDown := newServerEnv(t, downloader.MaxBlockFetch+15, protocol, nil, false, true, 0, true)
 	defer tearDown()
 
 	bc := server.handler.blockchain
@@ -269,7 +269,7 @@ func TestGetCodeLes4(t *testing.T) { testGetCode(t, 4) }
 
 func testGetCode(t *testing.T, protocol int) {
 	// Assemble the test environment
-	server, tearDown := newServerEnv(t, 4, protocol, nil, false, true, 0)
+	server, tearDown := newServerEnv(t, 4, protocol, nil, false, true, 0, true)
 	defer tearDown()
 	bc := server.handler.blockchain
 
@@ -299,7 +299,7 @@ func TestGetStaleCodeLes3(t *testing.T) { testGetStaleCode(t, 3) }
 func TestGetStaleCodeLes4(t *testing.T) { testGetStaleCode(t, 4) }
 
 func testGetStaleCode(t *testing.T, protocol int) {
-	server, tearDown := newServerEnv(t, core.TriesInMemory+4, protocol, nil, false, true, 0)
+	server, tearDown := newServerEnv(t, core.TriesInMemory+4, protocol, nil, false, true, 0, true)
 	defer tearDown()
 	bc := server.handler.blockchain
 
@@ -325,7 +325,7 @@ func TestGetReceiptLes4(t *testing.T) { testGetReceipt(t, 4) }
 
 func testGetReceipt(t *testing.T, protocol int) {
 	// Assemble the test environment
-	server, tearDown := newServerEnv(t, 4, protocol, nil, false, true, 0)
+	server, tearDown := newServerEnv(t, 4, protocol, nil, false, true, 0, true)
 	defer tearDown()
 
 	bc := server.handler.blockchain
@@ -353,7 +353,7 @@ func TestGetProofsLes4(t *testing.T) { testGetProofs(t, 4) }
 
 func testGetProofs(t *testing.T, protocol int) {
 	// Assemble the test environment
-	server, tearDown := newServerEnv(t, 4, protocol, nil, false, true, 0)
+	server, tearDown := newServerEnv(t, 4, protocol, nil, false, true, 0, true)
 	defer tearDown()
 
 	bc := server.handler.blockchain
@@ -388,7 +388,7 @@ func TestGetStaleProofLes3(t *testing.T) { testGetStaleProof(t, 3) }
 func TestGetStaleProofLes4(t *testing.T) { testGetStaleProof(t, 4) }
 
 func testGetStaleProof(t *testing.T, protocol int) {
-	server, tearDown := newServerEnv(t, core.TriesInMemory+4, protocol, nil, false, true, 0)
+	server, tearDown := newServerEnv(t, core.TriesInMemory+4, protocol, nil, false, true, 0, true)
 	defer tearDown()
 	bc := server.handler.blockchain
 
@@ -436,7 +436,7 @@ func testGetCHTProofs(t *testing.T, protocol int) {
 			time.Sleep(10 * time.Millisecond)
 		}
 	}
-	server, tearDown := newServerEnv(t, int(config.ChtSize+config.ChtConfirms), protocol, waitIndexers, false, true, 0)
+	server, tearDown := newServerEnv(t, int(config.ChtSize+config.ChtConfirms), protocol, waitIndexers, false, true, 0, true)
 	defer tearDown()
 
 	bc := server.handler.blockchain
@@ -485,7 +485,7 @@ func testGetBloombitsProofs(t *testing.T, protocol int) {
 			time.Sleep(10 * time.Millisecond)
 		}
 	}
-	server, tearDown := newServerEnv(t, int(config.BloomTrieSize+config.BloomTrieConfirms), protocol, waitIndexers, false, true, 0)
+	server, tearDown := newServerEnv(t, int(config.BloomTrieSize+config.BloomTrieConfirms), protocol, waitIndexers, false, true, 0, true)
 	defer tearDown()
 
 	bc := server.handler.blockchain
@@ -523,7 +523,7 @@ func TestTransactionStatusLes3(t *testing.T) { testTransactionStatus(t, 3) }
 func TestTransactionStatusLes4(t *testing.T) { testTransactionStatus(t, 4) }
 
 func testTransactionStatus(t *testing.T, protocol int) {
-	server, tearDown := newServerEnv(t, 0, protocol, nil, false, true, 0)
+	server, tearDown := newServerEnv(t, 0, protocol, nil, false, true, 0, true)
 	defer tearDown()
 	server.handler.addTxsSync = true
 
@@ -620,7 +620,7 @@ func TestStopResumeLes3(t *testing.T) { testStopResume(t, 3) }
 func TestStopResumeLes4(t *testing.T) { testStopResume(t, 4) }
 
 func testStopResume(t *testing.T, protocol int) {
-	server, tearDown := newServerEnv(t, 0, protocol, nil, true, true, testBufLimit/10)
+	server, tearDown := newServerEnv(t, 0, protocol, nil, true, true, testBufLimit/10, true)
 	defer tearDown()
 
 	server.handler.server.costTracker.testing = true
diff --git a/les/odr_test.go b/les/odr_test.go
index b47a4d080b..b6836a057f 100644
--- a/les/odr_test.go
+++ b/les/odr_test.go
@@ -236,7 +236,7 @@ func testOdr(t *testing.T, protocol int, expFail uint64, checkCached bool, fn od
 
 	// still expect all retrievals to pass, now data should be cached locally
 	if checkCached {
-		client.handler.backend.peers.Unregister(client.peer.peer.id)
+		client.handler.backend.peers.Disconnect(client.peer.peer.id)
 		time.Sleep(time.Millisecond * 10) // ensure that all peerSetNotify callbacks are executed
 		test(5)
 	}
diff --git a/les/peer.go b/les/peer.go
index cc5ee95df0..0e5e4d196c 100644
--- a/les/peer.go
+++ b/les/peer.go
@@ -101,6 +101,9 @@ type peer struct {
 	responseCount uint64
 	invalidCount  uint32
 
+	active               bool
+	activate, deactivate func()
+
 	poolEntry      *poolEntry
 	hasBlock       func(common.Hash, uint64, bool) bool
 	responseErrors int
@@ -297,12 +300,20 @@ func (p *peer) updateCapacity(cap uint64) {
 	p.responseLock.Lock()
 	defer p.responseLock.Unlock()
 
-	p.fcParams = flowcontrol.ServerParams{MinRecharge: cap, BufLimit: cap * bufLimitRatio}
-	p.fcClient.UpdateParams(p.fcParams)
-	var kvList keyValueList
-	kvList = kvList.add("flowControl/MRR", cap)
-	kvList = kvList.add("flowControl/BL", cap*bufLimitRatio)
-	p.queueSend(func() { p.SendAnnounce(announceData{Update: kvList}) })
+	if !p.active && cap != 0 && p.activate != nil {
+		p.activate()
+	}
+	if cap != 0 || p.version >= lpv4 {
+		p.fcParams = flowcontrol.ServerParams{MinRecharge: cap, BufLimit: cap * bufLimitRatio}
+		p.fcClient.UpdateParams(p.fcParams)
+		var kvList keyValueList
+		kvList = kvList.add("flowControl/BL", cap*bufLimitRatio)
+		kvList = kvList.add("flowControl/MRR", cap)
+		p.queueSend(func() { p.SendAnnounce(announceData{Update: kvList}) })
+	}
+	if p.active && cap == 0 && p.deactivate != nil {
+		p.deactivate()
+	}
 }
 
 func (p *peer) responseID() uint64 {
@@ -628,8 +639,15 @@ func (p *peer) Handshake(td *big.Int, head common.Hash, headNum uint64, genesis
 			send = send.add("serveRecentState", stateRecent)
 			send = send.add("txRelay", nil)
 		}
-		send = send.add("flowControl/BL", server.defParams.BufLimit)
-		send = send.add("flowControl/MRR", server.defParams.MinRecharge)
+
+		p.active = p.version < lpv4
+		if p.active {
+			p.fcParams = server.defParams
+		} else {
+			p.fcParams = flowcontrol.ServerParams{}
+		}
+		send = send.add("flowControl/BL", p.fcParams.BufLimit)
+		send = send.add("flowControl/MRR", p.fcParams.MinRecharge)
 
 		var costList RequestCostList
 		if server.costTracker.testCostList != nil {
@@ -639,7 +657,6 @@ func (p *peer) Handshake(td *big.Int, head common.Hash, headNum uint64, genesis
 		}
 		send = send.add("flowControl/MRC", costList)
 		p.fcCosts = costList.decode(ProtocolLengths[uint(p.version)])
-		p.fcParams = server.defParams
 
 		// Add advertised checkpoint and register block height which
 		// client can verify the checkpoint validity.
@@ -710,7 +727,7 @@ func (p *peer) Handshake(td *big.Int, head common.Hash, headNum uint64, genesis
 				// set default announceType on server side
 				p.announceType = announceTypeSimple
 			}
-			p.fcClient = flowcontrol.NewClientNode(server.fcManager, server.defParams)
+			p.fcClient = flowcontrol.NewClientNode(server.fcManager, p.fcParams)
 		}
 	} else {
 		if recv.get("serveChainSince", &p.chainSince) != nil {
@@ -747,6 +764,7 @@ func (p *peer) Handshake(td *big.Int, head common.Hash, headNum uint64, genesis
 		p.fcParams = sParams
 		p.fcServer = flowcontrol.NewServerNode(sParams, &mclock.System{})
 		p.fcCosts = MRC.decode(ProtocolLengths[uint(p.version)])
+		p.active = p.paramsUseful()
 
 		recv.get("checkpoint/value", &p.checkpoint)
 		recv.get("checkpoint/registerHeight", &p.checkpointNumber)
@@ -772,10 +790,12 @@ func (p *peer) updateFlowControl(update keyValueMap) {
 	}
 	// If any of the flow control params is nil, refuse to update.
 	var params flowcontrol.ServerParams
+	updated := false
 	if update.get("flowControl/BL", &params.BufLimit) == nil && update.get("flowControl/MRR", &params.MinRecharge) == nil {
 		// todo can light client set a minimal acceptable flow control params?
 		p.fcParams = params
 		p.fcServer.UpdateParams(params)
+		updated = true
 	}
 	var MRC RequestCostList
 	if update.get("flowControl/MRC", &MRC) == nil {
@@ -783,7 +803,16 @@ func (p *peer) updateFlowControl(update keyValueMap) {
 		for code, cost := range costUpdate {
 			p.fcCosts[code] = cost
 		}
+		updated = true
 	}
+	if updated {
+		p.active = p.paramsUseful()
+	}
+}
+
+func (p *peer) paramsUseful() bool {
+	reqRecharge, reqBufLimit := p.fcCosts.reqParams()
+	return p.fcParams.MinRecharge >= reqRecharge && p.fcParams.BufLimit >= reqBufLimit
 }
 
 // String implements fmt.Stringer.
@@ -803,16 +832,17 @@ type peerSetNotify interface {
 // peerSet represents the collection of active peers currently participating in
 // the Light Ethereum sub-protocol.
 type peerSet struct {
-	peers      map[string]*peer
-	lock       sync.RWMutex
-	notifyList []peerSetNotify
-	closed     bool
+	active, inactive map[string]*peer
+	lock             sync.RWMutex
+	notifyList       []peerSetNotify
+	closed           bool
 }
 
 // newPeerSet creates a new peer set to track the active participants.
 func newPeerSet() *peerSet {
 	return &peerSet{
-		peers: make(map[string]*peer),
+		active:   make(map[string]*peer),
+		inactive: make(map[string]*peer),
 	}
 }
 
@@ -820,8 +850,8 @@ func newPeerSet() *peerSet {
 func (ps *peerSet) notify(n peerSetNotify) {
 	ps.lock.Lock()
 	ps.notifyList = append(ps.notifyList, n)
-	peers := make([]*peer, 0, len(ps.peers))
-	for _, p := range ps.peers {
+	peers := make([]*peer, 0, len(ps.active))
+	for _, p := range ps.active {
 		peers = append(peers, p)
 	}
 	ps.lock.Unlock()
@@ -839,11 +869,13 @@ func (ps *peerSet) Register(p *peer) error {
 		ps.lock.Unlock()
 		return errClosed
 	}
-	if _, ok := ps.peers[p.id]; ok {
+	if _, ok := ps.active[p.id]; ok {
 		ps.lock.Unlock()
 		return errAlreadyRegistered
 	}
-	ps.peers[p.id] = p
+	ps.active[p.id] = p
+	delete(ps.inactive, p.id)
+
 	p.sendQueue = newExecQueue(100)
 	peers := make([]peerSetNotify, len(ps.notifyList))
 	copy(peers, ps.notifyList)
@@ -856,14 +888,15 @@ func (ps *peerSet) Register(p *peer) error {
 }
 
 // Unregister removes a remote peer from the active set, disabling any further
-// actions to/from that particular entity. It also initiates disconnection at the networking layer.
-func (ps *peerSet) Unregister(id string) error {
+// actions to/from that particular entity.
+func (ps *peerSet) Unregister(p *peer) error {
 	ps.lock.Lock()
-	if p, ok := ps.peers[id]; !ok {
+	if _, ok := ps.active[p.id]; !ok {
 		ps.lock.Unlock()
 		return errNotRegistered
 	} else {
-		delete(ps.peers, id)
+		delete(ps.active, p.id)
+		ps.inactive[p.id] = p
 		peers := make([]peerSetNotify, len(ps.notifyList))
 		copy(peers, ps.notifyList)
 		ps.lock.Unlock()
@@ -871,22 +904,38 @@ func (ps *peerSet) Unregister(id string) error {
 		for _, n := range peers {
 			n.unregisterPeer(p)
 		}
-
 		p.sendQueue.quit()
-		p.Peer.Disconnect(p2p.DiscUselessPeer)
-
 		return nil
 	}
 }
 
-// AllPeerIDs returns a list of all registered peer IDs
+// Disconnect removes a remote peer from either the active or inactive set and
+// initiates disconnection at the networking layer.
+func (ps *peerSet) Disconnect(id string) error {
+	ps.lock.Lock()
+	p, ok := ps.active[id]
+	if ok {
+		delete(ps.active, id)
+	} else {
+		if p, ok = ps.inactive[id]; !ok {
+			ps.lock.Unlock()
+			return errNotRegistered
+		}
+		delete(ps.inactive, id)
+	}
+	ps.lock.Unlock()
+	p.Peer.Disconnect(p2p.DiscUselessPeer)
+	return nil
+}
+
+// AllPeerIDs returns a list of all active peer IDs
 func (ps *peerSet) AllPeerIDs() []string {
 	ps.lock.RLock()
 	defer ps.lock.RUnlock()
 
-	res := make([]string, len(ps.peers))
+	res := make([]string, len(ps.active))
 	idx := 0
-	for id := range ps.peers {
+	for id := range ps.active {
 		res[idx] = id
 		idx++
 	}
@@ -898,15 +947,18 @@ func (ps *peerSet) Peer(id string) *peer {
 	ps.lock.RLock()
 	defer ps.lock.RUnlock()
 
-	return ps.peers[id]
+	if p, ok := ps.active[id]; ok {
+		return p
+	}
+	return ps.inactive[id]
 }
 
-// Len returns if the current number of peers in the set.
+// Len returns if the current number of peers in the active set.
 func (ps *peerSet) Len() int {
 	ps.lock.RLock()
 	defer ps.lock.RUnlock()
 
-	return len(ps.peers)
+	return len(ps.active)
 }
 
 // BestPeer retrieves the known peer with the currently highest total difficulty.
@@ -918,7 +970,7 @@ func (ps *peerSet) BestPeer() *peer {
 		bestPeer *peer
 		bestTd   *big.Int
 	)
-	for _, p := range ps.peers {
+	for _, p := range ps.active {
 		if td := p.Td(); bestPeer == nil || td.Cmp(bestTd) > 0 {
 			bestPeer, bestTd = p, td
 		}
@@ -926,14 +978,14 @@ func (ps *peerSet) BestPeer() *peer {
 	return bestPeer
 }
 
-// AllPeers returns all peers in a list
+// AllPeers returns all active peers in a list
 func (ps *peerSet) AllPeers() []*peer {
 	ps.lock.RLock()
 	defer ps.lock.RUnlock()
 
-	list := make([]*peer, len(ps.peers))
+	list := make([]*peer, len(ps.active))
 	i := 0
-	for _, peer := range ps.peers {
+	for _, peer := range ps.active {
 		list[i] = peer
 		i++
 	}
@@ -946,7 +998,10 @@ func (ps *peerSet) Close() {
 	ps.lock.Lock()
 	defer ps.lock.Unlock()
 
-	for _, p := range ps.peers {
+	for _, p := range ps.active {
+		p.Disconnect(p2p.DiscQuitting)
+	}
+	for _, p := range ps.inactive {
 		p.Disconnect(p2p.DiscQuitting)
 	}
 	ps.closed = true
diff --git a/les/retrieve.go b/les/retrieve.go
index c806117902..a0d494b6c3 100644
--- a/les/retrieve.go
+++ b/les/retrieve.go
@@ -345,7 +345,7 @@ func (r *sentReq) tryRequest() {
 		if hrto {
 			pp.Log().Debug("Request timed out hard")
 			if r.rm.peers != nil {
-				r.rm.peers.Unregister(pp.id)
+				r.rm.peers.Disconnect(pp.id)
 			}
 		}
 
diff --git a/les/server.go b/les/server.go
index 706c7506ac..9d9fba3876 100644
--- a/les/server.go
+++ b/les/server.go
@@ -116,7 +116,7 @@ func NewLesServer(e *eth.Ethereum, config *eth.Config) (*LesServer, error) {
 		srv.maxCapacity = totalRecharge
 	}
 	srv.fcManager.SetCapacityLimits(srv.freeCapacity, srv.maxCapacity, srv.freeCapacity*2)
-	srv.clientPool = newClientPool(srv.chainDb, srv.minCapacity, srv.freeCapacity, mclock.System{}, func(id enode.ID) { go srv.peers.Unregister(peerIdToString(id)) })
+	srv.clientPool = newClientPool(srv.chainDb, srv.minCapacity, srv.freeCapacity, mclock.System{}, func(id enode.ID) { go srv.peers.Disconnect(peerIdToString(id)) })
 	srv.clientPool.setDefaultFactors(priceFactors{0, 1, 1}, priceFactors{0, 1, 1})
 	srv.tokenSale = newTokenSale(srv.clientPool, 0.1)
 
diff --git a/les/server_handler.go b/les/server_handler.go
index 6014ceeb98..f1a798eb67 100644
--- a/les/server_handler.go
+++ b/les/server_handler.go
@@ -58,10 +58,7 @@ const (
 	MaxTxStatus              = 256 // Amount of transactions to queried per request
 )
 
-var (
-	errTooManyInvalidRequest = errors.New("too many invalid requests made")
-	errFullClientPool        = errors.New("client pool is full")
-)
+var errTooManyInvalidRequest = errors.New("too many invalid requests made")
 
 // serverHandler is responsible for serving light client and process
 // all incoming light requests.
@@ -139,28 +136,58 @@ func (h *serverHandler) handle(p *peer) error {
 	}
 	defer p.fcClient.Disconnect()
 
-	// Disconnect the inbound peer if it's rejected by clientPool
-	if !h.server.clientPool.connect(p, 0) {
-		p.Log().Debug("Light Ethereum peer registration failed", "err", errFullClientPool)
-		return errFullClientPool
+	var (
+		connectedAt mclock.AbsTime
+		wg          *sync.WaitGroup // Wait group used to track all in-flight task routines.
+	)
+	p.activate = func() {
+		// Register the peer locally
+		if err := h.server.peers.Register(p); err != nil {
+			h.server.clientPool.disconnect(p)
+			p.Log().Error("Light Ethereum peer registration failed", "err", err)
+			return
+		}
+		clientConnectionGauge.Update(int64(h.server.peers.Len()))
+		connectedAt = mclock.Now()
+		wg = new(sync.WaitGroup)
+		p.active = true
 	}
-	// Register the peer locally
-	if err := h.server.peers.Register(p); err != nil {
-		h.server.clientPool.disconnect(p)
-		p.Log().Error("Light Ethereum peer registration failed", "err", err)
-		return err
-	}
-	clientConnectionGauge.Update(int64(h.server.peers.Len()))
-
-	var wg sync.WaitGroup // Wait group used to track all in-flight task routines.
-
-	connectedAt := mclock.Now()
-	defer func() {
-		wg.Wait() // Ensure all background task routines have exited.
-		h.server.peers.Unregister(p.id)
-		h.server.clientPool.disconnect(p)
+	p.deactivate = func() {
+		h.server.peers.Unregister(p)
+		if p.version < lpv4 {
+			h.server.peers.Disconnect(p.id)
+		}
 		clientConnectionGauge.Update(int64(h.server.peers.Len()))
 		connectionTimer.Update(time.Duration(mclock.Now() - connectedAt))
+		p.active = false
+	}
+	if p.active {
+		p.activate()
+	}
+
+	if capacity, err := h.server.clientPool.connect(p, 0); err != nil {
+		// Disconnect the inbound peer if it's rejected by clientPool
+		p.Log().Debug("Light Ethereum peer registration failed", "err", err)
+		return err
+	} else if capacity != p.fcParams.MinRecharge {
+		if p.version < lpv4 {
+			h.server.peers.Disconnect(p.id)
+		} else {
+			p.updateCapacity(capacity)
+		}
+	}
+
+	defer func() {
+		wg.Wait() // Ensure all background task routines have exited.
+		h.server.clientPool.disconnect(p)
+		p.responseLock.Lock()
+		if p.active {
+			p.deactivate()
+		}
+		p.activate = nil
+		p.deactivate = nil
+		p.responseLock.Unlock()
+		h.server.peers.Disconnect(p.id)
 	}()
 
 	// Spawn a main loop to handle all incoming messages.
@@ -171,7 +198,7 @@ func (h *serverHandler) handle(p *peer) error {
 			return err
 		default:
 		}
-		if err := h.handleMsg(p, &wg); err != nil {
+		if err := h.handleMsg(p, wg); err != nil {
 			p.Log().Debug("Light Ethereum message handling failed", "err", err)
 			return err
 		}
diff --git a/les/test_helper.go b/les/test_helper.go
index 544c3d9e59..3fd0844cba 100644
--- a/les/test_helper.go
+++ b/les/test_helper.go
@@ -77,10 +77,10 @@ var (
 	processConfirms = big.NewInt(1)
 
 	// The token bucket buffer limit for testing purpose.
-	testBufLimit = uint64(1000000)
+	testBufLimit = uint64(6000)
 
 	// The buffer recharging speed for testing purpose.
-	testBufRecharge = uint64(1000)
+	testBufRecharge = uint64(1)
 )
 
 /*
@@ -393,8 +393,13 @@ func (p *testPeer) handshake(t *testing.T, td *big.Int, head common.Hash, headNu
 	expList = expList.add("serveStateSince", uint64(0))
 	expList = expList.add("serveRecentState", uint64(core.TriesInMemory-4))
 	expList = expList.add("txRelay", nil)
-	expList = expList.add("flowControl/BL", testBufLimit)
-	expList = expList.add("flowControl/MRR", testBufRecharge)
+	if p.peer.version >= lpv4 {
+		expList = expList.add("flowControl/BL", uint64(0))
+		expList = expList.add("flowControl/MRR", uint64(0))
+	} else {
+		expList = expList.add("flowControl/BL", testBufLimit)
+		expList = expList.add("flowControl/MRR", testBufRecharge)
+	}
 	expList = expList.add("flowControl/MRC", costList)
 
 	if err := p2p.ExpectMsg(p.app, StatusMsg, expList); err != nil {
@@ -403,9 +408,16 @@ func (p *testPeer) handshake(t *testing.T, td *big.Int, head common.Hash, headNu
 	if err := p2p.Send(p.app, StatusMsg, sendList); err != nil {
 		t.Fatalf("status send: %v", err)
 	}
-	p.peer.fcParams = flowcontrol.ServerParams{
-		BufLimit:    testBufLimit,
-		MinRecharge: testBufRecharge,
+}
+
+func (p *testPeer) expectCapUpdate(t *testing.T) {
+	if p.peer.version >= lpv4 {
+		var expList keyValueList
+		expList = expList.add("flowControl/BL", testBufLimit)
+		expList = expList.add("flowControl/MRR", testBufRecharge)
+		if err := p2p.ExpectMsg(p.app, AnnounceMsg, announceData{Update: expList}); err != nil {
+			t.Fatalf("status recv: %v", err)
+		}
 	}
 }
 
@@ -436,7 +448,7 @@ type testServer struct {
 	bloomTrieIndexer *core.ChainIndexer
 }
 
-func newServerEnv(t *testing.T, blocks int, protocol int, callback indexerCallback, simClock bool, newPeer bool, testCost uint64) (*testServer, func()) {
+func newServerEnv(t *testing.T, blocks int, protocol int, callback indexerCallback, simClock bool, newPeer bool, testCost uint64, expectCapUpdate bool) (*testServer, func()) {
 	db := rawdb.NewMemoryDatabase()
 	indexers := testIndexers(db, nil, light.TestServerIndexerConfig)
 
@@ -477,6 +489,9 @@ func newServerEnv(t *testing.T, blocks int, protocol int, callback indexerCallba
 		cIndexer.Close()
 		bIndexer.Close()
 	}
+	if expectCapUpdate {
+		server.peer.expectCapUpdate(t)
+	}
 	return server, teardown
 }
 
diff --git a/les/ulc_test.go b/les/ulc_test.go
index 861cf7cd82..9353d115b9 100644
--- a/les/ulc_test.go
+++ b/les/ulc_test.go
@@ -126,7 +126,7 @@ func connect(server *serverHandler, serverId enode.ID, client *clientHandler, pr
 
 // newServerPeer creates server peer.
 func newServerPeer(t *testing.T, blocks int, protocol int) (*testServer, *enode.Node, func()) {
-	s, teardown := newServerEnv(t, blocks, protocol, nil, false, false, 0)
+	s, teardown := newServerEnv(t, blocks, protocol, nil, false, false, 0, false)
 	key, err := crypto.GenerateKey()
 	if err != nil {
 		t.Fatal("generate key err:", err)