diff --git a/les/costtracker.go b/les/costtracker.go
new file mode 100644
index 0000000000..fa3ce8bd81
--- /dev/null
+++ b/les/costtracker.go
@@ -0,0 +1,378 @@
+// Copyright 2016 The go-ethereum Authors
+// This file is part of the go-ethereum library.
+//
+// The go-ethereum library is free software: you can redistribute it and/or modify
+// it under the terms of the GNU Lesser General Public License as published by
+// the Free Software Foundation, either version 3 of the License, or
+// (at your option) any later version.
+//
+// The go-ethereum library is distributed in the hope that it will be useful,
+// but WITHOUT ANY WARRANTY; without even the implied warranty of
+// MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the
+// GNU Lesser General Public License for more detailct.
+//
+// You should have received a copy of the GNU Lesser General Public License
+// along with the go-ethereum library. If not, see <http://www.gnu.org/licenses/>.
+
+package les
+
+import (
+	"encoding/binary"
+	"math"
+	"sync"
+	"sync/atomic"
+	"time"
+
+	"github.com/ethereum/go-ethereum/common/mclock"
+	"github.com/ethereum/go-ethereum/eth"
+	"github.com/ethereum/go-ethereum/ethdb"
+	"github.com/ethereum/go-ethereum/les/flowcontrol"
+	"github.com/ethereum/go-ethereum/log"
+)
+
+const makeCostStats = false // make request cost statistics during operation
+
+var (
+	// average request cost estimates based on serving time
+	reqAvgTimeCost = requestCostTable{
+		GetBlockHeadersMsg:     {150000, 30000},
+		GetBlockBodiesMsg:      {0, 700000},
+		GetReceiptsMsg:         {0, 1000000},
+		GetCodeMsg:             {0, 450000},
+		GetProofsV1Msg:         {0, 600000},
+		GetProofsV2Msg:         {0, 600000},
+		GetHeaderProofsMsg:     {0, 1000000},
+		GetHelperTrieProofsMsg: {0, 1000000},
+		SendTxMsg:              {0, 450000},
+		SendTxV2Msg:            {0, 450000},
+		GetTxStatusMsg:         {0, 250000},
+	}
+	// maximum incoming message size estimates
+	reqMaxInSize = requestCostTable{
+		GetBlockHeadersMsg:     {40, 0},
+		GetBlockBodiesMsg:      {0, 40},
+		GetReceiptsMsg:         {0, 40},
+		GetCodeMsg:             {0, 80},
+		GetProofsV1Msg:         {0, 80},
+		GetProofsV2Msg:         {0, 80},
+		GetHeaderProofsMsg:     {0, 20},
+		GetHelperTrieProofsMsg: {0, 20},
+		SendTxMsg:              {0, 66000},
+		SendTxV2Msg:            {0, 66000},
+		GetTxStatusMsg:         {0, 50},
+	}
+	// maximum outgoing message size estimates
+	reqMaxOutSize = requestCostTable{
+		GetBlockHeadersMsg:     {0, 556},
+		GetBlockBodiesMsg:      {0, 100000},
+		GetReceiptsMsg:         {0, 200000},
+		GetCodeMsg:             {0, 50000},
+		GetProofsV1Msg:         {0, 4000},
+		GetProofsV2Msg:         {0, 4000},
+		GetHeaderProofsMsg:     {0, 4000},
+		GetHelperTrieProofsMsg: {0, 4000},
+		SendTxMsg:              {0, 0},
+		SendTxV2Msg:            {0, 100},
+		GetTxStatusMsg:         {0, 100},
+	}
+	minBufLimit = uint64(50000000 * maxCostFactor)          // minimum buffer limit allowed for a client
+	minCapacity = uint64((minBufLimit-1)/bufLimitRatio + 1) // minimum capacity allowed for a client
+)
+
+const (
+	maxCostFactor    = 2 // ratio of maximum and average cost estimates
+	gfInitWeight     = time.Second * 10
+	gfMaxWeight      = time.Hour
+	gfUsageThreshold = 0.5
+	gfUsageTC        = time.Second
+	gfDbKey          = "_globalCostFactor"
+)
+
+// costTracker is responsible for calculating costs and cost estimates on the
+// server side. It continously updates the global cost factor which is defined
+// as the number of cost units per nanosecond of serving time in a single thread.
+// It is based on statistics collected during serving requests in high-load periods
+// and practically acts as a one-dimension request price scaling factor over the
+// pre-defined cost estimate table. Instead of scaling the cost values, the real
+// value of cost units is changed by applying the factor to the serving times. This
+// is more convenient because the changes in the cost factor can be applied immediately
+// without always notifying the clients about the changed cost tables.
+type costTracker struct {
+	db     ethdb.Database
+	stopCh chan chan struct{}
+
+	inSizeFactor, outSizeFactor float64
+	gf, utilTarget              float64
+
+	gfUpdateCh      chan gfUpdate
+	gfLock          sync.RWMutex
+	totalRechargeCh chan uint64
+
+	stats map[uint64][]uint64
+}
+
+// newCostTracker creates a cost tracker and loads the cost factor statistics from the database
+func newCostTracker(db ethdb.Database, config *eth.Config) *costTracker {
+	utilTarget := float64(config.LightServ) * flowcontrol.FixedPointMultiplier / 100
+	ct := &costTracker{
+		db:         db,
+		stopCh:     make(chan chan struct{}),
+		utilTarget: utilTarget,
+	}
+	if config.LightBandwidthIn > 0 {
+		ct.inSizeFactor = utilTarget / float64(config.LightBandwidthIn)
+	}
+	if config.LightBandwidthOut > 0 {
+		ct.outSizeFactor = utilTarget / float64(config.LightBandwidthOut)
+	}
+	if makeCostStats {
+		ct.stats = make(map[uint64][]uint64)
+		for code, _ := range reqAvgTimeCost {
+			ct.stats[code] = make([]uint64, 10)
+		}
+	}
+	ct.gfLoop()
+	return ct
+}
+
+// stop stops the cost tracker and saves the cost factor statistics to the database
+func (ct *costTracker) stop() {
+	stopCh := make(chan struct{})
+	ct.stopCh <- stopCh
+	<-stopCh
+	if makeCostStats {
+		ct.printStats()
+	}
+}
+
+// makeCostList returns upper cost estimates based on the hardcoded cost estimate
+// tables and the optionally specified incoming/outgoing bandwidth limits
+func (ct *costTracker) makeCostList() RequestCostList {
+	maxCost := func(avgTime, inSize, outSize uint64) uint64 {
+		globalFactor := ct.globalFactor()
+
+		cost := avgTime * maxCostFactor
+		inSizeCost := uint64(float64(inSize) * ct.inSizeFactor * globalFactor * maxCostFactor)
+		if inSizeCost > cost {
+			cost = inSizeCost
+		}
+		outSizeCost := uint64(float64(outSize) * ct.outSizeFactor * globalFactor * maxCostFactor)
+		if outSizeCost > cost {
+			cost = outSizeCost
+		}
+		return cost
+	}
+	var list RequestCostList
+	for code, data := range reqAvgTimeCost {
+		list = append(list, requestCostListItem{
+			MsgCode:  code,
+			BaseCost: maxCost(data.baseCost, reqMaxInSize[code].baseCost, reqMaxOutSize[code].baseCost),
+			ReqCost:  maxCost(data.reqCost, reqMaxInSize[code].reqCost, reqMaxOutSize[code].reqCost),
+		})
+	}
+	return list
+}
+
+type gfUpdate struct {
+	avgTime, servingTime float64
+}
+
+// gfLoop starts an event loop which updates the global cost factor which is
+// calculated as a weighted average of the average estimate / serving time ratio.
+// The applied weight equals the serving time if gfUsage is over a threshold,
+// zero otherwise. gfUsage is the recent average serving time per time unit in
+// an exponential moving window. This ensures that statistics are collected only
+// under high-load circumstances where the measured serving times are relevant.
+// The total recharge parameter of the flow control system which controls the
+// total allowed serving time per second but nominated in cost units, should
+// also be scaled with the cost factor and is also updated by this loop.
+func (ct *costTracker) gfLoop() {
+	var gfUsage, gfSum, gfWeight float64
+	lastUpdate := mclock.Now()
+	expUpdate := lastUpdate
+
+	data, _ := ct.db.Get([]byte(gfDbKey))
+	if len(data) == 16 {
+		gfSum = math.Float64frombits(binary.BigEndian.Uint64(data[0:8]))
+		gfWeight = math.Float64frombits(binary.BigEndian.Uint64(data[8:16]))
+	}
+	if gfWeight < float64(gfInitWeight) {
+		gfSum = float64(gfInitWeight)
+		gfWeight = float64(gfInitWeight)
+	}
+	gf := gfSum / gfWeight
+	ct.gf = gf
+	ct.gfUpdateCh = make(chan gfUpdate, 100)
+
+	go func() {
+		for {
+			select {
+			case r := <-ct.gfUpdateCh:
+				now := mclock.Now()
+				max := r.servingTime * gf
+				if r.avgTime > max {
+					max = r.avgTime
+				}
+				dt := float64(now - expUpdate)
+				expUpdate = now
+				gfUsage = gfUsage*math.Exp(-dt/float64(gfUsageTC)) + max*1000000/float64(gfUsageTC)
+
+				if gfUsage >= gfUsageThreshold*ct.utilTarget*gf {
+					gfSum += r.avgTime
+					gfWeight += r.servingTime
+					if time.Duration(now-lastUpdate) > time.Second {
+						gf = gfSum / gfWeight
+						if gfWeight >= float64(gfMaxWeight) {
+							gfSum = gf * float64(gfMaxWeight)
+							gfWeight = float64(gfMaxWeight)
+						}
+						lastUpdate = now
+						ct.gfLock.Lock()
+						ct.gf = gf
+						ch := ct.totalRechargeCh
+						ct.gfLock.Unlock()
+						if ch != nil {
+							select {
+							case ct.totalRechargeCh <- uint64(ct.utilTarget * gf):
+							default:
+							}
+						}
+						log.Debug("global cost factor updated", "gf", gf, "weight", time.Duration(gfWeight))
+					}
+				}
+			case stopCh := <-ct.stopCh:
+				var data [16]byte
+				binary.BigEndian.PutUint64(data[0:8], math.Float64bits(gfSum))
+				binary.BigEndian.PutUint64(data[8:16], math.Float64bits(gfWeight))
+				ct.db.Put([]byte(gfDbKey), data[:])
+				log.Debug("global cost factor saved", "sum", time.Duration(gfSum), "weight", time.Duration(gfWeight))
+				close(stopCh)
+				return
+			}
+		}
+	}()
+}
+
+// globalFactor returns the current value of the global cost factor
+func (ct *costTracker) globalFactor() float64 {
+	ct.gfLock.RLock()
+	defer ct.gfLock.RUnlock()
+
+	return ct.gf
+}
+
+// totalRecharge returns the current total recharge parameter which is used by
+// flowcontrol.ClientManager and is scaled by the global cost factor
+func (ct *costTracker) totalRecharge() uint64 {
+	ct.gfLock.RLock()
+	defer ct.gfLock.RUnlock()
+
+	return uint64(ct.gf * ct.utilTarget)
+}
+
+// subscribeTotalRecharge returns all future updates to the total recharge value
+// through a channel and also returns the current value
+func (ct *costTracker) subscribeTotalRecharge(ch chan uint64) uint64 {
+	ct.gfLock.Lock()
+	defer ct.gfLock.Unlock()
+
+	ct.totalRechargeCh = ch
+	return uint64(ct.gf * ct.utilTarget)
+}
+
+// updateStats updates the global cost factor and (if enabled) the real cost vs.
+// average estimate statistics
+func (ct *costTracker) updateStats(code, amount, servingTime, realCost uint64) {
+	avg := reqAvgTimeCost[code]
+	avgTime := avg.baseCost + amount*avg.reqCost
+	select {
+	case ct.gfUpdateCh <- gfUpdate{float64(avgTime), float64(servingTime)}:
+	default:
+	}
+	if makeCostStats {
+		realCost <<= 4
+		l := 0
+		for l < 9 && realCost > avgTime {
+			l++
+			realCost >>= 1
+		}
+		atomic.AddUint64(&ct.stats[code][l], 1)
+	}
+}
+
+// realCost calculates the final cost of a request based on actual serving time,
+// incoming and outgoing message size
+//
+// Note: message size is only taken into account if bandwidth limitation is applied
+// and the cost based on either message size is greater than the cost based on
+// serving time. A maximum of the three costs is applied instead of their sum
+// because the three limited resources (serving thread time and i/o bandwidth) can
+// also be maxed out simultaneously.
+func (ct *costTracker) realCost(servingTime uint64, inSize, outSize uint32) uint64 {
+	cost := float64(servingTime)
+	inSizeCost := float64(inSize) * ct.inSizeFactor
+	if inSizeCost > cost {
+		cost = inSizeCost
+	}
+	outSizeCost := float64(outSize) * ct.outSizeFactor
+	if outSizeCost > cost {
+		cost = outSizeCost
+	}
+	return uint64(cost * ct.globalFactor())
+}
+
+// printStats prints the distribution of real request cost relative to the average estimates
+func (ct *costTracker) printStats() {
+	if ct.stats == nil {
+		return
+	}
+	for code, arr := range ct.stats {
+		log.Info("request", "code", code, "1/16", arr[0], "1/8", arr[1], "1/4", arr[2], "1/2", arr[3], "1", arr[4], "2", arr[5], "4", arr[6], "8", arr[7], "16", arr[8], ">16", arr[9])
+	}
+}
+
+type (
+	// requestCostTable assigns a cost estimate function to each request type
+	// which is a linear function of the requested amount
+	// (cost = baseCost + reqCost * amount)
+	requestCostTable map[uint64]*requestCosts
+	requestCosts     struct {
+		baseCost, reqCost uint64
+	}
+
+	// RequestCostList is a list representation of request costs which is used for
+	// database storage and communication through the network
+	RequestCostList     []requestCostListItem
+	requestCostListItem struct {
+		MsgCode, BaseCost, ReqCost uint64
+	}
+)
+
+// getCost calculates the estimated cost for a given request type and amount
+func (table requestCostTable) getCost(code, amount uint64) uint64 {
+	costs := table[code]
+	return costs.baseCost + amount*costs.reqCost
+}
+
+// decode converts a cost list to a cost table
+func (list RequestCostList) decode() requestCostTable {
+	table := make(requestCostTable)
+	for _, e := range list {
+		table[e.MsgCode] = &requestCosts{
+			baseCost: e.BaseCost,
+			reqCost:  e.ReqCost,
+		}
+	}
+	return table
+}
+
+// testCostList returns a dummy request cost list used by tests
+func testCostList() RequestCostList {
+	cl := make(RequestCostList, len(reqAvgTimeCost))
+	for i, req := range reqBenchMap {
+		cl[i].MsgCode = req.code
+		cl[i].BaseCost = 0
+		cl[i].ReqCost = 0
+	}
+	return cl
+}