status-go/vendor/github.com/ethereum/go-ethereum/_assets/patches/0038-ulc.patch

diff --git a/cmd/geth/config.go b/cmd/geth/config.go
index b0749d2..d724562 100644
--- a/cmd/geth/config.go
+++ b/cmd/geth/config.go
@@ -124,6 +124,7 @@ func makeConfigNode(ctx *cli.Context) (*node.Node, gethConfig) {
 	}
 
 	// Apply flags.
+	utils.SetULC(ctx, &cfg.Eth)
 	utils.SetNodeConfig(ctx, &cfg.Node)
 	stack, err := node.New(&cfg.Node)
 	if err != nil {
diff --git a/cmd/geth/main.go b/cmd/geth/main.go
index fae4b57..bdc624d 100644
--- a/cmd/geth/main.go
+++ b/cmd/geth/main.go
@@ -83,6 +83,10 @@ var (
 		utils.TxPoolAccountQueueFlag,
 		utils.TxPoolGlobalQueueFlag,
 		utils.TxPoolLifetimeFlag,
+		utils.ULCModeConfigFlag,
+		utils.OnlyAnnounceModeFlag,
+		utils.ULCTrustedNodesFlag,
+		utils.ULCMinTrustedFractionFlag,
 		utils.SyncModeFlag,
 		utils.GCModeFlag,
 		utils.LightServFlag,
diff --git a/cmd/utils/flags.go b/cmd/utils/flags.go
index 429c2bb..878847c 100644
--- a/cmd/utils/flags.go
+++ b/cmd/utils/flags.go
@@ -19,6 +19,7 @@ package utils

 import (
 	"crypto/ecdsa"
+	"encoding/json"
 	"fmt"
 	"io/ioutil"
 	"math/big"
@@ -157,6 +158,23 @@ var (
 		Usage: "Document Root for HTTPClient file scheme",
 		Value: DirectoryString{homeDir()},
 	}
+	ULCModeConfigFlag = cli.StringFlag{
+		Name:  "les.ulcconfig",
+		Usage: "Config file to use for ULC mode",
+	}
+	OnlyAnnounceModeFlag = cli.BoolFlag{
+		Name:  "les.onlyannounce",
+		Usage: "LES server sends only announce",
+	}
+	ULCMinTrustedFractionFlag = cli.IntFlag{
+		Name:  "les.mintrustedfraction",
+		Usage: "LES server sends only announce",
+	}
+	ULCTrustedNodesFlag = cli.StringFlag{
+		Name:  "les.trusted",
+		Usage: "List of trusted nodes",
+	}
+
 	defaultSyncMode = eth.DefaultConfig.SyncMode
 	SyncModeFlag    = TextMarshalerFlag{
 		Name:  "syncmode",
@@ -816,6 +834,40 @@ func setIPC(ctx *cli.Context, cfg *node.Config) {
 	}
 }

+// SetULC setup ULC config from file if given.
+func SetULC(ctx *cli.Context, cfg *eth.Config) {
+	// ULC config isn't loaded from global config and ULC config and ULC trusted nodes are not defined.
+	if cfg.ULC == nil && !(ctx.GlobalIsSet(ULCModeConfigFlag.Name) || ctx.GlobalIsSet(ULCTrustedNodesFlag.Name)) {
+		return
+	}
+	cfg.ULC = &eth.ULCConfig{}
+
+	path := ctx.GlobalString(ULCModeConfigFlag.Name)
+	if path != "" {
+		cfgData, err := ioutil.ReadFile(path)
+		if err != nil {
+			Fatalf("Failed to unmarshal ULC configuration: %v", err)
+		}
+
+		err = json.Unmarshal(cfgData, &cfg.ULC)
+		if err != nil {
+			Fatalf("Failed to unmarshal ULC configuration: %s", err.Error())
+		}
+	}
+
+	if trustedNodes := ctx.GlobalString(ULCTrustedNodesFlag.Name); trustedNodes != "" {
+		cfg.ULC.TrustedServers = strings.Split(trustedNodes, ",")
+	}
+
+	if trustedFraction := ctx.GlobalInt(ULCMinTrustedFractionFlag.Name); trustedFraction > 0 {
+		cfg.ULC.MinTrustedFraction = trustedFraction
+	}
+	if cfg.ULC.MinTrustedFraction <= 0 && cfg.ULC.MinTrustedFraction > 100 {
+		log.Error("MinTrustedFraction is invalid", "MinTrustedFraction", cfg.ULC.MinTrustedFraction, "Changed to default", eth.DefaultUTCMinTrustedFraction)
+		cfg.ULC.MinTrustedFraction = eth.DefaultUTCMinTrustedFraction
+	}
+}
+
 // makeDatabaseHandles raises out the number of allowed file handles per process
 // for Geth and returns half of the allowance to assign to the database.
 func makeDatabaseHandles() int {
@@ -1143,6 +1195,9 @@ func SetEthConfig(ctx *cli.Context, stack *node.Node, cfg *eth.Config) {
 	if ctx.GlobalIsSet(LightPeersFlag.Name) {
 		cfg.LightPeers = ctx.GlobalInt(LightPeersFlag.Name)
 	}
+	if ctx.GlobalIsSet(OnlyAnnounceModeFlag.Name) {
+		cfg.OnlyAnnounce = ctx.GlobalBool(OnlyAnnounceModeFlag.Name)
+	}
 	if ctx.GlobalIsSet(NetworkIdFlag.Name) {
 		cfg.NetworkId = ctx.GlobalUint64(NetworkIdFlag.Name)
 	}
diff --git a/core/headerchain.go b/core/headerchain.go
index d209311..8904dd8 100644
--- a/core/headerchain.go
+++ b/core/headerchain.go
@@ -219,14 +219,18 @@ func (hc *HeaderChain) ValidateHeaderChain(chain []*types.Header, checkFreq int)

 	// Generate the list of seal verification requests, and start the parallel verifier
 	seals := make([]bool, len(chain))
-	for i := 0; i < len(seals)/checkFreq; i++ {
-		index := i*checkFreq + hc.rand.Intn(checkFreq)
-		if index >= len(seals) {
-			index = len(seals) - 1
+	if checkFreq != 0 {
+		// In case of checkFreq == 0 all seals are left false.
+		for i := 0; i < len(seals)/checkFreq; i++ {
+			index := i*checkFreq + hc.rand.Intn(checkFreq)
+			if index >= len(seals) {
+				index = len(seals) - 1
+			}
+			seals[index] = true
 		}
-		seals[index] = true
+		// Last should always be verified to avoid junk.
+		seals[len(seals)-1] = true
 	}
-	seals[len(seals)-1] = true // Last should always be verified to avoid junk

 	abort, results := hc.engine.VerifyHeaders(hc, chain, seals)
 	defer close(abort)
diff --git a/eth/config.go b/eth/config.go
index efbaafb..7d1db9f 100644
--- a/eth/config.go
+++ b/eth/config.go
@@ -87,8 +87,12 @@ type Config struct {
 	NoPruning bool

 	// Light client options
-	LightServ  int `toml:",omitempty"` // Maximum percentage of time allowed for serving LES requests
-	LightPeers int `toml:",omitempty"` // Maximum number of LES client peers
+	LightServ    int  `toml:",omitempty"` // Maximum percentage of time allowed for serving LES requests
+	LightPeers   int  `toml:",omitempty"` // Maximum number of LES client peers
+	OnlyAnnounce bool // Maximum number of LES client peers
+
+	// Ultra Light client options
+	ULC *ULCConfig `toml:",omitempty"`

 	// Database options
 	SkipBcVersionCheck bool `toml:"-"`
diff --git a/eth/gen_config.go b/eth/gen_config.go
index d401a91..382d4d9 100644
--- a/eth/gen_config.go
+++ b/eth/gen_config.go
@@ -23,10 +23,12 @@ func (c Config) MarshalTOML() (interface{}, error) {
 		NetworkId               uint64
 		SyncMode                downloader.SyncMode
 		NoPruning               bool
-		LightServ               int  `toml:",omitempty"`
-		LightPeers              int  `toml:",omitempty"`
-		SkipBcVersionCheck      bool `toml:"-"`
-		DatabaseHandles         int  `toml:"-"`
+		LightServ               int `toml:",omitempty"`
+		LightPeers              int `toml:",omitempty"`
+		OnlyAnnounce            bool
+		ULC                     *ULCConfig `toml:",omitempty"`
+		SkipBcVersionCheck      bool       `toml:"-"`
+		DatabaseHandles         int        `toml:"-"`
 		DatabaseCache           int
 		TrieCache               int
 		TrieTimeout             time.Duration
@@ -51,6 +53,8 @@ func (c Config) MarshalTOML() (interface{}, error) {
 	enc.NoPruning = c.NoPruning
 	enc.LightServ = c.LightServ
 	enc.LightPeers = c.LightPeers
+	enc.OnlyAnnounce = c.OnlyAnnounce
+	enc.ULC = c.ULC
 	enc.SkipBcVersionCheck = c.SkipBcVersionCheck
 	enc.DatabaseHandles = c.DatabaseHandles
 	enc.DatabaseCache = c.DatabaseCache
@@ -79,10 +83,12 @@ func (c *Config) UnmarshalTOML(unmarshal func(interface{}) error) error {
 		NetworkId               *uint64
 		SyncMode                *downloader.SyncMode
 		NoPruning               *bool
-		LightServ               *int  `toml:",omitempty"`
-		LightPeers              *int  `toml:",omitempty"`
-		SkipBcVersionCheck      *bool `toml:"-"`
-		DatabaseHandles         *int  `toml:"-"`
+		LightServ               *int `toml:",omitempty"`
+		LightPeers              *int `toml:",omitempty"`
+		OnlyAnnounce            *bool
+		ULC                     *ULCConfig `toml:",omitempty"`
+		SkipBcVersionCheck      *bool      `toml:"-"`
+		DatabaseHandles         *int       `toml:"-"`
 		DatabaseCache           *int
 		TrieCache               *int
 		TrieTimeout             *time.Duration
@@ -122,6 +128,12 @@ func (c *Config) UnmarshalTOML(unmarshal func(interface{}) error) error {
 	if dec.LightPeers != nil {
 		c.LightPeers = *dec.LightPeers
 	}
+	if dec.OnlyAnnounce != nil {
+		c.OnlyAnnounce = *dec.OnlyAnnounce
+	}
+	if dec.ULC != nil {
+		c.ULC = dec.ULC
+	}
 	if dec.SkipBcVersionCheck != nil {
 		c.SkipBcVersionCheck = *dec.SkipBcVersionCheck
 	}
diff --git a/eth/ulc_config.go b/eth/ulc_config.go
new file mode 100644
index 0000000..960cb0d
--- /dev/null
+++ b/eth/ulc_config.go
@@ -0,0 +1,9 @@
+package eth
+
+const DefaultUTCMinTrustedFraction = 75
+
+// ULCConfig is a Ultra Light client options.
+type ULCConfig struct {
+	TrustedServers     []string `toml:",omitempty"` // A list of trusted servers
+	MinTrustedFraction int      `toml:",omitempty"` // Minimum percentage of connected trusted servers to validate trusted (1-100)
+}
diff --git a/les/backend.go b/les/backend.go
index 8e9cca6..d54b466 100644
--- a/les/backend.go
+++ b/les/backend.go
@@ -20,6 +20,7 @@ package les
 import (
 	"fmt"
 	"sync"
+	"time"

 	"github.com/ethereum/go-ethereum/accounts"
 	"github.com/ethereum/go-ethereum/common"
@@ -108,8 +109,12 @@ func New(ctx *node.ServiceContext, config *eth.Config) (*LightEthereum, error) {
 		bloomIndexer:   eth.NewBloomIndexer(chainDb, params.BloomBitsBlocksClient, params.HelperTrieConfirmations),
 	}

+	var trustedNodes []string
+	if leth.config.ULC != nil {
+		trustedNodes = leth.config.ULC.TrustedServers
+	}
 	leth.relay = NewLesTxRelay(peers, leth.reqDist)
-	leth.serverPool = newServerPool(chainDb, quitSync, &leth.wg)
+	leth.serverPool = newServerPool(chainDb, quitSync, &leth.wg, trustedNodes)
 	leth.retriever = newRetrieveManager(peers, leth.reqDist, leth.serverPool)

 	leth.odr = NewLesOdr(chainDb, light.DefaultClientIndexerConfig, leth.retriever)
@@ -135,10 +140,33 @@ func New(ctx *node.ServiceContext, config *eth.Config) (*LightEthereum, error) {
 	}

 	leth.txPool = light.NewTxPool(leth.chainConfig, leth.blockchain, leth.relay)
-	if leth.protocolManager, err = NewProtocolManager(leth.chainConfig, light.DefaultClientIndexerConfig, true, config.NetworkId, leth.eventMux, leth.engine, leth.peers, leth.blockchain, nil, chainDb, leth.odr, leth.relay, leth.serverPool, quitSync, &leth.wg); err != nil {
+
+	if leth.protocolManager, err = NewProtocolManager(
+		leth.chainConfig,
+		light.DefaultClientIndexerConfig,
+		true,
+		config.NetworkId,
+		leth.eventMux,
+		leth.engine,
+		leth.peers,
+		leth.blockchain,
+		nil,
+		chainDb,
+		leth.odr,
+		leth.relay,
+		leth.serverPool,
+		quitSync,
+		&leth.wg,
+		config.ULC); err != nil {
 		return nil, err
 	}
+
+	if leth.protocolManager.isULCEnabled() {
+		log.Warn("Ultra light client is enabled", "trustedNodes", len(leth.protocolManager.ulc.trustedKeys), "minTrustedFraction", leth.protocolManager.ulc.minTrustedFraction)
+		leth.blockchain.DisableCheckFreq()
+	}
 	leth.ApiBackend = &LesApiBackend{leth, nil}
+
 	gpoParams := config.GPO
 	if gpoParams.Default == nil {
 		gpoParams.Default = config.MinerGasPrice
@@ -253,6 +281,7 @@ func (s *LightEthereum) Stop() error {

 	s.eventMux.Stop()

+	time.Sleep(time.Millisecond * 200)
 	s.chainDb.Close()
 	close(s.shutdownChan)

diff --git a/les/fetcher.go b/les/fetcher.go
index f0d3b18..16cfc00 100644
--- a/les/fetcher.go
+++ b/les/fetcher.go
@@ -43,7 +43,7 @@ const (
 type lightFetcher struct {
 	pm    *ProtocolManager
 	odr   *LesOdr
-	chain *light.LightChain
+	chain lightChain

 	lock            sync.Mutex // lock protects access to the fetcher's internal state variables except sent requests
 	maxConfirmedTd  *big.Int
@@ -52,11 +52,19 @@ type lightFetcher struct {
 	syncing         bool
 	syncDone        chan *peer

-	reqMu      sync.RWMutex // reqMu protects access to sent header fetch requests
-	requested  map[uint64]fetchRequest
-	deliverChn chan fetchResponse
-	timeoutChn chan uint64
-	requestChn chan bool // true if initiated from outside
+	reqMu             sync.RWMutex // reqMu protects access to sent header fetch requests
+	requested         map[uint64]fetchRequest
+	deliverChn        chan fetchResponse
+	timeoutChn        chan uint64
+	requestChn        chan bool // true if initiated from outside
+	lastTrustedHeader *types.Header
+}
+
+// lightChain extends the BlockChain interface by locking.
+type lightChain interface {
+	BlockChain
+	LockChain()
+	UnlockChain()
 }

 // fetcherPeerInfo holds fetcher-specific information about each active peer
@@ -144,9 +152,11 @@ func (f *lightFetcher) syncLoop() {
 				rq    *distReq
 				reqID uint64
 			)
+
 			if !f.syncing && !(newAnnounce && s) {
 				rq, reqID = f.nextRequest()
 			}
+
 			syncing := f.syncing
 			f.lock.Unlock()

@@ -206,8 +216,11 @@ func (f *lightFetcher) syncLoop() {
 		case p := <-f.syncDone:
 			f.lock.Lock()
 			p.Log().Debug("Done synchronising with peer")
-			f.checkSyncedHeaders(p)
+			res, h, td := f.checkSyncedHeaders(p)
 			f.syncing = false
+			if res {
+				f.newHeaders([]*types.Header{h}, []*big.Int{td})
+			}
 			f.lock.Unlock()
 		}
 	}
@@ -223,7 +236,6 @@ func (f *lightFetcher) registerPeer(p *peer) {

 	f.lock.Lock()
 	defer f.lock.Unlock()
-
 	f.peers[p] = &fetcherPeerInfo{nodeByHash: make(map[common.Hash]*fetcherTreeNode)}
 }

@@ -276,8 +288,10 @@ func (f *lightFetcher) announce(p *peer, head *announceData) {
 		fp.nodeCnt = 0
 		fp.nodeByHash = make(map[common.Hash]*fetcherTreeNode)
 	}
+	// check if the node count is too high to add new nodes, discard oldest ones if necessary
 	if n != nil {
-		// check if the node count is too high to add new nodes, discard oldest ones if necessary
+		// n is now the reorg common ancestor, add a new branch of nodes
+		// check if the node count is too high to add new nodes
 		locked := false
 		for uint64(fp.nodeCnt)+head.Number-n.number > maxNodeCount && fp.root != nil {
 			if !locked {
@@ -321,6 +335,7 @@ func (f *lightFetcher) announce(p *peer, head *announceData) {
 			fp.nodeByHash[n.hash] = n
 		}
 	}
+
 	if n == nil {
 		// could not find reorg common ancestor or had to delete entire tree, a new root and a resync is needed
 		if fp.root != nil {
@@ -407,25 +422,13 @@ func (f *lightFetcher) requestedID(reqID uint64) bool {
 // to be downloaded starting from the head backwards is also returned
 func (f *lightFetcher) nextRequest() (*distReq, uint64) {
 	var (
-		bestHash   common.Hash
-		bestAmount uint64
+		bestHash    common.Hash
+		bestAmount  uint64
+		bestTd      *big.Int
+		bestSyncing bool
 	)
-	bestTd := f.maxConfirmedTd
-	bestSyncing := false
+	bestHash, bestAmount, bestTd, bestSyncing = f.findBestValues()

-	for p, fp := range f.peers {
-		for hash, n := range fp.nodeByHash {
-			if !f.checkKnownNode(p, n) && !n.requested && (bestTd == nil || n.td.Cmp(bestTd) >= 0) {
-				amount := f.requestAmount(p, n)
-				if bestTd == nil || n.td.Cmp(bestTd) > 0 || amount < bestAmount {
-					bestHash = hash
-					bestAmount = amount
-					bestTd = n.td
-					bestSyncing = fp.bestConfirmed == nil || fp.root == nil || !f.checkKnownNode(p, fp.root)
-				}
-			}
-		}
-	}
 	if bestTd == f.maxConfirmedTd {
 		return nil, 0
 	}
@@ -435,72 +438,131 @@ func (f *lightFetcher) nextRequest() (*distReq, uint64) {
 	var rq *distReq
 	reqID := genReqID()
 	if f.syncing {
-		rq = &distReq{
-			getCost: func(dp distPeer) uint64 {
-				return 0
-			},
-			canSend: func(dp distPeer) bool {
-				p := dp.(*peer)
-				f.lock.Lock()
-				defer f.lock.Unlock()
-
-				fp := f.peers[p]
-				return fp != nil && fp.nodeByHash[bestHash] != nil
-			},
-			request: func(dp distPeer) func() {
-				go func() {
-					p := dp.(*peer)
-					p.Log().Debug("Synchronisation started")
-					f.pm.synchronise(p)
-					f.syncDone <- p
-				}()
-				return nil
-			},
-		}
+		rq = f.newFetcherDistReqForSync(bestHash)
 	} else {
-		rq = &distReq{
-			getCost: func(dp distPeer) uint64 {
-				p := dp.(*peer)
-				return p.GetRequestCost(GetBlockHeadersMsg, int(bestAmount))
-			},
-			canSend: func(dp distPeer) bool {
+		rq = f.newFetcherDistReq(bestHash, reqID, bestAmount)
+	}
+	return rq, reqID
+}
+
+// findBestValues retrieves the best values for LES or ULC mode.
+func (f *lightFetcher) findBestValues() (bestHash common.Hash, bestAmount uint64, bestTd *big.Int, bestSyncing bool) {
+	bestTd = f.maxConfirmedTd
+	bestSyncing = false
+
+	for p, fp := range f.peers {
+		for hash, n := range fp.nodeByHash {
+			if f.checkKnownNode(p, n) || n.requested {
+				continue
+			}
+
+			//if ulc mode is disabled, isTrustedHash returns true
+			amount := f.requestAmount(p, n)
+			if (bestTd == nil || n.td.Cmp(bestTd) > 0 || amount < bestAmount) && (f.isTrustedHash(hash) || f.maxConfirmedTd.Int64() == 0) {
+				bestHash = hash
+				bestTd = n.td
+				bestAmount = amount
+				bestSyncing = fp.bestConfirmed == nil || fp.root == nil || !f.checkKnownNode(p, fp.root)
+			}
+		}
+	}
+	return
+}
+
+// isTrustedHash checks if the block can be trusted by the minimum trusted fraction.
+func (f *lightFetcher) isTrustedHash(hash common.Hash) bool {
+	if !f.pm.isULCEnabled() {
+		return true
+	}
+
+	var numAgreed int
+	for p, fp := range f.peers {
+		if !p.isTrusted {
+			continue
+		}
+		if _, ok := fp.nodeByHash[hash]; !ok {
+			continue
+		}
+
+		numAgreed++
+	}
+
+	return 100*numAgreed/len(f.pm.ulc.trustedKeys) >= f.pm.ulc.minTrustedFraction
+}
+
+func (f *lightFetcher) newFetcherDistReqForSync(bestHash common.Hash) *distReq {
+	return &distReq{
+		getCost: func(dp distPeer) uint64 {
+			return 0
+		},
+		canSend: func(dp distPeer) bool {
+			p := dp.(*peer)
+			if p.isOnlyAnnounce {
+				return false
+			}
+
+			fp := f.peers[p]
+			return fp != nil && fp.nodeByHash[bestHash] != nil
+		},
+		request: func(dp distPeer) func() {
+			if f.pm.isULCEnabled() {
+				//keep last trusted header before sync
+				f.setLastTrustedHeader(f.chain.CurrentHeader())
+			}
+			go func() {
 				p := dp.(*peer)
-				f.lock.Lock()
-				defer f.lock.Unlock()
+				p.Log().Debug("Synchronisation started")
+				f.pm.synchronise(p)
+				f.syncDone <- p
+			}()
+			return nil
+		},
+	}
+}

-				fp := f.peers[p]
-				if fp == nil {
-					return false
-				}
+// newFetcherDistReq creates a new request for the distributor.
+func (f *lightFetcher) newFetcherDistReq(bestHash common.Hash, reqID uint64, bestAmount uint64) *distReq {
+	return &distReq{
+		getCost: func(dp distPeer) uint64 {
+			p := dp.(*peer)
+			return p.GetRequestCost(GetBlockHeadersMsg, int(bestAmount))
+		},
+		canSend: func(dp distPeer) bool {
+			p := dp.(*peer)
+			if p.isOnlyAnnounce {
+				return false
+			}
+
+			fp := f.peers[p]
+			if fp == nil {
+				return false
+			}
+			n := fp.nodeByHash[bestHash]
+			return n != nil && !n.requested
+		},
+		request: func(dp distPeer) func() {
+			p := dp.(*peer)
+
+			fp := f.peers[p]
+			if fp != nil {
 				n := fp.nodeByHash[bestHash]
-				return n != nil && !n.requested
-			},
-			request: func(dp distPeer) func() {
-				p := dp.(*peer)
-				f.lock.Lock()
-				fp := f.peers[p]
-				if fp != nil {
-					n := fp.nodeByHash[bestHash]
-					if n != nil {
-						n.requested = true
-					}
+				if n != nil {
+					n.requested = true
 				}
-				f.lock.Unlock()
-
-				cost := p.GetRequestCost(GetBlockHeadersMsg, int(bestAmount))
-				p.fcServer.QueueRequest(reqID, cost)
-				f.reqMu.Lock()
-				f.requested[reqID] = fetchRequest{hash: bestHash, amount: bestAmount, peer: p, sent: mclock.Now()}
-				f.reqMu.Unlock()
-				go func() {
-					time.Sleep(hardRequestTimeout)
-					f.timeoutChn <- reqID
-				}()
-				return func() { p.RequestHeadersByHash(reqID, cost, bestHash, int(bestAmount), 0, true) }
-			},
-		}
+			}
+
+			cost := p.GetRequestCost(GetBlockHeadersMsg, int(bestAmount))
+			p.fcServer.QueueRequest(reqID, cost)
+			f.reqMu.Lock()
+			f.requested[reqID] = fetchRequest{hash: bestHash, amount: bestAmount, peer: p, sent: mclock.Now()}
+			f.reqMu.Unlock()
+			go func() {
+				time.Sleep(hardRequestTimeout)
+				f.timeoutChn <- reqID
+			}()
+			return func() { p.RequestHeadersByHash(reqID, cost, bestHash, int(bestAmount), 0, true) }
+		},
 	}
-	return rq, reqID
 }

 // deliverHeaders delivers header download request responses for processing
@@ -518,6 +580,7 @@ func (f *lightFetcher) processResponse(req fetchRequest, resp fetchResponse) boo
 	for i, header := range resp.headers {
 		headers[int(req.amount)-1-i] = header
 	}
+
 	if _, err := f.chain.InsertHeaderChain(headers, 1); err != nil {
 		if err == consensus.ErrFutureBlock {
 			return true
@@ -542,6 +605,7 @@ func (f *lightFetcher) processResponse(req fetchRequest, resp fetchResponse) boo
 // downloaded and validated batch or headers
 func (f *lightFetcher) newHeaders(headers []*types.Header, tds []*big.Int) {
 	var maxTd *big.Int
+
 	for p, fp := range f.peers {
 		if !f.checkAnnouncedHeaders(fp, headers, tds) {
 			p.Log().Debug("Inconsistent announcement")
@@ -551,6 +615,7 @@ func (f *lightFetcher) newHeaders(headers []*types.Header, tds []*big.Int) {
 			maxTd = fp.confirmedTd
 		}
 	}
+
 	if maxTd != nil {
 		f.updateMaxConfirmedTd(maxTd)
 	}
@@ -632,28 +697,100 @@ func (f *lightFetcher) checkAnnouncedHeaders(fp *fetcherPeerInfo, headers []*typ
 // checkSyncedHeaders updates peer's block tree after synchronisation by marking
 // downloaded headers as known. If none of the announced headers are found after
 // syncing, the peer is dropped.
-func (f *lightFetcher) checkSyncedHeaders(p *peer) {
+func (f *lightFetcher) checkSyncedHeaders(p *peer) (bool, *types.Header, *big.Int) {
 	fp := f.peers[p]
 	if fp == nil {
 		p.Log().Debug("Unknown peer to check sync headers")
-		return
+		return false, nil, nil
 	}
+
 	n := fp.lastAnnounced
 	var td *big.Int
+
+	var h *types.Header
+	if f.pm.isULCEnabled() {
+		var unapprovedHashes []common.Hash
+		// Overwrite last announced for ULC mode
+		h, unapprovedHashes = f.lastTrustedTreeNode(p)
+		//rollback untrusted blocks
+		f.chain.Rollback(unapprovedHashes)
+		//overwrite to last trusted
+		n = fp.nodeByHash[h.Hash()]
+	}
+
+	//find last valid block
 	for n != nil {
 		if td = f.chain.GetTd(n.hash, n.number); td != nil {
 			break
 		}
 		n = n.parent
 	}
-	// now n is the latest downloaded header after syncing
+
+	// Now n is the latest downloaded/approved header after syncing
 	if n == nil {
 		p.Log().Debug("Synchronisation failed")
 		go f.pm.removePeer(p.id)
-	} else {
-		header := f.chain.GetHeader(n.hash, n.number)
-		f.newHeaders([]*types.Header{header}, []*big.Int{td})
+		return false, nil, nil
+	}
+	header := f.chain.GetHeader(n.hash, n.number)
+	return true, header, td
+}
+
+// lastTrustedTreeNode return last approved treeNode and a list of unapproved hashes
+func (f *lightFetcher) lastTrustedTreeNode(p *peer) (*types.Header, []common.Hash) {
+	unapprovedHashes := make([]common.Hash, 0)
+	current := f.chain.CurrentHeader()
+
+	if f.lastTrustedHeader == nil {
+		return current, unapprovedHashes
 	}
+
+	canonical := f.chain.CurrentHeader()
+	if canonical.Number.Uint64() > f.lastTrustedHeader.Number.Uint64() {
+		canonical = f.chain.GetHeaderByNumber(f.lastTrustedHeader.Number.Uint64())
+	}
+	commonAncestor := rawdb.FindCommonAncestor(f.pm.chainDb, canonical, f.lastTrustedHeader)
+	if commonAncestor == nil {
+		log.Error("Common ancestor of last trusted header and canonical header is nil", "canonical hash", canonical.Hash(), "trusted hash", f.lastTrustedHeader.Hash())
+		return current, unapprovedHashes
+	}
+
+	for !f.isStopValidationTree(current, commonAncestor) {
+		if f.isTrustedHash(current.Hash()) {
+			break
+		}
+		unapprovedHashes = append(unapprovedHashes, current.Hash())
+		current = f.chain.GetHeader(current.ParentHash, current.Number.Uint64()-1)
+	}
+	return current, unapprovedHashes
+}
+
+//isStopValidationTree found when we should stop on finding last trusted header
+func (f *lightFetcher) isStopValidationTree(current *types.Header, commonAncestor *types.Header) bool {
+	if current == nil {
+		return true
+	}
+
+	currentHash := current.Hash()
+	ancestorHash := commonAncestor.Hash()
+
+	//found lastTrustedHeader
+	if currentHash == f.lastTrustedHeader.Hash() {
+		return true
+	}
+
+	//found common ancestor between lastTrustedHeader and
+	if current.Hash() == ancestorHash {
+		return true
+	}
+
+	return false
+}
+
+func (f *lightFetcher) setLastTrustedHeader(h *types.Header) {
+	f.lock.Lock()
+	defer f.lock.Unlock()
+	f.lastTrustedHeader = h
 }

 // checkKnownNode checks if a block tree node is known (downloaded and validated)
@@ -745,6 +882,7 @@ func (f *lightFetcher) updateMaxConfirmedTd(td *big.Int) {
 		if f.lastUpdateStats != nil {
 			f.lastUpdateStats.next = newEntry
 		}
+
 		f.lastUpdateStats = newEntry
 		for p := range f.peers {
 			f.checkUpdateStats(p, newEntry)
@@ -767,6 +905,7 @@ func (f *lightFetcher) checkUpdateStats(p *peer, newEntry *updateStatsEntry) {
 		p.Log().Debug("Unknown peer to check update stats")
 		return
 	}
+
 	if newEntry != nil && fp.firstUpdateStats == nil {
 		fp.firstUpdateStats = newEntry
 	}
diff --git a/les/fetcher_test.go b/les/fetcher_test.go
new file mode 100644
index 0000000..e5b6ef3
--- /dev/null
+++ b/les/fetcher_test.go
@@ -0,0 +1,155 @@
+package les
+
+import (
+	"math/big"
+	"testing"
+
+	"net"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/p2p"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+)
+
+func TestFetcherULCPeerSelector(t *testing.T) {
+
+	var (
+		id1 enode.ID = newNodeID(t).ID()
+		id2 enode.ID = newNodeID(t).ID()
+		id3 enode.ID = newNodeID(t).ID()
+		id4 enode.ID = newNodeID(t).ID()
+	)
+
+	ftn1 := &fetcherTreeNode{
+		hash: common.HexToHash("1"),
+		td:   big.NewInt(1),
+	}
+	ftn2 := &fetcherTreeNode{
+		hash:   common.HexToHash("2"),
+		td:     big.NewInt(2),
+		parent: ftn1,
+	}
+	ftn3 := &fetcherTreeNode{
+		hash:   common.HexToHash("3"),
+		td:     big.NewInt(3),
+		parent: ftn2,
+	}
+	lf := lightFetcher{
+		pm: &ProtocolManager{
+			ulc: &ulc{
+				trustedKeys: map[string]struct{}{
+					id1.String(): {},
+					id2.String(): {},
+					id3.String(): {},
+					id4.String(): {},
+				},
+				minTrustedFraction: 70,
+			},
+		},
+		maxConfirmedTd: ftn1.td,
+
+		peers: map[*peer]*fetcherPeerInfo{
+			{
+				id:        "peer1",
+				Peer:      p2p.NewPeer(id1, "peer1", []p2p.Cap{}),
+				isTrusted: true,
+			}: {
+				nodeByHash: map[common.Hash]*fetcherTreeNode{
+					ftn1.hash: ftn1,
+					ftn2.hash: ftn2,
+				},
+			},
+			{
+				Peer:      p2p.NewPeer(id2, "peer2", []p2p.Cap{}),
+				id:        "peer2",
+				isTrusted: true,
+			}: {
+				nodeByHash: map[common.Hash]*fetcherTreeNode{
+					ftn1.hash: ftn1,
+					ftn2.hash: ftn2,
+				},
+			},
+			{
+				id:        "peer3",
+				Peer:      p2p.NewPeer(id3, "peer3", []p2p.Cap{}),
+				isTrusted: true,
+			}: {
+				nodeByHash: map[common.Hash]*fetcherTreeNode{
+					ftn1.hash: ftn1,
+					ftn2.hash: ftn2,
+					ftn3.hash: ftn3,
+				},
+			},
+			{
+				id:        "peer4",
+				Peer:      p2p.NewPeer(id4, "peer4", []p2p.Cap{}),
+				isTrusted: true,
+			}: {
+				nodeByHash: map[common.Hash]*fetcherTreeNode{
+					ftn1.hash: ftn1,
+				},
+			},
+		},
+		chain: &lightChainStub{
+			tds: map[common.Hash]*big.Int{},
+			headers: map[common.Hash]*types.Header{
+				ftn1.hash: {},
+				ftn2.hash: {},
+				ftn3.hash: {},
+			},
+		},
+	}
+	bestHash, bestAmount, bestTD, sync := lf.findBestValues()
+
+	if bestTD == nil {
+		t.Fatal("Empty result")
+	}
+
+	if bestTD.Cmp(ftn2.td) != 0 {
+		t.Fatal("bad td", bestTD)
+	}
+	if bestHash != ftn2.hash {
+		t.Fatal("bad hash", bestTD)
+	}
+
+	_, _ = bestAmount, sync
+}
+
+type lightChainStub struct {
+	BlockChain
+	tds                         map[common.Hash]*big.Int
+	headers                     map[common.Hash]*types.Header
+	insertHeaderChainAssertFunc func(chain []*types.Header, checkFreq int) (int, error)
+}
+
+func (l *lightChainStub) GetHeader(hash common.Hash, number uint64) *types.Header {
+	if h, ok := l.headers[hash]; ok {
+		return h
+	}
+
+	return nil
+}
+
+func (l *lightChainStub) LockChain()   {}
+func (l *lightChainStub) UnlockChain() {}
+
+func (l *lightChainStub) GetTd(hash common.Hash, number uint64) *big.Int {
+	if td, ok := l.tds[hash]; ok {
+		return td
+	}
+	return nil
+}
+
+func (l *lightChainStub) InsertHeaderChain(chain []*types.Header, checkFreq int) (int, error) {
+	return l.insertHeaderChainAssertFunc(chain, checkFreq)
+}
+
+func newNodeID(t *testing.T) *enode.Node {
+	key, err := crypto.GenerateKey()
+	if err != nil {
+		t.Fatal("generate key err:", err)
+	}
+	return enode.NewV4(&key.PublicKey, net.IP{}, 35000, 35000)
+}
diff --git a/les/handler.go b/les/handler.go
index de3b5f8..5e60fc8 100644
--- a/les/handler.go
+++ b/les/handler.go
@@ -33,6 +33,7 @@ import (
 	"github.com/ethereum/go-ethereum/core/rawdb"
 	"github.com/ethereum/go-ethereum/core/state"
 	"github.com/ethereum/go-ethereum/core/types"
+	"github.com/ethereum/go-ethereum/eth"
 	"github.com/ethereum/go-ethereum/eth/downloader"
 	"github.com/ethereum/go-ethereum/ethdb"
 	"github.com/ethereum/go-ethereum/event"
@@ -119,12 +120,29 @@ type ProtocolManager struct {

 	// wait group is used for graceful shutdowns during downloading
 	// and processing
-	wg *sync.WaitGroup
+	wg  *sync.WaitGroup
+	ulc *ulc
 }

 // NewProtocolManager returns a new ethereum sub protocol manager. The Ethereum sub protocol manages peers capable
 // with the ethereum network.
-func NewProtocolManager(chainConfig *params.ChainConfig, indexerConfig *light.IndexerConfig, lightSync bool, networkId uint64, mux *event.TypeMux, engine consensus.Engine, peers *peerSet, blockchain BlockChain, txpool txPool, chainDb ethdb.Database, odr *LesOdr, txrelay *LesTxRelay, serverPool *serverPool, quitSync chan struct{}, wg *sync.WaitGroup) (*ProtocolManager, error) {
+func NewProtocolManager(
+	chainConfig *params.ChainConfig,
+	indexerConfig *light.IndexerConfig,
+	lightSync bool,
+	networkId uint64,
+	mux *event.TypeMux,
+	engine consensus.Engine,
+	peers *peerSet,
+	blockchain BlockChain,
+	txpool txPool,
+	chainDb ethdb.Database,
+	odr *LesOdr,
+	txrelay *LesTxRelay,
+	serverPool *serverPool,
+	quitSync chan struct{},
+	wg *sync.WaitGroup,
+	ulcConfig *eth.ULCConfig) (*ProtocolManager, error) {
 	// Create the protocol manager with the base fields
 	manager := &ProtocolManager{
 		lightSync:   lightSync,
@@ -149,6 +167,10 @@ func NewProtocolManager(chainConfig *params.ChainConfig, indexerConfig *light.In
 		manager.reqDist = odr.retriever.dist
 	}

+	if ulcConfig != nil {
+		manager.ulc = newULC(ulcConfig)
+	}
+
 	removePeer := manager.removePeer
 	if disableClientRemovePeer {
 		removePeer = func(id string) {}
@@ -237,7 +259,11 @@ func (pm *ProtocolManager) runPeer(version uint, p *p2p.Peer, rw p2p.MsgReadWrit
 }

 func (pm *ProtocolManager) newPeer(pv int, nv uint64, p *p2p.Peer, rw p2p.MsgReadWriter) *peer {
-	return newPeer(pv, nv, p, newMeteredMsgWriter(rw))
+	var isTrusted bool
+	if pm.isULCEnabled() {
+		isTrusted = pm.ulc.isTrusted(p.ID())
+	}
+	return newPeer(pv, nv, isTrusted, p, newMeteredMsgWriter(rw))
 }

 // handle is the callback invoked to manage the life cycle of a les peer. When
@@ -279,6 +305,7 @@ func (pm *ProtocolManager) handle(p *peer) error {
 	if rw, ok := p.rw.(*meteredMsgReadWriter); ok {
 		rw.Init(p.version)
 	}
+
 	// Register the peer locally
 	if err := pm.peers.Register(p); err != nil {
 		p.Log().Error("Light Ethereum peer registration failed", "err", err)
@@ -290,6 +317,7 @@ func (pm *ProtocolManager) handle(p *peer) error {
 		}
 		pm.removePeer(p.id)
 	}()
+
 	// Register the peer in the downloader. If the downloader considers it banned, we disconnect
 	if pm.lightSync {
 		p.lock.Lock()
@@ -374,16 +402,15 @@ func (pm *ProtocolManager) handleMsg(p *peer) error {
 	// Block header query, collect the requested headers and reply
 	case AnnounceMsg:
 		p.Log().Trace("Received announce message")
-		if p.requestAnnounceType == announceTypeNone {
+		if p.announceType == announceTypeNone {
 			return errResp(ErrUnexpectedResponse, "")
 		}
-
 		var req announceData
 		if err := msg.Decode(&req); err != nil {
 			return errResp(ErrDecode, "%v: %v", msg, err)
 		}

-		if p.requestAnnounceType == announceTypeSigned {
+		if p.announceType == announceTypeSigned {
 			if err := req.checkSignature(p.ID()); err != nil {
 				p.Log().Trace("Invalid announcement signature", "err", err)
 				return err
@@ -1178,6 +1205,14 @@ func (pm *ProtocolManager) txStatus(hashes []common.Hash) []txStatus {
 	return stats
 }

+// isULCEnabled returns true if we can use ULC
+func (pm *ProtocolManager) isULCEnabled() bool {
+	if pm.ulc == nil || len(pm.ulc.trustedKeys) == 0 {
+		return false
+	}
+	return true
+}
+
 // downloaderPeerNotify implements peerSetNotify
 type downloaderPeerNotify ProtocolManager

@@ -1222,7 +1257,8 @@ func (pc *peerConnection) RequestHeadersByNumber(origin uint64, amount int, skip
 			return peer.GetRequestCost(GetBlockHeadersMsg, amount)
 		},
 		canSend: func(dp distPeer) bool {
-			return dp.(*peer) == pc.peer
+			p := dp.(*peer)
+			return p == pc.peer
 		},
 		request: func(dp distPeer) func() {
 			peer := dp.(*peer)
@@ -1249,5 +1285,7 @@ func (d *downloaderPeerNotify) registerPeer(p *peer) {

 func (d *downloaderPeerNotify) unregisterPeer(p *peer) {
 	pm := (*ProtocolManager)(d)
-	pm.downloader.UnregisterPeer(p.id)
+	if pm.ulc == nil || p.isTrusted {
+		pm.downloader.UnregisterPeer(p.id)
+	}
 }
diff --git a/les/handler_test.go b/les/handler_test.go
index 43be7f4..72ba266 100644
--- a/les/handler_test.go
+++ b/les/handler_test.go
@@ -494,7 +494,7 @@ func TestGetBloombitsProofs(t *testing.T) {

 func TestTransactionStatusLes2(t *testing.T) {
 	db := ethdb.NewMemDatabase()
-	pm := newTestProtocolManagerMust(t, false, 0, nil, nil, nil, db)
+	pm := newTestProtocolManagerMust(t, false, 0, nil, nil, nil, db, nil)
 	chain := pm.blockchain.(*core.BlockChain)
 	config := core.DefaultTxPoolConfig
 	config.Journal = ""
diff --git a/les/helper_test.go b/les/helper_test.go
index b46d41f..02b1668 100644
--- a/les/helper_test.go
+++ b/les/helper_test.go
@@ -146,7 +146,7 @@ func testRCL() RequestCostList {
 // newTestProtocolManager creates a new protocol manager for testing purposes,
 // with the given number of blocks already known, potential notification
 // channels for different events and relative chain indexers array.
-func newTestProtocolManager(lightSync bool, blocks int, generator func(int, *core.BlockGen), odr *LesOdr, peers *peerSet, db ethdb.Database) (*ProtocolManager, error) {
+func newTestProtocolManager(lightSync bool, blocks int, generator func(int, *core.BlockGen), odr *LesOdr, peers *peerSet, db ethdb.Database, ulcConfig *eth.ULCConfig) (*ProtocolManager, error) {
 	var (
 		evmux  = new(event.TypeMux)
 		engine = ethash.NewFaker()
@@ -176,7 +176,7 @@ func newTestProtocolManager(lightSync bool, blocks int, generator func(int, *cor
 	if lightSync {
 		indexConfig = light.TestClientIndexerConfig
 	}
-	pm, err := NewProtocolManager(gspec.Config, indexConfig, lightSync, NetworkId, evmux, engine, peers, chain, nil, db, odr, nil, nil, make(chan struct{}), new(sync.WaitGroup))
+	pm, err := NewProtocolManager(gspec.Config, indexConfig, lightSync, NetworkId, evmux, engine, peers, chain, nil, db, odr, nil, nil, make(chan struct{}), new(sync.WaitGroup), ulcConfig)
 	if err != nil {
 		return nil, err
 	}
@@ -200,8 +200,8 @@ func newTestProtocolManager(lightSync bool, blocks int, generator func(int, *cor
 // with the given number of blocks already known, potential notification
 // channels for different events and relative chain indexers array. In case of an error, the constructor force-
 // fails the test.
-func newTestProtocolManagerMust(t *testing.T, lightSync bool, blocks int, generator func(int, *core.BlockGen), odr *LesOdr, peers *peerSet, db ethdb.Database) *ProtocolManager {
-	pm, err := newTestProtocolManager(lightSync, blocks, generator, odr, peers, db)
+func newTestProtocolManagerMust(t *testing.T, lightSync bool, blocks int, generator func(int, *core.BlockGen), odr *LesOdr, peers *peerSet, db ethdb.Database, ulcConfig *eth.ULCConfig) *ProtocolManager {
+	pm, err := newTestProtocolManager(lightSync, blocks, generator, odr, peers, db, ulcConfig)
 	if err != nil {
 		t.Fatalf("Failed to create protocol manager: %v", err)
 	}
@@ -343,7 +343,7 @@ func newServerEnv(t *testing.T, blocks int, protocol int, waitIndexers func(*cor
 	db := ethdb.NewMemDatabase()
 	cIndexer, bIndexer, btIndexer := testIndexers(db, nil, light.TestServerIndexerConfig)

-	pm := newTestProtocolManagerMust(t, false, blocks, testChainGen, nil, nil, db)
+	pm := newTestProtocolManagerMust(t, false, blocks, testChainGen, nil, nil, db, nil)
 	peer, _ := newTestPeer(t, "peer", protocol, pm, true)

 	cIndexer.Start(pm.blockchain.(*core.BlockChain))
@@ -383,8 +383,8 @@ func newClientServerEnv(t *testing.T, blocks int, protocol int, waitIndexers fun
 	lcIndexer, lbIndexer, lbtIndexer := testIndexers(ldb, odr, light.TestClientIndexerConfig)
 	odr.SetIndexers(lcIndexer, lbtIndexer, lbIndexer)

-	pm := newTestProtocolManagerMust(t, false, blocks, testChainGen, nil, peers, db)
-	lpm := newTestProtocolManagerMust(t, true, 0, nil, odr, lPeers, ldb)
+	pm := newTestProtocolManagerMust(t, false, blocks, testChainGen, nil, peers, db, nil)
+	lpm := newTestProtocolManagerMust(t, true, 0, nil, odr, lPeers, ldb, nil)

 	startIndexers := func(clientMode bool, pm *ProtocolManager) {
 		if clientMode {
diff --git a/les/odr.go b/les/odr.go
index 9def05a..f759235 100644
--- a/les/odr.go
+++ b/les/odr.go
@@ -109,7 +109,10 @@ func (odr *LesOdr) Retrieve(ctx context.Context, req light.OdrRequest) (err erro
 		},
 		canSend: func(dp distPeer) bool {
 			p := dp.(*peer)
-			return lreq.CanSend(p)
+			if !p.isOnlyAnnounce {
+				return lreq.CanSend(p)
+			}
+			return false
 		},
 		request: func(dp distPeer) func() {
 			p := dp.(*peer)
diff --git a/les/peer.go b/les/peer.go
index 678384f..9ae94b2 100644
--- a/les/peer.go
+++ b/les/peer.go
@@ -56,7 +56,7 @@ type peer struct {
 	version int    // Protocol version negotiated
 	network uint64 // Network ID being on

-	announceType, requestAnnounceType uint64
+	announceType uint64

 	id string

@@ -74,9 +74,12 @@ type peer struct {
 	fcServer       *flowcontrol.ServerNode // nil if the peer is client only
 	fcServerParams *flowcontrol.ServerParams
 	fcCosts        requestCostTable
+
+	isTrusted      bool
+	isOnlyAnnounce bool
 }

-func newPeer(version int, network uint64, p *p2p.Peer, rw p2p.MsgReadWriter) *peer {
+func newPeer(version int, network uint64, isTrusted bool, p *p2p.Peer, rw p2p.MsgReadWriter) *peer {
 	id := p.ID()

 	return &peer{
@@ -86,6 +89,7 @@ func newPeer(version int, network uint64, p *p2p.Peer, rw p2p.MsgReadWriter) *pe
 		network:     network,
 		id:          fmt.Sprintf("%x", id[:8]),
 		announceChn: make(chan announceData, 20),
+		isTrusted:   isTrusted,
 	}
 }

@@ -401,23 +405,32 @@ func (p *peer) Handshake(td *big.Int, head common.Hash, headNum uint64, genesis
 	send = send.add("headNum", headNum)
 	send = send.add("genesisHash", genesis)
 	if server != nil {
-		send = send.add("serveHeaders", nil)
-		send = send.add("serveChainSince", uint64(0))
-		send = send.add("serveStateSince", uint64(0))
-		send = send.add("txRelay", nil)
+		if !server.onlyAnnounce {
+			//only announce server. It sends only announse requests
+			send = send.add("serveHeaders", nil)
+			send = send.add("serveChainSince", uint64(0))
+			send = send.add("serveStateSince", uint64(0))
+			send = send.add("txRelay", nil)
+		}
 		send = send.add("flowControl/BL", server.defParams.BufLimit)
 		send = send.add("flowControl/MRR", server.defParams.MinRecharge)
 		list := server.fcCostStats.getCurrentList()
 		send = send.add("flowControl/MRC", list)
 		p.fcCosts = list.decode()
 	} else {
-		p.requestAnnounceType = announceTypeSimple // set to default until "very light" client mode is implemented
-		send = send.add("announceType", p.requestAnnounceType)
+		//on client node
+		p.announceType = announceTypeSimple
+		if p.isTrusted {
+			p.announceType = announceTypeSigned
+		}
+		send = send.add("announceType", p.announceType)
 	}
+
 	recvList, err := p.sendReceiveHandshake(send)
 	if err != nil {
 		return err
 	}
+
 	recv := recvList.decode()

 	var rGenesis, rHash common.Hash
@@ -452,25 +465,33 @@ func (p *peer) Handshake(td *big.Int, head common.Hash, headNum uint64, genesis
 	if int(rVersion) != p.version {
 		return errResp(ErrProtocolVersionMismatch, "%d (!= %d)", rVersion, p.version)
 	}
+
 	if server != nil {
 		// until we have a proper peer connectivity API, allow LES connection to other servers
 		/*if recv.get("serveStateSince", nil) == nil {
 			return errResp(ErrUselessPeer, "wanted client, got server")
 		}*/
 		if recv.get("announceType", &p.announceType) != nil {
+			//set default announceType on server side
 			p.announceType = announceTypeSimple
 		}
 		p.fcClient = flowcontrol.NewClientNode(server.fcManager, server.defParams)
 	} else {
+		//mark OnlyAnnounce server if "serveHeaders", "serveChainSince", "serveStateSince" or "txRelay" fields don't exist
 		if recv.get("serveChainSince", nil) != nil {
-			return errResp(ErrUselessPeer, "peer cannot serve chain")
+			p.isOnlyAnnounce = true
 		}
 		if recv.get("serveStateSince", nil) != nil {
-			return errResp(ErrUselessPeer, "peer cannot serve state")
+			p.isOnlyAnnounce = true
 		}
 		if recv.get("txRelay", nil) != nil {
-			return errResp(ErrUselessPeer, "peer cannot relay transactions")
+			p.isOnlyAnnounce = true
 		}
+
+		if p.isOnlyAnnounce && !p.isTrusted {
+			return errResp(ErrUselessPeer, "peer cannot serve requests")
+		}
+
 		params := &flowcontrol.ServerParams{}
 		if err := recv.get("flowControl/BL", &params.BufLimit); err != nil {
 			return err
@@ -486,7 +507,6 @@ func (p *peer) Handshake(td *big.Int, head common.Hash, headNum uint64, genesis
 		p.fcServer = flowcontrol.NewServerNode(params)
 		p.fcCosts = MRC.decode()
 	}
-
 	p.headInfo = &announceData{Td: rTd, Hash: rHash, Number: rNum}
 	return nil
 }
@@ -576,8 +596,10 @@ func (ps *peerSet) Unregister(id string) error {
 		for _, n := range peers {
 			n.unregisterPeer(p)
 		}
+
 		p.sendQueue.quit()
 		p.Peer.Disconnect(p2p.DiscUselessPeer)
+
 		return nil
 	}
 }
diff --git a/les/peer_test.go b/les/peer_test.go
new file mode 100644
index 0000000..0ba9cbf
--- /dev/null
+++ b/les/peer_test.go
@@ -0,0 +1,297 @@
+package les
+
+import (
+	"math/big"
+	"testing"
+
+	"github.com/ethereum/go-ethereum/common"
+	"github.com/ethereum/go-ethereum/les/flowcontrol"
+	"github.com/ethereum/go-ethereum/p2p"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+	"github.com/ethereum/go-ethereum/rlp"
+)
+
+const (
+	test_networkid   = 10
+	protocol_version = 2123
+)
+
+var (
+	hash    = common.HexToHash("some string")
+	genesis = common.HexToHash("genesis hash")
+	headNum = uint64(1234)
+	td      = big.NewInt(123)
+)
+
+//ulc connects to trusted peer and send announceType=announceTypeSigned
+func TestPeerHandshakeSetAnnounceTypeToAnnounceTypeSignedForTrustedPeer(t *testing.T) {
+
+	var id enode.ID = newNodeID(t).ID()
+
+	//peer to connect(on ulc side)
+	p := peer{
+		Peer:      p2p.NewPeer(id, "test peer", []p2p.Cap{}),
+		version:   protocol_version,
+		isTrusted: true,
+		rw: &rwStub{
+			WriteHook: func(recvList keyValueList) {
+				//checking that ulc sends to peer allowedRequests=onlyAnnounceRequests and announceType = announceTypeSigned
+				recv := recvList.decode()
+				var reqType uint64
+
+				err := recv.get("announceType", &reqType)
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				if reqType != announceTypeSigned {
+					t.Fatal("Expected announceTypeSigned")
+				}
+			},
+			ReadHook: func(l keyValueList) keyValueList {
+				l = l.add("serveHeaders", nil)
+				l = l.add("serveChainSince", uint64(0))
+				l = l.add("serveStateSince", uint64(0))
+				l = l.add("txRelay", nil)
+				l = l.add("flowControl/BL", uint64(0))
+				l = l.add("flowControl/MRR", uint64(0))
+				l = l.add("flowControl/MRC", RequestCostList{})
+
+				return l
+			},
+		},
+		network: test_networkid,
+	}
+
+	err := p.Handshake(td, hash, headNum, genesis, nil)
+	if err != nil {
+		t.Fatalf("Handshake error: %s", err)
+	}
+
+	if p.announceType != announceTypeSigned {
+		t.Fatal("Incorrect announceType")
+	}
+}
+
+func TestPeerHandshakeAnnounceTypeSignedForTrustedPeersPeerNotInTrusted(t *testing.T) {
+	var id enode.ID = newNodeID(t).ID()
+	p := peer{
+		Peer:    p2p.NewPeer(id, "test peer", []p2p.Cap{}),
+		version: protocol_version,
+		rw: &rwStub{
+			WriteHook: func(recvList keyValueList) {
+				//checking that ulc sends to peer allowedRequests=noRequests and announceType != announceTypeSigned
+				recv := recvList.decode()
+				var reqType uint64
+
+				err := recv.get("announceType", &reqType)
+				if err != nil {
+					t.Fatal(err)
+				}
+
+				if reqType == announceTypeSigned {
+					t.Fatal("Expected not announceTypeSigned")
+				}
+			},
+			ReadHook: func(l keyValueList) keyValueList {
+				l = l.add("serveHeaders", nil)
+				l = l.add("serveChainSince", uint64(0))
+				l = l.add("serveStateSince", uint64(0))
+				l = l.add("txRelay", nil)
+				l = l.add("flowControl/BL", uint64(0))
+				l = l.add("flowControl/MRR", uint64(0))
+				l = l.add("flowControl/MRC", RequestCostList{})
+
+				return l
+			},
+		},
+		network: test_networkid,
+	}
+
+	err := p.Handshake(td, hash, headNum, genesis, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if p.announceType == announceTypeSigned {
+		t.Fatal("Incorrect announceType")
+	}
+}
+
+func TestPeerHandshakeDefaultAllRequests(t *testing.T) {
+	var id enode.ID = newNodeID(t).ID()
+
+	s := generateLesServer()
+
+	p := peer{
+		Peer:    p2p.NewPeer(id, "test peer", []p2p.Cap{}),
+		version: protocol_version,
+		rw: &rwStub{
+			ReadHook: func(l keyValueList) keyValueList {
+				l = l.add("announceType", uint64(announceTypeSigned))
+				l = l.add("allowedRequests", uint64(0))
+
+				return l
+			},
+		},
+		network: test_networkid,
+	}
+
+	err := p.Handshake(td, hash, headNum, genesis, s)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if p.isOnlyAnnounce {
+		t.Fatal("Incorrect announceType")
+	}
+}
+
+func TestPeerHandshakeServerSendOnlyAnnounceRequestsHeaders(t *testing.T) {
+	var id enode.ID = newNodeID(t).ID()
+
+	s := generateLesServer()
+	s.onlyAnnounce = true
+
+	p := peer{
+		Peer:    p2p.NewPeer(id, "test peer", []p2p.Cap{}),
+		version: protocol_version,
+		rw: &rwStub{
+			ReadHook: func(l keyValueList) keyValueList {
+				l = l.add("announceType", uint64(announceTypeSigned))
+
+				return l
+			},
+			WriteHook: func(l keyValueList) {
+				for _, v := range l {
+					if v.Key == "serveHeaders" ||
+						v.Key == "serveChainSince" ||
+						v.Key == "serveStateSince" ||
+						v.Key == "txRelay" {
+						t.Fatalf("%v exists", v.Key)
+					}
+				}
+			},
+		},
+		network: test_networkid,
+	}
+
+	err := p.Handshake(td, hash, headNum, genesis, s)
+	if err != nil {
+		t.Fatal(err)
+	}
+}
+func TestPeerHandshakeClientReceiveOnlyAnnounceRequestsHeaders(t *testing.T) {
+	var id enode.ID = newNodeID(t).ID()
+
+	p := peer{
+		Peer:    p2p.NewPeer(id, "test peer", []p2p.Cap{}),
+		version: protocol_version,
+		rw: &rwStub{
+			ReadHook: func(l keyValueList) keyValueList {
+				l = l.add("flowControl/BL", uint64(0))
+				l = l.add("flowControl/MRR", uint64(0))
+				l = l.add("flowControl/MRC", RequestCostList{})
+
+				l = l.add("announceType", uint64(announceTypeSigned))
+
+				return l
+			},
+		},
+		network:   test_networkid,
+		isTrusted: true,
+	}
+
+	err := p.Handshake(td, hash, headNum, genesis, nil)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	if !p.isOnlyAnnounce {
+		t.Fatal("isOnlyAnnounce must be true")
+	}
+}
+
+func TestPeerHandshakeClientReturnErrorOnUselessPeer(t *testing.T) {
+	var id enode.ID = newNodeID(t).ID()
+
+	p := peer{
+		Peer:    p2p.NewPeer(id, "test peer", []p2p.Cap{}),
+		version: protocol_version,
+		rw: &rwStub{
+			ReadHook: func(l keyValueList) keyValueList {
+				l = l.add("flowControl/BL", uint64(0))
+				l = l.add("flowControl/MRR", uint64(0))
+				l = l.add("flowControl/MRC", RequestCostList{})
+
+				l = l.add("announceType", uint64(announceTypeSigned))
+
+				return l
+			},
+		},
+		network: test_networkid,
+	}
+
+	err := p.Handshake(td, hash, headNum, genesis, nil)
+	if err == nil {
+		t.FailNow()
+	}
+}
+
+func generateLesServer() *LesServer {
+	s := &LesServer{
+		defParams: &flowcontrol.ServerParams{
+			BufLimit:    uint64(300000000),
+			MinRecharge: uint64(50000),
+		},
+		fcManager: flowcontrol.NewClientManager(1, 2, 3),
+		fcCostStats: &requestCostStats{
+			stats: make(map[uint64]*linReg, len(reqList)),
+		},
+	}
+	for _, code := range reqList {
+		s.fcCostStats.stats[code] = &linReg{cnt: 100}
+	}
+	return s
+}
+
+type rwStub struct {
+	ReadHook  func(l keyValueList) keyValueList
+	WriteHook func(l keyValueList)
+}
+
+func (s *rwStub) ReadMsg() (p2p.Msg, error) {
+	payload := keyValueList{}
+	payload = payload.add("protocolVersion", uint64(protocol_version))
+	payload = payload.add("networkId", uint64(test_networkid))
+	payload = payload.add("headTd", td)
+	payload = payload.add("headHash", hash)
+	payload = payload.add("headNum", headNum)
+	payload = payload.add("genesisHash", genesis)
+
+	if s.ReadHook != nil {
+		payload = s.ReadHook(payload)
+	}
+
+	size, p, err := rlp.EncodeToReader(payload)
+	if err != nil {
+		return p2p.Msg{}, err
+	}
+
+	return p2p.Msg{
+		Size:    uint32(size),
+		Payload: p,
+	}, nil
+}
+
+func (s *rwStub) WriteMsg(m p2p.Msg) error {
+	recvList := keyValueList{}
+	if err := m.Decode(&recvList); err != nil {
+		return err
+	}
+
+	if s.WriteHook != nil {
+		s.WriteHook(recvList)
+	}
+
+	return nil
+}
diff --git a/les/server.go b/les/server.go
index 2fa0456..2ded3c1 100644
--- a/les/server.go
+++ b/les/server.go
@@ -41,17 +41,34 @@ import (
 type LesServer struct {
 	lesCommons

-	fcManager   *flowcontrol.ClientManager // nil if our node is client only
-	fcCostStats *requestCostStats
-	defParams   *flowcontrol.ServerParams
-	lesTopics   []discv5.Topic
-	privateKey  *ecdsa.PrivateKey
-	quitSync    chan struct{}
+	fcManager    *flowcontrol.ClientManager // nil if our node is client only
+	fcCostStats  *requestCostStats
+	defParams    *flowcontrol.ServerParams
+	lesTopics    []discv5.Topic
+	privateKey   *ecdsa.PrivateKey
+	quitSync     chan struct{}
+	onlyAnnounce bool
 }

 func NewLesServer(eth *eth.Ethereum, config *eth.Config) (*LesServer, error) {
 	quitSync := make(chan struct{})
-	pm, err := NewProtocolManager(eth.BlockChain().Config(), light.DefaultServerIndexerConfig, false, config.NetworkId, eth.EventMux(), eth.Engine(), newPeerSet(), eth.BlockChain(), eth.TxPool(), eth.ChainDb(), nil, nil, nil, quitSync, new(sync.WaitGroup))
+	pm, err := NewProtocolManager(
+		eth.BlockChain().Config(),
+		light.DefaultServerIndexerConfig,
+		false,
+		config.NetworkId,
+		eth.EventMux(),
+		eth.Engine(),
+		newPeerSet(),
+		eth.BlockChain(),
+		eth.TxPool(),
+		eth.ChainDb(),
+		nil,
+		nil,
+		nil,
+		quitSync,
+		new(sync.WaitGroup),
+		config.ULC)
 	if err != nil {
 		return nil, err
 	}
@@ -70,8 +87,9 @@ func NewLesServer(eth *eth.Ethereum, config *eth.Config) (*LesServer, error) {
 			bloomTrieIndexer: light.NewBloomTrieIndexer(eth.ChainDb(), nil, params.BloomBitsBlocks, params.BloomTrieFrequency),
 			protocolManager:  pm,
 		},
-		quitSync:  quitSync,
-		lesTopics: lesTopics,
+		quitSync:     quitSync,
+		lesTopics:    lesTopics,
+		onlyAnnounce: config.OnlyAnnounce,
 	}

 	logger := log.New()
@@ -289,10 +307,8 @@ func (s *requestCostStats) getCurrentList() RequestCostList {
 	defer s.lock.Unlock()

 	list := make(RequestCostList, len(reqList))
-	//fmt.Println("RequestCostList")
 	for idx, code := range reqList {
 		b, m := s.stats[code].calc()
-		//fmt.Println(code, s.stats[code].cnt, b/1000000, m/1000000)
 		if m < 0 {
 			b += m
 			m = 0
diff --git a/les/serverpool.go b/les/serverpool.go
index 0fe6e49..c7edfc7 100644
--- a/les/serverpool.go
+++ b/les/serverpool.go
@@ -126,22 +126,22 @@ type serverPool struct {
 	discNodes     chan *enode.Node
 	discLookups   chan bool

+	trustedNodes         []string
 	entries              map[enode.ID]*poolEntry
 	timeout, enableRetry chan *poolEntry
 	adjustStats          chan poolStatAdjust

-	connCh     chan *connReq
-	disconnCh  chan *disconnReq
-	registerCh chan *registerReq
-
-	knownQueue, newQueue       poolEntryQueue
-	knownSelect, newSelect     *weightedRandomSelect
-	knownSelected, newSelected int
-	fastDiscover               bool
+	knownQueue, newQueue, trustedQueue poolEntryQueue
+	knownSelect, newSelect             *weightedRandomSelect
+	knownSelected, newSelected         int
+	fastDiscover                       bool
+	connCh                             chan *connReq
+	disconnCh                          chan *disconnReq
+	registerCh                         chan *registerReq
 }

 // newServerPool creates a new serverPool instance
-func newServerPool(db ethdb.Database, quit chan struct{}, wg *sync.WaitGroup) *serverPool {
+func newServerPool(db ethdb.Database, quit chan struct{}, wg *sync.WaitGroup, trustedNodes []string) *serverPool {
 	pool := &serverPool{
 		db:           db,
 		quit:         quit,
@@ -156,7 +156,10 @@ func newServerPool(db ethdb.Database, quit chan struct{}, wg *sync.WaitGroup) *s
 		knownSelect:  newWeightedRandomSelect(),
 		newSelect:    newWeightedRandomSelect(),
 		fastDiscover: true,
+		trustedNodes: trustedNodes,
 	}
+
+	pool.trustedQueue = newPoolEntryQueue(maxKnownEntries, nil)
 	pool.knownQueue = newPoolEntryQueue(maxKnownEntries, pool.removeEntry)
 	pool.newQueue = newPoolEntryQueue(maxNewEntries, pool.removeEntry)
 	return pool
@@ -168,6 +171,7 @@ func (pool *serverPool) start(server *p2p.Server, topic discv5.Topic) {
 	pool.dbKey = append([]byte("serverPool/"), []byte(topic)...)
 	pool.wg.Add(1)
 	pool.loadNodes()
+	pool.connectToTrustedNodes()

 	if pool.server.DiscV5 != nil {
 		pool.discSetPeriod = make(chan time.Duration, 1)
@@ -445,7 +449,7 @@ func (pool *serverPool) findOrNewNode(node *enode.Node) *poolEntry {
 	}
 	addr.lastSeen = now
 	entry.addrSelect.update(addr)
-	if !entry.known {
+	if !entry.known || !entry.trusted {
 		pool.newQueue.setLatest(entry)
 	}
 	return entry
@@ -475,6 +479,34 @@ func (pool *serverPool) loadNodes() {
 	}
 }

+func (pool *serverPool) connectToTrustedNodes() {
+	//connect to trusted nodes
+	if len(pool.trustedNodes) > 0 {
+		for _, trusted := range pool.parseTrustedServers() {
+			e := pool.findOrNewNode(trusted)
+			e.trusted = true
+			e.dialed = &poolEntryAddress{ip: trusted.IP(), port: uint16(trusted.TCP())}
+			pool.entries[e.node.ID()] = e
+			pool.trustedQueue.setLatest(e)
+		}
+	}
+}
+
+// parseTrustedServers returns valid and parsed by discovery enodes.
+func (pool *serverPool) parseTrustedServers() []*enode.Node {
+	nodes := make([]*enode.Node, 0, len(pool.trustedNodes))
+
+	for _, node := range pool.trustedNodes {
+		node, err := enode.ParseV4(node)
+		if err != nil {
+			log.Warn("Trusted node URL invalid", "enode", node, "err", err)
+			continue
+		}
+		nodes = append(nodes, node)
+	}
+	return nodes
+}
+
 // saveNodes saves known nodes and their statistics into the database. Nodes are
 // ordered from least to most recently connected.
 func (pool *serverPool) saveNodes() {
@@ -530,6 +562,10 @@ func (pool *serverPool) updateCheckDial(entry *poolEntry) {
 // checkDial checks if new dials can/should be made. It tries to select servers both
 // based on good statistics and recent discovery.
 func (pool *serverPool) checkDial() {
+	for _, e := range pool.trustedQueue.queue {
+		pool.dial(e, false)
+	}
+
 	fillWithKnownSelects := !pool.fastDiscover
 	for pool.knownSelected < targetKnownSelect {
 		entry := pool.knownSelect.choose()
@@ -566,15 +602,24 @@ func (pool *serverPool) dial(entry *poolEntry, knownSelected bool) {
 		return
 	}
 	entry.state = psDialed
-	entry.knownSelected = knownSelected
-	if knownSelected {
-		pool.knownSelected++
-	} else {
-		pool.newSelected++
+
+	if !entry.trusted {
+		entry.knownSelected = knownSelected
+		if knownSelected {
+			pool.knownSelected++
+		} else {
+			pool.newSelected++
+		}
+		addr := entry.addrSelect.choose().(*poolEntryAddress)
+		entry.dialed = addr
 	}
-	addr := entry.addrSelect.choose().(*poolEntryAddress)
-	log.Debug("Dialing new peer", "lesaddr", entry.node.ID().String()+"@"+addr.strKey(), "set", len(entry.addr), "known", knownSelected)
-	entry.dialed = addr
+
+	state := "known"
+	if entry.trusted {
+		state = "trusted"
+	}
+	log.Debug("Dialing new peer", "lesaddr", entry.node.ID().String()+"@"+entry.dialed.strKey(), "set", len(entry.addr), state, knownSelected)
+
 	go func() {
 		pool.server.AddPeer(entry.node)
 		select {
@@ -624,6 +669,7 @@ type poolEntry struct {

 	lastDiscovered              mclock.AbsTime
 	known, knownSelected        bool
+	trusted                     bool
 	connectStats, delayStats    poolStats
 	responseStats, timeoutStats poolStats
 	state                       int
@@ -843,7 +889,7 @@ func (q *poolEntryQueue) setLatest(entry *poolEntry) {
 	if q.queue[entry.queueIdx] == entry {
 		delete(q.queue, entry.queueIdx)
 	} else {
-		if len(q.queue) == q.maxCnt {
+		if len(q.queue) == q.maxCnt && q.removeFromPool != nil {
 			e := q.fetchOldest()
 			q.remove(e)
 			q.removeFromPool(e)
diff --git a/les/serverpool_test.go b/les/serverpool_test.go
new file mode 100644
index 0000000..05792fc
--- /dev/null
+++ b/les/serverpool_test.go
@@ -0,0 +1,68 @@
+package les
+
+import (
+	//"math/rand"
+	//"sync"
+	//"testing"
+
+	"github.com/ethereum/go-ethereum/ethdb"
+	//"github.com/ethereum/go-ethereum/p2p"
+	//"github.com/ethereum/go-ethereum/p2p/discover"
+	"github.com/ethereum/go-ethereum/rlp"
+	//"github.com/ethereum/go-ethereum/p2p/enode"
+)
+
+//func TestLoadTrustedNodes(t *testing.T) {
+//	node := enode.Node{
+//		id: discover.NodeID{},
+//	}
+//	rand.Read(node.ID[:])
+//
+//	var wg sync.WaitGroup
+//	q := make(chan struct{})
+//	sp := newServerPool(&dbStub{}, q, &wg, []string{node.String()})
+//	sp.server = &p2p.Server{}
+//	sp.server.TrustedNodes = []*enode.Node{
+//		&node,
+//	}
+//
+//	sp.loadNodes()
+//
+//	if len(sp.entries) == 0 {
+//		t.Fatal("empty nodes")
+//	}
+//	if _, ok := sp.entries[node.ID]; !ok {
+//		t.Fatal("empty entries")
+//	}
+//	if len(sp.trustedQueue.queue) != 1 {
+//		t.Fatal("incorrect trustedQueue.queue")
+//	}
+//	if sp.trustedQueue.queue[sp.entries[node.ID].queueIdx] != sp.entries[node.ID] {
+//		t.Fatal("not exist")
+//	}
+//	if sp.trustedQueue.newPtr != 1 {
+//		t.Fatal("incorrect ptr")
+//	}
+//}
+
+type dbStub struct{}
+
+func (db *dbStub) Put(key []byte, value []byte) error {
+	return nil
+}
+func (db *dbStub) Get(key []byte) ([]byte, error) {
+	list := make([]*poolEntry, 0)
+	return rlp.EncodeToBytes(&list)
+}
+func (db *dbStub) Has(key []byte) (bool, error) {
+	return false, nil
+}
+func (db *dbStub) Delete(key []byte) error {
+	return nil
+}
+func (db *dbStub) Close() {
+
+}
+func (db *dbStub) NewBatch() ethdb.Batch {
+	return nil
+}
diff --git a/les/sync.go b/les/sync.go
index eb15537..1ac6455 100644
--- a/les/sync.go
+++ b/les/sync.go
@@ -31,6 +31,7 @@ func (pm *ProtocolManager) syncer() {
 	// Start and ensure cleanup of sync mechanisms
 	//pm.fetcher.Start()
 	//defer pm.fetcher.Stop()
+	defer pm.downloader.Terminate()

 	// Wait for different events to fire synchronisation operations
 	//forceSync := time.Tick(forceSyncCycle)
diff --git a/les/txrelay.go b/les/txrelay.go
index 7a02cc8..38fc66a 100644
--- a/les/txrelay.go
+++ b/les/txrelay.go
@@ -121,7 +121,10 @@ func (self *LesTxRelay) send(txs types.Transactions, count int) {
 				return peer.GetRequestCost(SendTxMsg, len(ll))
 			},
 			canSend: func(dp distPeer) bool {
-				return dp.(*peer) == pp
+				if !dp.(*peer).isOnlyAnnounce {
+					return dp.(*peer) == pp
+				}
+				return false
 			},
 			request: func(dp distPeer) func() {
 				peer := dp.(*peer)
diff --git a/les/ulc.go b/les/ulc.go
new file mode 100644
index 0000000..d9f7dc7
--- /dev/null
+++ b/les/ulc.go
@@ -0,0 +1,39 @@
+package les
+
+import (
+	"fmt"
+
+	"github.com/ethereum/go-ethereum/eth"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+)
+
+type ulc struct {
+	trustedKeys        map[string]struct{}
+	minTrustedFraction int
+}
+
+func newULC(ulcConfig *eth.ULCConfig) *ulc {
+	if ulcConfig == nil {
+		return nil
+	}
+
+	m := make(map[string]struct{}, len(ulcConfig.TrustedServers))
+	for _, id := range ulcConfig.TrustedServers {
+		node, err := enode.ParseV4(id)
+		if err != nil {
+			fmt.Println("node:", id, " err:", err)
+			continue
+		}
+		m[node.ID().String()] = struct{}{}
+	}
+
+	return &ulc{m, ulcConfig.MinTrustedFraction}
+}
+
+func (u *ulc) isTrusted(p enode.ID) bool {
+	if u.trustedKeys == nil {
+		return false
+	}
+	_, ok := u.trustedKeys[p.String()]
+	return ok
+}
diff --git a/les/ulc_test.go b/les/ulc_test.go
new file mode 100644
index 0000000..91fdc77
--- /dev/null
+++ b/les/ulc_test.go
@@ -0,0 +1,247 @@
+package les
+
+import (
+	"fmt"
+	"reflect"
+	"testing"
+	"time"
+
+	"net"
+
+	"crypto/ecdsa"
+	"math/big"
+
+	"github.com/ethereum/go-ethereum/core"
+	"github.com/ethereum/go-ethereum/crypto"
+	"github.com/ethereum/go-ethereum/eth"
+	"github.com/ethereum/go-ethereum/ethdb"
+	"github.com/ethereum/go-ethereum/light"
+	"github.com/ethereum/go-ethereum/p2p"
+	"github.com/ethereum/go-ethereum/p2p/enode"
+)
+
+func TestULCSyncWithOnePeer(t *testing.T) {
+	f := newFullPeerPair(t, 1, 4, testChainGen)
+	ulcConfig := &eth.ULCConfig{
+		MinTrustedFraction: 100,
+		TrustedServers:     []string{f.Node.String()},
+	}
+
+	l := newLightPeer(t, ulcConfig)
+
+	if reflect.DeepEqual(f.PM.blockchain.CurrentHeader().Hash(), l.PM.blockchain.CurrentHeader().Hash()) {
+		t.Fatal("blocks are equal")
+	}
+
+	_, _, err := connectPeers(f, l, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	l.PM.fetcher.lock.Lock()
+	l.PM.fetcher.nextRequest()
+	l.PM.fetcher.lock.Unlock()
+
+	if !reflect.DeepEqual(f.PM.blockchain.CurrentHeader().Hash(), l.PM.blockchain.CurrentHeader().Hash()) {
+		t.Fatal("sync doesn't work")
+	}
+}
+
+func TestULCReceiveAnnounce(t *testing.T) {
+	f := newFullPeerPair(t, 1, 4, testChainGen)
+	ulcConfig := &eth.ULCConfig{
+		MinTrustedFraction: 100,
+		TrustedServers:     []string{f.Node.String()},
+	}
+
+	l := newLightPeer(t, ulcConfig)
+	fPeer, lPeer, err := connectPeers(f, l, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	l.PM.synchronise(fPeer)
+
+	//check that the sync is finished correctly
+	if !reflect.DeepEqual(f.PM.blockchain.CurrentHeader().Hash(), l.PM.blockchain.CurrentHeader().Hash()) {
+		t.Fatal("sync doesn't work")
+	}
+
+	l.PM.peers.lock.Lock()
+	if len(l.PM.peers.peers) == 0 {
+		t.Fatal("peer list should not be empty")
+	}
+	l.PM.peers.lock.Unlock()
+
+	time.Sleep(time.Second)
+	//send a signed announce message(payload doesn't matter)
+	td := f.PM.blockchain.GetTd(l.PM.blockchain.CurrentHeader().Hash(), l.PM.blockchain.CurrentHeader().Number.Uint64())
+	announce := announceData{
+		Number: l.PM.blockchain.CurrentHeader().Number.Uint64() + 1,
+		Td:     td.Add(td, big.NewInt(1)),
+	}
+	announce.sign(f.Key)
+
+	lPeer.SendAnnounce(announce)
+	time.Sleep(time.Millisecond)
+
+	l.PM.peers.lock.Lock()
+	if len(l.PM.peers.peers) == 0 {
+		t.Fatal("peer list after receiving message should not be empty")
+	}
+	l.PM.peers.lock.Unlock()
+}
+
+func TestULCShouldNotSyncWithTwoPeersOneHaveEmptyChain(t *testing.T) {
+	f1 := newFullPeerPair(t, 1, 4, testChainGen)
+	f2 := newFullPeerPair(t, 2, 0, nil)
+	ulcConf := &ulc{minTrustedFraction: 100, trustedKeys: make(map[string]struct{})}
+	ulcConf.trustedKeys[f1.Node.ID().String()] = struct{}{}
+	ulcConf.trustedKeys[f2.Node.ID().String()] = struct{}{}
+	ulcConfig := &eth.ULCConfig{
+		MinTrustedFraction: 100,
+		TrustedServers:     []string{f1.Node.String(), f2.Node.String()},
+	}
+	l := newLightPeer(t, ulcConfig)
+	l.PM.ulc.minTrustedFraction = 100
+
+	_, _, err := connectPeers(f1, l, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+	_, _, err = connectPeers(f2, l, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	l.PM.fetcher.lock.Lock()
+	l.PM.fetcher.nextRequest()
+	l.PM.fetcher.lock.Unlock()
+
+	if reflect.DeepEqual(f1.PM.blockchain.CurrentHeader().Hash(), l.PM.blockchain.CurrentHeader().Hash()) {
+		t.Fatal("Incorrect hash: second peer has empty chain")
+	}
+}
+
+func TestULCShouldNotSyncWithThreePeersOneHaveEmptyChain(t *testing.T) {
+	f1 := newFullPeerPair(t, 1, 3, testChainGen)
+	f2 := newFullPeerPair(t, 2, 4, testChainGen)
+	f3 := newFullPeerPair(t, 3, 0, nil)
+
+	ulcConfig := &eth.ULCConfig{
+		MinTrustedFraction: 60,
+		TrustedServers:     []string{f1.Node.String(), f2.Node.String(), f3.Node.String()},
+	}
+
+	l := newLightPeer(t, ulcConfig)
+	_, _, err := connectPeers(f1, l, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, _, err = connectPeers(f2, l, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	_, _, err = connectPeers(f3, l, 2)
+	if err != nil {
+		t.Fatal(err)
+	}
+
+	l.PM.fetcher.lock.Lock()
+	l.PM.fetcher.nextRequest()
+	l.PM.fetcher.lock.Unlock()
+
+	if !reflect.DeepEqual(f1.PM.blockchain.CurrentHeader().Hash(), l.PM.blockchain.CurrentHeader().Hash()) {
+		t.Fatal("Incorrect hash")
+	}
+}
+
+type pairPeer struct {
+	Name string
+	Node *enode.Node
+	PM   *ProtocolManager
+	Key  *ecdsa.PrivateKey
+}
+
+func connectPeers(full, light pairPeer, version int) (*peer, *peer, error) {
+	// Create a message pipe to communicate through
+	app, net := p2p.MsgPipe()
+
+	peerLight := full.PM.newPeer(version, NetworkId, p2p.NewPeer(light.Node.ID(), light.Name, nil), net)
+	peerFull := light.PM.newPeer(version, NetworkId, p2p.NewPeer(full.Node.ID(), full.Name, nil), app)
+
+	// Start the peerLight on a new thread
+	errc1 := make(chan error, 1)
+	errc2 := make(chan error, 1)
+	go func() {
+		select {
+		case light.PM.newPeerCh <- peerFull:
+			errc1 <- light.PM.handle(peerFull)
+		case <-light.PM.quitSync:
+			errc1 <- p2p.DiscQuitting
+		}
+	}()
+	go func() {
+		select {
+		case full.PM.newPeerCh <- peerLight:
+			errc2 <- full.PM.handle(peerLight)
+		case <-full.PM.quitSync:
+			errc2 <- p2p.DiscQuitting
+		}
+	}()
+
+	select {
+	case <-time.After(time.Millisecond * 100):
+	case err := <-errc1:
+		return nil, nil, fmt.Errorf("peerLight handshake error: %v", err)
+	case err := <-errc2:
+		return nil, nil, fmt.Errorf("peerFull handshake error: %v", err)
+	}
+
+	return peerFull, peerLight, nil
+}
+
+// newFullPeerPair creates node with full sync mode
+func newFullPeerPair(t *testing.T, index int, numberOfblocks int, chainGen func(int, *core.BlockGen)) pairPeer {
+	db := ethdb.NewMemDatabase()
+
+	pmFull := newTestProtocolManagerMust(t, false, numberOfblocks, chainGen, nil, nil, db, nil)
+
+	peerPairFull := pairPeer{
+		Name: "full node",
+		PM:   pmFull,
+	}
+	key, err := crypto.GenerateKey()
+	if err != nil {
+		t.Fatal("generate key err:", err)
+	}
+	peerPairFull.Key = key
+	peerPairFull.Node = enode.NewV4(&key.PublicKey, net.ParseIP("127.0.0.1"), 35000, 35000)
+	return peerPairFull
+}
+
+// newLightPeer creates node with light sync mode
+func newLightPeer(t *testing.T, ulcConfig *eth.ULCConfig) pairPeer {
+	peers := newPeerSet()
+	dist := newRequestDistributor(peers, make(chan struct{}))
+	rm := newRetrieveManager(peers, dist, nil)
+	ldb := ethdb.NewMemDatabase()
+
+	odr := NewLesOdr(ldb, light.DefaultClientIndexerConfig, rm)
+
+	pmLight := newTestProtocolManagerMust(t, true, 0, nil, odr, peers, ldb, ulcConfig)
+	peerPairLight := pairPeer{
+		Name: "ulc node",
+		PM:   pmLight,
+	}
+
+	key, err := crypto.GenerateKey()
+	if err != nil {
+		t.Fatal("generate key err:", err)
+	}
+	peerPairLight.Key = key
+	peerPairLight.Node = enode.NewV4(&key.PublicKey, net.IP{}, 35000, 35000)
+	return peerPairLight
+}
diff --git a/light/lightchain.go b/light/lightchain.go
index 8e2734c..0b5571b 100644
--- a/light/lightchain.go
+++ b/light/lightchain.go
@@ -71,6 +71,8 @@ type LightChain struct {
 	wg            sync.WaitGroup

 	engine consensus.Engine
+
+	disableCheckFreq bool
 }

 // NewLightChain returns a fully initialised light chain using information
@@ -355,6 +357,9 @@ func (self *LightChain) postChainEvents(events []interface{}) {
 // In the case of a light chain, InsertHeaderChain also creates and posts light
 // chain events when necessary.
 func (self *LightChain) InsertHeaderChain(chain []*types.Header, checkFreq int) (int, error) {
+	if self.disableCheckFreq {
+		checkFreq = 0
+	}
 	start := time.Now()
 	if i, err := self.hc.ValidateHeaderChain(chain, checkFreq); err != nil {
 		return i, err
@@ -533,3 +538,17 @@ func (self *LightChain) SubscribeLogsEvent(ch chan<- []*types.Log) event.Subscri
 func (self *LightChain) SubscribeRemovedLogsEvent(ch chan<- core.RemovedLogsEvent) event.Subscription {
 	return self.scope.Track(new(event.Feed).Subscribe(ch))
 }
+
+//DisableCheckFreq disables header validation. It needs for ULC
+func (self *LightChain) DisableCheckFreq() {
+	self.mu.Lock()
+	defer self.mu.Unlock()
+	self.disableCheckFreq = true
+}
+
+//EnableCheckFreq enables header validation
+func (self *LightChain) EnableCheckFreq() {
+	self.mu.Lock()
+	defer self.mu.Unlock()
+	self.disableCheckFreq = false
+}
diff --git a/metrics/counter.go b/metrics/counter.go
index c7f2b4b..fbb14b8 100644
--- a/metrics/counter.go
+++ b/metrics/counter.go
@@ -1,6 +1,8 @@
 package metrics

-import "sync/atomic"
+import (
+	"sync/atomic"
+)

 // Counters hold an int64 value that can be incremented and decremented.
 type Counter interface {
@@ -28,6 +30,12 @@ func NewCounter() Counter {
 	return &StandardCounter{0}
 }

+// NewCounterForced constructs a new StandardCounter and returns it no matter if
+// the global switch is enabled or not.
+func NewCounterForced() Counter {
+	return &StandardCounter{0}
+}
+
 // NewRegisteredCounter constructs and registers a new StandardCounter.
 func NewRegisteredCounter(name string, r Registry) Counter {
 	c := NewCounter()
@@ -38,6 +46,19 @@ func NewRegisteredCounter(name string, r Registry) Counter {
 	return c
 }

+// NewRegisteredCounterForced constructs and registers a new StandardCounter
+// and launches a goroutine no matter the global switch is enabled or not.
+// Be sure to unregister the counter from the registry once it is of no use to
+// allow for garbage collection.
+func NewRegisteredCounterForced(name string, r Registry) Counter {
+	c := NewCounterForced()
+	if nil == r {
+		r = DefaultRegistry
+	}
+	r.Register(name, c)
+	return c
+}
+
 // CounterSnapshot is a read-only copy of another Counter.
 type CounterSnapshot int64

diff --git a/mobile/geth.go b/mobile/geth.go
index e3e2e90..4d674b2 100644
--- a/mobile/geth.go
+++ b/mobile/geth.go
@@ -76,6 +76,9 @@ type NodeConfig struct {

 	// Listening address of pprof server.
 	PprofAddress string
+
+	// Ultra Light client options
+	ULC *eth.ULCConfig
 }

 // defaultNodeConfig contains the default node configuration values to use if all
diff --git a/p2p/enode/node.go b/p2p/enode/node.go
index 84088fc..b454ab2 100644
--- a/p2p/enode/node.go
+++ b/p2p/enode/node.go
@@ -98,6 +98,13 @@ func (n *Node) Pubkey() *ecdsa.PublicKey {
 	return &key
 }

+// Record returns the node's record. The return value is a copy and may
+// be modified by the caller.
+func (n *Node) Record() *enr.Record {
+	cpy := n.r
+	return &cpy
+}
+
 // checks whether n is a valid complete node.
 func (n *Node) ValidateComplete() error {
 	if n.Incomplete() {