diff --git a/core/access/chain_access.go b/core/access/chain_access.go
index b41dd296f8..6e5d68f4f5 100644
--- a/core/access/chain_access.go
+++ b/core/access/chain_access.go
@@ -56,15 +56,18 @@ type ChainAccess struct {
 type requestFunc func(*Peer) error
 type validatorFunc func(*Msg) bool
 
+// Request waiting for an answer that satisfies its valFunc
 type sentReq struct {
 	valFunc     validatorFunc
 	deliverChan chan *Msg
 }
 
+// Create a ChainAccess with ODR disabled
 func NewDbChainAccess(db ethdb.Database) *ChainAccess {
 	return NewChainAccess(db, false)
 }
 
+// Create a ChainAccess
 func NewChainAccess(db ethdb.Database, odr bool) *ChainAccess {
 	return &ChainAccess{
 		db:       db,
@@ -107,6 +110,11 @@ type Msg struct {
 	Obj     interface{}
 }
 
+// ODR request interface (passed to Retrieve, functions called by Retrieve and Deliver)
+//	DbGet() tries to retrieve the object from the local database (object is stored by the request struct in memory if retrieved)
+//	DbPut() stores it in the local database
+//	Request(*Peer) requests it from a LES peer
+//	Valid(*Msg) checks if a message is a valid answer to this request and stores the retrieved object in memory
 type ObjectAccess interface {
 	// database storage
 	DbGet() bool
@@ -116,6 +124,7 @@ type ObjectAccess interface {
 	Valid(*Msg) bool // if true, keeps the retrieved object
 }
 
+// Deliver is called by the LES protocol manager to deliver ODR reply messages to waiting requests
 func (self *ChainAccess) Deliver(id string, msg *Msg) (processed bool) {
 	self.lock.Lock()
 	defer self.lock.Unlock()
@@ -130,6 +139,7 @@ func (self *ChainAccess) Deliver(id string, msg *Msg) (processed bool) {
 	return false
 }
 
+// Send a request to known peers until an answer is received or the context is cancelled
 func (self *ChainAccess) networkRequest(rqFunc requestFunc, valFunc validatorFunc, ctx *OdrContext) (*Msg, error) {
 	req := &sentReq{
 		deliverChan: make(chan *Msg),
@@ -175,6 +185,8 @@ func (self *ChainAccess) networkRequest(rqFunc requestFunc, valFunc validatorFun
 	}
 }
 
+// Retrieve tries to fetch an object from the local db, then from the LES network.
+// If the network retrieval was successful, it stores the object in local db.
 func (self *ChainAccess) Retrieve(obj ObjectAccess, ctx *OdrContext) (err error) {
 	// look in db
 	if obj.DbGet() {
diff --git a/core/access/context.go b/core/access/context.go
index 652c9a1cd6..ee9b4e2384 100644
--- a/core/access/context.go
+++ b/core/access/context.go
@@ -23,6 +23,7 @@ import (
 	"time"
 )
 
+// Context for ODR requests, can be timed out or cancelled manually
 type OdrContext struct {
 	cancel, cancelOrTimeout chan struct{}
 	id                      *OdrChannelID
@@ -64,6 +65,10 @@ func (self *OdrContext) IsCancelled() bool {
 	return atomic.LoadInt32(&self.cancelled) == 1
 }
 
+// While contexts are created for each request, channel ID is a permanent
+//  identifier of a source from where requests can come (like an RPC channel).
+//  (needed for future functions like "list of my waiting requests" and
+//  "cancel all requests from this channel")
 type OdrChannelID struct {
 	timeout time.Duration
 }
diff --git a/core/access/peer.go b/core/access/peer.go
index 2b30a400b0..43d1d2a67e 100644
--- a/core/access/peer.go
+++ b/core/access/peer.go
@@ -42,6 +42,7 @@ type getNodeDataFn func([]common.Hash) error
 type getReceiptsFn func([]common.Hash) error
 type getProofsFn func([]*ProofReq) error
 
+// access.Peer stores ODR-specific information about LES peers that are able to serve requests
 type Peer struct {
 	id   string      // Unique identifier of the peer
 	head common.Hash // Hash of the peers latest known block
diff --git a/core/blockchain.go b/core/blockchain.go
index 5bb452869f..43e7ed530d 100644
--- a/core/blockchain.go
+++ b/core/blockchain.go
@@ -374,6 +374,7 @@ func (self *BlockChain) CurrentBlock() *types.Block {
 	return self.CurrentBlockOdr(access.NoOdr)	
 }
 
+// CurrentBlockOdr retrieves the current head block, using ODR in light mode
 func (self *BlockChain) CurrentBlockOdr(ctx *access.OdrContext) *types.Block {
 	self.mu.RLock()
 	defer self.mu.RUnlock()
diff --git a/core/core_access.go b/core/core_access.go
index a5a108ceaf..d7a68c4798 100644
--- a/core/core_access.go
+++ b/core/core_access.go
@@ -28,6 +28,7 @@ import (
 	"github.com/ethereum/go-ethereum/rlp"
 )
 
+// ODR request type for block bodies, see access.ObjectAccess interface
 type BlockAccess struct {
 	db        ethdb.Database
 	blockHash common.Hash
@@ -87,6 +88,7 @@ func (self *BlockAccess) DbPut() {
 	glog.V(access.LogLevel).Infof("ODR: put body %08x  len = %d", self.blockHash[:4], len(self.rlp))
 }
 
+// ODR request type for block receipts by block hash, see access.ObjectAccess interface
 type ReceiptsAccess struct {
 	db        ethdb.Database
 	blockHash common.Hash
diff --git a/core/state/state_access.go b/core/state/state_access.go
index c4145b5791..68e0949ebc 100644
--- a/core/state/state_access.go
+++ b/core/state/state_access.go
@@ -53,6 +53,7 @@ func (self *TrieAccess) OdrEnabled() bool {
 	return self.ca.OdrEnabled()
 }
 
+// ODR request type for state/storage trie entries, see access.ObjectAccess interface
 type TrieEntryAccess struct {
 	root       common.Hash
 	trieDb     trie.Database
@@ -101,6 +102,7 @@ func (self *TrieEntryAccess) DbPut() {
 	trie.StoreProof(self.trieDb, self.proof)
 }
 
+// ODR request type for node data (used for retrieving contract code), see access.ObjectAccess interface
 type NodeDataAccess struct {
 	db   ethdb.Database
 	hash common.Hash
diff --git a/core/state/statedb.go b/core/state/statedb.go
index 39632407ac..152335e2c9 100644
--- a/core/state/statedb.go
+++ b/core/state/statedb.go
@@ -54,6 +54,7 @@ type StateDB struct {
 }
 
 // Create a new state from a given trie
+//  When ODR is used, context is specified when creating/copying a state.
 func New(root common.Hash, ca *access.ChainAccess, ctx *access.OdrContext) (*StateDB, error) {
 	tr, err := trie.NewSecure(root, ca.Db(), NewTrieAccess(ca, root, ca.Db()))
 	if err != nil {
@@ -297,10 +298,12 @@ func (self *StateDB) CreateAccount(addr common.Address) vm.Account {
 // Setting, copying of the state methods
 //
 
+// Copy state, keep the original ODR context
 func (self *StateDB) CopyWithCtx() *StateDB {
 	return self.Copy(self.ctx)
 }
 
+// Copy with a new context
 func (self *StateDB) Copy(ctx *access.OdrContext) *StateDB {
 	// ignore error - we assume state-to-be-copied always exists
 	state, _ := New(common.Hash{}, self.ca, ctx)
diff --git a/rpc/shared/types.go b/rpc/shared/types.go
index 7dd6fb2d9a..94ea5530d7 100644
--- a/rpc/shared/types.go
+++ b/rpc/shared/types.go
@@ -40,6 +40,8 @@ type EthereumApi interface {
 }
 
 // RPC request
+// (ODR context is propagated inside the request struct because every
+//  request has its own context. It does not influence JSON encoding.)
 type Request struct {
 	Id      interface{}     `json:"id"`
 	Jsonrpc string          `json:"jsonrpc"`