diff --git a/internal/handler/msgpack.go b/internal/handler/msgpack.go
index 80d4a8a..2ad12ec 100644
--- a/internal/handler/msgpack.go
+++ b/internal/handler/msgpack.go
@@ -21,6 +21,7 @@ import (
 	"errors"
 	"fmt"
 	"sync"
+	"time"
 
 	"github.com/shamaton/msgpackgen/msgpack"
 	"github.com/sirupsen/logrus"
@@ -32,185 +33,186 @@ import (
 	"git.cacert.org/cacert-gosigner/pkg/messages"
 )
 
-// MsgPackHandler is a Handler implementation for the msgpack serialization format.
+const readCommandTimeOut = 5 * time.Second
+
+var errReadCommandTimeout = errors.New("read command timeout expired")
+
+// MsgPackHandler is a ServerHandler implementation for the msgpack serialization format.
 type MsgPackHandler struct {
 	logger          *logrus.Logger
 	healthHandler   *health.Handler
 	fetchCRLHandler *revoking.FetchCRLHandler
-	currentCommand  *protocol.Command
-	currentResponse *protocol.Response
 	lock            sync.Mutex
 }
 
-func (m *MsgPackHandler) HandleCommandAnnounce(frame []byte) error {
+func (m *MsgPackHandler) CommandAnnounce(frames chan []byte) (*protocol.Command, error) {
 	m.lock.Lock()
 	defer m.lock.Unlock()
 
+	frame := <-frames
+
 	var ann messages.CommandAnnounce
 
 	if err := msgpack.Unmarshal(frame, &ann); err != nil {
-		return fmt.Errorf("could not unmarshal command announcement: %w", err)
+		return nil, fmt.Errorf("could not unmarshal command announcement: %w", err)
 	}
 
 	m.logger.WithField("announcement", &ann).Info("received command announcement")
 
-	m.currentCommand = &protocol.Command{Announce: &ann}
-
-	return nil
+	return &protocol.Command{Announce: &ann}, nil
 }
 
-func (m *MsgPackHandler) HandleCommand(frame []byte) error {
+func (m *MsgPackHandler) CommandData(frames chan []byte, command *protocol.Command) error {
 	m.lock.Lock()
 	defer m.lock.Unlock()
 
-	err := m.parseCommand(frame)
-	if err != nil {
-		m.currentResponse = m.buildErrorResponse(err.Error())
-
-		m.logCommandResponse()
+	select {
+	case frame := <-frames:
+		err := m.parseCommand(frame, command)
+		if err != nil {
+			return err
+		}
 
 		return nil
+	case <-time.After(readCommandTimeOut):
+		return errReadCommandTimeout
 	}
+}
 
-	err = m.handleCommand()
+func (m *MsgPackHandler) HandleCommand(command *protocol.Command) (*protocol.Response, error) {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+
+	var (
+		response *protocol.Response
+		err      error
+	)
+
+	response, err = m.handleCommand(command)
 	if err != nil {
 		m.logger.WithError(err).Error("command handling failed")
 
-		return err
+		response = m.buildErrorResponse(command.Announce.ID, "command handling failed")
 	}
 
-	m.logCommandResponse()
+	m.logCommandResponse(command, response)
 
-	m.currentCommand = nil
+	return response, nil
+}
+
+func (m *MsgPackHandler) logCommandResponse(command *protocol.Command, response *protocol.Response) {
+	m.logger.WithField("command", command.Announce).Info("handled command")
+	m.logger.WithField("command", command).WithField("response", response).Debug("command and response")
+}
+
+func (m *MsgPackHandler) Respond(response *protocol.Response, out chan []byte) error {
+	m.lock.Lock()
+	defer m.lock.Unlock()
+
+	announce, err := msgpack.Marshal(response)
+	if err != nil {
+		return fmt.Errorf("could not marshal response announcement: %w", err)
+	}
+
+	m.logger.WithField("length", len(announce)).Debug("write response announcement")
+
+	out <- announce
+
+	data, err := msgpack.Marshal(response.Response)
+	if err != nil {
+		return fmt.Errorf("could not marshal response: %w", err)
+	}
+
+	m.logger.WithField("length", len(data)).Debug("write response")
+
+	out <- announce
 
 	return nil
 }
 
-func (m *MsgPackHandler) logCommandResponse() {
-	m.logger.WithField("command", m.currentCommand.Announce).Info("handled command")
-	m.logger.WithField(
-		"command",
-		m.currentCommand,
-	).WithField(
-		"response",
-		m.currentResponse,
-	).Debug("command and response")
-}
-
-func (m *MsgPackHandler) ResponseAnnounce() ([]byte, error) {
-	m.lock.Lock()
-	defer m.lock.Unlock()
-
-	announceData, err := msgpack.Marshal(m.currentResponse.Announce)
-	if err != nil {
-		return nil, fmt.Errorf("could not marshal response announcement: %w", err)
-	}
-
-	m.logger.WithField("announcement", m.currentResponse.Announce).Debug("write response announcement")
-
-	return announceData, nil
-}
-
-func (m *MsgPackHandler) ResponseData() ([]byte, error) {
-	m.lock.Lock()
-	defer m.lock.Unlock()
-
-	responseData, err := msgpack.Marshal(m.currentResponse.Response)
-	if err != nil {
-		return nil, fmt.Errorf("could not marshal response: %w", err)
-	}
-
-	m.logger.WithField("response", m.currentResponse.Response).Debug("write response")
-
-	return responseData, nil
-}
-
-func (m *MsgPackHandler) parseHealthCommand(frame []byte) error {
+func (m *MsgPackHandler) parseHealthCommand(frame []byte) (*messages.HealthCommand, error) {
 	var command messages.HealthCommand
 
 	if err := msgpack.Unmarshal(frame, &command); err != nil {
 		m.logger.WithError(err).Error("unmarshal failed")
 
-		return errors.New("could not unmarshal health command")
+		return nil, errors.New("could not unmarshal health command")
 	}
 
-	m.currentCommand.Command = &command
-
-	return nil
+	return &command, nil
 }
 
-func (m *MsgPackHandler) parseFetchCRLCommand(frame []byte) error {
+func (m *MsgPackHandler) parseFetchCRLCommand(frame []byte) (*messages.FetchCRLCommand, error) {
 	var command messages.FetchCRLCommand
 
 	if err := msgpack.Unmarshal(frame, &command); err != nil {
 		m.logger.WithError(err).Error("unmarshal failed")
 
-		return errors.New("could not unmarshal fetch crl command")
+		return nil, errors.New("could not unmarshal fetch crl command")
 	}
 
-	m.currentCommand.Command = &command
-
-	return nil
+	return &command, nil
 }
 
-func (m *MsgPackHandler) currentID() string {
-	return m.currentCommand.Announce.ID
-}
-
-func (m *MsgPackHandler) handleCommand() error {
+func (m *MsgPackHandler) handleCommand(command *protocol.Command) (*protocol.Response, error) {
 	var (
-		err          error
-		responseData interface{}
 		responseCode messages.ResponseCode
+		responseData interface{}
 	)
 
-	switch m.currentCommand.Command.(type) {
+	switch cmd := command.Command.(type) {
 	case *messages.HealthCommand:
 		response, err := m.handleHealthCommand()
 		if err != nil {
-			return err
+			return nil, err
 		}
 
 		responseCode, responseData = messages.RespHealth, response
 	case *messages.FetchCRLCommand:
-		response, err := m.handleFetchCRLCommand()
+		response, err := m.handleFetchCRLCommand(cmd)
 		if err != nil {
-			return err
+			return nil, err
 		}
 
 		responseCode, responseData = messages.RespFetchCRL, response
 	default:
-		return fmt.Errorf("unhandled command %s", m.currentCommand.Announce)
+		return nil, fmt.Errorf("unhandled command %s", command.Announce)
 	}
 
-	if err != nil {
-		return fmt.Errorf("error from command handler: %w", err)
-	}
-
-	m.currentResponse = &protocol.Response{
-		Announce: messages.BuildResponseAnnounce(responseCode, m.currentID()),
+	return &protocol.Response{
+		Announce: messages.BuildResponseAnnounce(responseCode, command.Announce.ID),
 		Response: responseData,
-	}
-
-	return nil
+	}, nil
 }
 
-func (m *MsgPackHandler) buildErrorResponse(errMsg string) *protocol.Response {
+func (m *MsgPackHandler) buildErrorResponse(commandID string, errMsg string) *protocol.Response {
 	return &protocol.Response{
-		Announce: messages.BuildResponseAnnounce(messages.RespError, m.currentID()),
+		Announce: messages.BuildResponseAnnounce(messages.RespError, commandID),
 		Response: &messages.ErrorResponse{Message: errMsg},
 	}
 }
 
-func (m *MsgPackHandler) parseCommand(frame []byte) error {
-	switch m.currentCommand.Announce.Code {
+func (m *MsgPackHandler) parseCommand(frame []byte, command *protocol.Command) error {
+	switch command.Announce.Code {
 	case messages.CmdHealth:
-		return m.parseHealthCommand(frame)
+		healthCommand, err := m.parseHealthCommand(frame)
+		if err != nil {
+			return err
+		}
+
+		command.Command = healthCommand
 	case messages.CmdFetchCRL:
-		return m.parseFetchCRLCommand(frame)
+		fetchCRLCommand, err := m.parseFetchCRLCommand(frame)
+		if err != nil {
+			return err
+		}
+
+		command.Command = fetchCRLCommand
 	default:
-		return fmt.Errorf("unhandled command code %s", m.currentCommand.Announce.Code)
+		return fmt.Errorf("unhandled command code %s", command.Announce.Code)
 	}
+
+	return nil
 }
 
 func (m *MsgPackHandler) handleHealthCommand() (*messages.HealthResponse, error) {
@@ -235,27 +237,20 @@ func (m *MsgPackHandler) handleHealthCommand() (*messages.HealthResponse, error)
 	return response, nil
 }
 
-func (m *MsgPackHandler) handleFetchCRLCommand() (*messages.FetchCRLResponse, error) {
-	fetchCRLPayload, ok := m.currentCommand.Command.(*messages.FetchCRLCommand)
-	if !ok {
-		return nil, fmt.Errorf("could not use payload as FetchCRLPayload")
-	}
-
-	res, err := m.fetchCRLHandler.FetchCRL(fetchCRLPayload.IssuerID)
+func (m *MsgPackHandler) handleFetchCRLCommand(command *messages.FetchCRLCommand) (*messages.FetchCRLResponse, error) {
+	res, err := m.fetchCRLHandler.FetchCRL(command.IssuerID)
 	if err != nil {
 		return nil, fmt.Errorf("could not fetch CRL: %w", err)
 	}
 
-	response := &messages.FetchCRLResponse{
+	return &messages.FetchCRLResponse{
 		IsDelta:   false,
 		CRLNumber: res.Number,
 		CRLData:   res.CRLData,
-	}
-
-	return response, nil
+	}, nil
 }
 
-func New(logger *logrus.Logger, handlers ...RegisterHandler) (protocol.Handler, error) {
+func New(logger *logrus.Logger, handlers ...RegisterHandler) (protocol.ServerHandler, error) {
 	messages.RegisterGeneratedResolver()
 
 	h := &MsgPackHandler{
diff --git a/internal/serial/seriallink.go b/internal/serial/seriallink.go
index 41cc9a7..8f6557e 100644
--- a/internal/serial/seriallink.go
+++ b/internal/serial/seriallink.go
@@ -20,8 +20,8 @@ package serial
 
 import (
 	"context"
+	"errors"
 	"fmt"
-	"sync"
 
 	"github.com/sirupsen/logrus"
 	"github.com/tarm/serial"
@@ -35,22 +35,15 @@ type protocolState int8
 const (
 	cmdAnnounce protocolState = iota
 	cmdData
-	respAnnounce
-	respData
+	handleCommand
+	respond
 )
 
-var validTransitions = map[protocolState]protocolState{
-	cmdAnnounce:  cmdData,
-	cmdData:      respAnnounce,
-	respAnnounce: respData,
-	respData:     cmdAnnounce,
-}
-
 var protocolStateNames = map[protocolState]string{
-	cmdAnnounce:  "CMD ANNOUNCE",
-	cmdData:      "CMD DATA",
-	respAnnounce: "RESP ANNOUNCE",
-	respData:     "RESP DATA",
+	cmdAnnounce:   "CMD ANNOUNCE",
+	cmdData:       "CMD DATA",
+	handleCommand: "RESP ANNOUNCE",
+	respond:       "RESP DATA",
 }
 
 func (p protocolState) String() string {
@@ -62,13 +55,12 @@ func (p protocolState) String() string {
 }
 
 type Handler struct {
-	protocolHandler protocol.Handler
+	protocolHandler protocol.ServerHandler
 	protocolState   protocolState
 	framer          protocol.Framer
 	config          *serial.Config
 	port            *serial.Port
 	logger          *logrus.Logger
-	lock            sync.Mutex
 	framesIn        chan []byte
 	framesOut       chan []byte
 }
@@ -95,152 +87,129 @@ func (h *Handler) Close() error {
 
 func (h *Handler) Run(ctx context.Context) error {
 	h.protocolState = cmdAnnounce
-	errors := make(chan error)
+	protocolErrors, framerErrors := make(chan error), make(chan error)
 
 	go func() {
 		err := h.framer.ReadFrames(h.port, h.framesIn)
 
-		errors <- err
+		framerErrors <- err
 	}()
 
 	go func() {
 		err := h.framer.WriteFrames(h.port, h.framesOut)
 
-		errors <- err
+		framerErrors <- err
+	}()
+
+	go func() {
+		err := h.handleProtocolState()
+
+		protocolErrors <- err
 	}()
 
 	for {
 		select {
 		case <-ctx.Done():
 			return nil
-
-		case err := <-errors:
+		case err := <-framerErrors:
 			if err != nil {
-				return fmt.Errorf("error from handler loop: %w", err)
+				return fmt.Errorf("error from framer: %w", err)
 			}
 
 			return nil
-
-		default:
-			if err := h.handleProtocolState(); err != nil {
-				return err
+		case err := <-protocolErrors:
+			if err != nil {
+				return fmt.Errorf("error from protocol handler: %w", err)
 			}
+
+			return nil
 		}
 	}
 }
 
-func (h *Handler) nextState() error {
-	next, ok := validTransitions[h.protocolState]
-	if !ok {
-		return fmt.Errorf("illegal protocol state %s", h.protocolState)
-	}
-
-	h.protocolState = next
-
-	return nil
-}
+var errCommandExpected = errors.New("command must not be nil")
+var errResponseExpected = errors.New("response must not be nil")
 
 func (h *Handler) handleProtocolState() error {
-	h.logger.Tracef("handling protocol state %s", h.protocolState)
+	var (
+		command  *protocol.Command
+		response *protocol.Response
+		err      error
+	)
 
-	h.lock.Lock()
-	defer h.lock.Unlock()
+	for {
+		h.logger.Debugf("handling protocol state %s", h.protocolState)
 
-	switch h.protocolState {
-	case cmdAnnounce:
-		if err := h.handleCmdAnnounce(); err != nil {
-			return err
+		switch h.protocolState {
+		case cmdAnnounce:
+			command, err = h.protocolHandler.CommandAnnounce(h.framesIn)
+			if err != nil {
+				h.logger.WithError(err).Error("could not handle command announce")
+
+				break
+			}
+
+			h.protocolState = cmdData
+		case cmdData:
+			if command == nil {
+				return errCommandExpected
+			}
+
+			err = h.protocolHandler.CommandData(h.framesIn, command)
+			if err != nil {
+				h.logger.WithError(err).Error("could not handle command data")
+
+				h.protocolState = cmdAnnounce
+
+				break
+			}
+
+			h.protocolState = handleCommand
+		case handleCommand:
+			if command == nil {
+				return errCommandExpected
+			}
+
+			response, err = h.protocolHandler.HandleCommand(command)
+			if err != nil {
+				h.logger.WithError(err).Error("could not handle command")
+
+				h.protocolState = cmdAnnounce
+
+				break
+			}
+
+			command = nil
+
+			h.protocolState = respond
+		case respond:
+			if response == nil {
+				return errResponseExpected
+			}
+
+			err = h.protocolHandler.Respond(response, h.framesOut)
+			if err != nil {
+				h.logger.WithError(err).Error("could not respond")
+
+				h.protocolState = cmdAnnounce
+
+				break
+			}
+
+			response = nil
+
+			h.protocolState = cmdAnnounce
+		default:
+			return fmt.Errorf("unknown protocol state %s", h.protocolState)
 		}
-	case cmdData:
-		if err := h.handleCmdData(); err != nil {
-			return err
-		}
-	case respAnnounce:
-		if err := h.handleRespAnnounce(); err != nil {
-			return err
-		}
-	case respData:
-		if err := h.handleRespData(); err != nil {
-			return err
-		}
-	default:
-		return fmt.Errorf("unknown protocol state %s", h.protocolState)
 	}
-
-	return nil
 }
 
-func (h *Handler) handleCmdAnnounce() error {
-	h.logger.Trace("waiting for command announce")
-
-	frame := <-h.framesIn
-
-	if frame == nil {
-		return nil
-	}
-
-	if err := h.protocolHandler.HandleCommandAnnounce(frame); err != nil {
-		return fmt.Errorf("command announce handling failed: %w", err)
-	}
-
-	if err := h.nextState(); err != nil {
-		return err
-	}
-
-	return nil
-}
-
-func (h *Handler) handleCmdData() error {
-	h.logger.Trace("waiting for command data")
-
-	frame := <-h.framesIn
-
-	if frame == nil {
-		return nil
-	}
-
-	if err := h.protocolHandler.HandleCommand(frame); err != nil {
-		return fmt.Errorf("command handler failed: %w", err)
-	}
-
-	if err := h.nextState(); err != nil {
-		return err
-	}
-
-	return nil
-}
-
-func (h *Handler) handleRespAnnounce() error {
-	frame, err := h.protocolHandler.ResponseAnnounce()
-	if err != nil {
-		return fmt.Errorf("could not get response announcement: %w", err)
-	}
-
-	h.framesOut <- frame
-
-	if err := h.nextState(); err != nil {
-		return err
-	}
-
-	return nil
-}
-
-func (h *Handler) handleRespData() error {
-	frame, err := h.protocolHandler.ResponseData()
-	if err != nil {
-		return fmt.Errorf("could not get response data: %w", err)
-	}
-
-	h.framesOut <- frame
-
-	if err := h.nextState(); err != nil {
-		return err
-	}
-
-	return nil
-}
-
-func New(cfg *config.Serial, logger *logrus.Logger, protocolHandler protocol.Handler) (*Handler, error) {
+func New(
+	cfg *config.Serial,
+	logger *logrus.Logger,
+	protocolHandler protocol.ServerHandler,
+) (*Handler, error) {
 	h := &Handler{
 		protocolHandler: protocolHandler,
 		logger:          logger,
diff --git a/pkg/protocol/protocol.go b/pkg/protocol/protocol.go
index 58dbda6..f2b6ba8 100644
--- a/pkg/protocol/protocol.go
+++ b/pkg/protocol/protocol.go
@@ -51,16 +51,16 @@ func (r *Response) String() string {
 	return fmt.Sprintf("Rsp[announce={%s}, data={%s}]", r.Announce, r.Response)
 }
 
-// Handler is responsible for parsing incoming frames and calling commands
-type Handler interface {
-	// HandleCommandAnnounce handles the initial announcement of a command.
-	HandleCommandAnnounce([]byte) error
-	// HandleCommand handles the command data.
-	HandleCommand([]byte) error
-	// ResponseAnnounce generates the announcement for a response.
-	ResponseAnnounce() ([]byte, error)
-	// ResponseData generates the response data.
-	ResponseData() ([]byte, error)
+// ServerHandler is responsible for parsing incoming frames and calling commands
+type ServerHandler interface {
+	// CommandAnnounce handles the initial announcement of a command.
+	CommandAnnounce(chan []byte) (*Command, error)
+	// CommandData handles the command data.
+	CommandData(chan []byte, *Command) error
+	// HandleCommand executes the command, generating a response.
+	HandleCommand(*Command) (*Response, error)
+	// Respond generates the response for a command.
+	Respond(*Response, chan []byte) error
 }
 
 // Framer handles bytes on the wire by adding or removing framing information.