diff --git a/.idea/.name b/.idea/.name
new file mode 100644
index 0000000..966d5bf
--- /dev/null
+++ b/.idea/.name
@@ -0,0 +1 @@
+wfr
\ No newline at end of file
diff --git a/.idea/vcs.xml b/.idea/vcs.xml
new file mode 100644
index 0000000..94a25f7
--- /dev/null
+++ b/.idea/vcs.xml
@@ -0,0 +1,6 @@
+<?xml version="1.0" encoding="UTF-8"?>
+<project version="4">
+  <component name="VcsDirectoryMappings">
+    <mapping directory="$PROJECT_DIR$" vcs="Git" />
+  </component>
+</project>
\ No newline at end of file
diff --git a/CMakeLists.txt b/CMakeLists.txt
index 0f3430a..459d152 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -7,7 +7,7 @@ set(CMAKE_CXX_STANDARD 14)
 
 add_executable(${APP_NAME} main.cpp src/ALSADevice.cpp src/ALSADevice.h src/MemoryPool.cpp src/MemoryPool.h utils/Semaphore.h utils/Semaphore.cpp src/SampleWriter.h src/Timestamp.h
         #src/SampleReceiver.h
-        src/audio_types.h)
+        src/audio_types.h src/ServerBeacon.cpp src/ServerBeacon.h)
 
 find_package(Threads REQUIRED)
 if (THREADS_FOUND)
diff --git a/MATLAB/read_syncdata.m b/MATLAB/read_syncdata.m
index 4f3bf44..4fc769d 100644
--- a/MATLAB/read_syncdata.m
+++ b/MATLAB/read_syncdata.m
@@ -1,39 +1,46 @@
-% settings
-DATASET_DIR = 'test';
-TS_FILE = 'ts';
-SAMPLE_FILE_PREFIX = 'ch_';
-FILE_EXT = 'dat';
-CHANNELS = 2;
+function ds = read_syncdata(DATASET_DIR)
+  % settings
+  %DATASET_DIR = 'test_20221';
+  TS_FILE = 'ts';
+  SAMPLE_FILE_PREFIX = 'ch_';
+  FILE_EXT = 'dat';
+  CHANNELS = 2;
 
-% computed values
-FN_TS = strcat(DATASET_DIR, '/', TS_FILE, '.', FILE_EXT);
+  % computed values
+  FN_TS = strcat(DATASET_DIR, '/', TS_FILE, '.', FILE_EXT);
 
-for ch=0:1:(CHANNELS-1)
-  FN_SAMPLE{ch+1} = strcat(DATASET_DIR, '/', SAMPLE_FILE_PREFIX, num2str(ch), '.', FILE_EXT);
-end
+  for ch=0:1:(CHANNELS-1)
+    FN_SAMPLE{ch+1} = strcat(DATASET_DIR, '/', SAMPLE_FILE_PREFIX, num2str(ch), '.', FILE_EXT);
+  end
 
 
-% load timestamps
-f = fopen(FN_TS ,'r');
-ts = fread(f,[2,Inf],'uint32');
-fclose(f);
-
-% take first element as t0
-ts(1,:) = ts(1,:) - ts(1,1);
-
-% create fractional timestamp
-ts = ts(1,:) + ts(2,:) / 1E+09;
-
-% get sample count
-sample_cnt = length(ts);
-
-% load samples
-s = zeros(CHANNELS, sample_cnt);
-for ch=1:CHANNELS
-  f = fopen(FN_SAMPLE{ch},'r');
-  d = fread(f, [1,Inf],'int16');
-  s(ch,:) = d;
+  % load timestamps
+  f = fopen(FN_TS ,'r');
+  ts = fread(f,[2,Inf],'uint32');
   fclose(f);
-end
 
-plot(ts(1,1:100), s(1,1:100))
\ No newline at end of file
+  % take first element as t0
+  %ts(1,:) = ts(1,:) - 1636036145;
+
+  % create fractional timestamp
+  ts = ts(1,:) + ts(2,:) / 1E+09;
+
+  % get sample count
+  sample_cnt = length(ts);
+
+  % load samples
+  s = zeros(CHANNELS, sample_cnt);
+  for ch=1:CHANNELS
+    f = fopen(FN_SAMPLE{ch},'r');
+    d = fread(f, [1,Inf],'int16');
+    s(ch,:) = d;
+    fclose(f);
+  end
+
+  %figure(1)
+  %plot(ts(1,1:100), s(1,1:100), 'x')
+  %xlim([ts(1) ts(100)])
+  %hold on
+  
+  ds = [ts' s'];
+end
\ No newline at end of file
diff --git a/MATLAB/sync_datasets.m b/MATLAB/sync_datasets.m
new file mode 100644
index 0000000..71319f8
--- /dev/null
+++ b/MATLAB/sync_datasets.m
@@ -0,0 +1,72 @@
+function sds = sync_datasets(dss)
+  % load datasets
+  len = length(dss);
+  sds = {};
+  first_ts = [];
+  last_ts = [];
+  for i=1:len
+    ds = read_syncdata(dss{i});
+    first_ts(i) = ds(1:1);
+    last_ts(i) = ds(end,1);   
+    sds{i} = ds;
+  end
+  
+  % get first and last common timestamp
+  ts0 = max(first_ts);
+  tsend = min(last_ts);
+  
+  for i=1:len
+    ds = sds{i}; 
+    ds = ds(ds(:,1) > ts0 + (ds(2,1) - ds(1,1)) / 2 & ds(:,1) < tsend, :); % drop non-common sections
+    ds(:,1) = ds(:,1) - ts0; % substract ts0 from each dataset's timestamp array
+    sds{i} = ds;
+  end
+  
+  % create plot
+  figure(1)
+  
+  % plot samples
+  subplot(2,1,1);
+  
+  marks = ['-', '-o'];
+  
+  PLOTRANGE = 1:100;
+  
+  % get beginning indices
+  for i=1:len
+    ds = sds{i};
+    ts = ds(:,1);
+    
+    s = size(ds);
+    
+    %for k = 2:s(2);
+    for k = 2:2
+      %plot(ts(1:100),ds(1:100,k), marks(k-1));
+      plot(ts(PLOTRANGE),ds(PLOTRANGE,k), 'x');
+      hold on
+    end
+  end
+  
+  grid on
+  xlabel("Time [s]");
+  ylabel("Sample");
+  xlim([ts(PLOTRANGE(1)) ts(PLOTRANGE(end))]);
+  
+  % plot timestamp errors
+  subplot(2,1,2);
+
+  ds_ref = sds{1};
+  ts_ref = ds_ref(:,1);
+  
+  for i = 2:len
+    ts_err = ts(PLOTRANGE) - ts_ref(PLOTRANGE);
+    plot(ts_ref(PLOTRANGE), ts_err * 1E+09);
+    hold on
+  end
+  
+  grid on
+  xlabel("Time [s]");
+  ylabel("Time error [ns]");
+  xlim([ts(PLOTRANGE(1)) ts(PLOTRANGE(end))]);
+  
+endfunction
diff --git a/main.cpp b/main.cpp
index 8b58bb3..87a72eb 100644
--- a/main.cpp
+++ b/main.cpp
@@ -144,7 +144,7 @@ uint8_t pRecvBuf[8096] __attribute__ ((aligned (32)));
 int main(int argc, char * argv[]) {
     ALSADevice dev(PERIOD_LEN, SAMPLE_RATE);
     MemoryPool<int16_t> pool(STEREO_BUF_LEN, 1000);
-    //SampleWriter<AudioSampleType> sw("test", 2, STEREO_BUF_LEN / 2);
+    //SampleWriter<AudioSampleType> sw(std::string("test_") + argv[1], 2, STEREO_BUF_LEN / 2);
 
     //std::this_thread::sleep_for(std::chrono::seconds(1));
 
diff --git a/src/ServerBeacon.cpp b/src/ServerBeacon.cpp
new file mode 100644
index 0000000..c098f34
--- /dev/null
+++ b/src/ServerBeacon.cpp
@@ -0,0 +1,133 @@
+//
+// Created by epagris on 2021. 11. 11..
+//
+
+#include <iostream>
+#include <memory>
+#include <unistd.h>
+#include "ServerBeacon.h"
+
+const in_addr ServerBeacon::DEFAULT_MULTICAST_ADDR = {inet_addr("224.0.2.21")};
+
+ServerBeacon::ServerBeacon() : mRunning(false) {
+    setMulticastAddr(DEFAULT_MULTICAST_ADDR);
+    setPort(DEFAULT_PORT);
+    setAnnouncePeriod(DEFAULT_ANNOUNCE_PERIOD_MS);
+}
+
+ServerBeacon::ServerBeacon(const in_addr &addr, unsigned short port, size_t announcePeriod_ms) : mRunning(false) {
+    setMulticastAddr(addr);
+    setPort(port);
+    setAnnouncePeriod(announcePeriod_ms);
+}
+
+void ServerBeacon::setMulticastAddr(const in_addr &addr) {
+    mAddr = addr;
+}
+
+in_addr ServerBeacon::getMulticastAddr() const {
+    return mAddr;
+}
+
+
+void ServerBeacon::setPort(unsigned short port) {
+    mBeaconPort = port;
+}
+
+unsigned short ServerBeacon::getPort() const {
+    return mBeaconPort;
+}
+
+void ServerBeacon::setAnnouncePeriod(size_t period_ms) {
+    mAnnPeriod_ms = period_ms;
+}
+
+size_t ServerBeacon::getAnnouncePeriod() const {
+    return mAnnPeriod_ms;
+}
+
+void ServerBeacon::startBeacon() {
+    if (mRunning) {
+        std::cerr << "Could not start beacon: already running!" << std::endl;
+        return;
+    }
+
+    mBeaconSoc = socket(AF_INET, SOCK_DGRAM, 0); // create socket
+    if (mBeaconSoc == -1) {
+        std::cerr << "Could not open socket in " << __FUNCTION__ << "!" << std::endl;
+        return;
+    }
+
+    // set socket options
+    int opt = 1;
+    setsockopt(mBeaconSoc, SOL_SOCKET, SO_REUSEADDR | SO_REUSEPORT, &opt, sizeof(opt));
+
+    // bind to ip-address and port
+    sockaddr_in addr;
+    addr.sin_family = AF_INET;
+    addr.sin_addr = mAddr;
+    addr.sin_port = htons(mBeaconPort);
+
+    if (bind(mBeaconSoc, (const sockaddr *) &addr, sizeof(addr)) == -1) {
+        std::cerr << "Could not bind to IP address and/or port in " << __FUNCTION__ << "!" << std::endl;
+        close(mBeaconSoc);
+        return;
+    }
+
+    // the beacon is running now!
+    mRunning = true;
+
+    // start beacon thread
+    mpBeaconThread = std::make_shared<std::thread>(fn_BeaconThread, this);
+}
+
+void ServerBeacon::stopBeacon() {
+    mRunning = false;
+}
+
+std::list<in_addr> ServerBeacon::getNodesOnNetwork() {
+    return std::list<in_addr>();
+}
+
+
+// -------------------------------------------
+
+void ServerBeacon::fn_BeaconThread(ServerBeacon *pSB) {
+    // beacon message used to send and receive information
+    BeaconMsg msg;
+
+    //
+
+    // select-related structures
+    fd_set read_fds;
+    timeval tv;
+
+    // fill-in select parameters
+    FD_ZERO(&read_fds);
+    FD_SET(pSB->mBeaconSoc, &read_fds);
+
+    // fill-in timeout value
+    tv.tv_sec = pSB->mAnnPeriod_ms / 1000;
+    tv.tv_usec = (pSB->mAnnPeriod_ms  % 1000) * 1000;
+
+    while (pSB->mRunning) {
+        msg.server_nClient = 1; // we are the server
+        msg.terminalPort = 0; // we have no inbound terminal port
+
+        send(pSB->mBeaconSoc, &msg, sizeof(BeaconMsg), 0); // send the announce message
+
+        // ------------------
+
+        // copy parameters
+        fd_set cur_rfds = read_fds;
+        timeval cur_tv = tv;
+
+        while (select(1, &cur_rfds, nullptr, nullptr, &cur_tv) != 0) {
+            // receive response
+            recv(pSB->mBeaconSoc, &msg, sizeof(BeaconMsg), 0);
+
+            // store response
+        }
+
+    }
+}
diff --git a/src/ServerBeacon.h b/src/ServerBeacon.h
new file mode 100644
index 0000000..a1279d2
--- /dev/null
+++ b/src/ServerBeacon.h
@@ -0,0 +1,56 @@
+//
+// Created by epagris on 2021. 11. 11..
+//
+
+#ifndef WFR_SERVERBEACON_H
+#define WFR_SERVERBEACON_H
+
+#include <cstddef>
+#include <list>
+#include <netinet/in.h>
+#include <arpa/inet.h>
+#include <thread>
+
+class ServerBeacon {
+public:
+    static constexpr unsigned short DEFAULT_PORT = 8021; // default port for multicast messages
+    static const in_addr DEFAULT_MULTICAST_ADDR; // default multicast address
+    static constexpr size_t DEFAULT_ANNOUNCE_PERIOD_MS = 1000; // default announce period
+private:
+    // structure for storing nodes
+    struct ClientNodeInfo {
+        in_addr addr; // address of client
+        uint16_t terminalPort;
+    };
+private:
+    int mBeaconSoc; // beacon socket
+    in_addr mAddr; // address
+    unsigned short mBeaconPort; // port
+    size_t mAnnPeriod_ms; // announce period
+    std::list<ClientNodeInfo> mNodes; // nodes
+    bool mRunning; // does the beacon operate?
+private:
+    std::shared_ptr<std::thread> mpBeaconThread; // thread running the beacon
+    static void fn_BeaconThread(ServerBeacon * pSB); // function running in beacon thread
+private:
+    // structure for beacon MSG
+    struct BeaconMsg {
+        uint8_t server_nClient; // server or client
+        uint16_t terminalPort; // port of terminal
+    };
+public:
+    ServerBeacon(); // constr.
+    explicit ServerBeacon(const in_addr& addr, unsigned short port, size_t announcePeriod_ms); // constr. with beacon port and announce period
+    void setMulticastAddr(const in_addr& addr); // set multicasting address
+    in_addr getMulticastAddr() const; // set multicasting address
+    void setPort(unsigned short port); // set port BEFORE starting beacon
+    unsigned short getPort() const; // get beacon port
+    void setAnnouncePeriod(size_t period_ms); // set announce period
+    size_t getAnnouncePeriod() const; // get announce period
+    void startBeacon(); // start the beacon
+    void stopBeacon(); // stop the beacon
+    std::list<in_addr> getNodesOnNetwork(); // get nodes connected to the same network
+};
+
+
+#endif //WFR_SERVERBEACON_H
diff --git a/src/audio_types.h b/src/audio_types.h
index 3cbd64b..09cc7df 100644
--- a/src/audio_types.h
+++ b/src/audio_types.h
@@ -7,7 +7,7 @@
 
 #include <cstdint>
 
-#define STEREO_BUF_LEN (648)
+#define STEREO_BUF_LEN (2 * 192)
 #define PERIOD_LEN (STEREO_BUF_LEN / 2)
 #define SAMPLE_RATE (48000)