diff --git a/src/sync/submit_tcp.py b/src/sync/submit_tcp.py
new file mode 100755
index 000000000..79f26edb8
--- /dev/null
+++ b/src/sync/submit_tcp.py
@@ -0,0 +1,108 @@
+#!/usr/bin/python
+"""
+Master script for xgboost submit_tcp
+This script can be used to start jobs of multi-node xgboost using sync_tcp
+
+Tianqi Chen
+"""
+
+import sys
+import os
+import socket
+import struct
+import subprocess
+
+class ExSocket:
+    def __init__(self, sock):
+        self.sock = sock
+    def recvall(self, nbytes):
+        res = []
+        sock = self.sock
+        nread = 0    
+        while nread < nbytes:
+            chunk = self.sock.recv(min(nbytes - nread, 1024), socket.MSG_WAITALL)
+            nread += len(chunk)
+            res.append(chunk)
+        return ''.join(res)
+    def recvint(self):
+        return struct.unpack('!i', self.recvall(4))[0]
+    def sendint(self, n):
+        self.sock.sendall(struct.pack('!i', n))
+    def sendstr(self, s):
+        self.sendint(len(s))
+        self.sock.sendall(s)
+
+# magic number used to verify existence of data
+kMagic = 0xff99
+
+class Master:
+    def __init__(self, port = 9000, port_end = 9999):
+        sock = socket.socket(socket.AF_INET, socket.SOCK_STREAM)
+        for port in range(port, port_end):
+            try:
+                sock.bind(('', port))
+                self.port = port
+                break
+            except socket.error:
+                continue
+        sock.listen(16)
+        self.sock = sock
+        print 'start listen on %s:%d' % (socket.gethostname(), self.port)
+    def __del__(self):
+        self.sock.close()
+    def slave_args(self):
+        return ['master_uri=%s' % socket.gethostname(),
+                'master_port=%s' % self.port]    
+    def accept_slaves(self, nslave):        
+        slave_addrs = []
+        for rank in range(nslave):
+            while True:
+                fd, s_addr = self.sock.accept()
+                print 'accept connection from %s' % s_addr
+                slave = ExSocket(fd)
+                nparent = int(rank != 0)
+                nchild = 0
+                if (rank + 1) * 2 - 1 < nslave:
+                    nchild += 1
+                if (rank + 1) * 2 < nslave:
+                    nchild += 1                
+                try:
+                    magic = slave.readint()
+                    if magic != kMagic:
+                        slave.sock.close()
+                        continue
+                except socket.error:
+                    slave.sock.close()
+                    continue
+                slave.sendint(kMagic)
+                slave.sendint(rank)
+                slave.sendint(nslave)
+                slave.sendint(nparent)
+                slave.sendint(nchild)
+                if nparent != 0:
+                    parent_index = (rank + 1) / 2 - 1
+                    ptuple = slave_addrs[parent_index]
+                    slave.sendstr(ptuple[0])
+                    slave.sendint(ptuple[1])
+                s_port = slave.recvint()
+                assert rank == len(slave_addrs)
+                slave_addrs.append(s_addr, s_port)
+                break
+        print 'all slaves setup complete'
+        
+def mpi_submit(nslave, args):
+    cmd = ' '.join(['mpirun -n %d' % nslave] + args)
+    print cmd
+    os.system(cmd)
+    
+def submit(nslave, args, fun_submit = mpi_submit):
+    master = Master()
+    fun_submit(nslave, args + master.slave_args())
+    master.accept_slaves(nslave)
+
+if __name__ == '__main__':
+    if len(sys.argv) < 2:
+        print 'Usage: <nslave> <cmd>'
+        exit(0)
+    submit(int(sys.argv[1]), sys.argv[2:])
+
diff --git a/src/sync/sync_tcp.cpp b/src/sync/sync_tcp.cpp
index dd851d05a..3ae1bf8a5 100644
--- a/src/sync/sync_tcp.cpp
+++ b/src/sync/sync_tcp.cpp
@@ -23,16 +23,64 @@ class SyncManager {
  public:
   const static int kMagic = 0xff99;
   SyncManager(void) {
-    master_uri = "localhost";
+    master_uri = "NULL";
     master_port = 9000;
+    host_uri = "";
     slave_port = 9010;
     nport_trial = 1000;
+    rank = 0;
+    world_size = 1;
+    reduce_buffer_size = 128; 
   }
   ~SyncManager(void) {
     this->Shutdown();
   }
+  inline void Shutdown(void) {
+    for (size_t i = 0; i < links.size(); ++i) {
+      links[i].sock.Close();
+    }
+    links.clear();
+  }
+  /*! \brief set parameters to the sync manager */
+  inline void SetParam(const char *name, const char *val) {
+    if (!strcmp(name, "master_uri")) master_uri = val;
+    if (!strcmp(name, "master_port")) master_port = atoi(val);
+    if (!strcmp(name, "reduce_buffer")) {
+      char unit;
+      unsigned long amount;
+      if (sscanf(val, "%lu%c", &amount, &unit) == 2) {
+        switch (unit) {
+          case 'B': reduce_buffer_size = amount; break;
+          case 'K': reduce_buffer_size = amount << 10UL; break;
+          case 'M': reduce_buffer_size = amount << 20UL; break;
+          case 'G': reduce_buffer_size = amount << 30UL; break;
+          default: utils::Error("invalid format for reduce buffer");
+        }
+      } else {
+        utils::Error("invalid format for reduce_buffer, shhould be {integer}{unit}, unit can be {B, KB, MB, GB}");
+      }
+    }
+  }
+  /*! \brief get rank */
+  inline int GetRank(void) const {
+    return rank;
+  }
+  /*! \brief check whether its distributed mode */
+  inline bool IsDistributed(void) const {
+    return links.size() != 0;
+  }
+  /*! \brief get rank */
+  inline int GetWorldSize(void) const {
+    return world_size;
+  }
+  /*! \brief get rank */
+  inline std::string GetHost(void) const {
+    return host_uri;
+  }
   // initialize the manager
   inline void Init(void) {
+    // single node mode
+    if (master_uri == "NULL") return;
     utils::Assert(links.size() == 0, "can only call Init once");
     int magic = kMagic;
     int nchild = 0, nparent = 0;
@@ -108,29 +156,6 @@ class SyncManager {
     }
     // done
   }
-  inline void Shutdown(void) {
-    for (size_t i = 0; i < links.size(); ++i) {
-      links[i].sock.Close();
-    }
-    links.clear();
-  }
-  /*! \brief set parameters to the sync manager */
-  inline void SetParam(const char *name, const char *val) {
-    if (!strcmp(name, "master_uri")) master_uri = val;
-    if (!strcmp(name, "master_port")) master_port = atoi(val);
-  }
-  /*! \brief get rank */
-  inline int GetRank(void) const {
-    return rank;
-  }  
-  /*! \brief get rank */
-  inline int GetWorldSize(void) const {
-    return world_size;
-  }
-  /*! \brief get rank */
-  inline std::string GetHost(void) const {
-    return host_uri;
-  }
   /*!
    * \brief perform in-place allreduce, on sendrecvbuf 
    *        this function is NOT thread-safe
@@ -159,7 +184,9 @@ class SyncManager {
 
     // initialize the link ring-buffer and pointer
     for (int i = 0; i < nlink; ++i) {
-      if (i != parent_index) links[i].InitBuffer(type_nbytes, count);
+      if (i != parent_index) {
+        links[i].InitBuffer(type_nbytes, count, reduce_buffer_size);
+      }
       links[i].ResetSize();
     }
     // if no childs, no need to reduce
@@ -301,8 +328,6 @@ class SyncManager {
     }
   }
  private:  
-  // 128 MB
-  const static size_t kBufferSize = 128;
   // an independent child record
   struct LinkRecord {
    public:
@@ -317,10 +342,10 @@ class SyncManager {
     // buffer size, in bytes
     size_t buffer_size;
     // initialize buffer
-    inline void InitBuffer(size_t type_nbytes, size_t count) {
-      utils::Assert(type_nbytes < kBufferSize, "too large type_nbytes");
+    inline void InitBuffer(size_t type_nbytes, size_t count, size_t reduce_buffer_size) {
+      utils::Assert(type_nbytes < reduce_buffer_size, "too large type_nbytes");
       size_t n = (type_nbytes * count + 7)/ 8;
-      buffer_.resize(std::min(kBufferSize, n));
+      buffer_.resize(std::min(reduce_buffer_size, n));
       // make sure align to type_nbytes
       buffer_size = buffer_.size() * sizeof(uint64_t) / type_nbytes * type_nbytes;
       // set buffer head
@@ -377,6 +402,8 @@ class SyncManager {
   int master_port;
   // port of slave process
   int slave_port, nport_trial;
+  // reduce buffer size
+  size_t reduce_buffer_size;
   // current rank
   int rank;
   // world size
@@ -405,9 +432,8 @@ int GetWorldSize(void) {
 std::string GetProcessorName(void) {
   return manager.GetHost();
 }
-
 bool IsDistributed(void) {
-  return true;
+  return manager.IsDistributed();
 }
 /*! \brief intiialize the synchronization module */
 void Init(int argc, char *argv[]) {
diff --git a/test/Makefile b/test/Makefile
index 6c943e155..b03c91720 100644
--- a/test/Makefile
+++ b/test/Makefile
@@ -11,19 +11,24 @@ else
 endif
 
 # specify tensor path
-BIN = test_group_data test_quantile test_sock
-
+BIN = test_group_data test_quantile test_allreduce
+OBJ = sync_tcp.o
 .PHONY: clean all
 
 all: $(BIN) $(MPIBIN)
 
+sync_tcp.o: ../src/sync/sync_tcp.cpp ../src/utils/*.h
+
 test_group_data: test_group_data.cpp ../src/utils/*.h
 test_quantile: test_quantile.cpp ../src/utils/*.h
-test_sock: test_sock.cpp ../src/utils/*.h
+test_allreduce: test_allreduce.cpp ../src/utils/*.h ../src/sync/sync.h sync_tcp.o
 
 $(BIN) : 
 	$(CXX) $(CFLAGS) $(LDFLAGS) -o $@ $(filter %.cpp %.o %.c, $^)
 
+$(OBJ) : 
+	$(CXX) -c $(CFLAGS) -o $@ $(firstword $(filter %.cpp %.c, $^) )
+
 $(MPIBIN) : 
 	$(MPICXX) $(CFLAGS) $(LDFLAGS) -o $@ $(filter %.cpp %.o %.c, $^)
 
diff --git a/test/test_allreduce.cpp b/test/test_allreduce.cpp
new file mode 100644
index 000000000..6df6ed0fa
--- /dev/null
+++ b/test/test_allreduce.cpp
@@ -0,0 +1,22 @@
+#include <sync/sync.h>
+
+using namespace xgboost;
+
+int main(int argc, char *argv[]) {
+  sync::Init(argc, argv);
+  int rank = sync::GetRank();
+  std::string name = sync::GetProcessorName().c_str();
+  printf("start %s rank=%d\n", name.c_str(), rank);
+
+  std::vector<float> ndata(16);
+  for (size_t i = 0; i < ndata.size(); ++i) {
+    ndata[i] = i + rank;
+  }
+  sync::AllReduce(&ndata[0], ndata.size(), sync::kMax);
+  sync::Finalize();
+  for (size_t i = 0; i < ndata.size(); ++i) {
+    printf("%lu: %f\n", i, ndata[i]);
+  }
+  printf("all end\n");
+  return 0;
+}