diff --git a/Makefile b/Makefile
index 62c389e..297cd12 100644
--- a/Makefile
+++ b/Makefile
@@ -102,8 +102,8 @@ navcat: navcat.o ext/fmt-6.1.2/src/format.o  $(SIMPLESOCKETS) ubx.o bits.o navmo
 	$(CXX) -std=gnu++17 $^ -o $@ -L/usr/local/lib -pthread -lprotobuf
 
 
-navrecv: navrecv.o ext/fmt-6.1.2/src/format.o $(SIMPLESOCKETS) navmon.pb.o storage.o githash.o
-	$(CXX) -std=gnu++17 $^ -o $@ -L/usr/local/lib -pthread -lprotobuf  
+navrecv: navrecv.o ext/fmt-6.1.2/src/format.o $(SIMPLESOCKETS) navmon.pb.o storage.o githash.o zstdwrap.o navmon.o
+	$(CXX) -std=gnu++17 $^ -o $@ -L/usr/local/lib -pthread -lprotobuf -lzstd 
 
 tlecatch: tlecatch.o $(patsubst %.cc,%.o,$(wildcard ext/sgp4/libsgp4/*.cc)) githash.o
 	$(CXX) -std=gnu++17 $^ -o $@ -L/usr/local/lib -pthread -lprotobuf  
@@ -111,12 +111,12 @@ tlecatch: tlecatch.o $(patsubst %.cc,%.o,$(wildcard ext/sgp4/libsgp4/*.cc)) gith
 rinreport: rinreport.o rinex.o githash.o navmon.o ext/fmt-6.1.2/src/format.o  ephemeris.o osen.o
 	$(CXX) -std=gnu++17 $^ -o $@ -lz -pthread
 
-rtcmtool: rtcmtool.o navmon.pb.o githash.o ext/fmt-6.1.2/src/format.o  bits.o nmmsender.o $(SIMPLESOCKETS)  navmon.o rtcm.o
-	$(CXX) -std=gnu++17 $^ -o $@ -lz -pthread -lprotobuf
+rtcmtool: rtcmtool.o navmon.pb.o githash.o ext/fmt-6.1.2/src/format.o  bits.o nmmsender.o $(SIMPLESOCKETS)  navmon.o rtcm.o zstdwrap.o
+	$(CXX) -std=gnu++17 $^ -o $@ -lz -pthread -lprotobuf -lzstd
 
 
-ubxtool: navmon.pb.o ubxtool.o ubx.o bits.o ext/fmt-6.1.2/src/format.o galileo.o  gps.o beidou.o navmon.o ephemeris.o $(SIMPLESOCKETS) osen.o githash.o nmmsender.o
-	$(CXX) -std=gnu++17 $^ -o $@ -L/usr/local/lib -lprotobuf -pthread
+ubxtool: navmon.pb.o ubxtool.o ubx.o bits.o ext/fmt-6.1.2/src/format.o galileo.o  gps.o beidou.o navmon.o ephemeris.o $(SIMPLESOCKETS) osen.o githash.o nmmsender.o zstdwrap.o 
+	$(CXX) -std=gnu++17 $^ -o $@ -L/usr/local/lib -lprotobuf -pthread -lzstd
 
 testrunner: navmon.pb.o testrunner.o ubx.o bits.o ext/fmt-6.1.2/src/format.o galileo.o  gps.o beidou.o ephemeris.o sp3.o osen.o navmon.o rinex.o githash.o
 	$(CXX) -std=gnu++17 $^ -o $@ -L/usr/local/lib -lprotobuf -lz 
diff --git a/navrecv.cc b/navrecv.cc
index 8fb7d9a..ef11364 100644
--- a/navrecv.cc
+++ b/navrecv.cc
@@ -11,7 +11,7 @@
 #include <sys/types.h>
 #include <sys/stat.h>
 #include <fcntl.h>
-
+#include "zstdwrap.hh"
 #include "CLI/CLI.hpp"
 #include "version.hh"
 
@@ -138,10 +138,51 @@ void writeToDisk(time_t s, uint64_t sourceid, std::string_view message)
   }
 }
 
+// note that this moves the socket
+void recvSession2(Socket&& uns, ComboAddress client)
+{
+  cerr << "Entering compressed session for "<<client.toStringWithPort()<<endl;
+  ZStdReader zsr(uns);
+  int s = zsr.getFD();
+  //  time_t start = time(0);
+  for(;;) {
+    // enable this to test ubxtool resilience & buffering
+    //    if(time(0) - start > 30)
+    //  sleep(10);
+    string num=SRead(s, 4);
+    if(num.empty()) {
+      cerr<<"EOF from "<<client.toStringWithPort()<<endl;
+      break;
+    }
+    string out="bert";
+    
+    string part = SRead(s, 2);
+    out += part;
+    
+    uint16_t len;
+    memcpy(&len, part.c_str(), 2);
+    len = htons(len);
+    
+    part = SRead(s, len);
+    out += part;
+    
+    NavMonMessage nmm;
+    nmm.ParseFromString(part);
+    uint32_t denum;
+    
+    memcpy(&denum, num.c_str(), 4);
+    denum = htonl(denum);
+    //    cerr<<"Received message "<<denum<< " "<<nmm.localutcseconds()<<" " << nmm.localutcnanoseconds()/1000000000.0<<endl;
+    writeToDisk(nmm.localutcseconds(), nmm.sourceid(), out);
+    SWrite(uns, num);
+  }
+}
+
+
 void recvSession(int s, ComboAddress client)
 {
   try {
-    Socket sock(s);
+    Socket sock(s); // this closes on destruction
     cerr<<"Receiving messages from "<<client.toStringWithPort()<<endl;
     for(;;) {
       string part=SRead(sock, 4);
@@ -150,6 +191,8 @@ void recvSession(int s, ComboAddress client)
         break;
       }
       if(part != "bert") {
+        if(part == "RNIE")
+          return recvSession2(std::move(sock), client);  // protocol v2, socket is moved cuz cleanup is special
         cerr << "Wrong magic from "<<client.toStringWithPort()<<": "<<part<<endl;
         break;
       }
diff --git a/nmmsender.cc b/nmmsender.cc
index 5e244d1..c54bdb0 100644
--- a/nmmsender.cc
+++ b/nmmsender.cc
@@ -5,6 +5,7 @@
 #include <random>
 #include "navmon.hh"
 #include <algorithm>
+#include "zstdwrap.hh"
 
 using namespace std;
 
@@ -13,6 +14,7 @@ void NMMSender::sendTCPThread(Destination* d)
   struct NameError{};
   for(;;) {
     ComboAddress chosen;
+    map<uint32_t, string> unacked;
     try {
       vector<ComboAddress> addrs;
       for(;;) {
@@ -36,8 +38,40 @@ void NMMSender::sendTCPThread(Destination* d)
         SocketCommunicator sc(s);
         sc.setTimeout(3);
         sc.connect(addr);
+        time_t connStartTime = time(0);
         if (d_debug) { cerr<<humanTimeNow()<<" Connected to "<<d->dst<<" on "<<addr.toStringWithPort()<<endl; }
+        auto emit = [&sc](const char*buf, uint32_t len) {
+          sc.writen(string(buf, len));
+        };
+        std::unique_ptr<ZStdCompressor> zsc;
+        if(d_compress) {
+          sc.writen("RNIE"); // the other magic value is "bert". hence. 
+          zsc = std::make_unique<ZStdCompressor>(emit, 20);
+        }
+        bool hadMessage=false;
+        int msgnum = 0;
+
         for(;;) {
+          uint32_t num;
+          // read acks
+          for(;;) {
+            int res = read(s, &num, 4);
+            if(res < 0) {
+              if(errno != EAGAIN)
+                unixDie("Reading acknowledgements in nmmsender");
+              break;
+            }
+            if(res==0)
+              throw std::runtime_error("EOF while reading acks");
+            if(res==4) {
+              num = ntohl(num);
+              unacked.erase(num);
+            }
+            else
+              throw std::runtime_error("Partial read of "+to_string(res)+" bytes");
+          }
+
+          
           std::string msg;
           {
             std::lock_guard<std::mutex> mut(d->mut);
@@ -46,18 +80,46 @@ void NMMSender::sendTCPThread(Destination* d)
             }
           }
           if(!msg.empty()) {
-            sc.writen(msg);
+            hadMessage=true;
+            if(zsc) {
+              
+              uint32_t num = htonl(msgnum);
+              string encap((const char*)&num, 4);
+              encap += msg;
+              zsc->give(encap.c_str(), encap.size());
+              unacked[msgnum] = msg;
+              msgnum++;
+
+            }
+            else
+              sc.writen(msg);
             std::lock_guard<std::mutex> mut(d->mut);
             d->queue.pop_front();
+
+          }
+          else {
+            if(zsc && hadMessage) {
+              cerr << "Compressed to: "<< 100.0*zsc->d_outputBytes/zsc->d_inputBytes<<"%, buffered compressed: "<<zsc->outputBufferBytes()<<" out of " <<zsc->outputBufferCapacity()<<" bytes. Unacked: "<<unacked.size()<<endl;
+
+              zsc->flush();
+
+              if(time(0) - connStartTime > 10 && unacked.size() > 1000)
+                throw std::runtime_error("Too many messages unacked, recycling connection");
+
+
+              
+            }
+            hadMessage = false;
+            usleep(100000);
+
           }
-          else usleep(100000);
         }
       }
     }
     catch(NameError&) {
       {
         std::lock_guard<std::mutex> mut(d->mut);
-        if (d_debug) { cerr<<humanTimeNow()<<" There are now "<<d->queue.size()<<" messages queued for "<<d->dst<<endl; }
+        if (d_debug) { cerr<<humanTimeNow()<<" There are now "<<d->queue.size()<<" messages queued for "<<d->dst<<", and "<<unacked.size()<<" unacknowledged"<<endl; }
       }
       sleep(30);
     }
@@ -65,7 +127,7 @@ void NMMSender::sendTCPThread(Destination* d)
       if (d_debug) { cerr<<humanTimeNow()<<" Sending thread for "<<d->dst<<" via "<<chosen.toStringWithPort()<<" had error: "<<e.what()<<endl; }
       {
         std::lock_guard<std::mutex> mut(d->mut);
-        if (d_debug) { cerr<<humanTimeNow()<<" There are now "<<d->queue.size()<<" messages queued for "<<d->dst<<endl; }
+        if (d_debug) { cerr<<humanTimeNow()<<" There are now "<<d->queue.size()<<" messages queued for "<<d->dst<<", and "<<unacked.size()<<" unacknowledged"<<endl; }
       }
       sleep(1);
     }
@@ -73,10 +135,18 @@ void NMMSender::sendTCPThread(Destination* d)
       if (d_debug) { cerr<<humanTimeNow()<<" Sending thread for "<<d->dst <<" via "<<chosen.toStringWithPort()<<" had error"; }
       {
         std::lock_guard<std::mutex> mut(d->mut);
-        if (d_debug) { cerr<<"There are now "<<d->queue.size()<<" messages queued for "<<d->dst<<" via "<<chosen.toStringWithPort()<<endl; }
+        if (d_debug) { cerr<<"There are now "<<d->queue.size()<<" messages queued for "<<d->dst<<", and "<<unacked.size()<<" unacknowledge via "<<chosen.toStringWithPort()<<endl; }
       }
       sleep(1);
     }
+    std::lock_guard<std::mutex> mut(d->mut);
+    if(!unacked.empty()) {
+      cerr<<humanTimeNow()<< " Stuffing "<<unacked.size()<<" messages back into the queue"<<endl;
+      for(auto iter= unacked.rbegin(); iter != unacked.rend(); ++iter) {
+        d->queue.push_front(iter->second);
+      }
+      unacked.clear();
+    }
   }
 }
 
@@ -84,15 +154,17 @@ void NMMSender::sendTCPThread(Destination* d)
 void NMMSender::emitNMM(const NavMonMessage& nmm)
 {
   for(auto& d : d_dests) {
-    d->emitNMM(nmm);
+    d->emitNMM(nmm, d_compress);
   }
 }
 
-void NMMSender::Destination::emitNMM(const NavMonMessage& nmm)
+void NMMSender::Destination::emitNMM(const NavMonMessage& nmm, bool compressed)
 {
   string out;
   nmm.SerializeToString(& out);
-  string msg("bert");
+  string msg;
+  if(!compressed)
+    msg="bert";
   
   uint16_t len = htons(out.size());
   msg.append((char*)&len, 2);
diff --git a/nmmsender.hh b/nmmsender.hh
index de482d8..2b60e4d 100644
--- a/nmmsender.hh
+++ b/nmmsender.hh
@@ -16,7 +16,7 @@ class NMMSender
 
     std::deque<std::string> queue;
     std::mutex mut;
-    void emitNMM(const NavMonMessage& nmm);
+    void emitNMM(const NavMonMessage& nmm, bool compress);
   };
   
 public:
@@ -47,7 +47,8 @@ public:
 
   void emitNMM(const NavMonMessage& nmm);
   bool d_debug{false};
-private:
+  bool d_compress{false}; // set BEFORE launch
 
+private:
   std::vector<std::unique_ptr<Destination>> d_dests;
 };
diff --git a/ubxtool.cc b/ubxtool.cc
index af31853..53524a6 100644
--- a/ubxtool.cc
+++ b/ubxtool.cc
@@ -426,9 +426,10 @@ int main(int argc, char** argv)
   unsigned int fuzzPositionMeters=0;
   string owner;
   string remark;
-
+  bool doCompress=false;
   app.add_option("--destination,-d", destinations, "Send output to this IPv4/v6 address");
   app.add_flag("--wait", doWait, "Wait a bit, do not try to read init messages");
+  app.add_flag("--compress,-z", doCompress, "Use compressed protocol for network transmission");
   app.add_flag("--reset", doReset, "Reset UBX device");
   app.add_flag("--beidou,-c", doBeidou, "Enable BeiDou reception");
   app.add_flag("--gps,-g", doGPS, "Enable GPS reception");
@@ -878,6 +879,7 @@ int main(int argc, char** argv)
   */
 
   int curCycleTOW{-1}; // means invalid
+  ns.d_compress = doCompress;
   ns.launch();
   
   cerr<<humanTimeNow()<<" Entering main loop"<<endl;