diff --git a/doc/plan.org b/doc/plan.org
index 9f389e2..e7d7721 100644
--- a/doc/plan.org
+++ b/doc/plan.org
@@ -4596,7 +4596,6 @@ Exception in thread "AWT-EventQueue-0" java.lang.IllegalArgumentException: Windo
 #+END_CENTER
 
 Reason was a hidden window.
-***
 *** 2019-06-13: try using external card for packets
 *** 2019-06-14: test adding table entry with ubuntu 16.04, kernel 4.15.0-51-generic
 #+BEGIN_CENTER
@@ -5301,6 +5300,8 @@ p4@ubuntu:~/master-thesis/bin$ mx h3 "echo V4-OK | socat - UDP:10.1.1.1:2342"
 
 My code is +1 too high
 
+*** 2019-07-17: continuing on wrap around issue
+
 *** DONE 2019-07-16: understood scapy code
     CLOSED: [2019-07-16 Tue 11:25]
 meta.v6sum = (bit<16>) ((((tmp>>8) & 0xff)|tmp<<8) & 0xffff) ;
@@ -5335,7 +5336,8 @@ Gives off-by-one in udp, sometimes!
 
 10:08:52.626713 IP6 (hlim 64, next-header UDP (17) payload length: 14) 2001:db8:1::a00:1.51345 > 2001:db8::1.2342: [bad udp cks
 
-*** TODO 2019-07-16: get values from P4: v6sum, v4sum and co.
+*** DONE 2019-07-16: get values from P4: v6sum, v4sum and co.
+    CLOSED: [2019-07-16 Tue 13:15]
     - v6sum = 0x9a6b
     - v4sum = 0xeadd
 
@@ -5348,7 +5350,12 @@ Gives off-by-one in udp, sometimes!
     hdr.udp.checksum = 0x4a8a + 0x9a6b - 0xeadd;
     Result: 0xfa18!
 
-
+*** TODO 2019-07-16: debug v3.3: even positive wrap around fails!!
+    -   hdr.udp.checksum = 0x91ef + 0x9a6b;
+../p4src/actions_delta_checksum.p4(66): warning: 76890: value does not fit in 16 bits
+    hdr.udp.checksum = 0x91ef + 0x9a6b;
+11:52:13.177826 IP6 (hlim 64, next-header UDP (17) payload length: 14)
+    2001:db8:1::a00:1.50705 > 2001:db8::1.2342: [bad udp cksum 0x2c5a -> 0xfc97!] UDP, length 6
 
 ** The NetPFGA saga
 Problems encountered:
diff --git a/p4src/actions_delta_checksum.p4 b/p4src/actions_delta_checksum.p4
index 0cf219f..3721b74 100644
--- a/p4src/actions_delta_checksum.p4
+++ b/p4src/actions_delta_checksum.p4
@@ -1,6 +1,18 @@
 #ifndef NICO_DELTA_CHECKSUM
 #define NICO_DELTA_CHECKSUM
 
+/* copied from
+https://p4.org/p4-spec/docs/PSA-v1.1.0.html#appendix-internetchecksum-implementation
+*/
+
+bit<16> ones_complement_sum(in bit<16> x, in bit<16> y) {
+    bit<17> ret = (bit<17>) x + (bit<17>) y;
+    if (ret[16:16] == 1) {
+        ret = ret + 1;
+    }
+    return ret[15:0];
+}
+
 action v4sum() {
     bit<16> tmp = 0;
 
@@ -12,7 +24,7 @@ action v4sum() {
     tmp = tmp + (bit<16>) hdr.ipv4.totalLen -20;                // 16 bit
     tmp = tmp + (bit<16>) hdr.ipv4.protocol;                    // 8 bit
 
-    meta.v4sum = tmp;
+    meta.v4sum = ~tmp;
 }
 
 action v6sum() {
@@ -39,7 +51,7 @@ action v6sum() {
     tmp = tmp + (bit<16>) hdr.ipv6.payload_length;              // 16 bit
     tmp = tmp + (bit<16>) hdr.ipv6.next_header;                 // 8 bit
 
-    meta.v6sum = tmp;
+    meta.v6sum = ~tmp;
 }
 
 action delta_prepare()
@@ -52,28 +64,41 @@ action delta_udp_from_v4_to_v6()
 {
     delta_prepare();
 
-    bit<16> tmp = ~hdr.udp.checksum;
-    tmp = tmp + meta.v6sum;
-    tmp = tmp - meta.v4sum;
-    hdr.udp.checksum = ~tmp;
+    bit<16> tmp = 0;
+    tmp = ones_complement_sum(hdr.udp.checksum, meta.v6sum);
+    hdr.udp.checksum = ones_complement_sum(tmp, 0xffff - meta.v6sum);
 }
 
 action delta_tcp_from_v4_to_v6()
 {
     delta_prepare();
-
-    bit<16> tmp = ~hdr.tcp.checksum;
-    tmp = tmp + meta.v6sum;
-    tmp = tmp - meta.v4sum;
-    hdr.tcp.checksum = ~tmp;
+    bit<16> tmp = 0;
+    tmp = ones_complement_sum(hdr.tcp.checksum, meta.v6sum);
+    hdr.tcp.checksum = ones_complement_sum(tmp, 0xffff - meta.v6sum);
 }
 
 action delta_ipv4_from_v6_to_v4()
 {
-    delta_prepare();
+    bit<16> tmp = 0;
 
+
+    tmp = tmp + (bit<16>) hdr.ipv4.version;          /* 4 bit */
+	tmp = tmp + (bit<16>) hdr.ipv4.ihl;              /* 4 bit */
+    tmp = tmp + (bit<16>) hdr.ipv4.diff_serv;        /* 6 bit */
+    tmp = tmp + (bit<16>) hdr.ipv4.ecn;              /* 2 bit */
+    tmp = tmp + (bit<16>) hdr.ipv4.totalLen;         /* 16 bit */
+    tmp = tmp + (bit<16>) hdr.ipv4.identification;   /* 16 bit */
+    tmp = tmp + (bit<16>) hdr.ipv4.flags;            /* 3 bit */
     /* we don't have ANY checksum, but tcp or udp: we can
        base on that ones for calculating the diff for IPv4
+
+    Does NOT contain payload! -> can be done manually
+    tmp = tmp + (bit<16>) hdr.ipv4.fragOffset;
+    tmp = tmp + (bit<16>) hdr.ipv4.ttl,
+    tmp = tmp + (bit<16>) hdr.ipv4.protocol,
+    tmp = tmp + (bit<16>) hdr.ipv4.src_addr,
+    tmp = tmp + (bit<16>) hdr.ipv4.dst_addr
+
     */
     hdr.ipv4.checksum = 0;    /* TO BE DONE! */
 }