diff -dur -x '*~' sipp-3.3.orig/call.cpp sipp-3.3/call.cpp
--- sipp-3.3.orig/call.cpp	2013-06-14 15:24:31.000000000 +0200
+++ sipp-3.3/call.cpp	2013-06-14 15:37:04.000000000 +0200
@@ -3963,7 +3963,7 @@
     return E_AM_UNEXP_BYE;
   } else if (strcmp(P_recv, "CANCEL") == 0) {
     return E_AM_UNEXP_CANCEL;
-  } else if (strcmp(P_recv, "PING") == 0) {
+  } else if (strcmp(P_recv, "PING") == 0 || strcmp(P_recv, "OPTIONS") == 0) {
     return E_AM_PING;
   } else if (((strcmp(P_recv, "INFO") == 0) || (strcmp(P_recv, "NOTIFY") == 0) || (strcmp(P_recv, "UPDATE") == 0)) 
                && (auto_answer == true)){
Only in sipp-3.3.orig: call.cpp.orig
diff -dur -x '*~' sipp-3.3.orig/sipp.cpp sipp-3.3/sipp.cpp
--- sipp-3.3.orig/sipp.cpp	2013-02-07 00:11:47.000000000 +0100
+++ sipp-3.3/sipp.cpp	2013-06-14 15:38:04.000000000 +0200
@@ -3410,6 +3410,7 @@
     } else if (auto_answer &&
               ((strstr(msg, "NOTIFY") == msg)  ||
                (strstr(msg, "INFO")   == msg)  ||
+               (strstr(msg, "OPTIONS")== msg)  ||
                (strstr(msg, "UPDATE") == msg))) {
 	  // If auto answer mode, try to answer the incoming message
 	  // with automaticResponseMode