diff --git a/core/plug-in/sipctrl/SipCtrlInterface.cpp b/core/plug-in/sipctrl/SipCtrlInterface.cpp
index e216ee9b..2f9542ed 100644
--- a/core/plug-in/sipctrl/SipCtrlInterface.cpp
+++ b/core/plug-in/sipctrl/SipCtrlInterface.cpp
@@ -438,7 +438,7 @@ void SipCtrlInterface::handle_sip_request(const char* tid, sip_msg* msg)
     if(msg->contact){
 
 	sip_nameaddr na;
-	char* c = msg->contact->value.s;
+	const char* c = msg->contact->value.s;
 	if(parse_nameaddr(&na,&c,msg->contact->value.len) < 0){
 	    DBG("Contact parsing failed\n");
 	}
@@ -496,7 +496,7 @@ void SipCtrlInterface::handle_sip_reply(sip_msg* msg)
 
     if(msg->contact){
 
-	char* c = msg->contact->value.s;
+	const char* c = msg->contact->value.s;
 	sip_nameaddr na;
 	
 	int err = parse_nameaddr(&na,&c,msg->contact->value.len);
diff --git a/core/plug-in/sipctrl/cstring.h b/core/plug-in/sipctrl/cstring.h
index bb33a211..26dc2ea8 100644
--- a/core/plug-in/sipctrl/cstring.h
+++ b/core/plug-in/sipctrl/cstring.h
@@ -32,7 +32,7 @@
 
 struct cstring 
 {
-    char*  s;
+    const char*  s;
     int  len;
 
     cstring()
@@ -43,11 +43,15 @@ struct cstring
 	: s(s), len(strlen(s))
     {}
 
-    cstring(char* s, int l)
-	: s(s), len(l)
+     cstring(const char* s) 
+     : s(s), len(strlen(s)) 
+     {} 
+
+    cstring(const char* s, int l)
+    : s(s), len(l)
     {}
 
-    void set(char* _s, int _len){
+    void set(const char* _s, int _len){
 	s = _s;
 	len = _len;
     }
@@ -56,6 +60,7 @@ struct cstring
 	s = 0;
 	len = 0;
     }
+  
 };
 
 #define c2stlstr(str) \
diff --git a/core/plug-in/sipctrl/hash_table.cpp b/core/plug-in/sipctrl/hash_table.cpp
index b4753d3d..dc6f03ee 100644
--- a/core/plug-in/sipctrl/hash_table.cpp
+++ b/core/plug-in/sipctrl/hash_table.cpp
@@ -101,7 +101,7 @@ sip_trans* trans_bucket::match_request(sip_msg* msg)
     DBG("do_3261_match = %i\n",do_3261_match);
     if(do_3261_match){
 	
-	char* branch = msg->via_p1->branch.s + MAGIC_BRANCH_LEN;
+	const char* branch = msg->via_p1->branch.s + MAGIC_BRANCH_LEN;
 	int   len = msg->via_p1->branch.len - MAGIC_BRANCH_LEN;
 	
 	trans_list::iterator it = elmts.begin();
@@ -273,7 +273,7 @@ sip_trans* trans_bucket::match_reply(sip_msg* msg)
     
     sip_trans* t = NULL;
 
-    char* branch = msg->via_p1->branch.s + MAGIC_BRANCH_LEN;
+    const char* branch = msg->via_p1->branch.s + MAGIC_BRANCH_LEN;
     int   len = msg->via_p1->branch.len - MAGIC_BRANCH_LEN;
     
     assert(get_cseq(msg));
diff --git a/core/plug-in/sipctrl/parse_common.cpp b/core/plug-in/sipctrl/parse_common.cpp
index e2e8ea9d..d0274ccd 100644
--- a/core/plug-in/sipctrl/parse_common.cpp
+++ b/core/plug-in/sipctrl/parse_common.cpp
@@ -38,16 +38,16 @@ using std::auto_ptr;
 // SIP version constants
 //
 
-char* SIP = "SIP";
+const char* SIP = "SIP";
 #define SIP_len 3
 
-char* SUP_SIPVER = "2.0";
+const char* SUP_SIPVER = "2.0";
 #define SUP_SIPVER_len 3
 
 
-int parse_sip_version(char* beg, int len)
+int parse_sip_version(const char* beg, int len)
 {
-    char* c = beg;
+    const char* c = beg;
     //char* end = c+len;
 
     if(len!=7){
@@ -76,7 +76,7 @@ int parse_sip_version(char* beg, int len)
 }
 
 
-int parse_gen_params(list<sip_avp*>* params, char** c, int len, char stop_char)
+int parse_gen_params(list<sip_avp*>* params, const char** c, int len, char stop_char)
 {
     enum {
 	VP_PARAM_SEP=0,
@@ -88,8 +88,8 @@ int parse_gen_params(list<sip_avp*>* params, char** c, int len, char stop_char)
 	VP_PVALUE_QUOTED
     };
 
-    char* beg = *c;
-    char* end = beg+len;
+    const char* beg = *c;
+    const char* end = beg+len;
     int saved_st=0,st=VP_PARAM_SEP;
 
     auto_ptr<sip_avp> avp(new sip_avp());
diff --git a/core/plug-in/sipctrl/parse_common.h b/core/plug-in/sipctrl/parse_common.h
index 23a6ba5f..89ef955a 100644
--- a/core/plug-in/sipctrl/parse_common.h
+++ b/core/plug-in/sipctrl/parse_common.h
@@ -144,9 +144,9 @@ struct sip_avp
 // Functions
 //
 
-inline int lower_cmp(char* l, char* r, int len)
+inline int lower_cmp(const char* l, const char* r, int len)
 {
-    char* end = l+len;
+    const char* end = l+len;
 
     while(l!=end){
 	if( LOWER_B(*l) != *r ){
@@ -158,8 +158,8 @@ inline int lower_cmp(char* l, char* r, int len)
     return 0;
 }
 
-int parse_sip_version(char* beg, int len);
+int parse_sip_version(const char* beg, int len);
 
-int parse_gen_params(list<sip_avp*>* params, char** c, int len, char stop_char);
+int parse_gen_params(list<sip_avp*>* params, const char** c, int len, char stop_char);
 
 #endif
diff --git a/core/plug-in/sipctrl/parse_cseq.cpp b/core/plug-in/sipctrl/parse_cseq.cpp
index f4c21cb7..d8efa58b 100644
--- a/core/plug-in/sipctrl/parse_cseq.cpp
+++ b/core/plug-in/sipctrl/parse_cseq.cpp
@@ -30,7 +30,7 @@
 
 #include "log.h"
 
-int parse_cseq(sip_cseq* cseq, char* beg, int len)
+int parse_cseq(sip_cseq* cseq, const char* beg, int len)
 {
     enum {
 	C_NUM=0,
@@ -39,8 +39,8 @@ int parse_cseq(sip_cseq* cseq, char* beg, int len)
     };
 
 
-    char* c = beg;
-    char* end = c+len;
+    const char* c = beg;
+    const char* end = c+len;
 
     int saved_st=0, st=C_NUM;
 
diff --git a/core/plug-in/sipctrl/parse_cseq.h b/core/plug-in/sipctrl/parse_cseq.h
index 085fc937..6e342475 100644
--- a/core/plug-in/sipctrl/parse_cseq.h
+++ b/core/plug-in/sipctrl/parse_cseq.h
@@ -45,7 +45,7 @@ struct sip_cseq: public sip_parsed_hdr
     {}
 };
 
-int parse_cseq(sip_cseq* cseq, char* beg, int len);
+int parse_cseq(sip_cseq* cseq, const char* beg, int len);
 
 inline sip_cseq* get_cseq(sip_msg* msg)
 {
diff --git a/core/plug-in/sipctrl/parse_from_to.cpp b/core/plug-in/sipctrl/parse_from_to.cpp
index 2b84bb65..d3146a70 100644
--- a/core/plug-in/sipctrl/parse_from_to.cpp
+++ b/core/plug-in/sipctrl/parse_from_to.cpp
@@ -38,7 +38,7 @@ sip_from_to::~sip_from_to()
     }
 }
 
-int parse_nameaddr(sip_nameaddr* na, char** c, int len)
+int parse_nameaddr(sip_nameaddr* na, const char** c, int len)
 {
     enum {
 
@@ -52,10 +52,10 @@ int parse_nameaddr(sip_nameaddr* na, char** c, int len)
     };
 
 
-    char* beg = *c;
-    char* end = *c + len;
+    const char* beg = *c;
+    const char* end = *c + len;
     
-    char* uri_end=0;
+    const char* uri_end=0;
 
     int saved_st=0, st=NA_SWS;
     //int ret=0;
@@ -232,7 +232,7 @@ int parse_nameaddr(sip_nameaddr* na, char** c, int len)
 }
 
 
-int parse_from_to(sip_from_to* ft, char* beg, int len)
+int parse_from_to(sip_from_to* ft, const char* beg, int len)
 {
     enum {
 	FTP_BEG,
@@ -244,8 +244,8 @@ int parse_from_to(sip_from_to* ft, char* beg, int len)
 	FTP_OTHER
     };
 
-    char* c = beg;
-    char* end = c+len;
+    const char* c = beg;
+    const char* end = c+len;
 
     int ret = parse_nameaddr(&ft->nameaddr,&c,len);
     if(ret) return ret;
@@ -257,8 +257,8 @@ int parse_from_to(sip_from_to* ft, char* beg, int len)
 	list<sip_avp*>::iterator it = ft->params.begin();
 	for(;it!=ft->params.end();++it){
 
-	    char* c = (*it)->name.s;
-	    char* end = c + (*it)->name.len;
+	    const char* c = (*it)->name.s;
+	    const char* end = c + (*it)->name.len;
 	    int st = FTP_BEG;
 	    
 	    for(;c!=end;c++){
diff --git a/core/plug-in/sipctrl/parse_from_to.h b/core/plug-in/sipctrl/parse_from_to.h
index af799db1..a6a27dc4 100644
--- a/core/plug-in/sipctrl/parse_from_to.h
+++ b/core/plug-in/sipctrl/parse_from_to.h
@@ -56,8 +56,8 @@ struct sip_from_to: public sip_parsed_hdr
     ~sip_from_to();
 };
 
-int parse_nameaddr(sip_nameaddr* na, char** c, int len);
-int parse_from_to(sip_from_to* ft, char* beg, int len);
+int parse_nameaddr(sip_nameaddr* na, const char** c, int len);
+int parse_from_to(sip_from_to* ft, const char* beg, int len);
 
 inline sip_from_to* get_from(sip_msg* msg)
 {
diff --git a/core/plug-in/sipctrl/parse_header.cpp b/core/plug-in/sipctrl/parse_header.cpp
index bda1abf4..931bc37a 100644
--- a/core/plug-in/sipctrl/parse_header.cpp
+++ b/core/plug-in/sipctrl/parse_header.cpp
@@ -58,16 +58,16 @@ using std::auto_ptr;
 // Low case headers 
 //
 
-char* TO_lc = "to";
-char* VIA_lc = "via";
-char* FROM_lc = "from";
-char* CSEQ_lc = "cseq";
-char* ROUTE_lc = "route";
-char* CALL_ID_lc = "call-id";
-char* CONTACT_lc = "contact";
-char* CONTENT_TYPE_lc = "content-type";
-char* RECORD_ROUTE_lc = "record-route";
-char* CONTENT_LENGTH_lc = "content-length";
+const char* TO_lc = "to";
+const char* VIA_lc = "via";
+const char* FROM_lc = "from";
+const char* CSEQ_lc = "cseq";
+const char* ROUTE_lc = "route";
+const char* CALL_ID_lc = "call-id";
+const char* CONTACT_lc = "contact";
+const char* CONTENT_TYPE_lc = "content-type";
+const char* RECORD_ROUTE_lc = "record-route";
+const char* CONTENT_LENGTH_lc = "content-length";
 
 
 sip_header::sip_header()
diff --git a/core/plug-in/sipctrl/parse_uri.cpp b/core/plug-in/sipctrl/parse_uri.cpp
index 0e1a9dfe..a75fe8ae 100644
--- a/core/plug-in/sipctrl/parse_uri.cpp
+++ b/core/plug-in/sipctrl/parse_uri.cpp
@@ -48,7 +48,7 @@ sip_uri::~sip_uri()
 }
 
 
-static int parse_sip_uri(sip_uri* uri, char* beg, int len)
+static int parse_sip_uri(sip_uri* uri, const char* beg, int len)
 {
     enum {
 	URI_USER=0, 
@@ -62,7 +62,7 @@ static int parse_sip_uri(sip_uri* uri, char* beg, int len)
     };
 
     int st  = URI_HOST;
-    char* c = beg;
+    const char* c = beg;
     //int escaped = 0;
 
     cstring tmp1, tmp2;
@@ -316,7 +316,7 @@ static int parse_sip_uri(sip_uri* uri, char* beg, int len)
     return 0;
 }
 
-int parse_uri(sip_uri* uri, char* beg, int len)
+int parse_uri(sip_uri* uri, const char* beg, int len)
 {
     enum {
 	URI_BEG=0,
@@ -327,7 +327,7 @@ int parse_uri(sip_uri* uri, char* beg, int len)
     };
 
     int st = URI_BEG;
-    char* c = beg;
+    const char* c = beg;
 
     for(;c!=beg+len;c++){
 	switch(st){
diff --git a/core/plug-in/sipctrl/parse_uri.h b/core/plug-in/sipctrl/parse_uri.h
index 34c9de64..459dfbc5 100644
--- a/core/plug-in/sipctrl/parse_uri.h
+++ b/core/plug-in/sipctrl/parse_uri.h
@@ -57,6 +57,6 @@ struct sip_uri
     ~sip_uri();
 };
 
-int parse_uri(sip_uri* uri, char* beg, int len);
+int parse_uri(sip_uri* uri, const char* beg, int len);
 
 #endif
diff --git a/core/plug-in/sipctrl/parse_via.cpp b/core/plug-in/sipctrl/parse_via.cpp
index e26fcee1..27b3c45f 100644
--- a/core/plug-in/sipctrl/parse_via.cpp
+++ b/core/plug-in/sipctrl/parse_via.cpp
@@ -51,7 +51,7 @@ sip_via::~sip_via()
     }
 }
 
-static int parse_transport(sip_transport* t, char** c, int len)
+static int parse_transport(sip_transport* t, const char** c, int len)
 {
     enum {
 
@@ -85,7 +85,7 @@ static int parse_transport(sip_transport* t, char** c, int len)
     t->val.s = *c;
 
     len -= SIPVER_len+1;
-    char* end = *c + len;
+    const char* end = *c + len;
 
     for(;**c && (*c!=end);(*c)++){
 
@@ -189,7 +189,7 @@ static int parse_transport(sip_transport* t, char** c, int len)
     return 0;
 }
 
-static int parse_by(cstring* host, cstring* port, char** c, int len)
+static int parse_by(cstring* host, cstring* port, const char** c, int len)
 {
     enum {
 	BY_HOST=0,
@@ -201,8 +201,8 @@ static int parse_by(cstring* host, cstring* port, char** c, int len)
 
     int saved_st=0, st=BY_HOST;
 
-    char* beg = *c;
-    char* end = beg+len;
+    const char* beg = *c;
+    const char* end = beg+len;
 
     for(;*c!=end;(*c)++){
 
@@ -347,7 +347,7 @@ static int parse_by(cstring* host, cstring* port, char** c, int len)
     return 0;
 }
 
-inline int parse_via_params(sip_via_parm* parm, char** c, int len)
+inline int parse_via_params(sip_via_parm* parm, const char** c, int len)
 {
     enum {
 	VP_BEG=0,
@@ -368,8 +368,8 @@ inline int parse_via_params(sip_via_parm* parm, char** c, int len)
     list<sip_avp*>::iterator it = parm->params.begin();
     for(;it != parm->params.end();++it){
 	
-	char* c   = (*it)->name.s;
-	char* end = c + (*it)->name.len;
+	const char* c   = (*it)->name.s;
+	const char* end = c + (*it)->name.len;
 	int   st  = VP_BEG;
 
 	for(;c!=end;c++){
@@ -413,7 +413,7 @@ inline int parse_via_params(sip_via_parm* parm, char** c, int len)
 }
 
 
-int parse_via(sip_via* via, char* beg, int len)
+int parse_via(sip_via* via, const char* beg, int len)
 {
     enum {
 	
@@ -424,8 +424,8 @@ int parse_via(sip_via* via, char* beg, int len)
     };
 
 
-    char* c   = beg;
-    char* end = beg+len;
+    const char* c   = beg;
+    const char* end = beg+len;
 
     int saved_st=0, st=V_TRANS;
 
diff --git a/core/plug-in/sipctrl/parse_via.h b/core/plug-in/sipctrl/parse_via.h
index 1e16054f..84ebedb1 100644
--- a/core/plug-in/sipctrl/parse_via.h
+++ b/core/plug-in/sipctrl/parse_via.h
@@ -67,7 +67,7 @@ struct sip_via: public sip_parsed_hdr
     ~sip_via();
 };
 
-int parse_via(sip_via* via, char* beg, int len);
+int parse_via(sip_via* via, const char* beg, int len);
 
 #define MAGIC_BRANCH_COOKIE "z9hG4bK"
 #define MAGIC_BRANCH_LEN    7
diff --git a/core/plug-in/sipctrl/sip_parser.cpp b/core/plug-in/sipctrl/sip_parser.cpp
index 43988238..201c106f 100644
--- a/core/plug-in/sipctrl/sip_parser.cpp
+++ b/core/plug-in/sipctrl/sip_parser.cpp
@@ -112,29 +112,29 @@ sip_msg::~sip_msg()
 }
 
 
-char* INVITEm = "INVITE";
+const char* INVITEm = "INVITE";
 #define INVITE_len 6
 
-char* ACKm = "ACK";
+const char* ACKm = "ACK";
 #define ACK_len 3
 
-char* OPTIONSm = "OPTIONS";
+const char* OPTIONSm = "OPTIONS";
 #define OPTIONS_len 7
 
-char* BYEm = "BYE";
+const char* BYEm = "BYE";
 #define BYE_len 3
 
-char* CANCELm = "CANCEL";
+const char* CANCELm = "CANCEL";
 #define CANCEL_len 6
 
-char* REGISTERm = "REGISTER";
+const char* REGISTERm = "REGISTER";
 #define REGISTER_len 8
 
 
-int parse_method(int* method, char* beg, int len)
+int parse_method(int* method, const char* beg, int len)
 {
-    char* c = beg;
-    char* end = c+len;
+    const char* c = beg;
+    const char* end = c+len;
 
     *method = sip_request::OTHER_METHOD;
 
diff --git a/core/plug-in/sipctrl/sip_parser.h b/core/plug-in/sipctrl/sip_parser.h
index 31b20e01..b9a7b12e 100644
--- a/core/plug-in/sipctrl/sip_parser.h
+++ b/core/plug-in/sipctrl/sip_parser.h
@@ -127,7 +127,7 @@ struct sip_msg
     ~sip_msg();
 };
 
-int parse_method(int* method, char* beg, int len);
+int parse_method(int* method, const char* beg, int len);
 int parse_sip_msg(sip_msg* msg);
 
 #endif
diff --git a/core/plug-in/sipctrl/trans_layer.cpp b/core/plug-in/sipctrl/trans_layer.cpp
index fba12bca..b78d2493 100644
--- a/core/plug-in/sipctrl/trans_layer.cpp
+++ b/core/plug-in/sipctrl/trans_layer.cpp
@@ -260,7 +260,7 @@ int trans_layer::set_next_hop(list<sip_header*>& route_hdrs,
 	sip_header* fr = route_hdrs.front();
 	
 	sip_nameaddr na;
-	char* c = fr->value.s;
+	const char* c = fr->value.s;
 	if(parse_nameaddr(&na, &c, fr->value.len)<0) {
 	    
 	    DBG("Parsing name-addr failed\n");
@@ -309,7 +309,7 @@ int trans_layer::set_next_hop(list<sip_header*>& route_hdrs,
 	    };
 
 	    int st = RR_PARAMS;
-	    char* end = fr->value.s + fr->value.len;
+	    const char* end = fr->value.s + fr->value.len;
 	    for(;c<end;c++){
 		
 		switch(st){
@@ -469,8 +469,8 @@ int trans_layer::send_request(sip_msg* msg, char* tid)
 				       msg->u.request->ruri_str);
 
     char branch_buf[BRANCH_BUF_LEN];
+    compute_branch(branch_buf,msg->callid->value,msg->cseq->value);
     cstring branch(branch_buf,BRANCH_BUF_LEN);
-    compute_branch(branch.s,msg->callid->value,msg->cseq->value);
     
     string via(transport->get_local_ip());
     if(transport->get_local_port() != 5060)
@@ -609,8 +609,8 @@ int trans_layer::cancel(trans_bucket* bucket, sip_trans* t)
 				       req->u.request->ruri_str);
 
     char branch_buf[BRANCH_BUF_LEN];
+    compute_branch(branch_buf,req->callid->value,get_cseq(req)->num_str);
     cstring branch(branch_buf,BRANCH_BUF_LEN);
-    compute_branch(branch.s,req->callid->value,get_cseq(req)->num_str);
     
     string via(transport->get_local_ip());
     if(transport->get_local_port() != 5060)
@@ -1091,7 +1091,7 @@ void trans_layer::send_200_ack(sip_msg* reply)
     }
     
     sip_nameaddr na;
-    char* c = reply->contact->value.s;
+    const char* c = reply->contact->value.s;
     if(parse_nameaddr(&na,&c,reply->contact->value.len) < 0){
 	DBG("Sorry, reply's Contact parsing failed: could not send ACK\n");
 	return;
@@ -1112,8 +1112,8 @@ void trans_layer::send_200_ack(sip_msg* reply)
     int request_len = request_line_len(cstring("ACK",3),r_uri);
    
     char branch_buf[BRANCH_BUF_LEN];
+    compute_branch(branch_buf,reply->callid->value,reply->cseq->value);
     cstring branch(branch_buf,BRANCH_BUF_LEN);
-    compute_branch(branch.s,reply->callid->value,reply->cseq->value);
 
     sip_header* max_forward = new sip_header(0,cstring("Max-Forwards"),cstring("10"));
 
@@ -1134,21 +1134,21 @@ void trans_layer::send_200_ack(sip_msg* reply)
     char* ack_buf = new char[request_len];
 
     // generate it
-    c = ack_buf;
+    char* msg = ack_buf;
 
-    request_line_wr(&c,cstring("ACK",3),r_uri);
-    via_wr(&c,via,branch);
+    request_line_wr(&msg,cstring("ACK",3),r_uri);
+    via_wr(&msg,via,branch);
 
-    copy_hdrs_wr(&c,route_hdrs);
+    copy_hdrs_wr(&msg,route_hdrs);
 
-    copy_hdr_wr(&c,reply->from);
-    copy_hdr_wr(&c,reply->to);
-    copy_hdr_wr(&c,reply->callid);
-    copy_hdr_wr(&c,max_forward);
-    cseq_wr(&c,get_cseq(reply)->num_str,cstring("ACK",3));
+    copy_hdr_wr(&msg,reply->from);
+    copy_hdr_wr(&msg,reply->to);
+    copy_hdr_wr(&msg,reply->callid);
+    copy_hdr_wr(&msg,max_forward);
+    cseq_wr(&msg,get_cseq(reply)->num_str,cstring("ACK",3));
 
-    *c++ = CR;
-    *c++ = LF;
+    *msg++ = CR;
+    *msg++ = LF;
 
     DBG("About to send 200 ACK: \n<%.*s>\n",request_len,ack_buf);