diff --git a/src/modules/tm/README b/src/modules/tm/README
index f1b236e936e..511f95f792b 100644
--- a/src/modules/tm/README
+++ b/src/modules/tm/README
@@ -74,6 +74,7 @@ Daniel-Constantin Mierla
               3.45. dns_reuse_rcv_socket (boolean)
               3.46. xavp_contact (string)
               3.47. event_callback (str)
+              3.48. relay_100 (str)
 
         4. Functions
 
@@ -215,53 +216,54 @@ Daniel-Constantin Mierla
    1.45. Set dns_reuse_rcv_socket parameter
    1.46. Set xavp_contact parameter
    1.47. Set event_callback parameter
-   1.48. t_relay usage
-   1.49. t_relay_to_udp usage
-   1.50. t_on_failure usage
-   1.51. t_on_branch_failure usage
-   1.52. t_on_reply usage
-   1.53. t_on_branch usage
-   1.54. t_newtran usage
-   1.55. t_reply usage
-   1.56. t_send_reply usage
-   1.57. t_lookup_request usage
-   1.58. t_retransmit_reply usage
-   1.59. t_release usage
-   1.60. t_forward_nonack usage
-   1.61. t_set_fr usage
-   1.62. t_reset_fr usage
-   1.63. t_set_max_lifetime usage
-   1.64. t_reset_max_lifetime usage
-   1.65. t_set_retr usage
-   1.66. t_reset_retr usage
-   1.67. t_set_auto_inv_100 usage
-   1.68. t_branch_timeout usage
-   1.69. t_branch_replied usage
-   1.70. t_any_timeout usage
-   1.71. t_any_replied usage
-   1.72. t_grep_status usage
-   1.73. t_is_canceled usage
-   1.74. t_is_expired usage
-   1.75. t_relay_cancel usage
-   1.76. t_lookup_cancel usage
-   1.77. t_drop_replies() usage
-   1.78. t_save_lumps() usage
-   1.79. t_load_contacts usage
-   1.80. t_next_contacts usage
-   1.81. t_next_contact_flow usage
-   1.82. t_check_status usage
-   1.83. t_check_trans usage
-   1.84. t_set_disable_6xx usage
-   1.85. t_set_disable_failover usage
-   1.86. t_set_disable_internal_reply usage
-   1.87. t_replicate usage
-   1.88. t_relay_to usage
-   1.89. t_set_no_e2e_cancel_reason usage
-   1.90. t_replicate usage
-   1.91. t_use_uac_headers usage
-   1.92. t_is_retr_async_reply usage
-   1.93. t_uac_send usage
-   1.94. event_route[tm:branch-failure] usage
+   1.48. Set relay_100 parameter
+   1.49. t_relay usage
+   1.50. t_relay_to_udp usage
+   1.51. t_on_failure usage
+   1.52. t_on_branch_failure usage
+   1.53. t_on_reply usage
+   1.54. t_on_branch usage
+   1.55. t_newtran usage
+   1.56. t_reply usage
+   1.57. t_send_reply usage
+   1.58. t_lookup_request usage
+   1.59. t_retransmit_reply usage
+   1.60. t_release usage
+   1.61. t_forward_nonack usage
+   1.62. t_set_fr usage
+   1.63. t_reset_fr usage
+   1.64. t_set_max_lifetime usage
+   1.65. t_reset_max_lifetime usage
+   1.66. t_set_retr usage
+   1.67. t_reset_retr usage
+   1.68. t_set_auto_inv_100 usage
+   1.69. t_branch_timeout usage
+   1.70. t_branch_replied usage
+   1.71. t_any_timeout usage
+   1.72. t_any_replied usage
+   1.73. t_grep_status usage
+   1.74. t_is_canceled usage
+   1.75. t_is_expired usage
+   1.76. t_relay_cancel usage
+   1.77. t_lookup_cancel usage
+   1.78. t_drop_replies() usage
+   1.79. t_save_lumps() usage
+   1.80. t_load_contacts usage
+   1.81. t_next_contacts usage
+   1.82. t_next_contact_flow usage
+   1.83. t_check_status usage
+   1.84. t_check_trans usage
+   1.85. t_set_disable_6xx usage
+   1.86. t_set_disable_failover usage
+   1.87. t_set_disable_internal_reply usage
+   1.88. t_replicate usage
+   1.89. t_relay_to usage
+   1.90. t_set_no_e2e_cancel_reason usage
+   1.91. t_replicate usage
+   1.92. t_use_uac_headers usage
+   1.93. t_is_retr_async_reply usage
+   1.94. t_uac_send usage
+   1.95. event_route[tm:branch-failure] usage
 
 Chapter 1. Admin Guide
 
@@ -318,6 +320,7 @@ Chapter 1. Admin Guide
         3.45. dns_reuse_rcv_socket (boolean)
         3.46. xavp_contact (string)
         3.47. event_callback (str)
+        3.48. relay_100 (str)
 
    4. Functions
 
@@ -685,6 +688,7 @@ failure_route["serial"]
    3.45. dns_reuse_rcv_socket (boolean)
    3.46. xavp_contact (string)
    3.47. event_callback (str)
+   3.48. relay_100 (str)
 
 3.1. fr_timer (integer)
 
@@ -1626,6 +1630,23 @@ function ksr_tm_event(evname)
 end
 ...
 
+3.48. relay_100 (str)
+
+   This parameter controls whether or not a SIP 100 response is proxied.
+   Note that this is not valid behavior when operating in stateful mode
+   per RFC 3261 Section 21.1.1, and therefore is useful only when
+   operating as a stateless proxy. When using this feature, it is possible
+   to control which 100 responses are proxied and which are not by
+   detecting whether they are part of an existing transaction and setting
+   up the appropriate logic in onreply_route.
+
+   Default value is 0 (disabled).
+
+   Example 1.48. Set relay_100 parameter
+...
+modparam("tm", "relay_100", 1)
+...
+
 4. Functions
 
    4.1. t_relay([host, port])
@@ -1701,7 +1722,7 @@ end
    Returns a negative value on failure -- you may still want to send a
    negative reply upstream statelessly not to leave upstream UAC in lurch.
 
-   Example 1.48. t_relay usage
+   Example 1.49. t_relay usage
 ...
 if (!t_relay())
 {
@@ -1728,7 +1749,7 @@ if (!t_relay())
    derived from the message uri (using sip specific DNS lookups), but with
    the protocol corresponding to the function name.
 
-   Example 1.49. t_relay_to_udp usage
+   Example 1.50. t_relay_to_udp usage
 ...
 if (src_ip==10.0.0.0/8)
         t_relay_to_udp("1.2.3.4", "5060"); # sent to 1.2.3.4:5060 over udp
@@ -1768,7 +1789,7 @@ else
    Meaning of the parameters is as follows:
      * failure_route - Failure route block to be called.
 
-   Example 1.50. t_on_failure usage
+   Example 1.51. t_on_failure usage
 ...
 route {
     t_on_failure("1");
@@ -1804,7 +1825,7 @@ failure_route[1] {
      * branch_failure_route - Name of the branch_failure route block to be
        called (it is prefixed internally with 'tm:branch-failure:').
 
-   Example 1.51. t_on_branch_failure usage
+   Example 1.52. t_on_branch_failure usage
 ...
 route {
     t_on_branch_failure("myroute");
@@ -1827,7 +1848,7 @@ event_route[tm:branch-failure:myroute] {
    Meaning of the parameters is as follows:
      * onreply_route - Onreply route block to be called.
 
-   Example 1.52. t_on_reply usage
+   Example 1.53. t_on_reply usage
 ...
 loadmodule "/usr/local/lib/ser/modules/nathelper.so"
 ...
@@ -1859,7 +1880,7 @@ es');
    Meaning of the parameters is as follows:
      * branch_route - branch route block to be called.
 
-   Example 1.53. t_on_branch usage
+   Example 1.54. t_on_branch usage
 ...
 route {
         t_on_branch("1");
@@ -1878,7 +1899,7 @@ branch_route[1] {
    the only way a script can add a new transaction in an atomic way.
    Typically, it is used to deploy a UAS.
 
-   Example 1.54. t_newtran usage
+   Example 1.55. t_newtran usage
 ...
 if (t_newtran()) {
     log("UAS logic");
@@ -1908,7 +1929,7 @@ if (t_newtran()) {
      * code - Reply code number.
      * reason_phrase - Reason string.
 
-   Example 1.55. t_reply usage
+   Example 1.56. t_reply usage
 ...
 t_reply("404", "Not found");
 ...
@@ -1926,7 +1947,7 @@ t_reply("404", "Not found");
      * code - Reply code number.
      * reason - Reason string.
 
-   Example 1.56. t_send_reply usage
+   Example 1.57. t_send_reply usage
 ...
 t_send_reply("404", "Not found");
 ...
@@ -1939,7 +1960,7 @@ t_send_reply("404", "Not found");
    none was found. However this is safely (atomically) done using
    t_newtran.
 
-   Example 1.57. t_lookup_request usage
+   Example 1.58. t_lookup_request usage
 ...
 if (t_lookup_request()) {
     ...
@@ -1950,7 +1971,7 @@ if (t_lookup_request()) {
 
    Retransmits a reply sent previously by UAS transaction.
 
-   Example 1.58. t_retransmit_reply usage
+   Example 1.59. t_retransmit_reply usage
 ...
 t_retransmit_reply();
 ...
@@ -1960,7 +1981,7 @@ t_retransmit_reply();
    Remove transaction from memory (it will be first put on a wait timer to
    absorb delayed messages).
 
-   Example 1.59. t_release usage
+   Example 1.60. t_release usage
 ...
 t_release();
 ...
@@ -1974,7 +1995,7 @@ t_release();
      * ip - IP address where the message should be sent.
      * port - Port number.
 
-   Example 1.60. t_forward_nonack usage
+   Example 1.61. t_forward_nonack usage
 ...
 t_forward_nonack("1.2.3.4", "5060");
 ...
@@ -2013,7 +2034,7 @@ t_forward_nonack("1.2.3.4", "5060");
 
    See also: fr_timer, fr_inv_timer, t_reset_fr().
 
-   Example 1.61. t_set_fr usage
+   Example 1.62. t_set_fr usage
 ...
 route {
         t_set_fr(10000); # set only fr invite timeout to 10s
@@ -2040,7 +2061,7 @@ branch_route[1] {
 
    See also: fr_timer, fr_inv_timer, t_set_fr.
 
-   Example 1.62. t_reset_fr usage
+   Example 1.63. t_reset_fr usage
 ...
 route {
 ...
@@ -2066,7 +2087,7 @@ route {
 
    See also: max_inv_lifetime, max_noninv_lifetime, t_reset_max_lifetime.
 
-   Example 1.63. t_set_max_lifetime usage
+   Example 1.64. t_set_max_lifetime usage
 ...
 route {
     if (src_ip=1.2.3.4)
@@ -2088,7 +2109,7 @@ route {
 
    See also: max_inv_lifetime, max_noninv_lifetime, t_set_max_lifetime.
 
-   Example 1.64. t_reset_max_lifetime usage
+   Example 1.65. t_reset_max_lifetime usage
 ...
 route {
 ...
@@ -2126,7 +2147,7 @@ route {
 
    See also: retr_timer1, retr_timer2, t_reset_retr().
 
-   Example 1.65. t_set_retr usage
+   Example 1.66. t_set_retr usage
 ...
 route {
         t_set_retr(250, 0); # set only T1 to 250 ms
@@ -2153,7 +2174,7 @@ branch_route[1] {
 
    See also: retr_timer1, retr_timer2, t_set_retr.
 
-   Example 1.66. t_reset_retr usage
+   Example 1.67. t_reset_retr usage
 ...
 route {
 ...
@@ -2169,7 +2190,7 @@ route {
 
    See also: auto_inv_100.
 
-   Example 1.67. t_set_auto_inv_100 usage
+   Example 1.68. t_set_auto_inv_100 usage
 ...
 route {
 ...
@@ -2184,7 +2205,7 @@ route {
    timeout. It can be used from FAILURE_ROUTE and BRANCH_FAILURE_ROUTE
    event route.
 
-   Example 1.68. t_branch_timeout usage
+   Example 1.69. t_branch_timeout usage
 ...
 failure_route[0]{
         if (t_branch_timeout()){
@@ -2200,7 +2221,7 @@ failure_route[0]{
    taken into account). It can be used from failure_route and
    branch-failure event route.
 
-   Example 1.69. t_branch_replied usage
+   Example 1.70. t_branch_replied usage
 ...
 failure_route[0]{
         if (t_branch_timeout()){
@@ -2217,7 +2238,7 @@ failure_route[0]{
    Returns true if at least one of the current transactions branches did
    timeout.
 
-   Example 1.70. t_any_timeout usage
+   Example 1.71. t_any_timeout usage
 ...
 failure_route[0]{
         if (!t_branch_timeout()){
@@ -2234,7 +2255,7 @@ failure_route[0]{
    receive some reply in the past. If called from a failure or onreply
    route, the "current" reply is not taken into account.
 
-   Example 1.71. t_any_replied usage
+   Example 1.72. t_any_replied usage
 ...
 onreply_route[0]{
         if (!t_any_replied()){
@@ -2248,7 +2269,7 @@ onreply_route[0]{
    Returns true if "code" is the final reply received (or locally
    generated) in at least one of the current transactions branches.
 
-   Example 1.72. t_grep_status usage
+   Example 1.73. t_grep_status usage
 ...
 onreply_route[0]{
         if (t_grep_status("486")){
@@ -2261,7 +2282,7 @@ onreply_route[0]{
 
    Returns true if the current transaction was canceled.
 
-   Example 1.73. t_is_canceled usage
+   Example 1.74. t_is_canceled usage
 ...
 failure_route[0]{
         if (t_is_canceled()){
@@ -2275,7 +2296,7 @@ failure_route[0]{
    Returns true if the current transaction has already been expired, i.e.
    the max_inv_lifetime/max_noninv_lifetime interval has already elapsed.
 
-   Example 1.74. t_is_expired usage
+   Example 1.75. t_is_expired usage
 ...
 failure_route[0]{
         if (t_is_expired()){
@@ -2296,7 +2317,7 @@ failure_route[0]{
    CANCELs were successfully sent to the pending branches, true if the
    INVITE was not found, and false in case of any error.
 
-   Example 1.75. t_relay_cancel usage
+   Example 1.76. t_relay_cancel usage
 if (method == CANCEL) {
         if (!t_relay_cancel()) {  # implicit drop if relaying was successful,
                                   # nothing to do
@@ -2323,7 +2344,7 @@ if (method == CANCEL) {
    overwritten with the flags of the INVITE. isflagset() can be used to
    check the flags of the previously forwarded INVITE in this case.
 
-   Example 1.76. t_lookup_cancel usage
+   Example 1.77. t_lookup_cancel usage
 if (method == CANCEL) {
         if (t_lookup_cancel()) {
                 log("INVITE transaction exists");
@@ -2353,7 +2374,7 @@ if (method == CANCEL) {
    Dropping replies works only if a new branch is added to the
    transaction, or it is explicitly replied in the script!
 
-   Example 1.77. t_drop_replies() usage
+   Example 1.78. t_drop_replies() usage
 ...
 failure_route[0]{
         if (t_check_status("5[0-9][0-9]")){
@@ -2384,7 +2405,7 @@ failure_route[0]{
    The transaction must be created by t_newtran() before calling
    t_save_lumps().
 
-   Example 1.78. t_save_lumps() usage
+   Example 1.79. t_save_lumps() usage
 route {
         ...
         t_newtran();
@@ -2443,7 +2464,7 @@ failure_route[1] {
 
    This function can be used from REQUEST_ROUTE and FAILURE_ROUTE.
 
-   Example 1.79. t_load_contacts usage
+   Example 1.80. t_load_contacts usage
 ...
 if (!t_load_contacts()) {
         sl_send_reply("500", "Server Internal Error - Cannot load contacts");
@@ -2484,7 +2505,7 @@ if (!t_load_contacts()) {
    contact_flows_avp are not anymore set. Based on that test, you can then
    use t_set_fr() function to set timers according to your needs.
 
-   Example 1.80. t_next_contacts usage
+   Example 1.81. t_next_contacts usage
 ...
 # First call after t_load_contacts() when transaction does not exist yet
 # and contacts should be available
@@ -2522,7 +2543,7 @@ if (!t_next_contacts()) {
    syslog). This function can be used from a BRANCH_FAILURE_ROUTE event
    route.
 
-   Example 1.81. t_next_contact_flow usage
+   Example 1.82. t_next_contact_flow usage
 ...
 event_route[tm:branch-failure:outbound]
 {
@@ -2545,7 +2566,7 @@ event_route[tm:branch-failure:outbound]
 
    This function can be used from ANY_ROUTE .
 
-   Example 1.82. t_check_status usage
+   Example 1.83. t_check_status usage
 ...
 if (t_check_status("(487)|(408)")) {
     log("487 or 408 negative reply\n");
@@ -2599,7 +2620,7 @@ Note
 
    See also: t_lookup_request(), t_lookup_cancel().
 
-   Example 1.83. t_check_trans usage
+   Example 1.84. t_check_trans usage
 if ( method == "CANCEL" && !t_check_trans())
         sl_reply("403", "cancel out of the blue forbidden");
 # note: in this example t_check_trans() can be replaced by t_lookup_cancel()
@@ -2614,7 +2635,7 @@ if ( method == "CANCEL" && !t_check_trans())
 
    See also: disable_6xx_block.
 
-   Example 1.84. t_set_disable_6xx usage
+   Example 1.85. t_set_disable_6xx usage
 ...
 route {
 ...
@@ -2629,7 +2650,7 @@ route {
 
    See also: use_dns_failover.
 
-   Example 1.85. t_set_disable_failover usage
+   Example 1.86. t_set_disable_failover usage
 ...
 route {
 ...
@@ -2642,7 +2663,7 @@ route {
 
    Turn off/on sending internally a SIP reply in case of relay errors.
 
-   Example 1.86. t_set_disable_internal_reply usage
+   Example 1.87. t_set_disable_internal_reply usage
 ...
 t_set_disable_internal_reply(1); # turn off sending internal reply on error
 if(!t_relay()) {
@@ -2675,7 +2696,7 @@ if(!t_relay()) {
      * hostport - address in "host:port" format. It can be given via an
        AVP.
 
-   Example 1.87. t_replicate usage
+   Example 1.88. t_replicate usage
 ...
 # sent to 1.2.3.4:5060 over tcp
 t_replicate("sip:1.2.3.4:5060;transport=tcp");
@@ -2709,7 +2730,7 @@ t_replicate_to_udp("1.2.3.4", "5060");
           + 0x02 - do not generate reply on internal error.
           + 0x04 - disable dns failover.
 
-   Example 1.88. t_relay_to usage
+   Example 1.89. t_relay_to usage
 ...
 # sent to 1.2.3.4:5060 over tcp
 t_relay_to("tcp:1.2.3.4:5060");
@@ -2735,7 +2756,7 @@ t_relay_to("0x01");
 
    See also: e2e_cancel_reason.
 
-   Example 1.89. t_set_no_e2e_cancel_reason usage
+   Example 1.90. t_set_no_e2e_cancel_reason usage
 ...
 route {
 ...
@@ -2758,7 +2779,7 @@ opying
      * onreply_route - the function returns true if an onreply route is
        set to be executed.
 
-   Example 1.90. t_replicate usage
+   Example 1.91. t_replicate usage
 ...
 if(!t_is_set("failure_route"))
     LM_DBG("no failure route will be executed for current transaction\n");
@@ -2772,7 +2793,7 @@ if(!t_is_set("failure_route"))
 
    It returns true.
 
-   Example 1.91. t_use_uac_headers usage
+   Example 1.92. t_use_uac_headers usage
 ...
 t_use_uac_headers();
 ...
@@ -2791,7 +2812,7 @@ t_use_uac_headers();
    returns true if the transaction is currently reply suspended or false
    if not.
 
-   Example 1.92. t_is_retr_async_reply usage
+   Example 1.93. t_is_retr_async_reply usage
 ...
 if (t_is_retr_async_reply()) {
         xlog("L_DBG", "Dropping retransmitted reply which is still currently sus
@@ -2816,7 +2837,7 @@ pended\n");
        Content-Type header must exist.
      * body - SIP message body (can be empty).
 
-   Example 1.93. t_uac_send usage
+   Example 1.94. t_uac_send usage
 ...
 t_uac_send("OPTIONS", "sip:alice@kamailio.org", "", "",
     "From: bob@kamailio.org;tag=2w3e\r\nTo: bob@kamailio.org", "");
@@ -2933,7 +2954,7 @@ t_uac_send("OPTIONS", "sip:alice@kamailio.org", "", "",
    enabled with the t_on_branch_failure function. This event_route uses
    the BRANCH_FAILURE_ROUTE route type.
 
-   Example 1.94. event_route[tm:branch-failure] usage
+   Example 1.95. event_route[tm:branch-failure] usage
 ...
 request_route {
     ...