---
title: "tm Module"
description: "TM module enables stateful processing of SIP transactions."
---

## Admin Guide


### Overview


TM module enables stateful processing of SIP 
transactions. The main use of stateful logic, which is costly in 
terms of memory and CPU, is some services 
inherently need state. For example, transaction-based accounting 
(module acc) needs to process transaction state as opposed to 
individual messages, and any kinds of forking must be implemented 
statefully. Other use of stateful processing is it trading
CPU caused by retransmission processing for memory.
That makes however only sense if CPU consumption 
per request is huge. For example, if you want to avoid costly 
DNS resolution for every retransmission of a 
request to an unresolvable destination, use stateful mode. Then,
only the initial message burdens server by DNS 
queries, subsequent retransmissions will be dropped and will not 
result in more processes blocked by DNS resolution.
The price is more memory consumption and higher processing latency.


From user's perspective, the major function is t_relay(). It setup 
transaction state, absorb retransmissions from upstream, generate 
downstream retransmissions and correlate replies to requests.


In general, if TM is used, it copies clones of 
received SIP messages in shared memory. That costs the memory and 
also CPU time (memcpys, lookups, shmem locks, etc.)
Note that non-TM functions operate over the 
received message in private memory, that means that any core 
operations will have no effect on statefully processed messages after 
creating the transactional state. For example, calling record_route 
*after* t_relay is pretty useless, as the 
RR is added to privately held message whereas its
TM clone is being forwarded.


TM is quite big and uneasy to program--lot of 
mutexes, shared memory access, malloc and free, timers--you really 
need to be careful when you do anything. To simplify 
TM programming, there is the instrument of 
callbacks. The callback mechanisms allow programmers to register 
their functions to specific event. See t_hooks.h for a list of 
possible events.


Other things programmers may want to know is UAC--it is a very 
simplistic code which allows you to generate your own transactions. 
Particularly useful for things like NOTIFYs or IM 
gateways. The UAC takes care of all the transaction machinery: 
retransmissions , FR timeouts, forking, etc.  See t_uac prototype 
in uac.h for more details. Who wants to see the transaction result 
may register for a callback.


#### Per-Branch flags


First what is the idea with the branch concept: branch route is a 
route to be execute separately for each branch before being sent 
out - changes in that route should reflect only on that branch.


There are several types of flags in OpenSIPS :


- *message/transaction* flags - they are 
visible everywhere in the transaction (in all routes and in 
all sequential replies/request).
- *branch* flags - flags that are visible only
from a specific branch - in all replies and routes connected 
to this branch.
- *script* flags - flags that exist only
during script execution. They are not store anywhere and are
lost once the top level route was left.


For example: I have a call parallel forking to GW and to a user. And I 
would like to know from which branch I will get the final negative 
reply (if so). I will set a branch route before relaying the calls 
(with the 2 branches). The branch route will be separately executed 
for each branch; in the branch going to GW (I can identified it by 
looking to RURI), I will set a branch flag. This flag will appear 
only in the onreply route run for replied from GW. It will be also be 
visible in failure route if the final elected reply belongs to the 
GW branch. This flags will not be visible in the other branch 
(in routes executing replies from the other branch).


For how to define branch flags and use via script, see 
[t on branch](#t_on_branchbranch_route) and the setbflag(), resetbflag() and
isbflagset() script functions.


Also, modules may set branch flags before transaction creation 
(for the moment this feature is not available in script). The 
REGISTRAR module was the first to use this type of flags. The NAT flag 
is pushed in branch flags instead in message flags


#### Timeout-Based Failover


Timeouts can be used to trigger failover behavior. E.g. if we send a call
to a gateway and the gateway does not send a provisional response within 3
seconds, we want to cancel this call and send the call to another 
gateway. Another example is to ring a SIP client only for 30 seconds 
and then redirect the call to the voicemail.


The transaction module exports two types of timeouts:


- **[fr timeout](#fr_timeout-integer)** - used when no response was
received yet. If there is no response after
*[fr timeout](#fr_timeout-integer)* seconds, the timer triggers
(and failure route will be executed if t_on_failure() was
called). For INVITE transactions, if a provisional response was
received, the timeout is reset to *[fr inv timeout](#fr_inv_timeout-integer)*
seconds and RT_T2 for all other transactions. Once a final response
is received, the transaction has finished.
- **fr_inv_timeout** - this timeout
starts counting down once a provisional response was received
for an INVITE transaction.


For example: You want to have failover if there is no provisional 
response after 3 seconds, but you want to ring for 60 seconds. 
Thus, set the *[fr timeout](#fr_timeout-integer)* to 3 and 
*fr_inv_timeout* to 60.


#### DNS Failover


DNS based failover can be use when relaying stateful requests. 
According to RFC 3263, DNS failover should be done on transport level
or transaction level. TM module supports them both.


Failover at transport level may be triggered by a failure of sending
out the request message. A failure occurs if the corresponding 
interface was found for sending the request, if the TCP connection
was refused or if a generic internal error happened during send. There
is no ICMP error report support.


Failover at transaction level may be triggered when the transaction
completed either with a 503 reply, either with a timeout without
any received reply. In such a case, automatically, a new branch will
be forked if any other destination IPs can be used to deliver the 
requests. The new branch will be a clone of the winning branch.


The set of destinations IPs is step-by-step build (on demand) based on
the NAPTR, SRV and A records available for the destination domain.


DNS-based failover is by default applied excepting when this failover
is globally disabled (see the core parameter disable_dns_failover) or
when the relay flag (per transaction) is set (see the t_relay()
function).


#### Anycast Scenario


Doing a load balancing scenario using
[Anycast IPs](https://en.wikipedia.org/wiki/Anycast),
one might run into an issue where a transaction request comes on
one instance, and the reply (or replies) comes on different ones.
This would normaly break the transaction state, because the local
transaction will start re-transmissios and would eventually timeout.
Moreover, from UA's perspective, the reply whould have been sent,
but since it reaches a proxy that is not aware of that transaction,
it will not be forwarded (nor ACKed in case of INVITES). And from
this point things can escalade quickly.


To sort out these problems, the module uses a distributed mechanism
to figure out where the transaction for a specific reply was created.
When an instance receives a reply that does not have an associated
transaction, it replicates it to be handled by the instance that
"owns" it. This is achieved using the
*clusterer* module support.


Setting up an anycast scenario is very simple: all the instances
that are part of an anycast secnario must be set up in a cluster
(more info at the [tm replication cluster](#tm_replication_cluster-integer) param).
When a transaction is created, a special identifier is appended to
the branch parameter, namely the instance that created the
transaction. When a reply comes in, the transaction module checks who
"owns" the transaction. If the identifier is the
instance's own id, then the reply is processed locally. Otherwise
it is replicated to the node indicated by the id. Replication is
done in a very efficient manner, using the
*proto_bin* transport.


Special handling is applied to *CANCEL* and
*ACK* methods. Due to the fact that these
methods do not contain the special identifier in the branch
parameter (since they are generated by the UAC and not by us),
there is no way to determine who "owns" the transaction.
Therefore, if we do not find a local transaction for these
requests, we broadcast them to all the other instances using
the [t anycast replicate](#t_anycast_replicate) function. Again,
this is done in a very efficient manner using the
*proto_bin* transport.


#### Usage Scope


Transaction functions and variables are only designed to be
called on SIP request messages where a transaction can be created, or
in routes that are transaction aware, such as
*branch_route[name]*,
*failure_route[name]* or
*onreply_route[name]*. Using TM functtions or
variables in a route that is not transaction aware, such as
the generic *onreply_route*,
*error_route* or
*timer_route[name, timer]* may lead to undefined
behavior, and most of the time in bogus or malformed signalling.
Therefore it is strongly recommended to avoid using them in non-tm
context aware routes.


### Dependencies


#### OpenSIPS Modules


The following modules must be loaded before this module:


- *clusterer* module, if the anycast
scenario is enabled (see [tm replication cluster](#tm_replication_cluster-integer)
param for more information).


#### External Libraries or Applications


The following libraries or applications must be installed before 
running OpenSIPS with this module loaded:


- *None*.


### Exported Parameters


#### fr_timeout (integer)


Timeout which is triggered if no final reply for a request or ACK for a 
negative INVITE reply arrives (in seconds).


*Default value is 30 seconds.*


```opensips title="Set fr_timeout parameter"
...
modparam("tm", "fr_timeout", 10)
...
```


#### fr_inv_timeout (integer)


Timeout which is triggered if no final reply for an INVITE arrives after a 
provisional message was received (in seconds). This timeout starts
counting down once the first provisional response is received. Thus,
fast failover (no 100 trying from gateway) can be achieved by setting
*[fr timeout](#fr_timeout-integer)* to low values.
See example below.


*Default value is 120 seconds.*


```opensips title="Set fr_inv_timeout parameter"
...
modparam("tm", "fr_inv_timeout", 200)
...
```


#### wt_timer (integer)


Time for which a transaction stays in memory to absorb delayed 
messages after it completed; also, when this timer hits, 
retransmission of local cancels is stopped (a puristic but complex 
behavior would be not to enter wait state until local branches
are finished by a final reply or FR timer--we simplified).


For non-INVITE transaction this timer relates to timer J of RFC 3261 
section 17.2.2. According to the RFC this timer should be 64*T1 
(= 32 seconds). But this would increase memory usage as the transactions
are kept in memory very long.


*Default value is 5 seconds.*


```opensips title="Set wt_timer parameter"
...
modparam("tm", "wt_timer", 10)
...
```


#### delete_timer (integer)


Time after which a to-be-deleted transaction currently ref-ed by a
process will be tried to be deleted again.


*Default value is 2 seconds.*


```opensips title="Set delete_timer parameter"
...
modparam("tm", "delete_timer", 5)
...
```


#### T1_timer (integer)


Retransmission T1 period, in milliseconds.


*Default value is 500 milliseconds.*


```opensips title="Set T1_timer parameter"
...
modparam("tm", "T1_timer", 700)
...
```


#### T2_timer (integer)


Maximum retransmission period, in milliseconds.


*Default value is 4000 milliseconds.*


```opensips title="Set T2_timer parameter"
...
modparam("tm", "T2_timer", 8000)
...
```


#### ruri_matching (integer)


Should be request-uri matching used as a part of pre-3261 transaction
matching as the standard wants us to do so? Turn only off for better 
interaction with devices that are broken and send different r-uri in
CANCEL/ACK than in original INVITE.


*Default value is 1 (true).*


```opensips title="Set ruri_matching parameter"
...
modparam("tm", "ruri_matching", 0)
...
```


#### via1_matching (integer)


Should be top most VIA matching used as a part of pre-3261 transaction
matching as the standard wants us to do so? Turn only off for better 
interaction with devices that are broken and send different top most
VIA in CANCEL/ACK than in original INVITE.


*Default value is 1 (true).*


```opensips title="Set via1_matching parameter"
...
modparam("tm", "via1_matching", 0)
...
```


#### unix_tx_timeout (integer)


Send timeout to be used by function which use UNIX sockets 
(as t_write_unix).


*Default value is 2 seconds.*


```opensips title="Set unix_tx_timeout parameter"
...
modparam("tm", "unix_tx_timeout", 5)
...
```


#### restart_fr_on_each_reply (integer)


If true (non null value), the final response timer will be re-triggered
for each received provisional reply. In this case, final response
timeout may occur after a time longer than *[fr inv timeout](#fr_inv_timeout-integer)*
(if UAS keeps sending provisional replies)


*Default value is 1 (true).*


```opensips title="Set restart_fr_on_each_reply parameter"
...
modparam("tm", "restart_fr_on_each_reply", 0)
...
```


#### tw_append (string)


List of additional information to be appended by t_write_req and
t_write_unix functions.


*Default value is null string.*


Syntax of the parameter is:


- *tw_append = append_name':' element (';'element)**
- *element = ( [name '='] variable)*


Each element will be appended per line in 
"name: value" format. Element 
"$rb (message body)"
is the only one which does not accept name; the body it will be
printed all the time at the end, disregarding its position in the
definition string.


```opensips title="Set tw_append parameter"
...
modparam("tm", "tw_append",
   "test: ua=$hdr(User-Agent) ;avp=$avp(avp);$rb;time=$Ts")
...
```


#### pass_provisional_replies (integer)


Enable/disable passing of provisional replies to FIFO applications.


*Default value is 0.*


```opensips title="Set pass_provisional_replies parameter"
...
modparam("tm", "pass_provisional_replies", 1)
...
```


#### syn_branch (integer)


Enable/disable the usage of stateful synonym branch IDs in the 
generated Via headers. They are faster but not reboot-safe.


*Default value is 1 (use synonym branches).*


```opensips title="Set syn_branch parameter"
...
modparam("tm", "syn_branch", 0)
...
```


#### onreply_avp_mode (integer)


Describes how the AVPs should be handled in reply route:


- *0* - the AVPs will be per message only; they 
will not interfere with the AVPS stored in transaction; initially
there will be an empty list and at the end of the route, all AVPs
that were created will be discarded.
- *1* - the AVPs will be the transaction AVPs;
initially the transaction AVPs will be visible; at the end of the
route, the list will attached back to transaction (with all the 
changes)


In mode 1, you can see the AVPs you set in request route, branch route
or failure route. The side effect is performance as more locking is 
required in order to keep the AVP's list integrity.


*Default value is 0.*


```opensips title="Set onreply_avp_mode parameter"
...
modparam("tm", "onreply_avp_mode", 1)
...
```


#### disable_6xx_block (integer)


Tells how the 6xx replies should be internally handled:


- *0* - the 6xx replies will block any further
serial forking (adding new branches). This is the RFC3261
behaviour.
- *1* - the 6xx replies will be handled as any
other negative reply - serial forking will be allowed.
Logically, you need to break RFC3261 if you want to do redirects
to announcement and voicemail services.


*Default value is 0.*


```opensips title="Set disable_6xx_block parameter"
...
modparam("tm", "disable_6xx_block", 1)
...
```


#### enable_stats (integer)


Enables statistics support in TM module - If enabled, the TM module
will internally keep several statistics and export them via the 
MI - Management Interface.


*Default value is 1 (enabled).*


```opensips title="Set enable_stats parameter"
...
modparam("tm", "enable_stats", 0)
...
```


#### minor_branch_flag (string/integer)


A branch flag index to be used in script to mark the minor branches 
( before t_relay() ).


A minor branch is a branch OpenSIPS will not wait to complete during
parallel forking. So, if the rest of the branches are negativly replied
OpenSIPS will not wait for a final answer from the minor branch, but
it will simply cancel it.


Main applicability of minor branch is to fork a branch to a media 
server for injecting (via 183 Early Media) some pre-call media - of
course, this branch will be transparanent for the rest of the call
branches (from branch selection point of view).


*Default value is none (disabled).*


```opensips title="Set minor_branch_flag parameter"
...
modparam("tm", "minor_branch_flag", "MINOR_BFLAG")
...
```


#### timer_partitions (integer)


The number of partitions for the internal TM timers (retransmissions,
delete, wait, etc). Partitioning the timers increase the throughput
under heavly load by handling timer events in parallel, rather than
all serial.


Recomanded range for timer partitions is max 16 (soft limit).


*Default value is 1 (disabled).*


```opensips title="Set timer_partitions parameter"
...
# Enable two timer partitions
modparam("tm", "timer_partitions", 2)
...
```


#### auto_100trying (integer)


This parameter controls if the TM module should automatically 
generate an 100 Trying stateful reply when an INVITE transaction
is created.


You may want to disable this behavior if you want to control from
script level when the 100 Trying is to be sent out.


*Default value is 1 (enabled).*


```opensips title="Set auto_100trying parameter"
...
# Disable automatic 100 Trying
modparam("tm", "auto_100trying", 0)
...
```


#### tm_replication_cluster (integer)


This parameter should be used in an anycast setup, and specifies
the cluster id of all the nodes that use an anycast IP.


Check out the [tm anycast](#anycast-scenario) section for more details.


*Anycast replication is disabled by default.*


```opensips title="Set tm_replication_cluster parameter"
...
# replicate anycast messages in cluster 1
modparam("tm", "tm_replication_cluster", 1)
...
```


#### cluster_param (string)


This parameter should be used in an anycast setup, and specifies
the name of the parameter used in the VIA branch param to specifiy
the instance id that created the transaction.


Check out the [tm anycast](#anycast-scenario) section for more details.


*Default value is *cid*.*


```opensips title="Set the cluster_param parameter"
...
modparam("tm", "cluster_param", "tid")
...
```


#### cluster_auto_cancel (boolean)


This parameter should be used in an anycast setup, and specifies
whether a *CANCEL* message received on a
listener that is marked as anycast should be automatically handled,
or should get in the OpenSIPS script. If this parameter is enabled
(default), *CANCEL* messages received on an
anycast listener will never enter the script, thus making the
script cleaner.


Check out the [tm anycast](#anycast-scenario) section for more details.


*Default value is *yes* (enabled).*


```opensips title="Set the cluster_auto_cancel parameter"
...
# disable auto-cancel handling
modparam("tm", "cluster_auto_cancel", no)
...
```


#### local_request_route (string)


This parameter points to a route, which is executed whenever TM is
about to send out a locally generated request (e.g., through the 
B2B modules or through MI).


The purpose of this route is limited to exposing the content of the 
request as SIP message


The route is executed with the generated message by TM, incorporating
all modifications.


> [!IMPORTANT]
> This route is executed AFTER the local_route (if defined)
> and it expose all the changes from that route.


> [!IMPORTANT]
> This route is to be used in a read-only manner, inspection
> only. Any changes you do here will discarded.


> [!IMPORTANT]
> This route does not offer any message, transactional or
> dialog context, so do not rely on any variables with scope (like AVPs).


```opensips title="Set the local_request_route parameter"
...
# Execute the route "local_request_route" upon sending a request
modparam("tm", "local_request_route", "tm_local_request")

route[tm_local_request] {
	if (is_method("INVITE") && $rb(application/sdp) && !has_totag()) {
		$avp(sdp_request) := $rb(application/sdp);
	}
}
...
```


#### local_reply_route (string)


This parameter points to a route, which is executed whenever TM is
about to send out a locally generated reply (e.g., through the 
B2B modules or through MI).


The purpose of this route is limited to exposing the content of the 
reply as SIP message


> [!IMPORTANT]
> This route is to be used in a read-only manner, inspection
> only. Any changes you do here will discarded.


> [!IMPORTANT]
> This route does not offer any message, transactional or
> dialog context, so do not rely on any variables with scope (like AVPs).


```opensips title="Set the local_reply_route parameter"
...
# Execute the route "tm_local_reply" upon sending a request
modparam("tm", "local_reply_route", "tm_local_reply")

route[tm_local_reply] {
	if (is_method("BYE")) {
		$var(rc) = rest_get("http://localhost/qos/delete",
					$var(recv_body), $var(recv_ct), $var(rcode));
	}
}

...
```


### Exported Functions


#### t_relay([flags],[outbound_proxy])


Relay a message statefully to destination indicated in current URI. 
(If the original URI was rewritten by UsrLoc, RR, strip/prefix, etc., 
the new URI will be taken). Returns a negative value on failure--you 
may still want to send a negative reply upstream statelessly not to 
leave upstream UAC in lurch.


The coresponding transaction may or may not be already created. If not
yet created, the function will automatically create it.


The function may take two optional parameters.


The first parameter is a comma separated list of string flags for
controlling the internal behaviour. The supported flags are:


- *no-auto-477* - (old
*0x02* flag) do not internally generate
and send a "477 Send failed (477/TM)" SIP reply in case of a
global forwarding failure (i.e. forwarding for each branch has
failed due to internal errors, bad R-URI, bad message, lack of
network reachability, etc.).

	This flag only applies if the transaction was
	not previously created by [t newtran](#t_newtran).
	When a global forwarding failure occurs, no SIP request is
	relayed and therefore no negative SIP reply or timeout will
	show up on the failure_route, if one is set.
Useful if you want to implement a failover logic for when none
of the currently created branches can be forwarded to.
- *no-dns-failover* - (old
*0x04* flag) disable the DNS failover
for the transaction. Only first IP will be used. It disables
the failover both at transport and transaction level.
- *pass-reason-hdr* - (old
*0x08* flag) If the request is a CANCEL,
trust and pass further the Reason header from the received
CANCEL - shortly, will propagate the Reason header.
- *allow-no-cancel* - (old
*0x10* flag) Allows OpenSIPS to inspect
and follow the Content-Disposition "no-cancel" indication (if
present). As per RFC3841, section 9.1, the TM module may be 
instructed not to cancel all ongoing branches when a 2xx reply
is received. It will keep the pending branches ongoing until
(1) all branches will receive a final reply or (2) the 
transactionhits the timeout.


The second parameter is a string representing an outbound proxy
(a fixed destination) where the message should be sent. The
destination is specified as "[proto:]host[:port]". If a 
destination URI "$du" for this message was set before the
function is called then this value will be used as the destination 
instead of the function parameter.


In case of error, the function returns the following codes:


- *-1* - generic internal error
- *-2* - bad message (parsing errors)
- *-3* - no destination available 
(no branches were added or request already cancelled)
- *-4* - bad destination 
(unresolvable address)
- *-5* - destination filtered 
(black listed)
- *-6* - generic send failed


This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.


```opensips title="t_relay usage"
...
if (!t_relay()) {
    sl_reply_error();
    exit;
}
...
t_relay( ,"tcp:192.168.1.10:5060");
...
t_relay(0x1, "mydomain.com:5070");
...
```


#### t_reply(code, reason_phrase)


Sends a stateful SIP reply to the currently processed requests. Note 
that if the transaction was not created yet, it will automatically
created by internally using the
`t_newtran` function.


Meaning of the parameters is as follows:


- *code (int)* - Reply code number.
- *reason_phrase (string)* - Reason string.


This function can be used from REQUEST_ROUTE, FAILURE_ROUTE.


```opensips title="t_reply usage"
...
t_reply(404, "Use $rU not found");
...
```


#### t_reply_with_body(code, reason_phrase, body)


Sends a stateful SIP reply with a body to the currently processed 
requests. Note that if the transaction was not created yet, it will 
automatically created by internally using the
`t_newtran` function.


Meaning of the parameters is as follows:


- *code (int)* - Reply code number.
- *reason_phrase (string)* - Reason string.
- *body (string)* - Reply body.


This function can be used from REQUEST_ROUTE and FAILURE_ROUTE.


```opensips title="t_reply_with_body usage"
...
	if(is_method("INVITE"))
	{
		append_to_reply("Contact: $var(contact)\r\n"
				"Content-Type: application/sdp\r\n");
		t_reply_with_body(200, "Ok", $var(body));
		exit;
	}
...
```


#### t_newtran()


Creates the SIP transaction for the currently processed SIP request,
thus switching to stateful processing.  For INVITE requests, a 100
Trying reply will be immediately sent, unless
[auto 100trying](#auto_100trying-integer) is disabled.  Once a SIP
transaction is created, calling [t newtran](#t_newtran) for
retransmitted requests will end the OpenSIPS script execution, with the
lastly sent reply being retransmitted upstream.


This function can be used from REQUEST_ROUTE.


```opensips title="t_newtran usage"
...
t_newtran();  # 100 Trying is fired here
xlog("doing my complicated routing logic\n");
....
t_relay(); # send the call further
...
```


#### t_check_trans()


Returns true if the current request is associated to a transaction. 
The relationship between the request and transaction is defined as
follows:


- *non-CANCEL/non-ACK requests* - if the
request belongs to a transaction (it's a retransmision), the
function will do a standard processing of the retransmission and
will break/stop the script. The function returns false if the
request is not a retransmission.
- *CANCEL request* - true if the cancelled
INVITE transaction exists.
- *ACK request* - true if the ACK is a
hop-by-hop ACK (to a negative reply) corresponding to an previous
INVITE transaction. [!IMPORTANT] this function returns false (return
code *-2*) for end-to-end ACKs (to 2xx replies
from a different transaction).


> [!NOTE]
> To detect retransmissions using this function you have to make 
> sure that the initial request has already created a transaction, e.g. 
> by using t_relay(). If the processing of requests may take long time 
> (e.g. DB lookups) and the retransmission arrives before t_relay() is 
> called, you can use the t_newtran() function to manually create a 
> transaction.


This function can be used from REQUEST_ROUTE and BRANCH_ROUTE.


```opensips title="t_check_trans usage"
...
if ( is_method("CANCEL") ) {
	if ( t_check_trans() )
		t_relay();
	exit;
}
...
```


#### t_check_status(re)


Returns true if the regualr expression "re" match the 
reply code of the response message as follows:


- *in routing block* - the code of the
last sent reply.
- *in on_reply block* - the code of the
current received reply.
- *in on_failure block* - the code of the
selected negative final reply.


This function can be used from REQUEST_ROUTE, ONREPLY_ROUTE, 
FAILURE_ROUTE and BRANCH_ROUTE .


```opensips title="t_check_status usage"
...
if (t_check_status("(487)|(408)")) {
    log("487 or 408 negative reply\n");
}
...
```


#### t_local_replied(reply)


Returns true if all or last (depending of the parameter) reply(es) were
local generated (and not received).


Parameter may be "all" or "last".


This function can be used from REQUEST_ROUTE, BRANCH_ROUTE,
FAILURE_ROUTE and ONREPLY_ROUTE.


```opensips title="t_local_replied usage"
...
if (t_local_replied("all")) {
	log ("no reply received\n");
}
...
```


#### t_was_cancelled()


Retuns true if called for an INVITE transaction that was explicitly
cancelled by UAC side via a CANCEL request.


This function can be used from ONREPLY_ROUTE, FAILURE_ROUTE.


```opensips title="t_was_cancelled usage"
...
if (t_was_cancelled()) {
    log("transaction was cancelled by UAC\n");
}
...
```


#### t_cancel_branch([flags])


This function is to be call when a reply is received for cancelling a
set of branches (see flags) of the current call.


Meaning of the parameters is as follows:


- *flags (string, optional)* - set of flags 
(char based flags) to control what branches to be cancelled:

  - *a* - all - cancel all pending 
branches
  - *o* - others - cancel all the other
pending branches except the current one
  - *empty* - current - cancel only the
current branch


This function can be used from ONREPLY_ROUTE.


```opensips title="t_cancel_branch usage"
onreply_route[3] {
...
	if (t_check_status(183)) {
		# no support for early media
		t_cancel_branch();
	}
...
}
```


#### t_new_request( method, RURI, from, to [, body[, ctx]])


This function generates and sends out a new SIP request (in a stateful way).
The new request is completly unrelated to the currently processed SIP message.


Meaning of the parameters is as follows (all do accept variables):


- *method (string)* - the SIP method
- *RURI (string)* - the SIP Request URI (the request 
will be sent out to this destination)
- *from (string)* - the SIP From hdr information as
"[display ]URI"
- *to (string)* - the SIP To hdr information as
"[display ]URI"
- *body (string, optional)* - the SIP body content
starting with the content type string: "conten_type body"
- *ctx (string, optional)* - a context string that will
be added to the new transaction as an AVP with name "uac_ctx" (it may be visible
in local route)


```opensips title="t_new_request usage"
...
	# send a MESSAGE request
	t_new_request("MESSAGE","sip:alice@192.168.2.2","BOB sip:userB@mydomain.net","ALICE sip:userA@mydomain.net","text/plain Hello Alice!")) {
...
```


#### t_on_failure(failure_route)


Sets reply routing block, to which control is passed after a 
transaction completed with a negative result but before sending a 
final reply. In the referred block, you can either start a new branch 
(good for services such as forward_on_no_reply) or send a final reply 
on your own (good for example for message silo, which received a 
negative reply from upstream and wants to tell upstream "202 I 
will take care of it").


As not all functions are available from failure route, please check 
the documentation for each function to see the permissions.
Any other commands may result in unpredictable behavior and 
possible server failure.


Only one failure_route can be armed for a request. If you use many
times t_on_failure(), only the last one has effect.


Note that whenever failure_route is entered, RURI is set to value 
of the winning branch.


Meaning of the parameters is as follows:


- *failure_route (string)* - Reply route block to be 
called.


This function can be used from REQUEST_ROUTE, BRANCH_ROUTE, 
ONREPLY_ROUTE and FAILURE_ROUTE.


```opensips title="t_on_failure usage"
...
route { 
	t_on_failure("1"); 
	t_relay();
} 

failure_route[1] {
	seturi("sip:user@voicemail");
	t_relay();
}
...
```


#### t_on_reply(reply_route)


Sets reply routing block, to which control is passed each time a reply
(provisional or final) for the transaction is received. 
The route is not called for local generated replies! In the referred 
block, you can inspect the reply and perform text operations on it.


As not all functions are available from this type of route, please 
check  the documentation for each function to see the permissions.
Any other commands may result in unpredictable behavior and 
possible server failure.


If called from branch route, the reply route will be set only for the
current branch - that's it, it will be called only for relies belonging
to that particular branch. Of course, from branch route, you can set
different reply routes for each branch.


When called from a non-branc route, the reply route will be globally 
set for tha current transaction - it will be called for all replies 
belonging to that transaction. NOTE that only 
*one>* onreply_route can be armed for a transaction.
If you use many times t_on_reply(), only the last one has effect.


If the processed reply is provisionla reply (1xx code), by calling
the drop() function (exported by core), the execution of the route
will end and the reply will not be forwarded further.


Meaning of the parameters is as follows:


- *reply_route (string)* - Reply route block to be 
called.


This function can be used from REQUEST_ROUTE, BRANCH_ROUTE, 
ONREPLY_ROUTE and FAILURE_ROUTE.


```opensips title="t_on_reply usage"
...
route {
	seturi("sip:bob@opensips.org");  # first branch
	append_branch("sip:alice@opensips.org"); # second branch

	t_on_reply("global"); # the "global" reply route 
	                      # is set the whole transaction
	t_on_branch("1");

	t_relay();
}

branch_route[1] {
	if ($rU=="alice")
		t_on_reply("alice"); # the "alice" reply route
		                      # is set only for second branch
}

onreply_route[alice] {
	xlog("received reply from alice\n");
}

onreply_route[global] {
	if (t_check_status("1[0-9][0-9]")) {
		setflag(LOG_FLAG);
		log("provisional reply received\n");
		if (t_check_status("183"))
			drop;
	}
}
...
```


#### t_on_branch(branch_route)


Sets a branch route to be execute separately for each branch of the
transaction before being sent out - changes in that route should 
reflect only on that branch.


As not all functions are available from this type of route, please 
check  the documentation for each function to see the permissions.
Any other commands may result in unpredictable behavior and 
possible server failure.


Only one branch_route can be armed for a request. If you use many
time t_on_branch(), only the last one has effect.


By calling the drop() function (exported by core), the execution of 
the branch route will end and the branch will not be forwarded further.


Meaning of the parameters is as follows:


- *branch_route (string)* - Branch route block to be 
called.


This function can be used from REQUEST_ROUTE, BRANCH_ROUTE, 
ONREPLY_ROUTE and FAILURE_ROUTE.


```opensips title="t_on_branch usage"
...
route { 
	t_on_branch("1"); 
	t_relay();
} 

branch_route[1] {
	if ($ru=~"bad_uri") {
		xlog("dropping branch $ru \n");
		drop;
	}
	if ($ru=~"GW_uri") {
		append_rpid();
	}
}
...
```


#### t_inject_branches(source[,flags])


The function adds new SIP branches (destinations) to an existing 
transaction and fires them (sends them out). The transaction may 
already have ongoing branches (like in ringing state), which will not
be affected by the injection of the new branches. Also it is possible 
for the transaction not to have any ongoing branches at the moment of
the injection (still, the transaction must wait for new branches, even
if all existing ones are completed - see 
the [t wait for new branches](#t_wait_for_new_branchesbranches) function for this).


The main usage scenario for this function (and also what makes it
different from [t relay](#t_relayflagsoutbound_proxy) is the ability to add new
branches to an ongoing transaction from script routes not related to 
the transaction ( like timer route, event route, notification route,
and other). In such routes, other functions/module used before the
injection will point to the transaction to be affected by this
injection - see the *event_routing* module.


Parameters:


- *source (string)* - where to take the description
for the new branches to be injected. It can be:
	- *event* - the branch will be taken from
	the event attributes exposed in an event notification route
	(see *event_routing* module).
	- *msg* - the branches will be taken from
	the RURI of the SIP message and from the additional
	branches (created by append_branch() function or similar).
- *flags (string, optional)* - some additional flags 
related to the injection process:
	- *cancel* or *c* - cancel all the ongoing existing branches from the transaction before injecting the new branches.
	- *l* (last) - this is the last injected branch on this transaction, do not wait for any other branches to be injected.


```opensips title="t_inject_branches usage"
...
route[event_notification] {
	t_inject_branches("event");
}
...
```


#### t_wait_for_new_branches([branches])


This function instructs the existing SIP transaction to wait for new
branches to be injected even after the completion of the existing 
branches. This waiting will be done until the Final Response INVITE 
timer (fr_inv_timeout) will hit for the transaction OR until the 
maximum number of branches were injected (see parameter); of course,
the waiting will be terminated if the transaction gets a 2xx final
reply from one of the branches.


Normally if you have a transaction with two branches and 
they get, let's say, a 404 and 486 replies, the branches will be
completed and transaction terminated by sending the 404 reply to the 
caller. Still, if you do *t_wait_for_new_branches*
before relaying the transaction, the transaction will not terminate
upon the completion of the branches and not send the 404 to the caller
		- it will wait for new branches to be injected (see 
[t inject branches](#t_inject_branchessourceflags) function) until the fr_inv timer
hits.


Parameters:


- *branches (integer, options)* - what is the
maximum number of branches to be waited for.


```opensips title="t_wait_for_new_branches usage"
...
t_newtran();
t_wait_for_new_branches();
t_relay();
...
```


#### t_wait_no_more_branches()


This function instructs the existing SIP transaction to stop wait
for new any new branches to be injected. This functions should be 
used for a transaction that is waiting for dynamic branches, via the
[t wait for new branches](#t_wait_for_new_branchesbranches) function.


Usage scenario: your transaction is waiting for dynamic new branches
(as a reusult of Push Notification). To a point, on an ongoing
branch you receive a final reply - and the fact that the branch fails
translates into stop waiting for any more branche (this is an example
of a logic on deciding how long to wait for more branches, depending 
on the answers you get from various devices, fix or mobile).


```opensips title="t_wait_no_more_branches usage"
...
t_wait_no_more_branches();
...
```


#### t_add_hdrs("sip_hdrs")


Attach a set of headers to the existing transaction - these headers
will be appended to all requests related to the transaction (outgoing
branches, local ACKS, CANCELs).


Parameters:


- *sip_hdrs (string)*


```opensips title="t_add_hdrs usage"
...
t_add_hdrs("X-origin: 1.1.1.1\r\n");
...
```


#### t_add_cancel_reason("Reason_hdr")


This function is used to enforce from the script level a custom
"Reason" header into a CANCEL request. Normally, the Reason header is
inherited form the received CANCEL (note that CANCEL propagates in a
hop-by-hop manner - it is re-generated at each hop), but this function
can overwrite it. It must be called before relaying the CANCEL request
and its input must be a fully formated Reason header with name, body 
and CRLF.


Parameters:


- *reason_hdr (string)*


```opensips title="t_add_cancel_reason usage"
...
t_add_cancel_reason("Reason: SIP ;cause=200 ;text=\"Call completed elsewhere\"\r\n");
t_relay();
...
```


#### t_replicate(URI,[flags])


Replicates a request to another destination. No information due the
replicated request (like reply code) will be forwarded to the 
original SIP UAC.


The destination is specified by a SIP URI. If multiple destinations are
to be used, the additional SIP URIs have to be set as branches.


Parameters:


- *uri (string)*
- *flags (string, optional)* - a set of flags for
controlling the internal behaviour - for description see the above 
"t_relay([flags])" function. Note that only
*no-dns-failover* is
applicable here.


This functions can be used from REQUEST_ROUTE.


```opensips title="t_replicate usage"
...
t_replicate("sip:1.2.3.4:5060");
t_replicate("sip:1.2.3.4:5060;transport=tcp");
t_replicate("sip:1.2.3.4",0x4);
...
```


#### t_write_req(info,fifo) t_write_unix(info,sock)


Write via FIFO file or UNIX socket a lot of information regarding the
request. Which information should be written may be control via the
"tw_append" parameter.


Parameters:


- *info (string)*
- *path (string)*


This functions can be used from REQUEST_ROUTE, FAILURE_ROUTE and 
BRANCH_ROUTE.


```opensips title="t_write_req/unix usage"
...
modparam("tm","tw_append","append1:Email=$avp(email);UA=$ua")
modparam("tm","tw_append","append2:body=$rb")
...
t_write_req("voicemail/append1","/tmp/appx_fifo");
...
t_write_unix("logger/append2","/var/run/logger.sock");
...
```


#### t_flush_flags()


Flush the flags from current request into the already created 
transaction. It make sense only in routing block if the transaction was
created via t_newtran() and the flags have been altered since.


This function can be used from REQUEST_ROUTE and BRANCH_ROUTE .


```opensips title="t_flush_flags usage"
...
t_flush_flags();
...
```


#### t_anycast_replicate()


This function is used in an anycast setup to replicate a
*CANCEL* or *ACK* method
for whom there are no local transactions found. The function
broadcasts the message to all the other nodes in the cluster,
but only the "owner" of the transaction will be
able to handle it.


```opensips title="t_anycast_replicate usage"
...
if (is_method("ACK|CANCEL") && !t_check_trans()) {
	t_anycast_replicate();
	exit;
}
...
```


#### t_reply_by_callid(code, reason_phrase, [callid], [cseq])


This function is used to send a reply to an existing INVITE
transaction. The usual use case is when OpenSIPS is used as an UAS
and when an INVITE is receveid, it is "parked" locally on
OpenSIPS by replying to it with
"t_reply(180, "Ringing")" or 
"t_reply(183, "Session Progress")"
and later we need to handle CANCEL or BYE for it and send
'487 Request Terminated' to the original INVITE transaction.


The callid and cseq used to identify the transaction
will be obtained from the current messsage being processed.
But they can be passed explicitly so that for example we can
handle a BYE where the cseq must be the cseq
of the INVITE minus one.


This function can be used from REQUEST_ROUTE.


```opensips title="t_reply_by_callid usage"
...
route{
	if($rU == "LOCAL_PARK") {
		if(is_method("INVITE")) {
			$T_fr_timeout = 10;
			$T_fr_inv_timeout = 10;
			append_to_reply("Contact: sip:LOCAL_PARK@$socket_in(ip):$socket_in(port)\r\n");
			t_reply(180, "Ringing");
			t_wait_for_new_branches();
		} else if(is_method("CANCEL")) {
			if(!t_reply_by_callid(487, "Request Terminated")) {
				sl_send_reply(481, "Call Leg/Transaction Does Not Exist");
			} else {
				sl_send_reply(200, "OK");
			}
		} else if(is_method("BYE")) {
			$var(prev_cseq) = ($(cs{s.int}) - 1);
			if(!t_reply_by_callid(487, "Request Terminated", , $var(prev_cseq))) {
				sl_send_reply(481, "Call Leg/Transaction Does Not Exist");
			} else {
				sl_send_reply(200, "OK");
			}
		} else if(is_method("ACK")) {
			t_relay();
		}
		exit;
	}
}
...
```


#### t_get_branch_idx_by_attr(attr, [val_str], [val_int], [result_var], [offset])


This function may be used to search for the index of another branch
of the current transaction. The searching is done based on the
per-branch attribute - you need to provide the name of the attribute
at least. Optionally you can provide a value (string or integer) for
the attribute used for searching. As input, the function may take an
optional branch offset (absolute value, covering all branches of the 
transaction) where the search should start from.


The function returns true if a branch (having the given name and
value for the attribute) was found. The status of the branch (like
if ongoing, completed ) is not relevant. If found, the "result_var" 
variable will be populated with the branch index (as integer).


This function can be used from ONREPLY_ROUTE, BRANCH_ROUTE and
FAILURE_ROUTE.


```opensips title="t_get_branch_idx_by_attr usage"
...
	# search for a branch which has the "name" attribute
	# with string value "pstn"
	if (t_get_branch_idx_by_attr("name", "pstn", , $var(idx))) {
		xlog("found branch has index $var(idx)\n");
	}
...
```


### Exported Pseudo-Variables


Exported variables are listed in the next sections.


#### $T_branch_idx


*$T_branch_idx* - the index (starting with 0
for the first branch) of the currently proccessed branch. This
index makes sense only in BRANCH and REPLY routes (where the
processing is per branch) and in FAILURE route (where it points
to the branch with the last final reply on the transaction). In all
the other types of routes, the value of this index will be NULL.


#### $T_reply_code


*$T_reply_code* - the code of the reply, as 
follows: in request_route will be the last stateful sent reply;
in reply_route will be the current processed reply; in 
failure_route will be the negative winning reply. In case of 
no-reply or error, '0' value is returned.


#### $T_fr_timeout


*$T_fr_timeout (R/W)* - the timeout
for the final reply to the current transaction


With each different
request received, *$T_fr_timeout* will initially
be equal to the
**[fr timeout](#fr_timeout-integer)** parameter.


*"$T_fr_timeout = NULL;"* will reset it to
**[fr timeout](#fr_timeout-integer)**.


#### $T_fr_inv_timeout


*$T_fr_inv_timeout (R/W)* - the timeout
for the final reply to an INVITE request, after a 1XX reply
was received.  This variable may also be set in an onreply_route
(e.g. on 180 Ringing, after 100 Trying) and still take effect.


With each different request received,
*$T_fr_inv_timeout* will initially be equal to the
**[fr inv timeout](#fr_inv_timeout-integer)** parameter.


*"$T_fr_inv_timeout = NULL;"* will reset it to
**[fr inv timeout](#fr_inv_timeout-integer)**.


#### $T_ruri


*$T_ruri* - the ruri of the current branch; this
information is taken from the transaction structure, so you can
access this information for any sip message (request/reply) that
has a transaction.


#### $bavp(name)


*$bavp(name)* - a particular type of avp that
can have different values for each branch. They can only be used in
BRANCH, REPLY and FAILURE routes. Otherwise NULL value is returned.


#### $T_id


*$T_id* - returns the ID of the current 
transaction. The ID is an opaque hexa string, unique for each
transaction. If there is no current transaction,  NULL value is
returned.


#### $T_branch_last_reply_code


*$T_branch_last_reply_code* - returns the last reply
code received for a branch specified as parameter. If no parameter is
specified, the last reply for the current branch is retrieved.


#### $tm.branch.uri[]


*$tm.branch.uri* - gives read-only 
access over the Request URI (as string) of a TM existing
branch. The status of the  branch (completed, ongoing, etc)
is not relevant.


The TM (UAC side) branches are created when the request is
sent to new destinations via "t_relay()" or "t_inject()".


The indexing of the branches starts from 0, giving access to 
all branches (past and active) of the transaction. Nevertheless
the indexing supports two optional suffixes, to simplify the
scripting:


- */active* - the indexing starts also
from 0, but it is relative to the last set of branches -
the parallel branches created by the last "t_relay()"-ing.
- */all* - similar to "no suffix" case, 
meaning it is an absolute index, covering all the 
branches of the trasactions (resulted from all "t_relay()"s
performed over the transaction).


IF no index is specified, the current branch used. This depends
on the scripting context. Like in reply route, the current
branch is the branch the reply came for; in branch route, the
current branch is the branch to be sent out; in failure route,
the current branch is the winning branch.


> [!NOTE]
> The index ALL ( "*" ) is not supported.

> [!NOTE]
> In branch route, only the "$tm.branch.attr" and 
> "$tm.branch.flag" variables work for the current branch 
> (the rest of the branch related variables will return NULL).

> [!NOTE]
> Negative values are accepted, meaning indexing from the 
> end ( -1 is the latest/higher branch).


The variable can be used in BRANCH, ONREPLY and FAILURE routes.


#### $tm.branch.duri[]


*$tm.branch.duri* - 100% similar to
**[tm branch uri](#tmbranchuri)**, but returning the Detination-URI value of the branch.


#### $tm.branch.path[]


*$tm.branch.path* - 100% similar to
**[tm branch uri](#tmbranchuri)**, but returning the PATH value of the branch.


#### $tm.branch.q[]


*$tm.branch.q* - 100% similar to
**[tm branch uri](#tmbranchuri)**, but returning the Q value of the branch.


#### $tm.branch.flags[]


*$tm.branch.flags* - 100% similar to
**[tm branch uri](#tmbranchuri)**, but returning the list (comma separated) of per-branch flags which are 
set for the branch.


#### $tm.branch.socket[]


*$tm.branch.socket* - 100% similar to
**[tm branch uri](#tmbranchuri)**, but returning the socket description (proto:ip:port) used for sending the
branch out.


#### $tm.branch.flag()[]


*$tm.branch.flag(name)* - similar to
**[tm branch uri](#tmbranchuri)**, but gives read/write access to a single branch flag (by its name).


The accepted values are 0 for FALSE, pozitive non-zero for
TRUE. The returned values are 0 for FALSE and 1 for TRUE.


The flags operated here are the same as the bflags you can
operated with via the "[re]setbflag()" functions.


#### $tm.branch.attr()[]


*$tm.branch.attr(name)* - similar to
**[tm branch uri](#tmbranchuri)**, but gives read/write access to the attributed attached to the branch.


An attribute can have whatever name (no need to be 
pre-defined) and it can have a single value (at a time),
string or integer.


#### $tm.branch.last_received[]


*$tm.branch.last_received* - 100% similar to
**[tm branch uri](#tmbranchuri)**, but returning the reply code of the last received reply (from the
network) on this branch. NULL is returned in no reply was
received so far.


#### $tm.branch.type[]


*$tm.branch.type* - 100% similar to
**[tm branch uri](#tmbranchuri)**, but returning the type of the current branch. This may be "phone" if it 
not a real branch (has no SIP signalling, used by waiting for
branch injection) or "sip" (a real signalling branch).


### Exported MI Functions


#### tm:uac_dlg


Replaces obsolete MI command: *t_uac_dlg*.


Generates and sends a local SIP request.


Parameters:


- *method* - request method
- *ruri* - request SIP URI
- *headers* - set of additional headers to
be added to the request; at least 
"From" and "To" headers must be
specified)
- *next_hop* (optional) - next hop SIP URI (OBP).
- *socket* (optional) - local socket to be used for
sending the request.
- *body* (optional) - request body (if present, requires the 
"Content-Type" and "Content-length"
headers)


MI FIFO Command Format:


```bash
opensips-cli -x mi tm:uac_dlg method=INVITE ruri="sip:alice@127.0.0.1:7050" headers="From: sip:bobster@127.0.0.1:1337\r\nTo: sip:alice@127.0.0.1:7050\r\nContact: sip:bobster@127.0.0.1:1337\r\n"
```


#### tm:uac_cancel


Replaces obsolete MI command: *t_uac_cancel*.


Generates and sends a CANCEL for an existing SIP request.


Parameters:


- *callid* - callid of the INVITE request
to be cancelled.
- *cseq* - cseq of the INVITE request to be
cancelled.


MI FIFO Command Format:


```bash
opensips-cli -x mi tm:uac_cancel "1-23454@127.0.0.1" "1 INVITE"		
```


#### tm:hash


Replaces obsolete MI command: *t_hash*.


Gets information about the load of TM internal hash table.


Parameters:


- *none*


MI FIFO Command Format:


```bash
opensips-cli -x mi tm:hash		
```


#### tm:reply


Replaces obsolete MI command: *t_reply*.


Generates and sends a reply for an existing inbound SIP transaction.


Parameters:


- *code* - reply code
- *reason* - reason phrase.
- *trans_id* - transaction identifier
(has the hash_entry:label format)
- *to_tag* - To tag to be added to TO header
- *new_headers* (optional) - extra headers to be
appended to the reply.
- *body* - (optional) reply body (if present, requires the
"Content-Type" and "Content-length"
headers)


MI FIFO Command Format:


```bash
opensips-cli -x mi tm:reply 403 Forbidden 46961:1279687637 abcde .		
```


### Exported Statistics


Exported statistics are listed in the next sections. All statistics
except "inuse_transactions" can be reset.


#### received_replies


Total number of total replies received by TM module.


#### relayed_replies


Total number of replies received and relayed by TM module.


#### local_replies


Total number of replies local generated by TM module.


#### UAS_transactions


Total number of transactions created by received requests.


#### UAC_transactions


Total number of transactions created by local generated requests.


#### 2xx_transactions


Total number of transactions completed with 2xx replies.


#### 3xx_transactions


Total number of transactions completed with 3xx replies.


#### 4xx_transactions


Total number of transactions completed with 4xx replies.


#### 5xx_transactions


Total number of transactions completed with 5xx replies.


#### 6xx_transactions


Total number of transactions completed with 6xx replies.


#### inuse_transactions


Number of transactions existing in memory at current time.


#### retransmission_req_T1_1


Number of request retransmissions due to T1 1 timer,
the first retransmission interval (typical 500ms).


#### retransmission_req_T1_2


Number of request retransmissions due to T1 2 timer,
the second retransmission interval (typical 1s).


#### retransmission_req_T1_3


Number of request retransmissions due to T1 3 timer,
the third retransmission interval (typical 2s).


#### retransmission_req_T2


Number of request retransmissions due to T2 ,
the final retransmission interval (typical 4s).


#### retransmission_rpl_T2


Number of reply retransmissions, all done with the same 
retransmission interval T2, typical 4s.


#### timeout_finalresponse


Number of transactional timeouts without receiving any kind of reply (not
even provisional) from the B side. Such timeouts indicate a 
communication / reachability issue. Note: a single transaction may count
multiple such timeouts due forking.


#### timeout_finalresponse


Number of transactional INVITE timeouts without receiving a FINAL reply
(provisional may be received) from the B side. Such timeouts indicate a 
"not answer" event and it is not a signalling issue.
Note: a single transaction may count multiple such timeouts due forking.


## Developer Guide


### Functions


#### load_tm(*import_structure)


For programmatic use only--import the  TM API.
See the cpl_c, acc or jabber modules to see how it works.


Meaning of the parameters is as follows:


- *import_structure* - Pointer to 
the import structure - see "struct tm_binds" in 
modules/tm/tm_load.h


## Frequently Asked Questions


**Q: What happened with old cancel_call() function**


The function was replace (as functionality) by cancel_branch("a") -
cancel all braches.


**Q: How can I report a bug?**


Please follow the guidelines provided at:
[https://github.com/OpenSIPS/opensips/issues](https://github.com/OpenSIPS/opensips/issues).
<!-- CONTRIBUTORS -->

### License

All documentation files (i.e. .md extension) are licensed under the Creative Common License 4.0
