# &adminguide;

## Overview

This module provides C-API functions to enable &kamailio; to be used as an outbound Edge Proxy (see &rfc5626; section 5).

The path and rr modules will bind to this module if it is loaded before they are.

### Conditions

The module analyses SIP requests so that other module (e.g. path, rr) can determine whether to apply RFC5626 processing. This section applies if outbound processing is not forced by the `force_outbound_flag` flag, or disabled with `force_no_outbound_flag`.

`REGISTER` request:

- single `Via:` header (first hop) and `Contact:` header has `;reg-id` parameter

Non-`REGISTER` requests if either of the following conditions is true:

- top Route header URI is myself and has `;ob` parameter

- `Supported: outbound...` header, single `Via:` header, and `Contact:` header has `;ob` parameter

### Edge Proxy Keep-Alives (STUN)

Outbound Edge Proxies MUST support STUN NAT keep-alives on their SIP UDP ports. &kamailio; supports this though the stun module.

### Flow Timer

The maximum interval at which a User Agent must send a keep-alive may be specified by the Registrar using the Flow-Timer: header in 2xx responses to REGISTERs.

When using TCP or TLS as the SIP transport care should be taken to set the tcp_connection_lifetime on the Edge Proxy to a value slightly larger than the interval the Registrar is using for flow timer. Setting tcp_connection_lifetime to less than the interval could cause connections to be lost, and setting it to a value much larger than the interval will keep connections open far longer than is required (which is wasteful).

Application-layer keep-alives are optional when the underlying transport already has a keep-alive mechanism. The WebSocket transport has a transport-layer keep-alive. When using the WebSocket transport the keepalive_timeout should be set to a value a little greater than the Registrar flow timer interval and a little less than the tcp_connection_lifetime.

#### Edge Proxy Configuration

    #!KAMAILIO
    #
    # Edge proxy configuration
    #

    #!subst "/REGISTRAR_IP/192.168.122.3/"
    #!subst "/REGISTRAR_PORT/5060/"
    #!substdef "/FLOW_TIMER/20/"

    ####### Global Parameters #########

    debug=2
    log_stderror=no
    log_facility=LOG_LOCAL0
    fork=yes
    children=4
    alias="example.com"
    mpath="/usr/lib64/kamailio/modules"
    tcp_connection_lifetime=30 # FLOW_TIMER + 10
    force_rport=yes

    ####### Modules Section ########

    loadmodule "tm.so"
    loadmodule "sl.so"
    loadmodule "outbound.so"
    loadmodule "rr.so"
    loadmodule "path.so"
    loadmodule "pv.so"
    loadmodule "maxfwd.so"
    loadmodule "xlog.so"
    loadmodule "sanity.so"
    loadmodule "ctl.so"
    loadmodule "textops.so"
    loadmodule "siputils.so"
    loadmodule "stun.so"

    # ----------------- setting module-specific parameters ---------------

    # ----- tm params -----
    modparam("tm", "failure_reply_mode", 3)

    # ----- rr params -----
    modparam("rr", "append_fromtag", 0)

    ####### Routing Logic ########

    request_route {
    	route(REQINIT);

    	if (is_method("CANCEL")) {
    		if (t_check_trans()) {
    			route(RELAY);
    		}
    		exit;
    	}

    	route(WITHINDLG);

    	t_check_trans();

    	if (is_method("REGISTER")) {
    		remove_hf("Route");
    		add_path();
    		$du = "sip:REGISTRAR_IP:REGISTRAR_PORT";
    	} else {
    		if (is_method("INVITE|SUBSCRIBE"))
    			record_route();

    		if (@via[2] == "") {
    			# From client so route to registrar...

    			if ($rU == $null) {
    				sl_send_reply("484", "Address Incomplete");
    				exit;
    			}
    			remove_hf("Route");
    			$du = "sip:REGISTRAR_IP:REGISTRAR_PORT";
    		} else {
    			# From registrar so route using "Route:" headers...

    			if (!loose_route()) {
    				switch($rc) {
    				case -2:
    					sl_send_reply("403", "Forbidden");
    					exit;
    				default:
    					xlog("L_ERR", "in request_route\n");
    					sl_reply_error();
    					exit;
    				}
    			}

    			t_on_failure("FAIL_OUTBOUND");
    		}
    	}

    	route(RELAY);
    }

    route[RELAY] {
    	if (!t_relay()) {
    		sl_reply_error();
    	}
    	exit;
    }

    route[REQINIT] {
    	if (!mf_process_maxfwd_header("10")) {
    		sl_send_reply("483","Too Many Hops");
    		exit;
    	}

    	if(!sanity_check("1511", "7"))
    	{
    		xlog("Malformed SIP message from $si:$sp\n");
    		exit;
    	}
    }

    route[WITHINDLG] {
    	if (has_totag()) {
    		if (!loose_route()) {
    			switch($rc) {
    			case -2:
    				sl_send_reply("403", "Forbidden");
    				exit;
    			default:
    				if (is_method("ACK")) {
    					if ( t_check_trans() ) {
    						route(RELAY);
    						exit;
    					} else {
    						exit;
    					}
    				}
    				sl_send_reply("404","Not Found");
    			}
    		} else {
    			if (is_method("NOTIFY")) {
    				record_route();
    			}
    			route(RELAY);
    		}
    		exit;
    	}
    }

    onreply_route {
    	if (!t_check_trans()) {
    		drop;
    	}

    	if ($rm == "REGISTER" && $rs >= 200 && $rs <= 299) {
    		remove_hf("Flow-Timer");
    		if ($(hdr(Require)[*])=~"outbound")
    			insert_hf("Flow-Timer: FLOW_TIMER\r\n", "Call-ID");
    	}
    }

    failure_route[FAIL_OUTBOUND] {
    	if (t_branch_timeout() && !t_branch_replied()) {
    		send_reply("430", "Flow Failed");
    	}
    }

#### Registrar Configuration

    MAILIO
    #
    # Registrar configuration
    #

    ####### Global Parameters #########

    debug=2
    log_stderror=no
    log_facility=LOG_LOCAL0
    fork=yes
    children=4
    alias="example.com"
    mpath="/usr/lib64/kamailio/modules"

    ####### Modules Section ########

    loadmodule "tm.so"
    loadmodule "tmx.so"
    loadmodule "sl.so"
    loadmodule "rr.so"
    loadmodule "pv.so"
    loadmodule "maxfwd.so"
    loadmodule "xlog.so"
    loadmodule "sanity.so"
    loadmodule "ctl.so"
    loadmodule "textops.so"
    loadmodule "siputils.so"
    loadmodule "usrloc.so"
    loadmodule "registrar.so"

    # ----------------- setting module-specific parameters ---------------

    # ----- tm params -----
    modparam("tm", "failure_reply_mode", 3)
    modparam("tm", "restart_fr_on_each_reply", 0)
    modparam("tm", "contact_flows_avp", "tm_contact_flows")
    modparam("tm", "contacts_avp", "tm_contacts")

    # ----- rr params -----
    modparam("rr", "append_fromtag", 0)

    # ----- registrar params -----
    modparam("registrar", "use_path", 1)
    modparam("registrar", "gruu_enabled", 1)
    modparam("registrar", "outbound_mode", 1)

    ####### Routing Logic ########

    request_route {
    	route(REQINIT);

    	if (is_method("CANCEL")) {
    		if (t_check_trans()) {
    			route(RELAY);
    		}
    		exit;
    	}

    	route(WITHINDLG);

    	t_check_trans();

    	remove_hf("Route");
    	if (is_method("INVITE|SUBSCRIBE"))
    		record_route();

    	route(REGISTRAR);

    	if ($rU==$null) {
    		xlog("L_INFO", "Address Incomplete\n");
    		send_reply("484","Address Incomplete");
    		exit;
    	}

    	route(LOCATION);
    }

    route[RELAY] {
    	if (!t_relay()) {
    		xlog("L_ERR", "t_relay() failed\n");
    		sl_reply_error();
    	}
    	exit;
    }

    route[REQINIT] {
    	if (!mf_process_maxfwd_header("10")) {
    		xlog("L_INFO", "Too Many Hops\n");
    		send_reply("483","Too Many Hops");
    		exit;
    	}

    	if(!sanity_check("1511", "7"))
    	{
    		xlog("Malformed SIP message from $si:$sp\n");
    		exit;
    	}
    }

    route[WITHINDLG] {
    	if (has_totag()) {
    		if (loose_route()) {
    			if (is_method("NOTIFY")) {
    				record_route();
    			}
    			route(RELAY);
    		} else {
    			if (is_method("ACK")) {
    				if (t_check_trans()) {
    					route(RELAY);
    					exit;
    				} else {
    					exit;
    				}
    			}
    			xlog("L_INFO", "Not Found");
    			send_reply("404","Not Found");
    		}
    		exit;
    	}
    }

    route[REGISTRAR] {
    	if (is_method("REGISTER"))
    	{
    		if (!save("location")) {
    			xlog("L_ERR", "Unable to save location\n");
    			sl_reply_error();
    		}
    		exit;
    	}
    }

    route[LOCATION] {
    	if (!lookup("location")) {
    		$var(rc) = $rc;
    		t_newtran();
    		switch ($var(rc)) {
    			case -1:
    			case -3:
    				send_reply("404", "Not Found");
    				exit;
    			case -2:
    				send_reply("405", "Method Not Allowed");
    				exit;
    		}
    	}

    	if (!t_load_contacts() || !t_next_contacts()) {
    		xlog("L_ERR", "t_(load|next)_contacts() failed\n");
    		sl_reply_error();
    		exit;
    	}

    	t_on_failure("FAIL_TRANSACTION");
    	t_on_branch_failure("FAIL-BRANCH");
    	route(RELAY);
    	exit;
    }

    onreply_route {
    	if (!t_check_trans()) {
    		drop;
    	}
    }

    failure_route[FAIL_TRANSACTION] {
    	if (!t_check_status("6[0-9][0-9]")) {
    		if (t_next_contacts()) {
    			t_relay();
    			exit;
    		}
    	}

    	if (t_check_status("430")) {
    		t_reply("480", "Temporarily Unavailable");
    		exit;
    	}
    }

    event_route[tm:branch-failure:FAIL-BRANCH] {
    	if (t_check_status("403|430")
    			|| (t_branch_timeout() && !t_branch_replied())) {
    		unregister("location", "$tu", "$T_reply_ruid");

    		if (t_next_contact_flow()) {
    			t_on_branch_failure("FAIL-BRANCH");
    			t_relay();
    		}
    	}
    }

## Dependencies

### &kamailio; Modules

The following modules must be loaded before this module:

- None

The following modules are required to make proper use of this module:

- stun.

### External Libraries or Applications

The following libraries must be installed before running &kamailio; with this module loaded:

- &openssl;.

## Functions

### `check_flow_token()`

This function search flow token for the current message and make checks:

1. headers can be parsed;

2. Route header can be parsed;

3. top route header is myself;

4. flow token present in the Route header;

5. flow token can be decoded;

6. TCP/TLS or WS/WSS connection present;

7. flow token is not expired;

Return codes:

1. 1 - flow token is valid and can be used to route message to the next hop

2. -1 - no Route header present

3. -2 - host in the first Route value is not current host

4. -3 - no flow token present

5. -4 - cannot decode flow token

6. -5 - connection associated with this token does not exist

7. -6 - flow token expired

8. -7 - cannot parse Route header

9. -8 - cannot parse headers

#### `check_flow_token` usage

    ...
    	check_flow_token();
    	switch $rc {
    		case -8:
    			xlog("cannot parse headers\n");
    			sl_send_reply("403", "Forbidden");
    			break;
    		case -7:
    			xlog("cannot parse Route header\n");
    			sl_send_reply("403", "Forbidden");
    			break;
    		case -6:
    			xlog("expired flow token\n");
    			sl_send_reply("430", "Flow Failed");
    			break;
    		case -5:
    			xlog("no TCP conection\n");
    			sl_send_reply("430", "Flow Failed");
    			break;
    		case -4:
    			xlog("cannot decode flowtoken\n");
    			sl_send_reply("403", "Forbidden");
    			break;
    		case -3:
    			xlog("no flow token\n");
    			loose_route();
    			break;
    		case -2:
    			xlog("Route is not my self\n");
    			sl_send_reply("403", "Forbidden");
    			break;
    		case -1:
    			xlog("no Route header\n");
    			break;
    		case 1:
    			xlog("correct flow token\n");
    			loose_route();
    			break;
    		default:
    			xlog("not supported return code: $rc\n");
    			sl_send_reply("403", "Forbidden");
    			break;
    	}
    ...

## Parameters

### `force_outbound_flag` (integer)

A flag which, if set for a request, will force path and rr to add flow tokens to Path: and Record-Route: headers regardless of the request contents.

Default value is -1.

#### Set `force_outbound_flag` parameter

    ...
    modparam("outbound", "force_outbound_flag", 1)
    ...

### `force_no_outbound_flag` (integer)

A flag which, if set for a request, will force path and rr not to add flow tokens to Path: and Record-Route: headers regardless of the request contents.

Default value is -1.

#### Set `force_no_outbound_flag` parameter

    ...
    modparam("outbound", "force_no_outbound_flag", 2)
    ...

### `flow_token_secret` (string)

Secret phrase used to calculate the outbound key value used for flow tokens validation. Allows to set persistent outbound key.

If not specified, outbound will use randomly generated outbound key

#### Set `flow_token_secret` parameter

    ...
    modparam("outbound", "flow_token_secret", "johndoessecretphrase")
    ...