1.2.1. OpenSER Modules

The following modules must be loaded before this module:

• No dependencies on other OpenSER modules.

1.2.2. External Libraries or Applications

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

• None.

1.3.1. natping_interval (integer)

Period of time in seconds between sending short UDP packets to all currently registered UAs to keep their NAT bindings alive. Value of 0 disables this functionality.

Default value is 0.

...
modparam("nathelper", "natping_interval", 10)
...

1.3.2. ping_nated_only (integer)

If this variable is set then only contacts that have "behind_NAT" flag in user location database set set will get ping.

Default value is 0.

...
modparam("nathelper", "ping_nated_only", 1)
...

1.3.3. received_avp (integer)

The number of the Attribute-Value-Pair (AVP) used to store the URI containing the received IP, port, and protocol. The URI is created by fix_nated_register function of nathelper module and the attribute is then used by the registrar to store the received parameters. Do not forget to change the value of corresponding parameter in registrar module if you change the value of this parameter.

Default value is 42.

...
modparam("nathelper", "received_avp", 43)
...

1.3.4. rtpproxy_sock (string)

Socket used to connect to RTPProxy. It may specify a UNIX socket or an IPv4/IPv6 UDP socket.

Default value is "unix:/var/run/rtpproxy.sock".

...
modparam("nathelper", "rtpproxy_sock", "udp:localhost:12221")
...

1.3.5. rtpproxy_disable (integer)

If true (set to a non 0 value), the RTPProxy support will be desabled - no connection to it will be established.

Default value is "0 (false)".

...
modparam("nathelper", "rtpproxy_disable", 1)
...

1.3.6. rtpproxy_disable_tout (integer)

Once RTPProxy was found unreachable and marked as disable, nathelper will not attempt to establish communication to RTPProxy for rtpproxy_disable_tout seconds.

Default value is "60".

...
modparam("nathelper", "rtpproxy_disable_tout", 20)
...

1.3.7. rtpproxy_tout (integer)

Timeout value in waiting for reply from RTPProxy.

Default value is "1".

...
modparam("nathelper", "rtpproxy_tout", 2)
...

1.3.8. rtpproxy_retr (integer)

How many times nathelper should retry to send and receive after timeout was generated.

Default value is "5".

...
modparam("nathelper", "rtpproxy_retr", 2)
...

1.3.9. force_socket (string)

Socket to be forced in communicating to RTPProxy. It makes sense only for UDP communication. If no one specified, the OS will choose.

Default value is "NULL".

...
modparam("nathelper", "force_socket", "localhost:33333")
...

1.4.1. fix_nated_contact()

Rewrites Contact HF to contain request's source address:port.

...
if (search("User-Agent: Cisco ATA.*") {fix_nated_contact();};
...

1.4.2. fix_nated_sdp(mode)

Alters the SDP information in orer to facilitate NAT traversal. What changes to be performed may be controled via the "parameter".

The parameter value may be a bitwise OR of the following flags:

• 0x01 - adds "a=direction:active" SDP line;

• 0x02 - rewrite media IP address (c=) with source address of the message.

• 0x04 - adds "a=nortpproxy:yes" SDP line;

...
if (search("User-Agent: Cisco ATA.*") {fix_nated_sdp("3");};
...

1.4.3. force_rtp_proxy()

Rewrites SDP body to ensure that media is passed through an RTP proxy.

...
if (search("User-Agent: Cisco ATA.*") {force_rtp_proxy();};
...

1.4.4. force_rtp_proxy(flags)

Same as force_rtp_proxy, but forces additional flags.

Meaning of the parameters is as follows:

• flags - flags to turn on some features.

  • a - flags that UA from which message is received doesn't support symmetric RTP.

  • l - force "lookup", that is, only rewrite SDP when corresponding session is already exists in the RTP proxy. Only makes sense for SIP requests, replies are always processed in "lookup" mode.

  • i - flags that message is received from UA in the LAN (internal network). Only makes sense when RTP proxy is running in the bridge mode.

  • e - flags that message is received from UA in the WAN (external network). Only makes sense when RTP proxy is running in the bridge mode.

  • f - instructs nathelper to ignore marks inserted by another nathelper in transit to indicate that the session is already goes through another proxy. Allows creating chain of proxies.

  • r - flags that IP address in SDP should be trusted. Without this flag, nathelper ignores address in the SDP and uses source address of the SIP message as media address which is passed to the RTP proxy.

...
if (src_ip=1.2.3.4) {force_rtp_proxy("i");};
...

1.4.5. force_rtp_proxy(flags, ip_address)

Same as force_rtp_proxy(flags), but it may force a new SDP IP address.

Meaning of the parameters is as follows:

• flags - flags to turn on some features.

• ip_address - new SDP IP address.

...
if (search("User-Agent: Cisco ATA.*") {force_rtp_proxy("","1.2.3.4");};
...

1.4.6. unforce_rtp_proxy()

Tears down the RTPProxy session for the current call.

...
unforce_rtp_proxy();
...

1.4.7. add_rcv_param()

Add received parameter to Contact header fields. The parameter will contain URI created from the source IP, port, and protocol of the packet containing the SIP message. The parameter can be then processed by another registrar, this is useful, for example, when replicating register messages using t_replicate function to another registrar.

...
add_rcv_param();
...

1.4.8. fix_nated_register()

The function creates a URI consisting of the source IP, port, and protocol and stores the URI in an Attribute-Value-Pair. The URI will be appended as "received" parameter to Contact in 200 OK and registrar will store it in the user location database.

...
fix_nated_register();
...

1.4.9. nat_uac_test(flags)

Tries to guess if client's request originated behind a nat. The parameter determines what heuristics is used.

Meaning of the flags is as follows:

• 1 - Contact header field is searched for occurrence of RFC1918 addresses.

• 2 - the "received" test is used: address in Via is compared against source IP address of signaling

• 4 - Top Most VIA is searched for occurrence of RFC1918 addresses

• 8 - SDP is searched for occurrence of RFC1918 addresses

• 16 - test if the source port is different from the port in Via

All flags can be bitwise combined, the test returns true if any of the tests identified a NAT.