There are three different main sections for a host in the config file, which are role, interfaces and the actual interface definitions.

Addtional main parameters of a node:

By default, the load-balancer listens on the UDP and TCP ports 5060 (kamailio→lb→port) and TLS port 5061 (kamailio→lb→tls→port). If you need to setup one or more extra SIP listening ports or IP addresses in addition to those standard ports, please edit the kamailio→lb→extra_sockets option in your /etc/ngcp-config/config.yml file.

The correct format consists of a label and value like this:

    extra_sockets:
      port_5064: udp:10.15.20.108:5064
      test: udp:10.15.20.108:6060

The label is shown in the outbound_socket peer preference (if you want to route calls to the specific peer out via specific socket); the value must contain a transport specification as in example above (udp, tcp or tls). After adding execute ngcpcfg apply:

ngcpcfg apply 'added extra socket'

The direction of communication through this SIP extra socket is incoming+outgoing. The sip:provider CE will answer the incoming client registrations and other methods sent to the extra socket. For such incoming communication no configuration is needed. For the outgoing communication the new socket must be selected in the outbound_socket peer preference. For more details read the next section Section 12.2.2, “Extra SIP and RTP Sockets” that covers peer configuration for SIP and RTP in greater detail.

If you want to use an additional interface (with a different IP address) for SIP signalling and RTP traffic you need to add your new interface in the /etc/network/interfaces file. Also the interface must be declared in /etc/ngcp-config/network.yml.

Suppose we need to add a new SIP socket and a new RTP socket on VLAN 100. You can use the ngcp-network tool for adding interfaces without having to manually edit this file:

ngcp-network --set-interface=eth0.100 --ip=auto --netmask=auto --hwaddr=auto --type=sip_ext_incoming --type=rtp_int_100

The generated file should look like the following:

..
..
    eth0.100:
      hwaddr: ff:ff:ff:ff:ff:ff
      ip: 192.168.1.3
      netmask: 255.255.255.0
      type:
        - sip_ext_incoming
        - rtp_int_100
..
..
    interfaces:
      - lo
      - eth0
      - eth0.100
      - eth1
..
..

As you can see from the above example, extra SIP interfaces must have type sip_ext_incoming. While sip_ext should be listed only once per host, there can be multiple sip_ext_incoming interfaces. The direction of communication through this SIP interface is incoming only. The sip:provider CE will answer the incoming client registrations and other methods sent to this address and remember the interfaces used for clients' registrations to be able to send incoming calls to him from the same interface.

In order to use the interface for the outbound SIP communication it is necessary to add it to extra_sockets section in /etc/ngcp-config/config.yml and select in the outbound_socket peer preference. So if using the above example we want to use the vlan100 IP as source interface towards a peer, the corresponding section may look like the following:

    extra_sockets:
      port_5064: udp:10.15.20.108:5064
      test: udp:10.15.20.108:6060
      int_100: udp:192.168.1.3:5060

The changes have to be applied:

ngcpcfg apply 'added extra SIP and RTP socket'

After applying the changes, a new SIP socket will listen on IP 192.168.1.3 and this socket can now be used as source socket to send SIP messages to your peer for example. In above example we used label int_100. So the new label "int_100" is now shown in the outbound_socket peer preference.

Also, RTP socket is now listening on 192.168.1.3 and you can choose the new RTP socket to use by setting parameter rtp_interface to the Label "int_100" in your Domain/Subscriber/Peer preferences.

Normally, each interface that was configured with a type that starts with rtp_ can be selected individually as RTP interface in the Domain/Subscriber/Peer preferences. For example, if the interface types rtp_ext, rtp_int, and rtp_int_100 have been configured, the Domain/Subscriber/Peer preferences will allow the RTP interfaces to be selected as either ext, int, or int_100 in addition to "default".

The same rtp_ interface type can be configured on multiple interfaces. If this is the case, and if ICE (Interactive Connectivity Establishment) is enabled for a Domain/Subscriber/Peer, it is possible to use ICE to automatically negotiate which interface should be used for RTP communications. ICE must be supported by the remote client for this to work.

For example, rtp_ext can be configured on multiple interfaces like so (abbreviated):

..
..
    eth0.100:
      type:
        - rtp_ext
..
    eth0.150:
      type:
        - rtp_ext
..
    eth1:
      type:
        - rtp_ext
..
..

In this example, the RTP interface ext will be available for selection in the Domain/Subscriber/Peer preferences. If selected and if ICE is enabled, the addresses of all three interfaces will be presented to the remote client, and ICE will be used to negotiate which one of them will be used for communications. This can be useful in multi-homed environments, or when remote clients are on private networks.

If the RTP port range configured via the config.yml keys rtpproxy.minport and rtpproxy.maxport is not sufficient to handle all concurrent calls, it is possible to load-balance the RTP ports across multiple interfaces. This is useful if the RTP proxy runs out of ports and if not enough additional ports are available.

To enable this, multiple interfaces with different addresses must be configured, and interface types of the format rtp_NAME:SUFFIX must be assigned to them. For example, if the RTP interface named ext should be load-balanced across three interfaces, they can be configured like so (abbreviated):

..
..
    eth0.100:
      type:
        - rtp_ext:1
..
    eth0.150:
      type:
        - rtp_ext:2
..
    eth1:
      type:
        - rtp_ext:3
..
..

In this example, all three given RTP interface types will be available for selection in the Domain/Subscriber/Peer preferences individually (as ext:1 and so on), but in addition to that, an interface named just ext will also be available for selection. If ext is selected, only one of the three RTP interfaces will be selected in a round-robin fashion, thus increasing the number of available RTP ports threefold. The round-robin algorithm only selects an interface if it actually has RTP ports available.