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Media Interface Overview

A media interface deals with all forms of media which goes in and out of the SBC.

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For the case of any appliance using a D100 (media interface without an external Ethernet port) the IP address assigned can be any IP because the interface will remain “hidden” within the appliance and the RTP packets end up using the IP of the signaling network interfaces.

Media Interface Configuration

The first step to configure media interfaces is select the media mode in which NSC will operate. 
There are three media interface IP modes: 

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*By default the hidden mode will be chosen when you go to “Configuration -> IP Settings -> Media Interfaces”. 
You must click Modify to change it and/or to perform the initial media interface discovery.

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Hidden Mode

The “Hidden” mode is simpler to operate. In this mode all the media interfaces are hidden within the system and all the IP traffic generated by the media interfaces is routed/forwarded through the NSC host operating system and NATed. This mode is simpler because you don’t have to worry about multiple IP addresses for your media interfaces. The media interfaces will still need an IP, but there is no possible conflict with your network as those interfaces will be hidden within NSC. You just have to choose a network that does not conflict with your real networks (ie, 192.168.168.0/24). The disadvantage of this mode is that all RTP is relayed thru the NSC host and therefore has an impact in the CPU load. Hidden mode works fine for call loads of up to 1,500 calls (3,000 call legs/sessions). If you require higher density you need to use “Exposed”.

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*Note that appliances using D100 cards have no other option but to use “Hidden” mode because the D100 card has no external Ethernet port. In practice this is not a problem because D100 users do not reach the high call loads at which “Hidden” mode is limited.

Exposed Mode

The “Exposed” mode requires more careful configuration as the media interfaces will be exposed to your network (whatever network you plug the Ethernet cable to), so you must choose the IP network information carefully to avoid conflicts with other network equipment. The clear advantage of this mode is that RTP does not go through the host operating system, instead the media interfaces send the RTP directly to the external Ethernet port to its destination. No interrupt or system load at all in the host operating system for any RTP stream.

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Each media interface was assigned a network configuration based on the discovery page input. You can manually edit each media module network configuration by clicking “Edit”.

Disabled Mode

Software SBC installations will not have any hardware DSP resources.
In this scenario one must set the Media Interface mode to Disable. In this mode RTP Media will be handled in software.

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Limitations of Software SBCs are:

  • Limited Transcoding capability

    • Sangoma SBC currently only support free software voice codecs, such as iLBC, GSM, G726

    • G729, AMR and other royalty codecs are not supported in software.

  • Limited Transcoding capacity

    • The transcoding capacity depends on VM or Host resources.

    • It is possible to transcode hundreds of calls using a VM with significant resources

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