媒体接口配置

Media Interface 介绍

媒体接口负责SBC语音的媒体流的处理，具有以下功能：

• 媒体接口负责处理语音编码的转换
  • 例如，G.729 到 G.722转换。
• 媒体接口同时负责处理和媒体相关的功能，例如(RTP/SRTP)。

Media interfaces 实际上执行RTP语音流数据之间的转换。媒体接口实际上也是网络设备，也需要有IP地址等等相关信息(IP addr, Netmask, Gateway)。

如果有的环境使用了sangoma D100 (无外网端口) ，此IP地址可以是任何IP地址，这个地址保持“隐藏” ，设备RTP语音流将使用这个地址来通信。

Media Interface 配置

第一步需要选择一个media mode模式。目前系统支持3种IP modes:

• Hidden
  • DSP Media interface IP addresses隐藏在网络中
  • 默认，推荐的模式
  • 使用单个IP address 来处理所有的Media/RTP
• Exposed
  • DSP Media interface IP addresses将暴露在网络环境中
  • 使用多个IP addresses 来处理Media/RTP，但是CPU使用效率更高
• Disabled
  • Software mode. 无 DSP interfaces
  • 使用在VM 环境中

默认环境下，我们将使用hidden mode，用户访问“Configuration -> IP Settings -> Media Interfaces”. 
用户必须点击 Modify 来修改添加媒体接口，以便系统可以发现默认的媒体接口。

Hidden Mode

Hidden” 模式相对比较容易操作。在这个模式下，所有的媒体接口已经被隐藏。这个模式比较简单的原因是因为用户无需担心多个媒体IP地址导致的IP地址冲突。用户仅现在网段保证不会和现有的网络环境冲突，例如(例如，192.168.168.0/24)。此模式的缺点是所有RTP都要通过NSC 主机转发，因此会增加CPU负载。Hidden 模式在呼叫量在1,500 calls (3,000 call legs/sessions)是正常的。如果用户需要搞密度的呼叫，则可以选择“Exposed”模式。

注意，使用 D100 编码卡的设备没有支持选项“Hidden” 模式，因为 D100 没有带外网端口。 实际上，这也不是一个问题，因为使用D100 的用户，没有达到以上所说的“Hidden” 模式的呼叫量。

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.

SBC Media Config Exposed

The first time you modify the media interfaces configuration you must go through a discovery procedure to find all media interfaces. Unless you are using a D150 device (stand-alone media interface) you should only select the network devices named “sngdsp[N]” for discovery (see “Detect Media Interfaces” field). If you are using a D150 (or several) you must select the ethernet interface the D150 device is attached to (they should share the same broadcast domain).

If you select the “Exposed” IP mode, the web ui will allow you to configure the IP settings for the media interfaces it finds.

In “Hidden” mode you are only asked to provide a starting UDP port range for the RTP streams. You can leave the default if you don’t require a particular port range.

Once you click “Save”, the web ui will perform the device discovery procedure which will take a few seconds. The discovery procedure will send Ethernet broadcast messages to auto-discover Sangoma media interfaces attached to the same network(s) of the selected Ethernet interfaces. Once done, you will receive a report of the hardware found.

SBC Media Config IP Addresses

In the example above, there is 2 network interfaces (sngdsp0 and sngdsp1) which correspond to one D500 card each. The first network interface (sngdsp0) has 4 media interfaces (also referred to as “media modules”). The network interface “sngdsp1” has attached 5 media interfaces.

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.

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
• Limited Session capacity
  • Session capacity depends on VM or Host resources