Configuring SBC Edge and SBC SWe Lite for various Media Modes

 

How Each Media Mode Works

The

supports the following media modes:

• DSP: The RTP media packets are processed through DSP. And the SBC would bridge any interop issues with the peer devices.
• Proxy Relay: The RTP media packets flow through the SBC's network processor and does not use DSP. The codecs and SRTP are passed through. The details are captured here: Working with RTP Proxies
• Proxy with local SRTP: This is same as the Proxy Relay. However, the SRTP is negotiated encryption/decryption and is processed locally while codecs are untouched.

• Direct: The SBC Edge would not involve in the media path at all. Instead, the peer devices have to exchange the media directly with each other while only the SIP messages go through the SBC Edge.

How Multiple Media Streams work

The 

enables multiple media streams, which includes Video Call Passthrough support. Video codecs are passed transparently through the SBC and are negotiated end to end.

Specific configuration allows multiple media streams to be bundled in the Proxy Relay Media Mode or Direct Media Mode (through Audio/Fax Stream Mode and Video/Application Stream Mode). As a result, all media streams (Audio/Video/Application) are supported by the

. The media streams can have mixed (hybrid) modes, which enables audio to be transcoded and video to be in Proxy Relay mode.

• Proxy Relay Mode enables multiple media streams to be bundled in Proxy Relay Media Mode; all media streams (Audio/Video/Application) are passed through the
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  .
• Mixed Media (Hybrid) mode allows the
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  to handle multiple streams with different media modes (DSP and Proxy Relay) in the same call; audio is transcoded and video/application is in Proxy Proxy Relay Media Mode.
• Direct Mode enables multiple media streams to be bundled in Direct Media mode; all media streams (Audio/Video/Application) are not passed through the
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  , but the reachable SIP devices are allowed to exchange media directly with each other.

Scenarios

The media streams can be a mixed (Hybrid) mode, allowing audio to be transcoded and video to be in Proxy Relay Media Mode for SIP to SIP calls.

The media streams can be an all-proxy mode, allowing both audio and video to be in the Proxy Relay Media Mode for SIP to SIP calls.

The media streams can be an all-direct mode, allowing both audio and video to be in the Direct Media Mode for SIP to SIP calls between UAs.

While the audio media codec parameters are configurable in the

, there is no video media codec parameter configuration provided by the and any type of video codec is passed transparently through end to end.

The following are the various modes and call outcomes due to end-to-end compatibility:

 

Configuration

The following steps outline the basic configuration for using a Video Call. See Usage Examples below for specific configuration information. For detailed field configuration, see Creating and Modifying SIP Signaling Groups and Creating and Modifying Entries to Call Routing Tables.

Step 1: Configure Media Stream Type

Through the SIP Signaling group's Media Information, a mode could be selected for each media stream type. See Creating and Modifying SIP Signaling Groups.

Step 2: Configure Priority for Media Stream Type

Through the Call Route Table, a media priority can be selected for each of these media stream types (Audio/Fax Stream, Video/Application Stream). See Creating and Modifying Entries to Call Routing Tables.

 

Usage Examples

Audio Stream Only - Video Disabled (Default configuration)

Proxy Relay Mode - Video Enabled

Proxy Mode enables multiple media streams to be bundled in Proxy Relay Media Mode; all media streams (audio/video/application) are passed through the

.

For this configuration there are two outcomes:

• For Audio Stream only: Audio stream on Proxy Relay Mode.
• For Multiple Streams: All streams on Proxy Relay Mode.

 

 

Direct Mode - Video Enabled

Direct Mode enables multiple media streams to be bundled in Direct Media Mode; all media streams (audio/video/application) are bypassed by the SBC.

For this configuration, there are two outcomes:

• For Audio Stream only: Audio Stream on Direct Mode
• For Multiple Streams: All Streams on Direct Mode.

 

 

 

Mixed Media (Hybrid) Mode - Video Enabled

Mixed Media (Hybrid) mode allows the

 to handle multiple streams with different media modes (DSP & Proxy) in the same call; audio is transcoded and video/application is in Proxy Media Mode.

For this configuration there are two outcomes:

• For Audio Stream only: Audio stream on DSP Mode.
• For Multiple Streams: Hybrid with DSP/Proxy Relay

 

Recommendations

Recommendation when using the video mode to avoid seeing video call failures:

• Disable video mode for E911 configuration.
• Before enabling video, review peers compatibility end-to-end to handle the offer/answer exchange reliably. In other words, no capability mismatch resolution is provided by the
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  .
• Any SMM or Call Router level message manipulation should be done carefully.
• If there is a potential mismatch of capabilities between two Route, disable Video.

Limitations

Limitations Due to End-to-End Compatibility

• Call un-hold, might have a period of no video depending upon the the video-fast-update in its SIP-INFO and/or RTCP. After observing different phone end points, this could range from 0(GrandStream) to 30 seconds(Bria).

• Early 183 does not function since the

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   does not negotiate codecs with remote peers.

• Ring-back generation is not available for all-proxy call.

• Dead call detection does not work for all-proxy calsl since the

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   cannot analyze RTP/RTCP streams.

Limitations Due to the Video Call Pass-through Feature

• Local transfer is not supported for video calls. Sonus recommends configuring the  Access Mode as Broadsoft Extension in order to support the transfer feature.
• Sonus recommends disabling the SIP Session Timer, since it requires SDP and the
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   cannot guarantee media parameter change.

Frequently Asked Questions

What is hybrid mode?
Audio media is processed through the DSPs and Video media is passed through the Network Processor level without involving the DSPs. 

 

When will you use hybrid mode?
This configuration best suitable for the call routes that need to have audio transcoded, and where the same route needs to handle video calls as well.

 

How does it compare with Proxy mode?
In Proxy Mode, both the audio and video media are passed through the Network Processor level without involving the DSPs. 

 

What comes extra compared with 3.0 release?
For audio calls, the call handling with respect to Offer/Answer remains identical.

 

What comes extra compared with 3.1 release?
For audio calls, the call handling with respect to Offer/Answer remains identical.

 

What is taken away enabling this? (transfer issues, etc.)
There is no difference in audio call processing. However, if the call is video, then transferring the call is supported only in Broadsoft like deployments, wherein it requires configuring the

 as Broadsoft extension.

This configuration is best suitable for call routes that need to have audio transcoded, and the same route needs to handle video calls as well. See How Sonus SBC Edge and SBC SWe Lite Transfers an RTP Stream.