Direct Media - AudioCodes Mediant 4000 SBC User Manual

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The device uses different local ports (e.g., for RTP, RTCP and fax) for each leg (inbound

and outbound). The local ports are allocated from the Media Realm associated with each

leg. The Media Realm assigned to the leg's IP Group (in the IP Groups table) is used. If not

assigned to the IP Group, the Media Realm assigned to the leg's SIP Interface (in the SIP

Interfaces table) is used. The following figure provides an example of SDP handling for a

call between a LAN IP Phone 10.2.2.6 and a remote IP Phone 212.179.1.13 on the WAN.

20.5.2 Direct Media

You can configure the device to allow the media (RTP/SRTP) session to flow directly

between the SIP endpoints, without traversing the device. This is referred to as No Media

Anchoring (also known as Anti-Tromboning or Direct Media). SIP signaling continues to

traverse the device, with minimal intermediation and involvement, to enable certain SBC

capabilities such as routing. By default, the device employs media anchoring, whereby the

media session traverses the device, as described in ''Media Anchoring'' on page 425.

Direct media offers the following benefits:

Saves network bandwidth

Reduces the device's CPU usage (as there is no media handling)

Avoids interference in SDP negotiation and header manipulation on RTP/SRTP

User's Manual

Figure 20-3: SDP Offer/Answer Example

Mediant 4000 SBC

Document #: LTRT-41729