In this section:
The NAT Direct Media Group is a collection of public signaling IP addresses for NAT devices supporting Direct Media (DM). A NAT Direct Media Group name can be maximum of 32 characters. However, "0.0.0.0" (IPv4) and "::0" (IPv6) are not allowed.
To allow Direct Media between NAT devices, or between NAT and Non-NAT devices, the following configuration is necessary.
The configuration of Direct Media with NAT is not allowed under following conditions:
addressContext
name of both the endpoints does not matchA flow diagram of this behavior is depicted in the figure below. Please see CLI Reference Guide for command details and examples.
For Direct Media calls (both audio and audio+video), the media does not flow through the SBC. However, SDP attributes need to be communicated to the endpoints. To accomplish this, enable the flag sdpAttributesSelectiveRelay
at the Trunk Group level to relay the SDP attributes to the endpoints (see example CLI syntax below)
Direct Media is not supported for H.323-H.323 or H.323-SIP calls involving Video. Secured RTP is not supported for H.323.
% set addressContext default zone ZONE1 sipTrunkGroup PERFIPS_SBX_INT media sdpAttributesSelectiveRelay enabled
For command details, refer to SIP Trunk Group - Media - CLI or SIP Trunk Group - Media (EMA) page.
Direct Media is intended for IAD-to-IAD calls where the SBC is positioned between each IAD and its registrar/application server whereby calls are set up between two endpoints so media is exchanged directly without consuming bandwidth to and from the SBC. The endpoints may be on the same IP subnet, in the same IP network, or on different IP networks. However, media packets from each IAD must be able to reach the other IAD without going through the SBC.
If the IADs share a common codec and do not need the SBC to transcode, then media flows directly between the IADs.
Note that even in a direct media configuration, if a call would require transcoding and involves codecs that require that specific licenses are available (DSP-AMRWB,DSP-AMRNB,DSP-EVRC VDSP-RTU) then the licenses must be installed on the SBC or the SBC rejects the call with a 488 response.
The SBC provides direct media support for SIP in the following scenarios:
The SBC supports the ability to perform media release and allows end points to have media flow directly between each other while signaling traverses the system.
When using Direct Media for IAD-to-IAD calls, the following parameters apply:
For SIP Direct Media calls, if you enable SIP Trunk Group level flag directMediaAllowed
and the Packet Service Profile level flag useDirectMedia
, the SBC supports a maximum of four media lines in the received INVITE. If the number of media lines exceeds four, the SBC fails to perform due to error conditions.
For Direct Media to function properly, the Application Server must not remove any SDP lines associated with unknown parameters. More specifically, if the Application Server receives an SDP with an unknown session-level attribute, it must pass this attribute and its value unchanged to the other leg
The SBC also supports the following Direct Media functionality in both Access and Peering scenarios:
SIP Gateway-to-SIP Gateway
SIP Gateway-to-GSX
In this model, the Direct Media feature causes the SBC to exhibit SIP proxy-like behavior wherein signaling passes through the SBC, and media directly flows between endpoints or between the endpoint and egress gateway.
Direct Media can apply to both Access and Peering scenarios.
Media Zone is a configurable parameter attached to a Gateway Trunk Group. If Media Zone of two legs is same, Direct Media is possible between the two legs.
If direct media is desired for GW-GW calls between the SBC and GSX, the media zone in the GSX must be named "INTERNAL" and directmediaGroupid parameter in the SBC must be set to "0". Any action taken by the GSX gateway protocol legs related to RTP inactivity (such as call tear down) must be withheld for Direct Media calls because media does not flow through the SBC gateway leg.
Direct Media between the SBC and GSX. Irrespective of the call leg on the egress GSX-2, we will be supporting direct media flow between ingress SIP peer and GSX-2 GW leg, provided media zone of GSX-2 and ingress peer is same. For this purpose, SBC-1 must publish the ingress peer's SDP to GSX-2 via GW protocol, so that GSX-2 sets its media peer as ingress SIP peer. Similarly GSX-2 must publish its ingress GW media IP and port back to SBC-1 so that SBC-1 can publish this as media IP and port in the SDP to ingress peer. Support for this deployment model has been available since GSX release 10.1.
In this deployment, the SBC sets up a Direct Media call between two SIP endpoints with only signaling passing through the SBCs in SIP-GW-SIP model. For this purpose SBC-1 and SBC-2 must publish peer's media proposal (SDP) within GW protocol so that the respective SIP legs can offer or answer with the Peer's SDP instead of the SBC's SDP.
In a direct media call, the SBC changes the SDP parameters (such as packet size) while sending out direct media SDP which results in a call failure. To overcome this limitation, the SBC is enhanced to remove any default value SDP parameters (if it is not correct) added by the SBC in direct media basic DM, DM Anti trombone and DM Xdmi calls. The SBC identified the SDP parameters (such as packet size) values that the SBC is modifying to default or based on configured value, while sending Direct Media Sdp parameters in outgoing INVITE. Currently, Direct Media SDP Information on Incoming INVITE to Outgoing INVITE in not fully supported for GW-GW Direct Media calls.
In the direct media call, the SBC adds the default/configured parameters in outgoing SDP and does not pass the exact incoming SDP as direct media, in an outgoing SDP. Neither the ingress and nor the egress leg have the same protocol (one leg is SIPS protocol and other leg is H323 protocol).
For example:
In this case, the SBC does not copy the exact content of SDP of the incoming INVITE from End Point 1 and add the copied SDP on the outgoing INIVTE toward End Point 2. Almost all the portions are copied, but the SBC adds the extra lines based on the default configuration.
End Point 1(Orig)/End Point 2(Term) — <TLS/SRTP> — <SBC> — <SIP/RTP/G711> — <C5 Registration>
As defined in the example, where the content of SDP in the incoming INVITE is not copied in the outgoing INVITE.
<Incoming INVITE> v=0 o=- 3727161348 3727161348 IN IP4 110.163.224.115 s=- c=IN IP4 110.163.224.115 <=== t=0 0 m=audio 4000 RTP/SAVP 120 <=== c=IN IP4 110.163.224.115 <=== a=sendrecv a=rtpmap:120 opus/48000/2 <=== a=fmtp:120 useinbandfec=1 <=== a=crypto:1 AES_256_CM_HMAC_SHA1_80 inline:uUDYq/NwP1KFCtogteM0UygvJHiCSaUHJYrXvBewe1ESnJGUkjh2ldWdCyyJ7w== <Outgoing INVITE> v=0 o=Sonus_UAC 444391 744030 IN IP4 192.168.0.2 s=SIP Media Capabilities c=IN IP4 110.163.224.115 <=== t=0 0 m=audio 4000 RTP/SAVP 120 <=== a=crypto:1 AES_256_CM_HMAC_SHA1_80 inline:uUDYq/NwP1KFCtogteM0UygvJHiCSaUHJYrXvBewe1ESnJGUkjh2ldWdCyyJ7w== a=rtpmap:120 opus/48000/2 <=== a=fmtp:120 minptime=10; useinbandfec=1; maxaveragebitrate=510000 <=== a=sendrecv a=ptime:150 <=== a=rtcp:4001 <===
This features identifies and removes the default/configured media parameters added by the SBC in direct media when sending the direct media SDP parameters in outgoing INVITE.
The SDP parameters whose default value is added in the direct media SDP include, but not limited to:
The SBC SDP functions include: