Installation & Maintenance Manual 19. Configuring Early Media
Version 6.8 169 Microsoft Lync Server
19 Configuring Early Media
Early media refers to audio and video that is exchanged before a call is accepted by the
recipient. Early media generated by the caller includes voice commands or dual-tone multi
frequency (DTMF) tones to activate interactive voice response (IVR) systems. Early media
generated by the call recipient include ringback tones, announcements, and requests for
input.
Enhanced early media support in Lync enables a caller to hear a ringback tone generated
by the call recipient’s mobile phone. This is also the case in team-call scenarios, where a
call is routed to two team members, one of whom has configured simultaneous ringing for
his or her mobile phone.
According to Lync requirements, AudioCodes PSTN Gateway must send a SIP 183 with
SDP immediately after it receives an INVITE. The RTP packets however, will not be sent
until the PSTN Gateway receives an ISDN Progress, Alerting and Progress Indicator or
Connect message. For example, if the PSTN Gateway receives ISDN Progress, it starts
sending RTP packets according to initial negotiation, but there is no need to re-send the
183 response.
You may need to configure the PSTN Gateway's early media feature to support Lync 2013
enhanced early media feature.
To configure the Early Media feature:
1. Open the SIP General Parameters page (Configuration tab > VoIP > SIP Definitions
> SIP General Parameters).
Figure 19-1: SIP General Parameters Page (1)
2. From the ‘Enable Early Media’ drop-down list, select Enable.
3. From the ‘Play Ringback Tone to Tel’ drop-down list, select Play Local Until Remote
Media Arrive. If a SIP 180 response is received and the voice channel is already
open (due to a previous 183 early media response or due to an SDP in the current
180 response), the PSTN Gateway plays a local ringback tone if there are no prior
received RTP packets. The PSTN Gateway stops playing the local ringback tone as
soon as it starts receiving RTP packets. At this stage, if the PSTN Gateway receives
additional 18x responses, it does not resume playing the local ringback tone.
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