AudioCodes Mediant 500 E-SBC, Руководство пользователя

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User's Manual 27. SBC Overview
Version 6.8 461 Mediant 500 E-SBC
27.7.6 Interworking SIP Early Media
The device supports various interworking modes for SIP early media between SIP UAs
(i.e., IP Groups):

Early Media Enabling: The device supports the interworking of early media between
SIP UAs that support early media and those that do not support receipt of early media.
Early media can arrive in provisional responses to an INVITE request. The device
forwards the request of early media for IP Groups that support this capability;
otherwise, the device terminates it. Provisional responses whose SDP are suppressed
are changed to a SIP 180 response. This feature is also supported for delayed offers.
This is configured using the IP Profile parameter, 'SBC Remote Early Media Support'.
The device refers to this parameter also for features that require early media such as
playing ringback tone.

Early Media Response Type: The device supports the interworking of different SIP
provisional response types between UAs for forwarding the early media to the caller.
This can support all early media response types (default), SIP 180 only, or SIP 183
only, and is configured by the IP Profile parameter, 'SBC Remote Early Media
Response Type'.

Multiple 18x: The device supports the interworking of different support for multiple
18x responses (including 180 Ringing, 181 Call is Being Forwarded, 182 Call Queued,
and 183 Session Progress) that are forwarded to the caller. The UA can be configured
as supporting only receipt of the first 18x response (i.e., the device forwards only this
response to the caller), or receipt of multiple 18x responses (default). This is
configured by the IP Profile parameter, 'SBC Remote Multiple 18x Support'.

Early Media RTP: The device supports the interworking with remote clients that send
18x responses with early media and whose subsequent RTP is delayed, and with
remote clients that do not support this and require RTP to immediately follow the 18x
response. Some clients do not support 18x with early media, while others require 18x
with early media (i.e., they cannot play ringback tone locally). These various
interworking capabilities are configured by the IP Profile parameters, 'SBC Remote
Early Media RTP', 'SBC Remote Supports RFC 3960', and 'SBC Remote Can Play
Ringback'. See the flowcharts below for the device's handling of such scenarios: