Interworking Sip Session Timer; Interworking Sip Early Media - AudioCodes Mediant 500L User Manual

sessions between such endpoints. SIP PRACK handling is configured using the IP Profile
parameter, 'SBC Prack Mode':

Optional: PRACK is optional for these UAs. If required, the device performs the
PRACK process on behalf of the destination UA.

Mandatory: PRACK is required for these UAs. Calls from UAs that do not support
PRACK are rejected. Calls destined to these UAs are also required to support
PRACK.

Transparent (default): The device does not intervene with the PRACK process and
forwards the request as is.

29.8.5 Interworking SIP Session Timer

The device supports interworking of the SIP signaling keep-alive mechanism. The SIP
standard provides a signaling keep-alive mechanism using re-INVITE and UPDATE
messages. In certain setups, keep-alive may be required by some SIP UAs while for others
it may not be supported. The device can resolve this mismatch by performing the keep-
alive process on behalf of SIP UAs that do not support it.
To configure the handling of session expires, use the IP Profile parameter, 'SBC Session
Expires Mode'.

29.8.6 Interworking SIP Early Media

The device supports early media. Early media is when the media flow starts before the SIP
call is established (i.e., before the 200 OK response). This occurs when the first SDP offer-
answer transaction completes. The offer-answer options can be included in the following
SIP messages:

Offer in first INVITE, answer on 180, and no or same answer in the 200 OK

Offer in first INVITE, answer on 180, and a different answer in the 200 OK (not
standard)

INVITE without SDP, offer in 180, and answer in PRACK

PRACK and UPDATE transactions can also be used for initiating subsequent offer-
answer transactions before the INVITE 200 OK response.

In a SIP dialog life time, media characteristics after originally determined by the first
offer-answer transaction can be changed by using subsequent offer-answer
transactions. These transactions may be carried either in UPDATE or re-INVITE
transactions. The media handling is similar to the original offer-answer handling. If the
offer is rejected by the remote party, no media changes occur (e.g., INVITE without
SDP, then 200 OK and ACK, offer-answer within an offer-answer, and Hold re-INVITE
with IP address of 0.0.0.0 - IP address is unchanged).
The device supports various interworking modes for 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 the 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
User's Manual
Mediant 500L Gateway & E-SBC
660 Document #: LTRT-10532