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Overview

The

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relays the INVITE requests it receives. Egressing The Egress INVITE may /or may not have the SDP depending on the presence of SDP in the received INVITE and late offer interworking configuration. TheThe 

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inserts the Allow header containing the following methods:

• INVITE

,

• ACK

,

• CANCEL

,

• BYE

,

• REGISTER

,

• REFER

,

• INFO

,

• SUBSCRIBE

,

• NOTIFY

,

• PRACK

,

• UPDATE

,

• MESSAGE

,

• PUBLISH
• OPTIONS

When the methods and OPTIONS. There are configurable options for the support of REFER, SUBSCRIBE, NOTIFY, OPTIONS, MESSAGE, PUBLISH and INFO, and when these methods INFO  are configured as not supported, these methods they are not added in the Allow header.

The

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adds a Supported supported header containing the following extensions: "100rel", "timer" and "path" extensions. Addition of “100rel”, “timer” and “path” extensions which is configurable. As a part of RCS support,

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relays “Require” header with “recipient-list-invite” option-tag.

You can  configure the The

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can be configured   to transparently pass the “From’ and “To” headers headers  transparently from ingress to egress call - leg. Additionally, for access deployments, you can configure the 

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can be configured to use Username in the To header instead of the Request-URI, while terminating calls to the IP-PBX.

The

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supports processing or relaying the ‘replaces header’ received in the incoming SIP request. This done , based on the ‘Relay Replaces Header flag’ Header’ flag in the SIP service on the

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. If the 

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is configured to process INVITE with Replaces locally and if the dialog doesn’t does not exist, the INVITE is rejected with 481 response. the The

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 processes INVITE with Replaces with  replaces locally only on confirmed dialogs.

The

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supports the reception of INVITE with and without SDP Offer.

• If the INVITE is received with

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  receives the INVITE with the SDP offer, the 

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  sends the SDP Answer in the first reliable provisional response or in the success final response.
• If the SBC receives the initial INVITE does not contain an without the SDP offer, the

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  it sends the SDP offer in the first reliable 18x or 200 OK response, and the answer is expected in PRACK or ACK method (as appropriate).  The

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  ignores any changes in the SDP when compared with the initial INVITE on receiving the authentication INVITE from the ingress peer.

Info
title Note
Even though the Spacevars 0 product sends Allow and Supported headers by default in the outgoing INVITE, it does not discard an incoming INVITE if these headers are NOT present.

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INVITE Support

The

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supports sending SIP INVITE requests to establish VoIP calls. When a User Agent Client (UAC) desires to initiate a session (for example, audio, video, or a game), it formulates an INVITE request. The INVITE request asks a server to establish a session. This request may be forwarded by proxiesThe proxies may forward the request , eventually arriving at one or more User Agent Servers (UASs) that can potentially accept the invitation. These UASs will frequently need to query queries the user about whether frequently to accept the invitation or not. After some time, those UASs can accept the invitation (meaning the session is to be established) by sending a 2xx response.

If the invitation is not accepted, a 3xx, 4xx, 5xx, or 6xx response is sent, depending on the reason for the rejection. Before sending a final response, the UAS can also send provisional responses (1xx) to advise the UAC of progress in contacting the called user.

Sending an INVITE request within an existing dialog to change addresses or ports, add or delete a media stream, and so forth is known as a re-INVITE.

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reINVITE Handling

Panel
Reference: RFC 6141

The

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does not provide any interworking between an error response and 200 (OK) for a reINVITE.

reINVITE Handling  by UAS

No There are no state changes are performed in the 

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if if the downstream entity rejects a reINVITE is rejected by the downstream entity. 

The

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supports the following UAS behavior for a call which is set up with only an audio stream:

• When a reINVITE is received adding with a video stream (SDP has both audio and video components), and if the reINVITE is rejected by the downstream entity rejects the reINVITE , the audio stream remains intact and is still active.

  Caption
  0 Figure 1 Call Flow Example

• When a reINVITE is received adding the 

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  receives the reINVITE with a video stream and also updating the updated IP address for the audio stream (SDP has both audio and video components), and if the downstream entity rejects the corresponding reINVITE on the other leg is rejected by the downstream entity, the 

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  continues to use the old IP address for the audio stream.

  Caption
  0 Figure 1 Call Flow Example

• When a reINVITE is received adding the 

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  receives a reINVITE  with a video stream and also updating the updated IP address for the audio component (SDP has both audio and video components), and if replies to the corresponding reINVITE on the other leg is replied with 200 (OK) , but with video component has as port=0. The , the video stream is not created and the 

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  replies with 200 (OK), video stream is not created and uses the new IP address is used for audio.

  Caption
  0 Figure 1 Call Flow Example

• When the

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  receives a reINVITE to add a video stream but does not have enough bandwidth to do so , the 

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  generates a 200 (OK) response with port=0 for video stream.
  
  
• The

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  does not propagate a reINVITE/UPDATE to the other leg if it does not change any characteristics (e.g. For example, codec, digit transfer mode) in the existing streams on the other leg.
• When an egress server changes the SDP from 18x message to 200 OK message (which is a violation of RFC 3261), the 

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  interworks by sending the last sent SDP in 200 OK and then sends a RE-INVITE to correct the SDP. This Re-INVITE can cause problems if the

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  challenges the INVITE/Re-INVITE is challenged INVITE   for authentication or because if the endpoints change Secure Real-Time Transport Protocol (SRTP) keys for every new SDP offer. In these scenarioscases, the 

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   updates the SDP in 200 OK itself.

UAC Behavior

The

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does not generate a reINVITE/UPDATE upon on receipt of an error response for a reINVITE. It is assumed that The 

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assumes that the downstream entity is RFC6131-compliant and keeps the session characteristics the characteristics  same as before the rejected reINVITE transaction.

Glare Situations

The

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replies with 491 (Request Pending) if it receives a reINVITE is received while a previous one is still when the previous reINVITE is pending.

Clarifications on Canceling re-INVITEs

When canceling the reINVITES, the

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always replies with 487 (Request Terminated).

Refreshing a Dialog’s Target and its Subsections

The

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 supports refreshing a dialog's target and its subsections as well as updating the remote target based on an unreliable response.

Non-reliable provisional response to the INVITE

 RFC 6377 requires that, after the 

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sends an answer in a reliable provisional response to an INVITE, it does not include any Session Description Protocol (SDP) in subsequent responses to the INVITE.

However, after the 

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(UAS) sends the answer in non-reliable provisional response to the INVITE , and  Send SDP in Subsequent 18x  is enabled, the 

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resends the SDP in all the subsequent 18x to maximize the possibility for SDP reception.

The call flow depicts the reliable and non-reliable 18x with the SDP call flow.

Caption
0 Figure 1 Non-reliable 18x with SDP
Image Added

Caption
0 Figure 1 Reliable 18x with SDP
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