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Overview

At a high level, the functions performed by the ATCF are:

• The ATCF is a function in the serving (visited if roaming) network. When SRVCC enhanced with ATCF, the ATCF is included in the session control plane for the duration of the call before and after access transfer. The ATCF may be co-located with one of the existing functional entities within the serving network (that is, P-CSCF or IBCF).
• Allocates an STN-SR.
• Includes itself for the SIP sessions.
• Instructs the ATGW to anchor the media path for originating and terminating sessions.
• Keeps track of sessions (either in pre-alerting state, alerting state, active, or held) to perform access transfer of the selected session.
• Performs the access transfer and updates the ATGW with the new media path for the (for example, CS) access leg, without requiring updating the remote leg.
• After Access Transfer, updates the SCC AS that access transfer has taken place to ensure that T-ADS have the information on the currently used access.
• Handles failure cases during the access transfer.

Deployment Scenarios

Call Flow

The call flow description for Figure 2 is as follows:

1. The 

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    SBC, acting

1. as an A-SBC and ATCF, receives REGISTER request from UE.

1. The SBC processes the REGISTER request and based on the local configuration applies ATCF procedures for REGISTER. It adds all the ATCF specific parameters (Feature-Caps header with g.3gpp.atcf, g.3gpp.atcf-mgmt-uri, and g.3gpp.atcf-path parameters) to the REGISTER. It also inserts a Path header pointing to itself as a part of ATCF procedures.

1. The SBC acting as a B2BUA, changes Contact header to point itself and forwards the REGISTER request towards P-CSCF.
2. P-CSCF forwards REGISTER towards I/S-CSCF.
3. I/S-CSCF responds to the REGISTER with 200 OK.
4. P-CSCF forwards 200 OK response (to REGISTER) towards

1. the SBC, acting as an A-SBC and ATCF.

1. The SBC stores the Path and Service-Route headers and forwards these headers transparently towards UE. It also inserts a Feature-Caps header field with g.3gpp.atcf feature-capability indicator containing the STN-SR allocated to ATCF.
2. SCC AS sends MESSAGE request towards

1. the SBC/ATCF’s Management URI (sent in Feature-Caps header while forwarding REGISTER request). The MESSAGE contains application/vnd.3gpp.SRVCC-info+xml. The message contains
   • ATU-STI for PS to CS SRVCC
   • b) C-MSISDN

1. The SBC acting as ATCF, processes MESSAGE request and binds the information present in the message-body against registration control block for that UE.

The call flow description for Figure 3 is as follows:

1. The initial call is established over LTE access between UE-A and UE-B. The signaling and media are anchored at

1. the A-SBC/ATCF.
2. UE-A moves to CS domain and attaches itself to CS domain.
3. The MSC that is attached to the UE, sends an INVITE request with STN-SR in Request-URI towards ATCF to initiate PS to CS handover. The INVITE request contains C-MSISDN in P-Asserted-Identity header.
4. After receiving an INVITE with STN-SR (that is, a PS to CS handover request),

1. the SBC/ATCF uses C-MSISDN to derive the UE’s identity and the associated session.
2. It allocates port towards MSC server and switches the media-ports towards MSC server.
3. It sends 200 OK towards MSC Server.
4. MSC Server responds with ACK. With this, the handover is completed and the media path is established towards the UE through MSC server that is, CS domain.

1. The SBC/ATCF establishes a new dialog with the SCC AS through I-CSCF by sending a new SIP INVITE request to the SCC AS using the stored ATU-STI for PS to CS SRVCC.
   The INVITE request contains:
   • SDP offer containing the currently used media with ATGW ports and IP addresses towards the remote UE as provided by the ATGW. The ATCF only includes the media of the media types in the SDP offer. The media types are offered in the received SIP INVITE request due to STN-SR.
   • Request-URI containing the ATU-STI for PS to CS SRVCC previously received from the SCC AS and associated with the session being transferred.
   • Target-Dialog header field with the dialog identifier of the session that is transferred.
2. I-CSCF forwards the INVITE to SCC AS.
3. SCC AS responds with 200 OK to INVITE.
4. I-CSCF forwards the 200 OK to INVITE to

1. the SBC/ATCF.
   In the remaining steps, SCC AS clears the old access leg established over LTE access.

Configuration

• Global Configuration
• Configuring SBC Towards UE
• Configuring SBC Towards IMS Core with an External P-CSCF
• Configuring SBC Towards IBCF
• Configuring SBC Towards MSC

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Global Configuration_atcf Global Configuration_atcf

Global Configuration

• ATCF Configuration
• Trunk Group Towards UE
• IPsec Support for SBC Only Mode
• Precondition Support
• MSRP Support
• Attaching ATCF Profile to IPSP

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ATCF Configuration ATCF Configuration

ATCF Configuration

set global signaling srvcc stnSr +1-237-555-3333 atcfUri atcf.visisted2.net callLingerTimer 32

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Trunk Group Towards UE1 Trunk Group Towards UE1

Trunk Group Towards UE

set profiles signaling ipSignalingProfile IPSP_PCSCF egressIpAttributes privacy transparency enable

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IPsec Support for SBC Only Mode_atcf IPsec Support for SBC Only Mode_atcf

IPsec Support for SBC Only Mode

set addressContext default ipsec spd spd2 action bypass localIpAddr 10.54.54.27 localIpPrefixLen 32 localPort 5061 precedence 11 state enabled
commit

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Precondition Support_atcf Precondition Support_atcf

Precondition Support

set addressContext default zone ZONE_ACCESSNW sipTrunkGroup TG_TOWARDS_UE services preconditions transparent
commit

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MSRP Support_atcf MSRP Support_atcf

MSRP Support

set system media dedicatedBWForNonRTPMedia 50
commit

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Attaching ATCF Profile to IPSP Attaching ATCF Profile to IPSP

Attaching ATCF Profile to IPSP

1. Select "ATCF" profile from the "Access Transfer Policy Type" option.

   Caption
   0 Figure 1 Selecting ATCF Profile
   Image Modified

2. Attach the ATCF profile to the Ip signaling profile of a Trunk Group.

   Caption
   0 Figure 1 Attaching ATCF profile to the IPSP Trunk group
   Image Modified

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Configuring SBC Towards UE Configuring SBC Towards UE

Configuring SBC Towards UE

The following profiles are configured:

• Transparency Profile
• Zone Index Profile
• Ip Signaling Profile
• Sip Trunk Group 
  

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Transparency Profile_ue Transparency Profile_ue

Transparency Profile

set addressContext default zone ZONE_ACCESSNW sipTrunkGroup TG_TOWARDS_UE services transparencyProfile TRANS_PROF_ACCESS
commit

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Zone Index Profile_ue Zone Index Profile_ue

Zone Index Profile

The following fields must be configured:

• Zone Index Profile
• Description
• Zone Index

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Ip Signaling Profile_ue Ip Signaling Profile_ue

Ip Signaling Profile

The following parameters must be configured under "Ip Signaling Profile".

• Common Ip Attributes
• Relay Flags
• Transparency Flags
• Egress Ip Attributes
• Ingress Ip Attributes

The following "Common IP Attributes" must be enabled in PSX under "IP SIGNALING PROFILE":

• No Port Number 5060

• Reject REFER

• ReQuery PSX on REGISTER Refresh

• Disable Host Translation

• End to End BYE

• End to End RE-INVITE

• End to End UPDATE

• Store P-Charging-Vector

• Validate Access Nw Info Header

• Insert UE Flow Info

The following "Relay Flags" must be enabled under "Ip Signaling profile":

• Dialog Event Package
• Info
• Options
• Select Reject the REFER request if no match is found from Refer To Header Relay option.

The following "Transparency Flags" must be enabled under "Ip Signaling profile":

• Contact Header*

The following "Egress IP Attributes" must be enabled:

• Select SIP Only from IP Protocol Type.
• Select BCI Interwork Encountered from BCI option.
• Select Transparency from Privacy option.
• Select Merge Received Contacts with Existing Contacts from Redirect option.
• Select Include None from Include Charge Information (under SIP Headers and Parameters option).
• Select None from SIP TO Header Mapping from SIP Headers and Parameters option.
• Select Include OLIP from Flags (under SIP Headers And Parameters option).
• Select Transparency For Destination Trunk Group Parameter from Flags (under SIP Headers And Parameters option).
• Select End To End Ack from Flags (under SIP Headers And Parameters option).
• Select Diversion from Call Forwarding (under SIP Headers And Parameters option).

The following "Ingress IP Attributes" must be enabled:

• 181 Supported (under Flags option)

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Sip Trunk Group_UE Sip Trunk Group_UE

Sip Trunk Group

The following profiles/fields must be enabled:

• Zone Index Profile
• IP Signaling Profile
• Feature Control Profile
• Signaling Profile
• SIP Domain
• IP Version Preference
• Use IPTG Routing (Hop By Hop Routing) For Ingress (Ingress > Flags)
• Do Not Use For Fallback Bearer Capability (Egress > Flags)
• IP Peer Supported (Egress > IPTG)
• Egress IP Signaling Profile (Egress > IPTG)
• Select Traffic Management Options from Trunk Group Reserved Level 1 and Trunk Group Reserved Level 2.
• Select Services as Not Screened.

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Configuring SBC Towards IMS Core with an External P-CSCF Configuring SBC Towards IMS Core with an External P-CSCF

Configuring SBC Towards IMS Core with an External P-CSCF

The following profiles are configured:

• Transparency Profile
• Zone Index profile
• Ip Signaling Profile
• Sip Trunk Group

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Transparency Profile_imscore Transparency Profile_imscore

Transparency Profile

set addressContext default zone ZONE_CORENW sipTrunkGroup TG_TOWARDS_CORENW services transparencyProfile TRANS_PROF_CORENW
commit

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Zone Index profile_IMSCore Zone Index profile_IMSCore

Zone Index Profile

The following fields must be configured:

• Zone Index Profile
• Description
• Zone Index

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Ip Signaling Profile_IMSCore Ip Signaling Profile_IMSCore

Ip Signaling Profile

• Common Ip Attributes
• Relay Flags 
• Egress Ip Attributes  

The following "Common IP Attributes" must be enabled in PSX under "IP SIGNALING PROFILE":

• Add P-Charging-Function Addr
• Create P-Charging-Vector
• Create P-Visited-Network Id
• Customized Session Timer Behavior
• Disable Host Translation
• End to End BYE
• End to End RE-INVITE
• End to End UPDATE
• End to End PRACK
• Enable Dial String Handling
• No Port Number 5060
• P-Called-Party-Id-Support
• Restrict History Info Header
• Store P-Charging Vector
• Store Service-Route Header
• Validate Access Nw Info Header
• Insert UE Flow Info

The following "Relay Flags" must be enabled under "Ip Signaling profile":

• Dialog Event Package
• Info
• Options
• Select Reject the REFER request if no match is found from Refer To Header Relay option.

The following "Egress IP Attributes" must be enabled:

• Select SIP Only from IP Protocol Type option.
• Select Transit PAI From Unregistered Peer from Flags.
• Select Use IP Signaling Peer Domain In R-URI from Domain Name option.
• Select Include npdi from NPDI Options (under Number Portability Attributes option).
• Select P-Preferred-ID from Privacy Information (under Privacy option).
• Select Merge Received Contacts with Existing Contacts (under Redirect)
• Select Include None from Include Charge Information (under SIP Headers and Parameters option).
• Select Not Send from Session-Expires Refresher (under SIP Headers and Parameters option).
• Select None from SIP TO Header Mapping (under SIP Headers and Parameters option).
• Select Transparency For Destination Trunk Group Parameter from Flags (under SIP Headers and Parameters option).
• Select End To End Ack from Flags (under SIP Headers and Parameters option).
• Select Diversion from Call Forwarding (under SIP Headers and Parameters).
• Select Retry Without ETS from the Action For ETS 400 Responses With 417 Reason Code drop-down box (under SIP RPH ETS).
• Set ETS Default Priority Value as 0 (under SIP RPH ETS).

Caption
0 Figure 1 PSX IPSP-Common IP Attributes-Egress IP Attributes
Image Modified

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Sip Trunk Group_imscore Sip Trunk Group_imscore

Sip Trunk Group

The following profiles/fields must be enabled:

• Zone Index Profile
• IP Signaling Profile
• Feature Control Profile
• Signaling Profile
• SIP Domain
• IP Version Preference
• Use IPTG Routing (Hop By Hop Routing) For Ingress (Ingress > Flags)
• Do Not Use For Fallback Bearer Capability (Egress > Flags)
• IP Peer Supported (Egress > IPTG)
• Egress IP Signaling Profile (Egress > IPTG)
• Select Traffic Management Options from Trunk Group Reserved Level 1 and Trunk Group Reserved Level 2.
• Select Services as Not Screened.

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Configuring SBC Towards IBCF Configuring SBC Towards IBCF

Configuring SBC Towards IBCF

The following profiles are configured:

• Transparency Profile
• Zone Index profile
• PSX Route URI Based Routing
• Ip Signaling Profile
• Sip Trunk Group

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Transparency Profile_IBCF Transparency Profile_IBCF

Transparency Profile

set addressContext default zone ZONE_IBCF sipTrunkGroup TG_TOWARDS_IBCF services transparencyProfile TRANS_PROF_IBCF
commit

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Zone Index profile_ibcf Zone Index profile_ibcf

Zone Index profile

Configuration Towards Peer in External:

set addressContext default zone ZONE_CORENW dialogTransparency enabled 

The following fields must be configured:

• Zone Index Profile
• Description
• Zone Index

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PSX Route URI Based Routing PSX Route URI Based Routing

PSX Route URI Based Routing

The following flags must be configured:

1. Create a Feature Profile.

   1. Enable Perform Route Header Based Routing.

      Caption
      0 Figure 1 Route Header Based Routing
      Image Modified

   2. On the SIP Trunk Group, select the mapped Feature Control Profile and IP Signaling Profile.

      Caption
      0 Figure 1 Ingress SIP TG
      Image Modified

2. Create Call Parameter Filter Profile and set the values for:
   
   1. Type as "Regex Group."
      
   2. Variable Type as "Route URI Host Part."

   3. Configure RouteURI as matching Regex String.
      

      Caption
      0 Figure 1 Call Parameter Filter Profile
      Image Modified

      
      

3. Create Policy Profile.
   1. Enable URI and URI Action as "Override IP Peer with Route URI Host Part".

   2. Map the created Call Parameter Filter Profile.

      Caption
      0 Figure 1 Policy Profile
      Image Modified

4. Map the Policy Profile under Policy Profile Group.
   

   Caption
   0 Figure 1 Policy Profile Group
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5. On the SIP Trunk Group under Egress, select the Output Policy Profile Group.

   Caption
   0 Figure 1 Egress SIP TG
   Image Modified

6. For domain based configuration, select UserName Routing.

   1. Select the already mapped Call Parameter Filter Profile and Domain Name from the drop-down menu.

      Caption
      0 Figure 1 Username Routing
      Image Modified

       

       

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Ip Signaling Profile_ibcf Ip Signaling Profile_ibcf

IP Signaling Profile

• Common Ip Attributes
• Relay Flags  
• Egress Ip Attributes  

The following "Common IP Attributes" must be enabled in PSX under "IP SIGNALING PROFILE":

• Add P-Charging-Function Addr
• Create P-Charging-Vector
• Create P-Visited-Network Id
• Create Path Header
• Customized Session Timer Behavior
• Disable Host Translation
• End to End BYE
• End to End RE-INVITE
• End to End UPDATE
• End to End PRACK
• Enable Dial String Handling
• No Port Number 5060
• P-Called-Party-Id-Support
• Restrict History Info Header
• Store P-Charging Vector
• Store Service-Route Header
• Validate Access Nw Info Header

The following "Relay Flags" must be enabled under "Ip Signaling profile":

• Dialog Event Package
• Info
• Options
• Select Reject the REFER request if no match is found from Refer To Header Relay option.

The following "Egress IP Attributes" must be enabled:

• Select SIP Only from IP Protocol Type.
• Select Transit PAI From Unregistered Peer from Flags.
• Select Use IP Signaling Peer Domain In R-URI from Domain Name option.
  
• Select Include npdi from NPDI Options from Number Portability Attributes option.
• Select P-Preferred-ID from Privacy Information from Privacy option.
• Select Include Privacy from Flags (under Privacy).
• Select Merge Received Contacts with Existing Contacts from Redirect option.
• Select Include None from Include Charge Information option (under SIP Headers and Parameters).
• Select Not Send from Session-Expires Refresher option (under SIP Headers and Parameters).
• Select None from SIP TO Header Mapping option (under SIP Headers and Parameters).
• Select Transparency For Destination Trunk Group Parameter from Flags (under SIP Headers and Parameters).
• Select End To End Ack from Flags (under SIP Headers and Parameters).
• Select Diversion from Call Forwarding (under SIP Headers and Parameters).
• Select Retry Without ETS from the Action For ETS 400 Responses With 417 Reason Code drop-down box (under SIP RPH ETS).
• Set ETS Default Priority Value as 0  (under SIP RPH ETS).

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Sip Trunk Group_ibcf Sip Trunk Group_ibcf

Sip Trunk Group

IBCF (Towards Peer IBCF/IPX)

set addressContext default zone ZONE_CORENW sipTrunkGroup IBCF transitIoi "IBCF"
commit

The following profiles/fields must be enabled:

• Zone Index Profile
• IP Signaling Profile
• Feature Control Profile
• Signaling Profile
• SIP Domain
• IP Version Preference
• Use IPTG Routing (Hop By Hop Routing) For Ingress (Ingress > Flags)
• Do Not Use For Fallback Bearer Capability (Egress > Flags)
• Select Traffic Management Options from Trunk Group Reserved Level 1 and Trunk Group Reserved Level 2.
• Select Services as Not Screened.

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Configuring SBC Towards MSC Configuring SBC Towards MSC

Configuring SBC Towards MSC

The following profiles are configured:

• Transparency Profile
• Zone Index Profile
• Ip Signaling Profile
• Sip Trunk Group

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Transparency Profile_msc Transparency Profile_msc

Transparency Profile

set addressContext default zone ZONE_MSC sipTrunkGroup TG_TOWARDS_MSC services transparencyProfile TRANS_PROF_MSC
commit

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Zone Index Profile_msc Zone Index Profile_msc

Zone Index Profile

The following fields must be configured:

• Zone Index Profile
• Description
• Zone Index

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Ip Signaling Profile_msc Ip Signaling Profile_msc

Ip Signaling Profile

•  Common Ip Attributes
•  Relay Flags
•  Transparency Flags
•  Egress Ip Attributes
•  Ingress Ip Attributes

The following "Common IP Attributes" must be enabled in PSX under "IP SIGNALING PROFILE":

• Add P-Charging Function Addr
• Create P-Charging-Vector
• Create P-Visited-Network Id
• Create Path Header
• Disable Host Translation
• End to End BYE
• End to End RE-INVITE
• End to End UPDATE
• End to End PRACK
• Enable Default Procedures
• Enable Dial String Handling
• No Port Number 5060
• P-Called-Party-Id-Support
• Restrict History Info Header
• Store P-Charging Vector
• Store Service-Route Header
• Validate Access Nw Info Header

The following "Relay Flags" must be enabled under "Ip Signaling profile":

• Dialog Event Package
• Info
• Options
• Select Reject the REFER request if no match is found from Refer To Header Relay option.

The following "Transparency Flag" must be enabled:

• Pass Complete Contact-Header

• Select SIP Only from IP Protocol Type.
• Select BCI Interwork Encountered from BCI option.
• Select Use IP Signaling Peer Domain In R-URI from Domain Name option.
• Select Include npdi from NPDI Options (under Number Portability Attributes option).
• Select P-Asserted-ID from Privacy Information (under Privacy option).
• Select Include Privacy from Flags (under Privacy).
• Select Do Not Include Tel URI In PAI Header from Flags (under Privacy option).
• Select Merge Received Contacts with Existing Contacts from Redirect option.
• Select Include None from Include Charge Information option (under SIP Headers and Parameters).
• Select Not Send from Session-Expires Refresher option (under SIP Headers and Parameters).
• Select None from SIP TO Header Mapping option (under SIP Headers and Parameters).
• Select Include CPC Information from Flags (under SIP Headers and Parameters option).
• Select Transparency For Destination Trunk Group Parameter from Flags (under SIP Headers and Parameters option).
• Select End To End Ack from Flags (under SIP Headers and Parameters option).
• Select Diversion from Call Forwarding (under SIP Headers and Parameters option).
• Select Retry Without ETS from the Action For ETS 400 Responses With 417 Reason Code drop-down box (under SIP RPH ETS option).
• Set ETS Default Priority Value as 0  (under SIP RPH ETS).

The following "Ingress Ip Attribute" must be enabled:

• Map Called Party Category In P-Sig-Info Header

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sip_trunk_group_msc sip_trunk_group_msc

Sip Trunk Group

The following profiles/fields must be enabled:

• Zone Index Profile
• IP Signaling Profile
• Feature Control Profile
• Signaling Profile
• SIP Domain
• IP Version Preference
• Do Not Use For Fallback Bearer Capability (Egress > Flags)
• IP Peer Supported (Egress > IPTG)
• Egress IP Signaling Profile (Egress > IPTG)
• Select Traffic Management Options from Trunk Group Reserved Level 1 and Trunk Group Reserved Level 2.
• Select Services as Not Screened.

Image Modified