As part of this feature, there are two sessions on the same UPF instance established by SGW-C/cnSGW and SMF. Once they are established, the software logic determines the peer session so that the converged/collapsed datapath for packet processing is possible at the UPF node.

In distributed architecture of UP/UPF, sessions (Sxa or N4) run on different SessMgr instances. To support collapsing or converging the sessions to a single SessMgr, the SessMgr instance is selected by both sessions during establishment.

At SxDemux, when Sx Establishment Request (Sxa or N4) is received for selecting the SessMgr instance, it’s parsed for finding the SessMgr instance from remote F-TEID, where corresponding sessions (N4 or Sxa respectively) are established. The F-TEID, that contains the Tunnel Identifier that is embedded with SessMgr instance, is extracted.

UPF also maintains IMSI entry at SxDemux. IMSI entry has information of SessMgr ID where the current session is hosted. When Converged Datapath feature is enabled, on receiving Sx Session Establishment Request, SxDemux first tries to find the SessMgr ID using F-TEID. If F-TEID is not present, IMSI lookup is done. If both F-TEID and IMSI is not present, then SxDemux doesn't select the same SessMgr ID for Sxa/N4 leg.

There are two sessions, Sxa and N4, that exist on the same SessMgr instance. To converge them, the following logic is used to identify the session:

• For Uplink Packet: Egress FARs F-TEID matches with Ingress PDRs F-TEID.

• For Downlink Packet: Ingress FAR’s F-TEID should match with Egress PDR’s F-TEID.

The F-TEID includes both Tunnel Identifier and the endpoint IP address. After the session is identified, the required information is used in datapath to build the converged datapath.

After convergence of session occurs at SessMgr, the SessMgr removes the existing Bearer stream (3 tuple) from Fast Path that is installed for Sxa session. It’s established only when flow-level stream (6 tuple), based on received packet, is analyzed.

The uplink packet is received by S-GW ingress PDR endpoint. The downlink packet is forwarded using S-GW Ingress FAR-based outer header.

UPF supports charging of SMF leg (N4 leg) and S-GW .

This section describes the call flows associated with Converged Datapath feature.

The following are the known limitations of the feature:

• If Sxa leg is of one user-plane-service and N4 leg is of another user-plane-service, then datapath won't be collapsed.

• If Sxa leg is under one context and N4 leg is in another context, then datapath can't be collapsed.

• The S-GW part of the show subscribers user-plane-only full all CLI output doesn't display ToS-marked Uplink and Downlink packets.

• For the S-GW part of the show user-plane-service statistics rat all CLI output, the session statistics for Unknown is incremented, however, the data statistics aren't incremented under RAT-type Unknown.

• Lawful Intercept for S-GW isn't supported.

• S-GW bearer inactivity timeout isn't honored, as it's determined by S-GW URR for which processing isn't done for collapsed datapath.

• If S-GW leg of call is locally purged for converged session, then the UPF continues to send data toward eNodeB.

For a converged call, SGW-U sends the usage report to SGW-C based on which the SGW-C generates the CDR. You can enable this feature through the converged-sxa-usage-reporting CLI command. Once enabled, SGW-U sends a usage report with volume accounting to SGW-C, based on which the SGW-C generates the CDR.

For the SGW-U to update a volume report, the URR linking happens between SGW-U bearer URR and PGW-U, UPF bearer, or SDF level URRs. While the reconciliation of charging on UPF, the reconciliation of charging on Sxa also happens simultaneously. Depending on the threshold triggers, the SGW-U generates the usage report. Examples of threshold triggers are time threshold, volume threshold, and Query URR. Then, SGW-U sends the usage report to SGW-C based on which the SGW-C generates CDR.

To update the volume count for SGW-U bearer URRs along with PGW-U or UPF URRs for a converged call, the following process happens:

• The reference pointer of SGW-U default bearer URR is stored at PGW-U or UPF default bearer URR.

• The reference pointer of SGW-U dedicated bearer URRs is stored at SDF level URRs of the corresponding dedicated bearer of PGW-U or UPF.

While reconciling the LC count, the URRs of PGW-U or UPF and SGW-U bearer are traversed. Then, the volume counts are updated for both the call ID URRs.

Note

If a call is established as a converged call, then the reference pointer of SGW-U bearer URR is stored at PGW-U, UPF bearer, or SDF level URR while call convergence. In the case of S-GW relocation from a nonconverged call to a converged call, the URR linking happens. The URR linking implies that the reference pointer of the SGW-U bearer URR is stored at PGW-U, UPF bearer, or SDF level URR. In the case of S-GW relocation from a converged call to a nonconverged call, the URR delinking happens. The URR delinking implies that the reference pointer of SGW-U bearer URR is removed from PGW-U, UPF bearer, or SDF level URR. In the case of recovery, recreation of the link happens, which implies that the reference pointer of SGW-U URR is stored at PGW-U or UPF URR during recovery to maintain consistent behavior.

The eGCDR configuration is required on PGW-U or UPF to create static default bearer URR at PGW-U or UPF.

The following is a sample configuration:

config
   active-charging service ACS
       rulebase starent
           billing-records egcdr 
   end

The GTPP group configuration is required on PGW-U or UPF to create static default bearer URR at PGW-U or UPF.

The following is a sample configuration:

config
   context ISP
      apn intershat
          gtpp group my_grp
   end

To generate the usage report with volume count for Sxa call, use the following sample configuration:

config 
   active-charging service service_name 
      converged-sxa-usage-reporting  
         end 

NOTES:

• converged-sxa-usage-reporting : Enable generation of usage reports for converged SxA calls. To disable this functionality, add the no converged-sxa-usage-reporting syntax. The default value is no converged-sxa-usage-reporting .

Use the following configuration to enable Converged Datapath at UPF.

configure 
   user-plane converged-mode 
   end 

NOTES:

• user-plane : Specifies the UPF related to the configuration.

• converged-mode : Specifies the collapse datapath of Sxa and N4 calls.

• By default, the CLI is disabled.

• It is recommended to add the CLI in boot configuration.

Use the following CLI commands to configure remote peers for Sxa and N4 interface.

configure 
   control-plane-group group_name 
      peer-node-id ipv4-address ipv4_address interface n4 
      peer-node-id ipv4-address ipv4_address  
      end  

Use the following CLI commands to configure UP Service for Sxa and N4 interface.

configure 
   user-plane-service service_name 
      associate gtpu-service gtpu_service upf-ingress 
      associate gtpu-service gtpu_service sgw-ingress 
      associate gtpu-service gtpu_service sgw-egress 
      associate gtpu-service gtpu_service cp-tunnel 
      associate sx-service sx_service  
      associate control-plane-group group_service  
      end  

This section provides information about the show CLI commands and/or outputs available in support of the Converged Datapath feature.