To provide IMS services to the UE that aren't VOLTE capable, P-GW uses the deep packet inspection (DPI) functionality to create dedicated bearers without interaction with PCRF. This helps in maintaining high QoS of the voice service although the default bearer for the internet APN gets created with interaction with PCRF.

SBC IP address (IPv4 or IPv6) and protocol RTP/RTCP are configured in ruledef and a dedicated bearer is created when a subscriber traffic matches with the ruledef without interaction with PCRF to detect voice services. If no data flows, then the dedicated bearer gets removed after the configured time limit and there's no interaction with PCRF.

The service schema framework in CUPS supports the dedicated bearer establishment in GW when default bearer is created via PCRF. Trigger condition and trigger action are configured under service schema to create new traffic flow. For dedicated bearer establishment, the rule name configured in trigger condition must match with the rule name in the rule base configuration which is the default bearer rule name.

The predefined rule trigger action gets activated when the traffic matches with the corresponding IP and the configured port range in the rule. This results in a new dedicated bearer activation without an interaction with PCRF. If no data flows on this bearer after the predefined configured time limit then it gets deleted.

Some of the key highlights are:

• There's a separate APN for non-VoLTE UEs, to avoid creation attempt of a dedicated bearer for VoLTE UEs.

• If dedicated bearer creation fails, call continues and the traffic continues to flow on this bearer.

• Retransmission for SX_Session_Report_Request intended for dedicated bearer creation works as per existing behavior.

• Feature support is provided for P-GW/SAEGW CUPS calls only. GGSN CUPS doesn't support dedicated bearer in this release.

This section describes call flow and procedure on how the dedicated bearer is established without involving PCRF.

Use the following example configuration to establish a dedicated bearer without interaction with PCRF.

config
  active-charging service acs
    ruledef Audio_dedicated_rule
      ip dst-address = 209.165.200.224/27
    #exit
    ruledef trigger_rule
      ip dst-address = 209.165.200.224/27
      udp either-port range 1024 to 5059
      udp either-port range 5062 to 43672
    #exit
    packet-filter tft1
      ip remote-port range 1024 to 5059
      ip remote-address = 209.165.200.224/27
    #exit
    packet-filter tft2
      ip remote-port range 5062 to 43672
      ip remote-address = 209.165.200.224/27
    #exit
    charging-action no_charge
    #exit	
    charging-action ca_audio
      content-id 2
      billing-action egcdr
      qos-class-identifier 1
      flow limit-for-bandwidth direction downlink peak-data-rate 256000 peak-burst-size 32000 violate-action discard
      flow limit-for-bandwidth direction uplink peak-data-rate 256000 peak-burst-size 300000 violate-action discard
      allocation-retention-priority 4 pvi 1 pci 1
      tft packet-filter tft1
      tft packet-filter tft2
    #exit
    rulebase prepaid
       billing-records egcdr
		#Install Audio_dedicated_rule on dedicated bearer to cater to VoLTE traffic
      action priority 1 dynamic-only ruledef Audio_dedicated_rule charging-action ca_audio
		#Use traffic matching to trigger_rule on default bearer as trigger condition
action priority 2 ruledef trigger_rule charging-action no_charge
    #exit
    trigger-action TA1
      #activate-predef-rule Audio_dedicated_rule
    #exit
    trigger-condition TC1
      rule-name = trigger_rule
    #exit
    trigger-condition tc
      rulebase = prepaid
    #exit
    service-scheme SS
      trigger flow-create 
        priority 1 trigger-condition TC1 trigger-action TA1 
      #exit
    subs-class SC1
      rulebase = prepaid
    #exit
    subscriber-base sb
      priority 1 subs-class SC1 bind service-scheme SS
    #exit
  #exit
context egress
    apn internet
	#Remove dedicated bearer after 300 seconds of inactivity
      timeout bearer-inactivity gbr 300 volume-threshold total 1 
	active-charging rulebase prepaid
    exit
  exit
end