Rx Interface

The Rx Interface supports the QoS resource reservation for reserving bandwidth in the IP access network.

The Rx reference point is used to exchange application level session information between the Policy and Charging Rules Function (PCRF) and the P-CSCF. The SBC, acting as P-CSCF creates a TCP connection with the configured PCRFs as shown in the example diagram below.

Figure 1: P-CSCF to PCRF Connection via RX Interface

The Rx Interface implementation is based on RFC 3588 (Diameter protocol) and 3GPP TS 29.214V8.2.0 (Policy and Charging Control over Rx Reference Point). Rx applies independently to the ingress and/or egress legs of a call, based on configurable parameters of the supporting SIP Services. The Rx interface may be provisioned on a per SIP Service Group basis.

To act as P-CSCF in the network, the SBC supports the Rx interface with the following messages.

• AAR (Authorization/Authentication Request)—sent to PCRF to request QOS reservation and to open firewall pinholes for specified media flows.
• AAA (Authorization/Authentication Answer)—received from PCRF with the result of an AAR request.
• RAR (ReAuthorization Request—received from PCRF as notification of a specific event. SBC can (but does not) register for events like "Indication of Loss of Bearer", "Indication of Recovery of Bearer", "Indication of Release of Bearer" RAR is therefore unexpected.
• RAA (ReAuthorization Answer—sent to PCRF to acknowledge an RAR.
• STR (Session Termination Request—sent to PCRF to end a session. This implies release of the QOS reservation and closing of the firewall pinholes for associated media flows.
• STA (Session Termination Answer—received from PCRF to acknowledge an STR. STA is consumed by the Diameter interface and is not passed on to the Rx application.
• ASR (Abort Session Request)—received from PCRF as notification that all media flows associated with a session have become unavailable.
• ASA (Abort Session Answer—sent to PCRF to acknowledge an ASR, and is followed by sending STR.

To configure Rx interface for PCRF from CLI, use command syntax:

% set addressContext <addressContexName> zone <zoneName> sipTrunkGroup <trunkGroupName> media pcrf pcrfCommitment <none | supported | required>

...where pcrfCommitment is the degree of commitment expected from the PCRF during call setup or call update. Refer to Configuring SBC as P-CSCF for additional details.

Example:

Below is an example of creating a system-level Rx node.

set addressContext default diamNode Diam primaryOriginHost primary-pcrf secondaryOriginHost secondary-pcrf ipV4Address 10.54.172.150 ipV6Address fd00:10:6b50:5410::96 originRealm pcscf-rx-ims.test transactionTimeout 6000 ipInterfaceGroupName LIF1
commit

set addressContext default diamNode Diam peer seagull.sonus.net fqdn seagull.sonus.net ipAddress 10.54.12.251 tcpPort 3868
commit

set addressContext default diamNode Diam realmRoute seagull.sonus.net realm seagull.sonus.net peer seagull.sonus.net appId rx priority 1
commit

set addressContext default diamNode Diam state enabled
commit

set addressContext default diamNode Diam peer seagull.sonus.net state enabled
commit

set addressContext default diamNode Diam realmRoute seagull.sonus.net state enabled
commit

set addressContext default zone ZONE_IAD sipTrunkGroup TG_PCSCF_INT_IP media pcrf pcrfRealm seagull.sonus.net pcrfCommitment supported cushionPacketSize enabled cushionNullSdp enabled 
commit

Additional topics in this section: