CSFB for 1xRTT Feature Description
The primary purpose of circuit-switched fallback (CSFB) for 1xRTT is to take the CDMA2000 messages received from the caller's phone (UE) and relay them to the CSFB interworking solution function for 3GPP2 (1xCS IWS) associated with the mobile switching center (1x RTT MSC) (or vice-versa) through S1-APP and S102 interfaces. This ensures the UE moves seamlessly from an LTE network to a CDMA2000 network.
The MME uses the S102 interface to tunnel the 1xRTT messages between the MME and IWS/MSC to support the following CS services:
- MO/MT Voice calls
- MO/MT SMS
- Emergency calls
This feature requires that a valid license key be installed to use the commands to configure this functionality. Speak with your Cisco Representative for information about this license. For information about the commands and their use, refer to the Configuring CSFB for 1xRTT section later in this chapter.
The MME provides the following features in support of CSFB for 1xRTT functionality:
MSC Pool Areas: Multiple MSCs would be handled by pooling all the MSCs mapping to a particular cell for load distribution. MSC pool areas can be configured for load balancing and intelligent selection of MSC servers based on IMSI hash values. Up to 10 MSC servers can be defined per S102 service.
MSC Non-Pool Areas: MSC selection, based on local MSC configuration.
MSC Selection: If an MSC pool area has been configured, the selection logic for the pool area is based on the CDMA2000 sector cell ID (includes the MSC ID and the Cell ID) in the CDMA2000 1xRTT network
- The MME attempts to match the
MSC ID and the Cell ID:
- If the match is found in the non-pool area configuration, then the configured MSC is selected.
- If the match is found in the pool area
- then IMSI hashing is used to select the MSC.
- if no hash corresponds, then the MSC selected is the one configured for the 'non-configured-values'.
- If no MSC is found, a failure message is returned.
When the UE attaches with IMEI, the MSC configured for the non-pool area is always selected because IMSI hashing cannot be performed for that UE.
DSCP Marking for S102 Interface
S102 interface allows Differentiated Services Code Point (DSCP) marking functionality. DSCP marking helps in packet traffic management. DSCP marking can be performed only on IPv4 packets leaving the S102 interface.
Either the pre-defined DSCP values can be used for marking, or any arbitrary value ranging from 0x01 to 0x3F can be assigned. The default DSCP value is 0x00 or be (Best Effort). The default DSCP value is automatically set when the configuration is disabled.
config context context_name S102-service service_name [no] ip qos-dscp dscp_value end
ip defines the Internet Protocol parameters for the packets leaving through the S102 interface.
qos-dscp designates the Quality of Service - Differentiated Services Code Point value to the packet leaving through the S102 interface.
dscp_value is a value assigned to the packet for DSCP marking. The value can be a pre-defined DSCP value or an arbitrary value ranging from 0x01 to 0x3F.
Relationships to Other Features
CSFB for 1xRTT is related to the SRVCC for 1xRTT feature. Each requires a separate license to take advantage of the separate functionality and use the configuration commands.
If licenses for both features are installed in the system and both features are configured, then the MME can use the S102 interface for both CSFB for 1xRTT and SRVCC for 1xRTT.
1xRTT CSFB and 1xRTT SRVCC calls will be decided based on the presence or absence of the CDMA2000 1xRTT SRVCC Info IEs in an UPLINK S1 CDMA2000 TUNNELING message. This IE should not present for a 1xRTT CSFB call. If only one feature is licensed and configured and if the above condition is not appropriately satisfied for any received call, then that call will be dropped.
The SRVCC for 1xRTT feature is described elsewhere in this administration guide.