top button
Flag Notify
    Connect to us
      Facebook Login
      Site Registration Why to Join

Facebook Login
Site Registration

Difference between CS fallback and 1xCS fall back ?

+2 votes
Difference between CS fallback and 1xCS fall back ?
posted Sep 16, 2013 by Neeraj Mishra

Share this question
Facebook Share Button Twitter Share Button LinkedIn Share Button

1 Answer

+2 votes

CS fallback is a generic name. 1xCS fallback is when the fallback CS network is CDMA 1xRTT.
And simply CSFB when the CS network is GSM/UMTS. Basically, for CSFB to be supported the UE should be performing Combined attach procedure (EPS attach type should be Combined EPS/IMSI attach)
1xCSFB needs a 1x-CS IWS(Interworking gateway between MME and MSC server).
MME<---S102---->1xCS IWS <----A1----->3GPP2 MSC

For 1xRTT CSFB feature, CSFB can be done with RRC connection release with redirection information or 1xSRVCC based signaling (known as enhanced 1xCSFB). 1xRTT CSFB UE may also have dual-Rx/dual-Tx or Dual-Rx/Single-Tx capability. Dual-Rx/dual-Tx 1xRTT CSFB UE can simultaneously transmit and receive on both EPS and 1x at the same time. This allows the UE to obtain 1x voice service from 1xRTT system while maintaining the data stream over EPS at the same time. This is also based on network configuration and deployment option, and UE capability. Dual-Rx/Single-Tx 1xRTT CSFB UE allows simplification in EPS network deployment because there is no coordination is required between the E UTRAN and 1xRTT network (i.e. S102 is not required).

In 1xCSFB, SIB8 informs UE about 1xCSFB support. The information in the SIB-8, together with additional information delivered to the device using Radio Resource Control (RRC) signaling,allows the UE to form a 1x Registration Message (RGM), encapsulated into a Generic Circuit Switched Notification Application (GCSNA) message. This GCSNA message is transparently carried by the eNodeB and the MME to the 1xCS IWS through the S102 tunnel. The 1xCS IWS extracts the RGM and updates the 1x MSC about the location of the UE using an A1-Location Update message. The MSC then knows how to reach the device when it receives a mobile terminated voice or SMS.

UE should support multiple radio interfaces LTE, UTRAN and GERAN
MME has SGs interface to the 3G MSC/VLR
MME<----SGs---->3G MSC/VLR

For the GSM-UMTS CSFB feature, EPS can perform the CSFB procedure with PS handover procedure, RRC connection release with redirection information, or cell change order with NACC (for GERAN only). This is based on network configuration and deployment option
The below description is for the Redirection procedure
When a MO call is attempted, UE triggers CSFB by sending EMM_Extended_service_request (with CSFB indicator). The nw will trigger RRC connection release with target RAT info(UTRAN/GERAN). Based on this info and SIB info, UE will start finding the target cells. Establishes the RRC with the target RAT, initiates the RAU procedure (Location update procedure in case of GSM) and simultaneously sends CM_service_req(with MO orig call req).This will trigger the Auth/Security procedures and further the call setup will proceed.
MT call procedure is same as above except that, UE will receive CS_Service_Notification with Paging Identity for incoming CS call(MSC ->MME->UE) before sending EMM_Extended_Service_Request (with CSFB Indicator).
MSC maintains a mapping of IMSI-MMEID, thus enabling MSC to select the right MME to send the Paging msg.

answer Sep 17, 2013 by Chandra Javalkar
Similar Questions
+4 votes

Sometimes due to coverage hole issue in the LTE network, the ongoing VoLTE is continued to UE by using the CS network like GSM network. This is known as SRVCC (Single Radio Voice Call continuity). What messages are exchanged between network nodes when UE moves from LTE to GSM ?

+1 vote

Is there any logic or its just random behavior based on availability of RAT or based on any rat priority etc ?

+2 votes

Whenever a new technology comes it provides better user experience. Since the role out of a new technology requires a lot of money investment. It makes services expensive for users. For what reasons an operator would like to deploy VoLTE when it is already have Circuit switch fall back for voice services. In India, Reliance Jio is a new player in telecom market that's why it is rolled out VoLTE since it was not having any legacy technology to provide voice services. What about others ? Are they deploying VoLTE just for the namesake that they also support VoLTE or really there is a need for that ?

Contact Us
+91 9880187415
#280, 3rd floor, 5th Main
6th Sector, HSR Layout
Karnataka INDIA.