what is VoLTE

What is VoLTE and what you need to use it? The VoLTE stands for Voice Over LTE.  LTE is a network that belongs to the fourth generation of telecommunication.  The …

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private LTE

What is Private LTE? Why need it if we have WiFi? With LTE, mobile phones have a much higher data speed on mobile devices.  Normally the mobile operators provide the  …

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guti in lte

What is GUTI in LTE? The GUTI full form is Globally Unique Temporary ID.  In the first initial Attach request, a UE sends the IMSI.  On attach request the MME does …

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srvcc call flow

 What is SRVCC call flow? 

In the LTE network, SRVCC is a feature by which a UE can roam from EUtran to Utran (or vice versa) and other networks without disrupting an ongoing call.  The LTE  is packet-based while UTRAN or GERAN is a circuit-based network for voice calls.

In this tutorial, we will describe the SRVCC call flow from E-UTRAN to UTRAN.  All the details are as per 3GPP specification ETSI TS 123 21.

What is the SRVCC call flow trigger point?

The triggering point is, when the UE sends a measurement report to the eNodeB, that the cell in another RAT type is more suitable.  After that eNodeB instruct the MME for handover required. Next, MME instructs the other network components to initiate the SRVCC procedure.

Before SRVCC call flow from EUtran to Utran, UE attaches to the HSS over Diameter protocol after the call flow the UE attaches to the HLR over the ss7 network. For the data, the UE moves from PGW to GGSN.

SRVCC call flow procedure:

This section details all steps in the SRVCC call procedure.

  • UE sends a measurement report to the eNodeB.
  • eNodeB sends a Handover required to the MME for the UE.
  • MME sends PS to CS requests to the MSC server over the Sv interface.
  • MSC server sends prepare handover command to the target MSC.
  • The target MSC sends relocation on handover requests to the target RNC in UTRAN (BSS for GERAN).

After the above handover sequence, there will be a circuit setup between the MSC server and MSC. Now the existing voice can use this path.


LTE ENodeB or Evolved Node B – What is GNodeB? LTE eNodeB is a component of the LTE Radio Access Network(RAN). The eNodeB full form is Evolved NodeB. The predecessor …

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