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Wednesday, May 27, 2015

VoLTE - Voice over LTE - Must Know!

How will UE know that VoLTE is supported by the EPC network?

    During the NAS Attach procedure or NAS TAU procedure, in the Attach Accept and/or RAU Accept message, additional IE called "EPS Network Feature" will be included indicating "IMS Over PS session" is available. This triggers the UE to register with IMS network.

VoLTE Call Procedures - Call flow:

  In VoLTE call establishment procedure is achieved using a application server called Telephony Application Server(TAS).
Procedure includes:
  • Establishment of Default EPS Bearer with  QCI = 5
  • SIP Call Establishment Procedures
  • Establishment of Dedicated EPS Bearer to support Media Bearer
  • SIP Call Termination Procedures
  • Termination of Dedicated EPS Bearer

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