S6a Interface

S6a interface is between the MME (Mobility Management Entity) and HSS (Home Subscriber Server).


S6a is an LTE 4G mobile-related interface between the MME and HSS used for authentication, location & service information about the subscriber. It uses Diameter over TCP, UDP, SCTP transport protocol. There are 4 messages initiated by the MME and 4 messages initiated by the HSS.

Network Diagram


  • Authentication Information requests/answers (AIR/AIA)
  • Update Location requests/answers  (ULR/ULA)
  • Notify requests/answers (NOR/NOA)
  • Purge requests/answers (PUR/PUA)
  • Delete requests/answers (DSR/DSA)
  • Insert Subscriber Info requests/answers (IDR/IDA)
  • Cancel Location requests/answers (CLR/CLA)
  • Reset requests/answers (RSR/RSA)

Call Flows

  • AIR/AIA initiated by MME
  • ULR/ULA initiated by MME
  • NOR/NOA initiated by MME
  • PUR/PUA initiated by MME
  • DSR/DSA initiated by HSS
  • IDR/IDA initiated by HSS
  • CLR/CLA initiated by HSS
  • RSR/RSA initiated by HSS


3GPP -https://www.3gpp.org/dynareport/29-series.htm

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