EPS NETWORK INTERFACES & ROLES

In the last discussion, we introduced the general topology of EPS N/W, Now we need to know what each interface does in brief:


  1. S1 INTERFACE: There are two S1 interfaces (S1-MME & S1-U), i will discuss each in turn:
S1-MME: Is the signaling interface btn the eNodeB & MME. The protocol layers for this are S1-AP - which is the application layer btn the eNodeB & MME. Second Protocol is Stream Control Transmission Protocol (SCTP) which guarantees the transmission of signaling messages btn the eNodeB & MME.
S1-U: Is a User plane interface btn eNodeB & S-GW. It is used to transmit the Uplink & Downlink user plane data btn eNodeB & S-GW & runs on GTP-V1 protocol.

     2. S6a INTERFACE: Is the signaling interface btn the MME & HSS.The protocol layers for this are Diameter- which supports the subscription & authentication data transmitted btn MME &HSS thus authorizes the EPS N/W access [Diameter protocol is defined in RFC 3588(31)] & SCTP  which guarantees the transmission of signaling messages btn the MME & HSS.

    3. S10 INTERFACE: Is the signaling interface btn MME's GTPC provides the tunnel for signalling messages btn MME's & the version of GTPC is GTPv2.

    4. S11 INTERFACE: Is the signaling interface btn MME & S-GW. GTP-C provides the tunnel for signalling messages btn MME & S-GW. The version of GTPC is GTPv2.

   5. S5/S8 INTERFACE: Is the interface in the signaling plane and the user plane btn the S-GW & P-GW.
  • The S5/S8 interface in the signaling plane is used to transmit messages for bearer establishment, update & deletion/ create beare context for data transmission.
  • The user plane is used to transmit UL/DL data btn S-GW & P-GW.
The difference  btn the S5 & S8 is that the S5 interface is used btn the S-GW & Home P-GW & the S8 interface is used btn the S-GW on a visited Network & the Home - PGW. GTP-C provides the tunnel for signalling messages btn S-GW & P-GW (S5 or S8)

NOTE ABOUT S5/S8 INTERFACE:
  • 3GPP23.401 (3gpp access): S5/S8 interface based on GTP. The signaling plane runs on GTPV2 & the user plane on GPTV1.
  • 3GPP23.402 (non-3gpp access): S5/S8 interface based on PMIP. 
   6. Gx/Gxc INTERFACE: Gx is the interface btn P-GW & PCRF while Gxc is the interface btn S-GW & PCRF.

NOTE:
Gxc is used  only in case of PMIP on S5/S8, if S5/S8 uses GTP protocl, Gxc is not needed. Because GTP can transfer QoS information while PMIP cannot.

 7. SGi INTERFACE: Is the interface btn P-GW & PDN. Sometimes it can work as an interface connecting the P-GW & AAA to transmit Authentication & Charging Control Messages..

Next Session we are diving dip into the Working Principle. Stay Tuned!!
#PerfectionIsANorm



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