LTE  (Long Term Evolution) is initiated by 3GPP to improve the mobile phone standard to cope with future technology evolutions and needs. The main targets for this evolution are increased data rates, improved spectrum efficiency, improved coverage, reduced latency and packet-optimized system that support multiple Radio Access Technologies. It is based on the GSM/EDGE and UMTS/HSPA network technologies, increasing the capacity and speed using a different radio interface together with core network improvements. The LTE standard is developed by the 3GPP (3rd Generation Partnership Project) and is specified in its Release 8 document series, with minor enhancements described in Release 9. LTE is the natural upgrade path for carriers with both GSM/UMTS networks and CDMA2000 networks.
                  For more information about LTE see LTE Troubleshooting White Paper. For more information about LTE Monitoring click here.

S1 Application Protocol (S1AP)  
S1AP provides the signalling service between E-UTRAN and the evolved packet core (EPC) and has following functions:
  • E-RAB management function
  • Initial Context Transfer function
  • UE Capability Info Indication function
  • Mobility Functions
  • S1 interface management functions
  • NAS Signaling transport function
  • S1 UE context Release function
  • UE Context Modification function
  • Status Transfer
  • Trace function
  • Location Reporting
  • S1 CDMA2000 Tunneling function
  • Warning message transmission function
  • RAN Information Management (RIM) function
  • Configuration Transfer function
The S1 Application Protocol (S1AP) supports the functions of the S1 interface by signaling procedures defined in the standard. S1AP consists of Elementary Procedures (EPs). An Elementary Procedure is a unit of interaction between eNBs and the EPC. S1AP provides the signaling service between E-UTRAN and the evolved packet core (EPC) that is required to fulfil the S1AP functions. S1AP services are divided into two groups: Non UE-associated services: They are related to the whole S1 interface instance between the eNB and MME utilizing a non UE-associated signaling connection. UE-associated services: They are related to one UE. S1AP functions that provide these services are associated with a UE-associated signaling connection that is maintained for the UE in question.

The GPRS tunneling protocol (GTP) establishes a GTP tunnel between a Serving GPRS Support Node (SGSN) and a Gateway GPRS Support Node (GGSN) for individual Mobile Stations (MS). GTPv0 and GTPv1 are implemented using SGSNs and GGSNs. However, in GTPv2, the traditional SGSNs and GGSNs are replaced by three logical nodes—a serving gateway (SGW), a packet data network gateway (PGW), and a mobility management entity (MME). The S5 interface connects an SGW and a PGW. It provides user plane tunneling and tunnel management capability between the SGW and the PGW. It is also used for SGW relocation that happens because of user equipment mobility or SGW connection to a non-collocated PGW. The S5 interface is equivalent to the Gn interface in a Third Generation (3G) mobile network. The S8 interface connects an SGW in a visited PLMN (VPLM) and a PGW in a home PLMN (HPLMN). S8 is the inter-PLMN variant of S5. The S8 interface is equivalent to the Gp interface in a 3G mobile network. The S4 interface connects an S4 SGSN and an SGW. It provides related control and mobility support between GPRS core network and 3GPP Anchor function. It also provides user plane tunneling if direct tunneling is not established. The S4 interface does not have any equivalent interface in the 3G mobile network, because it provides interoperability between 3G and 4G networks. The Control Plane GTP uses a variable length header. The Control Plane GTP header length is a multiple of 4 octets.
GTP defines a set of messages between two associated EPC network elements. Information elements can contain other IEs. This type of IE is called “Grouped IEs”. Grouped IEs have a length value in the TLIV encoding, which includes the added length of all the embedded IEs.

  SGs Application part protocol The SGs Application Part (SGsAP) messages are used on the SGs interface between the Mobility Management Entity (MME) in the EPS and the Visitor Location Register (VLR), to allow location management coordination and to relay certain messages related to GSM circuit switched services over the EPS system. The basis for the interworking between a VLR and an MME is the existence of a SGs association between those entities per UE. The SGs association is only applicable to UEs with CS Fallback capability activated. The SGs application implements the following SGsAP procedures when associations between an MME and a VLR have been established:
  • Paging for non-EPS Services
  • Location Update for Non-EPS Services
  • Non-EPS Alert
  • Explicit IMSI Detach from EPS Services
  • Explicit IMSI Detach from Non-EPS Services
  • Implicit IMSI Detach from Non-EPS services
  •  VLR Failure
  • MME Failure
  • MM Information
  • Tunneling of NAS Messages
  • Service Request.

X2 Application Protocol (X2AP)
    The X2AP protocol is used to handle the UE mobility within E-UTRAN and provides the following functions:
  • Mobility Management
  • Load Management
  • Reporting of General Error Situations
  • Resetting the X2
  • Setting up the X2
  • eNB Configuration Update
  • Mobility Parameters Management.
  • Mobility Robustness Optimisation.
  • Energy Saving.
  • X2 Release.
  • Message transfer.
  • Registration.
  • Removing the X2.
The X2AP protocol consists of Elementary Procedures (EPs). An X2AP Elementary Procedure is a unit of interaction between two eNBs. An EP consists of an initiating message and possibly a response message. Two kinds of EPs are used: – Class 1: Elementary Procedures with response (success or failure), – Class 2: Elementary Procedures without response..


For information on Diameter refer to Diameter