S1 Application Part (S1AP) is the control plane signaling protocol between the eNodeB and the Mobility Management Entity (MME). Trillium LTE S1AP is a standards-based implementation of the S1AP. It supports the S1-MME interface and utilizes SCTP in the transport layer. SCTP is for the control plane, which guarantees delivery of signaling messages between the MME and eNodeB.

Diagram Trillium S1AP

The functionality of S1AP is as follows:

  • Manage the SAE Bearer
  • Transfer initial context
  • Provide mobility functions for UE
  • Provide paging
  • Provide reset
  • Transport NAS signaling
  • Report errors
  • Provide UE context release
  • Transfer status

Trillium LTE S1AP enables network equipment providers of LTE infrastructure – such as eNodeB’s, MME / Serving Gateways, Femtocells, test equipment, or other products – to:

  • Accelerate time to market
  • Reduce development costs
  • Reduce project risk of internally developed S1AP applications

FEATURES + BENEFITS

  • Sets up, modifies, and releases SAE bearer planes triggered by the MME or eNodeB
  • Establishes an S1UE context in the eNodeB
  • Sets up the default IP connectivity
  • Sets up one or more SAE bearer(s) if requested by the MME
  • Transfers NAS signaling-related information to the eNodeB if required
  • Provides UE Capability Information when it is received from the UE to the MME
  • Responsible for Mobility Functions for UEs in LTE_ACTIVE in order to enable:
    • Change of eNodeBs within SAE/LTE (Inter MME/Serving SAE-GW Handovers) via the S1 interface (with EPC involvement)
    • Change of RAN nodes between different RATs (Inter-3GPP-RAT Handovers) via the S1 interface (with EPC involvement)
  • Provides the EPC the capability to page the UE
  • Resets functionality to ensure a well defined initialization on the S1 interface
  • Features Error Indication functionality on the S1 interface to allow proper error reporting / handling in cases where no failure messages are defined
  • Features overload functionality to indicate the load situation in the control plane of the S1 interface
  • NAS Signaling transport function between the UE and the MME is used to:
    • Transfer NAS signaling related information and to establish the S1 UE context in the eNodeB
    • Transfer NAS signaling related information when the S1 UE context in the eNodeB is already established
  • Manages the release of a UE specific context in the eNodeB and the MME
  • Transfers PDCP SN Status information from source eNodeB to target eNodeB in support of in-sequence delivery and duplication avoidance for intra LTE handover
  • Features a reference application for the S1-MME interface supporting:
    • Bearer setup and release
    • Initial UE context setup
    • NAS Node selection
    • Intra-LTE handover
  • Features a comprehensive test architecture and framework for simplified acceptance and regression test execution
  • Completely Multi-threaded stack; part of the Trillium Multi-Core family (Add-On)

PRODUCT INTERWORKING

Trillium LTE S1AP comes pre-integrated with Trillium SCTP and Trillium Kernel SCTP Convergence Layer (for OS provided SCTP transport).

CONFORMANCE

Trillium LTE S1AP software conforms to:

  • Trillium Advanced Portability Architecture (TAPA)
  • FlexTCA Trillium System Software suite
  • 3GPP TS 36.413 E-UTRA; S1 Application Protocol (S1AP)
  • 3GPP TS 36.412 E-UTRA; S1 Signaling Transport
  • 3GPP TS 36.410 E-UTRA; S1 Layer 1 general aspects & principals
  • 3GPP TS 36.411 E-UTRA; S1 Layer 1