TTCN-3 Based Automation Framework for LTE UE Protocol Stack Testing Theofanis Vassiliou-Gioles Testing Technologies Ranganath Mahapatra Larsen & Toubro Infotech

LTE Network Architecture GERAN SGSN HSS Operator IP Services UTRAN PCRF S3 S6a MME S7 S4 LTE-Uu S10 S11 Internet eNB Serving GW PDN GW UE LTE-Uu S1u S5 SGi S2a X2 S2b S2c ePDG Trusted non 3GPP IP Access Trusted/Untrusted non-3GPP/3GPP IP Access Wn* Untrusted non 3GPP IP Access UE

Network Simulator Need for Simulated Environment Before porting a UE protocol stack to a Modem, a simulated environment is required for test and verification Network simulator is implemented on a host environment consisting of an automation framework, test scripts and the UE side interface. Need for Simulated Environment Test environment emulates the functionality of the network elements. It interacts with the UE protocol stack through a common interface in a pre-determined manner as per the test cases. Emulating Network Element Functionality The frame work consists of a test manager, mechanism to capture logs, data analysis and debugging capability in text and graphical mode. It provides scope for integration of external codec and plug ins. Manager, Logger, Debugger

Protocol Stack Functionality RRC S1-AP PDCP SCTP RLC IP MAC L2 L1 NAS RRC PDCP RLC MAC L1 NAS S1-AP SCTP IP MAC L1 Relay UE LTE-Uu eNobeB S1-MME MME UE protocol stack communicates with multiple elements in the network side though eNodeB. UE control plane protocol layers are mapped to eNodeB and MME. Except for the NAS layer messages, the other layers of UE interact directly with eNodeB protocol stack.

ETSI Test Scripts in TTCN-3 Testing Architecture Test Management Control & Logging Automation Framework TCI ETSI Test Scripts in TTCN-3 UE Protocol Stack TRI RRC PDCP RLC MAC MAC-Phy SRB Codec ASN.1 DRB Codec Codec Layer PDCP RLC MAC L2 Layer Stubs MAC-Phy System Adaption Layer UDP / IP

Components Encodes and decodes the RRC messages which are defined in EUTRA_RRC_ASN1_Definitions. The default technique for encoding and decoding is as per RRC standard 36.331 is “PER-BASIC-UNALIGNED: 2002”. Codec PDCP, RLC and MAC header encapsulation and de-capsulation of messages and PDUs are some of the functionalities of this module. Other basic functionalities/procedures of PDCP, RLC and MAC, ex - RACH procedure, broadcast etc are also implemented. L2 Layer Stubs defines the communication protocol between eNodeB and UE protocol stack. The function of MAC-Phy interface is for the synchronization of eNodeB with UE protocol stack on UDP/IP. System Adaptation Layer MAC-Phy layer encapsulates its header into the messages. Wireshark doesn’t support these headers, so required dissectors are implemented in wire-shark to dissect and understand the LTE messages sent via PHYSAP interface. Wireshark Dissection Implementation Consists of test cases, templates, records, functions, interfaces and TTCN3 ports (TCI & TRI Ports). Additional test cases were also developed to improve the coverage. ETSI Test Script

Incremental Development & Testing

Test Execution Test case drives the specified procedures for validation of the stack. The Test Manager of IDE provides a GUI interface to run the test cases individually or in batches. The frame work provides log capturing and debugging mechanism both in text and graphical representation

Our Value Adds on ETSI’s Solution ETSI Test suite provides TTCN-3 scripts for protocol conformance testing. It provides parallel test components and ports for seamless mapping of protocol layers for network side entities. Our Value Adds In order to optimize the development cycle, we have utilized ETSI test suites, commercially available IDE and external plug ins. Adaptation layers were developed A pseudo MAC-Phy interface layer was implemented.

Challenges Codec’s and Adaptation Layers : Requires good understanding of protocol stack layers and specification Debugging and classification of issues: Differencing between test framework and UE issues Concurrent Development : Development of Test Framework (IDE), ETSI test cases and UE Protocol stack Identification of suitable commercial IDE

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