Implementing the S1 Application Protocol in a Cloud Radio Access Network Environment

Transcription

1 Implementing the S1 Application Protocol in a Cloud Radio Access Network Environment KeijoLehtinen Networking Technology Master s thesis seminar Supervisor: Prof. RikuJäntti Advisor: D.Sc. (Tech.) KalleRuttik

2 Table of contents Background Goals & motivation The S1 Application Protocol (S1AP) Abstract Syntax Notation One (ASN.1) Implementation Summary & conclusions

3 Background 3

4 LTE network architecture 4

5 Cloud Radio Access Network (C-RAN) Centralized, cloud computing-based architecture. Servers connected to Remote Radio Heads. Flexible, share resources dynamically. Cheaper to operate. 5

6 Aalto Radio Framework (ARF) Implements TDD LTE Release 8. Flexible research tool to study radio technologies. Test new radio features. Build proof-of-concepts. 6

7 ARF architecture 7

8 Goals & motivations 8

9 Goals & motivation To develop the ARF software closer to a full base station node by implementing the control plane of the S1 interface. 9

10 The S1 Application Protocol (S1AP) 10

11 S1 interface specifications Number TS TS TS TS TS Title Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 general aspects and principles Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 layer 1 Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 signalling transport Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 Application Protocol (S1AP) Evolved Universal Terrestrial Radio Access Network (E-UTRAN); S1 data transport 11

12 S1 interface protocol structure 12

13 S1AP messages Approximately 50 elementary procedures. Initiating message + optionally successful outcome & unsuccessful outcome response messages. Messages formed by a Protocol Data Unit (PDU) containing a treelike structure of Information Elements (IEs). All data structures defined with ASN.1. 13

14 Abstract Syntax Notation One (ASN.1) 14

15 Abstract Syntax Notation One (ASN.1) Originally defined in 1984, latest update 08/2015. Formal rules to represent data. Independent of machine-specific implementation. ASN.1 tools. Commersial tools. The open source ASN.1 compiler: asn1c ( 15

16 Abstract syntax Basic types: INTEGER, REAL, BOOLEAN, ENUMERATED, BIT STRING, OCTET STRING, various character strings, Constructed types: SEQUENCE, SET, CHOICE, ANY, Extensibility Extension marker Information object classes. 16

17 Encoding rules Basic encoding rules (BER). Canonical / Distinguished encoding rules (CER/DER). XML encoding rules (XER). Packed encoding rules (PER), aligned / non-aligned. + many others. 17

18 Example S1SetupRequest ::= SEQUENCE { protocolies ProtocolIE-Container { {S1SetupRequestIEs} },... } S1SetupRequestIEs S1AP-PROTOCOL-IES ::= { { ID id-global-enb-id CRITICALITY reject TYPE Global-ENB-ID PRESENCE mandatory } { ID id-enbname CRITICALITY ignore TYPE ENBname PRESENCE optional } { ID id-supportedtas CRITICALITY reject TYPE SupportedTAs PRESENCE mandatory } { ID id-defaultpagingdrx CRITICALITY ignore TYPE PagingDRX PRESENCE mandatory } { ID id-csg-idlist CRITICALITY reject TYPE CSG-IdList PRESENCE optional },... } Global-ENB-ID ::= SEQUENCE { plmnidentity PLMNidentity, enb-id ENB-ID, ie-extensions ProtocolExtensionContainer { {GlobalENB-ID-ExtIEs} } OPTIONAL,... } PLMNidentity ::= TBCD-STRING TBCD-STRING ::= OCTET STRING (SIZE (3)) ENB-ID ::= CHOICE { macroenb-id BIT STRING (SIZE(20)), homeenb-id BIT STRING (SIZE(28)),... } 18

19 Implementation 19

20 Code generation The asn1c compiler: Code for all basic data structures. Code for encoder & decoder for all S1AP data structures. Perl scripts: Parse all ASN.1 information object class structures. Mostly IE content for each S1AP message. 20

21 S1AP implementation API 21

22 S1AP communication process 22

23 Testing Google Test Framework. Also used by other ARF modules. Legal and illegal messages. Message encoding and decoding. Comparing to encodings from 3rd party sources. 23

24 Summary & conclusions 24

25 Summary & conclusions ASN.1: Learning and other uses. The asn1c compiler: Learning the tool, implementing other protocols. ARF future: S1 session management and control logic. X2 interface. MME node development. 25

26 Thank you! Questions? 26