Protocol Verification for Cellular Networks Chunyi Peng The Ohio State University

2 2 Protocol Verification is Gaining Momentum  Protocol verification for the Internet  Since 1990s  Single protocol with implementation  E.g., [Cohrs’89, SIGCOMM], [ Holzmann’91], [Smith’96], TCP [NSDI’04], Routing[SIGCOMM’05], …  Emerging techniques for network verification  E.g., Anteater [SIGCOMM’11], Head Space Analysis[NSDI’12], NICE [NSDI’12], Alloy[SIGCOMM’13], NetCheck[NSDI’14], Software Dataplane [NSDI’14] …  Largely unexplored territory in cellular networks  Few efforts, e.g., 2G handoff [Orava’92], Authentication [Tang’13] 2

Case for PV in Cellular Networks Historically, cellular network protocols did not go through rigorous screening by the research community  Cellular Protocol Characteristics  Technical Challenges  Key Research Aspects 3

Many Protocols for Cellular Networks Radio Resource Control (RRC) Mobility Management (MM) Connectivity Management (CM) 4 Control-plane protocols as an example  Layered protocol stack

Many Protocols for Cellular Networks Radio Resource Control (RRC) Mobility Management (MM) Connectivity Management (CM) 5 Radio Resource Control (RRC) CS Domain MM CM PS Domain MM CM Control-plane protocols as an example  Layered protocol stack  Spanning both CS and PS domains

Many Protocols for Cellular Networks 6 Radio Resource Control (RRC) CS Domain MM CM PS Domain MM CM PS Domain MM CM RRC 4G 3G Control-plane protocols as an example  Layered protocol stack  Spanning both CS and PS domains  Operating in hybrid 3G/4G deployment

Complex Protocol Operations  Protocols work together to offer vital 3G/4G utilities  Rich patterns along three dimensions 7 Radio Resource Control MM CM PS Domain MM CM PS Domain MM CM RRC CS Domain 3G4G cross-layer cross-domaincross-system

Challenge #1: Partial Access to Protocol Operations  Distributed protocol operations at both  Cellular infrastructure (base stations, MME, gateways, etc.)  Mobile devices  Partial access  Pretty “closed” core infrastructure  More efforts needed on the mobile device side 8 8 Closed Core Network

Challenge #2: Design & Operation  Verification problems stem from both  Design specifications  Operations  Implementations  Common-case vs Worst-case  No well-defined common cases Lack of wireless net benchmarks  Norm rather than exceptions Temporal-Spatial dynamics: Mobility, dynamic radio links 99

Challenge #3: Intra- and Inter-PV Protocol Verification  Intra-protocol operations  Inter-protocol interactions 10 Radio Resource Control MM CM PS Domain MM CM PS Domain MM CM RRC CS Domain 3G4G cross-layer cross-domaincross-system

Rich Protocol Interactions  Complex interactions in common scenarios  Inevitable interplay between radio, mobility, data/voice  Concurrent voice and data use  3G/4G switch due to hybrid deployment, mobility, voice  Two causes of problematic interactions  Design defects  Operation/Implementation slips 11 Diagnosis over one layer/domain/system is insufficient Diagnosis over one layer/domain/system is insufficient Single-type test fails to unveil both issues

Research Topics Many Topics remain:  New PV Methodology for Cellular Networks  (in)Validation of Results  Software Tools for Automated Verification  Verification for “Results from Protocol Verification Research”  Needs community testbed and data archive We are still at starting stage of PV research 12