Protocol Verification for Cellular Networks

Chunyi Peng The Ohio State University

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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]

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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

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Many Protocols for Cellular Networks

Radio Resource Control (RRC)

Mobility Management (MM)

Connectivity Management (CM)

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Control-plane protocols as an example

Layered protocol stack

Many Protocols for Cellular Networks

Radio Resource Control (RRC)

Mobility Management (MM)

Connectivity Management (CM)

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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 Networks6

Radio Resource Control (RRC)

CS Domain

MM

CM

PS Domain

MM

CM

PS Domain

MM

CM

RRC

4G3G

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

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Radio Resource Control

MM

CM

PS Domain

MM

CM

PS Domain

MM

CM

RRC

CS Domain

3G 4G

cross-layer

cross-domain cross-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

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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

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Challenge #3: Intra- and Inter-PV

Protocol Verification Intra-protocol operations Inter-protocol interactions

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Radio Resource Control

MM

CM

PS Domain

MM

CM

PS Domain

MM

CM

RRC

CS Domain

3G 4G

cross-layer

cross-domain cross-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

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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

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