CellularReliability.github.io

Diagnosis and Fixing Code for Cellular Failures at Scale

license license

Table of Contents

Introduction

Codebase Organization

Platform Requirements

For Developers

Introduction

This repository contains our continous monitoring infrasturcture (based on Android-MOD, a customized Android system that records system-level traces upon the occurrence of suspicious cellular failure events) for capturing cellular failures in the wild, as well as our efforts for improving cellular reliability on Android devices. Our Android-MOD system is built upon vanilla Andorid 9/10. Therefore, you’ll be able to run codes in this repo by patching these modifications to proper framework components.

Codebase Organization

[The entire codebase is available in our Github repo.]

Continous Monitoring Infrastructure

Our modifications mainly involve the telephony component in the framework layer (whose location in AOSP tree is frameworks/opt/telephony/src/java/com/android/internal/telephony, denoted later as TELEPHONY_SRC). Specifically, we modify the DcTracker.java and DefaultPhoneNotifier.java to instrument concerned failure points (currently we only list those related to the three major cellular failtures–Data_Stall, Data_Setup_Error, and Out_of_Service), as shown in Monitor:

Class Failure Point Purpose Location in AOSP
DcTracker onDataStallAlarm Tracking Data_Stall events TELEPHONY_SRC/dataconnection/DcTracker.java
DcTracker onDataSetupComplete Tracking Data_Setup_Error events TELEPHONY_SRC/dataconnection/DcTracker.java
DefaultPhoneNotifier notifyServiceState Tracking Out_of_Service events TELEPHONY_SRC/DefaultPhoneNotifier.java

Upon cellular failures, we then notify our dedicated event logging service CellularStateProcessor and CellularReliability to log critical cellular and device information:

Information Description
UID Unique ID generated to identify a user (cannot be related to the user’s true indentity)
TIME UNIX timestamp
RAT Current radio access technology
RSSI Signal strength in dBM
CELL Base Station ID (MCC+MNC+LAC+CID)
OS Android vesion
MODEL Device model
CAUSE Error code of Data_Setup_Error defined in DataFailCause
APN Current access point names

For event recovery, we provide similar tracing to record recovery events. In particular, for Data_Stall events we probe the network to more accurately monitor event recovery in DataStallDiagnostics.

Stability-Compatible RAT Transition

Upon RAT transitions, our control policy would kick in to check whether current system and network states are suitable for transitions. It currently runs as a daemon thread along side the telephony service, as shown in RATTransition.

TIMP-based Flexible Data_Stall Recovery

We currently provide our time-inhomogeneous Markov process (TIMP) that formalizes the Data_Stall recovery process and find proper triggers for entering each recovery stage.

We implement the TIMP model in Python (timp_model) which can automatically search in the time trigger space so as to find triggers that can minimize the expected recovery time.

Platform Requirements

Android

For Android-related modifications, currently our code is run and tested in Android 9 and Android 10 (AOSP). Note that despite quite a number of changes have been made in Android 10 since Android 9, our code is applicable to both given that concerned tracing points remain unchanged.

Others

For other code component such as our TIMP model, they can be run on Linux with proper Python supports.

For Developers

Our code is licensed under Apache 2.0 in accordance with AOSP’s license. Please adhere to the corresponding open source policy when applying modifications and commercial uses. Also, some of our code is currently not available but will be relased soon once we have obatained permissions.