NeTS: Small: Collaborative Research: Identifying Design and Operational Loopholes in Cellular Network Protocols

蜂窝网络是当今部署的最大的无线基础设施。它在为用户提供移动互联网接入和蜂窝语音服务方面发挥着重要作用。蜂窝网络的一个关键设计组件是其信令协议，这些协议在控制平面上运行。与互联网协议相比，这些信令协议更加复杂，以确保重要的控制功能，如移动性支持、无线电资源控制、数据和语音的会话管理等等。因此，它们的正确设计和操作对蜂窝运营商和用户都是至关重要的。该项目的目标是设计工具并通过以下方式验证当前蜂窝网络中信令协议的正确性：(I)识别3GPP标准定义的协议中的设计漏洞，以及运营商和供应商犯下的操作失误，(Ii)分析其根本原因和性能损失，以及(Iii)设计解决此类问题的技术。所提出的活动可以在设计和实践中提高蜂窝网络的可靠性。它们不仅有助于我们更好地了解如何避免蜂窝系统中的设计和实现错误，而且还将更新现有的协议设计，甚至影响即将到来的5G蜂窝技术的标准化。如果成功，结果将有助于为我们的社会设计和实践更可靠的移动互联网基础设施。该项目还将招聘和培养新一代学生和工程师，包括那些来自少数群体的学生和工程师，他们在技术上已经为移动互联网时代做好了准备。采购经理将与相关行业密切互动，以进行可能的技术转让。该项目的研究有两个主要推动力。一是设计工具，找出蜂窝网络中的设计漏洞和操作失误。该项目将开发一种特定于手机的验证器，该验证器将通用模型检查技术与特定于领域的手机知识相结合，并使用基于手机的经验验证。该项目将应用模型检查来识别潜在候选漏洞的超集，然后通过在运行的3G/4G运营商上进行实验来验证真实的漏洞，重点关注两类设计漏洞：(A)与共享特定上下文(例如，连接状态、命令、IP地址、虚拟连接)的协议交互，这在跨层、跨域和系统间协议通信中很常见；(B)无序信令传递。当指定的控制消息序列被中断时，其成本远远超过丢失或延迟的消息。错误排序的信号基于定义的语义进行反应，并且可能触发错误的协议操作。该项目还将通过对运营运营商的用户研究来评估这两类问题的现实影响。该项目的另一个主旨是对已发现的漏洞提出修复建议。建议的解决方案将新的启发式方法融入到蜂窝信令协议中，并要求在移动设备和网络基础设施上共同努力。

The cellular network is the largest wireless infrastructure deployed today. It plays an important role to provide users mobile Internet access and cellular voice service. A key design component of the cellular network is its signaling protocols, which operate on the control plane. Compared with their Internet counterparts, these signaling protocols are more complex to ensure vital control functions, such as mobility support, radio resource control, session management for data and voice, to name a few. Consequently, their proper design and operation are critical to both the cellular operators and the users. The objective of this project is to devise tools and verify the correctness of signaling protocols in current cellular networks by: (i)identifying design loopholes in the protocols defined by the 3GPP standards, as well as operational slips made by operators and vendors, (ii) analyzing their root causes and performance penalties, and (iii) devising techniques that fix such problems. The proposed activities can enhance the reliability of cellular networks in both design and practice. They will help us to not only better understand how to avoid design and implementation mistakes in a cellular system, but also to renovate the current protocol design and even affect the upcoming 5G cellular technology in its standardization. If successful, the results will facilitate the design and practice of a more reliable mobile Internet infrastructure for our society. The project will also recruit and train a new generation of students and engineers, including those from minority groups, who are technically ready for the mobile Internet era. The PIs will interact closely with the related industry for possible technology transfer. The research in this project has two main thrusts. One is to devise tools and identify design loopholes and operational slips in cellular networks. The project will develop a cellular-specific verifier that adapts generic model-checking techniques with domain-specific cellular knowledge, and uses phone-based empirical validation. The project will apply model checking to identify a superset of potential candidate loopholes, and then validate the real ones through experiments over operational 3G/4G carriers, by focusing on design slips in two categories: (a) protocols interaction with shared certain context (e.g., connection status, commands, IP address, virtual connection), which is popular in cross-layer, cross-domain, and inter-system protocol communications; (b) Out-of-sequenced signaling delivery. When the designated sequence of control messages is disrupted, its cost is way beyond lost or delayed messages. Missequenced signals are reacted based on defined semantics and may trigger wrong protocol operations. This project will also assess the real-world impact of both categories of issues through user studies over operational carriers. The other thrust of this project is to propose fixes to the identified loopholes. The proposed solutions incorporate new heuristics into cellular signaling protocols and call for concerted effort on the mobile device and the network infrastructure.