# Extending the Quality of Secure Service Model to Multi-Hop Networks
## 1 Introduction  
The concept of Quality of Service (QoS) is well understood as providing objective metrics to describe the traditional performance characteristics of a communication network, the set of wired or wireless channels that may exist between a transmitter and receiver. A network, though, may be vulnerable to either malicious disruptors or unauthorized listeners. Hence, metrics to describe the security of a communication network, including aspects, such as confidentiality and integrity, are also needed. Although investigated [1, 2, 3], such metrics have generally eluded researchers and service providers. In a recent publication, the Quality of Secure Service (QoSS) model was derived as a baseline approach to define the static security characteristics of a point-to-point network [4].  
QoSS describes in measurable and repeatable terms the security available to an end-user of a communication network. Security, in this context, refers to the ability to maintain a high-level of the traditional Information Technology (IT) qualities of confidentiality, integrity, and availability for a communication network. A communication network relies on one or more wired or wireless channels between intermediate nodes. In addition to noise, these channels may be affected by any combination of three malicious attack vectors: Denial of Service (DoS), data injection, or eavesdropping (data extraction). Managing those threats requires an ability to accurately gauge the likelihood and severity of the threat, and adapt the security features available in the system to mitigate the threat.  
Understanding that few communication networks are completely point-to-point, it is essential to examine the effect that multiple intermediaries, with varying levels of security, will have on the overall network QoS. This paper details, adapts, and extends the QoS model to multi-hop networks, and demonstrates the potential improvement in security when multiple channels are used throughout a complex communication network while also creating a broad foundation for the development of a simulation environment for the verification and validation of the model. This document illustrates an extension of the mathematical framework and analysis needed to define design requirements for multi-hopcommunication networks. It takes into consideration the probability of exploitation, and provides a foundation for subsequent work analyzing network security performance in the presence of varied environmental characteristics.  
The primary contribution of this work is the extension of the QoS model to a multi-hop scenario, wherein multiple parallel heterogeneous physical channels may exist between source and destination end points. Section 2 of this paper presents related work and previously derived calculations of the QoS metrics for single-channel and multiple channel, point-to-point communication architectures. Section 3 extends the calculations to cover multi-hop communication architectures. Section 4 provides case study examples for complex multi-channel and multi-hop communication architectures. Section 5 details future research and provides a conclusion.