# Model for Quantifying the Quality of Secure Service
## 3 Components of a Security Model
### Multiple Channels  
Using multiple channels can improve the performance of data-in-transit in diverse ways. A straightforward example is directly increasing the data rate, such that additional channels provide more bandwidth, e.g., channel bonding within IEEE 802.11 [13, 14, 15, 16]. Another example is frequency hopping through multiple channels, which is one of several techniques known as the spread spectrum and which provides protection from noise or jamming as the signal is \"spread across a channel greater than that necessary to transmit the information\" [17]. This technique is currently used in Bluetooth, and such transmission diversity is also a key element of 5G wireless [18, 19].  
An example of data-at-rest performance improvement through multiple channels is found in the Redundant Array of Inexpensive Disks (RAID) architecture. Developed in 1987, RAID demonstrated that by utilizing redundancy, an array could be more reliable than any one disk drive while allowing greater data throughput (In a RAID array, data is split across various disks so that if one disk should fail, the data may be fully recovered despite not having all the original blocks of data. Various combinations of nested RAID levels may be used to reduce the vulnerabilities of simultaneous disk failures [20]. The data may also be encrypted before or after splitting, or both, as a manner of increasing confidentiality.) Despite significant overhead, the ability to survive disk failures has made it very attractive in critical server environments.  
Many applications in control systems maintain separate channels for data and control. For example, in SS7, the signaling path is separate and distinct from the voice channels that carry the telephone conversation. Having different channels, at different frequencies and differing bandwidths, allows for greater flexibility and higher-speed communications between network assets without the need to rely upon the availability or limitations of analog voice channels (In reality, these two channels are not entirely separated. The dual-tone, multi-frequency (DTMF) digits dialed by a caller begin within the voice channel, but are recognized by the control channel and are an example of the signaling messages, including dialing a phone number, entering control functions like call-forwarding, or advanced billing information [21, 22]).  
An abstract form of multi-channel communication is two-factor authentication (2 FA), a subset of multi-factor authentication. This is an authentication methodology that requires a user to present two or more pieces of evidence to confirm the user's identity via separate delivery paths9[23]. By using multiple authentication factors sent via divergent paths, the likelihood that both messages are intercepted decreases. Even if a malicious actor intercepts one factor, full authentication by the malicious actor cannot occur without intercepting the other. Numerous other forms of 2 FA also exist [24].  
Central to the theme of this paper, _multiple channel_ architecture may also be used to improve security through data fragmentation across heterogeneous channels [25, 26, 27, 28]. This security focused capability, in concert with the performance advantages of multi-channel communications, is the motivation for creating a tunable multi-channel communication protocol and associated analysis techniques to determine the appropriate trade-offs under varying security and performance requirements.