ABSTRACT
Breakthrough . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 285 12.3 Fault Isolation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 286
12.3.1 Time-Triggered Sequenced Guardian Roles . . . . . . . . . . . . . . . . 286 12.3.1.1 Directional Integrity Exchange . . . . . . . . . . . . . . . . . 287 12.3.1.2 Skip Guardian Link Forwarding . . . . . . . . . . . . . . . . 287 12.3.1.3 Self-Checking Pair Neighbor Guardian . . . . . . . . . . 288
12.3.2 Asynchronous Guardian Roles . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 12.3.2.1 Startup Enforcement . . . . . . . . . . . . . . . . . . . . . . . . . . . 289 12.3.2.2 Source Authentication . . . . . . . . . . . . . . . . . . . . . . . . . . 290 12.3.2.3 Additional Guardian Fault Containment Behavior 291
12.4 Diagnostic and Agreement Services . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291 12.4.1 Host Task Set Agreement . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 291
12.5 Validation and Verification Efforts . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
Considerations . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 292
12.1 Protocol Overview The BRAIN (Braided Ring Availability Integrity Network) is a novel communication architecture supporting fault-tolerant time-triggered communication. As the name suggests, the BRAIN is built upon a braided-ring topology. This topology augments the standard ring topology with increased connectivity. In addition to the “direct link” connections between a node and its immediate neighboring nodes (as is used in simple rings), a braided-ring node also is connected to its neighbor’s neighbor via a link called the braid or skip link (see Figure 12.1). The BRAIN utilizes the additional connectivity to achieve both high-coverage integrity and availability concurrently. This is in contrast to previous braided rings, which use these additional links only for availability. The BRAIN can use almost any existing Local Area Network (LAN) technology to implement its communication links, including any of the IEEE 802.3 Ethernet variants.
