Since inception, the resilience of the Internet has been based upon multiple paths from source to destination. At the granularity of the AS, this is generally implemented by linking to more than one AS's. Without resolving this further into whether each link carries advertisements of all or only a subset of routes, this is the basis of resilience.
With particular reference to routers in Tier 1 networks, I am curious about whether the router at the end of each link is implemented as part of a set of redundant routers. I am familiar with VRRP and HSRP for the operation of such a set of redundant routers but I only know of their use in stub ASes, like those owned by end users who need to ensure the resilience of their connection to the Internet.
In other words, how common is the use of device redundancy as a means complementary to multiple links in order to strengthen the resilience of the Internet? I would guess that in cases where links between geographical regions are relatively few (such as links based on submarine cables), device redundancy is an important factor in the resilience of the Internet. This guess is based on the assumption that the portion of inter-region traffic carried by each such link is high, increasing the importance of redundancy at the end point - the router.