Final answer:
The believability of a routing protocol compared to others is indicated by its Administrative distance. Administrative distance is a value that helps routers determine the most trustworthy route source, with lower values indicating higher trustworthiness.
Step-by-step explanation:
The characteristic of a routing protocol that indicates the believability of the routing protocol in comparison to other routing protocols is known as Administrative distance (a). Administrative distance is a measure used by routers to choose the best path when there are two or more different routes to the same destination from two different routing protocols. The lower the administrative distance value, the more trustworthy the route source is. For example, if a router receives two updates for the same network, one from RIP with an administrative distance of 120 and another from OSPF with an administrative distance of 110, the router will choose the OSPF route because it has a lower administrative distance, indicating higher believability.