An ASN identifies an independently routed network.
An autonomous system number, or ASN, is a unique identifier used by a network that controls its own routing policy. I.T Communications operates AS203416.
BGP exchanges routes between networks.
Border Gateway Protocol tells neighbouring networks which IP address ranges can be reached through each path. Routers use those announcements and routing policies to select how traffic should travel.
Why diversity matters.
A network can connect to multiple transit providers and peers. If a path becomes unavailable, BGP can withdraw that route and traffic can use an alternative. Resilience depends on the physical routes and operating design as well as the number of BGP sessions.
Organisations with their own ASN commonly buy IP transit; most individual business sites instead use business broadband or a leased line.