3.3 The network map Every network requires a network map service, which may itself be composed of multiple cooperating nodes. This is similar to Tor’s concept of directory authorities. The network map publishes the IP addresses through which every node on the network can be reached, along with the identity certificates of those nodes and the services they provide. On receiving a connection, nodes check that the connecting node is in the network map. The network map abstracts the underlying IP addresses of the nodes from more useful business concepts like identities and services. Each participant on the network, called a party, publishes one or more IP addresses in the network map. Equivalent domain names may be helpful for debugging but are not required. User interfaces and APIs always work in terms of identities – there is thus no equivalent to Bitcoin’s notion of an address (hashed public key), and user-facing applications rely on auto-completion and search rather than QRcodes to identify a logical recipient. It is possible to subscribe to network map changes and registering with the map is the first thing a node does at startup. Nodes may optionally advertise their nearest city for load balancing and network visualisation purposes. The map is a document that may be cached and distributed throughout the network. The map is therefore not required to be highly available: if the map service becomes unreachable new nodes may not join the network and existing nodes may not change their advertised service set, but otherwise things continue as normal