Network Systems Exam 1 Practice Test

An application-layer service is something end-user applications provide to users by using application-layer protocols. Gmail fits because it delivers email as a service you access through a web browser or mail client, and it relies on application-layer protocols such as HTTP/HTTPS for the web interface and SMTP/IMAP/POP for sending and retrieving messages. The other items aren’t services at this layer: a MAC address is a data-link layer identifier used to address devices on a local network; an IP address is a network-layer identifier used to route packets; and Ethernet is a data-link technology for framing and transmitting data. So Gmail is the application-layer service.