Which group of protocols are considered Application Layer protocols?

• A. HTTP, TELNET, FTP, SMTP
• B. TCP, UDP, ICMP, ARP
• C. IPv4, IPv6, DNS, DHCP
• D. SSH, TLS, SSL, IPsec

Answer: (A)

Application Layer protocols are the ones used directly by applications to communicate over a network, defining the data formats and commands that end-user software relies on. HTTP handles web traffic, TELNET enables remote login, FTP transfers files, and SMTP handles email delivery. Together they represent the kinds of services you interact with through applications, with the underlying transport (like TCP) providing reliable delivery.

The other groups mix protocols that operate at different layers. The second set includes transport and network/link-layer protocols (TCP, UDP, ICMP, ARP), not all at the application level. The third set pairs IPv4/IPv6 (Internet Layer) with some application-layer protocols, so it isn’t a uniform application-layer group. The fourth set mixes application-layer protocols with IPsec, which functions at the network layer for security, making the grouping inconsistent.

So the first set is the clean, pure example of Application Layer protocols.