Which protocol is characterized by having four numeric fields each 8 bits long, known as octets?

The correct answer is the Internet Protocol version 4 (IPv4). This protocol is foundational to the Internet and is characterized by its address format, which consists of four numeric fields, each 8 bits long, constituting a total of 32 bits. Each field, referred to as an octet, is separated by periods (dots) and can take a value between 0 and 255 (inclusive). The standard notation for an IPv4 address is thus in the form of four decimal numbers, such as 192.168.1.1.

Understanding this address structure is vital for network configuration, routing, and identifying devices on a network. In contrast, the other protocols mentioned have different characteristics: Internet Protocol version 6 (IPv6) uses a much longer address format with eight groups of four hexadecimal digits, while Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) are associated with specific transport layer functions but do not define an address format like IPv4 does.