A link that is not able to send and receive data simultaneously. Consequently, in Half Duplex connections, it is necessary to wait until one is finished receiving data before any can be sent.
Base 16. The usual notation for hexadecimal is from 0 to 9, followed by A through F, where F represents the number 15. Hexadecimal is useful for representing the contents of 16-bit fields.
Hot Standby Routing Protocol. This is a Cisco proprietary standard that allows two routers to possess the same IP and MAC addresses, but to have only one active at a time while the other is a backup. This way, if the primary device fails, the backup can take over for it quickly. See also VRRP.
Hypertext Transfer Protocol. This TCP- based protocol is used by web browsers to transfer data from web servers.
Sometimes called a MAU in Token Ring networks, a Layer 2 device that allows connection of end devices into a network. In Ethernet networks, a hub is basically a multiport repeater.
One of the basic network topologies. In this book, the term star is used instead to avoid confusion with the network device called a hub.