While working at Xerox PARC, Bob Metcalfe and D. Boggs developed Ethernet beginning in 1972 and specifications based on this work appeared in IEEE 802.3 in 1980. Ethernet specifications define low-level data transmission protocols and the technology needed to support them. In the OSI model, Ethernet technology exists at the physical and data link layers. Ethernet is the least expensive high-speed LAN alternative. Ethernet adapter cards for a PC range from $60 to $120. They transmit and receive data at speeds of 10 million bits per second through up to 300 feet of telephone wire to a hub. .
DNS.
The Internet uses a distributed naming system called the Domain Naming System (DNS). DNS allows us to refer to computers by host names as well as by Internet Protocol (IP) addresses. IP addresses are hard to remember and are inconvenient to use. DNS allows us to use host names and domain names, which can represent IP addresses. DNS servers translate host names and domain names (for example, www.gc.peachnet.edu) to an associated IP address (for example, 192.168.1.10.) For example, peachnet Networks has registered the domain name "peachnet.edu" for use by our servers and others. The host names "mail" and "www" represent different servers registered in the same domain. A domain name is a computer name suffix shared by a group of computers in the same organization. A domain name should be associated with an IP address through a Forward Lookup record. Domain names are organized in a hierarchy; this hierarchy includes your company or server name, and a country code (for Example, .uk or .ca) or a top-level domain (for example, .com or .edu). A Web site on the server is created with one IP address; one host name and one domain name that together establish the identity of that Web site on the Internet. Each domain name requires a primary domain authority on one DNS server. A secondary DNS server acts as a backup to the primary.
