A
network is a group of communicating
computers known as
hosts, which
communicate data to other hosts via
communication protocols, as facilitated by
networking hardware. Within a computer network, computers are identified by
network addresses, which allow rule-based systems such as
Internet Protocol (IP) to locate and identify hosts. Hosts may also have
hostnames, memorable labels for the host
nodes, which are rarely changed after initial assignment. The
transmission medium that supports
information exchange includes
wired media like copper cables,
optical fibers, and wireless
radio-frequency media. The arrangement of hosts and hardware within a
network architecture is known as the
network topology. Apart from physical transmission media, networks comprise
network nodes such as
network interface controllers,
repeaters,
hubs,
bridges,
switches,
routers, and
modems: • The
network interface controller (NIC) is
computer hardware that connects the computer to the
network media. In Ethernet networks, each NIC has a unique
Media Access Control (MAC) address, usually stored in the controller's permanent memory. • A
repeater is an electronic device that receives a network
signal, cleans it of unnecessary noise and regenerates it. The signal is
retransmitted at a higher power level, or to the other side of obstruction so that the signal can cover longer distances without degradation. • An Ethernet repeater with multiple ports is known as an
Ethernet hub. In addition to reconditioning and distributing network signals, a hub assists with collision detection and fault isolation for the network. Hubs and repeaters in LANs have been largely made obsolete by modern network switches. • Unlike hubs, which forward communication to all ports,
network switches forward frames only to the ports involved in the communication. Switches normally have numerous ports, facilitating a star topology for devices, and for cascading additional switches.
Network bridges are analogous to a two-port switch. • Bridges and switches operate at the
data link layer of the
OSI model and bridge traffic between two or more
network segments to form a single local network. Both are devices that forward
frames of data between
ports based on the destination MAC address in each frame.
Network segmentation through bridging and switching helps break down a large, congested network into an aggregation of smaller, more efficient networks. • A
router is an internetworking device that forwards packets between networks by processing the addressing or routing information included in the packet. •
Modems (modulator-demodulator) are used to connect network nodes via wire not originally designed for digital network traffic, or for wireless.
Network communication A
communication protocol is a set of rules for exchanging information over a network. Communication protocols have various characteristics, such as being
connection-oriented or
connectionless, or using
circuit switching or
packet switching. In a
protocol stack, often constructed per the
OSI model, communications functions are divided into protocol layers, where each layer leverages the services of the layer below it until the lowest layer controls the hardware that sends information across the media. The use of protocol layering is ubiquitous across the field of computer networking. An important example of a protocol stack is
HTTP, the
World Wide Web protocol. HTTP runs over
TCP over IP, the internet protocols, which in turn run over
IEEE 802.11, the Wi-Fi protocol. This stack is used between a
wireless router and a personal computer when accessing the web. Most modern computer networks use protocols based on
packet-mode transmission. A
network packet is a formatted unit of
data carried by a
packet-switched network. Packets consist of two types of data: control information and user data (payload). The control information provides data the network needs to deliver the user data, for example, source and destination
network addresses,
error detection codes, and sequencing information. Typically, control information is found in
packet headers and
trailers, with
payload data in between. The
Internet protocol suite, also called TCP/IP, is the foundation of all modern networking and the defining set of protocols for the Internet. It offers connection-less and connection-oriented services over an inherently unreliable network traversed by datagram transmission using Internet protocol (IP). At its core, the protocol suite defines the addressing, identification, and routing specifications for
Internet Protocol Version 4 (IPv4) and for
IPv6, the next generation of the protocol with a much enlarged addressing capability. == Security ==