Computer network is a set of computers sharing resources located on or provided by network nodes. The computers use common communication protocols over digital interconnections based on physically wired, optical, and wireless radio-frequency methods that may be arranged in a variety of network arrangement of the elements to communicate with each other.
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.
With packets, the bandwidth of the transmission medium can be better shared among users than if the network were circuit switched.
When one user is not sending packets, the link can be filled with packets from other users, and so the cost can be shared, with relatively little interference, provided the link isn’t overused. Often the route a packet needs to take through a network is not immediately available. In that case, the packet is queued and waits until a link is free.
The physical link technologies of packet network typically limit the size of packets to a certain maximum transmission unit. A longer message may be fragmented before it is transferred and once the packets arrive, they are reassembled to construct the original message.
The transmission media used to link devices to form a computer network include electrical cable, optical fiber, and free space.
Apart from any physical transmission media, networks are built from additional basic system building blocks, such as network interface controllers (NICs), repeaters, hubs, bridges, switches, routers, modems, and firewalls. Any particular piece of equipment will frequently contain multiple building blocks and so may perform multiple functions.
Network connections can be established wirelessly using radio or other electromagnetic means of communication. For example:
- Terrestrial microwave
- Communications satellites
- Cellular networks
- Free-space optical communication
A computer network extends various technologies, such as email, instant messaging, online chat, voice and video telephone calls, and video conferencing.
A network allows sharing of network and computing resources. Users may access and use resources provided by devices on the network, such as printing a document on a shared network printer or use of a shared storage device. A network allows sharing of files, data, and other types of information giving authorized users the ability to access information stored on other computers on the network.
Networks are typically managed by the organizations that own them. Private enterprise networks may use a combination of intranets and extranets. They may also provide network access to the Internet, which has no single owner and permits virtually unlimited global connectivity.