Computer network

Additionally, networks allow for the sharing of files and information, giving authorized users access to data stored on other computers.

Overlay networks have also been proposed as a way to improve Internet routing, such as through quality of service guarantees achieve higher-quality streaming media.

Previous proposals such as IntServ, DiffServ, and IP multicast have not seen wide acceptance largely because they require modification of all routers in the network.

For example, Akamai Technologies manages an overlay network that provides reliable, efficient content delivery (a kind of multicast).

The transmission media (often referred to in the literature as the physical medium) used to link devices to form a computer network include electrical cable, optical fiber, and free space.

A widely adopted family that uses copper and fiber media in local area network (LAN) technology are collectively known as Ethernet.

Repeaters work on the physical layer of the OSI model but still require a small amount of time to regenerate the signal.

The vital role firewalls play in network security grows in parallel with the constant increase in cyber attacks.

It offers connection-less and connection-oriented services over an inherently unreliable network traversed by datagram transmission using Internet protocol (IP).

They were originally designed to transport circuit mode communications from a variety of different sources, primarily to support circuit-switched digital telephony.

However, due to its protocol neutrality and transport-oriented features, SONET/SDH also was the obvious choice for transporting Asynchronous Transfer Mode (ATM) frames.

This makes it a good choice for a network that must handle both traditional high-throughput data traffic, and real-time, low-latency content such as voice and video.

Networks may be characterized by many properties or features, such as physical capacity, organizational purpose, user authorization, access rights, and others.

Some examples of devices that are used in a PAN are personal computers, printers, fax machines, telephones, PDAs, scanners, and video game consoles.

The defining characteristics of a LAN, in contrast to a WAN, include higher data transfer rates, limited geographic range, and lack of reliance on leased lines to provide connectivity.

The cost and complexity of SANs dropped in the early 2000s to levels allowing wider adoption across both enterprise and small to medium-sized business environments.

VPNs, for example, can be used to separate the traffic of different user communities over an underlying network with strong security features.

It is the successor of the Advanced Research Projects Agency Network (ARPANET) developed by DARPA of the United States Department of Defense.

Service providers and large enterprises exchange information about the reachability of their address spaces through the Border Gateway Protocol (BGP), forming a redundant worldwide mesh of transmission paths.

In an Asynchronous Transfer Mode (ATM) network, performance can be measured by line rate, quality of service (QoS), data throughput, connect time, stability, technology, modulation technique, and modem enhancements.

[77] Network congestion occurs when a link or node is subjected to a greater data load than it is rated for, resulting in a deterioration of its quality of service.

When networks are congested and queues become too full, packets have to be discarded, and participants must rely on retransmission to maintain reliable communications.

Specific techniques include: exponential backoff in protocols such as 802.11's CSMA/CA and the original Ethernet, window reduction in TCP, and fair queueing in devices such as routers.

Network resilience is "the ability to provide and maintain an acceptable level of service in the face of faults and challenges to normal operation.

Computer and network surveillance programs are widespread today, and almost all Internet traffic is or could potentially be monitored for clues to illegal activity.

Surveillance is very useful to governments and law enforcement to maintain social control, recognize and monitor threats, and prevent or investigate criminal activity.

Examples of end-to-end encryption include HTTPS for web traffic, PGP for email, OTR for instant messaging, ZRTP for telephony, and TETRA for radio.

The end-to-end encryption paradigm does not directly address risks at the endpoints of the communication themselves, such as the technical exploitation of clients, poor quality random number generators, or key escrow.

The introduction and rapid growth of e-commerce on the World Wide Web in the mid-1990s made it obvious that some form of authentication and encryption was needed.

Again using TCP/IP architectural terminology, an intranet is a community of interest under private administration usually by an enterprise, and is only accessible by authorized users (e.g.

User Application Operating system Hardware
Network Packet
Common network topologies
A sample overlay network
Bundle of glass threads with light emitting from the ends
Fiber-optic cables are used to transmit light from one computer/network node to another.
World map with red and blue lines
2007 map showing submarine optical fiber telecommunication cables around the world
Black laptop with the router in the background
Computers are very often connected to networks using wireless links.
A network interface circuit with a port for ATM
An ATM network interface in the form of an accessory card. A lot of network interfaces are built-in.
A typical home or small office router showing the ADSL telephone line and Ethernet network cable connections
This is an image of a firewall separating a private network from a public network
Protocols in relation to the Internet layering scheme.
The TCP/IP model and its relation to common protocols used at different layers of the model
When a router is present, message flows go down through protocol layers, across to the router, up the stack inside the router, and back down again and is sent on to the final destination where it climbs back up the stack
Message flows between two devices (A-B) at the four layers of the TCP/IP model in the presence of a router (R). Red flows are effective communication paths, black paths are across the actual network links.
Routing calculates good paths through a network for information to take. For example, from node 1 to node 6 the best routes are likely to be 1-8-7-6, 1-8-10-6 or 1-9-10-6, as these are the shortest routes.
Partial map of the Internet based on 2005 data. [ 69 ] Each line is drawn between two nodes, representing two IP addresses . The length of the lines indicates the delay between those two nodes.