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Many installed networks use wires to provide connectivity. Ethernet is the most common wired internetworking technology found today. The wires, called cables, connect the computers and other devices that make up the networks. Wired networks are best for moving large amounts of data at high speeds, such as are required to support professional-quality multimedia. Network services are computer programs that support the human network. In the case of instant messaging, for example, an instant messaging service, provided by devices in the cloud, must be accessible to both the sender and recipient.

Important aspects of networks that are neither devices nor media are rules, or protocols. These rules are the standards and protocols that specify how the messages are sent, how they are directed through the network, and how they are interpreted at the destination devices. The Network architecture:. Networks must support a wide range of applications and services, as well as operate over many different types of physical infrastructures. The term network architecture, in this context, refers to both the technologies that support the infrastructure and the programmed services and protocols that move the messages across that infrastructure.

As the Internet, and networks in general, evolve, we are discovering that there are four basic characteristics that the underlying architectures need to address in order to meet user expectations: fault tolerance, scalability, quality of service, and security. The expectation that the Internet is always available to the millions of users who rely on it requires a network architecture that is designed and built to be fault tolerant.

A fault tolerant network is one that limits the impact of a hardware or software failure and can recover quickly when such a failure occurs. These networks depend on redundant links, or paths, between the source and destination of a message. If one link or path fails, processes ensure that messages can be instantly routed over a different link transparent to the users on either end.

Both the physical infrastructures and the logical processes that direct the messages through the network are designed to accommodate this redundancy. This is a basic premise of the architecture of current networks. A scalable network can expand quickly to support new users and applications without impacting the performance of the service being delivered to existing users. Thousands of new users and service providers connect to the Internet each week.

The ability of the network to support these new interconnections depends on a hierarchical layered design for the underlying physical infrastructure and logical architecture. The operation at each layer enables users or service providers to be inserted without causing disruption to the entire network. Technology developments are constantly increasing the message carrying capabilities and performance of the physical infrastructure components at every layer.

These developments, along with new methods to identify and locate individual users within an internetwork, are enabling the Internet to keep pace with user demand. The Internet is currently providing an acceptable level of fault tolerance and scalability for its users. But new applications available to users over internetworks create higher expectations for the quality of the delivered services. Voice and live video transmissions require a level of consistent quality and uninterrupted delivery that was not necessary for traditional computer applications.

Quality of these services is measured against the quality of experiencing the same audio or video presentation in person. Traditional voice and video networks are designed to support a single type of transmission, and are therefore able to produce an acceptable level of quality. New requirements to support this quality of service over a converged internetworking are changing the way network architectures are designed and implemented.

The Internet has evolved from a tightly controlled internetwork of educational and government organizations to a widely accessible means for transmission of business and personal communications. As a result, the security requirements of the network have changed. The security and privacy expectations that result from the use of internetworks to exchange confidential and business critical information exceed what the current architecture can deliver. Rapid expansion in communication areas that were not served by traditional data networks is increasing the need to embed security into the network architecture.

As a result, much effort is being devoted to this area of research and development. In the meantime, many tools and procedures are being implemented to combat inherent security flaws in the network architecture. Its primary goal was to have a communications medium that could withstand the destruction of numerous sites and transmission facilities without disruption of service. It only follows that fault tolerance was the focus of the effort of the initial internetwork design work. Early network researchers looked at the existing communication networks, which were primarily for the transmission of voice traffic, to determine what could be done to improve the fault tolerance level.

Circuit Switched Connection-oriented Networks. To understand the challenge that the DoD researchers were faced with, it is necessary to look at how early telephone systems work. When a person makes a call using a traditional telephone set, the call first goes through a setup process, where all of the telephone switching locations between the person and the phone set that they are calling are identified. A temporary path, or circuit, is created through the various switching locations to use for the duration of the telephone call. If any link or device participating in the circuit fails, the call is dropped.

To reconnect, a new call must be made, and a new circuit created between the source telephone set and the destination. This type of connection-oriented network is called a circuit-switched network. Early circuit switched networks did not dynamically recreate dropped circuits. In order to recover from failure, new calls had to be initiated and new circuits built end-to-end. Many circuit switched networks give priority to maintaining existing circuit connections, at the expense of new circuit requests.

In this type of connection-oriented network, once a circuit is established, even if no communication is occurring between the persons on either end of the call, the circuit remains connected and resources reserved until one of the parties disconnects the call. Since there is a finite capacity to create new circuits, it is possible to occasionally get a message that all circuits are busy and a call cannot be placed. The cost to create many alternate paths with enough capacity to support a large number of simultaneous circuits, and the technologies necessary to dynamically recreate dropped circuits in the event of a failure, led the DoD to consider other types of networks.

Packet Switched Connectionless Networks. In the search for a network that could withstand the loss of a significant amount of its transmission and switching facilities, the early Internet designers reevaluated early research regarding packet switched networks. The premise for this type of networks is that a single message can be broken into multiple message blocks. Individual blocks containing addressing information indicate both their origination point and their final destination. Using this embedded information, these message blocks, called packets, can be sent through the network along various paths, and can be reassembled into the original message upon reaching their destination.

The devices within the network itself are unaware of the content of the individual packets, only visible is the address of the final destination and the next device in the path to that destination. No reserved circuit is built between sender and receiver. Each packet is sent independently from one switching location to another. At each location, a routing decision is made as to which path to use to forward the packet towards its final destination. If a previously used path is no longer available, the routing function can dynamically choose the next best available path.

Because the messages are sent in pieces, rather than as a single complete message, the few packets that may be lost in the advent of a failure can be retransmitted to the destination along a different path. In many cases, the destination device is unaware that any failure or rerouting has occurred. Packet-switched Connectionless Networks.

The DoD researchers realized that a packet switched connectionless network had the features necessary to support a resilient, fault tolerant network architecture. The need for a single, reserved circuit from end-to-end does not exist in a packet switched network. Any piece of a message can be sent through the network using any available path. Packets containing pieces of messages from different sources can travel the network at the same time. The problem of underutilized or idle circuits is eliminated -- all available resources can be used at any time to deliver packets to their final destination.

By providing a method to dynamically use redundant paths, without intervention by the user, the Internet has become a fault tolerant, scalable method of communications. Connection-oriented Networks. Although packet-switched connectionless networks met the needs of the DoD, and continue to be the primary infrastructure for today's Internet, there are some benefits to a connection-oriented system like the circuit-switched telephone system. Because resources at the various switching locations are dedicated to providing a finite number of circuits, the quality and consistency of messages transmitted across a connection-oriented network can be guaranteed.

Another benefit is that the provider of the service can charge the users of the network for the period of time that the connection is active. The ability to charge users for active connections through the network is a fundamental premise of the telecommunication service industry. The fact that the Internet is able to expand at the rate that it is, without seriously impacting the performance experienced by individual users, is a function of the design of the protocols and underlying technologies on which it is built. The Internet, which is actually a collection of interconnected private and public networks, has a hierarchical layered structure for addressing, for naming and for connectivity services.

At each level or layer of the hierarchy, individual network operators maintain peering relationships with other operators at the same level. As a result, network traffic that is destined for local or regional services does not need to traverse to a central point for distribution. Common services can be duplicated in different regions, thereby keeping traffic off the higher level backbone networks. Although there is no single organization that regulates the Internet, the operators of the many individual networks that provide Internet connectivity cooperate to follow accepted standards and protocols.

The adherence to standards enables the manufacturers of hardware and software to concentrate on product improvements in the areas of performance and capacity, knowing that the new products can integrate with and enhance the existing infrastructure. The current Internet architecture, while highly scalable, may not always be able to keep up with the pace of user demand.

New protocols and addressing structures are under development to meet the increasing rate at which Internet applications and services are being added. Networks must provide secure, predictable, measurable, and, at times, guaranteed services. The packet-switched network architecture does not guarantee that all packets that comprise a particular message will arrive on time, in their correct in order, or even that they will arrive at all. Networks also need mechanisms to manage congested network traffic.

Congestion is caused when the demand on the network resources exceeds the available capacity. If all networks had infinite resources, there would not be a need to use QoS mechanisms to ensure quality of service. Unfortunately, that is not the case. There are some constraints on network resources that cannot be avoided. Constraints include technology limitations, costs, and the local availability of high-bandwidth service. Network bandwidth is the measure of the data carrying capacity of the network. When simultaneous communications are attempted across the network, the demand for network bandwidth can exceed its availability.

The obvious fix for this situation is to increase the amount of available bandwidth. But, because of the previously stated constraints, this is not always possible. In most cases, when the volume of packets is greater than what can be transported across the network, devices queue the packets in memory until resources become available to transmit them. Queuing packets causes delay. If the number of packets to be queued continues to increase, the memory queues fill up and packets are dropped. Achieving the required Quality of Service QoS by managing the delay and packet loss parameters on a network becomes the secret to a successful end-to-end application quality solution.

Thus, ensuring QoS requires a set of techniques to manage the utilization of network resources. In order to maintain a high quality of service for applications that require it, it is necessary to prioritize which types of data packets must be delivered at the expense of other types of packets that can be delayed or dropped. Ideally, we would like to assign a precise priority for each type of communication. Currently, this is neither practical nor possible. Therefore, we classify applications in categories based on specific quality of service requirements.


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To create QoS classifications of data, we use a combination of communication characteristics and the relative importance assigned to the application. We then treat all data within the same classification according to the same rules. For example, communication that is time-sensitive or important would be classified differently from communication that can wait or is of lesser importance. The characteristics of the information being communicated also affect its management. For example, the delivery of a movie uses a relatively large amount of network resources when it is delivered continuously without interruption.

The 88 recommendations made by the Special Rapporteur on the promotion and protection of the right to freedom of opinion and expression in a May report to the Human Rights Council of the United Nations General Assembly include several that bear on the question of the right to Internet access: []. Network neutrality also net neutrality, Internet neutrality, or net equality is the principle that Internet service providers and governments should treat all data on the Internet equally, not discriminating or charging differentially by user, content, site, platform, application, type of attached equipment, or mode of communication.

Natural disasters disrupt internet access in profound ways. This is important—not only for telecommunication companies who own the networks and the businesses who use them, but for emergency crew and displaced citizens as well. The situation is worsened when hospitals or other buildings necessary to disaster response lose their connection. Knowledge gained from studying past internet disruptions by natural disasters could be put to use in planning or recovery. Additionally, because of both natural and man-made disasters, studies in network resiliency are now being conducted to prevent large-scale outages.

One way natural disasters impact internet connection is by damaging end sub-networks subnets , making them unreachable. A second way natural disasters destroy internet connectivity is by severing submarine cables—fiber-optic cables placed on the ocean floor that provide international internet connection. A sequence of undersea earthquakes cut six out of seven international cables connected to that country and caused a tsunami that wiped out one of its cable and landing stations.

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With the rise in popularity of cloud computing , concern has grown over access to cloud-hosted data in the event of a natural disaster. AWS divides the globe into five regions and then splits each region into availability zones.

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A data center in one availability zone should be backed up by a data center in a different availability zone. Theoretically, a natural disaster would not affect more than one availability zone. The June major storm only disabled the primary data center, but human error disabled the secondary and tertiary backups, affecting companies such as Netflix, Pinterest, Reddit, and Instagram. From Wikipedia, the free encyclopedia.


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This article is about Internet access, including broadband Internet access. For telecommunications signaling methods, see Broadband. An Opte Project visualization of routing paths through a portion of the Internet. Information infrastructure. Book Index Outline.

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Main article: History of the Internet. Main articles: Data rates , Bit rates , Bandwidth computing , and Device data rates. See also: AS incident and List of web host service outages. Typical noises of a dial-up modem while establishing connection with a local ISP in order to get access to the Internet. Main article: Cable Internet access. See also: Hybrid Access Networks. See also: Project Loon. Main article: Sneakernet. Internet users in as a percentage of a country's population.

Fixed broadband Internet subscriptions in as a percentage of a country's population. Mobile broadband Internet subscriptions in as a percentage of a country's population. Main article: Global Internet usage. Main article: Broadband universal service. Further information: Digital rights and Right to Internet access. Main article: Net neutrality. Back-channel , a low bandwidth, or less-than-optimal, transmission channel in the opposite direction to the main channel Broadband mapping in the United States Comparison of wireless data standards Connectivity in a social and cultural sense Fiber-optic communication History of the Internet IP over DVB , Internet access using MPEG data streams over a digital television network List of countries by number of broadband Internet subscriptions National broadband plan Public switched telephone network PSTN Residential gateway Telecommunications network White spaces radio , a group of technology companies working to deliver broadband Internet access via unused analog television frequencies.

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Archived from the original on 29 April Accessed 5 December Telecommunications and Cybersecurity , Noblis. Internet access. Internet in Africa. Sahrawi Arab Democratic Republic Somaliland. Dependencies and other territories. Book Category Asia portal. Internet in Europe. Cook Islands Niue. Cellular network standards. List of mobile phone generations. Coaxial cable Fiber-optic communication Optical fiber Free-space optical communication Molecular communication Radio waves Transmission line.

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