Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. Packet loss is either caused by errors in data transmission, typically across wireless networks, or network congestion. Packet loss is measured as a percentage of packets lost with respect to packets sent.
The Transmission Control Protocol (TCP) detects packet loss and performs retransmissions to ensure reliable messaging. Packet loss in a TCP connection is also used to avoid congestion and thus produces an intentionally reduced throughput for the connection.
In real-time applications like streaming media or online games, packet loss can affect a user's quality of experience (QoE).
The Internet Protocol (IP) is designed according to the end-to-end principle as a best-effort delivery service, with the intention of keeping the logic routers must implement, as simple as possible. If the network made reliable delivery guarantees on its own, that would require store and forward infrastructure, where each router devotes a significant amount of storage space to packets while it waits to verify that the next node properly received them. A reliable network would not be able to maintain its delivery guarantees in the event of a router failure. Reliability is also not needed for all applications. For example, with live streaming media, it is more important to deliver recent packets quickly than to ensure that stale packets are eventually delivered. An application or user may also decide to retry an operation that is taking a long time, in which case another set of packets will be added to the burden of delivering the original set. Such a network might also need a command and control protocol for congestion management, adding even more complexity.
To avoid all of these problems, the Internet Protocol allows for routers to simply drop packets if the router or a network segment is too busy to deliver the data in a timely fashion. This is not ideal for speedy and efficient transmission of data, and is not expected to happen in an uncongested network.
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Best-effort delivery describes a network service in which the network does not provide any guarantee that data is delivered or that delivery meets any quality of service. In a best-effort network, all users obtain best-effort service. Under best-effort, network performance characteristics such as network delay and packet loss depend on the current network traffic load, and the network hardware capacity. When network load increases, this can lead to packet loss, retransmission, packet delay variation, and further network delay, or even timeout and session disconnect.
A computer network is a set of computers sharing resources located on or provided by network nodes. Computers use common communication protocols over digital interconnections to communicate with each other. These interconnections are made up of telecommunication network technologies based on physically wired, optical, and wireless radio-frequency methods that may be arranged in a variety of network topologies. The nodes of a computer network can include personal computers, servers, networking hardware, or other specialized or general-purpose hosts.
Latency, from a general point of view, is a time delay between the cause and the effect of some physical change in the system being observed. Lag, as it is known in gaming circles, refers to the latency between the input to a simulation and the visual or auditory response, often occurring because of network delay in online games. Latency is physically a consequence of the limited velocity at which any physical interaction can propagate. The magnitude of this velocity is always less than or equal to the speed of light.
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