In some cases, packets are intentionally dropped by routing routines, or through network dissuasion technique for operational management purposes. : 36 If a single router or link is constraining the capacity of the complete travel path or of network travel in general, it is known as a bottleneck. When content arrives for a sustained period at a given router or network segment at a rate greater than it is possible to send through, there is no other option than to drop packets. Network congestion is a cause of packet loss that can affect all types of networks. Ĭellular networks can experience packet loss caused by, "high bit error rate (BER), unstable channel characteristics, and user mobility." TCP's intentional throttling behavior prevents wireless networks from performing near their theoretical potential transfer rates because unmodified TCP treats all dropped packets as if they were caused by network congestion, and so may throttle wireless networks even when they aren't actually congested. Wi-Fi is inherently unreliable and even when two identical Wi-Fi receivers are placed within close proximity of each other, they do not exhibit similar patterns of packet loss, as one might expect. Wireless networks are susceptible to a number of factors that can corrupt or lose packets in transit, such as radio frequency interference (RFI), radio signals that are too weak due to distance or multi-path fading, faulty networking hardware, or faulty network drivers. Packet loss can also be caused by a packet drop attack. Packets may also be dropped if the IPv4 header checksum or the Ethernet frame check sequence indicates the packet has been corrupted. For example, using perceived packet loss as feedback to discover congestion, the Transmission Control Protocol (TCP) is designed so that excessive packet loss will cause the sender to throttle back and stop flooding the bottleneck point with data. Dropping of packets acts as an implicit signal that the network is congested, and may cause senders to reduce the amount of bandwidth consumed, or attempt to find another path. This is not ideal for speedy and efficient transmission of data, and is not expected to happen in an uncongested network. 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. Such a network might also need a command and control protocol for congestion management, adding even more complexity. 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. For example, with live streaming media, it is more important to deliver recent packets quickly than to ensure that stale packets are eventually delivered. Reliability is also not needed for all applications. A reliable network would not be able to maintain its delivery guarantees in the event of a router failure. 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. 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. In real-time applications like streaming media or online games, packet loss can affect a user's quality of experience (QoE). Packet loss in a TCP connection is also used to avoid congestion and thus produces an intentionally reduced throughput for the connection. The Transmission Control Protocol (TCP) detects packet loss and performs retransmissions to ensure reliable messaging. : 36 Packet loss is measured as a percentage of packets lost with respect to packets sent. Packet loss is either caused by errors in data transmission, typically across wireless networks, or network congestion. Packet loss occurs when one or more packets of data travelling across a computer network fail to reach their destination. ( February 2013) ( Learn how and when to remove this template message) Please help to improve this article by introducing more precise citations. This article includes a list of general references, but it lacks sufficient corresponding inline citations.
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