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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 network A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking is a method by which homes, telecommunications networks and business installations avoid the costly process of introducing ...
s, or
network congestion Network congestion in data networking and queueing theory is the reduced quality of service that occurs when a network node or link is carrying more data than it can handle. Typical effects include queueing delay, packet loss or the blocking of ...
.Kurose, J.F. & Ross, K.W. (2010). ''Computer Networking: A Top-Down Approach''. New York: Addison-Wesley. Packet loss is measured as a percentage of packets lost with respect to packets sent. The
Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonl ...
(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 Network throughput (or just throughput, when in context) refers to the rate of message delivery over a communication channel, such as Ethernet or packet radio, in a communication network. The data that these messages contain may be delivered ov ...
for the connection. In real-time applications like streaming media or
online game An online game is a video game that is either partially or primarily played through the Internet or any other computer network available. Online games are ubiquitous on modern gaming platforms, including PCs, consoles and mobile devices, and ...
s, packet loss can affect a user's
quality of experience Quality of experience (QoE) is a measure of the delight or annoyance of a customer's experiences with a service (e.g., web browsing, phone call, TV broadcast).Qualinet White Paper on Definitions of Quality of Experience (2012). European Network on Q ...
(QoE).


Causes

The
Internet Protocol The Internet Protocol (IP) is the network layer communications protocol in the Internet protocol suite for relaying datagrams across network boundaries. Its routing function enables internetworking, and essentially establishes the Internet. I ...
(IP) is designed according to the
end-to-end principle The end-to-end principle is a design framework in computer networking. In networks designed according to this principle, guaranteeing certain application-specific features, such as reliability and security, requires that they reside in the comm ...
as a
best-effort delivery 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 b ...
service, with the intention of keeping the logic routers must implement, as simple as possible. If the network made
reliable delivery In computer networking, a reliable protocol is a communication protocol that notifies the sender whether or not the delivery of data to intended recipients was successful. Reliability is a synonym for assurance, which is the term used by the ITU ...
guarantees on its own, that would require
store and forward Store and forward is a telecommunications technique in which information is sent to an intermediate station where it is kept and sent at a later time to the final destination or to another intermediate station. The intermediate station, or node i ...
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 Command and control (abbr. C2) is a "set of organizational and technical attributes and processes ... hatemploys human, physical, and information resources to solve problems and accomplish missions" to achieve the goals of an organization or en ...
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. 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. For example, using perceived packet loss as feedback to discover congestion, the
Transmission Control Protocol The Transmission Control Protocol (TCP) is one of the main protocols of the Internet protocol suite. It originated in the initial network implementation in which it complemented the Internet Protocol (IP). Therefore, the entire suite is commonl ...
(TCP) is designed so that excessive packet loss will cause the sender to throttle back and stop flooding the bottleneck point with data. Packets may also be dropped if the
IPv4 header checksum The Internet checksum, also called the IPv4 header checksum is a checksum used in version 4 of the Internet Protocol (IPv4) to detect corruption in the header of IPv4 packets. It is carried in the IP packet header, and represents the 16-bit resul ...
or the Ethernet
frame check sequence A frame check sequence (FCS) is an error-detecting code added to a frame in a communication protocol. Frames are used to send payload data from a source to a destination. Purpose All frames and the bits, bytes, and fields contained withi ...
indicates the packet has been corrupted. Packet loss can also be caused by a packet drop attack.


Wireless networks

Wireless network A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking is a method by which homes, telecommunications networks and business installations avoid the costly process of introducing ...
s are susceptible to a number of factors that can corrupt or lose packets in transit, such as
radio frequency interference Electromagnetic interference (EMI), also called radio-frequency interference (RFI) when in the radio frequency spectrum, is a disturbance generated by an external source that affects an electrical circuit by electromagnetic induction, electrost ...
(RFI), radio signals that are too weak due to distance or
multi-path fading In radio communication, multipath is the propagation phenomenon that results in radio signals reaching the receiving antenna by two or more paths. Causes of multipath include atmospheric ducting, ionospheric reflection and refraction, and ref ...
, faulty networking hardware, or faulty network drivers.
Wi-Fi Wi-Fi () is a family of wireless network Communication protocol, protocols, based on the IEEE 802.11 family of standards, which are commonly used for Wireless LAN, local area networking of devices and Internet access, allowing nearby digital d ...
is inherently unreliable and even when two identical
Wi-Fi Wi-Fi () is a family of wireless network Communication protocol, protocols, based on the IEEE 802.11 family of standards, which are commonly used for Wireless LAN, local area networking of devices and Internet access, allowing nearby digital d ...
receivers are placed within close proximity of each other, they do not exhibit similar patterns of packet loss, as one might expect.
Cellular network A cellular network or mobile network is a communication network where the link to and from end nodes is wireless. The network is distributed over land areas called "cells", each served by at least one fixed-location transceiver (typically thr ...
s can experience packet loss caused by, "high
bit error rate In digital transmission, the number of bit errors is the number of received bits of a data stream over a communication channel that have been altered due to noise, interference, distortion or bit synchronization errors. The bit error rate (BER ...
(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 Network congestion in data networking and queueing theory is the reduced quality of service that occurs when a network node or link is carrying more data than it can handle. Typical effects include queueing delay, packet loss or the blocking of ...
, and so may throttle
wireless network A wireless network is a computer network that uses wireless data connections between network nodes. Wireless networking is a method by which homes, telecommunications networks and business installations avoid the costly process of introducing ...
s even when they aren't actually congested.


Network congestion

Network congestion Network congestion in data networking and queueing theory is the reduced quality of service that occurs when a network node or link is carrying more data than it can handle. Typical effects include queueing delay, packet loss or the blocking of ...
is a cause of packet loss that can affect all types of networks. 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. 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 Bottleneck literally refers to the narrowed portion (neck) of a bottle near its opening, which limit the rate of outflow, and may describe any object of a similar shape. The literal neck of a bottle was originally used to play what is now known as ...
. In some cases, packets are intentionally dropped by routing routines, or through network dissuasion technique for operational management purposes.


Effects

Packet loss directly reduces
throughput Network throughput (or just throughput, when in context) refers to the rate of message delivery over a communication channel, such as Ethernet or packet radio, in a communication network. The data that these messages contain may be delivered ov ...
for a given sender as some sent data is never received and can't be counted as throughput. Packet loss indirectly reduces throughput as some transport layer protocols interpret loss as an indication of congestion and adjust their transmission rate to avoid congestive collapse. When reliable delivery is necessary, packet loss increases latency due to additional time needed for retransmission. Assuming no retransmission, packets experiencing the worst delays might be preferentially dropped (depending on the
queuing discipline A network scheduler, also called packet scheduler, queueing discipline (qdisc) or queueing algorithm, is an arbiter on a node in a packet switching communication network. It manages the sequence of network packets in the transmit and receive q ...
used), resulting in lower latency overall.


Measurement

Packet loss may be measured as ''frame loss rate'' defined as the percentage of frames that should have been forwarded by a network but were not.


Acceptable packet loss

Packet loss is closely associated with
quality of service Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantit ...
considerations. The amount of packet loss that is acceptable depends on the type of data being sent. For example, for
voice over IP Voice over Internet Protocol (VoIP), also called IP telephony, is a method and group of technologies for the delivery of voice communications and multimedia sessions over Internet Protocol (IP) networks, such as the Internet. The terms Internet ...
traffic, one commentator reckoned that " ssing one or two packets every now and then will not affect the quality of the conversation. Losses between 5% and 10% of the total packet stream will affect the quality significantly." Another described less than 1% packet loss as "good" for streaming audio or video, and 1–2.5% as "acceptable".


Diagnosis

Packet loss is detected by reliable protocols such as TCP. Reliable protocols react to packet loss automatically, so when a person such as a
network administrator A network administrator is a person designated in an organization whose responsibility includes maintaining computer infrastructures with emphasis on local area networks (LANs) up to wide area networks (WANs). Responsibilities may vary between org ...
needs to detect and diagnose packet loss, they typically use status information from network equipment or purpose-built tools. The
Internet Control Message Protocol The Internet Control Message Protocol (ICMP) is a supporting protocol in the Internet protocol suite. It is used by network devices, including routers, to send error messages and operational information indicating success or failure when commu ...
provides an ''echo'' functionality, where a special packet is transmitted that always produces a reply. Tools such as
ping Ping may refer to: Arts and entertainment Fictional characters * Ping, a domesticated Chinese duck in the illustrated book '' The Story about Ping'', first published in 1933 * Ping, a minor character in ''Seinfeld'', an NBC sitcom * Ping, a c ...
,
traceroute In computing, traceroute and tracert are computer network diagnostic commands for displaying possible routes (paths) and measuring transit delays of packets across an Internet Protocol (IP) network. The history of the route is recorded as ...
, and
MTR The Mass Transit Railway (MTR) is a major public transport network serving :Hong Kong. Operated by the MTR Corporation Limited (MTRCL), it consists of heavy rail, light rail, and feeder bus service centred on a 10-line rapid transit netwo ...
use this protocol to provide a visual representation of the path packets are taking, and to measure packet loss at each hop. Many routers have status pages or logs, where the owner can find the number or percentage of packets dropped over a particular period.


Packet recovery for reliable delivery

Per the
end-to-end principle The end-to-end principle is a design framework in computer networking. In networks designed according to this principle, guaranteeing certain application-specific features, such as reliability and security, requires that they reside in the comm ...
, the Internet Protocol leaves responsibility for packet recovery through the retransmission of dropped packets to the endpoints - the computers sending and receiving the data. They are in the best position to decide whether retransmission is necessary because the application sending the data should know whether a message is best retransmitted in whole or in part, whether or not the need to send the message has passed, and how to control the amount of bandwidth consumed to account for any congestion. Network transport protocols such as TCP provide endpoints with an easy way to ensure
reliable delivery In computer networking, a reliable protocol is a communication protocol that notifies the sender whether or not the delivery of data to intended recipients was successful. Reliability is a synonym for assurance, which is the term used by the ITU ...
of packets so that individual applications don't need to implement the logic for this themselves. In the event of packet loss, the receiver asks for retransmission or the sender automatically resends any segments that have not been acknowledged. Although TCP can recover from packet loss, retransmitting missing packets reduces the
throughput Network throughput (or just throughput, when in context) refers to the rate of message delivery over a communication channel, such as Ethernet or packet radio, in a communication network. The data that these messages contain may be delivered ov ...
of the connection as receivers wait for retransmissions and additional bandwidth is consumed by them. In certain variants of TCP, if a transmitted packet is lost, it will be re-sent along with every packet that had already been sent after it. Protocols such as
User Datagram Protocol In computer networking, the User Datagram Protocol (UDP) is one of the core communication protocols of the Internet protocol suite used to send messages (transported as datagrams in packets) to other hosts on an Internet Protocol (IP) network. ...
(UDP) provide no recovery for lost packets. Applications that use UDP are expected to implement their own mechanisms for handling packet loss, if needed.


Impact of queuing discipline

There are many
queuing discipline A network scheduler, also called packet scheduler, queueing discipline (qdisc) or queueing algorithm, is an arbiter on a node in a packet switching communication network. It manages the sequence of network packets in the transmit and receive q ...
s used for determining which packets to drop. Most basic networking equipment will use FIFO queuing for packets waiting to go through the bottleneck and they will drop the packet if the queue is full at the time the packet is received. This type of packet dropping is called
tail drop Tail drop is a simple queue management algorithm used by network schedulers in network equipment to decide when to drop packets. With tail drop, when the queue is filled to its maximum capacity, the newly arriving packets are dropped until the q ...
. Other full queue mechanisms include random early drop or weighted random early drop. Dropping packets is undesirable as the packet is either lost or must be retransmitted and this can impact real-time throughput; however, increasing the buffer size can lead to
bufferbloat Bufferbloat is a cause of high latency and jitter in packet-switched networks caused by excess buffering of packets. Bufferbloat can also cause packet delay variation (also known as jitter), as well as reduce the overall network throughput. ...
which has its own impact on latency and jitter during congestion. In cases where
quality of service Quality of service (QoS) is the description or measurement of the overall performance of a service, such as a telephony or computer network, or a cloud computing service, particularly the performance seen by the users of the network. To quantit ...
is
rate limiting In computer networks, rate limiting is used to control the rate of requests sent or received by a network interface controller. It can be used to prevent DoS attacks and limit web scraping. Research indicates flooding rates for one zombie machin ...
a connection, e.g., using a
leaky bucket The leaky bucket is an algorithm based on an analogy of how a bucket with a constant leak will overflow if either the average rate at which water is poured in exceeds the rate at which the bucket leaks or if more water than the capacity of the ...
algorithm, packets may be intentionally dropped in order to slow down specific services to ensure available bandwidth for other services marked with higher importance. For this reason, packet loss is not necessarily an indication of poor connection reliability or signs of a bandwidth bottleneck.


See also

*
Bit slip In digital transmission, bit slip is the loss or gain of a bit or bits, caused by clock drift – variations in the respective clock rates of the transmitting and receiving devices. One cause of bit slippage is overflow of a receive buffer that ...
*
Collision (telecommunications) A collision is the situation that occurs when two or more demands are made simultaneously on equipment that can handle only one at any given instant.Source: from Federal Standard 1037C and from MIL-STD-188 It may refer to: * Collision domain, a phy ...
*
Goodput In computer networks, goodput (a portmanteau of good and throughput) is the application-level throughput of a communication; i.e. the number of useful information bits delivered by the network to a certain destination per unit of time. The amoun ...
*
Packet loss concealment Packet loss concealment (PLC) is a technique to mask the effects of packet loss in voice over IP (VoIP) communications. When the voice signal is sent as VoIP packets on an IP network, the packets may (and likely will) travel different routes. A pa ...
*
Traffic shaping Traffic shaping is a bandwidth management technique used on computer networks which delays some or all datagrams to bring them into compliance with a desired ''traffic profile''. Traffic shaping is used to optimize or guarantee performance, impro ...


Notes


References

{{Reflist


External links


Packet loss test
- test your Internet connection for packet loss
Loss Loss may refer to: Arts, entertainment, and media Music * ''Loss'' (Bass Communion album) (2006) * ''Loss'' (Mull Historical Society album) (2001) *"Loss", a song by God Is an Astronaut from their self-titled album (2008) * Losses "(Lil Tjay son ...