Best-effort delivery describes a

network service In computer networking, a network service is an application running at the network application layer and above, that provides data storage, manipulation, presentation, communication or other capability which is often implemented using a client� ...

in which the

network Network, networking and networked may refer to: Science and technology * Network theory, the study of graphs as a representation of relations between discrete objects * Network science, an academic field that studies complex networks Mathematic ...

does ''not'' provide any guarantee that data is delivered or that delivery meets any

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 quantitat ...

. In a best-effort network, all users obtain best-effort service. Under best-effort, network performance characteristics such as

network delay Network delay is a design and performance characteristic of a telecommunications network. It specifies the latency for a bit of data to travel across the network from one communication endpoint to another. It is typically measured in multiples ...

and

packet loss 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.Ku ...

depend on the current network traffic load, and the network hardware capacity. When network load increases, this can lead to

, retransmission, packet delay variation, and further

, or even timeout and session disconnect. Best-effort can be contrasted with

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 ...

, which can be built on top of best-effort delivery (possibly without latency and throughput guarantees), or with virtual circuit schemes which can maintain a defined quality of service.

Network examples

Physical services

The

postal service The mail or post is a system for physically transporting postcards, letters, and parcels. A postal service can be private or public, though many governments place restrictions on private systems. Since the mid-19th century, national postal syst ...

(''snail mail'') physically delivers letters using a best-effort delivery approach. The delivery of a certain letter is not scheduled in advance – no resources are preallocated in the post offices. The service will make their "best effort" to try to deliver a message, but the delivery may be delayed if too many letters suddenly arrive at a postal office or triage center. The sender is generally not informed when a letter has been delivered successfully, unless one pays for this premium service. Conventional

telephone network A telephone network is a telecommunications network that connects telephones, which allows telephone calls between two or more parties, as well as newer features such as fax and internet. The idea was revolutionized in the 1920s, as more and mor ...

s are not based on best-effort communication, but on

circuit switching Circuit switching is a method of implementing a telecommunications network in which two network nodes establish a dedicated communications channel ( circuit) through the network before the nodes may communicate. The circuit guarantees the full ...

. During the connection phase of a new call, resources are reserved in the

telephone exchange telephone exchange, telephone switch, or central office is a telecommunications system used in the public switched telephone network (PSTN) or in large enterprises. It interconnects telephone subscriber lines or virtual circuits of digital syste ...

s, or a busy signal informs the user that the call failed due to a lack of capacity. An ongoing phone call can never be interrupted due to overloading of the network, and is guaranteed constant bandwidth (both of which are not guaranteed in a mobile telephone network).

Internet

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. ...

offers a best-effort service for delivering datagrams between hosts. IPv4 is a connectionless internet protocol that depends on the best-effort delivery approach. IPv4 datagrams may be lost, arbitrarily delayed, corrupted, or duplicated. The applications built on top of it implement the additional services they require on an

end-to-end End-to-end or End to End may refer to: * End-to-end auditable voting systems, a voting system * End-to-end delay, the time for a packet to be transmitted across a network from source to destination * End-to-end encryption, a cryptographic paradigm ...

basis.

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) provides a guaranteed delivery of an octet stream between a pair of hosts to the above layer, internally splitting the stream into packets and resending these when lost or corrupted.

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) netwo ...

(UDP) provides a thinner abstraction layer which only error-checks the datagrams. Both transport-layers are the base protocols and provide

multiplexing In telecommunications and computer networking, multiplexing (sometimes contracted to muxing) is a method by which multiple analog or digital signals are combined into one signal over a shared medium. The aim is to share a scarce resource - ...

between processes on the same host running over different port numbers.

Network examples

Physical services

Internet

Further reading