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 Mathematics ...

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 quantita ...

. 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 multiple ...

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 In computer networking, packet delay variation (PDV) is the difference in end-to-end one-way delay between selected packets in a flow with any lost packets being ignored.RFC 3393 The effect is sometimes referred to as packet jitter, although ...

, and further

, or even timeout and session disconnect. Best-effort can be contrasted with reliable delivery, which can be built on top of best-effort delivery (possibly without latency and throughput guarantees), or with

virtual circuit A virtual circuit (VC) is a means of transporting data over a data network, based on packet switching and in which a connection is established within the network between two endpoints. The network, rather than having a fixed data rate reservation ...

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 sys ...

(''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 more ...

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 syst ...

s, or a

busy signal Reanno Devon Gordon (born 24 January 1979), better known by his stage name Busy Signal, is a Jamaican dancehall reggae artist. Biography Reanno Devon Gordon p/k/a Busy Signal was born in Saint Ann Parish,Johnson, Carolyn (2006)A Very Busy Chi ...

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 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 common ...

(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) networ ...

(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 In computer networking, a port is a number assigned to uniquely identify a connection endpoint and to direct data to a specific service. At the software level, within an operating system, a port is a logical construct that identifies a specif ...

Network examples

Physical services

Internet

Further reading