Reliability is a synonym for assurance, which is the term used by the ITU and ATM Forum, and leads to fault-tolerant messaging.
For example, TCP is connection oriented, with the virtual-circuit ID consisting of source and destination IP addresses and port numbers.
Meanwhile, the developers of CYCLADES and of ALOHAnet demonstrated that it was possible to build an effective computer network without providing reliable packet transmission.
[citation needed] For example, Internet Protocol (IP) provides an unreliable service.
An example of a reliability property for a unicast protocol is "at least once", i.e. at least one copy of the message is guaranteed to be delivered to the recipient.
Strong reliability properties such as this one typically require that messages are retransmitted or forwarded among the recipients.
Strong reliability properties are offered by group communication systems (GCSs) such as IS-IS, Appia framework, JGroups or QuickSilver Scalable Multicast.
[10] It uses a bus controller (BC) to command the connected remote terminals (RTs) to receive or transmit this data.
The MIL-1553 protocol also allows for automatic retries that can still ensure timely delivery and increase the reliability above that of the physical layer.
The Asynchronous Transfer Mode (ATM), the Avionics Full-Duplex Switched Ethernet (AFDX), and Time Triggered Ethernet (TTEthernet) are examples of packet-switched networks protocols where the timeliness and reliability of data transfers can be assured by the network.
This allows the usage of the shared resources (switch buffers) in the network to be calculated from the parameters of the traffic to be carried in advance, i.e. at system design time.
[12] However, the techniques for predicting the resource requirements and proving that congestion is prevented are not part of the AFDX standard.
TTEthernet provides the lowest possible latency in transferring data across the network by using time-domain control methods – each time triggered transfer is scheduled at a specific time so that contention for shared resources is controlled and thus the possibility of congestion is eliminated.
The switches in the network enforce this timing to provide tolerance of faults in, and malicious actions on the part of, the other connected equipment.
With both AFDX and TTEthernet, there are additional functions required of the interfaces, e.g. AFDX's Bandwidth Allocation Gap control, and TTEthernet's requirement for very close synchronization of the sources of time-triggered data, that make it difficult to use standard Ethernet interfaces.