Reliability (computer networking): Difference between revisions

Revision as of 18:20, 5 May 2020

Revision as of 20:37, 16 July 2020

Line 47:

==Real-time systems==

There is, however, a problem with the definition of reliability as "delivery or notification of failure" in [[real-time computing]]. In such systems, failure to deliver the real-time data will adversely affect the performance of the systems, and some systems, e.g. [[safety-critical]], [[Safety-involved systems|safety-involved]], and some secure [[mission-critical]] systems, must be [[formal methods|proved]] to perform at some specified minimum level. This, in turn, requires that a specified minimum reliability for the delivery of the critical data be met. Therefore, in these cases, it is only the delivery that matters; Notification of the failure to deliver does ameliorate the failure. In [[hard real-time system]]s, all data must be delivered by the deadline or it is considered a system failure. In [[firm real-time system]]s, late data is still valueless but the system can tolerate some amount of late or missing data.<ref name = "Schneider et al 2001">S., Schneider, G.,Pardo-Castellote, M., Hamilton. “Can Ethernet Be Real Time?”, Real-Time Innovations, Inc., 2001</ref><ref name = "Rubenstein et al 1998">Dan Rubenstein, Jim Kurose, Don Towsley, ”Real-Time Reliable Multicast Using Proactive Forward Error Correction”, NOSSDAV ’98</ref><!--[[User:Kvng/RTH]]-->

In [[Real-time computing#Criteria for real-time computing|hard and firm real-time systems]] the data has to be delivered within a deadline, i.e. data that is delivered late is valueless. In hard real-time systems, all data must be delivered within its deadline or it is considered a system failure. In firm real-time systems, late data is still valueless but the system can tolerate some amount of late or missing data.<ref name = "Schneider et al 2001">S., Schneider, G.,Pardo-Castellote, M., Hamilton. “Can Ethernet Be Real Time?”, Real-Time Innovations, Inc., 2001</ref><ref name = "Rubenstein et al 1998">Dan Rubenstein, Jim Kurose, Don Towsley, ”Real-Time Reliable Multicast Using Proactive Forward Error Correction”, NOSSDAV ’98</ref>

There are a number of protocols that are capable of meeting real-time requirements for reliable delivery and timeliness, at least for firm real-time systems (due to the inevitable and unavoidable losses from, e.g., the physical layer [[bit error rate]]s):