Return to LIFO (computing)

Also called: FIFO (computing)

A queue (Queue (abstract data type)) operates first in, first out, referred to by the acronym FIFO (computing and electronics). By contrast, the order in which an element added to the stack (Stack (abstract data type) or an element removed from the stack is described as last in, first out, referred to by the acronym LIFO.

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First In, First Out (FIFO) is one of the simplest and most commonly used queuing algorithms in both networking and computer systems. The fundamental concept behind FIFO is that data packets, processes, or tasks are handled in the order they arrive. Once a packet enters the queue, it is processed without any prioritization or differentiation based on its characteristics. This simplicity makes FIFO a straightforward and efficient mechanism in scenarios where the order of processing is not critical, but it can suffer from inefficiencies in networks with varying traffic patterns. The related RFC is RFC 791, which defines the core structure of the Internet Protocol (IP) and includes basic queue management principles. https://en.wikipedia.org/wiki/First_in,_first_out https://tools.ietf.org/html/rfc791

In networking, FIFO is often used in basic routers and switches, where each packet is transmitted in the order it was received. This method ensures fairness in that all packets are treated equally, regardless of their priority or size. However, FIFO does not account for the specific needs of time-sensitive traffic, such as voice or video, leading to potential latency issues for these types of applications. The related RFC is RFC 2309, which discusses the limitations of FIFO and introduces the need for more advanced queue management algorithms to handle congestion and improve performance in modern networks. https://en.wikipedia.org/wiki/Network_packet https://tools.ietf.org/html/rfc2309

One of the key drawbacks of FIFO is its vulnerability to head-of-line blocking, where a large or slow packet at the front of the queue delays all other packets behind it. This can cause significant latency for time-sensitive packets, even if they require less processing time. In networks with mixed traffic types, FIFO can be inefficient because it does not prioritize real-time traffic over bulk data transfers. The related RFC is RFC 2475, which introduces Differentiated Services (DiffServ) as a mechanism to prioritize traffic based on the type of service, overcoming some of the limitations of FIFO. https://en.wikipedia.org/wiki/Head-of-line_blocking https://tools.ietf.org/html/rfc2475

To address the limitations of FIFO, many modern networks implement more advanced queuing algorithms, such as Weighted Fair Queuing (WFQ) or Priority Queuing, which prioritize packets based on their importance or the type of service they require. These algorithms allow for more efficient handling of time-sensitive applications while still processing other traffic in a fair manner. Nonetheless, FIFO remains useful in simpler or less congested networks where traffic is relatively uniform. The related RFC is RFC 3662, which discusses the role of weighted queuing mechanisms in managing network congestion more effectively than FIFO. https://en.wikipedia.org/wiki/Weighted_fair_queueing https://tools.ietf.org/html/rfc3662

FIFO is also a commonly used scheduling algorithm in operating systems, where processes are executed in the order they arrive. Just like in networking, this approach can lead to inefficiencies when processes with different execution times are treated equally. In both networking and operating systems, FIFO is optimal when the order of arrival is the primary concern, but it may need to be supplemented by other mechanisms in systems where response time or priority is more important. The related RFC is RFC 970, which discusses early approaches to fair queuing in packet-switched networks, highlighting the limitations of simple scheduling algorithms like FIFO. https://en.wikipedia.org/wiki/Scheduling_(computing) https://tools.ietf.org/html/rfc970

While FIFO is simple and ensures that no packet is starved of resources, it lacks the sophistication required to manage modern traffic loads effectively. In highly congested networks, FIFO can contribute to longer delays and increased packet loss, as it does not provide any mechanism for managing congestion. Techniques such as Random Early Detection (RED) have been developed to work in conjunction with queuing algorithms to improve performance by proactively dropping packets when the queue becomes too full. The related RFC is RFC 2309, which outlines the importance of active queue management in preventing congestion, a limitation of FIFO alone. https://en.wikipedia.org/wiki/Random_early_detection https://tools.ietf.org/html/rfc2309

Despite its limitations, FIFO remains a foundational concept in both networking and systems design due to its simplicity and fairness. It continues to be used in environments where the traffic pattern is predictable and uniform, or where the simplicity of implementation is more important than the need for sophisticated traffic management. However, as networks grow more complex and traffic patterns more diverse, more advanced algorithms are typically favored to ensure optimal performance. The related RFC is RFC 2475, which provides guidance on how modern networks can implement DiffServ to improve traffic handling beyond what FIFO can offer. https://en.wikipedia.org/wiki/Differentiated_services https://tools.ietf.org/html/rfc2475

The title of this RFC is “Internet Protocol.” First In, First Out (FIFO) is a basic but widely used queuing algorithm that processes packets or tasks in the order they arrive, ensuring fairness but often leading to inefficiencies in handling diverse traffic patterns. While simple to implement and suitable for less congested environments, FIFO does not account for traffic prioritization or congestion management, which are critical in modern, high-traffic networks. The related RFCs, such as RFC 2309 and RFC 2475, offer more advanced approaches to managing network traffic and mitigating the limitations of FIFO in complex systems.

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Snippet from Wikipedia: FIFO (computing and electronics)

In computing and in systems theory, first in, first out (the first in is the first out), acronymized as FIFO, is a method for organizing the manipulation of a data structure (often, specifically a data buffer) where the oldest (first) entry, or "head" of the queue, is processed first.

Such processing is analogous to servicing people in a queue area on a first-come, first-served (FCFS) basis, i.e. in the same sequence in which they arrive at the queue's tail.

FCFS is also the jargon term for the FIFO operating system scheduling algorithm, which gives every process central processing unit (CPU) time in the order in which it is demanded. FIFO's opposite is LIFO, last-in-first-out, where the youngest entry or "top of the stack" is processed first. A priority queue is neither FIFO or LIFO but may adopt similar behaviour temporarily or by default. Queueing theory encompasses these methods for processing data structures, as well as interactions between strict-FIFO queues.

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