computer science

Performance-enhancing proxy

Performance-enhancing proxy is a computer science topic covered in the lgStudy science library. This page brings together a partial reference excerpt, illustrations, worked examples, real-world applications and a short study plan, so you can understand Performance-enhancing proxy rather than just read about it. In short: Performance-enhancing proxies (PEPs) are network agents designed to improve the end-to-end performance of some communication protocols. PEP standards are defined in RFC 3135 (PEPs intended to mitigate link-related degradations) and RFC 3449 (TCP performance implications of network path asymmetry).

Key takeaways

Performance-enhancing proxy belongs to computer science; place it in that map before memorising details.
Learn the definition first, then one example that makes the definition concrete.
Connect Performance-enhancing proxy to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Performance-enhancing proxy from memory before moving on to harder problems.

Reference excerpt

Performance-enhancing proxies (PEPs) are network agents designed to improve the end-to-end performance of some communication protocols. PEP standards are defined in RFC 3135 (PEPs intended to mitigate link-related degradations) and RFC 3449 (TCP performance implications of network path asymmetry).

Classification Available PEP implementations use different methods to enhance performance.

Proxy type: A PEP can either 'split' a connection or 'snoop' into it. In the first case, the proxy pretends to be the opposite endpoint of the connection in each direction, literally splitting the connection into two. In the latter case, the proxy controls the transmissions of the TCP segments in both directions, by ack filtering and reconstruction in the existing connection (see protocol spoofing). This is based on the OSI level of implementation of the PEP. Distribution: PEPs can be either integrated or distributed. Integrated PEP will run on a single box, while distributed PEP will require to be installed on both sides of the link that cause the performance degradation. This is quite common in commercial PEP devices, which act as a black box, using more or less open protocols to communicate between them in the place of TCP. Symmetry: A PEP implementation may be symmetric or asymmetric. Symmetric PEPs use identical behavior in both directions; the actions taken by the PEP occur independent from which interface a packet is received. Asymmetric PEPs operate differently in each direction, which can cause, for example, only one link direction performance to be enhanced.

Types There are a range of different types of PEPs. Each is used to solve a link related problem. Some common types include:

Split-TCP Ack decimation Snoop D-proxy

Split TCP Split TCP is typically used to solve TCP problems with large round-trip delay times. A typical system uses Split TCP PEPs to improve TCP performance over a satellite link. Split TCP functions by breaking the end-to-end connection into multiple connections and using different parameters to transfer data across the different legs. The end systems use standard TCP with no modifications, and do not need to know of the existence of the PEPs in between. Split TCP intercepts TCP connections from the end systems and terminates them. This allows the end systems to run unmodified and can overcome some problems with TCP window sizes on the end systems being set too low for satellite communications.

Ack filtering/decimation Ack filtering or decimation is used on highly asymmetric links. In asymmetric links the upstream and downstream rates vary widely. A common example is satellite broadband where a downstream satellite link provides significantly greater bandwidths than the upstream dialup modem link. In this scenario, the speed at which the modem can return TCP acknowledgements can be a limiting factor. As TCP acknowledgements are cumulatively acknowledged some can be decimated or filtered to improve performance.

Snoop The Snoop proxy is an example of an integrated proxy. It is designed to hide interference or collision-based packet loss over a wireless link. Snoop proxies detect losses by monitoring TCP transmissions for duplicate acknowledgements. When duplicate TCP acknowledgements, indicating a packet loss, are received by Snoop, they will be silently dropped and lost data packet will be retransmitted. The TCP sender should have no knowledge of the loss. This should prevent TCP senders from unnecessarily reducing the TCP window.

D-Proxy D-Proxy is also designed to hide interference or collision based packet loss over a wireless link. D-Proxy is a new distributed TCP proxy, requiring a proxy on either side of the lossy link. Like Snoop, it uses TCP sequence numbers to detect lost packets. However, it has a proactive approach, monitoring the TCP sequence numbers on data packets rather than acknowledgements. When packet loss occurs, the TCP stream will be temporarily buffered until the missing packet can be recovered and re-sequenced.

See also Proxy server TCP congestion control

References

External links PEPsal : A GPL licensed, Linux-based, integrated splitting PEP implementation PEP server MediaSputnik : PEP server MediaSputnik 2402 has been developed by MediaSputnik as I-PEP compatible server compliant with SatLabs Group (ESA) recommendations to support DVB-RCS standards and networks RFC 3135 : The whole RFC (Performance Enhancing Proxies Intended to Mitigate Link-Related Degradations)

Illustrations

Worked examples

Example 1 — a first encounter with Performance-enhancing proxy

Start with the simplest possible case. Write down what Performance-enhancing proxy claims or describes in one sentence, then invent the smallest concrete situation in which that sentence is true. In computer science, the smallest case is usually a single object, a single equation or a single measurement. Check that every symbol or term in your sentence has a meaning in that case.

Example 2 — changing one variable

Take the situation from Example 1 and change exactly one quantity: double it, halve it, or set it to zero. Predict what should happen to Performance-enhancing proxy before you calculate. Comparing your prediction with the result is the fastest way to find out whether you understand the idea or only the words.

Example 3 — an exam-style question

Typical questions about Performance-enhancing proxy ask you to (a) state it precisely, (b) apply it to given data, and (c) explain a limitation. Practise writing all three answers in under five minutes; the third part is what separates a full-mark answer from an average one.

Applications of Performance-enhancing proxy

In research: Performance-enhancing proxy appears in computer science research whenever the underlying quantities have to be modelled precisely. Papers usually cite it as a starting assumption and then explore where it breaks down.
In technology and industry: Engineering practice reuses Performance-enhancing proxy in design rules, simulations and safety margins. Knowing the idea lets you read a specification sheet and understand why the numbers look the way they do.
In the classroom: Performance-enhancing proxy is common in secondary-school and first-year university syllabi. It links to neighbouring topics Network performance, Transmission Control Protocol, so understanding it makes those chapters shorter.
In everyday life: Look for Performance-enhancing proxy outside the textbook — in sport, cooking, traffic, electronics or the sky above you. An example you found yourself is remembered far longer than one you were given.

Ask Teacher Smith questions about this articleOpens your AI tutor with a question about “Performance-enhancing proxy” →

Affiliate

Preply — study more efficiently by working with a personal tutor. 50% off.

How to study Performance-enhancing proxy in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Performance-enhancing proxy means in your own words.
Compare your version with the excerpt and mark what you missed.
Work through the three examples above with pen and paper.
Explain Performance-enhancing proxy out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Performance-enhancing proxy in simple terms?

Why does Performance-enhancing proxy matter?

Because it connects several computer science ideas at once: it gives you a definition you can apply, a quantity you can calculate, and a way to check whether a result is plausible.

How should I study Performance-enhancing proxy?

Read the excerpt, restate it from memory, then work through the examples and applications listed on this page. The five-step study plan above takes about twenty minutes.

What does this page cover?

It gives you a compact reference excerpt plus original lgStudy explanations, examples, applications and study material on Performance-enhancing proxy.