computer science

Virtual Interface Architecture

Virtual Interface Architecture 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 Virtual Interface Architecture rather than just read about it. In short: The Virtual Interface Architecture (VIA) is an abstract model of a user-level zero-copy network, and is the basis for InfiniBand, iWARP and RoCE. Created by Microsoft, Intel, and Compaq, the original VIA sought to standardize the interface for high-performance network technologies known as System Area Networks (SANs; not to be confused with Storage Area Networks).

Key takeaways

Virtual Interface Architecture 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 Virtual Interface Architecture to a quantity you can measure, compute or draw — that is where exam questions come from.
Reproduce the core statement of Virtual Interface Architecture from memory before moving on to harder problems.

Reference excerpt

The Virtual Interface Architecture (VIA) is an abstract model of a user-level zero-copy network, and is the basis for InfiniBand, iWARP and RoCE. Created by Microsoft, Intel, and Compaq, the original VIA sought to standardize the interface for high-performance network technologies known as System Area Networks (SANs; not to be confused with Storage Area Networks).

Overview Networks are a shared resource. With traditional network APIs such as the Berkeley socket API, the kernel is involved in every network communication. This presents a tremendous performance bottleneck when latency is an issue. One of the classic developments in computing systems is virtual memory, a combination of hardware and software that creates the illusion of private memory for each process. In the same school of thought, a virtual network interface protected across process boundaries could be accessed at the user level. With this technology, the "consumer" manages its own buffers and communication schedule while the "provider" handles the protection. Thus, the network interface card (NIC) provides a "private network" for a process, and a process is usually allowed to have multiple such networks. The virtual interface (VI) of VIA refers to this network and is merely the destination of the user's communication requests. Communication takes place over a pair of VIs, one on each of the processing nodes involved in the transmission. In "kernel-bypass" communication, the user manages its own buffers. Another facet of traditional networks is that arriving data is placed in a pre-allocated buffer and then copied to the user-specified final destination. Copying large messages can take a long time, and so eliminating this step is beneficial. Another classic development in computing systems is direct memory access (DMA), in which a device can access main memory directly while the CPU is free to perform other tasks.

Data transmission In a network with "remote direct memory access" (RDMA), the sending NIC uses DMA to read data in the user-specified buffer and transmit it as a self-contained message across the network. The receiving NIC then uses DMA to place the data into the user-specified buffer. There is no intermediary copying and all of these actions occur without the involvement of the CPUs, which has an added benefit of lower CPU utilization. For the NIC to actually access the data through DMA, the user's page must be in memory. In VIA, the user must "pin-down" its buffers before transmission, so as to prevent the OS from swapping the page out to the disk. This action—one of the few that involve the kernel—ties the page to physical memory. To ensure that only the process that owns the registered memory may access it, the VIA NICs require permission keys known as "protection tags" during communication. So essentially VIA is a standard that defines kernel bypassing and RDMA in a network. It also defines a programming library called "VIPL". It has been implemented, most notably in cLAN from Giganet (now Emulex). Mostly though, VIA's major contribution has been in providing a basis for the InfiniBand, iWARP and RoCE standards.

Worked examples

Example 1 — a first encounter with Virtual Interface Architecture

Start with the simplest possible case. Write down what Virtual Interface Architecture 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 Virtual Interface Architecture 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 Virtual Interface Architecture 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 Virtual Interface Architecture

In research: Virtual Interface Architecture 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 Virtual Interface Architecture 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: Virtual Interface Architecture is common in secondary-school and first-year university syllabi. It links to neighbouring topics Computer network stubs, Computer networks engineering, Supercomputing, so understanding it makes those chapters shorter.
In everyday life: Look for Virtual Interface Architecture 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.

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How to study Virtual Interface Architecture in 20 minutes

Read the reference excerpt below once, without taking notes.
Close the page and write down what Virtual Interface Architecture 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 Virtual Interface Architecture out loud to somebody else — or to Teacher Smith in the lgStudy chat.

Frequently asked questions

What is Virtual Interface Architecture in simple terms?

Why does Virtual Interface Architecture 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 Virtual Interface Architecture?

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 Virtual Interface Architecture.