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POWhat are the bottlenecks inherent in networking?
 

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  1. POWhat are the bottlenecks inherent in networking?
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    <p>If a computer has to fetch some information, a network request is generally one of the slowest possible sources. My understanding is that, in general:</p> <ul> <li>Network access is much slower than disk</li> <li>Disk access is much slower than RAM</li> <li>RAM access is much slower than CPU registers</li> </ul> <p>My question is this: <strong>what makes network access so much slower, on average, than disk</strong>?</p> <p>Obviously this isn't always true: you <strong>could</strong> have a blazing-fast network connection to a server in the same room and a sluggish hard drive. But for the purposes of this question, please imagine <strong>an average user surfing the web</strong>: reading data from disk will be faster than fetching the same data from Google.</p> <p>Some of the pieces I can think of involved in, say, an HTTP request are:</p> <ul> <li>DNS lookup of the IP</li> <li>The three-way handshake to establish a TCP connection</li> <li>Packetization: breaking the HTTP request into TCP packets, and putting those into IP packets, with all the necessary counters and checksums, etc</li> <li>Transmission: the time required for electrical signals to move across wire</li> <li>Routing: the decision-making, buffering, etc that happens inside routers</li> <li>Processing: the server's formulation of a response</li> <li>All the transmission and routing of the response, including resending missing packets</li> <li>Ordering and assembling the TCP packets' contents and handing the HTTP response back to the client</li> </ul> <p>If I've missed any major steps, please let me know.</p> <p>Of these steps, ignoring server processing (which isn't really a network issue), are any parts particularly slow? Do any of them account for most of the inherent delay in network requests?</p> <h2>Update: Some numbers</h2> <blockquote> <p>An average DNS lookup takes 60~120ms, followed by a full round-trip (RTT) to perform the TCP handshake - combined, that creates 100-200ms of latency before we can even send the request!</p> </blockquote> <ul> <li>Source: <a href="http://www.igvita.com/2012/06/04/chrome-networking-dns-prefetch-and-tcp-preconnect" rel="nofollow">Chrome Networking: DNS Prefetch &amp; TCP Preconnect</a> by Ilya Grigorik, Developer Advocate at Google</li> </ul>
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    1. COIt curious me, why you asked such pointless question.
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      1. USAlan Kuras
    2. CO@AlanKuras - the short answer is "because I like to understand the systems I rely on." But it could have practical benefits. For instance: would moving our data center physically closer make a big difference in speed, or would it be better to buy faster routers?
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      1. USNathan Long
    3. COTo those voting to close: this question has a quantifiable, objective answer. It has practical consequences for every networked program. Please reconsider.
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