Category: Introduction to Networking

To close this series, the deepest example I know: the telephone. For its first hundred-plus years — from Bell’s patent in 1876 — it worked one way, called circuit switching. Then, in about fifteen years, it quietly became something else entirely. It is my favorite before-and-after story because you can put dates on the flip.

Circuit switching meant one dedicated path, reserved end to end for the whole call. The first commercial exchange opened in New Haven in 1878 with human operators plugging that path together by hand; Almon Strowger’s automatic switch (1891) mechanized them away, and by 1951 you could dial long distance yourself. The 1962 T1 carrier digitized the trunks: every call got a guaranteed 64 kbps channel in each direction, held even while nobody was speaking. Capacity equaled circuits — when the trunks filled, you got a busy signal — and long distance was priced by miles times minutes, which is why an earlier generation called after 7 p.m. to save money. A phone number was a place on a wall.

Packet switching inverted all of it. The idea dates to the early 1960s (Kleinrock, Baran, and Davies, who coined the term); the ARPANET carried its first packets on October 29, 1969; TCP/IP was designed in 1974 and became the rule on January 1, 1983. The 1984 breakup of AT&T cracked the pricing model, and dial-up modems spent the 1990s smuggling data over voice circuits. Then the smuggling reversed: commercial VoIP arrived in 1995, Skype in 2003, and VoLTE around 2012 — meaning the “phone call” on your cell phone today is literally packets. Carriers are now retiring the copper circuit network itself, with AT&T aiming to shut most of it down by 2029. Distance is nearly free, a number follows a person instead of a place, and voice is just one app among many.

The design bet underneath is the whole story. Circuits reserve capacity: guaranteed quality, wasteful in every silence, and a flat refusal — the busy signal — when full. Packets share capacity: radically efficient, best-effort, degrading gracefully instead of refusing. Best effort won because sharing is cheaper by orders of magnitude and smart endpoints can paper over the rough edges with buffers and codecs. Intelligence moved from the core of the network to its edge, and that single inversion is why the wire that once carried one conversation now carries everything. My entire intro networking course is, in a sense, a footnote to that trade.

Failure used to be local. That was not a design achievement — it was a side effect of disconnection.

Before networks, problems and outages often took longer to fix, but their effects were usually limited to one place or one organization. A crashed system was somebody’s bad day, not everybody’s.

Now, because systems are connected, one outage, software failure, or cyberattack can affect millions of people at once. A single bad update can ground airlines and close pharmacies on the same morning.

The links that share resources also share failures — coupling is the price of connection. Resilience used to come free with isolation; now it has to be designed in deliberately, with redundancy, backups, and people who think about failure for a living. This is a large part of why network engineers exist.

Waiting used to be a normal, unremarkable part of everyday life. It was built into everything.

Before networks, messages, information, purchases, and decisions simply took more time. People were accustomed to waiting days or even weeks, and life was arranged around those delays.

Now people expect immediate answers, rapid delivery, and constant access. The convenience is real, and so are its byproducts: distraction, impatience, and pressure to be continuously available.

We engineered the waiting out of our systems, and some of the patience out of ourselves. The latency of ordinary life fell from days to milliseconds, and expectations fell with it. I ask my students whether instant is a feature or a treadmill; the honest answer is usually both.

Planning a trip used to start days before you left, with paper.

Before networks, travelers used paper maps, contacted travel agents, and consulted printed bus, train, and airline timetables. Getting lost often meant stopping to ask a stranger for directions.

Now GPS apps provide turn-by-turn directions, live traffic reports, real-time transit updates, and instant travel reservations. The route recalculates before you have finished missing the exit.

A paper map is a snapshot; a navigation app is a live feed. Navigation became a real-time data service, and the map now updates faster than the road does. The quiet cost is that we outsourced our sense of direction to the network — when it is down, we are more lost than our grandparents ever were.

Entertainment used to run on schedules and shelves. You showed up when the program did.

Before networks, people watched programs according to printed television schedules, rented movies from video stores, and owned physical media — VHS tapes, records, DVDs. Missing the broadcast meant waiting for the rerun.

Now streaming services, online games, podcasts, and social media provide entertainment on demand, almost anywhere. The Friday night trip to the video store has been replaced by the infinite menu.

The scarcity was never natural. Channels, time slots, and shelf space were technical constraints, and when networks dissolved them, the gatekeepers went too. Anyone can publish a show now. The hard part — and the new business — is getting anyone to watch it.

Most transactions used to happen in person, because value could not move without paper or a handshake.

Before networks, people shopped in physical stores, visited brick-and-mortar banks, and commonly used cash or checks. The bank’s marble lobby was not decoration; it was an argument that your money was safe.

Now people shop, pay bills, deposit checks, and transfer money online — and they also face scams, hacking, and system outages. The same connection that lets you deposit a check at midnight lets someone on another continent try your password at the same hour.

Trust migrated from architecture to protocols. Convenience and attack surface scale together — every new thing you can do remotely is a new thing that can be done to you remotely. The trade is worth it, but only if you know you are making it.

Work and school used to be places before they were activities. Participating meant being bodily present.

Before networks, people worked and learned in offices and classrooms. They relied on printed forms and handouts, and job seekers completed paper applications in person or mailed printed résumés to employers.

Now people can apply for jobs, work, learn, and collaborate remotely through websites, video meetings, cloud services, and shared documents. I teach sections where I never share a room with my students, and it works.

The through-line: once work became information flow, it could travel wherever packets travel. Presence stopped being a building and became a connection. That redrew the geography of jobs and education — and it quietly made a reliable connection the new prerequisite for showing up at all.

For most of history, relationships were based mainly on physical location. Your community was, almost by definition, the people within walking distance.

Before networks, relationships developed through families, schools, workplaces, neighborhoods, and local organizations. People were more likely to know their physical neighbors, and businesses reached nearby customers through local newspaper ads.

Now people form communities with others anywhere in the world — around a hobby, a profession, a rare disease, a very specific joke — although they may interact less with the people on their own street.

Networks decoupled belonging from proximity. The gain is real: no one with an unusual interest or an unusual condition has to be alone with it anymore. The cost is real too: you can know someone nine time zones away better than the person next door. Both things are true at once, which is what makes this one hard to score as progress or loss.

Finding information used to require real time and effort. It was an errand — you went somewhere, asked someone, or paid for a shelf of books.

Before networks, people relied on libraries, card catalogs, expensive encyclopedias, and local experts. An encyclopedia set was a serious household purchase, sold door to door and out of date the day it arrived.

Now search engines and AI provide information in seconds — but users must decide whether it is accurate and trustworthy. The answer arrives instantly; the judgment still takes as long as it ever did.

The bottleneck moved from access to verification. The old gatekeepers were slow, but they curated; the network delivers everything, including the nonsense, at the same speed and in the same font. That is why I tell students the real skill is no longer finding an answer. It is deciding which answer deserves belief.

ITN 101 is a whole class about computer networks: how they connect, the Internet, Wi-Fi, and the technical skills involved in building and supporting all of the above. It is worth pausing at the beginning of the semester to contemplate how much our daily lives rely upon these networks—and how much society has changed as a result. What would your life look like without them? Do you ever unplug—or is it too intolerable? Over the next ten days, I will work through ten impacts, starting with the most obvious one.

Communication used to be much slower, often more expensive, and traditional correspondence was usually one-to-one. It could also feel more deliberate.

Before computer networks and the Internet became part of everyday life, people wrote letters with pen and paper, read printed notices and newspapers, and used landline phones. Long-distance calls were billed by the minute and expensive enough that some families scheduled them in advance and watched the clock while they talked. A printed message to another city could take days; an international letter could take weeks.

Of course, telephone, radio, and television systems predated computer networking. They were electronic communication networks, not computer networks, but they helped set the stage. Telephone circuit switching, copper wiring, coaxial cable, and radio transmission all contributed technologies or ideas that computer networks later adapted. I’ll return to telephony itself on Day 10 of this series.

Today, messaging services—including iMessage, RCS, WhatsApp, and countless others—along with email, social media, and video calls make communication nearly instant and inexpensive, even globally. Many modern services are cloud-hosted and designed mobile-first, while users often reach them through Wi-Fi or cellular networks. These services also allow large groups to connect at once. A modern group chat combines immediate conversation, images, video, and a persistent history—capabilities that once required several separate communication systems and much more advance coordination.

Notice that when the cost of sending one additional message approaches zero, delivery stops being the scarce resource and attention becomes the bottleneck. At the same time, digital communication creates new risks and dangers from (mis)information overload, to privacy and surveillance, to possible digital vulnerabilities of critical infrastructure. As much as we may daydream about life before the Internet, there really is no unwind button for society: we live, work, and play in sociotechnical systems that are heavily internetworked today.