About ALOHANet


The backbone of nearly every network you use on a daily basis is based on a system designed to be cheap and easy to implement.

Featuring Tom Merritt.



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Episode transcript:

You know what an ethernet cable is don’t you? Even if you don’t think you do, I bet you do. It’s that cable you plug into a computer, or a router that delivers the internet. I know, so many people are doing WiFi these days so your laptop might not even have an ethernet port anymore. But I bet your modem does. Probably your game console does. Heck even your TV might have one.
For most of the internet’s history the ethernet cable has been the most reliable and fastest way to deliver internet traffic. And we owe it all to Hawaii.
Not what you were expecting me to say?
1968 was the year of the Mother of All Demos, but halfway across the Pacific Ocean one more piece of the future was taking shape on its own.
See, in 1968, the University of Hawaii was like a lot of other colleges. It had a big time-share computer. But the University of Hawaii had a unique issue. At Stanford, if you wanted to use the computer you walked over to the building where it was. In Hawaii, that wasn’t always practical. If you were studying on the island of Maui, it wasn’t a simple matter to walk over to the building on Oahau where the computer was.
Now even Stanford could have remote terminals in other buildings that connected to the main timeshare computer. That was also tough in Hawaii. It would be pretty expensive to run a cable through the ocean between Oahu and the Big Island or any other island.
That’s where Franklin Kuo comes in. Until recently, you wouldn’t recognise where he was born. But Wuhan, China has become famous for other reasons now. When Ku0 was 16 though he arrived in the United States and finished high school in New York City. He then got his bachelors, masters and doctorate in electrical engineering at the University of Illinois in Urbana-Champaign. He caught on at Bell Labs after graduation and worked there until 1966 when he made a fateful decision.
He flew halfway back to his birthplace to take a job at the University of Hawaii as a full professor. And there he met fellow electrical engineering professor Norman Abramson. Together they led a team that solved that problem of how to connect those University campuses on other islands to the timesharing computer on Oahu. And their solution ended up as the foundation of ethernet.
Let’s help you know a little more, about ALOHANet.

ALOHA net sort of stands for Additive Links On-line Hawaii Area. But that’s something of a contrived acronym. They just wanted to call it Aloha. The idea was to use low-cost, off the shelf radio equipment.
So they needed a system that didn’t rely on precision. In fact it had to be fault tolerant.
They decided to use packets of data, an idea borrowed from the ARPANET which was also under development at the same time. But this wasn’t about using the ARPANET, not yet. This was just sharing local data from the central computer to clients on other islands.
The hub was the central computer. It broadcast its packets out to everyone on the outbound channel. It wasn’t trying to target the receiver.
The clients on the other islands broadcast their packets on the inbound channel.
The outbound channel was pretty easy to manage. Everybody got everything and the local client would sort out which packets were meant for it and ignore the rest.
But the inbound packets could be a mess. What if two users on Maui and one on the Big Island all sent their packets at the same time. How would you handle that? The answer? Don’t!
Just acknowledge when you did get a packet. The hub would send an acknowledgement everytime it successfully received a packet from a client. If the client didn’t get that acknowledgement after a certain amount of time, it sent the packet again. Eventually every packet found a clear space in the transmissions and the packet made it through.
This was the main difference of ALOHANet from ARPANET. AROANET nodes could only talk to a single node at a time. So each node had to know if it was OK to talk or it would remain silent. ALOHANet didn’t need to handle giving clients permission to send data. Just keep sending data until it makes it through.
Since the nodes, the hub and the client, didn’t have to coordinate on when to talk to each other the protocol and the hardware could be much simpler. You just needed a separate frequency for outbound and inbound, that way the broadcasts and the acknowledgements from the hub weren’t competing with the incoming requests.
And the packets from the hub needed an address so the client would know if they were meant for them or not.
The first packet broadcasting unit went online in June 1971
That version, now called Pure ALOHA was incredibly simple. If you have data broadcast it. If there’s a collision re-send the data later. The determination of later relied on a lot of math involving where the clients and hub were and how far apart and how long it took them to create packets. That math determined the efficiency of the network. But it worked.
Slotted ALOHA was an improvement that increased the maximum throughput. Stations were given timeslots and could only start transmission at the beginning of the timeslot. You could still send data any time as there were lots of timeslots, but the arrangement reduced collision.
Reservation ALOHA improved efficiency more by reserving a slot for any client that successfully used it. Clients had to wait for an open slot and then reserve it by sending a pocket. Again there were enough slots this didn’t slow things down much and the reduction of collision speed things up.
The principles of ALOHANet went on to be used in satellites, mobile phone networks and WiFi.
But the first and arguably most well known of its uses was by Robert Metcalfe at Xerox PARC in 1973.
Metcalfe was working at Xerox PARC and finishing his doctoral thesis about ARPANet. Harvard had rejected his first draft. He read a paper about ALOHA Net and figured out how to fix a few of its bugs. He then included his bug fixes in his thesis and was accepted by Harvard.
That stuck with him, so when he and David Boggs were figuring out a standard for connecting computers over short distances, Metcalfe included some of the ways ALOHA Net handled collisions as they traveled through the wires.
Two years after ALOHANet went live, ethernet first functioned on November 11, 1973.
It was one of many innovations to come out of Xerox PARC in the 1970s, many of them furthering the work of Douglas Engelbart, and many of them conducted by folks who had worked with Engelbart on the Mother of All Demos. We’ll get into Xerox PARC in the future. Stay tuned.
But let’s get back to the ALOHANet
In October 2020, the IEEE presented the University of Hawaii at Mānoa, the location of the ALOHANet hub, with a plaque commemorating the network as an official IEEE Milestone.
It notes that ALOHANet was the first to demonstrate that communication channels could be effectively and efficiently shared on a large scale using simple random access protocols. You didn’t need permission to send your data, just send it when you want.
Without the need to share computer resources between campuses on multiple islands there would be no need to build ALOHA Net. And without ALOHANet we don’t get wifi, cell networks, ethernet and more.
In other words, I hope you Know a Little More about ALOHANet.

Know A Little More is researched, written and hosted by me, Tom Merritt. Editing and production provided by Anthony Lemos and Dog and Pony Show Audio. The public key cryptography players were Sarah Lane as Alice, Shannon Morse as Eve and Andrew Heaton as Bob. It’s issued under a Creative Commons Share Attribution 4.0 International License.