we had a tweet recently suggesting we do a video on aloha net which i think we've
had brief discussions about before but it's some really early form of kind of um network
is it was it something to do with hawaii i mean you know you're the hawaiian shirt guy
yeah so um yeah no aloha is probably the sort of grandfather of pretty much all networks that we
use today i think it was 68 the norman abramson started to work on this technology along with
others and the technology that was used has influenced ethernet it's influenced gprs
satellite communication is still in use today in various forms so it was based in hawaii he
was at the university of hawaii and they had a big expensive ibm mainframe that they wanted to
provide access to but because hawaii is a series of islands they couldn't just run
cables everywhere and so they decided that they would build a wireless network in 1968
this wasn't off-the-shelf equipment right yeah they had to develop this all themselves you
couldn't just go and buy a cisco wi-fi access point and stick it up on top of a tower because
cisco hadn't been created yet that was still 12 years in the future if not more 15 years in the
future and of course cisco only existed because of the technology that was developed as part of aloha
so they were literally developing all this from themselves and so what they had is that they
had two radio frequencies that they'd use they used one to transmit from the ibm computer out
across all the islands of hawaii and then they had another radio frequency that they used to transmit
back from all the terminals that people were using back to the central computer now they had a sort
of a simple situation because they had a very definite model that they had one computer the
ibm mainframe it was at this point they had data going from the ibm mainframe to all of the other
machines and they were receiving data from many machines transmission was a one-to-many problem
and that's great because you then only have one computer that's sending anything so that computer
can break its data down into packets which is what they did and then sequence them so they get sent
out and there's no sort of corruption as that data is transmitted actually what they did was
that they had another computer that sat in front of the ibm mainframe they had a hp computer they
bought an hp mini computer and they dedicated that to doing all this processing and splitting
data into packets reassembling it passing the data back on to the ibm mainframe they refer to this
hp computer as the menu hewn and i apologize if i've mispronounced that name which is a hawaiian
word for elf they sort of played on the word elf because it was based on some of the ideas that
were being developed as part of the arpanet for the interface message processor so they were sort
of imp elf you can see how the sort of train of thought moves along so they have this secondary
computer the menu that was sitting between the ibm and everything else so it got data from the
ibm and could then transmit it out as packets to all the terminals wherever they are over the radio
frequency in a serial fashion modulating it deep as it needed to be and they just transmitted it
out so sending data from the ibm to the terminals was fine the terminals could then receive the
packets see if it was for them if it wasn't displayed on screen if it wasn't you just ignore
it and so on they didn't worry about security in those days i'm sure it was just clear text and
receive it but they had much more of a problem getting data back so when you type something into
the computer you need to send that data back to the ibm mainframe so that you can deal with things
and so what they realize what the sort of key contribution that norman abrams and and the
others who are working on this sort of realized was how can we send that data back to the ibm
computer via the menu in as simple a way as possible and the problem you've got is that
you've got several computers dotted all around the islands
and it's potentially possible that two of them might transmit at the same time and if two of them
were to transmit at the same time it's the same as two people speaking at the same time they would
interfere with each other and the computer at the other end wouldn't be able to receive the signal
and so they would corrupt each other's messages so they were trying to make sure that any computer
could transmit at any point but that you didn't have corruption of the messages as they were sent
what they realized was that they didn't need the data to be received correctly necessarily the
first time they received it that it would actually be okay if it could be eventually received that
you might transmit it and it wouldn't get received so then you'd have to transmit it again
and so what they realize if you relax things and say okay we want eventual packet delivery as it's
called we want to be able to receive it at some point you can actually start to say well okay we
can transmit at any point to make best use of the bandwidth i mean you could use say time division
multiplexing where you break your channel your radio channel up into segments that are some
percentage of a second long and you say okay this computer can only transmit in that point of time
and then this computer can only transmit at this point of time but if you do that you find that
you're not actually using the bandwidth that well because most of the time particularly on something
like a terminal people are typing and they'll type something then they'll read the response
and then they'll type something else actually that doesn't use the bandwidth you've got available
that effectively what they realized was they could make best use of the bandwidth by just saying okay
you can send the packet whenever you like so any of the terminals if they had some data to be sent
you type something into the keyboard it would then just attempt to send that data to the ibm via the
menu so it's modulated into the radio signal send it out over the radio transmitter it'd be received
by the menu and then it'd be sort of decoded and passed to the ibm computer to do whatever it
was you wanted it to do and if you were the only thing transmitting that would be absolutely great
you could send the data out and it would be received but what happens if there's two of you
transmitting at the same time so you're typing on your computer i'm typing on mine and we send the
data at the same time well of course the data is received by the menu is a mix of the two messages
so it won't make any sense it'll be corrupted but they realize that this was okay because what they
got the computer to do is that when you receive the data correctly it sent out another bit of
data back to the machine that sent it saying i've received what you sent correctly so you
would send your data from your terminal it would get sent up and the menu you would receive and
you would send a message back saying yep got that acknowledge and then you'd know it'd been received
and what they realized was if you just send it out and you don't get that response
that means the menu didn't receive it and if the many who didn't receive it you just send it again
and then hopefully that time he gets through and then you get the acknowledge response and
if you don't you send it again until you get the acknowledged response and your terminal
does exactly the same thing it gets the doesn't get an acknowledged response so waits a certain
amount of time and the key thing is you need some sort of algorithm in place to sort of decide
who sends after what sort of time if everyone just waited the same amount of time you'd get
the same sort of problem and things and so it just waited for a short amount of time
pick it randomly use it based on the station id various approaches they could use i can't remember
exactly which one they used in the low car it doesn't matter and then you resend your data and
eventually it will get through and what they found was that this actually provided really good use of
the bandwidth most people could transmit when they wanted to but could also detect packet collisions
when two people tried to transmit at the same time and recover from them by resending the packets now
it meant that the terminals had to have a little bit of intelligence to them to be able to sort of
keep track of the packets and check whether it'd been received or not but you could implement that
relatively straightforwardly and so it produced a system that could work and this was operational
by about 1971 and used all over hawaii and then as they were developing it they did some sort
of later improvements one thing they realized is that if you just allow people to send at any point
then you could have a packet collision which could destroy two packets
if only a single bit collided in between them both packets would be destroyed um you wouldn't
receive them correctly that's a better way of putting that and so you'd have to resend them
so what they actually did in a slightly later variation of it which is known as slotted aloha
is that they said okay you can transmit at any time but you must align it to certain time points
and so you have all the machines synchronized and so you can either transmit say that 0 seconds or
0.001 second or 0.002 second for example and if you do that you then either get a packet collision
where the whole packets collide because they're transmitted at the same time or you don't get
a packet collision because if someone starts transmitting something and someone else wants
to transmit say about halfway through it it has to wait until the next transmission point to
which to do it at which point they won't collide whereas if you can say transmit at any point then
you can sort of start transmitting and then i start transmitting and it destroys them and that
could just sink that could just be as simple as a single bits get corrupted at the end at which
point you've destroyed the whole transmission of two packets when if you'd waited one bit neither
packet would have been destroyed so that was the sort of improvement that they developed
now i said that aloha net was sort of the grandfather the granddaddy of all the sort
of different networks and that's because when people were developing things like ethernet and
xerox park in the sort of mid-70s they'd heard of the work it been published and they'd heard of the
word that norman abrams and his team had done in hawaii and they sort of took the same ideas
so ethernet for example run originally ran on a single piece of wire that stretched around
the office and the machines were literally physically clamped onto the ethernet cable
so they but they still use the same ideas they still said okay anyone can transmit at any point
um if the data doesn't get received then we'll retransmit things but because they were on a
physical piece of wire they could do some extra things to sort of for example they could see
whether someone was already transmitting and so they could sort of say okay someone's already
transmitting i'll wait until they've finished so they could sort of get better performance
but they were sort of very much aware of the work that norman and his team have done
and we're building on top of that and that's followed through into things like gprs
satellite communications they're all still using this sort of idea you still get straight aloha
networks out there i think laura wan the sort of iot things at times can work in that sort of a
fashion that you just literally send things out wait for acknowledgement if you don't get
that acknowledgement then you send it out again after a certain amount of time until the data is
eventually received so yeah really great piece of work it provided wireless networking for the
hawaii community of the hawaii academic community of computer scientists let's limit this to the
people who are actually using it probably way back in the 60s 70s and yeah has really influenced the
way that sort of networking technology has been developed diagram i'm drawing very badly here and
so on so you'd have two sets of pulses one delayed from the other it's what we call quadrature
encoding we can actually derive from that which direction the signal is moving in so yeah they're
very different to the originals and the important thing is that we don't know what went into here
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