Part 1 in a series. My take on "Computer or Digital Networking":
(compare to the New Oxford Dictionary definition at the end)
Digital or electronic devices talking to one another, often to facilitate conversations or messages between people.
Almost everybody is familiar with, and uses everyday, electrical and communication networks:
- Electricity, also called "Power Supply"
- Telephone
- Mobile Phone
We have many other "networks" that we rely on in daily life:
gas, road, rail, water, sewerage, storm water, bus, train, tram, airline, TV and radio, food & grocery delivery, ...
Networks are generally
drawn, not described in words, showing their relationship to a branch of Mathematics called
Graph Theory.
Network drawings, or
diagrams, have two essential features:
things and connections between those things. Connections are drawn by convention as lines, and many sorts of symbols are used for the "things" depicted, especially to distinguish and group them. Colour and other perceptual cues are used to make these diagrams more easily understood.
Importantly, the Network Diagram does
not have to be "drawn to scale" like a map to be useful, often the reverse. One of the most famous Network Diagrams, is the
Metro Map. It's useful
precisely because it's not an accurate, but highly stylised, representation of the Network.
Two types of NetworksDid you notice both "rail network"
and "train network" in the examples? Ditto for road and bus?
There's an important difference there,
infrastructure, and
services using them, can both form networks:
- Road and rail networks are fixed, or static. They're networks of physical things, often called "infrastructure", they don't move ("static"), can support multiple uses of them (passengers, freight, large & small vehicles, scheduled or on-demand) by multiple, different users or organisations. They are only of indirect value to people.
- Bus and train networks are not tangible, physical objects, but are dynamic and provide services directly of value (or "utility") to people and organisations using physical infrastructure and "equipment" like rolling stock, buses, trucks, cars, ...
- Services, such as ferry, shipping and airline networks, can operate without a tangible, built infrastructure. Shipping lanes and aviation routes are lines drawn on maps, not physical entities, though they always end with a port or airport, to allow passengers & freight to load/unload.
An example of an Infrastructure, or physical, Network:Think of your electricity power supply and how it gets to you from the power stations.
There are lots of wires & switches, transformers and branching of the wires, until a wire runs past
your house, a wire runs off that to your house's fuse box & meter + main switch, and then more wires run around your house, ending in power-points (power outlets) or fixed appliances or lights + switches.
These
power outlets allow you to access electricity to power devices you want to use as you want to.
That's the Electricity
network.
The
service is the being able to draw power
on demand in your home/premise, which is different to the physical network (
infrastructure) of wires, switches, transformers and generators that merely provide access to that power.
You buy electricity from a Retailer, or in NBN-speak, a "Retail Service Provider" (RSP). These are the same people you now know as ISP's (Internet Service Providers) or full "Telco"s like Telstra and Optus, short for Telecommunications Company. Telcos providing a full range of services across multiple types of networks, such as telephone (landline), mobile phone, leased lines and Internet services.
ServicesBefore you can have a
service, you need a physical
connection to the wires.
Before the Retailer
turns on your service, they have to get money from you, create an account and then
activate your service. To do that, your Retailer has to deal with the people
it buys services from, in NBN-speak either a
wholesale provider or
aggregator that act as a go-between between small Retailers and wholesalers.
The current main wholesaler, NBN Co, brings together lines for 100,000 premises at a "Point of Interconnect" (PoI). There are 121 PoI's. On one side are the wires to your house, on the other,
each RSP has to provide its own connection back to its offices or data centre. Another set of companies own and resell these links, or
backhaul. In the Electricity world, wires to houses are called the
Distribution Network and long-distance, high-voltage lines are called the
Transmission Network which finally connects to the various
Power Generators.
With the Internet, RSP's connect between their various facilities, "up-stream" to each other via either "peering networks", "Tier-1 providers" or directly overseas via international links owned by "Carriers" or Telcos.
But before you can
connect to a network, it has to
pass your house or premises.
These steps create three counts to measure the size of the Network:
- premises passed
- premises connected
- premises active (or activated)
The "take-up" rate is the proportion of premises
activated to premises
connected. [believed to be a correct definition]
Connecting to, or using, a network.Connecting to the Electricity Network, at home, is as simple as plugging a toaster/jug in.
A plug, on the end of a cord or electrical cable is inserted into the socket of a power outlet.
Connecting to the Internet at home, once you have an
active connection, is the same.
Either plug a network, or ethernet, cable (usually blue) into a socket on a modem, switch or router, or connect wirelessly, often called "WiFi" to distinguish it from wireless mobile phone (also called "3G" and "4G") and wireless "bluetooth", a short range way to connect devices like headsets or hands-free phones. You might have used "bluetooth" in your car with your mobile phone or smartphone.
You hire certified professionals to rework the wiring in your house and your Electricity connection, add the fuse box and attach your house to the main supply. Power flows out of the power stations, across the main transmission lines, into local distribution networks (plural) and then into your home for you to 'draw down' when you need/want.
Similarly, larger enterprises hire trained networking professionals to look after their internal Data Networks. Householders and small businesses can hire professionals or attempt to do the work themselves.
Communications Networks IThere are many devices that need to be configured to make
the internet function in your house.
None of those normally matter to you,
or should be seen by you. It's the job of the professionals working for your Retailer to provide you with a simple, reliable and understandable connection, just like the Electricity Network.
There is a
major difference in how you'll connect to the NBN and how you buy ADSL broadband services over your copper phone line now:
- currently, all an ISP provides you is configuring an activating their end,
- You have to provide and configure an ADSL modem/router yourself, trust a friend to do it or, if you're very lucky, some ISP's will sell you a pre-configured modem/router that you get to plug into the phone line and computers. A very few companies sell professional in-home support to make it work.
- in the new world of the NBN, NBN Co will install a device, an NTD (Network Termination Device) in your home that your RSP can configure and administer. It brings a working Internet connection into your home, without you need to buy or configure anything.
- You can plug a single device directly into your NTD, but it's unlikely you'll do just that, to get the best use out of your Internet connection, you'll want to spend more.
- At the very least, for security reasons, you should install a router/firewall. These are often available with WiFi, USB and multiple ethernet ports, useful in home offices.
- Most people will choose to wire their houses, just as Enterprises wire their offices. This means adding a router/firewall for security, ethernet switch(es) to connect more devices, a WiFi gateway to use laptops, tablets etc, and having ethernet sockets installed in wallplates.
- Fixed wiring & wallplates have to be installed by certified cablers.
- Anyone can plug in a lead (non-fixed cable), a switch or router.
Communications Networks II
A (digital) communications
network is pretty much the same as the Electricity Network. Think of the phone
network, a bunch of wires and specialist equipment connecting electronic devices together.
The only difference is there's more two-way flow:
while you download/draw-down lots of bits, you also upload a lot.
Data doesn't now come to you in a continuous flow, but in
packets. In Olden Times, data only came via a continuous stream: exactly the same transition as Direct Current (DC) to Alternating Current (AC).
Batteries use and produce DC - why you have special devices (chargers) to change AC into DC. It's
good for local use, bad because it doesn't work over long distances.
Resistance in the wires creates heat and the power is dissipated along the way, until nothing usable is left. Thinner wires create more heat, thicker wires less heat, but get very expensive. Resistance heating is how electric heaters and old light globes (
incandescent) work.
AC has a bunch of useful properties that make it possible to transmit power efficiently over long distance, all related to the stop-start nature of it. There are still losses, but they are managed and cabling costs can be minimised because the voltage can be changed easily.
Phones and the InternetA major difference between electricity and data is identifying destinations. Electricity is 'anonymous', you can't identify where any piece of power came from, and every watt is identical (though voltage
may vary).
But data is like a phone call, every
connection needs
two ends or parties (at least) AND conversations are 'directed', both parties need to be exactly identified AND the bits are all different, and order is important.
Think of phone calls - you want the sounds reproduced
exactly as they come out of your mouth. If they are jumbled up, it's not speech anymore, the principle that scramblers use.
Something less obvious with data is that
every download you make has to be checked for errors. Each of those data 'packets' is checked when it arrives and a tiny message sent back to the sender saying "OK" or "Not OK, send it again".
These are "
Acknowledgement Packets", shortened to "Acks" and "Nacks", or Negative Acknowledgements.
For most applications, you want a
perfect copy of the original data and are willing to trade time (resending) for perfection. A spreadsheet, email, digital photo or movie won't be intelligible if the bits are corrupted
"Download" capacity is as important as "upload" capacity. Data & phone networks need to work in both directions. If the Ack packets can't get back to the other end, it will slow sending, or stop all together.
Speed, Latency and Throughput: baffling you with B/S
There is no one measure of the "speed" of your Internet connection.
As an informed consumer, you need to understand the difference between three measures, how they relate and the questions to ask your Retail Provider or ISP when "the Internet is Slow".
- Politicians and salesmen will emphasise the raw speed of the line into your house. It may be 12Mbps (Mega-bits per second, not bytes, they are eight bits long) or 100Mbps.
- Obviously, 100Mbps is always faster than 12Mbps! Not necessarily. Which is why NBN Co goes to some lengths to try to inform consumers of what they can expect.
- Congestion, Throughput and Latency are networking terms you need to become familiar with.
- Anyone who's commuted in a large city is already too familiar with the concepts, if not the terms:
- Congestion, or Traffic Jams, as seen on roads in Peak Hour.
- Throughput is how many cars an hour travel down a road, or for an individual car, the average speed for the entire trip.
- Latency is the time taken for a car to get from Point A to Point B.
- Round-trip time, From A to B and back again, is also important on the Internet. If A to B is fast, but B to A is congested, connections will slow down.
- Link Speed, also Access Rate, is the fastest speed you travel at any point on your journey, not the much more important average speed. If you spend 15 minutes travelling at 100kph on a freeway, and a total for 45 minutes each end travelling just 5km, which matters most to you, the door-to-door time or whizzing along the freeway?
- If you buy a 100Mbps link from your Retail Provider, your RSP/ISP may only purchase 2.5Mbps of backhaul capacity for you, a 40:1 "over-subscription".
- Most of the day you'll not notice you're sharing the link with 39 others!
- At 6:30PM when everybody sits down to watch TV, you will all notice and not be happy.
- Although you have 100Mbps inside the NBN Co network, you will only get 2-4Mbps throughput from your RSP.
- Retailers offering cheaper plan can save costs outside the NBN Co network, they can buy very small "backhaul" and "upstream links".
- A 12Mbps link without congestion inside the provider network will beat the pants off a 100Mbps connection during Peak Times, but not for the rest of the day when its quiet and you, like everyone else, aren't using it.
- Congestion leads to high-latency which can lead to problems with streaming audio and TV, downloading files and webpages and especially, making phone calls over the Internet.
- Congestion inside your RSP will make any real-time service, like phone calls, Skype or streaming video, unusable during Peak Times.
- What you're interested in as a consumer is the sustained throughput that your Retail Provider is prepared to guarantee.
- ADSL, VDSL and Fibre to the Node, FTTN, networks have a common problem: congestion on the Fibre uplinks from the copper ADSL/VDSL modems or DSLAMs (Digital Subscriber Line Access Multiplexers) back into the NBN Co network.
- Direct Fibre to the home doesn't have this problem: you have a guaranteed access rate right back to the end of the NBN Co network, the PoI.
- Fixing congested uplinks from nodes is very expensive and very slow. This was a long-standing problem with Telstra RIM's, a hybrid phone & broadband node network, in Gungahlin, that took many years to fix.
- It is not considered "Cost Effective" by Telcos to install extra-capacity in the nodes or the fibre links that connect them back to the network. Demand for Internet capacity has consistently outstripped forecasts, leading to persistent local congestion for most users of FTTN services.
Conversations in Real-Time are different to downloading files and webpagesLike CD's, audio, such as a phone conversation, can be "lossy" - our hearing can tolerate some missing data, BUT it can't tolerate
delayed or scrambled data. Because speech is "real time" and connections must work within very tight timeframes, shorter than the "round-trip delay" between two ends, we can't Ack/Nack & resend.
Especially, our hearing can't tolerate packets taking different times to arrive. If you need 50 packets a
second for a phone call, one every 20 milliseconds (msec), then you can't send nothing for half-a-second and send 25 packets all together in a single burst.
For a phone to reconstruct reasonable quality audio, you need packets to arrive
predictably, with little variation. I.e one packet every 20 msec with maybe 0.5 - 1.0 msec variation... We call this "jitter" because when you look at traces of it, they dance around and look "jittery".
RecapTo recap, plugging a computer into a network is identical to plugging in your shaver, toaster, jug or a charger into electricity.
It's the job of Professionals to hide all the complexities from you, the end-user.
The NBN, with fully-installed and remotely configured and managed NTD's is a bit step forward: householder can just plug into
For security reasons and to get WiFi for laptops and tablets, you'll want to at least install a router/firewall. Some people will run fixed cabling around their homes so they can plug-in many devices and connect them to the Internet.
"Download" capacity is as important as "upload" capacity. Data & phone networks need to work in
both directions.
"Speed" isn't simply how fast your first link runs, but the
sustained throughput, especially at Peak Usage times and the "latency" or delay on the line.
Downloading files and webpages requires no congestion of uploads, or the packet Acks will slow and stop, stalling your downloads.
For real-time services, like phone calls & Skype over the Internet, we can tolerate the
odd wrong or lost packet, but can't tolerate not getting packets On-Time, or "jittery"
From the
New Oxford Dictionary.
Network:
1.
an arrangement of intersecting horizontal and vertical lines.- a complex system of roads, railroads, or other transportation routes : a network of railroads.
2.
a group or system of interconnected people or things : a trade network.
- a group of people who exchange information, contacts, and experience for professional or social purposes : a support network.
- a group of broadcasting stations that connect for the simultaneous broadcast of a program : the introduction of a second TV network | [as adj. ] network television.
- a number of interconnected computers, machines, or operations : specialized computers that manage multiple outside connections to a network | a local cellular phone network.
- a system of connected electrical conductors.
