AV Magazine Article

Just a quick note; I have an article in AV Magazine, Issue 21:

http://www.av.net.au/

http://www.av.net.au/contents/issue_21/soh_network.pdf

Since it relates to a lot of the things covered in this blog I thought I should post it.

Have a good one!

Layers of the Internet - Part 4

If you are new to this area, or are looking for the first three parts of this series, please use the following links:
Layer 1 - Link Layer
Layer 2- Internet Layer
Layer 3- Transport Layer

To recap quickly, the Link layer is the physical connection between devices (be it wireless, electrical or optical).
The Internet Layer is the layer that deals with the virtual separation of the entire Layer 1 network into smaller, virtual networks, and also allows traffic to be routed from one side of the planet to another.
The Transport Layer deals with two main things; where the data goes inside the devices that receive it, and also how the packets are passed around the networks (e.g. error correction protocols - re-sending a packet that never arrived at the destination.


Layer 4 - The Application Layer
For a second, let's think about what we are trying to achieve with a data network. We are trying to move information (be it computer data, an image, live audio... anything) from one point to another. If we look at what we've done in layers 1-3, we can see that we've done nothing but move the data from one end of the earth to the other.

Layers! Layer 4 is like the river and the clouds above; they rely on the lower layers of the earth, but they don't really care about them

.
But before any data can be delivered, we have to actually work out what data we are going to transport, why we around going to transport it and then what we are going to do with it at the other end. Data is useless unless we actually do something with it. For example, you could send a friend a photo, but if they can't view it then there was no point to transferring the data in the first place.

This is where the application layer comes in. It is the layer of the Internet that interfaces with the Users, but it is also the layer where we actually change the information that we are sending.

But Layer 4 isn't all about the Users, there's a lot of background processes involved. Let's have a quick look at a simple internet action; checking this blog:

• Step 1: You open your browser and type "http://arts-comms.blogspot.com". This is the start of the process; you enter a small amount of data; 30 characters. It's not much when you think about it.

• Step 2: Your browser tries to find the address of this page. If you were going to send a letter to a friend you couldn't just write their name on an envelope, post it, and hope for the best. The "Human-readable" Universal Resource Locator (URL) is similar to you friend's name; you can use it to describe them and look them up, but it isn't exactly an address. So, before your browser starts downloading this page, it looks out for a Domain Name Server (DNS) that will translate the URL into a TCP/IP Address.This address combines the Layer 2 and 3 addresses for the webpage. In this case the IP part of the address is 74.125.71.132, and the port is 80. This could be written 74.125.71.132:80.

• Step 3: Your browser now requests a session with the blogspot.com webserver. Now that your browser knows where to look, it will send a request to 74.125.71.132:80 to ask if it can start talking to the Server. The server will normally check that there are no bans on your device, or any other reasons that it wouldn't want to talk to you.

• Step 4: The Server opens a port and allows a session to begin. Should everything in Step 3 check out, the server will allocate a port number (this can be random, or fixed; it depends on the server) and then sends the information to your browser, letting it know that it's all good to go.

• Step 5: Your Browser requests the Webpage. Now that the Server and your browser are talking, the browser finally asks for this page, sending along with the request any additional information that might be required (e.g. your login details, or which exact page you're requesting).

• Step 6: The Server retrieves the webpage from its hard drive, and then transmits it as a series of packets. If you were to send a entire webpage as a single packet, it would be huge, and that would slow it down through the Internet. So the Server splits up the webpage into a number of small packets, adds a bit of information to let your browser know the order of the packets, and then transmits them through the network.

• Step 7: Your browser assembles the webpage, checking for errors as it goes. There is always a chance that some packets will get lost in transit. However, since the server has added information for your browser, it will know if anything is missing. If something doesn't make it then your browser will re-request the missing pieces.

• Step 8: Close the Session. Once everything has been checked, and you're happily reading away, the browser sends a message to the Server to finish off the session that was opened in Step 4. Once this is closed the connection disappears from the internet.

So, from your 31 keystrokes (including the "enter" key at the end) your browser and the Server have been communicating at Layer 4. You'll notice that I barely mentioned the Layer 1-3 protocols; and that is because  at Layer 4, just like all of the layers below it, the lower levels are transparent. It doesn't matter that I'm on a wireless connection and the server is on a optical fibre connection; they are connected up to Layer 3, and that's all that matters.

I'll be doing little write-ups on the various protocols as I continue to write this blog, so please stay tuned to the Glossary. Once I write an article on each protocol I will link it from the Glossary.

Layers of the Internet - Part 3

Before I start I would like to make a minor classification.
The "Layers" to which I am referring are the Internet Protocol layers, as specified in RFC 1122. I feel this model is more appropriate to the topics that I cover in this blog.


For those of you that wish to delve further into Networking as a subject, please refer to the Open Systems Interconnection (OSI) model. This model is the one that you would study in a networking degree, however it is slightly too specific for the purposes of this blog.




Layer 3 - The Transport Layer
In the previous two parts of this section of the blog, we looked at Layer 1 - The Link Layer and Layer 2 - The Internet Layer. In those layers, we say that each device was physically connected to all others, but with a bit of technology, we could divide up that huge network into smaller little sections.

I'll admit, it's difficult to visualise the Transport Layer. Here's some model trains.

As we have now connected on Layers 1 and 2, we can assume that our two devices are talking to each other. At this point it doesn't matter how that happens, or how many switches the packets have gone through in order to get from A to B. The tunnel through the Internet has been made, and for all intents and purposes, it isn't broken until the connection is shut off.

Layer 3 tells us two things; how a packet will move through a network, and where it will go when it gets there. In order to understand this we will examine two of the main Layer 3 Protocols, Transmission Control Protocol (TCP) and the User Datagram Protocol (UDP). And yes, if you noticed that the "TCP" looks very similar to the "TCP" in "TCP/IP", you'd be correct. Since TDP is the most common Layer 3 Protocol, and IP is the most common Layer 2 protocol, people refer to this model as the TCP/IP suite of protocols. However, due to the complexity of the protocol, I will start off with the UDP.

User Datagram Protocol
Take a moment to think about how many different network-enabled programs you are running now. On my machine I have two browsers with a few tabs in each, Skype, two email clients, a couple of automatic software updaters.... the list goes on. Now think about a lonely packet headed my way. It has the MAC address (from Layer 1) so it knows where my computer is. It has my IP address (from Layer 2) so it knows how to find me on the network. But once that packet finds its way into my wireless adaptor, where does it go? Is it a part of a webpage, or a message from a friend via Skype, or an email?

Both the UDP and TCP use a number, called a "Port," to direct a packet to the program that it needs to arrive at. Your network adaptor reads the Port number and forwards the data to the appropriate program for processing.

A UDP packet contains a bit of information that identifies it as a UDP packet and a Port number. That's about it. The advantage of this is that you have a smaller packet, which means faster transmission times. We'll look into this a bit later.

Transmission Control Protocol
Whilst a UDP packet basically only has the Port number, a TCP packet contains a lot of additional information. TCP packets can contain information relating to tracking and delivery protocols. For example, a TDP packet could identify that it was the 15th packet in a sequence, and that the receiving device should send notification of receipt.

This information can be used to make sure that packets that have been lost due to network errors can be re-requested and re-transmitted. Packets that take too long can killed off. Devices can send packets to each other to check the speed and path of the transmission.

All of this extra information makes the packets bigger, and hence slightly slower. However, in any non-real-time application this extra transmission time doesn't make much difference. Since very few transmissions actually require real-time transmission, the more Robust TCP is more common than UDP.

The main place we see UDP packets in the Arts industry is in audio/video transmissions, like Dante or AVB.  UDP also requires less programming, and thus it is more common in smaller applications, so you may come across UDP systems in some control software.

"Layer 3 Switches"
Normally a switch will read the Layer 2 information (the IP Address) in order to find out where to send the packet. As we saw in the Layer 2 article, this is used to prevent every device receiving every packet on the network. If a switch only does this, then it is known as a Layer 2 switch.

However, some switches can be programmed to read the Layer 3 information. Switches can read the TCP information to adjust flow control (e.g. if the switch is over capacity, it can request the sending device to slow down the transmission rates). This can also allow for the ability for a switch to send more important packets before standard packets (e.g. Telephone or real-time audio is transmitted before a webpage).

Interesting Enagadget article on Whitespace

http://www.engadget.com/2011/09/16/fcc-to-test-white-space-database-at-its-own-pace/

I know that I have been hoping to drip-feed information here, but occasionally I will need to jump the gun.

For those of you that don't know about the "White Space," it is referring to the spaces in the RF Spectrum that will be left between Television Channels, leaving clear bandwidth for devices to communicate on.

This spectrum remains unlicensed, and thus manufacturers can use this space for data transfer. Wireless Microphones operate in the same space; they are designed to work in the TV channel space, but in the "gaps" between channels. Of course, the introduction of more "White Space" devices sends shivers up most Radio Mic Technician's spine, because it potentially means that a device will suddenly appear in the middle of your spectrum... when you least expect it!


The reason White Space Devices didn't work so well in the past is due to the difference between Digital and Analogue TV transmission. Analogue is much less predictable, however Digital Channels stick out like a sore thumb to even the most basic devices. So, when you turn off the Analogue stations, you make it a lot easier to make White Space Devices.

It shouldn't be confused with the Digital Dividend, which is the space at the high end (~800MHz) of the spectrum that will be "empty" (i.e. no TV channels) once the Analogue TV stations are turned off. This spectrum will be sold off, and in the US it made a hell of a lot of money.

I will go into all of these topics in much greater detail, but for those of you that are hanging on any bit of Spectrum Information, please enjoy the link.

The layers of the Internet - Part 2

The Internet Layer
In the last post I explained the basics of Layer 1 of the Internet Protocol; the Link Layer.

The Link Layer is where all devices are physically connected, either by wireless (e.g. Wireless LAN or 3G) or by a wired (e.g. Ethernet "Blue String" or ADSL) connection.

Whilst this is a great concept, if every device were to receive all of the data transmitted on the Internet, then we would be slowing down the process beyond belief.

Enter Layer 2 - The Internet Layer

This is Layer 2

On a network drawing, a network was always drawn using standardised symbols. Since everything that was on the "Internet" was connected at Layer 1, it no longer mattered how things were connected. You only had to show that there was some kind of connection.

And so the network symbol for the "Internet" became a cloud. It was some ethereal entity, floating out of the reach of Network Administrators across the globe.

Unfortunately marketing departments caught hold of this analogy, and thus Cloud Computing was born. You can see the "Cloud", and it brings you good things (like shade, and rain for your crops) but you have little to no power over it. It's there whether you like it or not. 

So how does it work?

Packet-Switching Networks

In this previous blog post I explained the anatomy of a standard Internet Protocol (IP) Packet. Packets are the currency for IP networks, and indeed the entire Internet. Without repeating myself too much, they contain two main parts; a "Payload" (the data that you want to move around the network) and a "Header" (which contains the addresses relevant to the Data).

In order to understand how the Internet works, we are going to have to introduce our first specific piece of network hardware: the Switch.

The image above is that of a "Switch," and it is a common thing to be found in data centres across the world. However you are reading this blog, somewhere along the line you are connected to a Switch. It might be a little 4-port switch that came with your ADSL plan, or you might be connected to a commercial-grade switch (like the one above) at work.

Switches are the building blocks of the Internet, and they elevate matters from Layer 1 (Link Layer) to Layer 2 (Internet Layer).

Every blue or pink cable in the above image connects to a device; a telephone, a computer, a printer etc. This is the Layer 1 connection. You can tell they are working by the blinking green lights. The Orange cables connect those switches to other switches, which the connect to other switches... until they reach whatever destination they need to get to. These connections are called "Uplink Ports", as they are headed up towards the "Cloud".

When a packet is sent to a switch, it "opens" it up and reads the "Header" (not the "Payload"). In the "Header" is all of the addressing information that the Switch needs to send the packet to where it needs to go. If the destination address is connected directly to the switch, then the packet will be sent directly to that device. If not, then the switch will send the packet to the "Uplink" port, at which point the next Switch will repeat the same process until the packet arrives at its destination.

By doing this, Switches make sure that you only receive the packets that you need to read your emails, browse your websites, control your motors, or route audio. Switches don't care what your packet has in it, so long as the address in the Header is valid.

The address used by the Internet Layer is the Internet Protocol (IP) Address. I will go into (much) more details about IP Addresses in a later post as the topic is as broad as the Internet itself. Suffice to say, a common IP address is an 8-byte address, usually rendered in four groups of numbers from 0 to 255, e.g. 192.168.0.254.

Once two devices are connected at Layer 2 they are considered "Networked" and can now communicate as if they were in the same room. Layers 3 and 4 deal with how they communicate, and we will cover these in the next blog post.

The Layers of the Internet - Part 1

The Internet is a complex place. There are many articles about the history of the internet, and it's a little beyond the scope of what this blog is about, so I won't go into it too much.
Suffice to say, the only way the internet works is through rigorous adherence to global standards. These standards were developed over the 15-year genesis of the Internet from research labs to commercial use.

One of the best ways to describe how these standards, and indeed the entire internet, works is known as the "layer" method.

Layers are a great way to explain many things, and the layers that we will be looking at today not only apply to networking, but to almost every form of computing or digital signal processing.

There are four layers in the "standard" Internet topology:

• Layer 1: Link Layer. This is the physical link between devices
• Layer 2: Internet Layer. This is the "virtual" layer where the data moves around networks
• Layer 3: Transport Layer. This layer defines how data moves around devices
• Layer 4: Application Layer. This is the layer that shows how data is shared between programs.

Those short little descriptions probably mean very little to most of you, so let me break it down a little bit more.

The Link Layer
When I think of the best way to describe the Link Layer, this image comes to mind:

What you're looking at there is a fairly typical "Distribution" switch, and a lot of optical fibre.
The Link Layer is the only physical connection layer in the Internet Protocol. It defines all the different ways that you can connect devices together if you want them to be on the internet.
If you put your mind to it, you could easily rattle off a lot of the different standards that are in the Link Layer, for example:

• Wireless Networking 
• Ethernet networking (a.k.a. "Blue String" - those blue cables that we are all familiar with)
• Fibre Networking 
• ADSL (Asymmetric Digital Subscriber Line - The way most of us get our Home internet)
• 3G/HSDPA - The wireless Broadband that most of us use on our phones.
• DOCSIS, a.k.a "Cable Internet" - networking over Coaxial cable, similar to Cable TV (Thanks djzort)

The list goes on. The greatest thing about the "Layer" system of the Internet is that it doesn't matter how you connect devices together at the Link Layer, so long as they follow the Link Layer Standards. As soon as you have that "blinking light" that shows you are connected then you can start passing information around the Internet Layer.

The Link Layer extends across the entire Internet. Just ponder on that for a second; every device that is connected to the Internet is in some way, shape or form, connected. The Link Layer is the only layer at which every device is connected; once you start moving into the "Virtual" layers (layers 2-4) you start segregating devices into separate virtual networks (or "subnets"). But for now, let's just muse on the topic of every device acting together in synchronism.

The last thing that I will mention about the Link Layer is the address that applies to it. Obviously there is no point in connecting every device on the planet unless you knew which one you wanted to talk to. Therefore every device that connects to the internet has a unique address. This address, known as the Media Access Control (MAC) address, is a unique number assigned by the manufacturer.

The MAC Address is a 48-bit number (that is, 48 "1's" or "0's"), which makes for about 300 Trillion different addresses. Every single device that is capable of connecting to a network has a MAC address. This laptop, for example, has two addresses; one for the Wireless connection and one for the hard-wired connection. Even so, the IEEE doesn't expect that we'll run out of MAC addresses this century.


We'll look at the Internet Layer next time (probably in a couple of days). I thought it best to break things up for now.

Cisco Unveils new Wireless for Stadia etc

Just a quick one today (after my triumphant rant last week).

Cisco have just announced a new product for doing wireless networks in large areas, like stadia.

I obviously haven't covered the topic yet, however providing Wi-Fi access for an entire audience of thousands proves a lot harder than you'd expect. With the amount of access points (Wi-Fi Antennae, for want of a better word) required to support an entire audience you tend to get a lot of interference. 

I haven't tried, or even seen, Cisco's solution, but as mentioned in last week's post they are one of the world leaders in networking. If they say that it can work, then I have a fair degree of confidence that it will work.

Their press release is here:
http://www.cisco.com/web/strategy/sports/connected_stadium.html

I'll be reading this over the next couple of days, and if I determine anything I will post it here.

It can be done!

Converged Production Networks are possibile

 

After speaking to a lot of people in the last couple of days at SMPTE Sydney (and Entech... let's not forget about Entech....) I thought I'd write a quick post to summarise what it is that we are doing at the Opera House.

About three years ago I got talking to the in-house Information Systems (IS) team about the possibilities of a "converged" network. The IS world has been talking about Convergence for about a decade; I even operated the sound at a few of their conferences on the topic. Convergence was nothing new to them, and when I brought it up they were pretty confident that we could "do it".

By "it" I mean combine all of our IP-based services onto one network. At the moment, that includes:

• The SOH Webpage
• Ticketing/Box Office Services
• Security Cameras
• Telephones
• The Lighting Control Network
• Audio streams/distribution for the Concert Hall and Opera Theatre
• Audio and Amplifier Control for the Concert Hall, Opera Theatre and Drama Theatre
• Motor control for the Concert Hall PA
• Stage Communications

Plus all the other things that we don't think of on a daily basis.

I won't lie; it wasn't an easy path. We made a few blunders, but nothing too serious. Okay, we did crash the network, twice. But those crashes were actually caused by separating services rather than combining them.

Why did we do it?

There are a number of reasons.

Firstly, and most importantly, companies like Cisco and HP have been doing networking for decades. It's what they do best, and the reason they are on top is because their stuff works. All the time. If there is a fault then I get an email straight away. The Network admin gets an email. If we dont' fix it, then the Executive gets an email. 

In terms of reliability you can't beat these professional systems.

Next up is cost. There is only a need for one network administrator, one set of spare parts, one warranty contract. We don't need to duplicate infrastructure, and that means that things get cheap, quickly.

In terms of service, I can run out a single fibre cable, and within 10 minutes I can set up a whole production office/box office/security office, all running off one of my switches. We do this all the time. A production manager will want to be near their event, but will also need to answer their phone and check their emails. They can now do all of that, and sell tickets on the side. Or they can be on a comms panel, talking to the stage crews.

Basically, there are advantages for days. 

Separation and Show Criticality

Detractors will mention things like separated services and "Show Criticality". 

In terms of separation, the IS world are already leaps and bounds ahead of us in the production world. They've been keeping your Credit Card number safe every time you swipe it at an EFTPOS terminal for years. They can link offices half-way across the world and make you think you're in the same building. There are so many ways to keep networks "separated" over the same infrastructure that's it's a little scary.

And critically? Cisco switches are used in military installations and banks all over the world. I know that losing a show is a dreadful thing in our world, but in terms of really needing things to work first time, every time, those kinds of industries have us beaten, hands down. 

Besides, would you trust a product with a R&D team larger than most theatre companies, or a company that only has four people on staff? 

We all know that the best way to get results is to get trained professionals.

You don't ask a flyman to run a lighting console, so why would you ask a Lighting guy to run your network?

Anyway, I've gone on a little longer than expected here. The moral of the story is to plan your network. If you're not a network planner, then maybe ask around for one. Heck, email me on camoneillsystems@gmail.com if you'd like. I'm more than happy to look over network designs, or even just to chat about our network.

For now, let me just say it one more time; it can be done.

What is communication?

Communication is the transfer of information between two or more parties. It can take many forms.

It can range from something as simple as a Stop sign to networks as complex and infinite as the Internet.


Communication is the basis of society. Without the transfer of knowledge or ideas there is no framework for the interpersonal relationships that make up our, or any, species.


Take a TV drama for example.
This is a highly polished form of communication. The writer, director, actor, cameraman, vision mixer, audio mixer... all of these people communicate their own version of the story to the viewer.

Or take our Stop sign; it is a message from the city planners that the intersection you are approaching is dangerous, and you should stop and survey the road before proceeding.

Communication can be as hard or as simple as you would like it to be. Therefore, in order to pull focus on this blog, I would like to define which forms of communication I will be dealing with.

The purpose of this blog is to inform and encourage theatre and broadcast professionals (my definition of the Performing Arts) about the methods of communication that directly affect them.

This includes, but isn't limited to:

• Telephones
• Production Communication Systems (e.g. Clearcom, RTS, Riedel)
• FM Radio Transmission (including 2-way radio)
• Time Division Multiplexing (TDM)
• Packet-based networking

and so on.

The reason I'm doing this is to help both sides of the equation learn more about the other. Traditionally, performing arts technicians have had little to do with communications beyond a 2-channel "beltpack". Network administrators, on the other hand, had very little to do with the arts, and in many instances were banned from entering stage or studio areas except during planned maintenance.

However this has changed in the last few years. Many convergent technologies (I will define Convergence in a follow-up post) are meaning that networks are extending well into the realm of the arts to the point of running critical systems.

I hope that through my posts and the discussion created by them I can help spread the good word, as well as allay fears from both sides of the communication fence. Please feel free to comment at any time so that we can start a discussion.