Today we will be talking about voice and VoiP stuff. It'll be great. Doug is joining us to talk about GSM. He's trying to make a cell tower.

Uh-oh, no one has a quadband phone! Tom and Doug's plans may have been thwarted.

November 15 we have a guest speaker. DO THE READINGS so that you know who it is and make the best of the class.

We've touched briefly on the subject of phones. In your minds, what is the intersection of networks and phones? Jeremy suggested they run on the same cables.

What is the difference between circuit and packet switching networks? Circuit switch networks is a bunch of little wires that go through switches. Packets have information about where they're supposed to go and can be broken up and reassembled at the end. It's kind of like analog and digital. In the past, when you had a phone call, you would be making an anlog connection along a wire to transmit the data. That meant communication had to be serial (one but at a time) and you need more power to go linger distances. Now, with voice over IP, you can break that up into packages and sent it simultaneously then assemble it at the end.

TCP checks to see if your stuff is in the right order before it gives it to you. UDP just sends it along. When you do audio stream it tends to be UDP because the timing matters (you don't want to get it our of order because the sound will have no meaning, whereas when you miss a byte here or there, so long as it's in order, you can derive meaning).

Cable providers will prioritize TV over VoIP so that you don't get glitches when you're watching CSI. This is why net neutrality is a BIG DEAL. Advocates of net neutrality say that all content is equal and no content should take priority. Carriers are, naturally opposed.

Let's talk about the quality of VoIP. What are the problems people experience? Echoing. Old phones have better sound quality because Bell spent a lot of time optimizing this. People who talk loudly in the phone because they can't hear themselves or because the mic is so far away from their mouth.

We've ben talking about old telephone calls as if they're pure analog circuits, but they're not. There are signals such as tones and clicks. Touchtones used tones to indicate telephone numbers. There are only two tones, and the combinations of these tones indicate a number.

In voice telephony, the tone and click to initiate and end a phone call is replaced with SIP: session initiation protocol. SIP was not just designed as a tool for VoIP, but also for chat and SMS. Things you want in a SIP (we're assuming its a TCP based protocol): handshake, ID, communication method (protocol), speed, capabilities/services. Rather than an end to end connection, you'll have a SIP server. Why do you need a server? They give you reliability and persistence. For example, if Nick is not available for VoIP, then we can switch to another TCP protocol.

As a client, I can have multiple connections open at one time: push to talk, voice, txt. How is this possible? The phone is constantly pinging the tower and saying "Hey I'm here". The towers save the last known address and know where to send packets. PBX are a piece of software that you have in your laptop. NYU has a dedicated server just for voice.

Discussion about data and the future of telephony. Will all telephone services eventually become VoIP? Maybe.

Doug now is going to talk about GSM and the cell tower he's setting up. GSM is a cellular network, made up of many towers. Positioning is determined by signal strength. This project came out of the monkey class. How do you find the monkey in real time? How do you save power on the collar? Tom and Anthony decided that it would be worthwhile and not so expensive to set up their own GSM network in the jungle. The original documentation to get this project going came from burning man. Those guys are good at publishing plans of how to build things in the middle of nowhere. We're talking about 70k per tower, so in the territory of major grant money, but not impossible.

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Now let's talk about Twilio:

Twilio is a web-service API that lets you use your existing web languages and skills to build voice and SMS applications. You can set up a simple PHP script to use Twilio. It works exactly like an Asterisk conf file.

Now... projects! Who's doing what?

Lily and Tennie: High five tracker. Using Cakemix, which is faster than saving to the server at ITP:

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Nick Yulman: The arrival of elevators at ITP to derive a schedule.

JSD + Steve: noise sensors

Greg: Eureka button

Gaby: rats with hats voting box

Johnny and Maria: flushing