Learning Outcomes

Following this course a student should be able to:

Understand the relevant protocols (particularly SIP, SDP, RTP, and SRTP): what they are, how they can be used, and how they can be extended.
Enable you to utilize SIP in Presence and event-based communications.
Understand how SIP can provide application-level mobility along with other forms of mobility.
Understand how SIP can be used to facilitate communications access for users with disabilities (for example using real-time text, text-to-speech, and speech-to-text) and to know what the basic requirements are to provide such services.
Understand how SIP can be used as part of Internet-based emergency services and to know what the basic requirements are to provide such services.
Contrast "peer-to-peer" voice over IP systems (i.e., how they differ, how they might scale, what are the peers, ...)
Know the relevant standards and specifications - both of the protocols and of the requirements (for example, concerning legal intercept).
Understand the key issues regarding quality-of-service and security

Transcript

[slide6] Now, the learning outcomes are: you should understand the relevant protocols, first and foremost. To be able to utilize SIP in presence and event-based situations. And one of the interesting features of SIP is the idea that you can subscribe for an event to occur. When that event occurs, you get a notification. Now you can react to it. And this fundamentally changes things away from the traditional telephoning systems. Because in traditional telephoning systems, the only time you had a chance for signaling was at the start of the call, when you dialed, right, or when you hung up. This lets you have events long before that, and even in the midst of your session. Understand how SIP provides application-level mobility and other forms of mobility. So one of the interesting features is, you could think about having a SIP device, and when you walked into this room, transfer the video to the projector, the audio to a built-in speaker system in the room. And when you left, it all left with you. Because there isn't a strict binding any longer between the I/O devices associated with the session and the system that you're using to control it. But that causes a lot of interesting questions. Like, how can I know whether I'm authorized to use the projector of those speakers? And how, when the next person comes along and is using the room and is assigned the room, you're not controlling their projector? To understand how you can facilitate communications for users with disabilities. Because a very important thing in telecommunications systems is that they are to be usable even by people who are deaf and blind. So how do you manage to do that? And one of the interesting techniques for that is timed text. And we'll see that, just like audio can be sent out in time sequence, with the right separation between the sounds, we can do the same thing with text. So if you've ever listened to a good storyteller or a joke teller, you know the most important thing is timing. And in fact, when people write with timed text, it's the time delivery of that text that's very important. And of course, most of you got very nervous when you heard these pauses in the audio. And this also is a very important thing. How do we understand what are the good performance metrics so we can decide is it a well-performing VoIP system or not? Where are the flaws? How do we hide the fact that maybe there's a loss of audio for a moment? Right? And our ears are very good at filling in certain types of losses. And computationally, we can also use other techniques to hide the lost packets. Because we know there are going to be lost packets, and we'll come to that more later. To understand how SIP can be used as a part of emergency services. Because one of the typical problems when there's a big disaster, whether it's a hurricane, earthquake, whatever, is one of the first things to get damaged is, yes, of course, the telecommunication system. But what's the system you need to be able to coordinate the rescuers, etc.? Yes, it's the telecommunication system. So how do you manage to build a system that's going to be able to support those operations even under emergency conditions? But one of the fortunate features about VoIP systems, unlike traditional telephony systems, is it's packet-based. And we can send digital messages. We don't have to have analog conversations. And that opens up some interesting possibilities. Looking at peer-to-peer systems. Fundamentally, once we've set up the communication for a session, all of the communication just occurs between the parties participating in the session. This is the secret sauce for Skype, right? Because the advantage was they only had to build a system that could decide, yes, you're a valid user and you're logged in. And yes, we can help you find the other party that you want to communicate with. And yes, we can give you a copy of our software from our server. But after that, they don't have to provide any of the communications, which means the system scales very well. And they use peer-to-peer techniques to handle almost all of the administrative part of it. So the result was, yes, you could have a company with basically almost no infrastructure with enormous numbers of customers. And that scaling has some interesting properties. To understand some of the relevant standards and specifications, both of the protocols and, of course, the requirements. And in particular, one of the things we'll touch upon is the requirement in most countries for legal intercept or lawful intercept. So that the police, with a proper warrant, can manage to get the signaling information or the contents of calls. And understand some of the key issues regarding quality of service and security.