So, we went over the, the- >> SIP and the protocols. >> SIP and the protocols, or the operations of SIP. Now, we're gonna go into a kind of one little layer lower, right? Kinda talking about some of the elements that make up the network or the SIP operations that you're gonna be using. So, you can see up on the screen or on your slides right there. We have these six kind of elements that make up what we're doing. Now, There are more. But these are kind of the ones that we thought would be more interesting. So, we're gonna kinda just briefly go over these things, right? So, user agent, proxy server. What is all these stuff? Registrar, redirect server, session border control, and the gateway. Now, you'll kinda see, this is kinda cool, what it leads into but you'll see. So, user agent, what is a user agent? The user agent, first of the network elements that we're going to talk about, is essentially the object that manages your SIP session. Now, I'm not gonna go too in depth about this, but that's pretty much the gist of it. It controls all the functions that you would implement that essentially makes your SIP session Kind of similar to what a phone call would be like. >> Yeah. >> All right. So, that's enough about the user agent. You have a proxy server. The proxy server, interesting little thing about the proxy server, and I have a little animation or. Something after this. But it's the intermediate or intermediary object or entity in between you and the person you're trying to connect with. >> Yeah, in between the end points. >> In between the two end points, there you go. Yeah, so proxy servers in a lot of cases, for instance imagine you were a You are, you're a subscriber to a telephone company or a cell phone company and you didn't pay your bill, right? Well, you're trying to call so-and-so and the proxy server's not gonna let you because you didn't pay Pay your bill, right? So, it's kind of like that intermediary buffer, in a lot of cases that's what's happening, like that's how the control is maintained is. >> Right. >> Through these proxy servers. They're also used to protect people too, so I mean like, there's lots of uses for them, you can look up online. >> Yeah, probably like, maybe like call blocking. >> Call blocking, lots of stuff like that. But, yeah, so in short, you can kinda see up there, ensure request is sent to another entity closer to target user. Now, that's kinda like the routing of the proxy servers. Now let's see this alimentation we have here, all right so we have Alice and Bob Alice wants to call Bob, so Alice says, ask Bob what the current time is. Goes to the proxy server and the proxy servers says, Bob, what's the current time? And then Bob says, the time is 7 PM. We'll go through the proxy server and then the proxy says, oh, Bob says the time is 7 PM. So, you can kind of get the picture of what the proxy server is doing there. >> Right. [COUGH] Excuse me, sorry. >> Yeah. [LAUGH] Yeah, so you kinda get the picture what the box server's doing there. >> Yeah, it's a good inter-. >> Intermediary. >> [LAUGH] >> Yeah, intermediate. >> Intermediary. All right, cool. >> Exactly. >> Yeah, so next element that we have is the registrar. The registrar is a SIP endpoint. And it accept the REGISTER requests. So, you register say your username or whatever. It accepts the request from you. If for instance you're not registered with registrar. Well, then there is an issue. So, then you might need to register with the Registrar and then in which case then it has your information and so on and so forth. Right? So, this is just another piece of SIP. Next element is redirect server. So, I'm just gonna read this. Redirect server allows proxy servers to direct SIP sessions Invitation to external domains. Right? So, you can kind of follow the chart up there. Not so easy to follow. But this is off of Wikipedia. I'd recommend checking it out, going down to. Just clicking on the little sub-link for redirect server if you wanna know more about this. So, not such a super big deal for at least what we're gonna be working on. But, thought it was a little bit interesting when it gets to a more intricate system. Now, [CROSSTALK] Gateway in particular is what I like. But yeah, these are the last two elements. Now, you have the session border controller, which I'm just gonna read, exerts control over VoIP signaling, setup during and tear down. So the border controller is essentially kind of monitoring all of this and yeah, so the border controller's essentially monitoring all of this and making sure that everything's going right. Nothing's going out of bounds or maybe not losing stuff, things like that. >> Exactly. Then the last one is the gateway. The gateway we've talked about. You know the PSTN, the public switch telephone network, that's a gateway. So, this basically takes you from your SIP network to the public switch telephone network and backwards, right? >> Yeah. You know how we mentioned if you're on the VoIP network, or on the Internet, how are you gonna call someone on the local landline or on the telephone network? And that's what the gateways are for. >> Yeah and SIP has all this integrated into it, so that's why it's such a strong >> You know and prominent protocol to use in using VoIP. >> In using VoIP, yeah. >> Anyways, I hope that wasn't too confusing or too bad. We just wanted to walk you through some interesting things that we found and hopefully you found it useful as well. We will see you in the next videos, and stay tuned.
