Redline 911 Release Form PDF with airSlate SignNow

Redline 911 release form pdf

[Music] hello and welcome to this course that we here at APUs IP solutions like to call sip advanced my name is Martin and I will be your teacher throughout this course my background is in well first of all lots of IP stuff switching routing and then I work for for over a decade with VoIP sip IMS and voice over LTE both of which are totally founded in sip so it's really important stuff that you're going to learn today this course is going to be comprised of different kinds of modules we have the the foldouts those are the papers that were going to drawn together I'm going to show you presentations just PowerPoint slides and things that sort of complement the foldouts there's also available to you a set message walkthrough where I just look through a sip message to just sort essentially explain every detail of that one message show you a little bit about the format of a sip message and finally we have five exercises the material of which you've been given so you have some white shark files and you have some some questions and if you go to the exercise modules there will be a little intro and then I'll give you time to go through the exercises and then I will sort of summarize the the questions for that exercise so we will be essentially a little film in which you pause in the middle and then when when you're done with the exercise it will just hit play again and then I will tell you all the answers if you are if you need to you can download the software that we use white shark from white shark dot org and if you need any any hints or help with white shark there's a white shark intro on our website and our YouTube channel you have your full doubts ready I hope we're going to draw in these together so you have that and you have your your pens and your ruler but I will actually start off for the first section called sip review in in in showing you a couple of PowerPoint slides and then we'll go over to the fold out so so let's take a look at what VoIP really is so boy of course stands for voice over IP it's very nonspecific it's just voice and it has to be over IP so really we have two sides like this we have the Alice side and the Bob side is always going to be Alice and Bob they're like the the bread and butter of communications in the in the IT world its Alice over on the left side and Bob over in the right side it's always Alice calling Bob she probably has something from Bob so Alice and Bob have their IP addresses they've been given IP addresses in some way we don't know how really it could have been DHCP it could have been statically assigned to to their computers or phones if they're mobile phones they could have been given out by the mobile networks it really doesn't care and that it doesn't matter and that's the point VoIP sort of starts off after having been given an IP address so they both have IP addresses and what they want to do is this they want to sort of stretch a green line between them this green line is media this is IP packets with small snippets of voice how much voice well maybe 10 milliseconds 20 milliseconds 40 milliseconds that's sort of the the range we're talking about here for every IP packet so that's what we want to do and in order to do that they need to exchange information they need to to find each other in some way in order to be able to send this green line or or the packets in this green line to each other so how do they do that they need to they need to agree on or rather convey to each other a small small set of information so what they what they had to work with is really the IP stack right we have the lower layers down here which is which is the physical and Ethernet layers we have IP with IP addresses we have the transport layers TCP UDP and then higher layer applications the most important thing here is to be able to find each other you know addressing so in this layer right here in IP well there's a pretty important address in that it's called the IP address not very surprisingly so they need to they need to exchange each other's IP addresses or or get to know the other person's IP address that's not enough this this is enough to get you know right up to sort of the edge of this computer that's where the that's where the IP address sort of sits but then you need to hit one of the applications in this computer so if there's a set phone running in this computer then we need to address that particular sip phone that sift sip software and we do that with ports ports is how we address applications within an IP host that's how if you have to web browsers on your computer you download a web page and one of them it doesn't turn up in the other because they're using different ports so they need to exchange port numbers with each other so that Alice can say to Bob my sip phone is running on this port is listening on this particular port ports are up in the transport layers it's a little feel in TCP or UDP finally they also need to agree on how to encode the information in here what they're doing is talking to each other no analog sound waves in air that needs to be translated into ones and zeros in these are likely packets this is done with a codec may be familiar with Kodi such as mp3 mp3 is an audio codec is not a very common codec for telephony is very much an audio codec it turns analog sound into ones and zeros popular codecs in in the telephony world could be g.711 G 729 AMR AMR wideband so they need to sort of agree with each other which coatings are going to use so that when Alice sends ones and zeros to Bob Bob knows what to do with those ones and zeros but this is pretty much it this is what Alice and Bob need to exchange in order to be able to start sending media if they could meet up in the woods and just sort of swap small pieces of paper with each other and on those pieces of paper it only said I'm Alice this is my IP address this is my port number this is the codec I want to use and Bob did the same thing only it started with hello I'm Bob they will be able to do this that would be the signaling protocol meeting up in the woods and exchanging small pieces of paper it's not a very scalable signaling protocol it doesn't really sort of have an offer a good foundation for for global telephony but logically information wise it would work that's all you need the idea in order to avoid meeting up in the woods is to take the information on that piece of paper and store it somewhere let's say this server here one com it's a server of an operator that stores IP address port number in codec for users so let's say Alice stores her information there and Bob stores his information there that means when Alice wants to call Bob she doesn't need to meet up with Bob in the in the woods she can just ask one or com where is Bob and 1.com says back old Bob is at two two two two that's his IP address hmmm this is all good and well for the operator called 1.com you see the title here it says one domain solution it's not a one domain world there are more than one operators in the world if you're one calm perfect in the one domain world for all the other operators not so good in the one domain world we need to move to a multi domain world so Alice and Bob may be customers of different operators let's say alice is a customer of the operator a.net and bob is customer of the operator B dotnet so what they do is they sort of tag that along to their to their name so Alice is now at a dotnet Bob is at B dotnet and when they register their information they do it to their own respective domain to their own operator so Alice says I'm at 1 1 1 1 and Bob says I'm at 2 2 2 2 2 his operator excuse me now when Alice wants to call Bob she just sends it to her sort of operator which interns find finds Bob's operator it can do that by means of DNS because it's not a complete coincidence that a dotnet looks like sort of a URL or a web name or a domain name and this looks sort of like a mail address user at domain that's because we're reusing a mechanism that is working very very well in the internet world which is DNS so what we need is some kind of standardized protocol for this because I haven't said what this red stuff is yet it's just some kind of hello I want to call Bob where is he that kind of content should be in these red lines but it could be different formats and there have been a number of protocols for this there are a couple of examples sip hmm 8.3 to 3 from from ITU the international telecommunication union which is which is also a VoIP protocol and it has been a quite a popular VoIP protocol in fact but it's now being the world has been taking over taken over by sip so the users that age dot 3 to 3 users is is really a diminishing amount of people so what happened essentially was that sip became the de facto standard for VoIP signaling one argument for why that happened could be that the IMS that I talked about which we will which will mention at the end of this course the big framework first for classic telephony over sip they chose Surya for classic telephony over IP they chose a sip as signaling protocol this was in the beginning of this millennium and when they chose sip the rest of the world sort of saw mm-hmm this is probably an important voice protocol maybe we should go with that so let us now jump over to to the fold-out if you could take out or foldout called sip review so here we are at the sip review fold out let's break out our pencil ruler up there and up here we have a sort of a small network II kind of thing so if we start by sort of swimming in up there I like to say that in sip everything is either an endpoint or or not an endpoint and we have here Alice and we have Bob their endpoints so an endpoint in sip is hold a user-agent so let us put that over here this is a user agent or a UA just underline that and say this is some SIP endpoint like this hope you can read my writing so if this is an endpoint so where are the non endpoints well you can sort of see them in here right so those are sip rooters but they're not called citizenship they're called SIP proxies so let's put sip proxy and sip proxy like this now these things this is where I jump around in the folder this is also incidentally the view where I can I can play the hand of God and say repent repent sinner so enough fun now more fun sip sip proxies are by their very nature or acting as a sip proxy means taking in a sip message like this and forwarding it so obviously you can see that these hitboxes now have the capability to forward something because you see lines going in like this and this is an endpoint it doesn't have anywhere to forward something at all I need to just make a point here that you can't say you can't sort of pick up a thing and say this is a sip proxy it will always be a sip proxy or this is a sip user agent it will always be a sip user agent because it can act as a sip proxy for one sip message and as user agent for another so in this example for instance if Alice over here calls Bob well there will be some kind of message and invite going like this swish from from left to right if one of these proxies decide to sort of return error message of some kind you know I can't find Bob or something then it will create a response it will thereby by its very nature be the endpoint for that message so it will act as a user agent if it creates a response so in a way you can say a user agent is an endpoint and it's an entity that that creates a request or a response whereas a proxy is an entity that that forwards a request or a response so whenever you create a request or response your user agent whenever you forward it your you're a proxy okay so enough for that let me fade away so that I can continue drawing here so let's put down here sip proxy sip proxy and a sip proxy routes sip messages routes sip messages alright excuse me so we have then our our endpoints here our user agents we have Alice and we have Bob and as you saw in the presentation before they have an IP address that they've been given before and they have some kind of operator a sign name that they will use as as essentially a phone number so over here we have Alice and her sip address is sip : Alice at a.net a.net a because you sort of pronounce it as the letter A and then we'll have B dotnet over here at at Bob's so Alice also has an IP address so we'll give that to her IP she has 100 dot ten dot zero dot 151 over here on the right side we have Bob and Bob also has a sip address its zip : Bob at B dot net and Bob has an IP address as well IP 100 dot ten dot zero dot 150 they have to have different addresses otherwise we will have an IP in conflict all right so fair enough these addresses the this the the the Bob at B dotnet and the Alice at a dotnet they're called you are eyes Uniform Resource identifier that's a that's a difficult name to say and most people you know the the the acronym URI but don't know what it means so I will write it down here this is a sip URI I'll just put a little arrow like this so let me know that that's what we mean and whenever you here you are are just exchange it in your head for for address this is a sip address sip URI is a sip address now we said previously that you need to register with your with your with your domain with your operator right so so far we put in to set proxies or one in each domain and a proxy for words messages whoever receives a registration and where the registration will mean Bob saying hello I'm Bob I'm at this IP address needs to be sort of acting as as a user agent needs to say okay got your Bob I will make a note of that IP address that you have right now so in the in the standard there has been created this thing called the Registrar so I'm going to put registrar in here but it's good for you to know that a registrar you will almost never see it as a separate physical thing it will have a box right up here but it's almost always built into a thing that is also a sip proxy so let's put sip registrar or it's all sip so I'll just put Reggie's drawer in there that's the that's the thing that takes in registrations for the B dotnet domain and we will also put a registrar in here like this Alice's to me hmm all right actually let's make a little no to what a registrar does so we don't we don't forget so over here I will just put registrar underline it like this and I will put receives registrations it's fairly straightforward it has a good name but let's just put it down anyway so receives registrations like this hmm okay so what do you think it does with these registrations well it needs to store it somewhere right so the way it stores it is in a kind of a database I say kind of because it's not standardized how to do it it's very very likely to be a database I mean technically in the world we live in today but it's not standardized how it stores it it's just called the location service and it's up here no keishon service and of course there's one for B dotnet as well you know keishon so this this is where the different operators would store the information about where Alice and Bob really are let us put in the lines for the registration now so Alice sends her register to the Registrar this this is a red line because this is SIPP and when Bob registers he will send his registration to his registrar like this the forwarding of this information up to the location service is not SIPP is actually proprietary so I will just do this I will put a little line up here from the Registrar to the location service now we'll just put prop like this this is proprietary do the same thing over here on Alice's side prop excellent so now we got some some sip lines and we got a proprietary line with which the Registrar writes in the location service now what's going to end up in the location service is of course Alice and Bob's addresses so what do you say let's let's put that in Alice has this IP address down there so that's what's going to be recorded up here in the location service sir now the a dotnet domain knows that Alice is at 100 dot ten dot zero dot 151 and of course the corresponding information for Bob is in the location service over here in B dotnet Bob is at 100 dot ten zero dot one fifty so now we've seen the the the registration and we have some some red lines here for for registration we should probably put in some some lines for the actual calling each other right so over here when Alice wants to call Bob she will send things things through her SIP proxy right so that's but the red line in here and then there's kind of a gray line that you can use to follow I just put the red in on top of that bread with gray and gray line so now we are in the position where Alice has has registered and Bob is registered and she has sent her invite to the SIP proxy in her own domain but her sip proxy needs to find the SIP proxy of the B dotnet domain right how does it do that well remember how I said we reuse technology that has worked very well on the internet well up here we have the DNS so I will put in lines from the a.net SIP proxy to the DNS and the B dotnet sip proxy this line that I draw now on the right side isn't going to be used for this call that's in case there will be an outgoing call from the B dotnet domain later on that's not completely unlikely so using the DNS up here Alice's sip proxy will be able to find the SIP proxy of B dotnet so now we can put in the red line here and using the information in the location service the SIP proxy are in B not net we'll be able to talk to the location service in B dotnet in order to find the address that Bob has registered previously so up here Bob is registered as one hundred 10.0 dot 150 which means the SIP proxy can now forward the message to Bob's phone down here Bob's user-agent all right so now that they have found each other they have they have done the equivalent of meeting up in the woods and exchanging IP addresses and ports and codecs now they can actually start sending media to each other so I'm going to draw the green line now from Alice all the way over to Bob like this this is the media this is the line where the packets in which Alice's and Bob's voices are contained we might want to just add a little bit of information about the location service I suppose because we wrote things about the user agent down here and we have the SIP proxy and we have the Registrar we also have the location service so let's put some information in here about the location service underline it like this and I will put that it stores the IP address or fqdn and that's fully qualified domain name of the subscriber so stores IP address or fully qualified domain name of Serbs driver like this as you will see later on it can actually store more things than than that it will for instance it can store the port number if you're not using the standard port of SIP but we'll get back to that later on as this is a sip advanced course we haven't we haven't said so much about how the SIP is actually sent sort of in the in the IP stack we mentioned the IP stack a little bit in the PowerPoint up here we actually have a little IP stack we have the lower layers here we have the IP we have the transport layers UDP TCP and then this sort of third edition that is sort of a newcomer it is a couple of years old but it's not every day we get a new protocol on this layer right here so SCTP stream control transmission protocol is sort of a mix between TCP and UDP if you will it doesn't have anything to do with streaming movies or music it's it's a lot like it's not like TCP actual the streams in SCTP are essentially like TCP sessions or TCP connections so what do you say we can actually use this little stack up here and put in in sip and maybe even RTP that is used to carry the green stuff so if we start off with sip sip can actually be carried by all transport protocols you see how this box is sort of lying on top of SCTP TCP and UDP sntp isn't very common I'd say TCP and UDP are quite common both of them I'd say there is a slight advantage for it for UDP meaning that there are a little bit more implementations using UDP but that's that's just from my experience you can use both TCP and UDP and and it works fine the actual RTP is sent here RTP real-time transport protocol it's the little protocol that actually carries the the the sound the audio of Alice and Bob so in here we can put media I use sound as an example here because it's such such a good example to have a phone call but it could be if they had a video call this music carry video as well and we would like to see other things later on that can be carried in in in this protocol something that we will see later on that we're coming back to as well is something called SDP SDP is a session description protocol and it's right up here carried by carried by sip sort of as an as an attachment if you will now we are coming back to STP it's kind of important that's that's a little protocol that describes the green line this green line right there so it's it's it's kind of important and and we're coming back to it I just said that SIPC Aires SDP sort of like an attachment it's actually not just sort of as an attachment sip follows technically the exact same format as email and a few other protocols as well it's very popular to steal I'm also good so so as a sip message is essentially technically a piece of email and you will see this from the headers later on as well and much like email can carry attachments so can sip carry attachments you can send a sip message and attach a JPEG or or a PDF or an excel file if you want to it's not very common to do that but you very much technically can what is very very popular to do is to send SDP a little text file with a description of this green line as an attachment in a sip message so so that's sort of in the way in which SDP is on top of sip in this in this protocol stack continuing on there are requests and responses in sip everything in sip is either a request or response and the requests are called methods so here we see all the currently known methods in sip there are 14 of them there may be new added check in with a section on on sip extensions later on but currently these are the the SIP methods that we know of and we don't see any ones on the on the horizon just just right now there's also a number over here says RFC and a number RFC means request for comment and that's the name of all the standards from the internet Engineering Task Force IETF namely the guys who who standardize sip they're also the guys to standardize IP and TCP and DNS and DHCP HTTP and other very well-known protocols so essentially what this is it's just a reference to the standard that defines this particular method so you will see that a lot of them begin here with 3261 and that is you could call it the Bible of sip if you want to that is the the core standard for sip if want to read just one RFC on sip it should be 3261 because it's it's the one that is the basis for sip and then there are others and just adding stuff so we have here these 14 methods and we're going to see use for all of these methods throughout this course I'm not going to go through all of them right now but you can use this as a reference list later on to just see that we've actually sort of managed to check off every one of them and I'll problem I promise we will check check off each and every one of these methods in this course so one of these are requests remember what I said everything is request response everything is either a request or response so if these are requests then we have down here responses responses are special because they have numbers every response begins with a number and they exist in six different families of numbers the 100 all the way down to the 600's and if we want to group these things together a little bit we can see that the the 100 series of responses here is it says provisional response that's because it's not final all the others are final provisional response means just here's a response while we're waiting for the final response so the 200 s 2 X X means everything that begins with a the 2 is the final successful response I'll just put that in final successful like this where's all the others that a bracket like this final unsuccessful final unsuccessful like this you can even see that they are sort of in a in a ascending order of unsuccessful nests anyway it becomes worse and worse is what I'm saying we have the two hundreds which are success then we have redirection that's you know I can't find Bob here but I actually have another address he has a forwarding address so there's a little bit of hope then we are request failure server failure global failure which sounds like the end of the world it really isn't it will come back to the 600's later on in this course but sip actually make you makes use of the fact that this isn't an increasing level of failure so if you have several response messages and you want to choose the best one you just look at the number if I have a four hundred response and a five hundred response to choose from the best one is the four hundred response this could also be a good point in time to just note that this may not be the first time you've heard of three digits response codes because you've probably surf the web at some point in time and seen three digit response codes if I if I ask this in a in a course usually the first one that comes up it come on say it loud I'm betting that you said four-hour for right now because everyone has seen the 404 not found surfing the web but there are others as well we have some four hundreds for four non authentication that you're not allowed to see something the 500 server internal failure and other similar popular response codes can be seen on the on the web and also in insell very much like the 200 200 okay is essentially the only message either the successful family of responses and it's the same that's used in in HTTP and and many other protocols so again stealing is is good we don't need to have any bad feelings about this if we move a little bit further down here we have the sip message format we will look at sip messages a more concrete form later on a sip message format has this essentially three part there's a first line which has either one of these methods in it or a number depending on if it's a request or a response so so this this number here will be the status code in fact then we have a number of headers zip headers some of them just stolen from emails are to and from and things like that you can have any number of them in any order in fact it's all text-based so it's human readable and then body and body means attachment payload that's where I would put JPEG if I want to attach a JPEG picture to my sit message or the more likely attachment the SDP session description protocol that I mentioned that I mentioned earlier so this is the sort of basic format of a sip message now if we move over to the fold out and take our pens here again there is down here we have sort of a sort of a flow graph II thing going on and we can use this to actually make a flow graph for for a call in fact the call that we saw up here only now with arrows and real sip messages so if I take my black pen here but my red away this invite I can zoom in a little bit more for you so it's easier to read this invite is sent from Alice to Bob that means there the address that points it in the right direction will be Bob at B dotnet so here it says invite sip Bob at B dotnet the next thing that happens is a provisional response do you remember the provisional response is down here they were sent sort of not as a final response just to give some some information while we're working on things so the provisional response that's sent here is one hundred trying one hundred trying means I got your message you don't need to re transmit that's all it means we'll talk more about reliant reliability later and retransmissions I want to talk about the statefulness of sip but right now just learn that trying means I got your message don't read transmitted incidentally regarding the these numbers it says 100 trying and I am I put this word in trying but the fact is the word here doesn't really mean anything well you know what it means in English but to the machines getting this it doesn't mean anything when Alice's user agent gets this 100 trying it does not care about the trying it only looks at the number so when we have here response codes the numbers all that's important in the standard in the RFC in 3261 the response codes are written and they have numbers and they have their suggested text that doesn't mean that that text has to be what's used so so I've seen all kinds of texts looking at real networks in the world I've seen 100 giving a try for instance or I could put in 100 I really really really don't want to try and it would be the exact same thing or I'm not trying the 100 means what it means so it's the number that that sort of matters here so after this has happened the the SIP proxy here you can note here by the way just so you see that this line here means that this is the line of that SIP proxy see and over here this is the line of Alice's user agent we also have a line here for this SIP proxy and this is the line of the location service this is the Registrar and over here is Bob's user agent so what will be done now is is the the SIP proxy on on hauser side will make a DNS lookup up here so I will just put that in here just put a little blue dot here and make DNS lookup like this fine now it has done that so that it can forward it to Bob's domain B dotnet so taking my black bent pen here and I'm forwarding the invite to Bob at B dotnet so sip Bob at B dotnet now we need to make sure that the receiving end has sort of got this as well so that we don't need to read transmit so once again we have the 100 trying 100 trying if you wonder about the different arrows that we have here the different heads of the arrows in fact you can see that they're different and that's something that we try to do consistently the filled-in head is a request and they had that that looks like this is a response so that you can you can see that sometimes we we combine them like down here we have sort of combining the request and the response to make things simpler but if you only have one this is supposed to be a request and this is a response all right so we have the try now it comes a point in time where Bob's sip proxy wants to look in the location service in order for that to yield any results Bob has to have registered so let's put that in and you can note here that this is put in in a head in time of the Alice calling Bob so this has to happen before in order for Bob's sip proxy to be able to find Bob of course so there's a register the sip method register the the Registrar will make a note of this in the in the location service so we now know Bob is at 100 dot ten dot zero dot 150 and the Registrar will say back to Bob's phone 200 okay again it's only the numbers that matter this is a 200 response this makes it possible for Bob sip proxy to now ask the location service where Bob is so I'll just put in here Bob question mark because remember this is proprietary protocol this is not sip when sip the SIP proxy looks in the location service it's not it doesn't have to be any protocol strictly at all very often the location service is built in to a node a physical node that is both sip proxy and registrar so all of these three things is the same actual function in in the network apparently it it gets a response so it now knows where Bob is so it forwards the invite invite to Bob at and careful now appears as Bob at B dotnet Bob at p.net now the sip proxy has translated this using the location service it has translated Bob at B dotnet into the actual IP address of Bob so right now the sip message is the top line of the SIP batches will say invite Bob at 100 dot 10 dot 0 dot 150 all right now now we were waiting for Bob to pick up we need to tell Bob that the phone is ringing though of course that's that's this phone over here going ring ring in order to make Alice's phone go dude dude what's called the ring back tone notifying Alice that Bob's phone is in fact ringing is done with a provisional response called 180 180 ringing which will be sent back all the way like this ringing 180 ringing so when this 180 hits Alice's phone that's when Alice's phone or her handset starts going dude dude or whatever ring back is is configured in that phone eventually Bob picks up the phone that will be with the creation of the final response to this invite the final response is 200 okay if he picks up the successful response for invite is 200 okay that means Bob picked up the phone so this will be sent all the way back to Alice's phone over there now I said previously that everything in sip is request or response and that's true I'm building up just telling you why I just lied a little while ago but that was not a lie everything is request or response but I also said something that sounded like it's all pairing up a request in in in in companionship with a response that they're all sort of pairs and that's that would have been a slight lie if I said it like that a pedagogical lie though because I'm telling you now that it's like lie because there's one exception the exception to this is the request called ACK you can see up here in the top list of the method list so ACK it stands for acknowledge is a request in sip it doesn't always feel like a request because what's going to happen now is this arrow right here will carry an ACK and it just means I got your 200 okay this is sometimes called a 3-way handshake and is used in sip and lots of other protocol as well TCP does a three-way handshake meaning when we start something important we have three messages going ping pong and then paying again so in sip its invite 200 okay and then I'm going to put AK in here so AK is a request that does not trigger a response that's how I'd like you to think of a can that's how I think of AK and it's it's worked for me some people try to really argue well it's kind of a response no you're you're you're down a dead end if you go that path because responses and requests are handled completely differently in sip they're rooted differently they follow different rules responses and numbers act doesn't have a number so AK is the one request that does not require a response that's the exception to that rule so let us put in AK here the final message in the three-way handshake invite 200k act that's what I sometimes like to call the Holy Trinity of sip messages invite final response it doesn't need to be 200k could be some other final response but you always need to acknowledge the final response with an AK finally we can have some some media let's use green oh hang on we need to do this did you notice how how AK is sent sent end to end here it's a it's a it's an acknowledgment and to end the final final shake in the in the three-way handshake is actually sent directly between Alice's and Bob's phones so Alice sends to Bob through the proxies to find Bob that's the purpose of all of this up here once they have found each other's IP addresses and everything they can communicate directly so they will do that with the AK if not told otherwise that the basic behavior of SIP is to try to communicate as directly as possible so it's quite possible to to send sip messages directly between Alice and Bob so I will put a red line in in parallel to the green line like this just to show you that they can communicate directly like this so now we are in the position where they can actually start sending media so in this big fat arrow down here I will put media and this could for instance be audio or video using my green pen here green for for the media so I have a green line up there and I have my green media written in the big fat arrow down there so they talking talking talking talking talk and then finally one of them hangs up this is done with a sip method by in this case it's Bob who hangs up so he's going to send by to Alice and she responds with 200 okay I got your bye you don't need to retransmits this is the this is the bassist author of sip we see the the simple three three-way handshake to set up something you only need these three messages invite 200 okay ACK we have provisional messages here that it would still work if those were lost you don't need the 180 ringing really it would make alice's phone not go a ring ring or to toot the ring back but you would still be able to to make it work this up here is sometimes called the SIP trapezoid trapezoid is a funny word to say and it's it's it's a geometric form that is shaped by two parallel lines one down here and one the little one up there and then we have two sort of slanted lines like like this and it's it's used in in books and in the specification and they say if you if you know the SIP trapezoid you understand sip and by that they mean you use the top part of the trapezoid to find Bob you go through a local proxy a remote proxy and then Bob while you're using the base of the trapezoid to continue the communication both signaling and media alright I put in a sip URI up here so I will I will conclude this by showing you a couple of PowerPoint slides quite briefly on the topic of of addresses and what registration really looks like so we see addresses here and in sip these are called you are eyes Uniform Resource identifier but as I mentioned previously just replace that with address anytime you see it your eye is an address is also used in something called a request URI that's the address that's on top of every request where it says invite Bob that address is a URI it's in the top of the request and it's called a request URI but you can also just think of it as the request address so these are examples of of CPR eyes notice how they all begin with sip that's an important clue that there's sip your eyes if I just take that away if I just do like this these are not sip your eyes by definition they're not they could be you know the top one could be mail address for instance but they're not sip your eyes because they don't begin but sip so this is what you would put on your business card for instance you wouldn't put your IP address because that can change so we have some some examples here request your I could look like this invite when it says tyst acquiesced a diaper solution SC that would be the request URI in that in white here's an options request this is a method that we're going to talk about later on in the in the extensibility chapter of this course and then a request address requests URI Alice at ten one two three you also sometimes see the term address of record address of record means something that you put in essentially a phone book is something that doesn't change a lot so your business card address would be a typical example of an address of record so that would be pole at IP solutions dot SC or I sac at IP solutions dot SC very specifically you shouldn't put IP addresses in your in your phone book because you may have a new IP address tomorrow so sip your eyes can can look can I can have different performers well they can look differently there's one format and I will show you show it to you here but it may take different forms so for instance this is a sip your I it's just an IP address really I mean when you think of it what you what you use this address for is to sort of translate it in some way to an IP address that you can use and forward at the invite to so what if you just start off with an IP address well that works as well so this is a this is a legal sip your eye you can put you can put URI parameters after a URI and you use that by adding a little semicolon here so this is a sip URI and we've added the the URI parameter transport there are a couple of different parameters defining they do different things we will see a couple of them later on this is one that sort of indicates which transport protocol this we want the the the user of this address to use so essentially it's contact me on this address please send it over TCP that's what this means you can also put in sort of request to populate sip headers in a sip your I so this is a NASA PRI Cecilia at Finland dot F I then there's a question mark right there then subject equals sip course subject well that's a sip header as I mentioned previously we just steal things here so we've stole things from email lots of things in fact to and from which you will see but also subject so you can have the normal subject header that you see an email you can have that in a sip message as well it's not very common to have implementations that make use of that Henry but you very much can so this is if you want to mail me use this address also put in a subject header and write the word sip course in that header so these are sort of ways to modify or add to a request URI semicolon and question mark and those are pretty much the only ways that you can then you can sort of add things at the end of an address so so we will just see more examples here IPS dot SC something that can be translated into an IP address this is a domain name and then it says method this is the URI parameter method equals register and then question mark the two header equals taisto this is code for at IPS SC so what this means is if you want to use this link click here send a register to this address and put in a two header with this value in it we have the the URI parameter user which you pretty much only see with the user equals phone this is to indicate that the user part over here is a good old telephony number good old PSTN phone number from essentially you can say from the circuit switched world there are other ways to do this as well and we'll come back to that in the final chapter which has to do with interconnect between the new and the old between packet switched and circuit switched you may see oh isn't this the same thing as up there but there is a little s here sips so this means secure sip just like you have HTTP and HTTPS this means running sip over there's the the encryption protocols SSL or TLS this is this is legal and possible it is currently very rare to see that you've used at all but you will see it a lot mentioned in in books and specifications so just you know this exists it's not a typo if you see if you hear sips somewhere and finally to conclude this slide we have the complete format of all the sip you are eyes we have the user but also password okay we have the host of the domain but also port so there's a colon there colon between password and user colon between host and port and then URI parameters and headers that's the total format of sips URI if we see the use of this we can look at registration so here we have the registration of someone at this address to the strip registrar over there this is the registration of Bob you can see how this is from Bob at lab to dot zip so we see some some things here first of all we we see our first sip message now we have a request line up here it has the method register and the request URI lab 2 dot sip then we have a couple of headers via from two max forwards call ID see set contact and expires and contact length there's no pay low there's no attachment to this sip message so this register is sent to the sip registrar the Registrar sends a response back saying 200 ok you're now registered this contact address is where you are now registered Bob at 10 1 2 3 that's what Bob put in contact here as well Bob at 10 1 2 3 you may note that there's an expiration times as expires 7 to 200 that's counted in second so that means 2 hours that means this registration will be terminated unless Bob Ari registers within 2 hours which normally means he would register after like 1 hour or 1 & a half something like that you don't wait for the last millisecond and finally if expires is zero then that means the user is d registered so there's actually a very very tiny difference between registration and D registration it's only the value of this expires this is a function that's being used in other methods as well as we will see later on the expires being set to zero meaning negating something meaning we're shutting something down now and in this case we're shutting the registration down by setting expires to zero all right this concludes the first lesson we're going to continue on but right now we can take our sip review and take it away and reveal the message forwarding foldout which we will continue with in the next lesson see you then [Music]