 Now we are going to go a little more into detail on how the public enum or the user enum works. We'll take some example and then on the basis of that example, we'll look at how the connection can be established between two users. The public enum is actually organized as an end user accessible database that gives user the opt-in model. Opt-in model means it allows the user to add in as much information as possible that can be mapped onto the E.164 based telephone number written in reverse order as an enum. And correspondingly, it delegates this particular information to the national level and national level registry and the internet domain. RFC 3761 talks about how exactly public public enum works in detail. Let's take a simple example. Here we take a telephone number. This is again some country, European country. The international number starts with plus followed by the country code 3-1 and the telephone number. So if you really want to convert it into enum-compliant database acceptable format, then you need to reverse it and add dots to these. So I'll read it in reverse order. 9.8.7. We continue. . And then towards the end as a suffix, we add E.164.arpa. So from this example, we understand that we have the domain registry now as a DNS record that is available to us against a certain telephone number. This telephone number as in domain format is available to us to associate any kind of information with it. Now, there is an interesting concept called naming authority pointer records. That is, once we have an authoritative address, then we can use that address to point to certain other information that is other records. What we essentially do is if we look at the mirror or the inverse of a telephone number and we don't associate it in PSTN terminology, we'll understand it's a number written like an IP address. It has the attributes of a domain name. Once we have the attributes of a domain name like any other URL, then any data can be associated to an enum domain accordingly. Like a URL can actually refer to any resource on the Internet. And one URL can refer to more than one resources on the Internet. Now, this napter, the authority record pointer, allows us to specify all the services that can be attributed to this individual enum domain. Now, there are certain service details and preferences which can be utilized or which can be queried to start the communication with a certain host on the basis of preferences which are defined in the napter records. Let's take an example of establishing a communication with enum between two hosts. We'll start understanding this from the left-hand side where we have a number that is the caller dials the person's telephone number as plus one. It's a U.S. number, for instance, 202-555-1234. So, if it is to be utilized as an enum DNS record, then this number needs to be reversed and e164.rpa needs to be appended as a suffix. The calling party, now, calling party user agent client asks the DNS for endpoint location. Now, this DNS could be either tier zero, tier one or tier two, depending upon what exactly is the operation like. If it is based on an individual query, it could always be simply confined to DNS lookup or if it involves the carrier or infrastructure enum, it involves tier zero, tier one and tier two enums. So, once the query is responded, then a corresponding SIP identifier that is session initiation protocol identifier or a URL is returned to the user agent client that is the calling party. Then the calling party correspondingly initiates or dials the destination or the called party by using this SIP identifier. And definitely in a SIP environment, the call is routed to the called party through the SIP proxy server, so the call is established. So, what we understand from here is a simple approach how the public enum or the information related to an individual destination can be utilized to establish a call.