 Traditionally, both the networks, namely the telecommunication network and the internet have existed simultaneously with their own naming and addressing schemes. But with the emergence of next generation networks that promotes converse services, we have to come up with a mechanism that allows the addressing to be interchangeable between these two networks. Enum or E.164 number mapping is the scheme that has been adopted jointly by the IETF and ITU for consideration in NGNs. In this module, we should look at it and then we'd look at the mechanism how it is going to be implemented through an example. It is well known that the numbering and naming schemes are different in traditional telecommunication networks and internet. In traditional telecommunication networks, we use telephone numbers but on the internet we use IP addresses. But when these two worlds are going to converge into one, the carrier is going to be the internet but the mechanism is going to follow the traditional telecommunication approach. The traditional telecommunication approach given by the ITU E.164 is a standard that promotes and implements the telephone numbers based on geographical areas. These geographical areas are then divided into hierarchical codes. At Max, a 15 digit code is assigned to a certain user and that's called the dialing number. That is based on the specific country. The country code for instance in Pakistan is plus 92 plus shows that it's an international number or we can also replace it with 00. Then we have the network destination code and finally we have the subscriber code. You can actually look at a telephone number in Lahore or in Rawalpindi and you can interpret it in such a way that you can reach down to the suburb. As far as the internet addressing is concerned, ITF primarily has been promoting this through the use of IP addressing. In IP addressing, the IP address assignment is automatically done by the dynamic host configuration protocol in dynamic environments and of course the static IP addresses are assigned by the system administrator. As far as the naming is concerned, the domain name system which works on root servers on top level country and domain names is responsible for assigning names. With these two, recommended by the ITF and the former one recommended by ITU. Now we need to look at a mechanism that integrates both of these. The primary idea of Enum is we use DNS, we take it from ITF and we map it on to E.164 that is from ITU. So we converge both the words by picking the best from each. It is possible because we observe that both these schemes are hierarchical. Of course they are two different hierarchies. In the case of the address dialing, for instance in telecommunication networks, the country code starts from the left hand side. If we take the other example such as DNS where a fully qualified domain name is represented, the rightmost side is the top level domain. So although these two domains are significantly different, one starts from the right hand side, the other one from the left hand side. But in reality both of these are hierarchical and that is the beauty that we are going to utilize. So Enum essentially does what? It translates the digits in E.164 in DNS kind of structure. All it has to do is write it in reverse and then label it with E164. For instance if we look at the telephone number plus 389-2-123 up to 8. As an example, if we were to encode it using Enum, all we have to do is just start from the last suburb or the subscriber number, put it on the leftmost side and then we move on to the left hand side starting from 8, 7, 6, 5, 4, 3, 2, 1. We write it in the reverse manner and towards the end we write E164.ARPA to label it that it is basically an Enum translation. With this mechanism we can switch back and forth between the ITU standard that is E.164 and the DNS.