 The concept of portability is not new to us. We know to an extent what portability means in the context of number portability as in telecom networks that we use today here in Pakistan. But where did it start? What are the implications of it? How it is implemented is something very interesting. It gets further interesting and flexible once it is seen in the context of NGN, once NM based directories are utilized for number portability. Nonetheless, it is important to appreciate what number portability as a concept is, what are the local routing numbers and how the procedure is implemented to achieve portability. Local number portability also known as the porting of numbers is a system that enables the end users. It gives them a choice to keep their telephone numbers once they switch from one communication service provider to another. It is of some advantage from different perspectives once porting is considered. Let us look at the scenarios for number portability. I have taken this from Federal Commission of Communications USA, the Network Portability Administration Center. But we can also consider these to be exactly the same what happens in Pakistan. In Pakistan we also have a local network portability administration center. Now the types of porting which are provisioned are the inter-carrier or competitive portability. That is the number is moved from the carrier currently providing service to a new carrier. Now the effect on the telephone number as such is it changes the physical hardware or the switch where the number resides and the carrier providing services to that end user. So it means the carrier changes the hardware of the carrier changes. The next type of portability requirement is the intra-carrier portability. Here the carrier essentially is the same but the requirement is to physically change the location where the switch is going to be replaced. Now here what happens is a requirement comes in to have an additional record in the network portability administration center. It may be required to move a number from one switch to another within the same carrier's network. Once it is realized then it has an effect that once it is used when a carrier that holds the number puts it in the administrative center. The overall change in terms of business revenue is unaffected because as far as the autonomous administrative domain is concerned the carrier remains the same. As far as the number pooling is concerned now the numbers are assigned to a new service provider because a new service provider is there to compete with an existing service provider to have some unassigned phone numbers which were initially belonging to a service provider. What it means is if a service provider has some surplus telephone number pool it can share it with a new service provider. So what happens is from a user's point of view a user that belongs to the new service provider may get mistakenly be considered to be belonging to the first service provider. So it means here the requirement for number portability and to establish number portability correctly becomes very very critical. Since the new numbers which were unutilized in the previous service provider are put in the network portability administrative center. That is these particular range of telephone numbers are considered to be something which are not normal. So the calls to a telephone number in the block are routed to the block's local routing number. We will shortly talk about it unless the block is within the same range that has been utilized by the first service provider. If it sounds too complicated let me summarize it in this way. Different service providers once they bid in the open competition and they want to invest in a country to have a telecom deployment there they always define the range of IP the telephone numbers that they wish to use. If the telephone numbers that they take are much more than what their actual hardware can support or what their actual marketplace is these numbers remain unutilized. So these numbers should be provided to someone else. This number pooling is related to this particular issue. The local routing number or the LRN is the mechanism to implement number portability because the real telephone numbers are not enlisted with the network portability administrative center. It is a unique 10 digit identifier that looks like a telephone number it is assigned to every switch. What happens is against the telephone number this 10 digit number helps to translate that particular telephone number to a switch whenever a new switch is to be assigned to that telephone number then only the LRN is assigned to that particular switch. This helps to make the existing PSTN hardware readily usable otherwise number porting would not have been possible. Now the LRN is assigned to each ported telephone number it means all the telephone numbers which do not require portability do not need this LRN. These LRNs are then used to route or forward the calls through the PSTN to the current switch that is currently serving this ported number. Now the LRNs are only intended to be the network address of the currently serving switch. It means these are not intended to have some kind of additional information related to the geographical area and the rate and the tariffs for instance if it is a local call or if it is a long distance call. Now we quickly have a look at the procedure that follows in implementation of number portability using the LRN. Here let's look at the service providers as the new service provider that is it has the switch to which now the number has been ported to and the old service provider to which the number originally belonged. Now whenever a request is made to dial in for a number that has been ported the new service provider notifies the old service provider of the requested port. It means now the LRN is activated. The old service provider is then asked to validate if the subscriber against which the LRN is invoked is a valid subscriber. Once the old service provider confirms and notifies the new service provider that indeed this number is a valid number and the subscriber currently is part of the overall carrier. The new service provider then notifies the network portability administrative control center to the it shares the information that a new requested port has just been requested. The network portability administrative center creates a pending port that is the port is not fully realized till it gets a confirmation from the old and sends it to the new service provider. Now when the network portability administrative center contacts the old service provider the old service provider does notify that the network provisioning administrative center. The information against which port it has been asked is actually valid and the port for which the network portability administrative center has been requested is valid. Now the new service provider notifies again the NPSC to activate the port. And now the pending port is activated in NPSC and this information is broadcast in the telecom network. It means both the calling party and call party are associated service providers are notified. Now all this happens in just few milliseconds. Now after this portability has been activated let's look at the call flow. Now the call is made to the ported telephone number. The initiating service provider switch launches a query to its local number portability called routing database and determines whether the telephone number has been ported or not. If the database response says that yes the number has been ported it provides the switch with the corresponding local routing number needed to properly route the call and correspondingly all the procedure that we saw like couple of slides ago is implemented. If no such record is found then the database response indicates that the call should not be routed based on the telephone number. Now if we look at a scenario where more than one intermediate switches happen to fall between the old service provider switch and the new service provider switch. In that case the penultimate carrier switch which is just second last switch to the new service provider it has the responsibility to make the local network portability database query. Now the query actually is the responsibility of such service provider. Usually what happens is that one or two at best switches happen to fall between different service providers. So it is a rarity because if it has not already been made this switch is going to do that otherwise it is considered that such request would have already been made.