Number Portability Tutorial
The purpose of this note is to explain the basic concepts and terminology of number portability.
Number Portability Tutorial ..................................................................................................................... 1
1
Introduction .................................................................................................................................. 1
1.1
What number portability is ................................................................................................... 1
1.2
The use of telephone numbers .............................................................................................. 1
2
Network issues.............................................................................................................................. 2
2.1
Call routing without number portability ............................................................................... 2
2.2
Call routing with number portability .................................................................................... 2
2.3
Call routing in mobile networks ........................................................................................... 3
2.4
Call routing with mobile number portability ........................................................................ 4
2.5
B-number call routing solutions ........................................................................................... 5
2.6
CellOne’s call routing solution ............................................................................................. 5
2.7
Digicel call routing .............................................................................................................. 5
2.8
Text (SMS) routing ............................................................................................................... 5
2.9
CellOne text delivery ............................................................................................................ 6
2.10 Digicel text delivery ............................................................................................................. 6
3
Process and database issues .......................................................................................................... 6
3.1
Digicel’s Club System .......................................................................................................... 7
3.2
The RunMyProcess system................................................................................................... 8
3.3
Comparison of different systems .......................................................................................... 8
3,4
Overview of the porting process ........................................................................................... 9
IT Support Systems ............................................................................................................................ 11
1
Introduction
1.1
What number portability is
Number portability is the ability for a customer to keep his number when changing operator.
The customer goes to the new operator (called the recipient operator) and opens a new account and
asks for the new operator to close his account with the old operator (called the donor operator), and use
the old number for the new account.
In order to provide this facility the new and old operators interact with each other according to the
number portability process.
In order to route calls and text messages correctly to and from ported numbers, the operators have to
make changes to their networks.
1.2
The use of telephone numbers
Telephone numbers are no only used by customers and used within networks for routing calls and text
messages, but they are also used in most of the operator’s support systems as a means of customer
identification. Examples of such systems are billing, pre-pay credit management, pre-pay credit
retailing, anti-fraud measures etc. These support systems have many internal checks and may need
upgrading if an operator starts to provide services to customers using telephone numbers outside the
number blocks that were originally allocated to the operator and for which the support systems were
originally designed.
Hence the introduction of number portability requires careful analysis of ALL the systems that an
operator has, and not only the network equipment.
2
Network issues
2.1
Call routing without number portability
In a competitive telecommunications market, there are a number of alterative networks, which are
interconnected. Customers can choose which network to connect to and the networks are configured so
that any customer on one network can call any customer on another network. Each customer is
identified to others by their telephone number.
The caller is known as the A-party and the called the B-party, and their numbers are known as the Anumber and the B-number.
The customer is allocated their number by their network operator from a block of numbers allocated to
the operator by the regulator. Hence the network that serves the called party can be identified by a
simple analysis of the initial digits of the called number. The ability to do this easily is removed by
number portability.
Calls may traverse one or more switches each with several different outgoing routes. The switches
analyse the B-number by looking up a table to see which route to use for the particular value of the
initial digits of the B-number.
2.2
Call routing with number portability
There are two ways to handle the routing of calls to ported numbers:

Onward routing where the call is routed as normal to the operator with the block of numbers
that contains the ported number, and this operator (called the block operator) knows where the
number is now being served and onward routes the call to the correct operator. Onward
routing is concerned with the delivery of calls and involves the block operator and the
operator that is currently serving the customer.

All Call Query where the originating operator, or any operator to whom the call has been
passed, looks up the number in a list of ported numbers and the operators serving them and
routes the call accordingly. ACQ is concerned with outgoing calls in contrast with Onward
Routing.
In both these cases once the identity of the operator that is serving the number has been found, a prefix
is added in front of the B-number to indicate which network or switch the call should be routed to.
Onward routing is a requirement and without it number portability cannot work. However it results in
some cases in inefficient routings.
In contrast, All Call Query is not essential but is desirable to achieve the most efficient routings in all
cases.
Because All Call Query may require some new capital investment and taking account of the overall lo
number of portings expected in a small country such as Bermuda, the Authority has not made the
implementing of ACQ a requirement for fixed operators but has left it optional. In the case of mobile
operators because the expectation was that these operators would use the same technical solution for
both onward routing and ACQ and so there would not be an issue of additional capital expense for
ACQ, the Authority made ACQ a requirement for mobile operators only for outgoing calls.
The following diagram shows the two different systems and the routings that result from them.
Recipient
operator
All Call Query
Originating
operator
Choice
Porting
Block
operator
Onward routing
2.3
Call routing in mobile networks
A mobile customer may be located anywhere in the world and attached temporarily by radio to any
network. The customer’s “home” mobile network (eg CellOne or Digicel) needs to be able to deliver
calls to its customers wherever they may be. To be able to do this, the home network maintains a
second by second up to date list of the current location of its customers. This list or database is called
the Home Location Register (HLR)
Incoming calls are routed by the other networks to the switch of the home network. This switch then
looks up the HLR to see where the customer is and is given a Mobile Station Roaming Number
(MSRN) for the customer. This is a telephone number but one that is not visible to the calling and
called parties and is used internally by the networks only. The call is then routed onwards using the
MSRN to the switch where the customer is currently located.
This arrangement is shown in the following diagram.
Home
Location
Register
Mobile Station Roaming Number
(MSRN)
Where is B-number?
Incoming call to
B-number
Call to
MSRN
Switch
Visited
Switch
Block network
Visited network
2.4
Call routing with mobile number portability
With mobile number portability, an operator may be serving any mobile number from the range of
mobile numbers with in the country. Thus the operator’s HLR needs to contain not only information
relating to the numbers in the operator’s own number block but also numbers imported from other
operators.
Thus the scope of the “HLR system” needs to increase from handling:

Active own customer numbers from own number block



Active own customer numbers from own number block
Active own customer numbers from other operator’s number block (imported customers)
Non-active ex customer numbers from own number block (exported customers for onward
routing)
to
If ACQ is also being supported then there is a need also to support

Active other operator customer numbers from other operator’s number block (eg portable
fixed numbers
For own mobile customers the HLR needs to provide considerable functionality in continually tracking
the location of the customer, but for other numbers serviced by other networks whether fixed or
mobile, the system needs only to provide a prefix to add to the number to indicate which network is
currently serving the called number.
The common solution is therefore to provide a simple database between the switch and the HLR. This
is known as a Signalling Relay Function.
 For numbers that the operator is not currently serving this function adds the correct prefix in
front of the called number so that the switch can route the call correctly.
 For numbers that the operator is not currently serving, this function passes the handling to the
HLR.
Many operators use third party equipment produced by Tekelec called the Eagle 1 to provide the
Signalling Relay Function. Switch manufacturers such as Ericsson provide their own solution called
the Flexible Number Register (FNR)2
The following diagram shows the routing of calls with these arrangements.
SRF/FNR/
HLR
SRF/FNR/
HLR
Mobile Station Roaming Number
(MSRN)
Prefix + B-number
Where is B-number?
Where is B-number?
Incoming call to
B-number
Switch
Block network
1
2
Call to
Prefix + B-number
Call to
MSRN
Switch
Visited
Switch
Serving network
Visited network
See: http://www.tekelec.com/eagle-5.aspx
See: http://www.ericsson.com/ourportfolio/telecom-operators/unified-number-portability
2.5
B-number call routing solutions
The B-number is the called party number.
Switches look up tables of number blocks to find out which route to use for a given B-number. This is
called B-number analysis.
While these tables are normally organised in number blocks it is possible on some switches to include
individual numbers in the tables and so to use the table in the switch for ACQ instead of using an
external database.
2.6
CellOne’s call routing solution
CellOne’s Nokia Siemens switch offers more powerful B-number analysis facilities than Digicel’s
Ericsson switch and so CellOne can use the B-number analysis facility of their switch for ACQ routing.
The logic of CellOne’s call handling is therefore:



Look up a separate table of ported numbers in the switch to see if the number is ported and
where it is served;
If the number is not served on CellOne, do normal routing analysis and route the call
accordingly;
If the number is served on CellOne refer the call to the HLR, which contains imported
numbers as well as numbers from CellOne’s own number block, and route the call using the
MSRN obtained.
CellOne’s separate table supports both onward routing and ACQ.
2.7
Digicel call routing
Digicel say that their switch cannot perform a look up or a separate table of ported numbers and that it
can only integrate ported numbers into the main routing table. They claim that this is technically
demanding and time consuming. (see separate comments).
Digicel have not distinguished between the support of onward routing and ACQ.
The Authority understands that:

Digicel could use their existing HLR to support onward routing for calls to numbers that
Digicel has ported out. This would enable their customers to port to CellOne.

Digicel has refused to consider obtaining a Tekelec Eagle requirement, which might be
available more quickly that the Ericsson FNR.
2.8
Text (SMS) routing
The routing of text messages (Short message Service – SMS) is different from the routing of calls.
Texts are sent to the Short Message Service Centre (SMSC) of the sending network.
The original solution was for the SMSC to find out the identity of the operator who is serving the called
number and send a query to the HLR of that operator to find out where the called party is and then to
send the message to the switch to which the called party is temporarily attached so that the message can
be delivered. The following diagram shows this arrangement.
diagram
Due to the unexpected growth of the text service, the main routing system for text messages is now to
use transit hubs. These hubs are interconnected and handle the routing of text messages. One major hub
provider is Syniverse.
2.9
CellOne text delivery
The Authority understands that CellOne uses Syniverse for the delivery of nearly all its text messages
from customers of other networks. CellOne will give Syniverse an up-to-date list of ported numbers
and Syniverse will use ACQ with this list and route the SMS messages accordingly either to CellOne or
Digicel.
CellOne does not have the type of interconnection with Digicel to allow Digicel to access the CellOne
HLR as in the original solution for SMS delivery.
2.10 Digicel text delivery
The Authority understands that Digicel has more diverse arrangements for SMS delivery including
arrangements with several different hubs.
At present about 75% of Digicel subscribers use the Bermuda SMSC, but 25% use the Jamaica SMSC.
The identity of the Jamaica SMSC is stored in their handsets and there is a logistical problem in
persuading the subscribers to change this identity to point to the Bermuda SMSC. Digicel plans to
migrate all its subscribers to the Bermuda SMSC by around mid 2014.
The Bermuda SMSC will do ACQ and send outgoing SMS messages to the Syniverse hub if the Bnumber is served by CellOne. The ACQ will be supported by the Ericsson FNR.
The Authority has not been informed of the interim solutions that Digicel has considered.
3
Process and database issues
There is considerable confusion around the use of the term “database”.
A database is a collection of information and the means of storing and accessing it.
In the context of number portability, the information concerned is the list of ported numbers and the
identity of which operator is serving each number and the operator’s routing prefix.
There are three possible functions for a database in number portability:

To handle (monitor and vet) the messages that pass between operators during the process of
porting each number;

To compile and store a list of ported numbers and which operator is serving them and to make
this list available to any operator that needs it;

To handle queries on a call-by-call basis to find out which operator is serving a given number,
ie to support All Call Query routing within a network.
Served numbers 1
Routing
All numbers
1+2+3+4
Operator 1
Broadcasts results
Served numbers 2
Operator 2
VPN or
Internet
Routing
All numbers
1+2+3+4
Porting process
Operator 4
Routing
All numbers
1+2+3+4
Operator 3
Served numbers 3
Served numbers 4
Routing
All numbers
1+2+3+4
Porting
Many countries use a central database for the first two of these functions and there was considerable
discussion in the past about the possible procurement of a central database for Bermuda for these two
functions. Eventually the Authority decided that such a database was not essential given the small
number of operators and left this issue for the operators to decide.
The Authority proposed that emails could be used as a baseline system for exchanging messages during
the process of porting each number
The Authority did make it a requirement that each operator should make available up to date
information on the ported numbers that it serves so that any operator would have the information
needed to do ACQ routing. Such information could be accessed through downloading a file from a
website.
The third function of support of call by call routing is normally handled by each operator themselves
using copies of the information obtained under the second function. The reason is that satisfactory
operation of this third function is essential for routing calls and operators normally insist on handling
such a quality-sensitive matter themselves.
The third function is what is handled in mobile networks by the Signalling Relay Function, the Tekelec
Eagle or the Ericsson FNR.
3.1
Digicel’s Club System
At the workshop in July, Digicel proposed that the operators should club together to procure a
distributed database system to provide the second function. Digicel took the lead in preparing a
specification for this procurement.
See file LNBP_V2.jpg
The Authority had difficulty in understanding the exact scope of what was proposed. The initial version
of the specification said:
“This Requirements Definition Document (RDD) defines the technical and functional requirements for
local Number Portability (LNP) distributed Database for Telecommunication reform. The requirements
contained within will determine the basis for the Solution Architecture Document (SAD). Deviation
from the approved RDD will result in change document and inherent timelines.”
The Authority proposed additional text in an attempt to clarify the proposal and the working in the
second version was updated as follows:
“This Requirements Definition Document (RDD) defines the technical and functional requirements for
Local Number Portability (LNP) distributed Database for Telecommunication reform. The
requirements contained within will determine the basis for the Solution Architecture Document (SAD).
Deviation from the approved RDD will result in change document and inherent timelines.
This document is intended as a procurement specification to obtain quotations from potential suppliers
for a database to handle real-time routing queries for calls to ported numbers. The intention is that
each operator who wishes to use ACQ routing will separately procure such a database under the same
specification for use in their own network. The separate databases would have a common
synchronisation mechanism. The aim is to obtain a competitive quotation from suppliers for multiple
orders and so achieve some economy of scale as well as standardisation of the system to be used.
The database does not handle the porting process between donor and recipient and will be fed with the
results of this porting process, which is specified in other documents. The database allows for
automation from billing platforms to be built.
The databases will have a common core that is identical for all operators, and common interfaces
between the operators, but will have operator specific interfaces to the switches and support systems of
the individual operators.”
Although the other operators were invited to contribute to the drafting of the specification, the
Authority is not aware of any other operator making a significant contribution, and one of the purposes
of the Authority in convening the meeting on 24-25 September was to ascertain whether the proposal
had real support from other operators. At this meeting it became apparent that the likely costs would
exceed $100k per operator and the other operators indicated that they were not willing to commit to
such expenditure. Digicel expected that the total costs would be around $600k.
The draft specification circulated by Digicel on 18 July stated in section 7.1:
“Local Number Portability must be implemented by March 1st 2014 with testing between carriers to
occur January 31st 2014.”
indicating that Digicel had not doubt in its mind over the requirements.
3.2
The RunMyProcess system
At the meetings on 24/25 September, after realising that there was no support for the Digicel proposal,
the operators requested the introduction of a “ticketing system” to log the communications between
each operator and compile independent statistics on the response times during the porting process. The
aim was for a “cloud-based” system, ie one connected to and accessible from the internet and
developed using existing software services on the internet.
The Authority undertook to look into the possibility of such solutions and developed a simple
demonstration system using a host service called RunMyProcess (RMP). This system was presented at
the meeting on 4-5 December (postponed one week to enable Neil Lupsic to attend) and received
support from all present for further development. This system has been developed and is undergoing
final testing ready to support portability on 3 March.
The RMP system supports the functions first and second functions identified earlier.
3.3
Comparison of different systems
The following table compares the different systems considered and the functionality that they support
and is intended to help the reader relate the different systems to each other.
Function
Central
Determination
Digicel
RunMyProcess
1 - Monitor
and vet
exchange of
messages
2 - Compile
and maintain
list of ported
numbers
3 - Handle
call-by-call
ACQ routing
database
Supports
baseline
Email
proposal
Email
Supports
Supports
Download
from website
Club solution
Supports
Operator’s
internal matter
Operator’s
internal matter
Club solution
Operator’s
internal matter
The Ericsson FNR and the Tekelec Eagle are solutions for the third function. The Club solution is a
solution for the second and third function.
3.4
Overview of the porting process
(Taken from the specification)
QUOTE
In number portability, the Subscriber:

opens an account with the new (Recipient) Operator but using an existing number that they are
already using with the old (Donor) Operator;

requests the new Operator to close their service3 with the old Operator;

requests the Operators to change their routing arrangements so that calls will be routed to the
new Operator.
The total duration of the porting process is not more than one or two business days including all stages
unless either the subscriber or recipient operator wishes the process to take longer.
The design of this porting process is asynchronous and sequential; a sequence of actions is specified
with each action starting only after completion of the previous action.
The design limits the state information on the process that needs to be held by the operators and so
minimises the problems of re-establishing the process after some unforeseen disruption. If problems
occur then the porting transaction is failed, the Operators should cooperate to resolve the problem or
the Subscriber should take the necessary actions to resolve the problem and then a new porting
transaction should be started.
The process allows for a number to be ported to both a new account and to an account that is already
active with a number allocated by the Recipient Operator.
The procedure applies for both pre-pay and post-pay.
The "front end" of the procedure involving the Recipient Operator and the customer is specified only
where it is essential to ensure that the whole procedure works reliably. The parts that are unspecified
allow scope for an individual Operator to develop its own specific procedures.
Figure 2 gives and overview of the roles.
The administrative closure of the account may be at the end of the month when the service was
closed and the number ported.
3
Call or SMS to prove possession
Current
number
ID
Bill
(Donor)
Recipient
Shop
Internet/VPN
Explain
Checks
Normal Application Form
+ Porting Request Form
Recipient
Operator
Transaction
Messages
Recipient
Network
Donor
Operator
Donor
Network
Other
Network
Figure 2: Overview of the roles
The customer requests a new account with number portability from the Recipient Operator or their
Retailer.
The customer is given information about porting and their identity is checked and the necessary
information (different for pre-pay and post-pay) is collected.
Additional credit checks etc may be performed according to the Recipient Operator’s own practices.
The customer signs the Porting Request Form as the legal instrument appointing the Recipient Operator
as their agent to close their service with the Donor Operator.
The Recipient Operator requests the Subscriber to call (or send an SMS to) the Recipient from the
number to be ported using the account with the Donor Operator so that the Recipient can check that the
CLI of the call is the number to be ported.
The Recipient sends the Authorisation Request to the Donor Operator.
The Donor Operator performs the authorisation checks and sends the Authorisation Response
indicating whether or not the number can be ported.
If the Donor Operator fails the request then the problem must be resolved and the procedure started
again from the beginning.
The Recipient Operator then activates the ported number on its network and sends the Instruction to the
Donor Operator. The Donor Operator deactivates the number on its network and applies onward
routing for any incoming calls that are received without a prefix. See later for full details.
Figure 3 shows the process.
UNQUOTE
4
IT Support Systems
In addition to the networks the operators have extensive IT support systems for functions such as
billing, pre-pay credit managements and fraud prevention. Numbers are used pervasively for customer
identification and all these systems need to be analysed carefully to see what changes are needed if any
to support number portability.
The Authority at the workshop on 16/17 May included in slide 18 the advice:
“Importing operators need to review all their IT systems for operation with a number from a different
number block (especially pre-pay)”
There is no evidence that Digicel did this analysis until shortly before it wrote to the Authority in
December citing various IT support issues as factors in its request for postponement.
Whilst the Club System and the Ericsson FNR provide a source of the information on ported numbers
needed by other systems, the updating of those systems themselves in the major issue and would
require the same work whichever system is used for the information.