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Number Portability (NP) is a regulatory procedure allowing subscribers and businesses to change their service providers without changing their telephone numbers thus avoiding the need to publish new telephone numbers. This, in turn, creates a more competitive market environment, increasing the level of open competition among Telecom Service Providers on issues of concern to subscribers such as quality of service, customer care, value-added services, and so on.

Number Portability affects the routing mechanisms for terminating voice/data calls. The fundamental nature of the dialed number changes from a physical routing address to a virtual address. Transparency to subscribers is achieved by incorporating a translation function to map a potentially ported dialed number into a network routing address (either a number prefix or another number) for further routing.

Sonus' Number Portability solutions are based on the following two approaches:

  • Intelligent-Network-based (IN-based) NP solution

  • Mobile Number Portability Signal Relay Function-based (MNP-SRF-based) solution

Both solutions may be implemented as standalone or integrated with STP functionality. The following figure depicts these two solutions.

Figure : Relationship Between Central Database, LSMS, and STP


The ITU equivalent of a Local Service Management System (LSMS) is a Service Provisioning System (SPS).


The NP Service operates on DSC includes the following characteristics:

  • agnostic to the overall NP scenario (direct routing and indirect routing)

  • available to any application

    • Mobile, Fixed

    • Postpaid and Prepaid

    • Voice, Short Message Service (SMS), and Multimedia Messaging Service (MMS)

  • fully modular to support any business model and long term requirements

  • flexible operational environment

    • centralized management and provisioning

    • data measurements (statistics) and alarms 

  • scalable

  • carrier-grade platform

The centralized database is either hosted locally or separately managed by a third-party entity. In the latter, the third-party managed centralized database periodically updates the local database in the NP on new numbers ported.

For more information about NP, refer to the appropriate sections in the SS7 Application Guide 2.

Number Portability Architecture

The solution offered by the Sonus STP is based on the functionality of the SS7 signaling network and covers the following:

  • The correct routing of calls to ported (imported and exported) subscribers on any type of interconnected network Global System for Mobile Communication (GSM), Public Switched Telephone Network (PSTN), and so on.

  • The correct routing of non-call-related signaling messages such as Short Messages and Optimal Routing requests across interconnected GSM networks.

The following requirements and assumptions are the basis of the solution:

  • The network has access to a database containing all ported numbers and their serving network (ported PSTN and ISDN numbers may also be present in this database).

  • The network from where a call to a ported number originates is capable of routing this call directly to the serving (recipient) network.

  • The association between any additional Mobile Station Integrated Serviced Digital Network (MSISDN) numbers (fax and/or data number) and primary MSISDN number is required.

Sonus' NP solution in the following figure shows the Sonus NP as a universal solution for all types of carriers, service providers, and network operators. NP will become required throughout the network and will be integrated into call processing and completion. This solution addresses the unique needs of a ubiquitous, high-volume/high-availability database transaction requirement integral to basic call processing while maintaining the high-reliability standards expected in the telephone network.

Beside NP, the capabilities of the system will also support future network improvements, such as the flexible routing to mobile and intelligent application parts of Home Location Registries (HLRs), Service Control Points (SCPs) and Short Message Service Centers (SMSCs). The Flexible Routing feature is not part of the Mobile Number Portability (MNP) functionality and has no impact on the external network behavior.

Figure : Layered Network Architecture

Sonus' NP solution is comprised of the following elements:

  • real-time memory resident database used for storage of the ported and associated routing numbers

  • front-end protocol/application service handlers supporting both fixed and mobile solutions Flexible Routing feature

  • NP and Flexible Routing provisioning system

The DSC utilizes an architecture designed to allow for a fully featured and reliable provisioning experience while maintaining a fast, scalable and reliable message processing system. Management of a particular application is kept on separate CPUs from the Signal Processing CPUs (see the following figure).

In each major application group, two CPUs are used for management functions and at least two are used for routing. In the following figure, the Ethernet switches are shown in purple. The traditional STP components are shown in light blue. These consist of two Management CPUs, on which provisioning, logging, and statistics are kept. The light blue Routing CPUs (of which there can be many)] handle MTP Level 3 (MTP3) traffic and above, including Global Title Translation (GTT), Point Code Emulation (PCE) and Signaling Gateway (SG) functions. The light blue I/O cards handle MTP Level 1 and 2 for the Sonus STP. These cards handle all-time division multiplex (TDM) links such as low-speed links (LSL), Asynchronous Transfer Mode (ATM) links and Annex A links.

Figure : Cards used in Sonus STP and NP Application

In the preceding figure, the CPU cards used for NP are shown in dark blue. Two Flex Manager CPUs are supported. These CPUs hold the database used for NP and other Flex Routing Applications. The database is replicated on disk drives on both cards. The Flex Routing CPUs maintain the data used by the Distributed SS7 Services (DSS) CPUs for routing. The DSS CPUs are similar in role to the STP Routing CPUs. A minimum of two such CPUs are required, and more are added as scalability is required. The DSS holds in memory the portions of the database required to respond to SS7 queries and forward messages. 

For NP applications, another provisioning system must be considered. Unlike the STP provisioning, the NP and Flex Manager provisioning uses servers external to the DSC. The Services Provisioning System (SPS) is a Local Service Management System (LSMS) that allows for direct provisioning of the Flex Manager database, and interfaces with the Centralized Number Portability (CNP) databases. The CNP databases are often referred to National Portability Administration Centers (NPAC) and contain Number Portability information for the whole country. The Number Portability Administration Center (NPAC) may also utilize an architecture including a Service Management Systems (SMS) to act as intermediate provisioning systems. The SPS can interface to both SMS and NPAC Operation Support System (OSS) systems.

A further advantage of the SPS server is that it enables the updating of several Sonus STPs at one time, as shown in the following figure.

Figure : SPS Server Provisioning Multiple STPs


Flexible Routing

The Flexible Routing feature (see the following figure) provides the capability to migrate from a single location HLR/Voice Mail Messaging System (VMS) network to a multiple location HLR/VMS network with minimum impact at the Mobile Switching Center (MSC) nodes. Flexible Routing uses

  • International Mobile Based Identity-based (IMSI-based) addressing for the mobile customer Registration and Location Update procedure

  • MSISDN-based addressing for directing queries related to Send Routing Information for terminating a call

  • Forward Short Message for SMSC services

Figure : Flexible Routing

Flexible Routing mainly represents an enhanced Global Title Translation (GTT) analyzing all digits in the Called Party Address that allows the flexible routing of an E.164 or E.214 addressed SCCP messages to several physical systems inside the network. Flexible Routing is similar to, but not part of, the MNP functionality. Therefore, Flexible Routing is deployable on DSC in non-MNP environments.

The Flexible Routing feature provides the following benefits:

  • service GTT processing on the received IMSI and MSISDN

  • support E.164 and E.214 addressed SCCP messages

  • support for IMSI processing

  • support for MSISDN processing

  • support Location Update, Send Routing Information and Forward Short messages


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