Intelligent Network Services in Migration from PSTN ... - IEEE Xplore

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two IN services when migrating from Public Switched Telephone. Network, PSTN toward Next Generation Network, NGN. Next. Generation Network is one of the ...
Intelligent Network Services in Migration from PSTN toward NGN Mahmoud Saeidi, Mahmoud Pirhadi, Fattaneh Ayazi Iran Telecommunication Research Center Tehran, Iran [email protected], [email protected], [email protected] Abstract  In this paper we will propose two new scenarios for two IN services when migrating from Public Switched Telephone Network, PSTN toward Next Generation Network, NGN. Next Generation Network is one of the promising Networks in near future. Because of huge amount of investment on PSTN, the migration towards NGN implementation would be instant step by step and gradual not an instant replacement. . Therefore, we need to plan the interfaces between PSTN and NGN in order to convert data and signalling. By applying Intelligent Network services in PSTN, IN services scenarios will be changed while migrating to NGN. We assume that IN equipment is located in PSTN. We will propose two novel scenarios when users located in NGN request card calling and free phone Services. Keywords  Next Generation Network, Intelligent Network, Migration to NGN, Card Calling Service, Free Phone Service

1. Introduction With the increasing demand of the telephone services and wide variety of those services, the traditional telephone networks, composed of numerous interconnected switches, are not able to catch up with such a demand. Each demanded service must be implemented in every switch with the exactly same signaling protocols. During the development and maintenance, the coordination of different types of switches would be extremely difficult if not impossible. In other words, introducing new services in the Public Switched Telephone Network (PSTN) is a difficult process, as it requires the development from scratch and the modification of software of switches which are spread all over the network. To deal with this difficulty, communication operators have to evolve from hard coded switches to dynamically configurable distributed systems. Therefore a new architecture called Intelligent Network [1] was defined by ITU-T. The need of an intelligent service layer above the traditional transport layer to provide various kinds of value-added services is obvious. This layer of networks is called intelligent networks, IN. The IN is based on a simple principle: the service specific software is separated from the Basic Call Processing and is run on a specialized node This node is called the Service Control Point (SCP), while the switches are called Service Switching Point (SSP). The Service Management System (SMS) contains management functions of the IN systems. The Service Data Point (SDP) is a database that holds information related to the service. SDP could be either separated from SCP or loaded on SCP.

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Some of the IN services are Free Phone Service, Card Calling Service, Number Portability Service, Premium Rate Service, Universal Access Number Service, Universal Personal Communication Service, Televoting Service, Virtual Private Service and etceteras. There are different scenarios for them. These scenarios include exchanging INAP message among SSP, SCP and SDP. In these scenarios, the calling party and the called party are in PSTN. In other words, exchanging data and signaling is done by circuit-switched network. Many operators are now migrating their PSTNs from circuit switched network toward the packet-switched network paradigm. This new approach is often called the Next Generation Network (NGN). The term NGN is commonly used for changes in network infrastructure that have already started in the telecom and information technology (IT). As such, it is not a term that can be precisely defined but is rather an umbrella term that varies among individuals, vendors, and literature. The NGN enables network operators to run all services (i.e. voice, data and video) on a single network. The NGN concept is based on packet-based nodes called Media Gateways (MGs). Media Gateways take over the functionality of the switching hierarchy in the current PSTN system [2], [3]. The Intelligent Network concepts are very relevant to Next Generation Networks, and may provide a bridge from current telephony features to the new IP based network. In section 2 we describe the conceptual model of IN services. In section 3 we describe IN architecture. In section 4, IN Services Deployed in migration from PSTN to NGN is described. In addition, in this section we will propose two novel different scenarios for two IN requested service, Card Calling and Free Phone when migrating from PSTN to NGN.

2. IN Conceptual Model (INCM) [4] The INCM is composed of four planes, each representing a different abstract view of IN networks. According to Fig. 1, at the topmost level we have Service Plane, which describes services from user’s point of view. Service plane consists of different service features. Each service is composed of number of these features. CS-1implements 25 services using 38 service features. Also, CS-2 implements 60 services using 62 service features. Next plane is Global Functional Plane (GFP), which looks at services from the service provider’s viewpoint.

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This plane introduces concepts of SIBs, which are reusable functional blocks that can be chained together in various combinations to form a service. In the other words a service feature in the service plane needs several SIBs in the global functional plane to ensure its implementation. The linkage that combines the SIBs is called Global Service Logic (GSL). 15 SIBs are defined in CS-1 and 21 SIBs (including those in CS-1) are defined in CS-2. Third plane is Distributed Functional Plane (DFP). In this plane functional structure of IN is described from designer’s point of view. Functionality of SIBs is described with aid of Functional Entities (FE) and Functional Entity Actions (FEA). This plane also defines information flows (IFs) between these FEs. The last and lowest plane is Physical Plane. In this plane Physical Entities (PE) are used to implement the functions required in the distributed functional plane. There can be different mapping of FEs and PEs.

Network implementation independence also allows network and service operators to allocate functionality and resources within their networks and efficiently manage their networks, independent of network implementation specific developments by equipment vendors. Fig. 2 illustrates the IN architecture which includes a number of physical entities, SMP, SCP, SDP, SCE, SN, AD, IP, SSP, SSCP and NAP. The description of each physical entity is described in [6].

Fig. 2. IN Architecture

4. IN Services Developed in Migration from PSTN to NGN IN Services scenarios could happen when they are deployed in Next Generation Network.

Fig. 1: IN Conceptual Model

3. IN Architecture IN is applicable to a wide variety of networks, including but not limited to: Public Switched Telephone Network (PSTN), Packet Switched Public Data Network (PSPDN) and Integrated Services Digital Network (ISDN), both narrowband ISDN (N-ISDN) and broadband-ISDN (B-ISDN). IN supports a wide variety of services, including supplementary services. It also utilizes existing and future bearer services (e.g. as those defined in N-ISDN and BISDN contexts). The term Intelligent Network (IN) is used to describe an architectural concept, which is intended to be applicable to all telecommunications networks and aimed to ease the introducing and managing the new services. The objective of IN is to allow the inclusion of additional capabilities to facilitate provisioning of service, independent of the service or network implementation in a multi-vendor environment. Service implementation independence allows service providers to define their own services, independent of service specific developments by equipment vendors [5].

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When migrating to NGN, for providing IN services, not only SCP, SSP, STP and IP but also Media Gateway Control (MGC), Soft Switch or Call Server (CS), Signaling Gateway (SG), Media Gateway (MG) and Access Gateway (AG) will get involved in exchanging information. Call Server or MGC provides functions for the establishment and termination of sessions over the IP network. It maintains the state of all calls and tracks the resources that are allocated to them. The MGC interfaces various databases in the IP and SS7 networks (e.g., TCP/IP policy directories) to access user and service profiles. In addition, the CS provides address and protocol translation between the different network elements involved in the call. At the end of a call the MGC collects information that is required for billing. When a user located in NGN intend to request IN services, in order to establish a call to a user located in PSTN, Call Server in addition to controlling and establishing the connection between Access Gateway (AG) and Trunking Gateway (TG), it acts as an SSP. This means, it should detect IN services request and then creates INAP messages to notify SCP located in PSTN to provide those IN services. There are two protocols in NGN, Media Gateway Control Protocol (MGCP), and MEGACO (MEGACO is also called H.248). Interfaces to resources in an SS7 network are handled

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through SS7/IP protocols. Policy directories in an IP environment are accessed using the LDAP and COPS protocols. In the case of an IP client, the MGC will use SIP or H.323 to connect the IP client directly to establish the call and allocate the resources and services. It will also provide translation between H.323 and SIP to interconnect clients using different protocols. The Signaling Gateway (SG) provides functions for converting between the INAP messages carried over STP located in PSTN and the INAP messages carried over an IP-based network. When requesting IN Services, Signaling Gateway send the request to STP, which acts as an intelligent router and directs the request to the corresponding SCP. The Protocol we propose for IP-INAP connectivity is INAP over SIGTRAN. The role of the Signaling Gateway is to establish and tear down one or more IP-INAP links and to maintain the state of the connection between the two networks. IP congestion control, the detection of session failures and security are other important functions performed by the Signaling Gateway. Media Gateways (MGs) provide media adaptation between networks, one of which is presumed to be a packet, frame or cell network (i.e., an IP or ATM network). As a specific implementation of a media gateway, the Trunking Gateway (TG) provides conversion between basic T1/E1 circuits and an ATM or IP environment. A Media Gateway maintains knowledge of all its resources and, in the case of either occupied links on the SS7 signaling network side or congestion on the IP side, it makes sure that connections are handled in an appropriate way. At the end of the call the Media Gateway provides the MGC with usage and QoS information for billing purposes.

Fig. 3. IN Services deployed in migration to NGN

4. 1. The proposed IN Card Calling Service Scenario in Migration from PSTN to NGN Fig. 4 illustrates stages of the proposed scenario for providing IN Card Calling (Prepaid Calling) service. The scenario is composed of the following stages:

A Media Gateway would, for example, terminate a switched circuit network (trunk, loops), and then packetize the data stream if it is not already in packet form, and finally deliver the traffic to a packet network. The Media Gateway realizes point-to-point connection and conferences, and supports resource functions such as media conversion, resource allocation (including reservation) and event notification. An Access Gateway (AG), which combines a Signaling Gateway with a Trunking Gateway, is used for ISDN or Common Access Signaling (CAS) in which the signaling is embedded in a TDM signal. Access Gateway extracts the control information from signaling protocols such as DTMF or PRI and sends it to the MGC for processing. Fig. 3 illustrates a possible functional architecture for this deployment.

1- User located in IP network; enter Card Calling (Prepaid Calling) access code (200) 2- CS receives access code and detects an IN Service requested 3- CS creates INAP message (InitialDP) and sends it to SG by INAP over SIGTRAN protocol 4- SG sends INAP message to STP located in PSTN 5- STP directs INAP message to SCP located in PSTN 6- SCP refers to Databases in order to identify the type of requested service 7- SCP creates INAP message(Prompt and Collected User Information), and sends it to STP 8- STP directs the message to SG 9- SG sends INAP message to CS for Playing Announcement using INAP over SIGTRAN 10, 11, 12- CS requests IP to Play Announcement and connects IP (Intelligent Peripheral) to AG through TG. The establishment between TG and AG is done using RTP 13, 14 – IP play announcement and User located in IP network hears the announcement through TG and AG 15- User enters PIN and Password. AG sends this information to CS using MEGACO and CS receives PIN and Password, then creates INAP message (Prompt and Collected User Information) 16- CS sends it to SG using INAP over SIGTRAN

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17- SG sends this INAP message to STP 18- STP directs INAP message to SCP 19- SCP refers to Databases and checks the card validity and the entered PIN and Password 20- If the validity and the entered PIN and Password are all right then SCP will let CS establish the call. In this case, SCP creates INAP message “Connect” and “Apply Charging” and sends it to STP, otherwise the connection will be failed. Sending INAP messages “Connect” and “Apply Charging” could be sequential or simultaneous. The translated number of called party is sent by INAP message “Connect” and the information corresponding to charging is sent by INAP message “Apply Charging” 21- STP directs the messages to SG 22- SG sends the messages to CS using INAP over SIGTRAN and then CS establishes the call by SG with regard to the dial number entered by user located in IP network and user located in PSTN hears the ring and picks up the phone 23, 24- switches located in PSTN and TG do exchanging voice 25- When finishing the call, the user located in IP network hangs up. At this time, AG sends the corresponding signaling to CS 26- CS sends two operations “Tdisconnect” and “Apply Charging Report” to SG in parallel, reporting the status of the call and charging result

Fig. 4. The proposed IN Card Calling Service Scenario

4. 2. The proposed IN Free Phone Service Scenario in Migration from PSTN to NGN Fig. 5 illustrates stages of the proposed scenario for providing IN Free Phone service. The scenario is according to the following stages: 1- User located in IP network; enter Free Phone access code (800)

27- SG sends the messages reported to STP

2- CS receives access code and detects an IN Service request

28- STP directs the operations to SCP

3- CS creates INAP message (InitialDP) and sends it to SG by INAP over SIGTRAN protocol

29- SCP receives the operations and sends INAP operation “Release” to STP, informing CS to release the current call 30- STP directs INAP operation to SG 31- SG sends INAP operation to CS and CS clears the call. If user located in PSTN has not hung up, he/she will hear the busy tone In stages 7, 8, 9, 10, 11, and 12 of the above-proposed scenario, SCP sends INAP message (Prompt and Collected User Information) to CS and then CS connects IP to user located in IP network to hear the announcement. In these mentioned stages, the other proposed plan is that SCP sends INAP message (Prompt and Collected User Information) to IP directly and IP connects to TG, and then CS establishes connection between TG and user located in IP network.

4- SG sends INAP message to STP located in PSTN 5- STP directs INAP message to SCP located in PSTN 6- SCP refers to Databases and checks if the call could be established. If it is alright then SCP will let CS establish the call. In this case, SCP creates INAP message “Connect” and “Apply Charging”, otherwise the connection will be failed 7- SCP sends the created messages to STP 8- STP directs the messages to SG 9- SG sends the messages to CS using INAP over SIGTRAN and then CS establishes the call by SG with regard to the dial number entered by user located in IP network and then user located in PSTN hears the ring and picks up the phone 10, 11- Switches located in PSTN and TG do exchanging voice 12- When finishing the call, the user located in IP network hangs up. At this time, AG sends the corresponding signaling to CS

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13- CS sends two operations “Tdisconnect” and “Apply Charging Report” to SG in parallel, reporting the status of the call and charging result

addition we proposed scenarios for providing two IN services, Card Calling and Free Phone.

14- SG sends the messages reported to STP 15- STP directs the operations to SCP

REFERENCES

16- SCP receives the operations and sends INAP operation “Release” to STP, informing CS to release the current call 17- STP directs INAP operation to SG 18- SG sends INAP operation to CS and CS clears the call. If user located in PSTN has not hung up, he/she will hear the busy tone.

[1] I. Faynberg and al., "The Intelligent Network Standards, their application to services", In MCGraw-Hill Ed. N.Y., 1996. [2] "The migration story: Different Highways to a Multi-service Network," Ericsson whitepaper, 2001. [3] "Next Generation Networks," IEC. ORG tutorial. [4] ITU-T. Recommendation Q.1211, Introduction to Intelligent Network Capability Set1. Technical report, International Telecommunication Union, October 1992.Q.1211. [5] ITU-T, Recommendation Q.1201, Principles of Intelligent Network Architecture, Technical report, International Telecommunication Union, October 1992.Q.1215. [6] ITU-T. Recommendation Q.1215, Physical plane for Intelligent Network CS-1. Technical report, International Telecommunication Union, October 1992.Q.1215.

Fig. 5. The proposed Free Phone Service Scenario

5. Conclusion

The ultimate goal of the telecommunications networks is to provide rich services to fulfill the needs of different circles of people, and at the same time to increase the revenue of the operating companies. Intelligent Network as an additional network layer between the traditional transport layer and the final customer is able to provide services in a unified way and screens the differences in the switching systems. The intention of this paper was to present the current state in the convergence of different types of networks (PSTN/IN and IP), as well as to delineate the evolution process and migration scenarios of IN services toward NGN. When migrating to NGN, for providing IN services, not only SCP, SSP, STP and IP but also MGC (Soft Switch or Call Server (CS)), Signaling Gateway, Media Gateway and Access Gateway will get involved in exchanging information. In this case, CS performs the role of SSP in next generation network and should be able to create INAP messages and send it to SCP. We proposed a new connection between PSTN, IN and NGN in order to provide IN Services for user located in NGN. In

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