ZTE´s Softswitch Networking and Application Cases

1 Overview

In recent days, the rapid increase of data traffic and the development of IP networks have brought unprecedented challenges to the conventional telecom industry. During this course, the packet-based IP network is drawing increasing attention.

To integrate diversified services in the future on IP networks has become the common industry aim. But problems  inevitably arise:

What shall we do with the traditional circuit switch telecom network?

How should we protect trillions of global telecom network investment?

And, how can the current network smoothly transit to the future IP network?

To solve these problems, a next generation architecture is needed, which enables easy provision of integrated voice, data and multimedia services, full utilization of existing resources and prompt creation of new services.

2 Solution to Softswitch  Networking

ZTE Corporation is one of the few international vendors who can provide total network solutions     for    Softswitch－based     NGN. ZTE´s Softswitch architecture satisfies the networking demands of current fixed-line  operators, mobile operators and new entrants by its openness and high reliability. It protects operators´ investments through the convergence with existing networks and provides operators with new revenue streams and competitive opportunities by its complete integrated access capability, various service provision patterns and quick service delivery.

2.1 Long Distance VoIP Service  Solution over Data Backbone

ZTE´s Softswitch system, together with Trunking Gateway (TG) and Signaling Gateway (SG), can implement long distance voice service over IP backbone network. This solution is much more flexible and convenient for service creation than the traditional tandem/toll exchange function. It enables unified service implementation by using a service creation platform, which is also beneficial to the integration of voice, data and image and to the smooth transition from PSTN to NGN in the future.

As shown in Figure 1, ZTE´s Softswitch control device ZXSS10 SS1 may perform call control, signaling process, service proxy, resource allocation, accounting management and protocol adaptation within its domain. The trunking gateway (TG) provides the trunk access and handles the conversion of signaling and media stream, while the SG is in charge of SS7 adapting.

The Softswitch + TG + SG (Signaling Gateway) solution can provide the toll service over a backbone data network, and also achieve the interoperability of both the network and the server between the existing PSTN and intelligent network (IN). The complete set of services of legacy IN can be inherited by the interworking of Softswitch with the service control point (SCP) via the intelligent network application protocol (INAP). At the same time, carriers are able to provide customers with diversified and customized services and IP value-added services by using a new functional entity, the application server.

2.2 Local Voice and Data Service Solution over MAN

With the development of the metropolitan area network (MAN) and forthcoming fiber to the premise (FTTP), the traditional twisted-pair access cannot meet the market demand any longer due to its expensive operational cost, limited bandwidth and complicated construction process. As business competition becomes fiercer in the telecommunications field, carriers therefore begin or plan to build the broadband access data network in order to improve their competence.

ZTE can provide excellent solutions which help service providers to resolve these problems. The following gives four kinds of VoIP access options for carriers to use to provide voice and/or data services over MAN.

(1) SOHO Mode

The mode is a combination of Softswitch + TG + SG + IAD (Integrated Access Device) with a single telephony and data interface to the family customers. It is used for house/SOHO, school offices and office buildings, with advantages of simple implementation, abundant functions and full utilization of network resources.

(2) Community Mode

This mode is a combination of Softswitch + TG + SG + AG (Access Gateway) or Softswitch + TG + SG + IAD with multiple telephony interfaces to the resident customers or private customers. It is suitable for subscribers with telephone lines. This mode may be used for residential communities, small business corporations, office buildings, passageways and schools, with advantages of low cost and convenient access.

(3) Enterprise Mode

The mode is a combination of Softswitch + TG + SG + IAD with multiple telephony interfaces or Softswitch + TG + SG + I704 with multiple E1 interfaces to the existing private branch exchange (PBX) of enterprise customers, and may provide the accessing VoIP service.

(4) Intelligent Terminal Mode

The mode is a combination of Softswitch + TG + SG + Intelligent Terminal (SIP-phone, etc) for end users. It is suitable for subscribers with unshielded twisted Pair 5 (UTP-5) only. This configuration has the advantages of simple implementation and better utilization of the existing value-added services and intelligent services.

The access methods are shown in Figure 2. The core control device is the signaling system (SS); it interoperates with PSTN via TG and SG; the customer premise devices include AG, IAD and the intelligent terminal.

The Softswitch control device is responsible for the call control, signaling process, resource management, accounting management, user management and protocol adaptation within its domain, with the Ethernet interface to the data network. In addition, the TG performs media conversion between the PSTN and IP network, with the Ethernet interface at the media network side and E1 interface at the PSTN side. The protocol between TG and Softswitch is H.248 or the media gateway control protocol (MGCP).

The SG implements the No.7 signaling transfer between the PSTN and IP network, with the Ethernet interface to the data network and No.7 signaling link to PSTN. The signaling transport (SIGTRAN) is adopted between SG and Softswitch.

3 Application Cases

To date, ZTE´s NGN solution and products have been chosen in the commercial NGN deployments of all the six big service providers in China.

ZTE Corporation is also the only vendor who has product deployments with almost all carriers for Softswitch projects in China. We can say ZTE Corpoartion is indeed an NGN leader in China. At the same time, ZTE vigorously applies itself to the international market of Softswitch deployment and VoIP network applications. Recently ZTE has won several contracts to build its Softswitch networks in Thailand, Hongkong and other countries and regions.

3.1 China Netcom NGN Network Project

In 2001, ZTE´s Softswitch-based NGN solution was deployed in the live network of China Netcom in Ningbo. The whole deployment  was completed in three stages, which verified the integrality and practicability of ZTE´s NGN solution.

3.1.1 Network Environment

With a total transmission bandwidth of up to 40 Gb/s, China Netcom intended  to build a nation-wide broadband telephone network based on the Softswitch technology in order to take the advantage of its MAN in many big cities.

In order to guarantee the voice service quality for the whole network, China Netcom set up a voice virtual private network (VPN) all around China. The VPN network was used to logically separate the voice traffic from the data traffic in order to guarantee the priority of voice traffic and facilitate the management of voice network. Private IP addresses were used in the voice VPN. The voice interworking within a MAN was implemented via inner-MAN routing, and voice interworking between MANs was via a multiprotocol label switching (MPLS) VPN set between adjacent MANs. The data interworking with MANs of other communication companies or public networks was carried via the network address translation (NAT).

3.1.2 Networking

To meet the project requirements of China Netcom, ZTE proposed a local voice access solution with a combination of Softswitch + TG + SG + IAD to facilitate user access, as well as  to make full use of the existing network resources, as shown in Figure 3. The whole system consisted of the Softswitch core control device, trunk gateway, signaling gateway, IAD, and a whole set of network management and billing system.

The project covered several cities such as Beijing, Hangzhou, Ningbo, Guangzhou, Chongqing and Quanzhou with the core control device ZXSS10 SS1 located in Beijing and Ningbo. The  initial design capacity of the project is 50 000 subscribers.

3.2 China Telecom´s NGN Trial Project

In December 2001, ZTE won the tender for China Telecom´s NGN trial project. The service providers intended to test and gain more experience on the Softswitch technology and verify the advantages and feasibility of the Softswitch-based next generation network by the project.

The trial NGN was carried on the packet network, known as China PSTN. ZTE proposed a comprehensive end-to-end solution for the trial to test functions including large-scale networking, disaster recovery, network interoperability, network evolution, terminal access, image/video transfer and so on.

According to the system design, two sets of ZXSS10 SS1 Softswitch control devices and two sets of ZXSS10 S100 signaling gateway were installed in Shenzhen. In addition, one set of ZXSS10 M100 media gateway was installed in Guangzhou and another in Shenzhen. The user terminals used in the project included IAD series, SIP phones as well as PC phones.

The trial was successfully completed in 2002. The initial design capacity was 100 000 subscriber lines to cover 4 cities.

3.3 Rumanian POSTelecom´s NGN Network Project

In July 2003, ZTE won the contract of Rumana POSTelecom´s NGN network project. The project covers multi-layers of the network including the transport network, service network, access layer network and so on. ZTE has proposed an overall network solution and development layout with the coverage of the capital city and 6 metropolitan big cities (Bacau, Braila & Garati, Brosov, Cluj, Craiova and Timisoara), and meantime provided the capacity for 150 000 prepaid card customers. The whole network capacity is up to 500 000 subscriber lines. The Rumanian communication company is planning to spend 100 million USD to deploy their NGN network and services.

4 Conclusion

The NGN is a milestone of the new generation telecom network. It is a service-driven network, with services completely separated from the call control, and calls from the bearer; it is a combination of TDM-based PSTN voice network and IP/ATM-based packet network, with a fully open network platform system ready to drive   current   single-service  networks  to  a full-service information network. The NGN architecture characterizes the hierarchical system structure,   packet-switch-based   core transport, powerful service capability and policy-based network management.