IP Centrex Service Based on Softswitch

I. background

At present, the research on the Next Generation Network (NGN) has gone beyond the scope of the NGN concept and system framework, and began to fully penetrate into the business and application. Among the various applications provided by the next generation network, IP Centrex is more important to domestic operators and is expected to take the lead in making breakthroughs among many businesses. One of the strategic priorities of the softswitch network today is to provide solutions for group/major customers to attract major customers to ensure the main operating income of the network. The IP Centrex service can provide economic and convenient integrated business solutions for cross-region group users.

Ii. IP Centrex Softswitch Solution

Centrex (centralized user switch) is also called a virtual user switch. It uses public network resources to form a private network and provides public network users with a virtual PBX (dedicated group switch) function. For users with scattered locations and concentrated acceptance requirements, the wide-area Centrex (WAC) service is provided.

IP Centrex is an IP-based Centrex service. It is a value-added service that inherits the Centrex service in the PSTN network and integrates the flexibility of the IP network. As the softswitch system is hosted on the broadband IP data network, the Centrex service provided by the softswitch system has many new features compared with the Centrex service provided by the traditional PSTN switch.

1. Application Mode

Users in the IP Centrex group can be common voice users in the softswitch domain, multimedia users, and other users, it can also be a user of the PSTN, 2G, 3G mobile network connected to the softswitch domain, or another user in the softswitch domain. Currently, IP Centrex Service Based on Softswitch has the following three application modes:

For IP Centrex services in a single Softswitch, Softswitch completes service feature judgment, business data access, number translation, and other functions;

For networks that use the No. 7 Signaling connection across the PSTN to implement the wide-area Centrex service, the soft switch implements non-local networks (such as the PSTN, GSM, CDMA, and PHS networks) users in the group are included in the Centrex group, corresponding group numbers are allocated, and the interconnection between different networks and SoftSwitch systems is achieved using the No. 7 signaling;

For the wide-area Centrex service across Softswitch domains, the Routing Server is involved in the implementation.

For Application Mode 1, the network structure is relatively simple, mainly including Application Server, Softswitch, Media Gateway, and Access Gateway).

The Application Server contains the business execution environment, the business management function, and the business generation environment. Softswitch is the control center for IP Centrex signaling routing. The application server and SoftSwitch can adopt the SIP protocol. In the case of a cross-region call from the headquarters to the Branch, the enterprise resident gateway MG/AG converts this outbound message to a signaling method understandable by Softswitch, such as H.248, Megaco, and MGCP, it is sent to Softswitch for acceptance. Under the control of softswitch, the communication between the Headquarters and the branch offices starts from the voice or video channels.

For Application Mode 2, the network structure is complex. On the basis of Mode 1, network elements such as the signaling Gateway and the Trunk Gateway need to be added.

The signaling gateway is responsible for the conversion and transmission of signaling. It converts the No. 7 signaling in the PSTN to the corresponding signaling protocol of the IP network, such as the H.323 Message. Through SCTP protocol and SoftSwitch communication, SCTP is used for reliable transmission of part of user information (such as ISUP) of signaling 7 on the IP network. The signaling gateway transmits the converted signaling message to Softswitch through SCTP, on the contrary, after receiving the signaling messages on the IP network from the softswitch, it is converted to the No. 7 signaling message and then transmitted to the PSTN signaling network through the PSTN signaling interface.

The relay gateway is responsible for the interconnection between the PSTN and the Internet. When a call initiated by PSTN passes through the relay gateway, the gateway encodes the PCM voice data into a RTP packet through the compression algorithm, and decodes the packets in the reverse direction.

When a call is made between a user in the softswitch and an external PSTN user, the terminal controlled by the softswitch and the external PSTN is under the control of the softswitch, signaling gateway, and relay gateway, you can establish a voice channel for a session.

For application mode 3, you must add a Routing Server Based on Mode 2 to implement user communication in different Softswitch domains. The interface protocol between Softswitch generally uses SIP-T.

2. Business Networking example

The P Centrex business can easily achieve voice interconnection between branches in different cities for group users.

For organizations that originally had traditional PBX, they can be connected through the integrated access device IAD or Access Gateway. If the branch has an ip lan, IP Phone can be used within the LAN to provide voice services, and Video and multimedia services can be provided using Video Phone or desktop multimedia software, IAD is used to provide users with POTS ports and Data ports.

For branches with fewer employees, you can use multi-port IAD devices to provide users with POTS ports and Data ports for simultaneous access of multiple telephones.

For institutions of a certain scale, the Access Gateway AG is used to provide hundreds of lines of telephone access.

For new users, the new access mode under the softswitch architecture is used to access the service through soft terminals, IAD, IP phones, and video terminals.

In this method, the branches distributed in different cities belong to the same Centrex group, all terminals, this includes the general phone number for PBX access, the general phone number for IAD access, the general phone number for AG access, the SoftPhone number, and the visual terminal number.

In the IP Centrex solution, the IP Access Method of the existing PBX is provided, and the user can retain the original usage habits and services within the PBX. In this way, the original PBX investment can be effectively protected, saving a lot of money. In addition, users can directly access multimedia terminals and broadband telephones to upgrade the functions of the PBX.

Iii. Comparison

1. IP Centrex and traditional Centrex/WAC

IP Centrex is used to provide Centrex services to users in the IP Group phone solution. In other words, IP Centrex is equal to Packet + Centrex to some extent.

IP Centrex combines the traditional advantages of Centrex with the advantages of IP phones. Compared with the traditional Centrex/WAC, IP Centrex not only provides all traditional Centrex functions, it also provides audio, data, and video multimedia services, and supports video conferencing and Data Conferencing, remote work collaboration, Web push, file sharing, instant messaging, and other services; IP Centrex provides multiple access methods, such as ordinary phones, PBX, IAD, and SIP terminals. Traditional Centrex/WAC can only solve local internal communication problems, IP Centrex can easily establish internal communication between different regions.

2. IP Centrex and IP PBX

At present, voice communication is still the "big user" of enterprises' communication expenditures. How to deploy voice communication systems economically and efficiently has become the focus of enterprises' attention. With the increasingly mature and stable VoIP technology, more and more enterprises are considering deploying their communication networks through VoIP. There are two ways to implement enterprise VoIP services: one is IP Centrex and the other is self-built ip pbx.

In short, Private Branch Exchange is a group phone. It is widely used in enterprise offices and greatly improves the efficiency of the enterprise. The ip pbx telephone switch system integrates the functions of the computer network and telephone switch. Each telephone terminal in the system uses IP for data communication, it can also transmit text, data, and images to enable electronic office in the LAN.

Compared with ip pbx, IP Centrex has the following advantages: low initial investment costs, easy to control cash flow by means of office fees, and no maintenance of networks and business platforms; the scale of the platform increases along with the scale of the company. The platform is open to the public network, the office location is arbitrary and easy to expand, and enterprises are concentrated in the main business areas. The business scalability is good.

Iv. Outlook

At present, the biggest challenge facing telecom operators in the competition is "competition for high-end customers", because the business revenue of these customers accounts for a large proportion of the total business income. Major customers are characterized by regional decentralization and comprehensive and personalized business needs. IP Centrex enables the operator to provide the managed PBX service based on the operator's network, thus gaining the advantage of the enterprise user telecom market again, and is expected to become the next generation of business to stand out.

Contribution

[1] Franklin D. Ohrtman, translated by Li Xiaodong and Xu Gang, published by Electronic Industry Press

[2] building an IP Centrex, published by Zhang Lei, online world, Issue 1, 11th-04-07

[3] features and applications of Centrex sun shaoyun, Hua zengbin, Heilongjiang communication technology, 2001 (1)-35-36

[4] Zhao huiling, ye huazhang, people's post and telecommunications press, and

[5] Chen jianya, Yu Hao, Beijing University of Posts and Telecommunications press

Huang benxiong, Professor and Director of Shida Huazhong Research and Development Center, Department of Telecommunications, Huazhong University of Science and Technology.

Tan zhaomin, a master's degree in communication software and Exchange Technology, Department of Telecommunications, Huazhong University of Science and Technology.