The Next Generation Network (NGN) is a new public telecommunication network built on the IP technology. It can accommodate various forms of information. It is deployed on a unified management platform, it implements the transmission and Management of audio, video, and data signals, and provides various broadband applications and traditional telecom services, it is a comprehensive service network that truly realizes broadband and narrowband integration, wired and wireless integration, active and passive integration, and transmission and access integration.
Internet is the main body of next-generation networks, and IP technology is the key technology to achieve the convergence of computer Internet, traditional telephone networks and cable television networks. With the development of Internet technology, the computer Internet, Telephone Network (PSTN) and cable TV network will be integrated into the three networks.
In addition to providing users with voice, high-speed data, and video information services, the next generation network can also provide users with convenient video conferencing and teleconference functions, just like the broadcast network, provide unified messages and news to users with this requirement.
I. Composition of the Next Generation Network
Different from traditional networks, NGN provides, for example, business logic and access and transmission methods based on its ability to flexibly provide various integrated services in a unified network architecture, service resources provide capabilities and service authentication management. To this end, in NGN, the network architecture is built based on Softswitch devices that execute various business logic. In addition, the business logic can be completed on the application server in a unified manner, and open business application programming interfaces (APIS) can be provided to users ). Therefore, the business and business control layers in NGN are separated from the traditional networks and have become an important part (in the future, operators' competition will be concentrated on the business layer ). For the transmission and access layer of media streams, NGN will use various access methods to centralize the connected business flows to a unified grouped network platform for transmission. Another important point is that NGN emphasizes the openness of the network. Its principles include network architecture, network equipment, network signaling and protocols.
A segmented, open, and layered network architecture is a distinctive feature of the Next Generation Network. The industry is basically divided by four layers: business layer, control layer, transport layer (media layer), and access layer. The layers are connected through standard open interfaces.
Business Layer: an open and integrated business access platform that intelligently connects to various services and provides various value-added services in the telecom network environment. In the multimedia network environment, the corresponding business generation and maintenance environment is also required. In NGN, the business layer is composed of a series of business application servers, providing a variety of business control logic to complete value-added business processing. It also provides open third-party interfaces, making it easy to introduce new businesses.
Control Layer: mainly refers to the routing decision and data forwarding functions of the network for completing end-to-end data transmission. It is the core of network switching, the purpose is to build an end-to-end communication process on the basis of the transmission layer. Softswitch will be the core of the Next Generation Network and reflect the concept of NGN network convergence.
Transport Layer: it supports transparent TDM line access to the user end, provides high-bandwidth data transmission capabilities at the core of the network, and replaces the traditional distribution frame to build a flexible and reusable long-distance transmission network, generally, it is an all-optical network based on DWDM technology. The transport layer is a mass backbone transmission platform that provides QoS Assurance independent of business control.
Access layer: supports access to multiple services on the user end, and provides access to various wide and narrow band, mobile, or fixed users. The access device should be able to connect to the high-speed transmission line up and support multiple service interfaces down.
Ii. Media gateways in the Next Generation Network
Media Gateway plays an important role in NGN. If Softswitch is the "neural" of NGN and the application layer is the "brain" of NGN, then media gateway is the "four limbs" of NGN. any business needs to be implemented by media gateway under the control of SoftSwitch.
1. Main Functions of Media Gateway
In related standards (such as H.248 and MGCP), a media gateway is defined as converting media in one network to the media format required by another network. For example, a media gateway can convert a media stream between the bearer channel of the Circuit Switching Network and the media stream of the sub-network, and can process audio, video, or T. 120. It can also process any combination of the three and perform full-duplex media translation to demonstrate video/audio messages and implement other IVR functions, you can also perform media meetings.
The main functions of media gateway are as follows.
(1) user or network access functions
Media Gateway is responsible for integrated access to various users or access networks, for example, common telephone users, ISDN users, ADSL Access, Ethernet user access, PSTN/ISDN network access, V5 access, and 3G network access. In short, the media gateway device is the "interface Gateway" that connects the user or user network to the core media layer.
(2) Access to core media networks
Media gateway connects to the core media network through broadband access. Currently, core media networks are connected through ATM or IP addresses. As a connection-oriented layer-4 Technology with reliable service quality (QoS) assurance capability, ATM is currently widely used layer-4 technology.
(3) ing of media streams
In NGN, any business data is abstracted into a media stream. A media stream can be voice, video, or integrated data. Because of the inconsistency between the network transfer mechanism between the user access and the core media, you need to map one media stream to another media stream format required by the network. However, due to the complexity of business and network, media stream ing is not a simple ing. It involves Media Encoding formats, data compression algorithms, Resource Reservation and allocation. Special Resource detection and processing. The confidentiality of a media stream. In addition, it has special requirements for different business features, such as Echo suppression, mute compression, and comfortable noise insertion.
(4) controlled operation functions
Media Gateway is controlled by Softswitch, and most of its actions, especially business-related actions, are completed under the control of softswitch, such as the selection of encoding and compression algorithms, call Establishment, release, interruption, resource allocation and release, and special signal detection and processing. The special relationship between the media gateway and the softswitch determines the importance of the control protocol between them. MGCP and H.248 are the control protocols between the softswitch and the media gateway. MGCP defined by IETF, implementation is relatively simple, early application is more, but the current trend is switched to the H.248 standard defined by ITU-T (H.248 can be said that IETF and ITU-T combined standard, MEACO in IETF ).
(5) Management and statistics functions
As a member of the network, the media gateway is also centrally managed by the network management system. The media gateway must also report relevant statistics to the softswitch or network management system.
2. Classification of media gateways
From the perspective of the device itself, the media gateway does not have a clear classification, because the media gateway is responsible for integrating various users or networks into the core network, it does not mean that any media gateway device must support all access functions. Media gateways must also follow the openness principle. In the future, media gateways in NGN will be centrally controlled by the softswitch system. You can divide a media gateway device into the following types based on its location in the network.
(1) relay Media Gateway
It is mainly for the traditional PSTN/ISDN relay media gateway, which is responsible for the integration of C4 or C5 of PSTN/ISDN to an ATM or an IP network, and mainly implements VoATM or VoIP functions.
(2) integrated access to media gateway
Integrated Access Media Gateway is responsible for integrated access to various users or access networks. For example, PSTN/ISDN users, Ethernet users, ADSL users, or V5 users are directly connected. This type of Integrated Access Media Gateway is generally placed near the end of the user, and it also has the dial Modem data service delivery function.
(3) Media gateways for residential areas or enterprises
According to the current situation, media gateways placed in residential buildings or enterprises mainly provide integrated access to user voice and data (mainly Internet data, in the future, video services may be connected.
3. Media Gateway and H.248/MEGACO protocols
MGCP is a media gateway control protocol defined by IETF earlier. It mainly defines the behavior between a media gateway controller and a media gateway from a functional perspective, which is relatively simple to implement, without the detailed definition of packages and attributes like H.248, the event interaction mechanism is also relatively simple. Event interaction is composed of an operation and a response. There are not many definitions of attribute parameters. However, MGCP is easy to implement, but its interconnectivity and support capabilities are limited.
H.248/MEGACO is a mainstream protocol between media gateway and SoftSwitch because of its flexible functions and strong service support capabilities, and new accessories are constantly available to supplement its capabilities, at present, the H.248 protocol is recommended between SoftSwitch and media gateway in China.
H.248 and MECIACO share the same protocol text, but differ in the protocol message transmission syntax. H.248 uses ASN. 1 syntax format (ITU-T X. 680 1997), MEGACO adopts the ABNF syntax format (RFC2234)
To succeed in the Next Generation Network, the comprehensive service access capability of various media gateways and the ability to implement specific services under the control of the softswitch system are essential. The NGN technology is centered on the business, the business is related to various aspects. The media gateway device is only an important part of these business chains. To some extent, the cooperation between the media gateway and the softswitch system determines the network architecture of the Next Generation Network.
- Next Generation Network (NGN): Research Progress of Softswitch Technology
- Core Technology of the Next Generation Network NGN: Softswitch Technology
- Several Opinions on the Development Trend of NGN network technology