Introduction to the H.323 protocol and Softswitch Technology

Softswitch technology is an important part of the knowledge that we have to learn in Switch Applications. Have you ever heard of the H.323 protocol in the Softswitch technology? This Protocol plays an important role. Next we will introduce the Softswitch technology in detail. There are two strategies in the network architecture of the Next Generation Network: Smart endpoints and edges, simple network facilities, and simple endpoints and edges, SMART network facilities. For the former, because the driving force of end-to-end multimedia converged services comes from endpoints and edges, the flourishing innovation and prosperity of next-generation network services are dependent on this ｡

The success of the Internet also proves the importance of this strategy for multimedia services. For the latter, because only simple and unified endpoints and edge devices, the voice service provided by the PSTN network has verified the reliability of the commercial practices of this strategy. To some extent, the ITU H.323 protocol and the ietf sip protocol are exactly the same. it embodies the technical system of the first strategy. In order to achieve the telecom operation goal of end-to-end IP phones to a greater extent, the technical mechanism of Softswitch is designed for telecom operators. The IP telephone voice service is the most important and fundamental service function in soft switches ｡

Softswitch Technology

The concept of Soft switch was proposed by the Bell Laboratory of Lucent in 1997, the original intention is to integrate the existing traditional PSTN circuit switching network with the IP/ATM data network. The Softswitch technology is the control function entity of the Next Generation Network, for the Next Generation Network (NGN) services with real-time requirements provide call control and connection control functions, and are the core of next-generation network call and control. Softswitch technology has three basic features: integrated networking and circuit switching network; it has the ability of the Communications Bureau and the terminal Bureau, and the call control and media layer and service layer are separated ｡

The Softswitch device is located at the control layer, provides various service Connection Control, routing, network resource management, billing, authentication, and other functions. Softswitch devices communicate with various media gateways, terminals, application servers, and other Softswitch devices using standard protocols. h.323 is the recommendation of the ITU-T 16th Working Group, it consists of a group of protocols, including encoding, decoding, and packaging of audio and video signals, and signaling for sending, receiving, and controlling call signals, there is also a signaling mechanism responsible for capability exchange. Version 4th of H.323 has the characteristics of a carrier-level large network. The IP telephone network built based on it can be easily compatible with the traditional PSTN Telephone Network, from this point of view, H.323 is more suitable for building telecom-grade large networks from telephone to telephone ｡

The H.323 protocol family specifies the components, protocols, and procedures for Multimedia Communication on a group-based exchange network, which mainly includes IP networks. H.323 defines four components: terminal, gateway, network guard and multi-point control units. Use them, h.323 supports point-to-point or point-to-point communication of audio, video, and data. The H.323 protocol family includes H.225.0 for creating calls, H.245 for controlling, H.332 for large conferences, and supplementary services.. The H.264 protocol contains three signaling control channels: the RAS signaling channel, call signaling channel, and H.245 control channel. The coordination of the three channels allows the call of H.323. The following describes the components and channels of H.323: h.323 defines four main components to construct a network-based communication system: Terminal, Gateway, keeper, and MCU )｡

A client point on an IP-based network. It must support the following three features: Support for signaling and control, that is, support for H.245 (complex protocols related to channel usage and channel capabilities) and H.225 (a call signaling receiving and setup protocol similar to Q.931) and RAS (defined in H.225 for terminals and network guard communication protocols); Support for real-time communication, supports RTP/RTCP (a protocol for processing audio and video information packets in sequence), encoding, compression before transmission, and decompression after receiving, each H.323 terminal must support Q.711 and Other encoding methods as an option. It provides a connection between the packet switching Network and the Circuit switching Network (SCN, Switch Circuit Network ｡

It is optional in the H.323 system, but if it appears, they have certain mandatory functions, the Network guard also supports call control signaling, call authentication, bandwidth management, and call management. an H.323 system has network punctuality, all types of end users need to log on to the network guard and obtain the permission before creating a call ｡

The multi-point control unit supports more than three end users for sessions. A typical MCU includes one multi-point Controller (MC) and several (or none) Multi-Point processors (MP) MC provides control functions, such as negotiation between terminals, to determine the ability to process voice or video sharing. MP completes the processing of media streams in sessions, for example, voice mixing, voice/video switching. H.323 uses a channel to structure the information exchange between two communication entities. The channel is a connection at the transmission layer ｡

Comparison between H.323 and SIP

SIP was proposed by the IETF's MMUSIC team. Compared with the H.323 protocol family proposed by ITU, it is simple, scalable, well-scaled, and closely integrated with existing Internet applications. Both of them provide a complete solution for the signaling of the IP phone system. establish, manage, and revoke capabilities, with the network management function, the endpoint users can establish and interact with QoS, and easily expand new features to support different types of interoperability. Of course, both protocols contain requirements on the decompression of Speech Encoding, but these are the same for the two Protocols ｡

Currently, H.323 and SIP are two major competing protocols in the group network. Among them, the H.323 protocol is the standard set by the ITU-T, And the SIP protocol is the standard set by the IETF, both of them can complete call establishment, release, supplement service and capability exchange and other functions. The H.323 Protocol adopts the design concept of ISDN and uses the Q.931 protocol to complete call establishment and release, the Protocol is widely used on the Internet, and is more mature than SIP, therefore, the IP address and telephone network of China's operators all use this Protocol. The SIP protocol is simple, scalable, and closely integrated with existing Internet applications. Many people think that this Protocol is easier to implement, recently, it has developed rapidly in the United States. At the same time, SIP will be widely used in the third-generation mobile communication core network and smart services. supporting multiple protocols is one of the main features of SoftSwitch, therefore, the Softswitch technology can support both Protocols ｡

Conclusion

The Protocol Modification Process of H.323 indicates that network scalability is always a problem that cannot be ignored when constructing a VoIP network. with the construction of a broadband network, streaming media business becomes more and more important, the trend of gradually replacing PSTN with broadband grouping networks is beginning to show, which provides a good platform for the development of VoIP. As one of the Next Generation Network Support protocols, the H.323 protocol will play an increasingly important role ｡

The second version of H.323 is very similar to the features and services supported by the SIP. For supplementary services, H.323 is more strictly defined. Therefore, in terms of implementation, h.323 has very few interoperability issues. The two protocols can be compared in their QoS support (similar to call-based latency, resource reservation not supported, or CoS (Class of Server) but the third version of H.323 will allow the signaling required by CoS. Therefore, the third version of H.323 is suitable for giant telecom carriers. The Softswitch technology is only a means of implementation, it can be used in the H.323-based IP phone system or in the SIP-based IP phone system. H.323 provides a centralized processing and management mode, it matches the management mode of telecom networks. It has the ability to build an IP Phone System of any scale and is a good working mode ｡