The H.323 protocol stipulates the components, protocols and procedures for providing multimedia communication on a packet-switched network including IP networks. The ITU ’s H.323 protocol and the IETF ’s SIP protocol reflect to some extent. The technical system of the first strategy. In order to achieve the goal of end-to-end IP telecom operations to a greater extent, people have designed soft-switching technology mechanisms for telecom operators. The IP telephone voice service is the most important and fundamental business function in the soft switch.
Softswitch technology
The concept of soft switch technology (Soft switch) was proposed by Lucent's Bell Labs in 1997. The original intention was to integrate the existing traditional PSTN circuit-switched network with the IP / ATM data network. Softswitch technology is the control function entity of the next-generation network. It provides call control and connection control functions for NGN services with real-time requirements. It is the core of the next-generation network call and control. Softswitch technology has the following three basic characteristics: integrated packet network and circuit-switched network; with tandem office and end office capabilities; call control is separated from the media layer and business layer.
Softswitch equipment is located in the control layer and provides functions such as connection control, routing, network resource management, billing, and authentication for multiple services. Softswitch equipment communicates with various media gateways, terminals, application servers, and other softswitch equipment using standard protocols. H.323 is a recommendation of ITU-T Working Group 16, which is composed of a set of protocols, including the encoding, decoding, and packaging of audio and video signals, the signaling responsible for sending and receiving call control, and the capacity Exchanged signaling. The fourth version of H.323 has the characteristics of being a carrier-grade large network. The IP phone network built with it as a standard can be easily compatible with the traditional PSTN phone network. From this point of view, H.323 is more suitable for building phones Carrier-grade network to the phone.
The H.323 protocol family stipulates the components, protocols, and procedures for providing multimedia communications on packet-based networks, including IP networks. H.323 defines four components in total: terminal, gateway, gatekeeper and multipoint control unit. Using them, H.323 can support point-to-point or point-to-multipoint communication of audio, video, and data. The H.323 protocol family includes H.225.0 for call establishment, H.245 for control, H.332 for large conferences, and H.450.X for supplementary services. The H.323 protocol contains three signaling control channels: RAS signaling channel, call signaling channel and H.245 control channel. The coordination of the three channels makes H.323 calls possible. The following introduces the components and channels of H.323: H.323 defines four main components to build a network-based communication system: terminal, gateway, gatekeeper, and multipoint control unit ( MCU).
It is a client point on an IP-based network. It needs to support the following three functions: support signaling and control, that is, support H.245 (complex protocol on channel usage and channel capabilities) and H.225 (a Q.931-like call signaling transceiving and establishing protocol) and RAS (defined in H.225 for terminal and gatekeeper communication protocol); supports real-time communication, that is, supports RTP / RTCP (a protocol for the sequential processing of audio and video packets); supports encoding, that is, pre-transmission compression, receiving After decompression. For interoperability, each H.323 terminal needs to support Q.711, and other encoding methods are optional. Provides a connection between a packet-switched network and a circuit-switched network (SCN, Switch Circuit Network).
It is optional in the H.323 system, but if it appears, they have certain mandatory functions. The gatekeeper completes the four required functions of address translation, admission control, bandwidth control, and domain management. The gatekeeper also supports four optional functions: call control signaling, call authentication, bandwidth management and call management. When there is a gatekeeper in an H.323 system, all types of end users need to log in to the gatekeeper and obtain its permission before establishing a call.
The multipoint control unit supports more than 3 end users for conversation. A typical MCU includes a multipoint controller (MC) and several (or may not) multipoint processors (MP). MC provides control functions, such as negotiation between terminals, to decide the ability to handle voice or video sharing. MP completes the processing of media streams in the session, such as voice mixing and voice / video exchange. H.323 uses channels to structure information exchange between two communication entities. The channel is a transport layer connection.
Comparison of H.323 and SIP
SIP is proposed by the MMUSIC group of IETF. Compared with the H.323 protocol family proposed by ITU, it has the characteristics of simplicity, good scalability and scalability, and a close combination with existing Internet applications. Both provide a complete solution to the IP telephone system signaling. They all have the ability to establish, manage, and withdraw connections to the call. They have network management functions, which enable endpoint users to establish and interact with QoS. They can easily expand new functions and support different types of interoperability. Of course, both protocols contain requirements for the decompression of speech coding, but this part is the same for both protocols.
At present, H.323 and SIP are two competing protocols in the packet network. Among them, H.323 protocol is a standard formulated by ITU-T, and SIP protocol is a standard developed by IETF. Supplement functions such as business and capability exchange. The H.323 protocol adopts the design concept of ISDN, and uses Q.931 protocol to complete the call establishment and release, which obviously has the characteristics of manageability and concentration of the telecommunications network. At present, the H.323 protocol has been widely used on the Internet. Compared with SIP, H.323 is more mature. Therefore, the IP telephone networks of various operators in China are currently using this protocol. The SIP protocol has the characteristics of simplicity, good scalability, and close integration with existing Internet applications. Many people believe that the protocol is relatively easy to implement. Recently, it has been rapidly developed in the United States. Widely used in business. Supporting multiple protocols is one of the main features of softswitch, so softswitch technology can support both protocols.
in conclusion
The history of H.323 protocol revision shows that when building a VoIP network, the scalability of the network is always a problem that cannot be ignored. With the construction of broadband networks, streaming media services have become increasingly important, and the trend of broadband packet networks gradually replacing PSTN is beginning to emerge, which provides a good platform for the development of VoIP. As one of the supporting protocols of the next generation network, H.323 protocol will play an increasingly important role.
The second version of H.323 is very close to the functions and services supported by SIP. For supplementary services, H.323 is more strictly defined, so in terms of implementation, H.323 rarely has interoperability issues. The two protocols are comparable in their QoS support (similar to the delay in call establishment, does not support resource reservation or CoS (Class of Server) settings), but H.323 version 3 will allow the information required by CoS make. Therefore, the third edition of H.323 is more suitable for use by giant telecom operators. Softswitch technology is only a means of implementation, which can be used in the IP phone system based on H.323, and also in the IP phone system based on SIP. H.323 provides a working mode of centralized processing and management, which matches the management mode of the telecommunication network. It has the ability to make an IP phone system of any size and is a very good working mode.
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Applications:
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Operating temperature range:
Electric dc motor should be used at a temperature of -10~60℃.
The figures stated in the catalog specifications are based on use at ordinary room temperature catalog specifications re based on use at ordinary room temperature (approximately20~25℃.
If a electric dc motor is used outside the prescribed temperature range,the grease on the gearhead area will become unable to function normally and the motor will become unable to start.Depending on the temperature conditions ,it may be possible to deal with them by changing the grease of the motor's parts.Please feel free to consult with us about this.
Storage temperature range:
Electric dc motor should be stored ta a temperature of -15~65℃.
In case of storage outside this range,the grease on the gearhead area will become unable to function normally and the motor will become unable to start.
Service life:
The longevity of geared motors is greatly affected by the load conditions , the mode of operation,the environment of use ,etc.Therefore,it is necessary to check the conditions under which the product will actually be used .The following conditions will have a negative effect on longevity.Please consult with us should any of them apply.
â—Use with a load that exceeds the rated torque
â—Frequent starting
â—Momentary reversals of turning direction
â—Impact loads
â—Long-term continuous operation
â—Forced turning using the output shaft
â—Use in which the permitted overhang load or the permitted thrust load is exceeded
â—A pulse drive ,e.g.,a short break,counter electromotive force,PWM control
â—Use of a voltage that is nonstandard as regards the rated voltage
â—Use outside the prescribed temperature or relative-humidity range,or in a special environment.
â—Please consult with us about these or any other conditions of use that may apply,so that we can be sure that you select the most appropriate model.
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