Relationship between Softswitch technology and H.323 Protocol

　　1 Introduction
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 and smart network facilities. For the former, because the driving force of end-to-end multimedia convergence businesses comes from endpoints and edges, the flourishing innovation and prosperity of next-generation network businesses are dependent on this. The success of the internet proves the importance of this strategy to multimedia services. For the latter, only the uniform endpoints and edge devices are conducive to standardized management and control. The voice service provided by the PSTN network has verified the reliability of such commercial practices. H.323 of ITUProtocolAnd IETF SIPProtocolIt is to some extent the technical system of the first strategy. To achieve the telecom operation goal of end-to-end IP phones to a greater extent, people have designed a soft switch technology mechanism for telecom operators. The IP telephone voice service is the most important and fundamental service function in the soft switch.
　　
　　2. Softswitch Technology
The concept of Soft switch was proposed by Bell Laboratory of longxun in 1997 to integrate the existing traditional PSTN Circuit Switching Network with IP/ATM data network.
　　
As the control entity of the Next Generation Network, Softswitch provides Call Control and Connection Control functions for businesses with real-time requirements for the Next Generation Network (NGN). It is the core of the Next Generation Network call and control. Softswitch has the following three basic features: integrated networking and circuit switching network. It has the ability to connect bureaus and end bureaus. The call control and media layer are separated from the business layer.
　　
The Softswitch device is located at the control layer and provides Connection Control for multiple services,Routing, Network resource management, billing, authentication, and other functions. Standard is adopted between Softswitch devices and various media gateways, terminals, application servers, and other Softswitch devices.ProtocolCommunication.
　　
　　3 H.323Protocol
H.323 is the recommendation of the ITU-T 16th working group, composed of a groupProtocolIncluding the encoding, decoding, and packaging of audio and video signals, call signaling receiving and control, and capability exchange signaling. Version 4th of H.323 has the characteristics of a telecom-grade large network. The IP telephone network built based on it is easy to be 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.
　　
H.323ProtocolIt specifies the components that provide multimedia communication on the packet exchange-based network, including the IP network,ProtocolAnd procedures. H.323 defines four components: terminal, gateway, network guard, and multi-point control unit. Using them, H.323 supports point-to-point communication between audio, video, and data. H.323ProtocolIncluding H.225.0 for creating calls, H.245 for controlling, H.332 for large conferences, and h.22.16.x for supplementing services. H.323ProtocolIt contains three signaling control channels: RAS signaling channel, call signaling channel, and H.245 control channel. The coordination of the three channels enables H.323 calls.
　　
The following section describes the components and channels of H.323: 3.1 components.
　　
H.323 defines four main components to construct a network-based communication system: Terminal, Gateway, keeper, and MCU ).
　　
3.1.1 Terminal)
　　
An IP-based network is a client point. It must support the following three features: Support for signaling and control, that is, support for H.245 (the complexity of channel usage and channel capabilities)Protocol) And H.225 (a call signaling mechanism similar to Q.931 for sending and receiving and establishingProtocolAnd RAS (defined in H.225 for communication between the terminal and the network guard)Protocol); Supports real-time communication, that is, supports RTP/RTCP (one for processing audio and video information packets in sequence)Protocol); Supports encoding, that is, compression before uploading, and decompression after receiving. For interoperability, each H.323 terminal must support Q.711. Other encoding methods are used as an option.
　　
3.1.2 Gateway)
　　
Provides a connection between the packet switching Network and the Circuit switching Network (SCN, Switch Circuit Network.
　　
3.1.3 keeper)
　　
It is optional in the H.323 system, but if it appears, it has some mandatory functions. The network guard completes address translation, Admission Control, bandwidth control, and domain management. The Network guard also supports four optional functions: Call control signaling, call authentication, bandwidth management, and call management. When 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.
　　
3.1.4 multi-point control unit (MCU)
　　
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 shares. MP processes media streams in sessions, such as audio mixing and voice/video switching.
　　
3.2 Channels
　　
H.323 uses a channel to structure information exchange between two communication entities. A channel is a connection to the transport layer.
　　
3.2.1 RAS Channel
　　
This channel enables the endpoint user to communicate with their network guard. It is defined in H.225.0. Through the RAS channel, the endpoint user logs on to the network guard and requests to allow it to make calls with another end user. If the request is approved, a transmission address (including the IP address and port number) is sent as the call signaling channel of the called Point.
　　
3.2.2 call signaling channel
　　
This channel carries call and supplemental service control information, which is similar to Q.931Protocol,ProtocolDescription in H.225.0 and h.22.16.x, when the call is established, the transmission address of the H.245 control channel is specified in this channel.
　　
3.2.3 H.245 Control CHannel
　　
This channel carries H.245ProtocolInformation, which is used for media control with capability exchange support. After the caller completes the capability exchange, he/she creates a media logical channel through this channel.
　　
3.2.4 media Logical Channel
　　
This channel carries voice, video, and other media information. Each media type carries a one-to-one channel, and RTP and RTCP are used in each direction.
　　
H.323 requires the RAS channel and media logic channel to carry in a very reliable transmissionProtocolThe H.245 control channel is specified for reliable transmission.ProtocolFrom the third edition, you can choose to carryProtocol.
　　
　　4 Comparison between H.323 and SIP
Proposed by the ietf mmusic teamProtocolIt is simple, scalable, and scalable, and closely integrated with existing Internet applications.
　　
The two proposed a complete solution for the signaling of the IP phone system. They have the ability to establish, manage, and revoke call connections.Network ManagementFeature to enable end users to establish and interact with QoS, and easily expand new features to support different types of interoperability. Of course, these twoProtocolAll include the requirements on the decompression of Speech Encoding, but this part only applies to twoProtocolIt is the same.
　　
Currently, H.323 and SIP compete with each other in the group network.Protocol, Where, H.323ProtocolIs the standard set by ITU-T, SIPProtocolIt is a standard set by IETF. Both of them can complete call establishment, release, supplement business, capability exchange, and other functions. H.323ProtocolThe design concept of ISDN is adopted, and Q.931 is used.ProtocolCall Establishment and release are completed, which obviously have telecommunication network manageability and centralized features. Currently, H.323ProtocolIt has been widely used on the Internet and is more mature than SIP. Therefore, the IP address and telephone network of each operator in China currently use thisProtocol. And SIPProtocolIt is simple, scalable, and closely integrated with existing Internet applications.ProtocolIt is easy to implement and has developed rapidly in the United States recently. At the same time, SIP will be widely used in the third-generation mobile communication core network and smart services. Multiple supportedProtocolIs one of the main features of softswitch, so Softswitch can support bothProtocol.
　　
　　5 conclusion
H.323ProtocolThe revision process shows that network scalability is always a problem that cannot be ignored when constructing a VoIP network. With the construction of the broadband network, streaming media businesses become more and more important. The trend of gradually replacing the PSTN with the broadband grouping network is emerging, which provides a good platform for the development of VoIP. H.323ProtocolAs a support for next-generation networksProtocolOne will play more and more important roles.
　　
The second version of H.323 is very similar to the functions and services supported by the SIP. For supplementary services, H.323 is more strictly defined. Therefore, there are few interoperability problems in implementation. TwoProtocolThey can be compared in terms of QoS support (similar to call-based latency, does not support resource reservation or CoS (Class of Server) settings ), however, 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 method of implementation. It can be used in the IP Phone System Based on H.323 or in the SIP-based IP phone system.
　　
H.323 provides a centralized processing and management mode that matches the telecom network management mode. It has the ability to build an IP Phone System of any scale and is a good working mode.

Article entry: csh responsible editor: csh