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. ITU's H.323 protocol and IETF's SIP Protocol reflect the technical system of the first strategy to some extent. 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 softswitch Soft switch was proposed by the Bell lab of Lucent in 1997. The original intention was to integrate the existing traditional PSTN circuit switching network with the 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 various service Connection Control, routing, network resource management, billing, authentication, and other functions. The Softswitch device communicates with various media gateways, terminals, application servers, and other Softswitch devices using standard protocols.
3. H.323 Protocol
H.323 is the recommendation of the ITU-T 16th Working Group, which consists of a group of protocols, including the encoding, decoding, and packaging of audio and video signals, and the signaling for sending, receiving, and controlling call signaling, there are also Signaling Mechanisms Responsible for capability exchange. 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.
The H.323 protocol family specifies the components, protocols, and procedures for Multimedia Communication on a packet exchange-based network, including an IP network. 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. The H.225.0 protocol family is used to establish calls, H.245 is used for control, H.332 is used for large conferences, and h.22.16.x is used to supplement 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 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), network guard keeper, and multi-point control unit 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 complex protocols related to channel usage and channel capabilities) and H.225 a call Signaling Transceiver and establishment protocol similar to Q.931) also, RAS is defined in H.225 for terminals and network guard communication protocols. It supports real-time communication, that is, RTP/RTCP (a protocol for processing audio frequencies and video information packets in sequence) and encoding, that is, compress before uploading, and decompress it after receiving it. 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 Gatekeeper 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 a 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 the control information of the call and supplemental service. This channel adopts a protocol similar to Q.931, which is described in H.225.0 and h.22.16.x. After the call is established, the Transport Address of the H.245 control channel will be specified in this channel.
3.2.3 H.245 Control CHannel
This channel carries H.245 information, 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 that the RAS channel and media logic channel are carried on a very reliable transmission protocol, and the H.245 control channel is designated on the reliable transmission protocol, starting from the third version, it can be carried on unreliable transmission protocols.
4 Comparison between H.323 and SIP
SIP is proposed by the MMUSIC team of IETF. Compared with the H.323 protocol family proposed by ITU, SIP 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, and have the network management function, so that the endpoint users can establish and interact with QoS, and easy to expand new features, supports different types of interoperability. Of course, these two protocols both 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, service supplement, capability exchange, and other functions. The H.323 Protocol adopts the design concept of ISDN and uses the Q.931 protocol to establish and release a call, which is obviously characteristic of telecommunication network manageability and centralization. At present, the H.323 protocol has been widely used on the Internet. Compared with the SIP protocol, the H.323 protocol is more mature. Therefore, the IP address and telephone network of each operator in China currently use this protocol. The SIP protocol is simple, scalable, and closely integrated with existing Internet applications. Many people believe that the Protocol 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 protocols are one of the main features of softswitch, so Softswitch can support both Protocols at the same time.
5 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 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. As one of the supporting protocols for the next generation network, the H.323 protocol will play an increasingly important role.
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. The two protocols can be compared with the call-based latency in their QoS support, and do not support resource reservation or CoSClass 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.