Learning notes on Softswitch technology and H.323 Protocol

The Softswitch technology is worth learning a lot. Here we mainly introduce the detailed knowledge of the Softswitch technology and the H.323 protocol. Softswitch technology is the core technology of the Next Generation Network NGNNext Generation Networks that provides multiple services, such as voice, data, and video. It isolates business, media, and call control and adopts a hierarchical and open structure. This article briefly introduces the Softswitch technology, discusses the H.323 protocol, and compares it with the SIP 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 Softswitch technology mechanisms 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. The Softswitch technology has the following three basic features: integrated sub-networking and Circuit Switching Network; the ability to connect bureaus and terminals; the separation of Call Control and media layer and 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. H.323 defines four main components to construct a network-based communication system: Terminal, Gateway), network guard keeper, and multi-point control unit MCU ).

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.

Gateway)

Provides a connection between the packet switching Network and the Circuit switching Network (SCN, Switch Circuit Network.

Network guard 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.

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.

Channel

H.323 uses a channel to structure information exchange between two communication entities. A channel is a connection to the transport layer.

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.

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.