| With the fast development of IP technology, the appearance of VoIP technology has aroused wide attention of world. It is simply understand as a technology which is replace PSTN to transmit voice by internet, its the most advantage is that widely using internet environment to interconnect with IP of global, it provides more and better services than traditional services.During the 10 years, the bloom of VoIP product has been in the market, VoIP technology becomes one of the most popular topic in computer and telecommunication field. H.323 is the most important and the most influential protocol which was adopted first in the world. H.323 protocol adopts traditional mode of telephone signal, and its character includes delamination, master and slave, centralized control,the multimedia products and applications of various manufacturers can be co-operation, users do not have to consider the compatibility issues either, so the IP network will easy to unite with traditional PSTN if its architecture is base on H.323 protocol, H.323 is considered the key technology in the Next Generation Network technology.Voice Gateway is node which access the IP network to the PSTN, it is a important role in the VoIP architecture.Voice gateway have low-cost,high cost-effective character, if using the Voice gateway can make internal communications costs near zero and external communications costs also decreased by 40% to 60%.With the maturity of VoIP technology, Voice Gateway has been able to access to more different network, further to improving the communication with sorts of PSTN protocol, the transform of video/audio code, and let operators use more new supplementary service which is base on IP network.This paper is to illustrate the design and implementation of the H.323 protocol and its extension, with the project experience which the author participated in—The Development of Vanlink Voice Gateway. The first paragraph of the paper introduces the key technology of VoIP and the history of VoIP development. The second paragraph of the paper expounds the basic principles of the VoIP, then it summarizes SIP, MGCP, MEGACO/H.248, RTP / RTCP which are related with VoIP signal protocol, and it details on the H.323 protocol series, lastly, it compare the H.323 with the SIP which is popular recently in the round. The third paragraph of the paper analyzes Voice Gateway's hardware/software architecture, the emphasis of this paper is the illustration of the design and implementation of H.323 signaling module and call control module of the Voice Gateway. The fourth paragraph of the paper analyzes the H.450 protocol ofH.323 protocol series------call pickup functions,and expounds its implementation withthe Voice gateway in detail,then using the H.450.2 protocol of H.323 protocol series——call transfer functions to achieve a special local call transfer function of supplementary service. In the last part of this paper, functional test and pressure test of Voice Gateway are presented with results in the fifth paragraph. |
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