| Facsimile is an important way of business communication. The demand for facsimile communication from commercial organizations is really huge and is still on steady increase. So far, facsimile is mostly carried on PSTN (Public Switched Telephone Network), which brings numerous expenses together with the service. With the development of Internet, IP technology and traditional telecommunication technologies merge a lot and give birth to many new applications. VoIP (Voice over IP) is one of the most successful examples. First, VoIP provides higher bandwidth utility; second, VoIP avoids expensive international charge, which greatly benefits the users. On account of the increasing demand of facsimile communication and the great economy of IP technology, FoIP (Fax over IP) is widely required.FoIP is the facsimile mode that substitutes IP networks for PSTN, either completely or partially. When we look back to the structure of PSTN, we find that facsimile terminals and voice terminals share the same subscriber interfaces. This sharing hints the possibility of implementing FoIP on media gateways in NGN.This thesis provides a solution of implementing real-time IP facsimile on SIP-based media gateway, analyzes Procedures for Document Facsimile Transmission in the General Switched Telephone Network (ITU-T Recommendation T.30), Procedure for Real-Time Group 3 Facsimile Communication over IP Networks (ITU-T Recommendation T.38) and FoIP call control procedure based on SIP/SDP protocol. Afterwards, the thesis describes the system architecture and programming implementation of T.38 real-time IP facsimile functionality on SIP-based media gateway. Test principle and scenarios are also introduced.As a supplement of T.38 facsimile, VBD (Voice-band data) mode will take effect when T.38 attempts fail. With V.152 VBD mode as a backup, fax calls on media gateway get more stability. In this thesis, the implement of VBD mode fax and how to use it as a backup for T.38 fax is also described.According to the test results we get, FoIP can enhance the utility of network resources and hence significantly lowers the expenses of facsimile communication. With VBD mode as a backup, fax call completion rate can easily reach the level of 99.95%. It makes the product more competitive in market.This thesis only focuses on the basic FoIP functionality on POTS (Plain Old Telephone Service) interfaces without any discussion of supplementary services. Further researches are expected on the topics such as FoIP functionality on ISDN (Integrated Services Digital Network) interfaces, supplementary services (fax call transfer, fax call waiting, conference fax call etc.), fax broadcasting, security issues of FoIP etc. |
