| Summary: | 碩士 === 國立宜蘭大學 === 資訊工程學系碩士班 === 105 === In order to provide 4G and 5G mobile communication all-IP multimedia services, IP Multimedia Subsystem (IMS) as a service platform is deployed in the core network. As a solution to solve the NAT traversal problem, Application-Layer Gateway (ALG) (i.e. IMS-ALG) is deployed in the IMS. IMS-ALG gathers the media streams to the media gateway (MGW). After establishing the communication, media streams is exchanged through the MGW in the core network. If the mobile UEs reside in the same local network, the media transmission between the UEs has the redundant transmission paths. As a solution to reduce the end-to-end delay and the traffic load in the core network, 3GPP utilizes the Mobile Edge Computing (MEC) as one of the technologies that the 5G core network system architecture must support. This thesis moves the ALG from the core network to the edge device as an example of implementing the MEC concept into the mobile network. By improving the computing capability of the edge device, the edge device can modify the IP / port address in the SIP message to change the transmission path for the subsequent media streams. Although the existing MEC device has been able to implement the ALG translation, the call setup procedure still has some problems. This thesis analyzes the communication established by the MEC device in the local network, and proposes two solutions to improve the ALG mechanism on the MEC device. After the call setup procedure, the media streams are transmitted in the local network without the forwarding from the MGW. By removing the redundant transmission path of the media streams, the performance of the media transmission can be increased. By moving the call setup procedure out from the core network, the traffic load in the core network can also be reduced.
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