數位電子看板系統之伺服器推送內容的機制

Abstract

目前智勝國際的數位電子看板系統的更新機制，是採用client pulling的方式，由數位電子看板系統播放端的接收器每隔一段時間，便發送請求向伺服器要求下載清單，當伺服器收到數位電子看板的請求後，會回傳清單至數位電子看板，無論清單內容更新與否，而數位電子看板收到之後再依照清單內容進行相應動作。這個方法雖然簡單易作，並且可以保證數位電子看板從網路連線失敗復原後能夠取得播放的內容，但卻會占用過多的網路頻寬，以及重複無意義的處理動作在沒有改變的清單上，此外也無法讓數位電子看板於第一時間取得最新的內容，亦即，當使用者想即時插播內容時，因為伺服器不會主動進行通知，使得數位電子看板無法即時取得此訊息進行播放。而且，如果大量的數位電子看板在同一時間發送請求，伺服器勢必無法負擔，影響整體系統的運作。

本論文的目的在於提出一套伺服器推送的數位電子看板內容更新機制，以減少數位電子看板與伺服器之間傳遞的訊息數量，以降低網路頻寬的使用和系統的負擔，並避免伺服器因大量的數位電子看板在同一時間發送請求而造成伺服器負荷過重。

在伺服器推送的內容更新機制中，數位電子看板不會間隔性的主動向伺服器發送請求，而是改由在伺服器偵測到清單有更新的情況下，主動發送通知，告知數位電子看板可以發送請求以下載更新過的清單，得到清單後數位電子看板再根據清單做相對應的處理。我們已實作伺服器推送的更新機制，並以多個實驗實際驗證這個機制的效益。

Currently BestWise digital signage systems adopt client pulling update mechanism where a digital signage (DS) requests contents from a server periodically. When the server receives a request from a DS, it replies a list of contents and corresponding location of each content to the DS, regardless of whether the list changed or not. When the DS receives the response message, it will retrieve the new media when necessary according to the changes in the list. Client pulling update scheme is simple, easy to implement, and can guarantee that the DS can receive the newest content from the server after the DS recovers from some network failure. However client pulling scheme consumes extra network bandwidth and processing power for the list without any changes. Moreover, the DS cannot retrieve the newest content timely, that is, users cannot push instant messages or contents to the DS, because the server will not send any message to DS unless it receives requests from the DS. Furthermore, the server could be overloaded due to mass simultaneous requests from DSs.

This thesis aims to propose a server pushing update scheme for digital signage system that can decrease the number of messages exchanged between the server and DSs, reduce the consumption of network bandwidth usage and process powers, and avoid the sever overload caused by burst DS requests.

In the server pushing content delivery scheme, the DS does not send requests periodically. On the contrary the server will inform the DS of content changes when the server detects changes. We have implemented the server pushing content delivery scheme and conducted real experiments to demonstrate the effectiveness of the scheme.