一般分封無線數據服務之繞送最佳化

Abstract

GPRS全名是General Packet Radio Service，譯成一般分封無線數據服務，GPRS利用現有GSM網路架構，提供分封交換式數據通訊的技術，讓手機用戶能夠以較高的速率(115Kbps)來傳遞資料。原有GSM電信系統主要是提供語音服務，也提供線路交換式的數據傳送服務，但受限其無線傳輸頻寬太小的問題(9.6Kbps)，因此GPRS以更快傳輸速度、瞬間上網、持續連網等特點來改善原有問題。GPRS結合了行動通訊和網際網路(IP)新功能，就現有GSM電信系統而言，硬體需增加SSGN和GGSN二節點及軟體需作升級是業者主要的花費，原GSM系統仍可繼續使用。 但現有GPRS網路節點的繞送機制，存在著三角傳送問題，使得資料封包傳遞效能不佳，造成網路負擔增加。GPRS三角傳送問題發生的原因，是手機作網內互傳資料時都需經過GGSN節點，此外有二個以上GGSN的GPRS系統，手機換位執行Inter SGSN 繞送區域更新後也會產生三角傳送問題。因此，本篇論文提出二個方法來改善GPRS三角傳送問題，階層式GGSN架構是解決只有一個GGSN時三角繞送的問題，增加一個節點在GGSN和SGSN之間，幫助其對應SGSN作資料繞送服務。分散式 GGSN架構是解決GPRS的系統架構中多個GGSN時三角繞送的問題，在傳送端GGSN節點增加欄位，暫存收端PDP context資料協助收端手機資料繞送。改善時必須考慮註冊、位置更新、換位及資料的傳送機制，並修改原GPRS網路協定及封包繞送，以達到封包繞送最佳化，提高資料傳遞速度，使整個網路架構效能增加。 我們也對所提出二個改善方法，以電腦模擬的方式，來驗證評估新的通訊網路架構及繞送機制的效能。根據模擬的結果，不論是在階層式GGSN或分散式GGSN架構，傳送資料時可降低GGSN節點負擔度，GGSN節點可支援更多使用者，GPRS網路整體效能增加。

GPRS, General Packet Radio Service, is a technique, which allows network operators to offer a packet-oriented data communications service based on GSM infrastructure. Initial GSM telecommunications system mainly provides voice service and circuit switched connection. However, it is limited by the small bandwidth at the speed 9.6k Bits/s. Therefore, GPRS, a new telecommunications technique, is developed to solve the problem. GPRS comes with the features as fast data transfer speed and always-on-line connection. It also combines with mobile communication and the Internet new functions. To use GPRS by current GSM operators, the main cost is on the hardware by adding two new nodes (SGSN and GGSN) and on software upgrade. Original GSM equipment can be continually used by the operators. Though GPRS has great advantages described as above, its network node route still has the triangle transmission problem, that causes the inefficiency of packet data transfer and the increase of traffic load on the Internet. For GPRS triangle transmission problem, there are two reasons. First, it is necessary to pass GGSN nodes when MS end users perform intra data transfer. Second, in GPRS architecture with two more GGSN nodes, there's also a triangle transmission problem after MS implements handover with Inter SGSN routing area update. Therefore, the paper provides two approaches to solve the transmission problem. First approach is hierarchy GGSN solution for the architecture that only has one GGSN node. It solves the problem by adding a node between GGSN and SGSN to enhance SGSN packet route service. Second approach is distributed GGSN solution for GPRS with two GGSN nodes at least. It solves the problems by adding columns from senders and then storing PDP context to help data route. It needs to consider register, RA update, handoff and data transfer protocol. It also requires to modify original GPRS network protocol and packet route to optimize routing for GPRS. Meanwhile, we use computer to simulate our approaches to verify new protocol and routing efficiency. According to our simulation results, both of hierarchy GGSN and distributed GGSN solutions can reduce GGSN load when we transfer data. Consequently, GGSN node can support more users and GPRS network can improve its efficiency.