ADSL與WLAN雙網接取系統在多重使用者環境下之研究

為因應使用者對頻寬的需求日益增加，雖然目前已有許多成熟之寬頻網路技術，如ADSL、Cable Modem等，但其存取速度仍不足以滿足使用者日漸增加的需求。然而若要舖設Ethernet或光纖等高速之線路到用戶端，則又需要花費大量的成本。因此所謂WLAN-ADSL雙網接取系統(WLAN-ADSL Broadband Access WABA系統)以同時使用WLAN無線點對點之戶外連線與已存在之ADSL線路來共同作為寬頻之接取。以達到輕濟、花費較少之舖設成本，並提供快速之網路接取速度服務。因為戶外之無線網路可能因為氣候或其它因素而有所不穩定的情況，所以仍需保留原本較為穩定之ADSL線路。一方面做為網路之備援，另一方面也為網路應用提供較穩定之網路服務。由於無線網路具較不穩定及ADSL上下行頻寬不對稱之極為不同之特性，在進行寬頻接取時並不適合使用一般的Ethernet trunk或multi-link ppp等方式來做為線路間之負載平衡。對於這樣的情形，WABA雙網接取系統提出一個適應之路由決策法則，依據不同服務品質需求之網路應用，選擇使用符合他們要求特性的線路。而當WABA系統要進入多人接取的情境下時，在無線網路端便多了需要使用者來競爭無線網路頻寬的問題。因為802.11WLAN的DCF MAC機制是由使用者與無線網路接取點(Access Point ,AP)共同來競爭即時的網路頻寬使用權，因此衍伸出使用者無線頻寬分配不均及上下傳網路交通流量Unfairness的問題，如何搭配ADSL及WLAN兩種特性迥異的網路接取技術來提供多使用者高頻寬及高品質的寬頻網路服務建置策略，便是本論文的研究論述重點。

關鍵字

雙模網路接取；無線網路

並列摘要

According to the rapid growth of amount on Internet traffic, such as VoIP , VoD these multimedia network services, the demand of bandwidth is not satisfied in traditional broadband access strategies. Thus, WABA is introduced to be a new broadband access architecture, using outdoor wireless Lan a/b/g solution to provide users an additional link to increase their access bandwidth cheaply and quickly. Though WABA use a wireless link with higher bandwidth (about 4~27 Mbps in practice), we still recommend that users not to put away traditional broadband access techniques with lower bandwidth such as ADSL and Cable modem. Because of the stability of ADSL is much higher than outdoor wireless Lan, it can provide a stable bandwidth or even be a backup when the wireless access is unstable or failed. Thus, users can easily access to broadband network with high bandwidth and high reliability. In Multi-user strategy, according to 802.11 MAC, there will be several issues on the competition on wireless link bandwidth. We will try to adapt our algorithm to fit the multi-user strategy for best utilization and prove that in our simulation. The detailed system architecture will be addressed later.

並列關鍵字

ADSL ； WLAN ； Dual-network

參考文獻

[1] ITU-T, G.992.1 – Asymmetric Digital Subscriber Line (ADSL) transceivers, ITU-T, 1999.

[2] ITU-T, Draft G.992.3 AAP –ADSL2, Asymmetric Digital Subscriber Line, ITU-T, 2002.

[5] M. S. Gast, “802.11 Wireless Networks: The Definitive Guide,” 1st ed, USA, O’Reilly, April 2002, Section 3.2

[6] S. Pilosof, R. Ramjee, D. Raz, Y. Shavitt, and P.Sinha, “Understanding TCP Fairness over Wireless LAN”, INFOCOM 2003, April 2003.

[7] H. Balakrishnan, V. N. Padmanabhan, and R. H. Katz, “The Effects pf Asymmetric on TCP Performance,” Proc. 3rd ACM/IEEE Intel. Conference on MobiCom, pp.77-89, Sept. 1997.

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ADSL與WLAN雙網接取系統在多重使用者環境下之研究

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