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The Challenge of Wi-Fi (Wireless fidelity) Roaming

The Challenge of Wi-Fi (Wireless fidelity) Roaming. 報告者 : 周士倫. Outline. Technical roaming issues Implementation incompatibility Handoff standards Security and authentication ROAMING BETWEEN WI-FI AND CELLULAR BUSINESS-RELATED ROAMING ISSUES TODAY ’ S LIMITED APPROACHES Aggregators

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The Challenge of Wi-Fi (Wireless fidelity) Roaming

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  1. The Challenge of Wi-Fi (Wireless fidelity) Roaming 報告者:周士倫

  2. Outline • Technical roaming issues • Implementation incompatibility • Handoff standards • Security and authentication • ROAMING BETWEEN WI-FI AND CELLULAR • BUSINESS-RELATED ROAMING ISSUES • TODAY’S LIMITED APPROACHES • Aggregators • Hotspot networks

  3. A Quick Look At Wi-Fi Technologies • Most Wi-Fi hotspots currently use IEEE 802.11b technology • It’s cheap to deploy • Client-side devices are widely available • IEEE 802.11b use complementary-code-keying (CCK) • 802.11a,802.11g use orthogonal-frequency-division-multiplexing(OFDM)

  4. Introduction • The Wi-Fi technology faces a critical challenge to its continued popularity and success: Seamless roaming between different networks is difficult for various technical and business reasons

  5. Introduction • Roaming is difficult in part because the technologies used in different systems don’t always work together. • service providers’ billing and authentication systems sometimes aren’t compatible • Security is another concern

  6. Introduction • Finally, carriers want to figure out ways that Wi-Fi users can roam from their networks to cellular networks • for example, let users begin working at an airport on a laptop via a Wi-Fi hotspot and then continue via a cellular network until they get to their office and can switch to a traditional LAN.

  7. TECHNICAL ROAMING ISSUES –1.Implementation incompatibility • IEEE 802.11 standards are loose enough that vendors have been able to develop incompatible implementations • even with compatible equipment, there are no standards for the methodology used in handing off transmissions between networks

  8. TECHNICAL ROAMING ISSUES –2.Handoff standards • The IEEE 802 Handoff Executive Committee Study Group is working on developing a common-handoff-frame-work standard that will be useful to Wi-Fi roaming • If a certain quality of service is being maintained for a user, user does not necessarily want to hand off to a base station that cannot also support that QoS

  9. TECHNICAL ROAMING ISSUES –3.Security and authentication • WEP is designed to give wireless LANs (WLANs) similar protection to that offered by wired networks • WPA, though, is only a stopgap measure while the IEEE works on the proposed 802.11i standard, which would include the stronger Advanced Encryption Standard algorithm • Authorization to make sure people trying to sign on to a network are supposed to have access to a hotspot is also an issue for Wi-Fi

  10. Handoff ,Security and authentication • 802.11f:提供了無線網路使用者漫遊(Roaming)時,透過不同無線接取點(Access Point)連線的資料交換機制,其中定義了IAPP(Inter Access Point Protocol) 機制,讓使用者在切換無線接取點時,可以讓新的AP與舊的AP交換使用者的連線資料,以便於維持原有的連線,而不會導致連線中斷,影響使用者無線網路傳輸 • 802.11i: 定義了在802.11a/b/g MAC(Media Access Control) Layer的安全機制,主要以EAP-802.1x做為認證的方式,AES與TKIP(Temporal Key Integrity Protocol)作為加密的方法,當然目前跟802.11f,一樣都沒有最後定案的版本,不過在可預見的未來裡,802.11i肯定會成為無線網路安全方面最為重要的通訊協定架構.

  11. 802.11f和802.11i示意圖

  12. Handoff

  13. Handoff • 因為在目前的網路架構IPv4下並不支援可攜式IP位址(Mobile IP)，當資訊設備跨越了不同服務網路時，送出去的訊號無法被其他電腦所辨識，造成斷訊。這個問題將在下一代的網路架構IPv6獲得改善

  14. Handoff • 目前可以利用DHCP的架構，將所有上網的資訊設備採用DHCP模式取得網路IP位址，可暫時解決部分跨越服務網路的問題

  15. MN在原網路收到來自HA廣播之Agent Advertisement信息，得知所在網路為原網路及HA位址。 • MN移至其他網路，同時收到FA廣播之Agent Advertisement信息，得知已移至其他網路，同時得知FA位址。 • MN透過FA轉送註冊信息給HA，並告知HA其拜訪網路之CoA(MN在漫遊至其他網路之暫時網路位址)。 • HA廣播Proxy ARP信息至原網路所有節點，告知目前MN的封包需交由HA轉送。 • CN傳送至原網路的封包將路由至HA，HA查表得知MN之CoA透過通道機制(Tunneling)將封包包裝後再送至FA。 • FA收到後，解通道封包後，將原封包轉送至MN。 • MN送至外部之封包可以直接遞送，若拜訪網路有作封包過濾(Packet Filtering)，則可以透過FA轉送至HA再行傳送到CN。 • MN返回原網路，傳送解除註冊動作，封包路由回原MN。

  16. 安全性 • 目前WLAN的安全是利用WEP加解密的方式來達到安全需求，不過這樣的方式由於WEP加密上的缺失,導致容易被惡意使用者入侵破解。例如駭客只要在辦公大樓外面，架設天線，並進行加解密的動作，就容易侵入公司內部網路. • 在無線網路安全沒有進一步的保障前,最好的方式就是可以透過WLAN加上VPN的安全機制

  17. VPN的加密機制可以補足WLAN所缺乏的安全問題,例如可以在公司內部架設一個VPN Server,提供PPTP或是IPSec的機制,讓使用者在無線網路傳輸時,可以先透過PPTP簽入內部主機後再連結上網路資源,如此一來在無線部分傳輸的資料就可以透過加密的方式來傳輸了 • 不過,用VPN 來解決無線網路安全問題並不是一個最佳的方案,不過在目前更佳的無線網路安全標準尚未建立以前,有些廠商則採用這樣的架構作為暫時的系統解決方案

  18. 認證 • 在計費問題上，一般像是網路隨插即用的設備會提供簡單的帳號管理以及計費機制，這很適合於小範圍的公用空間上網，像咖啡館、旅社 • 若是提供大範圍的無線網路服務時，這要的機制顯然不足，因此必須搭配其他系統作為計費以及身份認證的需求，像是RADIUS伺服器

  19. 撥號接入用戶遠程驗證服務協議（RADIUS） • 票據結算中心將用戶資訊發往該用戶的開戶ISP，開戶ISP對用戶進行驗證和計費，並向為該用戶提供接入服務的ISP支付一定的費用，最後，該用戶就可以連接到其開戶ISP並透過他連接到自己的公司網路 • 無線ISP間共用用戶資訊的技術相對來說簡單而直接，而如何協調無線ISP間的利益分配，並制定相應標準則略顯複雜。 • WISPr的發言人 Homan認為，收費系統是最關鍵的部分。為此，WISPr對RADIUS協議進行了擴充，增添了一些新的協議屬性，如用戶名、在線時間、發出與接收字節數等等。此外，透過標識用戶所處位置的地域代碼，該協議還能向用戶提供某特定站點的服務

  20. RADIUS架構圖

  21. ROAMING BETWEEN WI-FI AND CELLULAR • Motorola、Avaya、及Proxim三家公司宣佈合作計畫，期盼能解決Wi-Fi漫遊的問題。此合作計畫將基於VoIP技術來整合蜂巢式(cellular)行動通訊技術及無線區域網路技術，目的在於讓Wi-Fi熱點也能提供語音的服務 • Motorola will develop the dual-mode phones, create the mobility management server that provides the handoff between Wi-Fi and cellular networks, and implement system design tools • Avaya will integrate its IP telephony technology and call-processing soft­ware to support mobile capabilities • Proxim will provide the Wi-Fi infra­structure, QoS software, and centralized management systems to facilitate network handoffs

  22. BUSINESS-RELATED ROAMING ISSUES • Some companies charge per-use, per-minute, or sub­scription fees for using their hotspots. Other individuals and groups deploy free hotspots as a public service • For roaming to succeed, carriers must resolve differences in their business models and their billing and authentication mechanisms

  23. TODAY’S LIMITED APPROACHES –Aggregators • Small wireless ISP (WISP) aggregators offer a single account that provides access to networks of many partners • Aggregators don’t build new hot-spots but instead sign up existing access-point operators

  24. 想要達到的目標

  25. Bad news • 位於紐約的Joltage公司成為最新的犧牲品。這家公司成立於去年年初(2002)，它的創始人希望成為“規劃外頻譜領域的世界頭號運營商”，同時向患有寬頻飢渴症的消費者提供無線網路服務提供商(wISP)的選擇。它的業務計劃聽起來確實可行。Joltage公司免費向所有擁有電腦、乙太網路連接和一些廉價網路設備的用戶提供軟體。這些人的電腦將成為全國性無線網路的節點，在理論上讓公司免於花費巨額成本建設自己的網路。用戶每小時支付1.99美元就可享受無線網路，而這筆收入將由Joltage公司和“熱點”托管方平均分配。 • 鑒于這項計劃十分具有創新意義，許多行業觀察家預測Joltage公司(還有其他幾家Wi-Fi技術發起公司，如Boingo無線公司)將成為新時代的先驅，並預測小型ISP將奪走大型無線和有線ISP的客戶。但不幸的是，甚至連Joltage公司相對較低的價格仍然不夠便宜。由於用戶太少，Joltage公司董事長Andrew Weinreich發出一封電子郵件，稱公司將停止運營。

  26. TODAY’S LIMITED APPROACHES –Hotspot networks • Large companies are also trying to form nationwide hotspot networks. For example, US wireless service providers T-Mobile USA and Wayport have their own extensive Wi-Fi net­works, largely in airports, coffee shops, and convention centers. • Several leading computer and tele­communications companies including AT&T, IBM, and Intel have formed Cometa Networks

  27. Conclusion • many companies currently don’t offer hotspots to make a profit. Instead, they frequently offer hotspots to enhance other services they offer and to attract customers • customers won’t pay a high usage fee for hotspots, especially when so many free ones exist • national Wi-Fi coverage would be a key factor for the technology’s success, as has been the case with cellular phone services. • BUT “It’s not here yet for the average consumer.”

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