計(jì)算機(jī)畢業(yè)設(shè)計(jì)外文翻譯---網(wǎng)絡(luò)體系結(jié)構(gòu)和關(guān)鍵的設(shè)計(jì)要素

1、<p>　　A Survey on Wireless Mesh Networks</p><p>　　IAN F. AKYILDIZ, GEORGIA INSTITUTE OF TECHNOLOGY</p><p>　　XUDONG WANG, KIYON, INC.</p><p><b>　　Abstract</b></p&

2、gt;<p>　　Wireless mesh networks (WMNs) have emerged as a key technology for next-generation wireless networking. Because of their advantages over other wireless networks, WMNs are undergoing rapid progress and ins

3、piring numerous applications. However, many technical issues still exist in this field. In order to provide a better understanding of the research challenges of WMNs, this article presents a detailed investigation of cur

4、rent state-of-the-art protocols and algorithms for WMNs. Open research issue</p><p>　　Introduction</p><p>　　Wireless mesh networks (WMNs) are dynamically self-organized and self-configured, with

5、 the nodes in the network automatically establishing an ad hoc network and maintaining the mesh connectivity. WMNs are comprised of two types of nodes: mesh routers and mesh clients. Other than the routing capability for

6、 gateway/bridge functions as in a conventional wireless router, a mesh router contains additional routing functions to support mesh networking. Through multi-hop communications, the same coverag</p><p>　　Mes

7、h routers have minimal mobility and form the mesh backbone for mesh clients. Thus, although mesh clients can also work as a router for mesh networking, the hardware platform and software for them can be much simpler than

8、 those for mesh routers. For example, communication protocols for mesh clients can be light-weight, gateway or bridge functions do not exist in mesh clients, only a single wireless interface is needed in a mesh client, a

9、nd so on.</p><p>　　In addition to mesh networking among mesh routers and mesh clients, the gateway/bridge functionalities in mesh routers enable the integration of WMNs with various other networks. Conventio

10、nal nodes equipped with wireless network interface cards (NICs) can connect directly to WMNs through wireless mesh routers. Customers without wireless NICs can access WMNs by connecting to wireless mesh routers through,f

11、or example, Ethernet. Thus, WMNs will greatly help users to be always-on-line anywhere, anyt</p><p>　　Consequently, instead of being another type of ad-hoc networking, WMNs diversify the capabilities of ad-h

12、oc networks.This feature brings many advantages to WMNs, such as low up-front cost, easy network maintenance, robustness, reliable service coverage, etc. Therefore, in addition to being widely accepted in the traditional

13、 application sectors of ad hoc networks, WMNs are undergoing rapid commercialization in many other application scenarios such as broadband home networking, community networkin</p><p>　　To date, several compa

14、nies have already realized the potential of this technology and offer wireless mesh networking products. A few testbeds have been established in university research labs. However, for a WMN to be all it can be,considerab

15、le research efforts are still needed. For example,the available MAC and routing protocols are not scalable;throughput drops significantly as the number of nodes or hops in WMNs increases. Thus, existing protocols need to

16、 be enhanced or re-invented for WMNs. </p><p>　　In this article we present a survey of recent advances in protocols and algorithms for WMNs. Our aim is to provide a better understanding of research challenge

17、s of this emerging technology. The rest of this article is organized as follows. The network architectures of WMNs are first presented, with an objective to highlight the characteristics of WMNs and the critical factors

18、influencing protocol design. A detailed study on recent advances of WMNs is then carried out, with an emphasis on open re</p><p>　　Network Architecture and Critical Design Factors</p><p>　　Netwo

19、rk Architecture</p><p>　　The architecture of WMNs can be classified into three types:</p><p>　　Infrastructure/Backbone WMNs. In this architecture, mesh routers form an infrastructure for clients

20、, as shown in Fig. 1,where dashed and solid lines indicate wireless and wired links,respectively. The WMN infrastructure/backbone can be built using various types of radio technologies, in addition to the mostly used IEE

21、E 802.11 technologies. The mesh routers form a mesh of self-configuring, self-healing links among themselves. With gateway functionality, mesh routers can be connected to the Intern</p><p>　　Client WMNs. Cli

22、ent meshing provides peer-to-peer networks among client devices. In this type of architecture, client nodes constitute the actual network to perform routing and configuration functionalities as well as providing end-user

23、 applications to customers. Hence, a mesh router is not required for these types of networks. Client WMNs are usually formed using one type of radios on devices. Thus, a Client WMN is actually the same as a conventional

24、ad hoc network.However, the requirements on </p><p>　　Hybrid WMNs. This architecture is the combination of infrastructure and client meshing, as shown in Fig. 2. Mesh clients can access the network through m

25、esh routers as well as directly meshing with other mesh clients. While the infrastructure provides connectivity to other networks such as the Internet, Wi-Fi, WiMAX, cellular, and sensor networks, the routing capabilitie

26、s of clients provide improved connectivity and coverage inside WMNs.</p><p>　　The characteristics of WMNs are outlined below, where the hybrid architecture is considered for WMNs, since it comprises all the

27、advantages of WMNs:</p><p>　　?WMNs support ad hoc networking, and have the capability of self-forming, self-healing, and self-organization.</p><p>　　?WMNs are multi-hop wireless networks, but wi

28、th a wireless infrastructure /backbone provided by mesh routers.</p><p>　　?Mesh routers have minimal mobility and perform dedicated routing and configuration, which significantly decreases the load of mesh c

29、lients and other end nodes.</p><p>　　?Mobility of end nodes is supported easily through the wireless infrastructure.</p><p>　　?Mesh routers integrate heterogeneous networks, including both wired

30、 and wireless. Thus, multiple types of network access exist in WMNs. </p><p>　　?Power-consumption constraints are different for mesh routers and mesh clients.</p><p>　　?WMNs are not stand-alone

31、and need to be compatible and interoperable with other wireless networks.</p><p>　　Therefore, WMNs diversify the capabilities of ad-hoc networks instead of simply being another type of ad hoc network.These a

32、dditional capabilities necessitate new algorithms and design principles for the realization of WMNs.</p><p>　　Critical Design Factors</p><p>　　The critical factors influencing the performance of

33、 WMNs are summarized as follows.</p><p>　　Radio Techniques. Many approaches have been proposed to increase capacity and flexibility of wireless systems in recent years. Typical examples include directional a

34、nd smart antennas, multiple input multiple output (MIMO) systems,and multi-radio/multi-channel systems.</p><p>　　To further improve the performance of a wireless radio and control by higher layer protocols,

35、more advanced radio technologies, such as reconfigurable radios, frequency agile/cognitive radios, and even software radios, have been used for wireless communication. Although these radio technologies are still in their

36、 infancy, they are expected to be the future platform for wireless networks due to their dynamic control capability. These advanced wireless radio technologies all require a revolutionar</p><p>　　Scalability

37、. Scalability is a critical requirement of WMNs.Without support of this feature, the network performance degrades significantly as the network size increases. For example, routing protocols may not be able to find a reli

38、able routing path, transport protocols may loose connections, and MAC protocols may experience significant throughput reduction. To ensure the scalability in WMNs, all protocols from the MAC layer to the application laye

39、r need to be scalable.</p><p>　　Mesh Connectivity. Many advantages of WMNs originate from mesh connectivity. To ensure reliable mesh connectivity,network self-organization and topology control algorithms are

40、 needed. Topology-aware MAC and routing protocols can significantly improve the performance of WMNs.</p><p>　　Broadband and QoS. Different from classical ad hoc networks, most applications of WMNs are broadb

41、and services with heterogeneous QoS requirements. Thus, in addition to end-to-end transmission delay and fairness, more performance metrics, such as delay jitter, aggregate and per-node throughput, and packet loss ratios

42、, must be considered by communication protocols.</p><p>　　Security. Although many security schemes have been proposed for wireless LANs in recent years, they are still not fully applicable for WMNs. For inst

43、ance, there is no centralized trusted authority to distribute a public key in a WMN due to the distributed system architecture. The existing security schemes proposed for ad hoc networks can be adopted for WMNs. However,

44、 most of the security solutions for ad hoc networks are still not mature enough to be implemented practically. Moreover, the differ</p><p>　　Ease of Use. Protocols must be designed to enable the network to b

45、e as autonomous as possible. In addition, network management tools need to be developed to efficiently maintain the operation, monitor the performance, and configure the parameters of WMNs. These tools, together with the

46、 autonomous mechanisms in networking protocols, enable rapid deployment of WMNs.</p><p>　　Compatibility and Inter-operability. In WMNs it is a default requirement to support network access for both conventio

47、nal and mesh clients. Therefore, WMNs need to be backward compatible with conventional client nodes. This demands that mesh routers need to be capable of integrating heterogeneous wireless networks.</p><p>　

48、　Conclusion</p><p>　　Although WMNs can be built up based on existing technologies, field trials and experiments with existing WMNs prove that the performance of WMNs is still far below expectations. As expla

49、ined throughout this article, there still remain many research problems. Among them, the most important and urgent ones are the scalability and the security.</p><p>　　Scalability. Based on existing MAC, rout

50、ing, and transport protocols, network performance is not scalable with either the number of nodes or the number of hops in the network. This problem can be alleviated by increasing the network capacity through using mult

51、iple channels/radios per node or developing wireless radios with higher transmission speed. However, these approaches do not truly enhance the scalability of WMNs, because resource utilization is not actually improved. T

52、herefore, in order t</p><p>　　Security. WMNs are vulnerable to security attacks in various protocol layers. Current security approaches may be effective to a particular attack in a specific protocol layer. H

53、owever, there still exists a need for a comprehensive mechanism to prevent or counter attacks in all protocol layers.</p><p>　　Moreover, self-organization and self-configuration capability is a desired featu

54、re in WMNs. It requires protocols in WMNs to be distributive and collaborative. However, current WMNs can only partially realize this objective. Furthermore, current WMNs still have very limited capabilities of integrati

55、ng heterogeneous wireless networks, due to the difficulty in building multiple wireless interfaces and the corresponding gateway/bridge functions in the same mesh Router.</p><p>　　In spite of these open rese

56、arch problems, we believe that WMNs will be one of the most promising technologies for next-generation wireless networking.</p><p>　　無(wú)線(xiàn)Mesh網(wǎng)絡(luò)調(diào)查</p><p>　　IAN F. AKYILDIZ，喬治亞理工學(xué)院</p><p&

57、gt;　　王旭東，KIYON，INC.</p><p><b>　　摘要</b></p><p>　　無(wú)線(xiàn)Mesh網(wǎng)路（無(wú)線(xiàn)Mesh）已成為一項(xiàng)針對(duì)下一代無(wú)線(xiàn)網(wǎng)絡(luò)的關(guān)鍵技術(shù)。由于他們較其他無(wú)線(xiàn)網(wǎng)絡(luò)的優(yōu)勢(shì)，無(wú)線(xiàn)Mesh正在快速進(jìn)步和引起眾多應(yīng)用。然而，在這個(gè)領(lǐng)域仍然存在許多技術(shù)問(wèn)題。為了提供一個(gè)無(wú)線(xiàn)Mesh的研究挑戰(zhàn)的更好地理解，本文介紹了當(dāng)前國(guó)家的最先進(jìn)的協(xié)議和算法的

58、無(wú)線(xiàn)Mesh的詳細(xì)調(diào)查。探討了所有協(xié)議層中的開(kāi)放性的研究問(wèn)題，客觀來(lái)引發(fā)了在此領(lǐng)域新的研究興趣。</p><p><b>　　介紹</b></p><p>　　無(wú)線(xiàn)Mesh網(wǎng)絡(luò)（無(wú)線(xiàn)Mesh）是動(dòng)態(tài)的自我組織和自我配置的網(wǎng)絡(luò)，在網(wǎng)絡(luò)節(jié)點(diǎn)自動(dòng)建立一個(gè)點(diǎn)對(duì)點(diǎn)網(wǎng)絡(luò)及維護(hù)該網(wǎng)狀連接。無(wú)線(xiàn)Mesh包含兩類(lèi)節(jié)點(diǎn)：Mesh路由器和網(wǎng)狀客戶(hù)端。除傳統(tǒng)無(wú)線(xiàn)路由器的網(wǎng)關(guān)/網(wǎng)橋功能的路由能

59、力，網(wǎng)狀路由器包含額外的路由功能，支持網(wǎng)狀網(wǎng)絡(luò)。通過(guò)多跳通信，相同的覆蓋面，網(wǎng)狀路由器可以實(shí)現(xiàn)更低的發(fā)射功率。為了進(jìn)一步提高網(wǎng)狀網(wǎng)絡(luò)的靈活性，網(wǎng)狀路由器通常配有多個(gè)基于相同或不同的無(wú)線(xiàn)接入技術(shù)的無(wú)線(xiàn)接口。盡管存在這些差異，網(wǎng)狀和傳統(tǒng)的無(wú)線(xiàn)路由器通常是建立在一個(gè)相似的硬件平臺(tái)的基礎(chǔ)上。</p><p>　　Mesh路由器有最小的流動(dòng)性并構(gòu)成網(wǎng)狀骨干網(wǎng)狀客戶(hù)端。因此，雖然網(wǎng)狀客戶(hù)端也可以作為Mesh網(wǎng)絡(luò)路由器工作，但

60、是它們的硬件平臺(tái)和軟件可能比網(wǎng)狀路由器的簡(jiǎn)單得多。例如，網(wǎng)狀客戶(hù)端的通信協(xié)議可以是輕重量，網(wǎng)關(guān)或網(wǎng)橋功能不存在于網(wǎng)狀客戶(hù)端中，只有一個(gè)單一的無(wú)線(xiàn)接口被放置在網(wǎng)狀客戶(hù)端等等。</p><p>　　除了介于網(wǎng)狀路由器和網(wǎng)狀客戶(hù)端之間的網(wǎng)狀網(wǎng)絡(luò)，Mesh路由器的網(wǎng)關(guān)/網(wǎng)橋功能，還能夠與其他各種網(wǎng)絡(luò)的無(wú)線(xiàn)Mesh網(wǎng)絡(luò)融合。配備了無(wú)線(xiàn)網(wǎng)絡(luò)接口卡（NIC）的常規(guī)節(jié)點(diǎn)可以直接連接到無(wú)線(xiàn)Mesh網(wǎng)絡(luò)，通過(guò)無(wú)線(xiàn)網(wǎng)狀路由器。沒(méi)有無(wú)線(xiàn)

61、網(wǎng)卡的客戶(hù)可以通過(guò)連接無(wú)線(xiàn)網(wǎng)狀路由器訪(fǎng)問(wèn)無(wú)線(xiàn)Mesh網(wǎng)絡(luò)，例如，以太網(wǎng)。因此，無(wú)線(xiàn)Mesh網(wǎng)絡(luò)將大大有助于用戶(hù)一直的在線(xiàn)，隨時(shí)隨地。</p><p>　　因此，無(wú)線(xiàn)Mesh網(wǎng)絡(luò)使Ad-hoc網(wǎng)絡(luò)的功能多樣化，而不是另一種類(lèi)型的點(diǎn)對(duì)點(diǎn)網(wǎng)絡(luò)。該功能給無(wú)線(xiàn)Mesh網(wǎng)絡(luò)帶來(lái)了許多優(yōu)點(diǎn)，如前期成本低，易網(wǎng)絡(luò)維護(hù)，魯棒性，可靠的服務(wù)覆蓋面等，因此，除了在傳統(tǒng)的Ad-hoc網(wǎng)絡(luò)的應(yīng)用領(lǐng)域被廣泛接受，無(wú)線(xiàn)Mesh網(wǎng)絡(luò)正在迅速商業(yè)

62、化，在許多其他的應(yīng)用程序案例，如寬帶家庭網(wǎng)絡(luò)，社區(qū)網(wǎng)絡(luò)，樓宇自動(dòng)化，高速城域網(wǎng)和企業(yè)網(wǎng)絡(luò)。</p><p>　　到目前為止，有幾家公司已經(jīng)實(shí)現(xiàn)了這種技術(shù)的潛力，并提供無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的產(chǎn)品。大學(xué)研究實(shí)驗(yàn)室已經(jīng)建立了幾個(gè)測(cè)試平臺(tái)。然而，若要無(wú)線(xiàn)Mesh網(wǎng)絡(luò)是一切它可以是的，還需要了相當(dāng)多的研究努力。例如，現(xiàn)有的MAC和路由協(xié)議是不可伸縮；吞吐量下降顯著影響著無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的節(jié)點(diǎn)或跳數(shù)數(shù)目的增加。因此，為了無(wú)線(xiàn)Me

63、sh網(wǎng)絡(luò)，現(xiàn)有的協(xié)議需要加強(qiáng)或重新設(shè)計(jì)了。研究人員已經(jīng)開(kāi)始從無(wú)線(xiàn)網(wǎng)狀網(wǎng)絡(luò)的角度來(lái)重新審視現(xiàn)有的無(wú)線(xiàn)網(wǎng)絡(luò)的協(xié)議設(shè)計(jì)，尤其是IEEE 802.11網(wǎng)絡(luò)，ad-hoc網(wǎng)絡(luò)，無(wú)線(xiàn)傳感器網(wǎng)絡(luò)。工業(yè)標(biāo)準(zhǔn)組織，如IEEE 802.11、IEEE 802.15和IEEE 802.16，都積極致力于無(wú)線(xiàn)Mesh網(wǎng)絡(luò)新規(guī)范。</p><p>　　在這篇文章中，我們提出無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的協(xié)議和算法的最新進(jìn)展的調(diào)查。我們的目的是提供一個(gè)

64、更好地了解這一新興技術(shù)的研究難題。我們的目的是提供一個(gè)更好地了解這一新興技術(shù)的研究難題。本文的其余部分安排如下：首先介紹無(wú)線(xiàn)網(wǎng)狀網(wǎng)的網(wǎng)絡(luò)架構(gòu)，以客觀的突出無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的特點(diǎn)和影響協(xié)議設(shè)計(jì)的關(guān)鍵因素。然后以一個(gè)開(kāi)放的研究問(wèn)題為重點(diǎn)，進(jìn)行無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的最新進(jìn)展的詳細(xì)研究。文章用結(jié)束語(yǔ)總結(jié)。</p><p>　　網(wǎng)絡(luò)體系結(jié)構(gòu)和關(guān)鍵的設(shè)計(jì)要素</p><p><b>　　網(wǎng)絡(luò)體系

65、結(jié)構(gòu)</b></p><p>　　無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的結(jié)構(gòu)可分為三種類(lèi)型：</p><p>　　基礎(chǔ)設(shè)施/骨干無(wú)線(xiàn)Mesh網(wǎng)絡(luò)。在這個(gè)架構(gòu)中，Mesh路由器形成一個(gè)為客戶(hù)提供的基礎(chǔ)設(shè)施，如圖1所示，其中虛線(xiàn)和實(shí)線(xiàn)分別表示無(wú)線(xiàn)和有線(xiàn)連接。除了大多采用的IEEE802.11技術(shù)，可以使用各類(lèi)無(wú)線(xiàn)電技術(shù)構(gòu)建無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的基礎(chǔ)設(shè)施/骨干。網(wǎng)絡(luò)路由器形成一個(gè)自我配置，自我修復(fù)，彼此間聯(lián)

66、系的網(wǎng)絡(luò)。網(wǎng)絡(luò)路由器具有網(wǎng)關(guān)功能，可以連接到互聯(lián)網(wǎng)。這種做法，也被稱(chēng)為網(wǎng)格化基礎(chǔ)設(shè)施，提供了傳統(tǒng)的客戶(hù)端的骨干，可以通過(guò)Mesh路由器的網(wǎng)關(guān)/網(wǎng)橋功能，融合現(xiàn)有的無(wú)線(xiàn)網(wǎng)絡(luò)與無(wú)線(xiàn)Mesh網(wǎng)絡(luò)。具有以太網(wǎng)接口的傳統(tǒng)客戶(hù)端可以通過(guò)以太網(wǎng)鏈路連接到網(wǎng)格路由器。對(duì)于傳統(tǒng)的客戶(hù)端與Mesh路由器相同的無(wú)線(xiàn)電技術(shù)，他們可以用Mesh路由器直接溝通。如果使用不同的無(wú)線(xiàn)電技術(shù)，客戶(hù)必須與擁有以太網(wǎng)連接的網(wǎng)狀路由器的基站進(jìn)行通信。</p>&

67、lt;p>　　客戶(hù)端無(wú)線(xiàn)Mesh網(wǎng)絡(luò)。網(wǎng)格化客戶(hù)端在客戶(hù)端設(shè)備之間提供對(duì)等網(wǎng)絡(luò)。在這種類(lèi)型的架構(gòu)中，客戶(hù)端節(jié)點(diǎn)構(gòu)成實(shí)際的網(wǎng)絡(luò)來(lái)執(zhí)行路由和配置的功能，以及向客戶(hù)提供終端用戶(hù)應(yīng)用程序。因此，對(duì)于這些類(lèi)型的網(wǎng)絡(luò)網(wǎng)狀路由器不是必須的?？蛻?hù)端無(wú)線(xiàn)Mesh網(wǎng)絡(luò)通常使用設(shè)備上的一類(lèi)無(wú)線(xiàn)電通訊設(shè)備組成。因此，客戶(hù)端無(wú)線(xiàn)Mesh網(wǎng)絡(luò)和傳統(tǒng)的ad-hoc網(wǎng)絡(luò)實(shí)際上是相同的。然而，當(dāng)與基礎(chǔ)設(shè)施網(wǎng)格化相比，終端用戶(hù)設(shè)備上的要求增加了，因?yàn)樵诳蛻?hù)端無(wú)線(xiàn)Me

68、sh網(wǎng)絡(luò)，終端用戶(hù)必須執(zhí)行附加功能，如路由和自配置。</p><p>　　混合無(wú)線(xiàn)Mesh網(wǎng)絡(luò)。這種體系結(jié)構(gòu)是基礎(chǔ)設(shè)施和客戶(hù)端網(wǎng)格化的組合，如圖2所示。Mesh客戶(hù)端可以通過(guò)Mesh路由器，以及直接與其他Mesh客戶(hù)聯(lián)網(wǎng)訪(fǎng)問(wèn)網(wǎng)絡(luò)。雖然基礎(chǔ)設(shè)施提供了連接其他網(wǎng)絡(luò)方式，如互聯(lián)網(wǎng)、Wi-Fi、WiMAX、蜂窩和傳感器網(wǎng)絡(luò)，但是服務(wù)對(duì)象的路由功能在無(wú)線(xiàn)Mesh網(wǎng)絡(luò)里提供改進(jìn)的連接和覆蓋范圍面。</p>&l

69、t;p>　　無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的特點(diǎn)概括如下，考慮了無(wú)線(xiàn)Mesh網(wǎng)絡(luò)混合架構(gòu)，因?yàn)樗藷o(wú)線(xiàn)Mesh網(wǎng)絡(luò)所有的優(yōu)點(diǎn)：</p><p>　　?無(wú)線(xiàn)Mesh網(wǎng)絡(luò)支持特設(shè)網(wǎng)絡(luò)，并有自我形成，自我愈合和自我組織的能力。</p><p>　　?無(wú)線(xiàn)Mesh網(wǎng)絡(luò)是多跳無(wú)線(xiàn)網(wǎng)絡(luò)，但由Mesh路由器提供無(wú)線(xiàn)基礎(chǔ)設(shè)施/骨干。</p><p>　　?Mesh路由器具有最小的流動(dòng)性

70、和執(zhí)行專(zhuān)用的路由和配置，從而顯著降低Mesh客戶(hù)及其他終端節(jié)點(diǎn)的負(fù)載。</p><p>　　?在無(wú)線(xiàn)基礎(chǔ)設(shè)施的支持下，終端節(jié)點(diǎn)的移動(dòng)很容易實(shí)現(xiàn)。</p><p>　　?Mesh路由器集成異構(gòu)網(wǎng)絡(luò)，包括有線(xiàn)和無(wú)線(xiàn)兩種。因此，在無(wú)線(xiàn)Mesh網(wǎng)絡(luò)中存在多種類(lèi)型的網(wǎng)絡(luò)接入。</p><p>　　?Mesh路由器和Mesh客戶(hù)對(duì)功耗約束不同。</p><p

71、>　　?無(wú)線(xiàn)Mesh網(wǎng)絡(luò)并不是獨(dú)立的，需要與其他無(wú)線(xiàn)網(wǎng)絡(luò)的兼容和互操作。</p><p>　　因此，無(wú)線(xiàn)Mesh網(wǎng)絡(luò)多樣化了ad hoc網(wǎng)絡(luò)的功能，而不是僅是另一種類(lèi)型的ad hoc網(wǎng)絡(luò)。這些額外的功能要求新的算法和實(shí)現(xiàn)無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的設(shè)計(jì)原則。</p><p><b>　　關(guān)鍵的設(shè)計(jì)要素</b></p><p>　　影響無(wú)線(xiàn)網(wǎng)狀網(wǎng)的性

72、能的關(guān)鍵因素歸納如下。</p><p>　　無(wú)線(xiàn)電技術(shù)。已經(jīng)提出了許多方法，近年來(lái)增加無(wú)線(xiàn)系統(tǒng)，容量和靈活性。典型的例子包括定向和智能天線(xiàn)，多輸入多輸出（MIMO）系統(tǒng)，和多射頻/多通道系統(tǒng)。</p><p>　　為了進(jìn)一步提高無(wú)線(xiàn)電臺(tái)的性能和由更高層協(xié)議來(lái)控制，更先進(jìn)的無(wú)線(xiàn)電技術(shù)已被用于無(wú)線(xiàn)通信，如重構(gòu)收音機(jī)，頻率捷變/感知無(wú)線(xiàn)電，軟件無(wú)線(xiàn)電。雖然這些無(wú)線(xiàn)電技術(shù)仍處于起步階段，他們有望成

73、為未來(lái)的無(wú)線(xiàn)網(wǎng)絡(luò)平臺(tái)，由于無(wú)線(xiàn)網(wǎng)絡(luò)的動(dòng)態(tài)控制能力。這些先進(jìn)的無(wú)線(xiàn)電技術(shù)，都需要在更高層協(xié)議，尤其是MAC和路由協(xié)議的革命性設(shè)計(jì)。</p><p>　　可擴(kuò)展性?？蓴U(kuò)展性是無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的一個(gè)關(guān)鍵要求。如果沒(méi)有此功能的支持，隨著網(wǎng)絡(luò)規(guī)模的增加，網(wǎng)絡(luò)性能顯著下降。例如，路由協(xié)議可能無(wú)法找到一個(gè)可靠的路由路徑，傳輸協(xié)議可能連接松動(dòng)，MAC協(xié)議可能會(huì)遇到吞吐量的顯著減少。為了確保無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的可擴(kuò)展性，從MAC層到

74、應(yīng)用層所有的協(xié)議需要具有可擴(kuò)展性。</p><p>　　網(wǎng)狀連接。無(wú)線(xiàn)網(wǎng)狀網(wǎng)的許多優(yōu)勢(shì)來(lái)源于網(wǎng)狀連接。為了確?？煽康木W(wǎng)狀連接，網(wǎng)絡(luò)自組織和拓?fù)浣Y(jié)構(gòu)控制算法是必要的。拓?fù)涓兄腗AC和路由協(xié)議，可以顯著提高無(wú)線(xiàn)網(wǎng)狀網(wǎng)的性能。</p><p>　　寬帶和QoS。與古典Ad-hoc網(wǎng)絡(luò)不同，無(wú)線(xiàn)網(wǎng)狀網(wǎng)的大多數(shù)應(yīng)用程序是具有異構(gòu)QoS要求的寬帶服務(wù)。因此，除了終端到終端的傳輸延遲和公平性，更多的性

75、能指標(biāo)，如時(shí)延抖動(dòng)、聚集點(diǎn)和每個(gè)節(jié)點(diǎn)的吞吐量、丟包率，必須考慮通信協(xié)議。</p><p>　　安全。雖然近年來(lái)已為無(wú)線(xiàn)局域網(wǎng)提出了許多安全方案，但是他們?nèi)匀徊煌耆m用于無(wú)線(xiàn)Mesh網(wǎng)絡(luò)。例如，有沒(méi)有集中的受信任的權(quán)威機(jī)權(quán)分發(fā)無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的公共密鑰，由于其分布式系統(tǒng)架構(gòu)?；贏d-hoc網(wǎng)絡(luò)提出的現(xiàn)有的安全方案，可以被無(wú)線(xiàn)Mesh網(wǎng)絡(luò)采納。然而，Ad-hoc網(wǎng)絡(luò)的大部分安全解決方案在實(shí)際實(shí)施上仍不夠成熟。此外，

76、無(wú)線(xiàn)Mesh網(wǎng)絡(luò)和Ad-hoc網(wǎng)絡(luò)之間的不同網(wǎng)絡(luò)架構(gòu)，通常呈現(xiàn)出Ad-hoc網(wǎng)絡(luò)的解決方案對(duì)于無(wú)線(xiàn)Mesh網(wǎng)絡(luò)是無(wú)效的。</p><p>　　易于使用。協(xié)議必須旨在實(shí)現(xiàn)網(wǎng)絡(luò)盡可能的自治。此外，網(wǎng)絡(luò)管理工具需要開(kāi)發(fā)，要高效地維持運(yùn)轉(zhuǎn)，有監(jiān)控性能，可配置無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的參數(shù)。這些工具，連同網(wǎng)絡(luò)協(xié)議的自治機(jī)制，使無(wú)線(xiàn)網(wǎng)狀網(wǎng)實(shí)現(xiàn)快速部署。</p><p>　　兼容性和互操作性。在無(wú)線(xiàn)Mesh網(wǎng)絡(luò)

77、里，支持傳統(tǒng)和網(wǎng)狀客戶(hù)端的網(wǎng)絡(luò)訪(fǎng)問(wèn)是默認(rèn)的規(guī)定。因此，無(wú)線(xiàn)Mesh網(wǎng)絡(luò)需要向后兼容傳統(tǒng)的客戶(hù)機(jī)節(jié)點(diǎn)。這要求Mesh路由器要能夠整合異構(gòu)無(wú)線(xiàn)網(wǎng)絡(luò)。</p><p><b>　　總結(jié)</b></p><p>　　雖然可以基于現(xiàn)有的技術(shù)建立無(wú)線(xiàn)Mesh網(wǎng)絡(luò)，利用現(xiàn)有的無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的現(xiàn)場(chǎng)試驗(yàn)和實(shí)驗(yàn)證明，無(wú)線(xiàn)網(wǎng)狀網(wǎng)的性能仍然遠(yuǎn)遠(yuǎn)低于預(yù)期。正如在整篇文章中解釋的，仍存在許多研

78、究的問(wèn)題。其中，最重要和最緊迫的是可擴(kuò)展性和安全性。</p><p>　　可擴(kuò)展性?；诂F(xiàn)有的MAC、路由和傳輸協(xié)議，網(wǎng)絡(luò)性能同節(jié)點(diǎn)的數(shù)量及網(wǎng)絡(luò)中的的跳數(shù)是不可擴(kuò)展的。增加網(wǎng)絡(luò)容量可以使這個(gè)問(wèn)題得到緩解，即通過(guò)采用多渠道/每節(jié)點(diǎn)無(wú)線(xiàn)電通訊設(shè)備或開(kāi)發(fā)具有更高傳輸速度的無(wú)線(xiàn)射頻技術(shù)。然而，這些方法沒(méi)有真正提高無(wú)線(xiàn)網(wǎng)狀網(wǎng)的可擴(kuò)展性，因?yàn)閷?shí)際上并未提高資源利用率。因此，為了實(shí)現(xiàn)可擴(kuò)展性，發(fā)展新的MAC，路由，無(wú)線(xiàn)Mesh

79、網(wǎng)絡(luò)的傳輸協(xié)議是必不可少的。</p><p>　　安全。無(wú)線(xiàn)Mesh網(wǎng)絡(luò)在各個(gè)協(xié)議層的安全攻擊是脆弱的。當(dāng)前的安全方法在特定協(xié)議層的特定攻擊可能是有效的。但是，仍然存在一種需求，防止或?qū)顾袇f(xié)議層的攻擊的全面的機(jī)制的需求。</p><p>　　此外，自我組織和自我配置能力是無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的所需功能。它需要無(wú)線(xiàn)Mesh網(wǎng)絡(luò)的協(xié)議來(lái)分配和協(xié)作。然而，目前的無(wú)線(xiàn)Mesh網(wǎng)絡(luò)只能部分實(shí)現(xiàn)這一目