電氣工程及自動化畢業(yè)設(shè)計論文外文翻譯-基于衛(wèi)星網(wǎng)絡(luò)的多路傳送協(xié)議-其他專業(yè)-資料下載頁
2025-01-19 03:08本頁面
【導(dǎo)讀】因為廣播衛(wèi)星信道的傳輸能力極強(qiáng)，所以通信衛(wèi)星技術(shù)很適合傳。盡管衛(wèi)星多路有著巨大的潛能，但是在衛(wèi)星網(wǎng)。絡(luò)上很少存在對多路傳送服務(wù)支持的協(xié)議。雖然幾份多路傳送協(xié)議已經(jīng)供因特網(wǎng)。的使用，但是他們對于衛(wèi)星網(wǎng)絡(luò)不是很好的選擇。協(xié)議的一關(guān)鍵部分受到了影響，這一部分是運(yùn)輸層。發(fā)展過程中一些相互矛盾的問題。此外，在許多情況下，地寬帶連接的基礎(chǔ)設(shè)施達(dá)不到這種要求。的下一代衛(wèi)星通信系統(tǒng)正在研究中。為了提供可靠性，一份協(xié)議需要鑒定不能到達(dá)規(guī)定的目的地的包。此外，NACK包的數(shù)量預(yù)計在在出錯率上少。包是否到達(dá)到了接受者了，因為NACK包可能在輸送過程中丟失。在ARQ內(nèi)，發(fā)送者對丟。復(fù)來說，由于幾個原因純ARQ結(jié)果是無效的。和進(jìn)一步消失在衛(wèi)星鏈路，就會導(dǎo)致高出錯率和高突發(fā)錯誤。反饋包的流，其目的是避免反饋破裂的問題。在面向無連接通訊里，反饋報告包返回發(fā)送人，發(fā)送人提出重傳。
【正文】 ckets are particularly important in satellite works because of the long propagation delays associated with satellite links. In a backbone deployment, satellite gateways are in a very good position to assist in the local recovery together with other intermediate routers. However, as it is the case with feedback aggregation, routerassisted local recovery requires support from intermediate work elements and its availability depends on existence of router extensions. A generalization of routerassisted local recovery is possible, if receiver nodes are also allowed to respond to retransmission requests. In this case, feedback packets need to be multicast to the set of receivers. However, efficient scoping of feedback and repair packets must be implemented to avoid flooding of work. In a directtohome deployment, all receivers receive packets directly from the satellite and there are no intermediate routers between satellite and the receivers. Therefore, it is difficult to implement local recovery for this type of works. 4. Protocol of data munications There is an effort in the research munity to provide a ubiquitous endtoend congestion control algorithm for hybrid satelliteterrestrial works. This requires careful modification of the TCP protocol to match the characteristics of the satellite channels. Another approach is to split a 11 connection at the terrestrialsatellite work interface, and to run TCP between the end nodes and the satellite work gateways, while running a customized algorithm in the satelliteonly core work. The latter approach has several advantages in practice. It allows satellite provider to optimize the traffic flow inside the core work to achieve high utilization. Also, it makes it possible to push the congestion to the edges of the satellite work and let the TCP protocol’ s congestion control mechanism to take care of the congestion in the terrestrial portion of the work. Inside the core work, the problem is reduced to a flow control problem rather than a congestion control problem since the satellite bandwidth is fixed and is to be shared among all the active connections. Hence, the satelliteonly tier is isolated from the rest of the Inter, and flow control can be implemented by a simple window control mechanism. There is also no need to differentiate between losses due to congestion and losses due to link losses. Isolating the satellite work from the rest of the Inter would require additional functionality at the gateway nodes. However, we believe that satellite providers would be willing to go with this design, since the implementation will allow them to have full control of the traffic flow in their works. Adding to this the challenges of having a TCPlike behavior for multicast services, we believe that, having a customized algorithm for the satellite work has considerable advantages. 5. Conclusion In this chapter, we have presented a taxonomy and survey of various design alternatives for supporting multicast services, and discussed how the design space of various multicast transport protocol ponents are constrained in the context of satellite works. Our classification is based on the IETF building blocks for multicast transport protocols, but highlights which ponents of a general transport protocol are affected by the two most mon satellite work deployment scenarios. We also outlined some of the issues that are critical in the development of next generation satellite multicast services. Some of these problems, such as feedback implosion avoidance and packet level FEC coding at the transport layer, have counterparts in terrestrial works, but they have to be addressed separately while taking into consideration the unique characteristics of satellite works. We believe that efficient solutions to these problems and development of new technologies, such as onboard processing and buffering, would demonstrate the true value of satellite works in the global munication infrastructure.
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