1、 外文翻译 毕业设计 题目： IP 网络中单速率多播拥塞控制 算法研究 原文 1： TCP-Friendly Multicast Congestion Control (TFMCC): Protocol Specification 译文 1： TCP 友好的多播拥塞控制协议 : 协议规范 原文 2： A Simple And Effective Single-Rate Multicast Congestion Control 译文 2： 一种简单而有效的单速率多播拥塞控制方案 浙江理工大学科技与艺术学院本科毕业设计（论文） TCP-Friendly Multicast Congestion C
2、ontrol (TFMCC): Protocol Specification 1. Introduction This document specifies TCP-Friendly Multicast Congestion Control (TFMCC). TFMCC is asource-based, single-rate congestion control scheme that builds upon the unicast TCP-FriendlyRate Control mechanism (TFRC). TFMCC is stable and responsive under
3、 a wide range of network conditions and scales to receiver sets on the order of several thousand receivers. Tosupport scalability, as much congestion control functionality as possible is located at the receivers. Each receiver continuously determines a desired receive rate that is TCP-friendly forth
4、e path from the sender to this receiver. Selected receivers then report the rate to the sender infeedback packets. TFMCC is a building block as defined in RFC 3048. Instead of specifying a completeprotocol, this document simply specifies a congestion control mechanism that could be used in atranspor
5、t protocol such as RTP, in an application incorporating end-to-end congestioncontrol at the application level. This document does not discuss packet formats, reliability, orimplementation-related issues. TFMCC is designed to be reasonably fair when competing for bandwidth with TCP flows. Amulticast
6、flow is reasonably fair if its sending rate is generally within a factor of two of thesending rate of a TCP flow from the sender to the slowest receiver of the multicast group underthe same network conditions. In general, TFMCC has a low variation of throughput, which makes it suitable for applicati
7、onssuch as streaming media where a relatively smooth sending rate is of importance. The penalty ofhaving smooth throughput while competing fairly for bandwidth is a reduced responsiveness tochanges in available bandwidth. Thus TFMCC should be used when the application has arequirement for smooth thr
8、oughput, in particular, avoiding halving of the sending rate in responseto a single packet drop. For applications that simply need to multicast as much data as possible in as short a time as possible, PGMCCmay be more suitable 2. Protocol Overview TFMCC extends the basic mechanisms of TFRC into the
9、multicast domain. In order to competefairly with TCP, TFMCC receivers individually measure the prevalent network conditions andcalculate a rate that is TCP-friendly on the path from the sender to themselves. The rate isdetermined using an equation for TCPthroughput, 浙江理工大学科技与艺术学院本科毕业设计（论文） which rou
10、ghly describes TCPs sending rate asa function of the loss event rate, round-trip time (RTT), and packet size. We define a loss event asone or more lost or marked packets from the packets received during one RTT, where a markedpacket refers to a congestion indication from Explicit Congestion Notifica
11、tion (ECN). Thesending rate of the multicast transmission is adapted to the receiver experiencing the worstnetwork conditions. Basically, TFMCCs congestion control mechanism works as follows: Each receiver measures the loss event rate and its RTT to the sender. Each receiver then uses this informati
12、on, together with an equation for TCP throughput, toderive a TCP-friendly sending rate. Through a distributed feedback suppression mechanism, only a subset of the receivers areallowed to give feedback to prevent a feedback implosion at the sender. The feedbackmechanism ensures that receivers reporti
13、ng a low desired transmission rate have a highprobability of sending feedback. Receivers whose feedback is not suppressed report the calculated transmission rate back to thesender in so-called receiver reports. The receiver reports serve two purposes: they inform thesender about the appropriate tran
14、smit rate, and they allow the receivers to measure their RTT. The sender selects the receiver that reports the lowest rate as current limiting receiver (CLR). Whenever feedback with an even lower rate reaches the sender, the corresponding receiverbecomes CLR and the sending rate is reduced to match
15、that receivers calculated rate. Thesending rate increases when the CLR reports a calculated rate higher than the current sendingrate. The dynamics of TFMCC are sensitive to how the measurements are performed and applied andwhat feedback suppression mechanism is chosen. We recommend specific mechanis
16、ms below toperform and apply these measurements. Other mechanisms are possible, but it is important tounderstand how the interactions between mechanisms affect the dynamics of TFMCC. 3. Data Sender Protocol The data sender multicasts a stream of data packets to the data receivers at a controlled rate.Whenever feedback is received, the sender checks if it is necessary to switch CLRs and toreadjust the sending rate. The main tasks that have to be provided by a TFMCC sender are: adjusting the sending rate,
