Reserch On Congestion Control Of Networks-on-Chip

With the development of micro-electronic industrial technology, the micromationtrend of Network-on-Chip is speeding up, and it makes possible to integrate hundreds oreven thousands of processing cores to a single chip.The good inheritance of traditionalparallel computer’s theory, makes NoC rise up with an amazing speed,it is quitewelcomed by people because of its excellent expansibility and abundant resources ofinterconnecting wires. NoC’s superiorities guarantee other advantages, such as highbandwidth design, predictable interconnecting wire length and delay, as well as itsspecificity and reusability.NoC’s development is bounded by chip area and power consumption, this directlyinfluences the amount of integratable storage units of the chip, as a result,the physicaland logical resource are under huge restriction. In order to meet with this shortcut, onlyconsidered in hardware design(router architecture), Virtual Channel Router, WormholeRouter and Bufferless Router are proposed and brought into real world usage insuccession, these routers can reduce buffers as a way to save chip area and powerconsumption.NoC’s performance depends on the network’s packet injection rate a lot. Underideal circumstances, the injection rate could increase with no boundary only if theresource (logical and physical) needed is enough, this is object to the idea of lower areaand low power designing. With a certain network resource when injection rate in-creases, a large number of packets might/will compete one(several) router’s(routers’)resource. Congestion problem arises if one wins/loses in the competition, otherwise,dead-lock problem arises, regional congestion/dead-lock can leads to the entire networkrelapses into congested/dead-locked.This paper’s research mainly eyes on the large scale congestion control stratedyunder high message injection rate, the main work done are those several fields as listedbelow:1. Proposes a kind of Congestion alleviation technology. This paper set chapter3to introduce the proposed congestion alleviation technology based on escape channel.Under the TDM management, the adjacent four routers may compete the shared escapechannel, so a reasonable routing algorithm to reduce message competion delay isneeded. The routing algorithm based on short-message-first can entrust the longmessage a higher competion priority, let the shorter one forward first. This idea makesfull use of short message needs less resource than longer’s, clear up router as quickly aspossible so that to alleviate its congestion state. The experiment indicates, alleviationeffections are related to routers’ communication mode between each other, range aboutfrom6.025%to16.66%. 2. Congestion avoidance strategy. This paper proposes a congestion avoidancestrategy based on dynamic injection rate in chapter4. The idea of dynamic injection ratedraws lessons from slide-window inside TCP-IP, it adjusts the injection rate in real-timewhile the recent network congestion state is set as a reference, it controls the number ofmessages maintain at a level, and never cross over the set congestion threshold value,thus avoid network congestion. However, the congestion avoidance is not absolutely,congestion may accur during congestion detection, to meet the problem and reduce theside effection, this paper decreses the detection interval when injection rate increasestoward a higher derection. At last the experiments stand that the strategy based ondynamic injection rate to avoid congestion is effective, it can decrease the averagemessage delay.3. The analysis of the router’s area and power consumption. Chapter5is set toanalysis the cost of area and power consumption of virtual channel router based onsome related softwares, it analyzes the escape channel both in area cost and powerconsumption when compared with one-escape-channel-just-for-one-router and datashows that each router’s area amplification just slightly crosses over3%while powerconsumption amplification does not reach4.7%. Through analysing large numbers ofexperiments’ result, the paper figures out a linear relationship between powerconsumption and the present injection rate.