Internet Service Quality Assurance

The congestion control of TCP greatly accelethed the development of the Internet. Itsuccessfully provides satisfactory quality of service to the data applications such as FTP, WWWand Email. With the building up of the processing power of the network devices, queuingalgorithms such as fair queuing and random early detection further provides fairness and highefficiency for network resource sharing. At present real-time multimedia applications such as IPtelephoning and disbot education has become the future direction of the Intemet, and the relevantnetwork technologies for providing quality of service guarantees to real-time applications aregradually maturing. This thesis mainly focuses on the following areast1. Congestion control and queuing for traditional traffic. This thesis gives an introduction ofthe development of the end system's TCP congestion control, the impact of delayed ACK andUDP traffic on TCP, and multi-queue scheduling algorithms such as fair queuing and random fairqueuing. After this, we give a detailed analysis of the RED algorithm. We elaborate on theparameter setting principles and the complexity of the algorithm. Based on our analysis, this thesispresents a method for estmating and setting the RED parmeters, which enables the algorithm toadapt to the current network traffic. We have also investigated the traffic oscillation problemcaused by actual RED packet loss rate under heavily congested network environment. We presentan improved algorithm that addresses this problem. Through dynamic simulation, we have alsoproven that our improvement can enhance RED's adaptability as well as reduce the network delayand delay jitter.2. Queuing for multimedia traffic. Real-time multimdia traffic requires strict quality ofservice guarantees such as bandwidth, delay and delay jitter Once the QoS is lower than needed,the service will be unable to continue. The GPS scheduling algorithm can provide zero latencyand absolute faimess. But GPS is only an ideal algorithm in theory and can not be implementedin practice. In packet switching networks, WFQ, the discrete form of GPS, also has gooddelay and fairness, but its computing complexity is O(N), which makes it unable to be widelydeployed. The most up-to-date research result is the SPFQ algorithm. Its comPuting complexityis O(log₂N) and can provide quality of service similar to WFQ This thesis analyzes thefaimess and delay jitter characteristics of SPFQ. We find that there is a strong inter-sessiondependence. We present a further improved SPJFQ algorithm, which enhances the SPFQalgorithIn by adding eligibility contrOl. A packet is sent only when itS starting potential is largerthan the system potenhal. The comPuting comPlexity of SPJF is also O(lOg, N), but it hasbetter fairness and delay jitter characteristics, which are indePendent of the resource reservation ofother sessions.3. Implementation and improvement of the Integrated Services. Integratd Services is aspecification proposed by the IETF IntServ working grOuP in l994. The aAn is to constrUct apacket switChing netWork which can provide service to both real-time and non real-time traffic.IntServ adopts the resource reservation protocol (RSVP) as the adInission control, and usuallyemPloys scheduling mechanisms such as mp to provide bandwidth and delay gUarantees ofdata transndssion. We have bolemented the RSVP protocol under Linux with CBQ as thescheduling algorithIn. Our imPlementation can provide controlled load service and guaranteedservice. Thrugh muh testing, we find that the link layer OPerahons constitUte the largestoverhead during the session set uP process. Research and improvement of Differentiated Services.The Differentiated Services is another QoS mechanism proPosed by the IETF. Unlike IntServ,which reserves resource for each data fiow DiffServ aggregates data flows to different servicelevels and provideS service to data packets accodrig to their service level. Because o...