课件大二上计算机网络l12network layer p2congestion

1、Introduction to ComputerNetworksTian Song (嵩天), Ph.D., Assoc. Prof.songtianIntroduction to ComputerNetworksCongestion Control and QoSTian Song (嵩天), Ph.D., Assoc. Prof.songtianOutline Congestion Control Quality of Service Interconnection3School of Computer Science and Technology, BIT,Congestion Cont

2、rolStoreandForward Packet Switching4School of Computer Science and Technology, BIT,Congestion ControlQuestion:When too many packets arrive, we got a serious problem.Congestion5cn/songtianCongestion Control53Question:52121312Why there is the congestion?Router Architecture6School of Computer Science a

3、nd Technology, BIT,Congestion ControlCongestion Control: (network & transport layer)Congestion control has to do with making sure the subnet is able to carry the offered traffic. It is a global issue, involving the behavior of all the hosts and all the routers.Flow Control: (data link layer)Flow

4、 control, in contrast, relates to the pointtopoint traffic between a given sender and a given receiver. Its job is tomake sure that a fasder cannot continually transmit datafaster than the receiver is able to absorb it.7School of Computer Science and Technology, BIT,Congestion ControlFlow ControlRRR

5、Flow ControlCongestion Control8School of Computer Science and Technology, BIT,Congestion ControlResources<=>Loads9School of Computer Science and Technology, BIT,Congestion Control(1) When and where congestion occurs The queue length The number of retransmitted packets The packet delay(2) Where

6、 and how to solve congestion Find the senders, or, collaborate with routers Increase resources or decrease the loads10School of Computer Science and Technology, BIT,Traffic aware RoutingRouting is aware of the traffic by adapting cost.c(x,x) = cost of link (x,x)cost= func( bandwith, delay, queue_len

7、, traffic)5v3vww522uzuz1y2x1y31x1221111School of Computer Science and Technology, BIT,Traffic aware RoutingRouting is aware of the traffic by adapting cost.12School of Computer Science and Technology, BIT,cost = func( bandwith, delay, queue_len)Traffic Throttling (流量调节)(1) Choke Packet (抑制包)Why is i

8、t not popular?(2) ECN (Explicit Congestion Notification)13School of Computer Science and Technology, BIT,Traffic Throttling(3) HopbyHop Backpressure (逐跳后压)14School of Computer Science and Technology, BIT,Load Shedding (负载脱落)(1) Wine Policy& Milk Policydrop new arrived packets or old packets in q

9、ueue(2) RED (Random Early Detection) (随机早期检测)MaxThresholdMinThreshold> max, drop all<min, no drop others, drop with pusually, p = 0.0002AvgLen15School of Computer Science and Technology, BIT,Quality of ServiceQuestion:How to measure the performance of network?QoS,what is QoS?bandwidth, delay,

10、jitter, and loss带宽、延迟、抖动、丢失16School of Computer Science and Technology, BIT,Quality of Service17School of Computer Science and Technology, BIT,Quality of ServicePSTN:FD, Connectionoriented, voice: 3kHzMobile Network:4G: FD and TD, voice and dataSatellite Network:long delay (DTN, delay tolerance netw

11、ork)Cable TV Network:TV deliveryQoS is critical to Internet!18School of Computer Science and Technology, BIT,Techniques for Good QoSOverprovisioning (过度配置) Buffer:Traffic Sha19School of Computer Science and Technology, BIT,Traffic ShaLeaky Bucket Algorithm: (漏桶)20School of Computer Science and Techn

12、ology, BIT,Traffic ShaLeaky Bucket Algorithm:RiRi = RRi > R, if actual(B)=0,Ri <= R21School of Computer Science and Technology, BIT,Traffic ShaToken Bucket Algorithm: (令牌桶)Tokens aded at a constant rate; as soon as enough tokenshave been saved, one or more packets can be sent.22School of Compu

13、ter Science and Technology, BIT,Packet SwitchingIf a router is handling multiple flows(1) fair queuing (2) weighted fair queuingBased on packets, or bytes with weighted and priority23School of Computer Science and Technology, BIT,Differentiated Services转发)Expedited Forwarding (Expedited packets expe

14、rience a trafficnetworkPriority queue and regular queueSchool of Computer Science and Technology, BIT,24InterconnectionQuestion:Now, we have networks with different protocols. How to connect them & let them talk to each other?Solutions:Build some gateways that can connect networks.Which layer sh

15、ould be applied to the gateway?25School of Computer Science and Technology, BIT,InterconnectionGateway:different data link layerIPX, SNA, AppleTalk26School of Computer Science and Technology, BIT,InterconnectionTunneling: (隧道)different network layer27School of Computer Science and Technology, BIT,InterconnectionAS: (自治域)different routing protocolsBGP:Border Gateway Protocol IGP:Interior Gateway Protocol28School of Computer Science and Technology, BIT,InterconnectionMTU um Transmission UnitpgypgInterconnecti