[互联网]ch8_第8章 网络互联与因特网基础.pptVIP

* TCP Slowstart（慢启动） 窗口尺寸按指数递增 (每隔RTT) (不算太慢!) 丢失事件：超时或出现三次重复的ACKs initialize: Congwin = 1 for (each segment ACKed) Congwin++ until (loss event OR CongWin threshold) Slowstart 算法 Host A one segment RTT Host B time two segments four segments * TCP 拥塞避免 /* slowstart is over */ /* Congwin threshold */ Until (loss event) { every w segments ACKed: Congwin++ } threshold = Congwin/2 Congwin = 1 perform slowstart 拥塞避免 1 1: 在出现三次重复的ACK后，TCP Reno将跳过slowstart (快速恢复) 在此阶段，Congwin以线性方式增长，发生超时，门限值减半 * 小 结 网络互联的基本概念、体系结构和接入 因特网的链路层与网络层 点对点协议 网络层与IP协议 IP路由 ARP协议和RARP协议 ARP与IP的交互 IP地址的分配（DHCP） ICMP协议 因特网的传输层 传输层的多任务处理与端口 无连接的传输：UDP协议 面向连接的传输：TCP协议 * Communications network that serves users within a confined area is known as a Local Area Network (LAN). Computers (server and workstations) are normally distributed around a single office or building, including and network device like hub, bridge or router. Messages are transmitted in LAN as a series of packet with high data rate (small propagation delay). The packets may be fixed or variable length. Most LANs have broadcast capability. * The topology of a network defines the structure of its logiacal layout. There are three main categories of LAN topologies: bus/tree, star and ring. * ICMP协议：Internet Control Message Protocol 用于主机、路由器、网关之间交换网络层信息 报告错误: unreachable host, network, port, protocol 进行request/reply 应答(ping命令) 同处于网络层但“凌驾”于IP之上： ICMP报文需要封装到IP分组中进行传输 ICMP报文（教材p322）: type和code两个字段的含义见右。 Type Code description 0 0 echo reply (ping) 3 0 dest. network unreachable 3 1 dest. host unreachable 3 2 dest. protocol unreachable 3 3 dest. port unreachable 3 6 dest. network unknown 3 7 dest. host unknown 4 0 source quench (congestion control - not used) 8 0 echo request (ping) 9 0 route advertisement 10 0 router discovery 1