Must choose routes for various origin destination pairs(O/D pairs) or for various sessions - Datagram routing: route chosen on packet by packet basis Using datagram routing is an easy way to split paths Virtual circuit routing: route chosen a session by session basis Static routing: route chosen in a prearranged way based on O/D pairs Eytan Modiano

Carrier Sense Multiple Access(CSMA) In certain situations nodes can hear each other by listening to the channel “Carrier Sensing CSMA: Polite version of Aloha Nodes listen to the channel before they start transmission Channel idle=> Transmit Channel busy = Wait (join backlog) When do backlogged nodes transmit? When channel becomes idle backlogged nodes attempt transmission with probability q=1 Persistent protocol, q=1 Non-persistent protocol,< 1

Queueing Systems Used for analyzing network performance In packet networks, events are random Random packet arrivals Random packet lengths While at the physical layer we were concerned with bit-error-rate, at the network layer we care about delays How long does a packet spend waiting in buffers

Routing Must choose routes for various origin destination pairs o/d pairs) or for various sessions Datagram routing: route chosen on a packet by packet basis Using datagram routing is an easy way to split paths Virtual circuit routing: route chosen a session by session basis Static routing: route chosen in a prearranged way based on O/D pairs Eytan Modiano

CSMA/CD and Ethernet Two way cable wsws Ws W CSMA with Collision Detection(CD)capability Nodes able to detect collisions Upon detection of a collision nodes stop transmission Reduce the amount of time wasted on collisions Protocol

Cyclic Codes a cyclic code is a linear block code where if c is a codeword, so are all cyclic shifts of c E.g., 1000, 110, 101,011 is a cyclic code Cyclic codes can be dealt with in the very same way as all other lbc s Generator and parity check matrix can be found a cyclic code can be completely described by a generator string G All codewords are multiples of the generator string In practice, cyclic codes are often used for error detection(CRc) Used for packet networks When an error is detected by the received, it requests retransmission

内容提要 1.广域网实例 2.PSTN 3.DDN 4.X.25 5.帧中继 6.ATM

网络接口卡 一、网络接口卡(NIC)简称网卡,也被称为网络适配器就物理外表而言,网络接N 口卡是与计算机主板或外围设备上的总线扩展槽相适应的一种印刷电路板 二、网络接口卡是网络通信的基本硬件组成部分,它能够把计算机产生的串行信号转换成可以在网络电缆上传送的串行格式

课前问题 1、以下IP地址各属于哪一类? (a)20.250.1.139(b)202.250.1.139(c) 120.250类139 C类 A类 2、已知子网掩码为255.255.255.192,下面各组IP地址是否属于同一子网? (a)200.200.200.224200.200.200.208 (b)200.200.200.224200.200.200.160

内容提要 1.802.3布线介质标准 2.高速局域网