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1、,Computer network,Network：Infrastructure for communication 1973: TCP/IP were tested and in-fact standardized. 1973-1988: NSFNet, further developed mainly inside academic organizations, filled with applications, e.g., Telnet, FTP, email, gopher, finger, etc. 1989-1999: Internet, towards commercial in
2、frastructure, more popular applications are invented, e.g., WWW in 1994. 2000- up to-now: More highly secure and bandwith-intensive applications are developed, e.g., VPN, IP-phone, real-time interactive multimedia, etc. IPng(IPv6) was standardized in 1997.,Preliminaries(1),Network is a system of com
3、puters： Network = Network Edge+ Network Core Network Core: communication-centric service providers, e.g., network equipments (routers, switches, gateways, firewalls, etc.) Network Edge: communication-service consumers, based-on which to implement distributed computations, e.g., workstations, Web ser
4、vers, RDBMS/SQL servers, etc.,Preliminaries(2),Distributed Applications Architecture Mode: Client/Server: Resource highly concentrated at (usually few) servers; Client (actively) requesting, servers (passively) responsing. P2P Resource nearly evenly distributed among peers; No strict clients b. stat
5、eful data exchange under control of “connection”; c. connection-closing after communication. example：TCP Note: connection-oriented communication is usually end-to-end, and no intermediate equipments involved in state-maintaining.,Preliminaries(3-2),Typical Communication modes in network core : Conne
6、ctionless(非连接式通讯): Stateless, messages independent each other - simply send whenever necessary. Example：IP, UDP, etc.,Preliminaries(4-1),Switch(交换): How information gets to their destination? In INTERNETs network core information gets to their destination via packet-switching(分组交换): Information (wha
7、tever is carried) is cut to packets transmission units； Any packet is formatted head + payload (首+数据 Network core transfers each packet independently, e.g., find the appropriate path for each packet, not caring likely inter-packets relationships.,Preliminaries(4-2),An example of packet-switching ove
8、r the internet: r.f.t. Kurose (2) internet = city (composed of lots of intersected streets) (3) router = policeman on internet (4) route table = a internet-world map owned by the router/policeman. (5) a route transfers (i.e., switches(!) each packet to the routers appropriate neighbor which is close
9、r to the packets destination. (6) Switch decision is made only according to where the packet is going and the route table (the routers own map). In particular, the packets source (where is comes) is NOT concerned.,Preliminaries(4-3),Circuit Switch(电路交换) We dont care”-). Working Example: PSTN (Public
10、 Switch Telephone Network),Preliminaries(5-1),OSI Hierarchical Reference Model,Representation Layer/表示层,Session Layer/会话层,Transport Layer/传输层,Network Layer/网络层,Data Link Layer/数据链路层,Physical Layer/物理层,Preliminaries(5-2),Characteristics of Hierarchical (Any) Model 1) Each layer provides a group of re
11、lated functionalities with similar complexities. 2) Each layer implements its own services via calling its neighbor underlying layer services. 3) Lower layers provide simpler but more general functionalities, while the upper layers provide more complicated and special ones.,Preliminaries(5-3),What d
12、oes the Data-Link Layer do? Bit transmission between interfaces connected by the same single media (cable, UTP/twisted pair, electromagnetic field/wireless, etc.) More details Addressing Frame Formatting Error Detecting Packets disorder recovery; Flow speed matching; How reliable? 100%(!) unless no
13、permanent failure.,Internet Protocol Stack Summary,Application：complicated data I/O Socket API, RPC/XDR, client/server model,Transport Layer：end-to-end reliable data transmision , TCP、UDP,Data link layer：frame transimision between neighbor interfaces e.g., Media Access Control,Netwk Layer：Host-Host
14、packet transmision, e.g., IP、ICMP、ARP、route learning(RIP，OSPF、BGP）,tcp_output,tcp_input,ip_output,ip_input,nic_intput,nic_output,Network Eaxmples(6-1):Group LAN,Server,PC,PC,IEEE802.3 Protocol,Switch,Examples(6-2):Access Network,End user,PC+Modem,IP/PPP Voice Link, CableTV Link,ISP,AAA Server NAS,RA
15、DIUS,Internet,TCP/IP,Examples(6-3):Campus/Enterprise LAN,Backbone Switch,Server,Dept. Svr.,Branch Sw.#1,1Gbps-Ethernet,100Mbps-Ethernet,LAN seg.#1(Collision domain#1),LAN seg.#2(Collision domain#2),Branch Sw.#2,Border Gateway + Fw.,TCP/IP协议,Example(6-4):Building LAN,1Gbps-Ethernet,100Mbps-Ethernet,G
16、1,Example(6-5): VPN,VPN Border Gateway G1,G2,G3 IP+IPSec + IKE + Sec. Policy,INTERNET,G1,G2,G3,Ent. LAN#2,Ent. LAN#3,Ent. LAN#1,Example(6-6): Embedded Network (real-time),100Mbps FDDI,Actuator#1,Actuator#2,Controller#1,Controller#2,Sensor#1,Display#1,Controller#3,Sensor#2,Example(6-7):Cellular Network,Mobile Switch
