1. Introduction and Overview

1. 1. Introduction and Overview MMlab

2. Internet Timeline • 3000 BC : Abacus • 1642 : Pascal : numerical wheel calculator • 1822 : Babbage : difference engine • 1945 : Eckert : ENIAC • 1969 : first ARPANET connection • UCLA, SRI, UCSB, Utah • 1972 : CYCLADES (France) • 1974 : V. Cerf : TCP MMlab

3. Internet Timeline • 1977 : e-mail over Telenet • 1980 : IBM : Bitnet • 1981 : IBM : PC • 1982 : Time : Computer • 1984 : Domain Name System • 1988 : Morris : Worm, and CERT • 1989 : number of hosts exceeds 100,000 • 1991 : Al Gore : High Performance Computing Act • 1991 : Tim Berners-Lee : WWW • 1992 : Internet Society • 1993 : Andreessen : Mosaic • 1994 : Yahoo ! MMlab

4. 인터넷 등장 배경 • 미 국방성의 요구: 많은 통신 시설이 파괴되더라도 계속 살아 남는 통신 네트워크를 고안할 것. 다양한 통신기술을 활용할 수 있을 것. • 과학기술계의 결론 • 패킷 (packet) 방식의 통신네트워크 • 연결을 만들지 않음 • 전체의 70% 이상이 파괴되어도 계속 생존하여 통신기능 유지함 MMlab

5. 패킷이란 ? • Packet  Circuit 대응개념 • 보내야 할 정보를 취급하기 쉬운 작은 단위 (패킷이라 부름)로 쪼갬 • 예 : 소설을 엽서로 옮겨 적어 보낸다. • 예 : 많은 화물은 여러 대의 트럭에 나누어 실어 보낸다 • 통신망은 패킷을 일일이 따로 구분하여 처리 • 엽서마다 보내는 이, 받는 이의 주소를 반복하여 적고 우체국은 엽서마다 이를 확인한다 • 받는 쪽에서 정보를 모아서 원래대로 재생 • 왜 패킷인가 ? • 전송효율/ 네트워크 구축비용 절감 : 화물회사마다 전용차선이 있다면 낭비 • 다양한 트래픽을 쉽게 지원 : 전보, 편지, 음성, 영상, 컴퓨터 데이타 MMlab

6. 패킷 통신의 예 A A • A A B B • • A A A • B 회선 공유 B B B MMlab

7. Internet Configuration subnet Packet Host subnet subnet subnet Host Packet Router subnet MMlab

8. roughly hierarchical national/international backbone providers (NBPs) e.g. BBN/GTE, Sprint, AT&T, IBM, UUNet interconnect (peer) with each other privately, or at public Network Access Point (NAPs) regional ISPs connect into NBPs local ISP, company connect into regional ISPs local ISP local ISP NAP NAP Internet structure: network of networks regional ISP NBP B NBP A regional ISP MMlab

9. Protocols • Protocol: rules for communication • Message formats, timing • Describes how a computer responds when a message arrives • Specifies how a computer handles errors or other abnormal conditions • All network services are described by protocols MMlab

10. a human protocol and a computer network protocol: TCP connection reply. Get http://gaia.cs.umass.edu/index.htm Got the time? 2:00 <file> time What’s a protocol? Hi TCP connection req. Hi MMlab

11. Key Elements of a Protocol • Syntax • Data formats • Signal levels • Semantics • Control information • Error handling • Timing • Speed matching • Sequencing MMlab

12. A Three Layer Model • Network Access Layer • Transport Layer • Application Layer MMlab

13. Simplified File Transfer Architecture MMlab

14. Network Access Layer • Exchange of data between the computer and the network • Sending computer provides address of destination • May invoke levels of service • Dependent on type of network used (LAN, packet switched etc.) MMlab

15. Transport Layer • Reliable data exchange • Independent of network being used • Independent of application MMlab

16. Application Layer • Support for different user applications • e.g. e-mail, file transfer MMlab

17. Open Systems Interconnection Developed by the International Organization for Standardization (ISO) Seven layers A theoretical system delivered too late! TCP/IP is the de facto standard A layer model Each layer performs a subset of the required communication functions Each layer relies on the next lower layer to perform more primitive functions Each layer provides services to the next higher layer Changes in one layer should not require changes in other layers OSI MMlab

18. OSI Layers MMlab

19. application: supporting network applications ftp, smtp, http transport: host-host data transfer tcp, udp network: routing of packets from source to destination ip, routing protocols link: data transfer between neighboring network elements ppp, Ethernet physical: bits on the wire application transport network link physical Internet protocol stack MMlab

20. OSI v TCP/IP MMlab

21. Some Protocols in TCP/IP Suite MMlab

22. Dialup via modem DSL: digital subscriber line : ADSL, VDSL Cable Modem LAN (wired, wireless : IEEE 802), WiBro (mobile WiMax) 802.16e Wireless Mesh Bluetooth Satellite Cellular (2, 2.5, 3, 4G) FTTH Sensor network Access Technologies MMlab

23. M H H H H H H H H H n n t l t n l t t M M application transport network link physical M Data Link Layer • two physically connected devices: • host-router, router-router, host-host • unit of data: frame network link physical data link protocol M frame phys. link MMlab

24. Link Layer Services • Framing, link access: • encapsulate datagram into frame, adding header, trailer • implement channel access if shared medium, • ‘physical addresses’ used in frame headers to identify source, destination • different from IP address • Reliable delivery between two physically connected devices: MMlab

25. Link Layer Services (more) • Flow Control: • pacing between sender and receivers • Error Detection: • errors caused by signal attenuation, noise. • receiver detects presence of errors: • signals sender for retransmission or drops frame • Error Correction: • receiver identifies and corrects bit error(s) without resorting to retransmission MMlab

26. Stop and Wait • The source transmits one frame • The destination receives one frame and replies with an acknowledgement • The source waits for ACK before sending the next frame • The destination can stop the flow by not sending ACK MMlab

27. Sliding Windows Flow Control • Allow multiple frames to be in transit • Receiver has buffer (size = W frames) • Transmitter can send up to W frames without ACK • Each frame is numbered • ACK includes the number of next frame expected • Sequence number MMlab

28. Error Control • Detection and correction of errors • Lost frames • Damaged frames • Automatic repeat request • Error detection • Positive acknowledgment • Retransmission after timeout • Negative acknowledgement and retransmission MMlab

29. Automatic Repeat Request (ARQ) • Stop and wait • Go back N • Selective reject (selective retransmission) MMlab

30. Stop and Wait -Diagram MMlab

31. Go Back N • Based on sliding window • If no error, ACK as usual with the number of the next frame expected • Use window to control the number of outstanding frames • If error, reply with rejection • Discard the bad frame and all future frames until the error frame is received correctly • Transmitter must go back and retransmit the bad frame and all subsequent frames MMlab

32. Go Back N :Diagram MMlab

33. Carriers Sense Multiple Access with Collision Detection IEEE 802.3 Random Access Stations access medium randomly Contention Stations contend for time on medium If medium idle, transmit, otherwise, step 2 If busy, listen for idle, then transmit If collision detected, jam then cease transmission After jam, wait random time then start from step 1 Ethernet : CSMA/CD MMlab

34. Hubs • Physical Layer devices: essentially repeaters operating at bit levels: repeat received bits on one interface to all other interfaces • Hubs can be arranged in a hierarchy (or multi-tier design), with backbone hub at its top MMlab

35. IEEE 802.11 Wireless LAN • IEEE 802.11 standard: • MAC protocol • unlicensed frequency spectrum: 900Mhz, 2.4Ghz • Basic Service Set (BSS) • wireless hosts • access point (AP) MMlab