A Whirlwind Introduction to the Internet. A Whirlwind Introduction to the Internet Overview

Transcription

1 CPSC 360 Network Programming A Whirlwind Introduction to the Internet Michele Weigle Department of Computer Science Clemson University mweigle@cs.clemson.edu January 11, A Whirlwind Introduction to the Internet Overview! What s the Internet local ISP*! What s a protocol?! Network edge regional ISP! Network core! Access networks! Performance: loss and delay company network *Internet Service Provider 2

2 Just What is the Internet? The nuts and bolts view! Millions of connected computing devices: hosts, end-systems» PCs, workstations, servers» PDAs, phones, toasters running network applications! Communication links» Different media (fiber, copper wire, radio, satellite)» Different transmission rates bits per second (bps) " 10 3 (Kbps) to 10 6 (Mbps) to 10 9 (Gbps)! Routers: forward packets of data though the network local ISP company network router server regional ISP workstation mobile 3 Just What is the Internet? The nuts and bolts view! Protocols: control sending, receiving of messages» E.g., TCP, IP, HTTP, SMTP,.! Internet: network of networks» Loosely hierarchical» Public Internet versus private intranet! Internet standards» RFC: Request for comments» IETF: Internet Engineering Task Force local ISP company network router server regional ISP workstation mobile 4

3 Just What is the Internet? The services view! A communication infrastructure enabling distributed applications:» WWW, , games, e- commerce, database, voting,...! Communication services provided:» Connectionless: No guarantees» Connection-oriented: Guarantees order and completeness local ISP company network regional ISP 5 The Nuts & Bolts View What is a protocol? Main Entry: pro-to-col 1: An original draft, minute, or record of a document or transaction 2a: A preliminary memorandum often formulated and signed by diplomatic negotiators as a basis for a final convention or treaty b: The records or minutes of a diplomatic conference or congress that show officially the agreements arrived at by the negotiators 3a: A code prescribing strict adherence to correct etiquette and precedence (as in diplomatic exchange and in the military services) b: A set of conventions governing the treatment and especially the formatting of data in an electronic communications system 4: A detailed plan of a scientific or medical experiment, treatment, or procedure 6

4 The Nuts & Bolts View What is a protocol?! Human protocols:» Do you have the time?» I have a question» Introductions! Both:» Specific messages sent» Specific actions taken when messages (or other events) received! Network protocols:» Machines rather than humans» All communication activity in Internet governed by protocols Protocols define format, order of messages sent and received among network entities, and actions taken on message transmission, receipt 7 What is a protocol? A specification for a set of message exchanges! Example:» Human protocols: Get the time from a stranger» Computer protocols: Get the class time from a web server Hi Hi Do you have the time? TCP connection request TCP connection reply Get Yes! It!s 2:00 Time <web page> 8

5 A Whirlwind Introduction to the Internet Overview! What s the Internet! What s a protocol? local ISP! Network edge regional ISP! Network core! Access networks! Performance: loss and delay company network 9 The Structure of the Internet The physical makeup of the Internet! Network edge:» Applications running on hosts " host = end system local ISP! Network core:» Routers» Network of networks regional ISP! In between: Access networks» Physical media: communication links company network 10

6 Network Structure The network edge! End systems (hosts)» Live at the edge of network» Run applications! Interaction paradigms:» Client/server model " Client requests, receives service from server " WWW browser/server; client/server» Peer-to-peer model: " Host interactions symmetric " File sharing (Napster, MusicCity, Gnutella, ) 11 The Network Edge Connection-oriented service! Goal: Transfer data between end systems» handshaking: setup data transfer ahead of time " Hello, hello-back human protocol " Set up state in two communicating hosts» Transmit data! Connection-oriented service on the Internet:» TCP - Transmission Control Protocol [RFC 793]! TCP service model» reliable, in-order byte-stream " Losses handled by acknowledgements and retransmissions» flow control: " Sender won t overwhelm receiver» congestion control: " Senders slow down sending rate when network congested 12

7 The Network Edge Connectionless service! Goal: Transfer data between end systems» Same as before!! Connectionless service on the Internet:» UDP - User Datagram Protocol [RFC 768] " Unreliable data transfer " No flow control " No congestion control! Applications using TCP:» HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP ( )! Applications using UDP:» DNS (name to address mapping), streaming media, teleconferencing, Internet telephony 13 Questions! What is an example of something that runs at the network edge?! What are some differences between a connectionoriented service and connectionless service?! What s the difference between flow control and congestion control? 14

8 Network Structure The network core! A mesh of interconnected routers! The fundamental question: How is data routed through the network?» Circuit switching: dedicated circuit (path) per call used by all data (e.g., telephone)» Packet switching: data sent in discrete chunks (packets); each has a path chosen for it 15 Network Map 16

9 The Network Core Circuit Switching! Resources reserved end-to-end for the connection ( call )» Resources: Link bandwidth, switch capacity» Reservation: Dedicated fraction of available bandwidth, buffers, etc.! Circuit-like (guaranteed) performance» Call setup required» Call rejection ( busy signal ) possible 17 Circuit Switching Allocating fractions of bandwidth Multiplexing! Network bandwidth divided into transmission slots» Slots allocated to calls» Slots are unused ( idle ) if not used by owning call» No sharing of slots!! How to divide link bandwidth into slots?» Frequency division multiplexing (FDM)» Time division multiplexing (TDM) Transmission Frequency FDM Time TDM 4 KHz Call 1 Call 2 Call 3 Call 4 Link capacity Slot Call data Frame frames/sec X bits/slot = TDM per-call transmission rate 18

10 The Network Core Packet Switching! Each sender divides its messages into packets (sequence of bits)» Senders packets share (compete for) network resources» Each packet uses full link capacity until transmission completed» Resources allocated & used as needed! Bandwidth division into slots! Dedicated allocation! Resource reservation! But now we have resource contention!» Aggregate resource demand can exceed amount available» Congestion: packets queue, wait for link availability» Store and forward: packets move one hop at a time " Transmit over link " Wait turn at next link 19 Packet Switching Statistical multiplexing A 10 Mbps Ethernet statistical multiplexing C B queue of packets waiting for output link 1.5 Mbps 45 Mbps D E! Packet-switching versus circuit switching:» Restaurant seating analogy 20

11 Packet Switching v. Circuit Switching Is packet switching a no brainer?! Great for bursty data» Resource sharing» No call setup! Excessive congestion: packet delay and loss» Protocols needed for reliable data transfer, congestion control! How to provide circuit-like behavior?» Bandwidth guarantees needed for audio/video applications?» Still an unsolved problem (that s why we do research!) 21 Packet Switching Why switch packets instead of entire messages? 1.5 Mbps 5 seconds 5 seconds 5 seconds 7.5 Mb Message! Message switching example» Transmit a 7.5 Mb message over a network with 1.5 Mbps links» What is the total elapsed time? 22

12 Packet Switching Why switch packets instead of entire messages? 1.5 Mbps Time 7.5 Mb Message 5,000 Packets ! Packet-switching: store and forward behavior» 1,500 bit packets, 1 packet forwarded every 1 ms 23 Discussion Question! What are two ways of multiplexing in a circuitswitched network?! What are some differences between packetswitching and circuit-switching?! What is the advantage of packet-switching over message-switching? 24

13 Network Taxonomy How this fits together Telecommunication networks FDM Circuit-switched networks TDM X.25, ATM Networks with VCs Packet-switched networks IP Datagram Networks Datagram network is not either connection-oriented or connectionless. Internet (IP) provides both connection-oriented (TCP) and connectionless services (UDP) to apps. 25 Packet Switching Routing! The process of moving packets among routers from source to destination» Lots of path selection algorithms! Datagram network:» Each packet carries a destination address» Destination address used to look up next hop» Route (next hop) may change at any time! Virtual circuit (path) network: local ISP company network regional ISP» Packets carry a tag (virtual circuit ID) that determines the next hop» Path determined at call setup time & remains fixed throughout call» Routers maintain per-call path state 26

14 Routing in Packet Switched Networks Datagram routing Network ID xxx.yyy. uuu.vvv. sss.ttt.... Next Hop b b c... a c b! Packets contain a destination address» Address specifies both a network and a host! Each router examines the destination address and forwards packet towards the next router closest to the destination network» Routers maintain a table of next hops to all networks! Routers maintain no per-connection state 27 The Structure of the Internet The physical makeup of the Internet! Network edge:» Applications and hosts local ISP! Network core:» Routers» Network of networks regional ISP! In between: Access networks» Physical media: communication links company network 28

15 Network Structure Access networks and physical media! How to connect end-systems to edge router?» Residential access nets» Institutional/enterprise access networks» Mobile access networks! Issues:» Transmission speed (bits per second) of access network» Shared or dedicated? 29 Access Networks and Physical Media Physical Media! Transmission is the propagation of an electromagnetic wave (or optical pulse) through a physical medium! Media types» Guided media signals propagate in solid media (copper, fiber)» Unguided media signals propagate freely (radio, infrared)! What do you use?» Twisted Pair (UTP) Two insulated copper wires! Category 3 UTP:» Traditional phone wires, 10 Mbps Ethernet! Category 5 UTP:» 100Mbps Ethernet» Gigabit possible» Distance limited (100 m) 30

16 Physical Media Coaxial and fiber optic cable! Coaxial cable» Wire (signal carrier) within a wire (shield) " Baseband: single channel on cable " Broadband: multiple channel on cable» Bi-directional transmission» Largely used for cable TV! Fiber optic cable» Glass fiber carrying light pulses» Higher-speed operation: " 100-1,000 Mbps Ethernet " High-speed point-to-point transmission (e.g., 10 Gbps)» Low signal attenuation long distances» Low error rate 31 Physical Media Radio! Signal carried in electromagnetic spectrum» No physical wire! Bi-directional! Physical environment effects propagation» Reflection» Obstruction by objects» Interference uplink base station! Radio link types:» Microwave " Up to 45 Mbps channels» LAN (e.g., ) " 2 Mbps, 11, 56 Mbps» Wide-area (e.g., cellular) " CDPD, 10 s Kbps» Satellite " Up to 50Mbps channel (or multiple smaller channels) " 270 msec end-end delay " Geosynchronous versus LEOS 32

17 Access Networks and Physical Media Residential access: point-to-point access! Dialup via modem» Modem (modulator-demodulator) does digital!"analog signal conversions» Up to 56Kbps direct access to router! ISDN: Integrated Services Digital Network» 128Kbps all-digital connection to router! DSL: Digital Subscriber Line» Asymmetric speeds " Up to 8 Mbps to the home " Up to 1 Mbps from the home " Distance-dependent, typical is 1-2 Mbps to home» Dedicated access Access Networks and Physical Media Residential access: cable modems! HFC (Hybrid Fiber-Coax)» Asymmetric speeds» Shared access! Issues:» Congestion» Provisioning! Providers:» Time Warner» AT&T» Cox» Comcast».. 200, ,000 homes 20,000 40,000 homes 2 Mbps to home 0.5 Mbps from home 500 1,000 homes 34

18 Access Networks and Physical Media Institutional access: local area networks! Local area network (LAN) connects end system to edge router! Ethernet is the dominant technology» Shared or dedicated cable connects end system and router» 10 Mbps, 100Mbps, 1Gbps Ethernet! Deployment: institutions, home LANs Access Networks and Physical Media Wireless access networks! Shared wireless access network connects end-system to router! Wireless LANs:» Radio spectrum replaces wire. e.g., Lucent Wavelan (2-12 Mbps)! Wider-area wireless access» CDPD: wireless access to ISP router via cellular network router base station mobile hosts 36

19 A Whirlwind Introduction to the Internet Overview! What s the Internet! What s a protocol? local ISP! Network edge regional ISP! Network core! Access networks! Performance: loss, delay company network 37 Understanding the Performance of the Internet Delay in packet-switched networks A transmission propagation B nodal processing! Packets experience variable delays along the path from source to destination! Four sources of delay at each hop» Nodal processing: " Check for bit errors " Determine the output interface to forward packet on» Queuing: queuing " Time spent waiting at outbound interface for transmission " Duration depends on the level of congestion at the interface» Transmission» Propagation 38

20 Understanding the Performance of the Internet Delay in packet-switched networks A transmission propagation B nodal processing d nodal = d proc + d queue + d trans + d prop! Transmission delay = time to put bits onto the link = L/R» R = link bandwidth (bps)» L = packet length (bits) queuing Beware: s and R are very different quantities!! Propagation delay = d/s» d = length of physical link» s = signal propagation speed in medium (~2x10 8 m/sec) 39 Transmission & Propagation Example Transmission on a slow link Time = 0 Time = 10 ms Time = 30 ms Time = 5,181.4 ms 1,000,000 bytes to send 998,070 bytes to send 994,210 bytes to send 0 bytes to send 1,544,000 bps (T-1) 193 bytes/ms 30 ms propagation latency 1,930 bytes in the link 5,790 bytes in the link Bandwidth-Delay Product (BDP) 5,790 bytes in the link 994,210 bytes recv d 40

21 Transmission & Propagation Example Transmission on a fast link Time = 0 Time = 10 ms Tme = 30 ms 1,000,000 bytes to send 222,400 bytes to send 0 bytes to send 622,080,000 bps (OC-12) 77,760 bytes/ms 30 ms propagation latency 777,600 bytes in the link 1,000,000 bytes in the link Time = ms 0 bytes in the link 0 bytes to send 1,000,000 bytes recv d Understanding the Performance of the Internet Delay in packet-switched networks A transmission propagation B nodal processing queueing! Typical transmission delay: 120 µs» 1,500 byte packet on a 100 Mbps Ethernet! Typical propagation delay:»! 1 µs on a small campus» " 25 ms to the West coast! Typical processing delay:»??! Typical queuing delay:»?? 42

22 Transmission Delay Telecommunications transmission speed alphabet soup! DS-1/T-1 = Mbps! DS-3/T-3 = Mbps! OC-1 = Mbps! OC-n = n! OC-1» OC-3 = 3! OC-1 ( Mbps)» OC-12 = 12! OC-1 ( Mbps)» OC-48 = 48! OC-1 (2, Mbps/2.5 Gbps)» OC-192 = 192! OC-1 (9, Mbps/10 Gbps) 43 Understanding the Performance of the Internet Delay in packet-switched networks A B transmission nodal processing propagation queuing Transmission delay = 120 µs Propagation delay = 10 µs Queuing delay = k x 120 µs Processing delay = 100 µs What is k?! What dominates end-to-end delay?! Note that processing, transmission, and queuing delays are encountered at each hop» End-to-end delay is largely a function of the number of routers encountered along the path from source to destination 44

23 Questions! What is the transmission delay for a 2000-byte packet over a 1 Mbps link?! Where is the last bit of the packet after the transmission delay has passed?! What is the transmission delay for a 250,000-bit packet over a 1 Mbps link? 45 Understanding the Performance of the Internet Example: What was the delay from my house? % ping access.cs.clemson.edu PING yoda.cs.clemson.edu ( ): 56 data bytes 64 bytes from : icmp_seq=0 ttl=240 time= ms 64 bytes from : icmp_seq=1 ttl=240 time= ms 64 bytes from : icmp_seq=2 ttl=240 time=57.3 ms 64 bytes from : icmp_seq=3 ttl=240 time= ms 64 bytes from : icmp_seq=4 ttl=240 time=57.5 ms 64 bytes from : icmp_seq=5 ttl=240 time= ms 64 bytes from : icmp_seq=6 ttl=240 time= ms 64 bytes from : icmp_seq=7 ttl=240 time= ms 64 bytes from : icmp_seq=8 ttl=240 time= ms 64 bytes from : icmp_seq=9 ttl=240 time= ms ^C --- yoda.cs.clemson.edu ping statistics packets transmitted, 10 packets received, 0% packet loss round-trip min/avg/max = /59.083/ ms 46

24 Understanding the Performance of the Internet Example: What was the route from my house? % traceroute access.cs.clemson.edu! A traceroute from my house Tracing route to yoda.cs.clemson.edu [ ] over a maximum of 30 hops: 1 3 ms 3 ms 3 ms ms 13 ms 13 ms ms 13 ms 25 ms ms 12 ms 13 ms ms 16 ms 17 ms axr00asm bellsouth.net [ ] 6 17 ms 47 ms 16 ms pxr00asm bellsouth.net [ ] 7 18 ms 17 ms 19 ms so gar1.atlanta1.level3.net [ ] 8 18 ms 18 ms 17 ms so gar2.atlanta1.level3.net [ ] 9 19 ms 51 ms 17 ms so bbr2.atlanta1.level3.net [ ] ms 31 ms 45 ms ae-0-0.bbr2.washington1.level3.net [ ] ms 31 ms 31 ms so edge1.washington1.level3.net [ ] ms 52 ms 30 ms qwest-level3-oc48.washington1.level3.net [ ] ms 31 ms 35 ms ms 32 ms 32 ms dca-core-02.inet.qwest.net [ ] ms 53 ms 51 ms atl-core-02.inet.qwest.net [ ] ms 33 ms 32 ms atl-edge-19.inet.qwest.net [ ] ms 57 ms 49 ms ms 49 ms 54 ms ms 50 ms 48 ms ms 46 ms 47 ms yoda.cs.clemson.edu [ ] 47 Protocol Layering in the Internet Internet protocol layers ( stack )! Application layer» Supporting network applications " ftp, SMTP, HTTP! Transport layer» Host-host data transfer " TCP, UDP! Network layer» Routing of packets from source to destination " IP, routing protocols! Link layer» Data transfer between directly connected network elements " Ethernet, , SONET,! Physical layer» The insertion of individual bits on the wire application transport network link physical Different services specified at each layer interface 48

25 Protocol Layering in the Internet Internet protocol layers ( stack )! Each layer implements a protocol with its peer layer in a distributed system application transport network link physical End system A Application protocol Transport protocol Network protocol Link protocol Physical (signaling) protocol application transport network link physical End system B 49 Whirlwind Introduction to the Internet! We ll start looking in depth at the application layer (Ch 2)» client-server architecture» writing our own network applications» HTTP» FTP and ! Transport Layer (Ch 3)! Network Layer (Ch 4) 50