ELE 543 Computer Network

Transcription

1 Ken Q. Yang, ECE, URI Ken Q. Yang What Do You Learn? 1. Network Concepts and rchitectures 2. Communication Protocols ELE 543 Computer Network (e.g. TCP/IP, Ethernet, wireless) 3. Doing Useful Work on a Network How? Lectures, Reading and programming Presented by Project (50% of total grade), Proposal Presentation (10% grade), Demo/ presentation 20%, Report 20% 2 Exams (20% and 30%, respectively). Ken Q. Yang Dept. Of ECE URI 1: 1 Chapter 1: introduction our goal: get feel and terminology more depth, detail later in course approach: use Internet as example overview: what s the Internet? what s a protocol? edge; hosts, access net, media core: packet/circuit switching, Internet structure performance: loss, delay, throughput security protocol layers, service models history 1.2 edge end systems, access s, s 1.3 core packet switching, circuit switching, structure 1.4 delay, loss, throughput in s 1.6 s under attack: security 1-3 What s the Internet: nuts and bolts view PC billions of connected computing devices: wireless hosts = end systems laptop running apps smartphone 1-4 Fun Internet-connected devices mobile server communication s fiber, copper, radio, wireless s satellite wired transmission rate: s bandwidth router packet switches: forward packets (chunks of data) routers and switches Web-enabled toaster + weather forecaster global ISP home IP picture frame regional ISP Slingbox: watch, control cable TV remotely institutional Internet refrigerator 1-5 Tweet-a-watt: monitor energy use sensorized, bed mattress Internet phones 1-6 1

2 What s the Internet: nuts and bolts view What s the Internet: a service view Internet: of s Interconnected ISPs protocols control sending, receiving of messages e.g., TCP, IP, HTTP, Skype, Internet standards RFC: Request for comments IETF: Internet Engineering Task Force mobile home institutional global ISP regional ISP infrastructure that provides services to applications: Web, VoIP, , games, e- commerce, social nets, provides programming interface to apps hooks that allow sending and receiving app programs to connect to Internet provides service options, analogous to postal service mobile home institutional global ISP regional ISP edge end systems, access s, s 1.3 core packet switching, circuit switching, structure 1.4 delay, loss, throughput in s 1.6 s under attack: security closer look at structure: edge: hosts: clients and servers servers often in data centers access s, media: wired, wireless communication s core: interconnected routers of s mobile home institutional global ISP regional ISP Host: sends packets of data host sending function: takes application message breaks into smaller chunks, known as packets, of length L bits transmits packet into access at transmission rate R transmission rate, aka capacity, aka bandwidth host 2 1 two packets, L bits each R: transmission rate Physical media bit: propagates between transmitter/receiver pairs : what lies between transmitter & receiver guided media: signals propagate in solid media: copper, fiber, coax unguided media: signals propagate freely, e.g., radio twisted pair (TP) two insulated copper wires Category 5: 100 Mbps, 1 Gbps Ethernet Category 6: 10Gbps packet transmission delay time needed to = transmit L-bit = packet into L (bits) R (bits/sec)

3 Physical media: coax, fiber Physical media: radio coaxial cable: two concentric copper conductors bidirectional broadband: multiple channels on cable HFC fiber optic cable: glass fiber carrying light pulses, each pulse a bit high-speed operation: high-speed point-to-point transmission (e.g., 10 s-100 s Gbps transmission rate) low error rate: repeaters spaced far apart immune to electromagnetic noise signal carried in electromagnetic spectrum no wire bidirectional propagation environment effects: reflection obstruction by objects interference radio types: microwave e.g. up to 45 Mbps channels LN (e.g., WiFi) 54 Mbps wide-area (e.g., cellular) 4G cellular: ~ 10 Mbps satellite Kbps to 45Mbps channel (or multiple smaller channels) 270 msec end-end delay edge end systems, access s, s 1.3 core packet switching, circuit switching, structure 1.4 delay, loss, throughput in s 1.6 s under attack: security The core mesh of interconnected routers packet-switching: hosts break application-layer messages into packets forward packets from one router to the next, across s on path from source to destination each packet transmitted at full capacity Packet-switching: store-and-forward Packet Switching: queueing delay, loss L bits per packet source R bps takes L/R seconds to transmit (push out) L-bit packet into at R bps store and forward: entire packet must arrive at router before it can be transmitted on next end-end delay = 2L/R (assuming zero propagation delay) R bps one-hop numerical example: L = 7.5 Mbits R = 1.5 Mbps one-hop transmission delay = 5 sec more on delay shortly des+na+on 1-17 R = 100 Mb/s queue of packets waiting for output R = 1.5 Mb/s queuing and loss: if arrival rate (in bits) to exceeds transmission rate of for a period of time: packets will queue, wait to be transmitted on packets can be dropped (lost) if memory (buffer) fills up C D E

4 .. Two key -core functions routing: determines sourcedestination route taken by packets routing algorithms routing algorithm local forwarding table header value output forwarding: move packets from router s input to appropriate router output destination address in arriving packet s header 1-19 lternative core: circuit switching end-end resources allocated to, reserved for call between source & dest: in diagram, each has four circuits. call gets 2 nd circuit in top and 1 st circuit in right. dedicated resources: no sharing circuit-like (guaranteed) performance circuit segment idle if not used by call (no sharing) commonly used in traditional telephone s 1-20 Circuit switching: FDM versus TDM Example: FDM 4 users frequency time TDM frequency time Packet switching versus circuit switching packet switching allows more users to use! example: 1 Mb/s each user: 100 kb/s when active active 10% of time circuit-switching: 10 users packet switching: with 35 users, probability > 10 active at same time is less than.0004 * N users 1 Mbps Q: how did we get value ? Q: what happens if > 35 users? * Check out the online interactive exercises for more examples: Packet switching versus circuit switching is packet switching a slam dunk winner? great for bursty data resource sharing simpler, no call setup excessive congestion possible: packet delay and loss protocols needed for reliable data transfer, congestion control Q: How to provide circuit-like behavior? bandwidth guarantees needed for audio/video apps still an unsolved problem (chapter 7) Q: human analogies of reserved resources (circuit switching) versus on-demand allocation (packet-switching)? 1.2 edge end systems, access s, s 1.3 core packet switching, circuit switching, structure 1.4 delay, loss, throughput in s 1.6 s under attack: security

5 How do loss and delay occur? Four sources of packet delay packets queue in router buffers packet arrival rate to (temporarily) exceeds output capacity packets queue, wait for turn packet being transmitted (delay) transmission nodal processing propagation queueing packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers d nodal = d proc + d queue + d trans + d prop d proc : nodal processing check bit errors determine output typically < msec d queue : queueing delay time waiting at output for transmission depends on congestion level of router Four sources of packet delay transmission nodal processing d trans : transmission delay: L: packet length (bits) R: bandwidth (bps) d trans = L/R d trans and d prop very different propagation queueing d nodal = d proc + d queue + d trans + d prop d prop : propagation delay: d: length of s: propagation speed (~2x10 8 m/sec) d prop = d/s * Check out the online interactive exercises for more examples: * Check out the Java applet for an interactive animation on trans vs. prop delay 1-27 Queueing delay (revisited) R: bandwidth (bps) L: packet length (bits) a: average packet arrival rate average queueing delay traffic intensity = La/R La/R ~ 0: avg. queueing delay small La/R -> 1: avg. queueing delay large La/R > 1: more work arriving than can be serviced, average delay infinite! * Check online interactive animation on queuing and loss La/R ~ 0 La/R -> Real Internet delays and routes Real Internet delays, routes what do real Internet delay & loss look like? traceroute program: provides delay measurement from source to router along endend Internet path towards destination. For all i: sends three packets that will reach router i on path towards destination router i will return packets to sender sender times interval between transmission and reply. 3 probes 3 probes 3 probes traceroute: gaia.cs.umass.edu to 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 cs-gw ( ) 1 ms 1 ms 2 ms 2 border1-rt-fa5-1-0.gw.umass.edu ( ) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu ( ) 6 ms 5 ms 5 ms 4 jn1-at wor.vbns.net ( ) 16 ms 11 ms 13 ms 5 jn1-so wae.vbns.net ( ) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu ( ) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu ( ) 22 ms 22 ms 22 ms ( ) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net ( ) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net ( ) 113 ms 121 ms 114 ms 11 renater-gw.fr1.fr.geant.net ( ) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr ( ) 111 ms 114 ms 116 ms 13 nice.cssi.renater.fr ( ) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr ( ) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net ( ) 135 ms 128 ms 133 ms ( ) 126 ms 128 ms 126 ms 17 * * * 18 * * * 19 fantasia.eurecom.fr ( ) 132 ms 128 ms 136 ms trans-oceanic * means no response (probe lost, router not replying) * Do some traceroutes from exotic countries at

6 Packet loss queue (aka buffer) preceding in buffer has finite capacity packet arriving to full queue dropped (aka lost) lost packet may be retransmitted by previous node, by source end system, or not at all Throughput throughput: rate (bits/time unit) at which bits transferred between sender/receiver instantaneous: rate at given point in time average: rate over longer period of time buffer (waiting area) packet being transmitted packet arriving to full buffer is lost server server, sends with bits (fluid) file of into F bits pipe to send to client pipe capacity that can carry R s bits/sec fluid at rate R s bits/sec) pipe capacity that can carry R c bits/sec fluid at rate R c bits/sec) * Check out the Java applet for an interactive animation on queuing and loss Throughput (more) Throughput: Internet scenario R s < R c What is average end-end throughput? R s bits/sec R c bits/sec R s > R c What is average end-end throughput? per-connection endend throughput: min(r c,r s,r/10) in practice: R c or R s is often bottleneck R s R s R s R R c R c R s bits/sec R c bits/sec R c bottleneck on end-end path that constrains end-end throughput 10 connections (fairly) share backbone bottleneck R bits/sec * Check out the online interactive exercises for more 1-33 examples: edge end systems, access s, s 1.3 core packet switching, circuit switching, structure 1.4 delay, loss, throughput in s 1.6 s under attack: security Protocol layers Networks are complex, with many pieces : hosts routers s of various media applications protocols hardware, software Question: is there any hope of organizing structure of?. or at least our discussion of s?

7 Organization of air travel Layering of airline functionality ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing a series of steps ticket (purchase) baggage (check) gates (load) runway (takeoff) departure airport intermediate air-traffic control centers ticket (complain) baggage (claim gates (unload) runway (land) arrival airport layers: each layer implements a service via its own internal-layer actions relying on services provided by layer below ticket baggage gate takeoff/landing Why layering? dealing with complex systems: explicit structure allows identification, relationship of complex system s pieces layered reference model for discussion modularization eases maintenance, updating of system change of implementation of layer s service transparent to rest of system e.g., change in gate procedure doesn t affect rest of system Internet protocol stack application: supporting applications FTP, SMTP, HTTP transport: process-process data transfer TCP, UDP : routing of datagrams from source to destination IP, routing protocols : data transfer between neighboring elements Ethernet, (WiFi), PPP : bits on the wire application transport message M segment H t M datagram H n H t M frame H l H n H t M H t M M H n H t M H l H n H t M destination application transport source application transport H n H t M H l H n H t M Encapsulation H n H t M switch router 1.2 edge end systems, access s, s 1.3 core packet switching, circuit switching, structure 1.4 delay, loss, throughput in s 1.6 s under attack: security

8 Network security field of security: how bad guys can attack computer s how we can defend s against attacks how to design architectures that are immune to attacks Internet not originally designed with (much) security in mind original vision: a group of mutually trusting users attached to a transparent J Internet protocol designers playing catch-up security considerations in all layers! ad guys: put malware into hosts via Internet malware can get in host from: virus: self-replicating infection by receiving/executing object (e.g., attachment) worm: self-replicating infection by passively receiving object that gets itself executed spyware malware can record keystrokes, web sites visited, upload info to collection site infected host can be enrolled in botnet, used for spam. DDoS attacks ad guys: attack server, infrastructure Denial of Service (DoS): attackers make resources (server, bandwidth) unavailable to legitimate traffic by overwhelming resource with bogus traffic 1. select target 2. break into hosts around the (see botnet) 3. send packets to target from compromised hosts target ad guys can sniff packets packet sniffing : broadcast media (shared Ethernet, wireless) promiscuous interface reads/records all packets (e.g., including passwords!) passing by src: dest: C payload wireshark software used for end-of-chapter labs is a (free) packet-sniffer edge end systems, access s, s 1.3 core packet switching, circuit switching, structure 1.4 delay, loss, throughput in s 1.6 s under attack: security Internet history : Early packet-switching principles 1961: Kleinrock : queueing theory shows RPnet public demo effectiveness of packetswitching NCP (Network Control Protocol) first host-host 1964: aran - packetswitching in military nets protocol first program 1967: RPnet RPnet has 15 nodes conceived by dvanced Research Projects gency 1969: first RPnet node operational

9 Internet history : Intering, new and proprietary nets Internet history : new protocols, a proliferation of s 1970: LOHnet satellite in Hawaii 1974: Cerf and Kahn - architecture for interconnecting s 1976: Ethernet at Xerox PRC late70 s: proprietary architectures: DECnet, SN, XN late 70 s: switching fixed length packets (TM precursor) 1979: RPnet has 200 nodes Cerf and Kahn s intering principles: minimalism, autonomy - no internal changes required to interconnect s best effort service model stateless routers decentralized control define today s Internet architecture 1983: deployment of TCP/ IP 1982: smtp protocol defined 1983: DNS defined for name-to-ip-address translation 1985: ftp protocol defined 1988: TCP congestion control new national s: CSnet, ITnet, NSFnet, Minitel 100,000 hosts connected to confederation of s Internet history 1990, 2000 s: commercialization, the Web, new apps early 1990 s: RPnet decommissioned 1991: NSF lifts restrictions on commercial use of NSFnet (decommissioned, 1995) early 1990s: Web hypertext [ush 1945, Nelson 1960 s] HTML, HTTP: erners-lee 1994: Mosaic, later Netscape late 1990 s: commercialization of the Web late 1990 s 2000 s: more killer apps: instant messaging, P2P file sharing security to forefront est. 50 million host, 100 million+ users backbone s running at Gbps Internet history 2005-present ~5 devices attached to Internet (2016) smartphones and tablets aggressive deployment of broadband access increasing ubiquity of high-speed wireless access emergence of online social s: Facebook: ~ one billion users service providers (Google, Microsoft) create their own s bypass Internet, providing instantaneous access to search, video content, , etc. e-commerce, universities, enterprises running their services in cloud (e.g., mazon EC2) : summary covered a ton of material! Internet overview what s a protocol? edge, core, access packet-switching versus circuit-switching Internet structure performance: loss, delay, throughput layering, service models security history you now have: context, overview, feel of ing more depth, detail to follow!