Computer Networking Lecture Week 4 PDF

Computer Networking Naeem Ul Islam Contact: [email protected] Office: 70928  Internet communication Internet communication technologies uses: ✓Circuit switching ✓Packet switching Introduction: 1-2  Internet communication...

Computer Networking Naeem Ul Islam Contact: [email protected] Office: 70928  Internet communication Internet communication technologies uses: ✓Circuit switching ✓Packet switching Introduction: 1-2  Internet communication Internet communication technologies uses: Circuit switching Packet switching Introduction: 1-3  Circuit switching: FDM and TDM Frequency Division Multiplexing (FDM) 4 users ▪ optical, electromagnetic frequencies frequency divided into (narrow) frequency bands ▪ each call allocated its own band, can transmit at max rate of that narrow band time ▪ In telephone networks, this frequency band typically has a width of 4 kHz Introduction: 1-4  Circuit switching: FDM and TDM 4 users Time Division Multiplexing (TDM) frequency ▪ time is divided into frames of fixed duration ▪ each frame is divided into a fixed number of time slots time ▪ each call allocated periodic slot(s), can transmit at maximum rate of (wider) frequency band, but only during its time slot(s) Introduction: 1-5 Packet-switching: queueing delay, loss R = 100 Mb/s A C D B R = 1.5 Mb/s E queue of packets waiting for output link Packet queuing and loss: if arrival rate (in bps) to link exceeds transmission rate (bps) of link for a period of time: ▪ packets will queue, waiting to be transmitted on output link ▪ packets can be dropped (lost) if memory (buffer) in router fills up Introduction: 1-6 Packet switching versus circuit switching packet switching allows more users to use network! Example: ▪ 1 Gb/s link ▪ each user: N 100 Mb/s when “active” users 1 Gbps link active 10% of time ▪ circuit-switching: 10 users Q: how did we get value 0.0004? ▪ packet switching: with 35 users, probability > 10 active at same time is less than.0004 * * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/interactive Introduction: 1-7 How do packet loss and delay occur? packets queue in router buffers ▪ packets queue, wait for turn ▪ arrival rate to link (temporarily) exceeds output link capacity: packet loss packet being transmitted (transmission delay) A B packets in buffers (queueing delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction: 1-8 Packet delay: four sources transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dproc: nodal processing dqueue: queueing delay ▪ check bit errors ▪ time waiting at output link for transmission ▪ determine output link ▪ depends on congestion level of router ▪ typically < msec Introduction: 1-9 Packet delay: four sources transmission A propagation B nodal processing queueing dnodal = dproc + dqueue + dtrans + dprop dtrans: transmission delay: dprop: propagation delay: ▪ L: packet length (bits) ▪ d: length of physical link ▪ R: link transmission rate (bps) ▪ s: propagation speed (~2x108 m/sec) ▪ dtrans = L/R ▪ dprop = d/s dtrans and dprop * Check out the online interactive exercises: http://gaia.cs.umass.edu/kurose_ross very different Introduction: 1-10 Packet queueing delay (revisited) average queueing delay ▪ R: link bandwidth (bps) ▪ L: packet length (bits) ▪ a: average packet arrival rate traffic intensity = La/R 1 ▪ La/R ~ 0: avg. queueing delay small ▪ La/R -> 1: avg. queueing delay large La/R ~ 0 ▪ La/R > 1: more “work” arriving is more than can be serviced - average delay infinite! La/R -> 1 Introduction: 1-11 Packet queueing delay (revisited) Introduction: 1-12 “Real” Internet delays and routes ▪ what do “real” Internet delay & loss look like? ▪ traceroute program: provides delay measurement from source to router along end-end 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 measures time interval between transmission and reply 3 probes 3 probes 3 probes Introduction: 1-13 “Real” Internet delays and routes Introduction: 1-14 Real Internet delays and routes traceroute: gaia.cs.umass.edu to www.eurecom.fr 3 delay measurements from gaia.cs.umass.edu to cs-gw.cs.umass.edu 1 cs-gw (128.119.240.254) 1 ms 1 ms 2 ms 3 delay measurements 2 border1-rt-fa5-1-0.gw.umass.edu (128.119.3.145) 1 ms 1 ms 2 ms 3 cht-vbns.gw.umass.edu (128.119.3.130) 6 ms 5 ms 5 ms to border1-rt-fa5-1-0.gw.umass.edu 4 jn1-at1-0-0-19.wor.vbns.net (204.147.132.129) 16 ms 11 ms 13 ms 5 jn1-so7-0-0-0.wae.vbns.net (204.147.136.136) 21 ms 18 ms 18 ms 6 abilene-vbns.abilene.ucaid.edu (198.32.11.9) 22 ms 18 ms 22 ms 7 nycm-wash.abilene.ucaid.edu (198.32.8.46) 22 ms 22 ms 22 ms trans-oceanic link 8 62.40.103.253 (62.40.103.253) 104 ms 109 ms 106 ms 9 de2-1.de1.de.geant.net (62.40.96.129) 109 ms 102 ms 104 ms 10 de.fr1.fr.geant.net (62.40.96.50) 113 ms 121 ms 114 ms looks like delays 11 renater-gw.fr1.fr.geant.net (62.40.103.54) 112 ms 114 ms 112 ms 12 nio-n2.cssi.renater.fr (193.51.206.13) 111 ms 114 ms 116 ms decrease! Why? 13 nice.cssi.renater.fr (195.220.98.102) 123 ms 125 ms 124 ms 14 r3t2-nice.cssi.renater.fr (195.220.98.110) 126 ms 126 ms 124 ms 15 eurecom-valbonne.r3t2.ft.net (193.48.50.54) 135 ms 128 ms 133 ms 16 194.214.211.25 (194.214.211.25) 126 ms 128 ms 126 ms 17 * * * 18 * * * * means no response (probe lost, router not replying) 19 fantasia.eurecom.fr (193.55.113.142) 132 ms 128 ms 136 ms * Do some traceroutes from exotic countries at www.traceroute.org Introduction: 1-15 Packet loss ▪ queue (aka buffer) preceding link 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 buffer (waiting area) packet being transmitted A B packet arriving to full buffer is lost * Check out the Java applet for an interactive animation on queuing and loss Introduction: 1-16 Packet loss https://www2.tkn.tu-berlin.de/teaching/rn/animations/queue/ * Check out the Java applet for an interactive animation on queuing and loss Introduction: 1-17  Throughput ▪ throughput: rate (bits/time unit) at which bits are being sent from sender to receiver instantaneous: rate at given point in time average: rate over longer period of time link capacity pipe that can carry linkthat pipe capacity can carry Rsfluid bits/sec at rate Rfluid c bits/sec at rate serverserver, sends with bits (fluid) into pipe (Rs bits/sec) (Rc bits/sec) file of F bits to send to client Introduction: 1-18 Throughput Rs < Rc What is average end-end throughput? Rs bits/sec Rc bits/sec Rs > Rc What is average end-end throughput? Rs bits/sec Rc bits/sec bottleneck link link on end-end path that constrains end-end throughput Introduction: 1-19 Throughput: network scenario ▪ per-connection end- Rs end throughput: Rs Rs min(Rc,Rs,R/10) ▪ in practice: Rc or Rs is R often bottleneck Rc Rc Rc * Check out the online interactive exercises for more examples: http://gaia.cs.umass.edu/kurose_ross/ 10 connections (fairly) share backbone bottleneck link R bits/sec Introduction: 1-20 Chapter 1: roadmap ▪ What is the Internet? ▪ What is a protocol? ▪ Network edge: hosts, access network, physical media ▪ Network core: packet/circuit switching, internet structure ▪ Performance: loss, delay, throughput ▪ Security ▪ Protocol layers, service models ▪ History Introduction: 1-21 Network security ▪ field of network security: how bad guys can attack computer networks how we can defend networks 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 network” ☺ Internet protocol designers playing “catch-up” security considerations in all layers! Introduction: 1-22 Bad guys: malware ▪ malware can get in host from: virus: self-replicating infection by receiving/executing object (e.g., e-mail 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 or distributed denial of service (DDoS) attacks Introduction: 1-23 Bad guys: denial of service 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 network (see botnet) 3. send packets to target target from compromised hosts Introduction: 1-24 Bad guys: packet interception packet “sniffing”: ▪ broadcast media (shared Ethernet, wireless) ▪ promiscuous network interface reads/records all packets (e.g., including passwords!) passing by A C src:B dest:A payload B Wireshark software used for our end-of-chapter labs is a (free) packet-sniffer Introduction: 1-25 Bad guys: fake identity IP spoofing: send packet with false source address A C src:B dest:A payload B … lots more on security (throughout, Chapter 8) Introduction: 1-26 Chapter 1: roadmap ▪ What is the Internet? ▪ What is a protocol? ▪ Network edge: hosts, access network, physical media ▪ Network core: packet/circuit switching, internet structure ▪ Performance: loss, delay, throughput ▪ Security ▪ Protocol layers, service models ▪ History Introduction: 1-27 Protocol “layers” and reference models Networks are complex, with many “pieces”: Question: ▪ hosts is there any hope of ▪ routers organizing structure of ▪ links of various media network? ▪ applications ▪ protocols ▪ hardware, software …. or at least our discussion of networks? Introduction: 1-28 Example: organization of air travel ticket (purchase) ticket (complain) baggage (check) baggage (claim) gates (load) gates (unload) runway takeoff runway landing airplane routing airplane routing airplane routing airline travel: a series of steps, involving many services Introduction: 1-29 Example: organization of air travel ticket (purchase) ticketing service ticket (complain) baggage (check) baggage service baggage (claim) gates (load) gate service gates (unload) runway takeoff runway service runway landing airplane routing routing service airplane routing airplane routing layers: each layer implements a service Q: describe in words ▪ via its own internal-layer actions the service provided in each layer above ▪ relying on services provided by layer below Introduction: 1-30 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 in layer's service implementation: transparent to rest of system e.g., change in gate procedure doesn’t affect rest of system ▪ layering considered harmful? Introduction: 1-31 Internet protocol stack application application presentation transport session network transport link network link physical physical The seven layer OSI/ISO reference model Introduction: 1-32 Internet protocol stack ▪ application: supporting network applications IMAP, SMTP, HTTP application ▪ transport: process-process data transfer (recognize source and dest processes for a specific message) transport TCP, UDP ▪ network: routing of datagrams from source to network destination IP, routing protocols link ▪ link: data transfer between neighboring physical network elements Ethernet, 802.11 (WiFi), PPP ▪ physical: bits “on the wire” Introduction: 1-33  ISO/OSI reference model Two layers not found in Internet application protocol stack! presentation ▪ presentation: allow applications to interpret meaning of data, e.g., encryption, session compression, machine-specific conventions transport ▪ session: synchronization, checkpointing, network recovery of data exchange link ▪ Internet stack “missing” these layers! physical these services, if needed, must be implemented in application The seven layer OSI/ISO reference model needed? Introduction: 1-34  source message M application Encapsulation segment Ht M transport datagram Hn Ht M network frame Hl Hn Ht M link physical link physical switch destination Hn Ht M network M application Hl Hn Ht M link Hn Ht M Ht M transport physical Hn Ht M network Hl Hn Ht M link router physical Introduction: 1-35 Chapter 1: roadmap ▪ What is the Internet? ▪ What is a protocol? ▪ Network edge: hosts, access network, physical media ▪ Network core: packet/circuit switching, internet structure ▪ Performance: loss, delay, throughput ▪ Security ▪ Protocol layers, service models ▪ History Introduction: 1-36 Internet history 1961-1972: Early packet-switching principles ▪ 1961: Kleinrock - queueing ▪ 1972: theory shows effectiveness of ARPAnet public demo packet-switching NCP (Network Control Protocol) ▪ 1964: Baran - packet-switching first host-host protocol in military nets first e-mail program ▪ 1967: ARPAnet conceived by ARPAnet has 15 nodes Advanced Research Projects Agency ▪ 1969: first ARPAnet node operational Introduction: 1-37 Internet history 1972-1980: Internetworking, new and proprietary nets ▪ 1970: ALOHAnet satellite network Cerf and Kahn’s internetworking in Hawaii principles: ▪ 1974: Cerf and Kahn - architecture ▪ minimalism, autonomy - no for interconnecting networks internal changes required to ▪ 1976: Ethernet at Xerox PARC interconnect networks ▪ best-effort service model ▪ late70’s: proprietary architectures: DECnet, SNA, XNA ▪ stateless routing ▪ decentralized control ▪ late 70’s: switching fixed length packets (ATM precursor) define today’s Internet architecture ▪ 1979: ARPAnet has 200 nodes Introduction: 1-38 Internet history 1980-1990: new protocols, a proliferation of networks ▪ 1983: deployment of TCP/IP ▪ new national networks: CSnet, ▪ 1982: smtp e-mail protocol BITnet, NSFnet, Minitel defined ▪ 100,000 hosts connected to ▪ 1983: DNS defined for name- confederation of networks to-IP-address translation ▪ 1985: ftp protocol defined ▪ 1988: TCP congestion control Introduction: 1-39 Internet history 1990, 2000s: commercialization, the Web, new applications ▪ early 1990s: ARPAnet late 1990s – 2000s: decommissioned ▪ more killer apps: instant ▪ 1991: NSF lifts restrictions on messaging, P2P file sharing commercial use of NSFnet ▪ network security to forefront (decommissioned, 1995) ▪ est. 50 million host, 100 million+ ▪ early 1990s: Web users hypertext [Bush 1945, Nelson 1960’s] HTML, HTTP: Berners-Lee ▪ backbone links running at Gbps 1994: Mosaic, later Netscape late 1990s: commercialization of the Web Introduction: 1-40 Internet history 2005-present: more new applications, Internet is “everywhere” ▪ ~18B devices attached to Internet (2017) rise of smartphones (iPhone: 2007) ▪ aggressive deployment of broadband access ▪ increasing ubiquity of high-speed wireless access: 4G/5G, WiFi ▪ emergence of online social networks: Facebook: ~ 2.5 billion users ▪ service providers (Google, FB, Microsoft) create their own networks bypass commercial Internet to connect “close” to end user, providing “instantaneous” access to search, video content, … ▪ enterprises run their services in “cloud” (e.g., Amazon Web Services, Microsoft Azure) Introduction: 1-41