ISM 50 - Business Information SystemsLecture 16Instructor: Mary Doyle, Geoff RyderUC Santa CruzMay 27, 2009Class announcementsSpeaker TodayDzintars GrinfeldsFor Monday 06/01***Database Project due***Folio Article 3 DueRead: Akamai Case Speaker: Tracie Kemmerle For Wednesday 06/03***Business Paper due***Two speaker slots still open...Today’s ScheduleAnnouncementsDatabase project helpBusiness paper helpDzintars’ presentationLecture topic 1: complete Chapter 18, NetworkingLecture topic 2: Chapter 8, Economics and PolicyDatabase Project HelpTurn in on WebCTPaste in screen shots of your querieshttp://www.soe.ucsc.edu/classes/ism050/Spring09/moreDBHints.htmBusiness paper theme: “How IT gives your company a competitive advantage.” You need to interpret what that means for your company.For most companies that sell non-IT products, you’ll talk about ERP system deployments (Frito-Lay, Mary Kay, McDonald’s,...)from the Oracle team: Oracle is an IT supplier. So Oracle is competing to supply IT solutions that give their customers an edge. Discuss IT product development/marketing decisions that give Oracle a competitive edge in the markets they serveBusiness paper theme: “How IT gives your company a competitive advantage.” You need to interpret what that means for your company.Frito Lay, McDonalds Trajectory: If the company successfully used information systems in its past, has it continued to innovate and improve up until today? Is the company effectively postured for the future?Oracle Trajectory: How is Oracle's business and industry changing? What are they doing to stay ahead in the industry?Chapter 18: Collective Issues inNetworkingConcepts from our study of networking and Chapter 18Layering of Network ArchitectureStatistical multiplexingPhysical LayerLink LayerEthernetHubs and SwitchesMAC AddressesNetwork LayerRouting Table IP Addresses Encapsulation of IP packets within an Ethernet Frame Order of 5 OSI Layers Transport Protocols –TCP and UDP ISP, NSP, Local Loop, Telephone Company Local Office Web CachingBig picture analysis of the architecture of the Internet, using 1-decomposition, 2-Metcalfe’s Law, 3-hierarchy, and 4-statistical multiplexingInternet hosts: n = 10^9 (~1 billion)1. Decompose into hosts and links2. Value according to Metcalfe’s Law(text, page 232)Internet links: n^2 = 10^18)/2, or 0.5 quintillion (too many!)...try to make the number of links (k*n) where k << n!INTERNET3. Hierarchy4. Statistical multiplexingNobody knows k, but a very low estimate might be...k=6? (Zhou and Mondragon, 2004)1. Decomposition, 2. Metcalfe’s Law, 3. Hierarchy, 4. Stat. MultiplexingAutonomousSystem (AS)Backbone or NSP: (MCI, ATT)ASISP or IAP(CRUZIO, AOL)Customer ASASISP 1. Decomposition, 2. Metcalfe’s Law, 3. Hierarchy, 4. Stat. MultiplexingHost AHost B3. Hierarchy: Network Service Provider (NSP)NetworkAccessPointNetworkAccessPointAbilene, NLR & NTNC3. Hierarchy: National Research Networks (NRN)3. Hierarchy: CalREN2-California GPoP MapSharing of Limited Resources How Should A and B share a link with limited bit rate?Source ASource BDestination ADestination BC bits per second1. Decomposition, 2. Metcalfe’s Law, 3. Hierarchy, 4. Statistical Multiplexing Time Division Multiplexing gives each connection the use of the link a fixed fraction of time Fixed fraction of resources reserved for each connection Technology called circuit switching.Source ASource BDestination ADestination Btime Problem When A is silent, A’s fraction of link goes unused.1. Decomposition, 2. Metcalfe’s Law, 3. Hierarchy, 4. Statistical Multiplexing4. Statistical multiplexingLink shared in such a way that connections are not assigned a fixedfraction of the link (unlike TDM) A and B unlikely to offer peak rate at the same time. max( A+ B) < max(A) + max(B)Source BSource ADestination ADestination BABA+BBecause resources aren’t reserved. It’s possible offered load too high.Packets are put into a queue.PROBLEM: if offered load remains too high, queue will fill up and overflow.Source ADestination ADestination BSource B4. Statistical multiplexingBA Problem System designer assumes this event is statistically unlikely.What if she’s wrong? Or what if user demand increases?CarriedtrafficOfferedtrafficNetwork “capacity”Increasing portion ofnetwork traffic is resentpacketsSocialoptimumCongestion instability(text, p. 502)4. Statistical multiplexingCongestion ControlWhen networks are congested, certain sessions (Source-destination pairs) should reduce offered rates. Today all TCP sessions slow down when they detect packet losses. UDP sessions do not slow down.What are some alternative strategies? Have those whose applications aren’t as sensitive slow down more?How would we know which are less sensitiveTransmission Control Protocol (TCP) Retransmit mechanism for reliability Receiver sends acknowledgements to sender If a packet is lost, source fails to get ACK, and then retransmits. Congestion control If congestion perceived (by lost packets) Source reduces its send rateWhen loss, sender reduces send rate by halfOtherwise slowly increasesACKPacket 1?Packet 2Packet 2TCP cont’d TCP port numbers TCP Header has a “port” number field Helps host sort out how to route packets to applicationsPort 80 PacketTCP HeaderIP HeaderPayloadEmail ClientPort 80Port 143Your ComputerAudiocoderAudiodecoderStream ofpacketsUDP For some applications packet retransmissions are not worthwhile Why? For those applications, we use UDP UDP is a transport protocol that Does not do retransmissions Does not do congestion controlTelephone network(circuit switching, TDM)+ good quality of service (QoS) guaranteed-lower throughput, inefficient, inflexibleARPANET(packet switching, St.Mux.)+ high throughput, flexible,easy to grow NETWORKEFFECT, LOCK IN!- mediocre QoSInternetAsynchronousTransfer Mode (packet switching with strict resource allocation, p. 507)Contemporary QoS: reintroduce TDM-like,sophisticated resource reservation schemes into Internet packet switching (Cisco’s new routers)Big picture architecture: statistical multiplexing (Internet) vs. time domain multiplexing (old telephone network)IP Addresses vs Mac AddressesHierarchical The beginning bits tell you which network the host is on Ex: UCSC addresses