Final Review v v Final Exam Venue this

Final Review v v Final Exam: Venue: this classroom May 10 (Thursday) 1: 30 pm-3: 30 pm (upto 4 pm) five big problems, 2 hours to 2 1/2 hours (not more than 3 hours!), similar to Quizzes I/II, similar to sample final exam v v “comprehensive”, emphasis on material covered later in the semester v v Everything in lecture notes (except “optional” material, e. g. , mobility) Open-book, open-notes; can bring laptop for classweb v v v short questions, “case study”, problem solving, etc. concepts, issues, mechanisms/algorithms, problem solving NO COMMUNICIATION w/ your classmates or others during the exam! Final conflict: please email us, and let us your availability – we’ll arrange a make-up exam for you! CSci 4211: Final Review 1

(Reference) Final Letter Grade Criteria • • • [93 --100] A [90 -- 93) A[85 -- 90) B+ [81 -- 85) B [78 -- 81) B[73 -- 78) C+ [68 -- 73) C [63 -- 68) C[58 -- 63) D+ [50 -- 58) D [00 -- 50) F Grades are to help you check how much you have learned, where your weaknesses lie. No Thecompetition ranges foramong lettermembers grades of the class! only revise down, not up! Everybody have a chance to get A if you work for it Depends on the situations/progress, extra credit would be available

Questions? CSci 4211: Final Review 3

Putting Everything Together Did you get the whole picture? CSci 4211: Final Review 4

Internet: A Huge Success Story • From the original four-node ARPNET research experiment to today’s global information infrastructure

Internet: a huge transformative & disruptive force! What has become of the Internet: • Information Service and E-Commerce Platform – deliver all kinds of information, news, music, video, shopping – web, spotify, i. Tune, youtube, Netflix, Hulu, … • Global Information Repository – store and search for all kinds of information – google, flickr, dropbox, icloud, … • Cyberspace and Virtual Communities – keep in touch with friends and strangers – email, facebook, twitter, snapchat, … • Enormous Super-Computer – mobile, cloud computing and services We’re increasingly depending on it!

Success of Today’s Internet can be primarily characterized by its success as a (human-centric, content-oriented) information delivery platform ØWeb access, search engine, e-commerce, social networking, multimedia (music/video) streaming, cloud storage, … – users search for and interact with websites (or “content”), or interact with other users; – users consume or generate information – static vs. dynamic content ØRise of web (and HTTP) – coupled with emergence of mobile technologies – led to cloud computing and CDNs – Huge data centers with massive compute and storage capacities to store information, process user requests and generate content they desire – CDNs with geographically distributed edge servers to “scale out” and facilitate “speedier” information delivery

More gadgets are plugged in … • servers, desktops, laptops, … • smart mobile phones, i. Pads, e-readers, … • now TVs, thermostats, smart meters, etc. , soon toasters, fridges, … Wireless technologies revolutionizing Internet! § Wi. Fi, bluetooth, 3/4 G cellular networks, NFC, RFID, … Low-tier High-tier mobile computing location services Local Area Wide Area High Mobility Internet of Things (Io. T) Low Mobility

Within the Internet Core • Large ISPs with large geographical span and • Large content providers with huge data centers • High capacity, dense and rich topology • Cloud Computing/Services and Mobile Computing

Content Distribution Ecosystem § Multiple major entities involved! – content providers (CPs), content distribution networks (CDNs), ISPs and of course, end systems & users – some entities may assume multiple roles • Complex business relationships: sometimes cooperative, but often competitive CP 2 data centers CDN 2 & its servers CDN 1 & its servers CP 1 ISP data centers media players ISP users

Static Content Distribution: You. Tube as a Case Study: world’s largest video sharing site • User interaction with content (e. g. , search for a video) is separated from video delivery • Employs a combination of various “tricks” and mechanisms to scale with You. Tube size & handle video delivery dynamics 11

Static Content Distribution: Netflix as a Case Study: “first” large-scale cloudsuccess § sourcing Has its own “data center” for certain crucial operations (e. g. , user registration, …) § § Most web-based user-video interaction, computation/storage operations are cloud-sourced to Amazon AWS Users need to use MS Silverlight or other players for video streaming Video delivery was/is partly out/cloud-sourced to 3 CDNs; but now most utilizes its “own” Open. Connect boxes placed at participating ISPs, forming its own CDN Open. Connect CDN 12

Dynamic Content Distribution § Web search as (dynamic) content delivery – e-commerce, social networking services have similar architectures – response contains both static content (e. g. , banner, css files) and dynamically generated search response (dynamic content) § User Qo. E metric: end-to-end search response time (SRT) § Generic Web Search System Architecture • backend data centers processing search queries & generating responses • front-end edge servers (CDN) Ø Google: deploy its own CDN handling search query delivery Ø Bing: utilized Akamai CDN (it now also builds its own CDN) Ø Amazon and Facebook have also built its own CDNs Front-End (FE) Servers (Edge Cloud/CDN) Back-end (BE) Data Centers

Data Center Networks • 10’s to 100’s of thousands of hosts, often closely coupled, in close proximity: – e-business (e. g. Amazon) – content-servers (e. g. , You. Tube, Akamai, Apple, Microsoft) – search engines, data mining (e. g. , Google) § challenges: § multiple applications, each serving massive numbers of clients § managing/balancing load, avoiding processing, networking, data bottlenecks Inside a 40 -ft Microsoft container, Chicago data center 14

Data center networks load balancer: application-layer routing § receives external client requests § directs workload within data center § returns results to external client (hiding data center internals from client) Internet Border router Load balancer Access router Tier-1 switches B A Load balancer C Tier-2 switches TOR switches Server racks 1 2 3 4 5 6 7 8 15

Data center networks § rich interconnection among switches, racks: • increased throughput between racks (multiple routing paths possible) • increased reliability via redundancy Tier-1 switches Tier-2 switches TOR switches Server racks 1 2 3 4 5 6 7 8 16

Facebook Data Center Fabric https: //code. facebook. com/posts/360346274145943/introducing-data-center-fabric-the-next-generationfacebook-data-center-network/ CSci 4211: Final Review 17

Facebook Data Center Fabric https: //code. facebook. com/posts/360346274145943/introducing-data-center-fabric-the-next-generationfacebook-data-center-network/ CSci 4211: Final Review 18

Putting Everything Together Did you get the whole picture? CSci 4211: Final Review 19

A Quick Review of What We Learned Basic concepts in computer networks • packet switching & statistical multiplexing • protocols and layered architecture • fundamental issues in networking • distributed & complex system • addressing, protocols, … • many things can go wrong: error, loss, … • correct operations, efficiency of protocols • Application Layer • application requirements & transport services • client-server vs. peer to peer paradigms • domain name system and DNS (name vs. address) CSci 4211: Final Review 20

A Quick Review of What We Learned… • Transport Layer: basic functions & services • multiplexing and de-multiplexing • UDP: connectionless transport service • src/dst port no. ’s, checksum • TCP: connection-oriented, reliable service • TCP segment format, seq. /ack. no, “flags” • connection set-up and tear down • reliable data transfer protocols • stop-&-wait, Go-back-N, selective repeat • Network Layer: basic functions & services end-to-end data delivery: addressing, routing & forwarding • network data plane vs. control plane • data plane: layer 3 routers (and also layer 2 switches) • IP addresses: network part (net prefix) vs. host part CSci 4211: Final Review 21

A Quick Review of What We Learned … § How to obtain an IP address: how does DHCP work? § Network service models: datagram vs. virtual circuit § IP Forwarding: datagram model • forwarding within vs. outside an IP subnet: How does a host know whether a destination is within or outside its subnet? n • within same IP network: • direct forwarding using data link layer • need to know MAC address of destination: ARP! • Outside its own IP network: • forward to its (default) router: • need to know router’s MAC address • router looks up its routing table (using longest prefix matching), and forwards to other routers if necessary; a packet finally reaches its destination host Understanding interaction with data link layer important! CSci 4211: Final Review 22

A Quick Review of What We Learned … § IP datagram format • source and destination IP addresses • IP datagram id, offset, length, “fragment flags” • why IP fragmentation may be necessary • link and path MTUs • how fragmentation and reassembly done • how these fields are used • TTL, header checksum, IP options, … • ICMP protocol: • When are ICMP messages generated • What ICMP messages are used for • error/info reporting to source, ICMP redirect, … § Virtual Circuit: how to set up a VC? • incoming and outgoing VCI numbers, input/output ports • MPLS (multi-protocol label switching) CSci 4211: Final Review 23

A Quick Review of What We Learned … v Network Control Plane: centralized vs. distributed § (Distributed) Network Routing: basic issues • two distributed routing algorithms link state vs. distance vector • routing information exchanged • how shortest paths computed • how routing tables constructed • count-to-infinity problem in DV § SDN and Centralized Control Plane: Openflow switches and SDN controllers v Routing in Internet • scaling issues and hierarchical routing • inter-domain vs. intra-domain routing • Intra-domain routing protocols: RIP, OSPF • Inter-domain: BGP and policy routing • customer-provider vs. peering relationships CSci 4211: Final Review 24

Routing & Forwarding: Logical View of a Router 5 A 2 1 B 2 D 3 3 1 C 5 1 E F 2 CSci 4211: Final Review 25

A Quick Review of What We Learned … • Data Link Layer : basic services and functions data delivery over a link: framing, access control, error checking, … • MAC addresses (typically 48 bits) • flat addressing: hexadecimal notation, 45: AF: 00: FF: 12: 01 • unicast vs. broadcast: how adapter deals with MAC addr. ? • Address resolution and ARP • why do we need ARP? (see previous slide) • how does ARP work? • how are ARP messages delivered? Interaction between IP layer and data link layer! • Broadcast local area network & media access control • Why do we need media access control (MAC? ) • shared media: issues and difficulties • addressing (MAC addresses) • Taxonomy of MAC mechanisms CSci 4211: Final Review 26

A Quick Review of What We Learned … • Data Link Layer …: • Random access control: • ALOHA vs. slotted ALOHA • CSMA vs. CSMA/CD (carrier sensing, collision detection) • Adaptive (on-demand) controlled access: • token passing vs. polling Efficiency of MAC protocols: light vs. heavy load • Ethernet • CSMA/CD, exponential random back-off • how does it work? basic algorithm • Some important concepts: • collision domain & network diameter • bit time, slot time (512 bit time) Why does Ethernet have a min. frame size constraint? • Ethernet frame format • 10 Base. T, 100 Base. T (Fast Ethernet), Gigabit Ethernet CSci 4211: Final Review 27

A Quick Review of What We Learned … • Data Link Layer …: • 802. 11 b and Wireless LAN: • key issues & difficulties: • hidden terminal problem, power saving requirement • receiver acknowledgement needed! • how does it work? SIFS < DIFS • CSMA/CA: • how does it work? RTS, CTS, NAV • PPP: point-to-point link layer protocol, byte stuffing • Bridging: connecting multiple LAN segments • basic functions: forwarding/filtering frames • bridge forwarding table & self-learning • looping issue: bride spanning tree • Special Networking Devices we have encountered: • repeaters (hubs), bridges/(layer 2) switches, routers What are their functions, and how do they work? CSci 4211: Final Review 28

Putting Everything Together Did you get the whole picture? CSci 4211: Final Review 29

Putting Everything Together… Walk through the whole picture, and do the following “gedanken” experiments, thinking about • operations performed at hosts/servers • source host, destination host (web, mail servers, …) • Internet infrastructure servers (DNS, DHCP, …) • addressing information at each layer • interaction between the layers (e. g. , various protocols used) • operations performed by hubs, bridges/switches, routers • what information maintained by each device, how do they get the information? what actions do they perform? • how host A downloads a web page from web server www. cs. umn. edu? • how host A telnets to host B? • how host C accesses the mail server mail. cs. umn. edu? • how host A downloads a web page from web server www. yahoo. com? • how host A accesses his/her email at his/her yahoo mail account? • how host C sends, say, an instant message, to a user logged on at host X? Fall 2003 CSci 4211: Final Review 30

Questions? CSci 4211: Final Review 31