Lecture 14 Summary - flashback

Transcription

1 Course on Computer Communication and Networks Lecture 14 Summary - flashback EDA344/DIT 420, CTH/GU Based on the book Computer Networking: A Top Down Approach, Jim Kurose, Keith Ross, Addison-Wesley. Marina Papatriantafilou Summary - flashback 1

2 Important for the exam When/where: wednesday March 18, , M You may have with you: English-X dictionary no calculators, PDAs, etc (if/where numbers matter, do rounding) Grading 30-40, 41-50, (out of 60)= 3, 4, 5 (CTH) 30-44, (out of 60) = G, VG (GU) To think during summary-study Overview; critical eye; explain, ask yourselves: why is this so? / How does it work? Marina Papatriantafilou Summary - flashback 2

3 Flashback Marina Papatriantafilou Summary - flashback Computer Communication 3

4 Principles, Organisation Network Problems (in the order faced in the 1st intro): producer-consumer problems, flow and error control, manage to shared (broadcast) transmission media, routing, congestion, connecting transparently different works, serving different types of traffic, performance, mobility security Layering : principle, why Marina Papatriantafilou Summary - flashback 4

5 Highlights work security issues Softwaredefined works TCP/IP, LAN protocol stack multiple protocols (wired, wireless) routing, also with mobility delays performance reliable data transfer datagram vs VC congestion control Marina Papatriantafilou Summary - flashback 5

6 Types of delay; performance Propagation, transmission, queueing, processing Throughput -- effective bandwidth Utilization -- efficiency Packet-switching: impact of store&forward TCP s slow start Sliding windows performance initiate TCP connection request object RTT first window = S/R second window = 2S/R third window = 4S/R fourth window = 8S/R object delivered complete transmission A transmission propagation time at client time at server B nodal processing queuing Marina Papatriantafilou Summary - flashback 6

7 Reliable data transfer Guaranteed, in-order, correct delivery: stop&wait sliding windows sequence numbers window sizes dynamic windows (TCP) performance Flow control Error detection: checksums, CRC Error control: go-back-n, selective repeat, FEC methods Marina Papatriantafilou Summary - flashback 7

8 Datagram vs VC endto-end comm. Congestion Control RT traffic/streaming Marina Papatriantafilou Summary - flashback 8

9 Datagram vs VC end-to-end communication Conceptual differences Decisions, comparison Marina Papatriantafilou Summary - flashback 9

10 Congestion control (CC) why, how congestion occurs CC in TCP and performance; implied weaknesses CC in other ways, e.g. VC-based works Real-time (RT)-traffic resource reservation: traffic shaping and policing rate-based initiate TCP connection request object RTT object delivered time at client time a serve Marina Papatriantafilou Summary - flashback 10

11 RT/streaming traffic Inter context Application-level solutions (FEC, playout delay, caching-cdn) Intserv, Diffserv Conceptual needs: packet/flow marking Admission control Traffic shaping & policing Packet scheduling Marina Papatriantafilou Summary - flashback 11

12 Highlights work security issues Softwaredefined works TCP/IP, LAN protocol stack multiple protocols (wired, wireless) routing, also with mobility delays performance reliable data transfer datagram vs VC congestion control Marina Papatriantafilou Summary - flashback 12

13 Routing, also with mobility Routing algorithms, protocols 5 Forwarding in routers Resource, policy issues Addressing mobility, tunneling A 1 2 B D C E F Complementary video links - IP addresses and subs &list=ple9f3f05c381ed8e8&feature=plcp - How does BGP choose its routes 4U&feature=plcp Mobile Switching Center Mobile Switching Center Public telephone work, and Inter Marina Papatriantafilou Summary - flashback 13

14 Medium : multiple methods Strategies: (functionality, appropriateness) Contention-based (random ), wired/wireless: Aloha, CSMA(CD/CA) Collision-free: Channel partitioning: TDMA, FDMA, CDMA Taking turns: e.g. tokens, reservation-based A B C A s signal strength C s signal strength Marina Papatriantafilou Summary - flashback space 14

15 Highlights work security issues Softwaredefined works TCP/IP, LAN protocol stack multiple protocols (wired, wireless) routing, also with mobility delays performance reliable data transfer datagram vs VC congestion control Marina Papatriantafilou Summary - flashback 15

16 LANs & related link technologies Protocol Examples: wired, wireless Ether, ( wimax), GSM: Functionality, performance under low/high load Connecting devices; functionalities and differences (Hubs, switches) Algorithms for switch- routing : learning& forwarding of packets ARP switch Marina Papatriantafilou Summary - flashback 16

17 TCP/IP protocol stack, applications, evolution Instantiation of work- solutions (Routing, Congestion Control, Flow & error control, applications, link layer technologies) Advantages, limitations, updates New types of applications and how they function given the existing state of Inter: multimedia/streaming applications, CDNs, P2P applications, overlays Marina Papatriantafilou Summary - flashback 17

18 Highlights work security issues Softwaredefined works TCP/IP, LAN protocol stack multiple protocols (wired, wireless) routing, also with mobility delays performance reliable data transfer datagram vs VC congestion control Marina Papatriantafilou Summary - flashback 18

19 Overlays, software-defined works P2P applications multimedia/streaming application-infrastructure complement the working infrastructure taking advantage of the work resources at the edge of the work Marina Papatriantafilou Summary - flashback 19

20 Security issues C, I, A and methods to achieve them Threats The language of cryptography Message integrity, signatures Instantiation in Inter: SSL, IPsec Alice channel data, control messages Bob data secure sender s secure receiver data Trudy Marina Papatriantafilou Summary - flashback 20

21 Synthesis: a day in the life of a web request putting-it-all-together: synthesis! goal: identify, review protocols (at all layers) involved in seemingly simple scenario: requesting www page scenario: student attaches laptop to campus work, requests/receives Marina Papatriantafilou Summary - flashback 5-21

22 A day in the life. : scenario browser Comcast work /13 DNS server school work /24 web page web server Google s work /19 Marina Papatriantafilou Summary - flashback 5-22

23 A day in the life connecting to the Inter UDP IP Eth Phy connecting laptop needs to get its own IP address: use UDP IP Eth Phy router (runs ) r r request encapsulated in UDP, encapsulated in IP, encapsulated in Ether Ether frame broadcast (dest: FFFFFFFFFFFF) on LAN, received at router running server r Ether demux ed to IP demux ed to UDP demux ed to Marina Papatriantafilou Summary - flashback 5-23

24 A day in the life connecting to the Inter UDP IP Eth Phy server formulates ACK containing client s IP address (and also IP address of first-hop router for client, name & IP address of DNS server) UDP IP Eth Phy router (runs ) r r frame forwarded (switch learning) through LAN, demultiplexing at client client receives ACK reply Client now has IP address, knows name & addr of DNS server, IP address of its first-hop router Marina Papatriantafilou Summary - flashback 5-24

25 A day in the life ARP (before DNS, before HTTP) DNS DNS DNS ARP query DNS UDP IP Eth Phy ARP ARP reply ARP Eth Phy before sending HTTP request, need IP address of DNS r r DNS query created, encapsulated in UDP, encapsulated in IP, encasulated in Eth. In order to send frame to router, need MAC address of router interface: ARP ARP query broadcast, received by router, which replies with ARP reply giving MAC address of router interface r client now knows MAC address of first hop router, so can now send frame containing DNS query Marina Papatriantafilou Summary - flashback 5-25

26 A day in the life using DNS DNS DNS DNS DNS DNS DNS UDP IP Eth Phy DNS DNS DNS DNS DNS UDP IP Eth Phy Comcast work /13 DNS server r IP datagram containing DNS query forwarded via LAN switch from client to 1 st hop router r r r IP datagram forwarded from campus work to destination (DNS-server) work, routed (tables created by RIP, OSPF and BGP routing protocols) to DNS server demux ed to DNS server DNS server replies to client with IP address of Marina Papatriantafilou Summary - flashback 26

27 A day in the life TCP connection carrying HTTP HTTP SYNACK SYNACK SYNACK HTTP TCP IP Eth Phy SYNACK SYNACK SYNACK TCP IP Eth Phy r to send HTTP request, client first opens TCP socket to web server r TCP SYN segment (step 1 in 3- way handshake) inter-domain routed to web server r web server responds with TCP SYNACK web server r TCP connection established! Marina Papatriantafilou Summary - flashback 5-27

28 A day in the life HTTP request/reply HTTP HTTP HTTP HTTP HTTP HTTP TCP IP Eth Phy r web page finally (!!!) displayed r HTTP request sent into TCP socket HTTP HTTP HTTP HTTP HTTP TCP IP Eth Phy r r IP datagram containing HTTP request routed to web server responds with HTTP reply (containing web page) web server r IP datgram containing HTTP reply routed back to client Marina Papatriantafilou Summary - flashback 5-28

29 Synthesis cont. Marina Papatriantafilou Summary - flashback 5-29

30 The Inter: virtualizing works 1974: multiple unconnected s ARPA data-over-cable works packet satellite work (Aloha) packet radio work differing in: m addressing conventions m packet formats m error recovery m routing ARPA satellite "A Protocol for Packet Network Intercommunication", V. Cerf, R. Kahn, IEEE Transactions on Communications, May, 1974, pp Marina Papatriantafilou Summary - flashback 5-30

31 The Inter: virtualizing works Interwork layer (IP): r addressing: interwork appears as single, uniform entity, despite underlying local work heterogeneity r work of works Gateway: embed interwork packets in local packet format route (at interwork level) to next gateway gateway ARPA satellite Marina Papatriantafilou Summary - flashback 5-31

32 Cerf & Kahn s Interwork Architecture What is virtualized? two layers of addressing: interwork and local work new layer (IP) makes everything homogeneous at interwork layer underlying local work technology Cable, satellite, 56K telephone modem Ether, other LAN ATM/ MPLS (Multiprotocol Label Switching Protocol) invisible at interwork layer. Looks like a link layer technology to IP Marina Papatriantafilou Summary - flashback 5-32

33 e.g. IP-Over-ATM Classic IP over eg Ether 3 works (e.g., LAN segments) MAC (eg802.3) and IP addresses IP over ATM r replace work (e.g., LAN segment) with ATM work r ATM addresses (as MAC addresses), IP addresses ATM work Ether LANs Ether LANs Marina Papatriantafilou Summary - flashback 5: DataLink Layer 5-33

34 Marina Papatriantafilou Summary - flashback Inter structure: work of works Question: given millions of ISPs, how to connect them together?

35 Marina Papatriantafilou Summary - flashback Inter structure: work of works Option: connect each ISP to every other ISP? connecting each ISP to each other directly doesn t scale: O(N 2 ) connections.

36 Marina Papatriantafilou Summary - flashback Inter structure: work of works Option: connect each ISP to a global transit (imaginary) ISP? Customer and provider ISPs have economic agreement. global ISP

37 Marina Papatriantafilou Summary - flashback Inter structure: work of works But if one global ISP is viable business, there will be competitors. ISP A ISP B ISP C

38 Marina Papatriantafilou Summary - flashback Inter structure: work of works But if one global ISP is viable business, there will be competitors. which must be interconnected Inter exchange point (ca 300 in the world; ISP A multiple ISPs peering/switching; 3 rd company) IXP ISP B ISP C peering link (no payment to each-other)

39 Marina Papatriantafilou Summary - flashback Inter structure: work of works and regional works may arise to connect s to ISPS ISP A IXP ISP B ISP C regional

40 Marina Papatriantafilou Summary - flashback Inter structure: work of works and content provider works (e.g., Google, Microsoft, Akamai ) may run their own work, to bring services, content close to end users ISP A ISP B Content provider work IXP regional ISP B

41 Inter structure: work of works Tier 1 ISP Tier 1 ISP Google IXP Regional ISP IXP Regional ISP IXP ISP ISP ISP ISP ISP ISP ISP ISP at center: small # of well-connected large works tier-1 commercial ISPs (e.g., Level 3, Sprint, AT&T, NTT), national & international coverage A new form of content provider work (e.g, Google): private work that connects it data centers to Inter, often bypassing tier-1, regional ISPs Marina Papatriantafilou Summary - flashback Introduction 1-41

42 End-of-recap. Marina Papatriantafilou Summary - flashback

43 Recall, important for the exam: Thank you When/where: wednesday March 18, , M You may have with you: English-X dictionary no calculators, PDAs, etc (if/where numbers matter, do rounding) To think during last, summary-study Overview; critical eye; explain, ask yourselves: why is this so? / How does it work? Good luck with all your efforts!!! If you hear a voice within you say you cannot paint, then by all means paint, and that voice will be silenced. Vincent Van Gogh Marina Papatriantafilou Summary - flashback 43