Presentation is loading. Please wait.

Presentation is loading. Please wait.

Computer Networks and the Internet. Describe what comprises the network edge Learning Outcomes Explain what the Internet is all about Explain what is.

Similar presentations


Presentation on theme: "Computer Networks and the Internet. Describe what comprises the network edge Learning Outcomes Explain what the Internet is all about Explain what is."— Presentation transcript:

1 Computer Networks and the Internet

2 Describe what comprises the network edge Learning Outcomes Explain what the Internet is all about Explain what is a protocol Describe what comprises the network core Explain connection-oriented service Explain connectionless service At the end of this session, the students should be able to: Compare circuit-switched network against packet-switched network Answer the short exercises given in the session

3 Introduction What’s the Internet? server Web-page server PDAs with wireless Internet connections toaster WebTV Automobile Digital cameras UNIX-based workstations laptop Household appliances HOSTSEND SYSTEMS HOSTS or END SYSTEMS

4 What’s the Internet? Nuts and bolts of the Internet Networking Infrastructure Hardware components Software provides services to distributed applications infrastructure where new applications are being constantly invented and deployed

5  Interconnects hundreds of millions of computing devices  provides: Global communication Storage Computation infrastructure global network of networks  global network of networks End-to-End System: What’s the Internet? End System Core “edge” “Nuts and Bolts” View

6 SETI DISTRIBUTED COMPUTING FOR SETI What is is a scientific experiment that uses Internet-connected computers in the Search for Extraterrestrial Intelligence (SETI). You can participate by running a free program that downloads and analyzes radio telescope data.

7 network edge: applications and hosts network core: –routers –network of networks access networks, physical media: communication links The Network Structure

8 End-to-End System End System=HOST End System Core Where much internet architecture complexity is placed Communication links Switches Transport data Connect end systems to the network core Communication links Made up of different types of physical media: Coaxial cable Copper wire Fiber optics Radio Spectrum Characterized in terms of bandwidth Link transmission rate Measured in bits/second What’s the Internet? “Nuts and Bolts” View Access networks Physical media

9 Where is the Network Core? ?

10 What’s in the Links? Router End System X Takes a chunk of information arriving on one of its incoming communication links and forwards that chunk of information on one of its outgoing communication links packet Router End System Sender Receiver path or route Internet uses packet switching to allow for multiple communicating end systems to share a path, or parts of a path, at the same time NETWORK CORE

11 Now let’s see how are links formed in terms of clusters i

12 a human protocol and a computer network protocol: Hi 2:00 time What’s a protocol? Got the time? TCP connection request TCP connection reply Get

13 What’s a protocol? Human Protocols: Something we execute all the time Offer a greeting Wait for a response Analyze the response Act accordingly Network Protocols: Similar to human protocol, except that entities are machines rather than humans all communication activities in the Internet are governed by protocols In order for protocols to work, both entities must observe the same protocol. There is a set of conventional actions taken when messages are sent and received. Networking – understanding the what, why and how of networking protocols

14 What’s a protocol? A protocol defines: format and order of messages sent and received among network entities and actions taken on the transmission and/or receipt of a message, or other event Communicating Entities: Hardware, Software components Different protocols are used to accomplish different communication tasks: * All activities in the Internet that involves 2 or more communicating entities are governed by a protocol. There are protocols in: Routers Protocols determine a packet’s path from source to destination NIC hardware-implemented protocols control the flow of the bits on the “wire” End Systems congestion-control protocols control the rate at which packets are transmitted between sender and receiver

15 TCP IP Two of the most important protocols in the Internet (principal protocols) What’s the Internet? “nuts & bolts” view Protocols - control the sending and receiving of information within the Internet - run by End Systems, routers, etc.; INTERNET STANDARDS Made possible through standards developed by (IETF) Internet Engineering Task Force RFCs (Request for Comments) IP IP – Internet Protocol – specifies the format of the packets that are sent and received among routers and end systems define protocols such as TCP, IP, HTTP, SMTP TCP TCP – Transmission Control Protocol

16 What’s the Internet? A Service View Provides a communication infrastructure that allows distributed applications running on its end systems to exchange data with each other. Remote login Web surfing Instant messaging Internet telephony “the Web” – distributed application that use the communication services provided by the Internet Connection-Oriented Reliable Service Connectionless Unreliable Service Guarantees that data is delivered orderly and completely (sender to receiver) Delivery is not guaranteed Communication services provided to distributed applications:

17 Question ? Why would we opt for a connectionless unreliable service when there is a connection-oriented reliable service that is available? Hold on to that thought for a while…

18 Network Edge A closer look at the Network Edge What happens in the network edge? The sending End System doesn’t know how messages are actually sent. It only needs to know what services are provided, and so the “nuts and bolts” of the Internet serves as a “black box” that transfers messages between distributed communicating components. There is some level of abstraction that hides the nitty- gritty part of the communication process between two end systems Client/Server Model - Most prevalent structure for Internet applications; although not all applications are purely client, or purely of server type (e.g. P2P file sharing)

19  Client/Server Model client host requests, receives service from server e.g. WWW client (browser)/server; client/server Network Edge A closer look at the Network Edge What happens in the network edge?  End Systems (Hosts): run application program e.g., WWW, at “edge of network” Client/Server Model - Most prevalent structure for Internet applications; although not all applications are purely client, or purely of server type (e.g. P2P file sharing)

20 “Connection” between two End Systems: (e.g. Web application or Internet phone application) –Nothing more than allocated buffers and state variables in the End-Systems The Network Edge “Connection” Internet provides two type of services to End-System Applications: 1. Connection-oriented service – (TCP) App’s using UDP: streaming media, teleconferencing, Internet telephony 2. Connectionless service – (UDP) App’s using TCP: HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP ( )

21 Goal: data transfer between end system. handshaking: setup (prepare for) data transfer ahead of time –Hello, hello back human protocol –set up “state” in two communicating hosts TCP service [RFC 793] Provides: Reliable data transfer:Reliable data transfer: –loss: handled using acknowledgements and retransmissions Flow Control:Flow Control: –Ensures that the sender won’t overwhelm receiver Congestion Control:Congestion Control: –Instructs senders to “slow down sending rate” when network is congested –Prevents gridlock connection-oriented Network edge: connection-oriented service performs handshaking Q*Q* Transmission Control Protocol (TCP) Internet’s connection-oriented service

22 3-way Handshake Network Edge: TCP Service Control packet CLIENT SERVER acknowledgement CONNECTION ESTABLISHED DATA Reliable data transfer is achieved through acknowledgements and retransmissions * Data is delivered without error and in proper order request

23 Handshaking Procedure: Network Edge: TCP Service Control packet CLIENT SERVER acknowledgement Client is waiting for Acknowledgement DATA Reliable data transfer is achieved through acknowledgements and retransmissions * Data is delivered without error and in proper order Client assumes packet was lost, decides to retransmit Case: Retransmission of Request

24 Flow control Network Edge: TCP Service Control packet CLIENT SERVER Problem occurs when one communicating End-System transmits faster than the other End-System forces the sending End System not to send too many packets too fast for the receiver TCP/IP provides the Flow control service This End-System does not receive an acknowledgement yet, and so it issues another packet CLIENT

25 Congestion control Network Edge: TCP Service CLIENT SERVER Problem: Gridlock sets-in when there is packet loss due to router congestion decrease the rate at which packets are sent forces the End Systems to decrease the rate at which packets are sent during periods of congestion The sending system’s message is lost due to congestion, and is alerted when it stops receiving acknowledgements of packets sent

26 Goal: data transfer between end systems –same as before! UDP - User Datagram Protocol –[RFC 768]: Internet’s connectionless service –unreliable data transfer –no flow control –no congestion control Network edge: connectionless service No handshaking procedure; End-Systems just simply send the packet

27 Something to ponder on ? bandwidthlatency quality of service digitized voice traffic Besides bandwidth and latency, what other parameter is needed to give a good characterization of the quality of service offered by a network used for digitized voice traffic? Transmission rate of the link (Bandwidth) Transmission rate of the link (Bandwidth) – how many bits per second a network can transport Propagation delay (Latency) Propagation delay (Latency) – how many seconds it takes for the first bit to get from the client to the server

28 Answer uniform delivery time A uniform delivery time is needed for voice, so the amount of jitter in the network is important. This could be expressed as the standard deviation of the delivery time. Having short delay but large variability is actually worse than a somewhat longer delay and low variability.

29 The Network Core mesh of interconnected routers

30 the fundamental question: how is data transferred through net? –circuit switching: dedicated circuit per call: telephone net –packet-switching: data sent through net in discrete “chunks” The Network Core Approaches to building a Network Core:

31 Circuit Switching vs. Packet Switching The Network CORE A Restaurant Analogy Circuit-switched Networks Packet-switched Networks Restaurant which requires reservation Restaurant which does not require any reservation With a reservation, you can order right away when you get there guaranteed seats you may have to wait on a queue to be served no sure seats Resources are reserved for the duration of the communication session Messages use the resources on demand; thus, may have to wait (queue) for access to a communication link What resources must be reserved?

32 End-end resources reserved for “call” –Reserved link bandwidth, switch capacity –Switches on the path between sender and receiver maintain connection state for the duration of the session no sharing –Resources are dedicated; thus, no sharing –Advantage: circuit-like (guaranteed) performance –call set-up required (unless infinite resources are available) Circuit Switching Network Core: Circuit Switching “Circuit”

33 How is it implemented? By dividing the link bandwidth into “pieces”  frequency division  time division Circuit Switching Network Core: Circuit Switching Inefficiency:idle Inefficiency: Resource piece is idle if not used by owning call (no sharing)

34 FDM frequency time TDM frequency time 4 users (or 4 circuits) Example: FDM and TDM Circuit Switching: FDM and TDM Slot Frame Used solely by one End System 4KHz Network dedicates one time slot in every frame of the connection Network dedicates a frequency band to each connection for the session

35 Question ? How long does it take to send a file of 640,000 bits from Host A to Host B over a circuit-switched network? Assume that all links in the network use TDM with 24 slots and have a bit rate of Mbps. Also suppose that it takes 500 msec. to establish an end-to-end circuit before Host A can begin to transmit the file. Further assume that propagation delay is negligible.

36 Question GIVEN: Size of file to send: 640,000 bits SOLUTION: 64kbps Each circuit has a transmission rate of (1.536 Mbps)/24 slots= 64kbps (or 64,000 bps). 10 sec So, it takes (640,000 bits)/(64,000 bps)= 10 sec. to transmit the file. 0.5 Considering the circuit establishment time, we add 0.5 sec; therefore, 10.5 sec It takes 10.5 sec. to transmit the file. 10 sec 1100 The transmission time would be 10 sec. if the end-to-end circuit passed through 1 link or 100 links. (but the actual end-to-end delay also includes a propagation delay) Answer How long does it take to send a file of 640,000 bits from Host A to Host B over a circuit-switched network? Assume that all links in the network use TDM with 24 slots and have a bit rate of Mbps. Also suppose that it takes 500 msec. to establish an end-to-end circuit before Host A can begin to transmit the file. Establishment time + transmission time

37 each end-end data stream divided into packets user A, B packets share network resources each packet uses full link bandwidth resources used as needed Resource Contention: can exceed  aggregate resource demand can exceed amount available  congestion:  congestion: packets queue, wait for link use  store and forward:  store and forward: packets move one hop at a time  transmit over link  wait turn at next link Bandwidth division into “pieces” Dedicated allocation Resource reservation Packet Switching Network Core: Packet Switching Q*Q*

38 We stopped here last time

39 A B C 10 Mbs Ethernet 1.5 Mbs 45 Mbs D E statistical multiplexing queue of packets waiting for transmission at the output link Network Core: Packet Switching Q*Q* E Receiver: Node E Sender: AB Nodes A and B Statistical multiplexing Statistical multiplexing - on-demand sharing of resources  sequence of A & B packets has no fixed timing pattern  bandwidth shared on demand: statistical multiplexing.  Compare this to TDM: each host gets same slot in revolving TDM frame.

40 7.5 x 10 6 bits Consider a message that is 7.5 x 10 6 bits long. Suppose that between 23 source and destination, there are 2 packet switches and 3 links, and that each link has a transmission rate of 1.5 Mbps. Assuming that there is no congestion in the network and negligible propagation delay, how much time is required to move the message from source to destination with packet switching? Network Core: Packet Switching 15 sec (7.5 Mbps/1.5 Mbps) * 3 = 15 sec. Transmission delay

41 store and forward behaviour:  break message into smaller chunks: “packets”  Store-and-forward: switch waits until chunk has completely arrived, then forwards/routes Store and Forward Behaviour Packet Switching: Store and Forward Behaviour Pattern that can be deduced from the packet flow depicted in the Figure: Time of arrival = packet_num + 2 Example:

42 1 Mbps 100 kbps 10% Suppose that users share a 1 Mbps link, where each user alternates between generating data at a constant rate of 100 kbps, and periods of inactivity. Also assume that each user is active only 10% of the time. Compare the performance of Circuit Switching against Packet Switching. Packet Switching vs. Circuit Switching

43 Example: 1 Mbit link shared by all users each user: –Generates 100Kbps when “active” (at constant rate) –active 10% of time circuit-switching: –10 users can only be supported –1,000,000 bits/sec divided by 100,000 bits/sec. packet switching: –with 35 users, probability > 10 are active is less than probability <= 10 users are active is Packet switching allows more users to use network! N users 1 Mbps link Packet Switching vs. Circuit Switching 10 Implies that 10 users can be using the circuit without competing, just like circuit-switching (bandwidth is equally distributed) Packet switching allows for more than 3 times the number of users as compared to circuit-switching

44 A factor in the delay of a store-and- forward packet-switching system is how long it takes to store and forward a packet through a switch. If switching time is 10 µsec, is this likely to be a major factor in the response of a client-server system where the client is in Adelaide, Australia and the server is in Auckland, New Zealand? Assume the propagation speed in copper and fiber to be 2/3 the speed of light in vacuum. ? Speed of light = 3 x 10 8 meters/sec. (Transmission delay) Question (Transmission delay)

45 200 meters/µsec % No. The speed of propagation is 200,000 km/sec or 200 meters/µsec. In 10 µsec the signal travels 2 km. Thus, each switch adds the equivalent of 2 km of extra cable. If the client and server are separated by 5000 km, traversing even 50 switches adds only 100 km to the total path, which is only 2%. Thus, switching delay is not a major factor under these circumstances. Answer 10 µsec A factor in the delay of a store-and-forward packet-switching system is how long it takes to store and forward a packet through a switch. If switching time is 10 µsec, is this likely to be a major factor in the response of a client-server system where the client is in Adelaide and the server is in Auckland? Assume the propagation speed in copper and fiber to be 2/3 the speed of light in vacuum.

46 Demo Total delay across a link = Transmission delay + Propagation delay

47 Advantages:Advantages: Great for bursty data –resource sharing –no call set-up Drawbacks:Drawbacks: Excessive congestion, packet delay and loss –protocols needed for reliable data transfer, congestion control Issue:Issue: How to provide circuit-like behaviour? –bandwidth guarantees needed for audio/video apps –this is still an unsolved problem! Network Core:Packet Switching Network Core: Packet Switching

48 Q: How to connect End- Systems to edge router? residential access nets institutional access networks (school, company) mobile access networks Keep in mind: bandwidth (bits per second) of access network? shared or dedicated? Access networks and physical media

49 telephone network Internet home dial-up modem ISP modem (e.g., AOL) home PC central office  uses existing telephony infrastructure  home directly-connected to central office  up to 56Kbps direct access to router (often less)  can’t surf, phone at same time: not “always on” Dial-up Modem Introduction 1-49

50 Central Office Example: A central office in Dakota, U.S.A.

51 telephone network DSL modem home PC home phone Internet DSLAM Existing phone line: 0-4KHz phone; 4-50KHz upstream data; 50KHz- 1MHz downstream data splitter central office Digital Subscriber Line (DSL)  uses existing telephone infrastructure  up to 1 Mbps upstream (today typically < 256 kbps)  up to 8 Mbps downstream (today typically < 1 Mbps)  dedicated physical line to telephone central office  Works only within 5 to 10 miles from the CO. Introduction 1-51 For more info:

52 Residential access: cable modems  uses cable TV infrastructure, rather than telephone infrastructure  HFC: hybrid fiber coax  asymmetric:  up to 30Mbps downstream,  2 Mbps upstream  network of cable, fiber attaches homes to ISP router  homes share access to router  unlike DSL, which has dedicated access Introduction 1-52

53 Residential access: cable internet access Diagram: Introduction 1-53 Shared broadcast medium

54 home cable headend cable distribution network (simplified) Typically 500 to 5,000 homes Introduction 1-54 Cable Network Architecture: Overview Homes can be up to 100 miles from the cable headend

55 home cable headend cable distribution network server(s) Introduction 1-55 Cable Network Architecture: Overview

56 home cable headend cable distribution network (simplified) Introduction 1-56

57 home cable headend cable distribution network Channels VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO VIDEOVIDEO DATADATA DATADATA CONTROLCONTROL FDM: Introduction 1-57 Cable Network Architecture: Overview

58 ONT OLT central office optical splitter ONT Shared optical fiber optical fibers Internet Fiber to the Home  optical links from central office to the home  two competing optical technologies:  Passive Optical network (PON)  Active Optical Network (AON) – switched ethernet  much higher Internet rates (download [10,20Mbps], upload [2,10Mbps]); fiber also carries television and phone services Introduction 1-58 Optical network terminator Optical line terminator

59 100 Mbps 1 Gbps server Ethernet switch institutional router to institution’s ISP Ethernet Internet access  typically used in companies, universities, etc –(Users:10 Mbps, 100Mbps), (Servers:1Gbps, 10Gbps Ethernet) –today, end systems typically connect into Ethernet switch Introduction 1-59

60 Wireless access networks  shared wireless access network connects end system to router  via base station aka “access point”  wireless LANs:  b/g (WiFi): 11 or 54 Mbps  Tens of meters from access point  wider-area wireless access  provided by telco operator  ~1Mbps over cellular system (3G – packet-switched wide-area wireless internet access)  Tens of kilometers from access point  next up (?): WiMAX – IEEE (10’s Mbps) over wide area base station mobile hosts router Introduction 1-60

61 Home networks Typical home network components:  DSL or cable modem  router/firewall/NAT  Ethernet  wireless access point wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet Introduction 1-61

62 Physical Media  bit: propagates between transmitter/rcvr pairs  physical link: 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 3: traditional phone wires, 10 Mbps Ethernet  Category 5: 100Mbps Ethernet Introduction 1-62

63 Physical Media: coax, fiber Coaxial cable:  two concentric copper conductors  bidirectional  baseband:  single channel on cable  legacy Ethernet  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 Gpbs)  low error rate: repeaters spaced far apart ; immune to electromagnetic noise Introduction 1-63

64 Physical media: radio  signal carried in electromagnetic spectrum  no physical “wire”  bidirectional  propagation environment effects:  reflection  obstruction by objects  interference Radio link types:  terrestrial microwave  e.g. up to 45 Mbps channels  LAN (e.g., WiFi)  11Mbps, 54 Mbps  wide-area (e.g., cellular)  3G cellular: ~ 1 Mbps  satellite  Kbps to 45Mbps channel (or multiple smaller channels)  280 msec end-end delay  geosynchronous versus low altitude (Low-Earth-Orbiting satellites) – future Internet access Introduction 1-64

65 Question ? An image of 1024x768 pixels with 3 bytes/pixel. Assume the image is uncompressed. How long does it take to transmit over a 56-kbps modem channel? Over a 1-Mbps cable modem? Over a 10-Mbps Ethernet? Over 100-Mbps Ethernet? Clue: Mega = 1 x 10 6 Kilo = 1 x 10 3

66 transmission delay Question: transmission delay SOLUTION: The image is 1024 x 768 x 3 bytes or 2,359,296 bytes. This is 18,874,368 bits. At 56,000 bits/sec., it takes about sec. At 1,000,000 bits/sec, it takes about sec. At 10,000,000 bits/sec., it takes about sec. At 100,000,000 bits/sec., it takes about sec. Answer How long does it take to transmit over a 56-kbps modem channel? Over a 1-Mbps cable modem? Over a 10-Mbps Ethernet? Over 100-Mbps Ethernet?

67 How do loss and delay occur? packets queue in router buffers  packet arrival rate to link exceeds output link capacity  packets queue, wait for turn A B packet being transmitted (delay) packets queueing (delay) free (available) buffers: arriving packets dropped (loss) if no free buffers Introduction 1-67

68 Loss in Packet-Switched Networks Queue - Retransmitted by application or transport layer protocol Lost packet Queue Incoming packet is dropped Incoming packet is dropped packet in queue is dropped packet in queue is dropped - Length of Queue is finite - Packets are lost when queue is full

69 Four sources of packet delay d proc : nodal processing  check bit errors  determine output link  typically < msec A B propagation transmission nodal processing queueing d queue : queueing delay  time waiting at output link for transmission  depends on congestion level of router Introduction 1-69 d nodal = d proc + d queue + d trans + d prop

70 Four sources of packet delay A B propagation transmission nodal processing queueing Introduction 1-70 d nodal = d proc + d queue + d trans + d prop d trans : transmission delay:  L: packet length (bits)  R: link bandwidth (bps)  d trans = L/R d prop : propagation delay:  d: length of physical link  s: propagation speed of medium (~2x10 8 m/sec)  d prop = d/s d trans and d prop very different

71 R=link bandwidth (bits/sec) L=packet length (bits) a=average packet arrival rate (packets/sec) traffic intensity = La/R  La/R ~ 0: average queueing delay small  La/R -> 1: delays become large  La/R > 1: more “work” arriving than can be serviced, average delay infinite! Queueing delay (revisited) This estimates the extent of queuing delay. Let’s look at a demo! Design your system so that traffic intensity is not greater than 1. Let’s look at a demo!

72 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 server, with file of F bits to send to client link capacity R s bits/sec link capacity R c bits/sec server sends bits (fluid) into pipe Introduction 1-72 pipe that can carry fluid at rate (R s bits/sec) pipe that can carry fluid at rate (R c bits/sec)

73 Throughput (more)  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? R s bits/sec R c bits/sec link on end-end path that constrains end-end throughput bottleneck link Introduction 1-73

74 Throughput: Internet scenario 10 connections (fairly) share backbone bottleneck link R bits/sec RsRs RsRs RsRs RcRc RcRc RcRc R  per-connection end-end throughput: min(R c,R s,R/10)  in practice: R c or R s is often bottleneck Introduction 1-74 e.g. 10 clients downloading with 10 servers R c =1 Mbps, R s =2Mbps, R=5Mbps

75 Program Delay and Routes in the Internet Program SOURCE HOST DESTINATION HOST TraceRoute(diagnostic program) RFC 1393 TraceRoute(diagnostic program) - defined in RFC 1393 If there are (N-1) routers, then SOURCE sends N special packets Each packet is addressed to the ultimate destination marked 1 to N When the ith router receives the ith packet marked i : router destroys the packet Sends a message containing name and address of router back to the source When DESTINATION host receives the Nth packet: DESTINATION destroys the packet, then returns the message back to the source SOURCE: records time elapsed (time received- time packet sent) determines the round-trip delays to all intervening routers Round-trip delays include: Router processing delay Router processing delay Queuing delay (varies with time) Queuing delay (varies with time) Transmission delay Transmission delay Propagation delay Propagation delay records name & address of router (or destination HOST) that returns the message reconstructs the route taken by the packets (source-to-destination)

76 Trace Route from MIT IMPORTANT: This tool works by sending a series of UDP packets with different port numbers and TTL (Time To Live). If you are running firewall software, your software may interpret the incoming packets as a hostile "port scan" originating from this server (jis.mit.edu). Rest assured, your system is not being attacked. 1 W92-RTR-1-W92SRV21.MIT.EDU ( ) ms ms ms 2 EXTERNAL-RTR-1-BACKBONE.MIT.EDU ( ) ms ms ms 3 leg CHE.sprinthome.com ( ) ms ms ms ( ) ms ms ms 5 sl-bb21-chi-6-2.sprintlink.net ( ) ms ms ms 6 sl-bb24-chi-9-0.sprintlink.net ( ) ms ms ms 7 sl-bb21-sj-8-0.sprintlink.net ( ) ms ms ms 8 sl-bb22-sj-15-0.sprintlink.net ( ) ms ms ms ( ) ms ms ms 10 sl-newzeal-1-0.sprintlink.net ( ) ms ms ms 11 p5-2.sjbr1.global-gateway.net.nz ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms 14 massey-uni-ak-int.tkbr4.global-gateway.net.nz ( ) ms ms ms 15 * * * 16 * * * 17 * * * 18 * * * 19 * * * 20 * * * 21 * * * 22 * * * 23 * * * 24 * * * 25 * * * 26 * * * 27 * * * 28 * * * 29 * * * 30 * * *www.TraceRoute.org 6 columns: n, name of router, address of router, trip delay1,trip delay2,trip delay3 Route trace: From MIT to Massey University Trans-oceanic link Trace:3x * - indicates packet loss Three delay measurements * means no response (probe lost, router not replying)

77 Trace Route from MIT IMPORTANT: This tool works by sending a series of UDP packets with different port numbers and TTL (Time To Live). If you are running firewall software, your software may interpret the incoming packets as a hostile "port scan" originating from this server (jis.mit.edu). Rest assured, your system is not being attacked. 1 W92-RTR-1-W92SRV21.MIT.EDU ( ) ms ms ms 2 EXTERNAL-RTR-1-BACKBONE.MIT.EDU ( ) ms ms ms 3 leg CHE.sprinthome.com ( ) ms ms ms ( ) ms ms ms 5 sl-bb21-chi-6-2.sprintlink.net ( ) ms ms ms 6 sl-bb24-chi-9-0.sprintlink.net ( ) ms ms ms 7 sl-bb21-sj-8-0.sprintlink.net ( ) ms ms ms 8 sl-bb22-sj-15-0.sprintlink.net ( ) ms ms ms ( ) ms ms ms 10 sl-newzeal-1-0.sprintlink.net ( ) ms ms ms 11 p5-2.sjbr1.global-gateway.net.nz ( ) ms ms ms ( ) ms ms ms ( ) ms ms ms 14 massey-uni-ak-int.tkbr4.global-gateway.net.nz ( ) ms ms ms 15 * * * 16 * * * 17 * * * 18 * * * 19 * * * 20 * * * 21 * * * 22 * * * 23 * * * 24 * * * 25 * * * 26 * * * 27 * * * 28 * * * 29 * * * 30 * * * 6 columns: n, name of router, address of router, trip delay1,trip delay2,trip delay3 Route trace: From MIT to Massey University The round-trip delay decreased between the two routers! * - indicates packet loss Can you explain why the delays sometimes decrease from one router to the next?www.TraceRoute.org

78 Tracert (from xtra to mit) C:\>tracert web.mit.edu Tracing route to web.mit.edu [ ] over a maximum of 30 hops: 1 1 ms 1 ms 1 ms ms 2 ms 2 ms ms 59 ms 55 ms dialup.xtra.co.nz [ ] 4 * 53 ms 54 ms * 66 ms * * * * Request timed out ms * * so labr3.global-gateway.net.nz [ ] 8 * * * Request timed out. 9 * 341 ms 290 ms g core01.lax05.atlas.cogentco.com [ ] ms 213 ms * t3-4.mpd01.lax01.atlas.cogentco.com [ ] ms 280 ms * g9-0-0.core01.lax01.atlas.cogentco.com [ ] 12 * 344 ms 325 ms p2-0.core01.dfw01.atlas.cogentco.com [ ] 13 * * 282 ms p15-0.core02.dfw01.atlas.cogentco.com [ ] ms * * p15-0.core01.mci01.atlas.cogentco.com [ ] 15 * * * Request timed out. 16 * 367 ms * p15-0.core01.ord01.atlas.cogentco.com [ ] 17 * 386 ms 434 ms p14-0.core01.alb02.atlas.cogentco.com [ ] 18 * 345 ms 448 ms p6-0.core01.bos01.atlas.cogentco.com [ ] 19 * 282 ms 285 ms g8.ba21.b bos01.atlas.cogentco.com [ ] 20 * * 408 ms MIT.demarc.cogentco.com [ ] ms * * W92-RTR-1-BACKBONE.MIT.EDU [ ] 22 * 344 ms * WEB.MIT.EDU [ ] 23 * 342 ms 380 ms WEB.MIT.EDU [ ] Trace complete. C:\> Tracert (also known as traceroute) is a Windows based tool that allows you to help test your network infrastructure.

79 Tracert (from Massey to MIT) D:\Massey Papers\159334\Codes\Game Protocol v3.6>tracert web.mit.edu Tracing route to web.mit.edu [ ] over a maximum of 30 hops: 1 <1 ms <1 ms <1 ms it vlan205.massey.ac.nz [ ] 2 <1 ms <1 ms <1 ms it vlan801.massey.ac.nz [ ] 3 1 ms <1 ms <1 ms ms <1 ms <1 ms ms 142 ms 142 ms ms 142 ms 142 ms abilene-1-lo-jmb-706.sttlwa.pacificwave.net [ ] ms 187 ms 180 ms dnvrng-sttlng.abilene.ucaid.edu [ ] ms 189 ms 202 ms kscyng-dnvrng.abilene.ucaid.edu [ ] ms 214 ms 201 ms iplsng-kscyng.abilene.ucaid.edu [ ] ms 215 ms 202 ms chinng-iplsng.abilene.ucaid.edu [ ] ms 206 ms 207 ms ge rtr.chic.net.internet2.edu [ ] ms 230 ms 220 ms so rtr.wash.net.internet2.edu [ ] ms 224 ms 224 ms ge rtr.chic.net.internet2.edu [ ] ms 229 ms 229 ms nox300gw1-Vl-110-NoX-ABILENE.nox.org [ ] ms 229 ms 229 ms nox230gw1-Vl-802-NoX.nox.org [ ] ms 230 ms 230 ms nox230gw1-PEER-NoX-MIT nox.org [ ] ms 230 ms 230 ms W92-RTR-1-BACKBONE.MIT.EDU [ ] ms 230 ms 230 ms WEB.MIT.EDU [ ] Trace complete. D:\Massey Papers\159334\Codes\Game Protocol v3.6>

80 Roadmap 1.1 What is the Internet? 1.2 Network edge end systems, access networks, links 1.3 Network core circuit switching, packet switching, network structure 1.4 Delay, loss and throughput in packet- switched networks 1.5 Protocol layers, service models Introduction 1-80

81 Protocol “Layers” Networks are complex, with many “pieces”: –hosts –routers –links of various media –applications –protocols –hardware, software Question: Is there any hope of organizing structure of network? Or at least our discussion of networks? Introduction 1-81

82 An analogy: Organization of air travel  a series of steps ticket (purchase) baggage (check) gates (load) runway takeoff airplane routing ticket (complain) baggage (claim) gates (unload) runway landing airplane routing Introduction 1-82 Ticketed passengers Baggage-checked, Ticketed passengers Baggage-checked, Ticketed, passed through the gate passengers Passenger in-flight

83 ticket (purchase) baggage (check) gates (load) runway (takeoff) airplane routing departure airport arrival airport intermediate air-traffic control centers airplane routing ticket (complain) baggage (claim gates (unload) runway (land) airplane routing ticket baggage gate takeoff/landing airplane routing Layering of airline functionality Layers: each layer implements a service –via its own internal-layer actions –relying on services provided by layer below Introduction 1-83

84 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., In the air travel analogy, a change in gate procedure doesn’t affect rest of system  layering considered harmful? Introduction 1-84

85 Segmentation and Reassembly Tasks of Layers Error Control Flow control Multiplexing Connection Set-up Duplication of services Each layer may perform one or more of the following tasks: Possible violation of layer dependency (conflicting information dependency among layers) Potential Drawbacks of Layering:

86 Communication in a Layered Architecture SOURCE DESTINATION Let’s consider 2 Network Entities Let’s consider 2 Network Entities (e.g. End Systems, Packet Switches) Comprised of 4 Layers; where each layer n is governed by a protocol. Layers communicate by exchanging layer-n messages called (n-PDUs) Protocol Data Units. Concept of Protocol Layering What happens when the SOURCE wants to send a message to the DESTINATION? Receiving side Sending side The contents, format, and procedure for exchanging PDUs are defined by Layer-n Protocol Layer 1 Layer 2 Layer 3 Layer 4 H3 M M1 M2 M1M2 H3 H2 M1 M2 H3 H2 H1 M1 H3H2 H1 M2 H3H2 H1 M1 H3H2 M2 H3H2 M1 H3 M2 H3 M

87

88 source application transport network link physical HtHt HnHn M segment HtHt datagram destination application transport network link physical HtHt HnHn HlHl M HtHt HnHn M HtHt M M network link physical link physical HtHt HnHn HlHl M HtHt HnHn M HtHt HnHn M HtHt HnHn HlHl M router switch Encapsulation message M HtHt M HnHn frame Introduction 1-88

89 Internet protocol stack  application: supporting network applications  FTP, SMTP, HTTP  transport: process-process data transfer  TCP, UDP  network: routing of datagrams from source to destination  IP, routing protocols  link: data transfer between neighboring network elements  Ethernet, (WiFi), PPP  physical: bits “on the wire” application Transport network link physical Introduction 1-89

90 application: supporting network applications –ftp, smtp, http transport: host-host data transfer –tcp, udp network: routing of datagrams from source to destination –ip, routing protocols (Hardware+Software) link: data transfer between neighbouring network elements –ppp, ethernet physical: bits “on the wire” application transport network link physical Internet protocol stack Mostly software implemented Guaranteed delivery of application layer messages Defines fields in IP datagrams (destination address), how end systems and routers act on them Moves packets from one node (host or packet switch) to the next node Move individual bits within frame from one node to the next Ethernet & ATM cards implement both link and Physical Layers

91 Introduction 1-91

92

93 Tier-1 ISP: e.g., Sprint … to/from customers peering to/from backbone ….…. … … … POP: point-of-presence Introduction 1-93

94 Internet structure: network of networks  roughly hierarchical  at center: small # of well-connected large networks  “tier-1” commercial ISPs (e.g., Verizon, Sprint, AT&T, Qwest, Level3), national & international coverage  large content distributors (Google, Akamai, Microsoft)  treat each other as equals (no charges) Tier 1 ISP Introduction 1-94 Large Content Distributor (e.g., Google ) Large Content Distributor (e.g., Akamai ) IXP Tier 1 ISP Tier-1 ISPs & Content Distributors, interconnect (peer) privately … or at Internet Exchange Points IXPs

95

96 Chapter 1 – True or False QuestionsExercises

97 1. Initially suppose there is only one link between source and destination. Also suppose that message switching is used, with the message consisting of the entire MP3 file. The transmission delay a) 3 seconds b) 3.05 seconds c) 50 milliseconds d) none of the above. We are sending a 30 Mbit MP3 file from a source host to a destination host. All links in the path between source and destination have a transmission rate of 10 Mbps. Assume that the propagation speed is 2 * 10 8 meters/sec, and the distance between source and destination is 10,000 km. Exercises

98 2. Referring to the above question, the end-to-end delay (transmission delay plus propagation delay) is a) 3.05 seconds b) 3 seconds c) 6 seconds d) none of the above We are sending a 30 Mbit MP3 file from a source host to a destination host. All links in the path between source and destination have a transmission rate of 10 Mbps. Assume that the propagation speed is 2 * 10 8 meters/sec, and the distance between source and destination is 10,000 km. Exercises

99 3. Referring to the above question, how many bits will the source have transmitted when the first bit arrives at the destination. a) 1 bit b) 30,000,000 bits c) 500,000 bits d) none of the above We are sending a 30 Mbit MP3 file from a source host to a destination host. All links in the path between source and destination have a transmission rate of 10 Mbps. Assume that the propagation speed is 2 * 10 8 meters/sec, and the distance between source and destination is 10,000 km. Exercises

100 4. Now suppose there are two links between source and destination, with one router connecting the two links. Each link is 5,000 km long. Again suppose the MP3 file is sent as one message. Suppose there is no congestion, so that the message is transmitted onto the second link as soon as the router receives the entire message. The end-to-end delay is a) 3.05 seconds b) 6.1 seconds c) 6.05 seconds d) none of the above We are sending a 30 Mbit MP3 file from a source host to a destination host. All links in the path between source and destination have a transmission rate of 10 Mbps. Assume that the propagation speed is 2 * 10 8 meters/sec, and the distance between source and destination is 10,000 km. Exercises

101 End of Session


Download ppt "Computer Networks and the Internet. Describe what comprises the network edge Learning Outcomes Explain what the Internet is all about Explain what is."

Similar presentations


Ads by Google