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  • When we think of the internet, so many things come to our mind. Nowadays, the internet connects almost anything imaginable. To take a peek of the few items connected to the internet, we have… portable device assistant, and so on and so forth. You must be wondering why a toaster appears in here.. Well, out of curiosity, I looked for that myself.. :http://news.bbc.co.uk/1/low/sci/tech/1264205.stm
  • We shall define the Internet in two ways in our discussions. First, we shall look at it based on its working parts or elements – and so we’re using the term “nuts and bolts”, then we shall also look at it in an abstract perspective, by looking at it as the underlying foundation or basic framework where new applications are constantly invented and deployed.
  • The internet is now viewed as the global network of networks. It now interconnects millions of computing devices, providing global communication, storage and computation infrastructure. Before delving into the nitty-gritty part, let’s have a look at the bigger picture first in a much simpler perspective… that is, in terms of an END-to-END SYSTEM.
  • Search For Extra-Terrestial Intelligence
  • Much of the Internet architecture can be found in the END SYSTEM and likewise, the bulk of work. According to Dr. Kurose, rapid application development has been seen on this component, triggering an expansion of Network technology because of the high demands of evolving applications. To mention a few, I think most of us are familiar with Peer 2 Peer networking, where you can get everything for free (that application however is barred from our network – because it disobeys copyright laws – it is illegal). Moreover, there is another interesting application called Skype that provides internet telephony – with that, you can call anyone in the world for free (if the other person is using Skype) in stereo quality. On the other hand, what can be found in the core are the communication links and switches that transport data, as well as Access networks and Physical media that are responsible for connecting the END SYSTEMS to the network core. The communication links are made up of different types of physical media like copper wire…. And are characterized in terms of bandwidth or link transmission rate, measured in terms of bits/second.
  • Let us just identify where in the figure is the network core…. All components colored RED in the figure corresponds to the network core. The structure that connects the end systems to the internet is the network core.
  • The most common component that can be found in the network core is the router . As you can see in the figure, the function of a router is to provide a path from a node on one network to a node on another network. The figure is a simplified illustration of how routers allow for the connection, but in real networks, the two networks may be actually separated by several intervening networks and, possibly, by many miles. The router provides the path by first determining a route and then providing the initial connection for the path.
  • Now let’s see how are links formed in terms of clusters.. Let’s see the bigger picture
  • The internet is governed by a set of predefined rules in order to allow processes to communicate and exchange data.. In internet jargon, that is referred to as protocols.
  • The term connection corresponds to nothing more but allocation of buffers and state variables. Only the communicating End-Systems are the ones who knows that they’re connected.. not even the routers of the intervening packet switches knows about any connection-state information between the communicating End-Systems.
  • Any protocol that performs handshaking is a connection-oriented service. We use the term “connection-oriented” because the end systems are connected in a loose manner, only the end systems are aware of the connection. The routers or intervening packet switches do not maintain any connection-state information about the connection. The services provided by TCP, such as reliable data transfer, flow control and congestion control are by no means requirements of a connection-oriented service. One or two of them may be missing, and yet still the network could offer connection-oriented service. Let’s just have a look at the definition here, then we shall see some animations later demonstrating them. DISCUSS THIS JUST QUICKLY – use the next animation slides to explain
  • CLICK TO ANIMATE
  • CLICK TO ANIMATE
  • CLICK TO ANIMATE
  • Due to router congestion, the packets sent by the sending End system is lost. When that happens, the sending end system is alerted of congestion if it does not receive an acknowledgement for the packets it sent. TCP provides a congestion control service that forces the End systems to decrease the rate at which packets are sent during periods of congestion. You can view the applet from Kurose’s site demonstrating network congestion.
  • There is no handshaking; therefore, data can be delivered sooner, but there is no reliable data transfer guaranteed The sending program simply sends the packets The source never knows for sure which packets have arrived at the destination Internet telephony uses the connectionless service because of the application’ demand for speed and the application doesn’t necessarily require acknowledgement of data all throughout the communication session
  • Jitter – irregular random transmission time in the network
  • So how is data transferred in the NETWORK CORE? There are primarily two approaches, either by circuit switching or by packet switching. Circuit-switching is used by the ubiquitous telephone network, while packet switching is being used by the Internet, and is said to be the future of telephone networks.
  • Let’s have a look at a simple restaurant analogy to be able to easily understand the difference between the two switching schemes. You can think of Circuit switched networks as being analogous to restaurants requiring reservations, giving you guaranteed seats. On the other hand, packet switched networks are analogous to restaurants that do not require any reservations whatsoever, therefore seats are not guaranteed; The network equivalent simply dispatch messages, which take up on resources on demand; therefore, messages may have to wait on a queue to be transported.
  • The resources reserved for the duration of the call are the link bandwidth and the switch capacity. Such resources will be made available solely to a specific user in the network. Therefore, there is absolutely no sharing of resources between users or circuits. The advantage of this scheme is that circuit-like performance is guaranteed.
  • In FDM, the frequency spectrum is shared among the users of the link. The link dedicates a frequency band to each user for the duration of the connection. (FM radio station – share microwave frequency spectrum, Telephone networks – freq. band = 4kHz or 4,000 cycles/sec). On the other hand, in TDM, the network dedicates one time slot in every frame of the connection. Two simple multiple access control techniques. Each mobile’s share of the bandwidth is divided into portions for the uplink and the downlink. Also, possibly, out of band signaling. As we will see, used in AMPS, GSM, IS-54/136
  • In contrast to circuit switching, packet switching allows for resource sharing. Data is transmitted on demand, without reservation, in terms of packets, using the full link bandwidth. This switching however could be fazed with a problem of catering to a multitude of packets exceeding the switch capacity, congestion, and store-and-forward delays
  • The figure demonstrates a simple packet-switched network. Assuming that Hosts A and B transmit a sequence of packets towards Host E. In the first packet switch, such packets will be received in random order. Therefore, this router employs statistical multiplexing to schedule them for transmission (this sharply contrasts circuit switching).
  • Let us analyze how packet switching transports a message of size 5,000 packets. Take note that the unit of time used here is msec. From source to destination, taking the first packet, we see that packet one reaches the first packet switch at time = 1 msec. By the time packet 2 is transmitted, packet 1 is also being transported to the second switch. At this point, simultaneous transmission occurs, therefore, at time = 2 msec., packet 2 reaches the first switch, and packet one reaches the 2 nd switch. Using this pattern, the last packet, 5,000 th packet reaches the first switch after 5,000 msec or 5 sec. adding 2 more switching, we get 5.002 sec = the time to reach its destination.
  • Packet switching can cater to up to 35 users using the given 1 Mbps link. Using statistics, the probability that less than or equal to 10 users are active at a time is 0.9996 (almost equal to 1). When that happens, 10 users can be serviced in the same speed as circuit-switching.
  • For tracking down the route taken by packets, we can use a program like TraceRoute provided by www.TraceRoute.org
  • Modulation is a prescribed method of encoding digital (or analog) signals onto a waveform (the carrier signal). Once encoded, the original signal may be recovered by an inverse process called demodulation. Modulation is performed to adapt the signal to a different frequency range than that of the original signal. Here's how it flows: bits -> modulator -> audio -> phone network -> audio -> demodulator -> bits Hence the name MODEM short for modulator/demodulator . The modem is necessary because the phone network transmits audio, not data bits . The modem is for compatibility with existing equipment.
  • 802.11b Most WLANs deployed today use 802.11b technology, which operates in the 2.4 GHz band and supports a maximum theoretical data rate of 11 Mbps, with average throughput falling in the 4 Mbps to 6 Mbps range. In a typical office environment, its maximum range is 75 meters (250 feet) at the lowest speed, but at higher speed its range is about 30 meters (100 feet). Bluetooth devices, 2.4 GHz cordless phones and even microwave ovens are sources of interference (and thus create poor performance) for 802.11b networks. Minimizing interference can be difficult because 802.11b uses only three non-overlapping channels. 802.11b products have been shipping in quantity for several years so you will find that products are plentiful and affordable. (source: http://www.devx.com/wireless/Door/11464)
  • Cellular Digital Packet Data ( CDPD ) uses unused bandwidth normally used by AMPS mobile phones between 800 and 900 MHz to transfer data. Speeds up to 19.2 kbit/s are possible.
  • Cellular Digital Packet Data ( CDPD ) uses unused bandwidth normally used by AMPS mobile phones between 800 and 900 MHz to transfer data. Speeds up to 19.2 kbit/s are possible.
  • IDSL uses a completely separate line. Thus, your connection will always be operating at 128 Kbps, no matter what you are doing on the regular, voice line.
  • Switched Ethernet - Ethernet network that is controlled by a switch instead of a shared hub. From Shared to Switched Migrating from shared Ethernet to switched Ethernet provides a dramatic increase in throughput. For example, a 24-port 100BaseT hub shares the total 200 Mbps bandwidth with all 24 attached nodes. By replacing the hub with a switch, each of the 12 sender/receiver pairs has the full 200 Mbps capacity.
  • NCR’s WaveLAN, which uses an unregulated 902 to 928 megahertz (MHz) bandwidth, can transmit over about 30 to 60 meters (100 to 200 feet) indoors and about 250 meters (800 feet) outdoors between nodes. AIRLAN CAN (Campus Area Network) products from Solectek use the 902–928 MHz frequency band for communicating within in-building LANs and a higher, 2.4 GHz frequency for transmitting between bridges in different buildings. In both cases, the products use spread spectrum technology. These products can transmit up to 800 feet. CDPD (Cellular Digital Packet Data) transmits data over any cellular channels that are not being used. CDPD uses telephone (voice) channels, but can switch to a new frequency, if necessary, when a voice transmission begins in the cell being used. CDPD was developed to provide data communications in the cellular frequency range without interfering with voice calls.
  • The term bridge generally refers to a hardware device that can pass packets from one network to another. Bridges operate at the OSI Reference Model’s second lowest layer, the data-link layer. A bridge makes the networks look like a single network to higher level protocols or programs. When routing packets, a bridge uses only node addresses; it does not take network addresses into account. A node address is a physical address, associated with a network interface card (NIC), rather than with a particular network. Router The function of a router is to provide a path from a node on one network to a node on another network. As a result, a router can be used as a packet filter based on network protocols (as well as addresses). Because it is independent of data-link layer protocols, a router can connect networks using different architectures (for example, Ethernet to Token Ring or Ethernet to FDDI). A hub is a component that serves as a common termination point for multiple nodes and that can relay signals along the appropriate paths. An Access Point is a wireless LAN transceiver that acts as the connection point between wireless and wired networks or as the center point of a standalone wireless network. In large installations, the roaming functionality provided by multiple access points enables wireless users to move freely throughout the facility while maintaining uninterrupted access to the network.
  • Geosynchronous (adj.): geo- , earth and synchronous , going on at the same rate and exactly together.
  • There is a formula that helps us gauge the traffic intensity, in order for us to determine whether the average queuing delay is tolerable or not. The graph depicts an exponential curve telling us that as the value of traffic intensity approaches 1, queuing delay becomes large. If we will examine the formula, as the average packet arrival rate picks up, and multiply that by the Packet length, the link’s bandwidth R may not be able to cope up in transmitting the packets.
  • 3 SEC
  • A) 3.05
  • C) 500,000 BITS
  • C) 6.05 seconds
  • download paper

    1. 1. Learning Outcomes Describe what comprises the network edge 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 159.334 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 Ask yourself these questions at the end of the session
    2. 2. Introduction What’s the Internet? Email server Web-page server PDAs with wireless Internet connections toaster WebTV Automobile Digital cameras UNIX-based workstations laptop Household appliances HOSTS or END SYSTEMS
    3. 3. What’s the Internet? Nuts and bolts of the Internet Networking Infrastructure <ul><li>Hardware components </li></ul><ul><li>Software </li></ul><ul><li>provides services to distributed applications </li></ul><ul><li>infrastructure where new applications are being constantly invented and deployed </li></ul>
    4. 4. What’s the Internet? <ul><li>Interconnects millions (soon billions) of computing devices </li></ul><ul><li>provides: </li></ul><ul><li>Global communication </li></ul><ul><li>Storage </li></ul><ul><li>Computation infrastructure </li></ul><ul><li>global network of networks </li></ul>End-to-End System: End System End System Core “ edge” “ edge” “ Nuts and Bolts” View
    5. 5. SETI@HOME—MASSIVELY DISTRIBUTED COMPUTING FOR SETI http://setiathome.ssl.berkeley.edu/ What is SETI@home? SETI@home 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.
    6. 6. <ul><li>network edge: applications and hosts </li></ul><ul><li>network core: </li></ul><ul><ul><li>routers </li></ul></ul><ul><ul><li>network of networks </li></ul></ul><ul><li>access networks, physical media: communication links </li></ul>The Bigger Picture
    7. 7. End-to-End System End System=HOST End System End System Core 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 Where much internet architecture complexity is placed Communication links Switches Access networks Physical media
    8. 8. Where is the Network Core? ?
    9. 9. What’s in the Links? Router End System End System 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 Router End System End System 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 packet Sender Receiver
    10. 10. Now let’s see how are links formed in terms of clusters i
    11. 11. <ul><li>a human protocol and a computer network protocol: </li></ul>What’s a protocol? Got the time? Get http://www.massey.ac.nz/ Hi Hi 2:00 time TCP connection request TCP connection reply <file>
    12. 12. What’s a protocol? <ul><li>Human Protocols: </li></ul><ul><li>Something we execute all the time </li></ul><ul><li>Offer a greeting </li></ul><ul><li>Wait for a response </li></ul><ul><li>Analyze the response </li></ul><ul><li>Act accordingly </li></ul><ul><li>Network Protocols: </li></ul><ul><li>Similar to human protocol, except that entities are machines rather than humans </li></ul><ul><li>all communication activities in the Internet are governed by protocols </li></ul><ul><li>In order for protocols to work, both entities must observe the same protocol. </li></ul><ul><li>There is a set of conventional actions taken when messages are sent and received. </li></ul>Networking – understanding the what, why and how of networking protocols
    13. 13. 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: <ul><li>* All activities in the Internet that involves 2 or more communicating entities are governed by a protocol. </li></ul><ul><li>There are protocols in: </li></ul><ul><li>Routers </li></ul><ul><ul><li>Protocols determine a packet’s path from source to destination </li></ul></ul><ul><li>NIC </li></ul><ul><ul><li>hardware-implemented protocols control the flow of the bits on the “wire” </li></ul></ul><ul><li>End Systems </li></ul><ul><li>congestion-control protocols control the rate at which packets are transmitted between sender and receiver </li></ul>
    14. 14. TCP IP Two of the most important protocols in the Internet (principal protocols) BASIC TERMINOLOGIES Protocols - control the sending and receiving of information within the Internet - run by End Systems, routers, etc.; Global network of networks (“The Internet”) Made possible through standards developed by (IETF) Internet Engineering Task Force RFC s (Request for Comments) 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 – Transmission Control Protocol
    15. 15. What’s the Internet? A Service View <ul><li>Provides a communication infrastructure that allows distributed applications running on its end systems to exchange data with each other. </li></ul>Remote login email 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 <ul><li>Provides communication services to distributed applications: </li></ul>
    16. 16. 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…
    17. 17. <ul><li>Client/Server Model </li></ul><ul><ul><li>client host </li></ul></ul><ul><ul><ul><li>Requests </li></ul></ul></ul><ul><ul><ul><li>& Receives service from server </li></ul></ul></ul><ul><ul><ul><li>e.g. WWW client (browser)/server; email client/server </li></ul></ul></ul>A closer look at the Network Edge What happens in the network edge? <ul><li>End Systems (Hosts): </li></ul><ul><ul><li>- run application programs </li></ul></ul><ul><ul><li>e.g., WWW, email </li></ul></ul><ul><ul><li>at “edge of network” </li></ul></ul>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. 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) There is some level of abstraction that hides the nitty-gritty part of the communication process between two end systems
    18. 18. <ul><li>“ Connection ” between two End Systems: (e.g. Web application or Internet phone application) </li></ul><ul><ul><li>Nothing more than allocated buffers and state variables </li></ul></ul>The Network Edge “ Connection” Internet provides two type of services to End-System Applications : <ul><li>Connection-oriented service – (TCP) </li></ul>App’s using UDP: streaming media, teleconferencing, Internet telephony <ul><li>Connectionless service – (UDP) </li></ul>App’s using TCP: HTTP (WWW), FTP (file transfer), Telnet (remote login), SMTP (email)
    19. 19. <ul><li>Goal: data transfer between end system. </li></ul><ul><li>handshaking: setup (prepare for) data transfer ahead of time </li></ul><ul><ul><li>Hello, hello back human protocol </li></ul></ul><ul><ul><li>set up “state” in two communicating hosts </li></ul></ul><ul><li>TCP service [RFC 793] </li></ul><ul><li>Provides: </li></ul><ul><li>Reliable data transfer: </li></ul><ul><ul><li>loss: handled using acknowledgements and retransmissions </li></ul></ul><ul><li>Flow Control: </li></ul><ul><ul><li>Ensures that the sender won’t overwhelm receiver </li></ul></ul><ul><li>Congestion Control: </li></ul><ul><ul><li>Instructs senders to “slow down sending rate” when network is congested </li></ul></ul><ul><ul><li>Prevents gridlock </li></ul></ul>Network edge: connection-oriented service performs handshaking Q * TCP - Transmission Control Protocol - Internet’s connection-oriented service
    20. 20. <ul><li>Handshaking Procedure: </li></ul>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 Case: No retransmission
    21. 21. <ul><li>Handshaking Procedure: </li></ul>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
    22. 22. <ul><li>Flow control </li></ul>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 CLIENT CLIENT
    23. 23. <ul><li>Congestion control </li></ul>Network Edge: TCP Service CLIENT SERVER Problem: Gridlock sets-in when there is packet loss due to router congestion 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 We will see more of this when we view the applet from Kurose’s site
    24. 24. <ul><li>Goal: data transfer between end systems </li></ul><ul><ul><li>same as before! </li></ul></ul><ul><li>UDP - User Datagram Protocol [RFC 768]: Internet’s connectionless service </li></ul><ul><ul><li>unreliable data transfer </li></ul></ul><ul><ul><li>no flow control </li></ul></ul><ul><ul><li>no congestion control </li></ul></ul>Network edge: connectionless service No handshaking procedure; End-Systems just simply send the packet
    25. 25. Something to ponder on ? 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? Bandwidth – how many bits per second a network can transport Latency – how many seconds it takes for the first bit to get from the client to the server
    26. 26. Answer 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.
    27. 27. <ul><li>mesh of interconnected routers </li></ul>The Network Core
    28. 28. <ul><li>the fundamental question: how is data transferred through net? </li></ul><ul><ul><li>circuit switching: dedicated circuit per call: telephone net </li></ul></ul><ul><ul><li>packet-switching: data sent through net in discrete “chunks” </li></ul></ul>The Network Core Approaches to building a Network Core:
    29. 29. 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 <ul><li>With a reservation, you can order right away when you get there </li></ul><ul><li>guaranteed seats </li></ul><ul><li>you may have to wait on a queue to be served </li></ul><ul><li>no sure seats </li></ul>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?
    30. 30. <ul><li>End-end resources reserved for “call” </li></ul><ul><ul><li>link bandwidth, switch capacity </li></ul></ul><ul><ul><li>Switches on the path between sender and receiver maintain connection state for the duration of the session </li></ul></ul><ul><ul><li>Resources are dedicated; thus, no sharing </li></ul></ul><ul><ul><li>Advantage: circuit-like (guaranteed) performance </li></ul></ul><ul><ul><li>call set-up required </li></ul></ul><ul><ul><li>(unless infinite resources are available) </li></ul></ul>Network Core: Circuit Switching “ Circuit”
    31. 31. <ul><li>How is it implemented? </li></ul><ul><li>By dividing the link bandwidth into “pieces” </li></ul><ul><ul><li>frequency division </li></ul></ul><ul><ul><li>time division </li></ul></ul>Network Core: Circuit Switching Inefficiency: Resource piece is idle if not used by owning call (no sharing)
    32. 32. Circuit Switching: FDM and TDM Slot Frame 4KHz Network dedicates one time slot in every frame of the connection Network dedicates a frequency band to each connection for the session FDM frequency time TDM frequency time 4 users (or 4 circuits) Example: Used solely by one End System
    33. 33. 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 1.536 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.
    34. 34. Question GIVEN: Size of file to send: 640,000 bits SOLUTION: Each circuit has a transmission rate of (1.536 Mbps)/24 = 64kbps (or 64,000 bps). So, it takes (640,000 bits)/(64,000 bps)= 10 sec . to transmit the file. Considering the circuit establishment time, we add 0.5 sec; therefore, It takes 10.5 sec . to transmit the file. 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 1.536 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
    35. 35. <ul><li>each end-end data stream divided into packets </li></ul><ul><li>user A, B packets share network resources </li></ul><ul><li>each packet uses full link bandwidth </li></ul><ul><li>resources used as needed </li></ul>Network Core: Packet Switching Q * <ul><li>Resource Contention: </li></ul><ul><li>aggregate resource demand can exceed amount available </li></ul><ul><li>congestion: packets queue, wait for link use </li></ul><ul><li>store and forward: packets move one hop at a time </li></ul><ul><ul><li>transmit over link </li></ul></ul><ul><ul><li>wait turn at next link </li></ul></ul>Bandwidth division into “pieces” Dedicated allocation Resource reservation
    36. 36. We stopped here last time 
    37. 37. Network Core: Packet Switching Q * Receiver: Node E Sender: Nodes A and B A B C 10 Mbs Ethernet 1.5 Mbs 45 Mbs D E statistical multiplexing queue of packets waiting for output link
    38. 38. Consider a message that is 7.5 x 10 6 bits long. Suppose that between 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, how much time is required to move the message from source to destination with packet switching? Network Core: Packet Switching (7.5 Mbps/1.5 Mbps) * 3 = 15 sec .
    39. 39. <ul><li>store and forward behaviour: </li></ul>Packet Switching: Store and Forward Behaviour Let’s see the applet of message segmenting to see how this works Pattern that can be deduced from the packet flow depicted in the Figure: Time of arrival = packet_num + 2 Example: <ul><li>break message into smaller chunks: “packets” </li></ul><ul><li>Store-and-forward: switch waits until chunk has completely arrived, then forwards/routes </li></ul>
    40. 40. Suppose that users share a 1 Mbps link, where each user alternates between generating data at a constant rate of 100 Mbps , 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
    41. 41. <ul><li>Example: 1 Mbit link shared by all users </li></ul><ul><li>each user: </li></ul><ul><ul><li>Generates 100Kbps when “active” </li></ul></ul><ul><ul><li>(at constant rate) </li></ul></ul><ul><ul><li>active 10% of time </li></ul></ul><ul><li>circuit-switching: </li></ul><ul><ul><li>10 users can only be supported </li></ul></ul><ul><ul><li>1,000,000 bits/sec divided by 100,000 bits/sec. </li></ul></ul><ul><li>packet switching: </li></ul><ul><ul><li>with 35 users, probability > 10 are active is less than .0004 </li></ul></ul><ul><ul><li>probability <= 10 users are active is 0.9996 </li></ul></ul><ul><li>Packet switching allows more users to use network! </li></ul>Packet Switching vs. Circuit Switching 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 N users 1 Mbps link
    42. 42. 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 Palmerston North and the server is in Auckland? Assume the propagation speed in copper and fiber to be 2/3 the speed of light in vacuum . Question ? Speed of light = 3 x 10 8 meters/sec.
    43. 43. Question 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 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 Palmerston North and the server is in Auckland? Assume the propagation speed in copper and fiber to be 2/3 the speed of light in vacuum .
    44. 44. <ul><li>Advantages: Great for bursty data </li></ul><ul><ul><li>resource sharing </li></ul></ul><ul><ul><li>no call set-up </li></ul></ul><ul><li>Drawbacks: </li></ul><ul><li>Excessive congestion, packet delay and loss </li></ul><ul><ul><li>protocols needed for reliable data transfer, congestion control </li></ul></ul><ul><li>Issue: How to provide circuit-like behaviour? </li></ul><ul><ul><li>bandwidth guarantees needed for audio/video apps; </li></ul></ul><ul><ul><li>this is still an unsolved problem </li></ul></ul>Network Core: Packet Switching
    45. 45. <ul><li>Goal: move packets among routers from source to destination </li></ul><ul><li>datagram network: </li></ul><ul><ul><li>destination address determines next hop </li></ul></ul><ul><ul><li>routes may change during session </li></ul></ul><ul><ul><li>analogy: driving, asking directions </li></ul></ul><ul><li>virtual circuit network: </li></ul><ul><ul><li>each packet carries tag (virtual circuit ID), tag determines next hop </li></ul></ul><ul><ul><li>fixed path determined at call set-up time , remains fixed through call </li></ul></ul><ul><ul><li>routers maintain per-call state </li></ul></ul>Packet-switched networks
    46. 46. <ul><li>Q: How to connect End-Systems to edge router? </li></ul><ul><li>residential access nets </li></ul><ul><li>institutional access networks (school, company) </li></ul><ul><li>mobile access networks </li></ul><ul><li>Keep in mind: </li></ul><ul><li>bandwidth (bits per second) of access network? </li></ul><ul><li>shared or dedicated? </li></ul>Access networks and physical media
    47. 47. ISPs Lower-Tier ISPs Web Site content providers Users National and International Upper-Tier ISPs High-speed routers interconnected with high-speed fiber-optic links e.g. UUNet and Sprint Managed independently Runs the IP protocol, conforms to certain naming and address conventions ACCESS NETWORKS local ISP Company Network Regional ISP router workstation server mobile
    48. 48. Program Delay and Routes in the Internet Program SOURCE HOST DESTINATION HOST TraceRoute (diagnostic program) - defined in RFC 1393 <ul><li>If there are (N-1) routers, then SOURCE sends N special packets </li></ul><ul><ul><li>Each packet is addressed to the ultimate destination </li></ul></ul><ul><ul><li>marked 1 to N </li></ul></ul><ul><li>When the ith router receives the ith packet marked i : </li></ul><ul><ul><li>router destroys the packet </li></ul></ul><ul><ul><li>Sends a message containing name and address of router back to the source </li></ul></ul><ul><li>When DESTINATION host receives the N th packet : </li></ul><ul><ul><li>DESTINATION destroys the packet, then </li></ul></ul><ul><ul><li>returns the message back to the source </li></ul></ul><ul><li>SOURCE: </li></ul><ul><ul><li>records time elapsed (time received- time packet sent) </li></ul></ul><ul><ul><li>determines the round-trip delays to all intervening routers </li></ul></ul><ul><ul><ul><li>Round-trip delays include: </li></ul></ul></ul><ul><ul><ul><ul><li>Transmission delay </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Propagation delay </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Router processing delay </li></ul></ul></ul></ul><ul><ul><ul><ul><li>Queuing delay (varies with time) </li></ul></ul></ul></ul><ul><ul><li>records name & address of router (or destination HOST) that returns the message </li></ul></ul><ul><ul><li>reconstructs the route taken by the packets (source-to-destination) </li></ul></ul>
    49. 49. <ul><li>Trace Route from MIT </li></ul><ul><li>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 &quot;port scan&quot; originating from this server (jis.mit.edu). Rest assured, your system is not being attacked. </li></ul><ul><li>1 W92-RTR-1-W92SRV21.MIT.EDU (18.7.21.1) 0.425 ms 0.287 ms 0.259 ms </li></ul><ul><li>2 EXTERNAL-RTR-1-BACKBONE.MIT.EDU (18.168.0.18) 21.179 ms 244.069 ms 223.625 ms </li></ul><ul><li>3 leg-208-30-223-5-CHE.sprinthome.com (208.30.223.5) 0.589 ms 0.459 ms 0.542 ms </li></ul><ul><li>4 144.232.21.50 (144.232.21.50) 2.951 ms 3.146 ms 2.966 ms </li></ul><ul><li>5 sl-bb21-chi-6-2.sprintlink.net (144.232.19.205) 21.073 ms 48.427 ms 20.784 ms </li></ul><ul><li>6 sl-bb24-chi-9-0.sprintlink.net (144.232.26.77) 141.917 ms 229.305 ms 219.150 ms </li></ul><ul><li>7 sl-bb21-sj-8-0.sprintlink.net (144.232.20.161) 68.260 ms 68.102 ms 68.044 ms </li></ul><ul><li>8 sl-bb22-sj-15-0.sprintlink.net (144.232.3.162) 68.016 ms 68.036 ms 68.608 ms </li></ul><ul><li>9 144.232.20.47 (144.232.20.47) 73.346 ms 73.617 ms 73.508 ms </li></ul><ul><li>10 sl-newzeal-1-0.sprintlink.net (144.223.243.18) 70.804 ms 71.082 ms 70.787 ms </li></ul><ul><li>11 p5-2.sjbr1.global-gateway.net.nz (203.96.120.213) 71.132 ms 70.990 ms 70.903 ms </li></ul><ul><li>12 203.96.120.118 (203.96.120.118) 195.054 ms 195.579 ms 196.648 ms </li></ul><ul><li>13 203.96.120.201 (203.96.120.201) 198.228 ms 211.397 ms 197.358 ms </li></ul><ul><li>14 massey-uni-ak-int.tkbr4.global-gateway.net.nz (202.49.163.230) 202.604 ms 218.925 ms 199.836 ms </li></ul><ul><li>15 * * * </li></ul><ul><li>16 * * * </li></ul><ul><li>17 * * * </li></ul><ul><li>18 * * * </li></ul><ul><li>19 * * * </li></ul><ul><li>20 * * * </li></ul><ul><li>21 * * * </li></ul><ul><li>22 * * * </li></ul><ul><li>23 * * * </li></ul><ul><li>24 * * * </li></ul><ul><li>25 * * * </li></ul><ul><li>26 * * * </li></ul><ul><li>27 * * * </li></ul><ul><li>28 * * * </li></ul><ul><li>29 * * * </li></ul><ul><li>30 * * * </li></ul>TraceRoute 6 columns: n, name of router, address of router, trip delay1,trip delay2,trip delay3 Route trace: From MIT to Massey University Trans-atlantic link Trace:3x * - indicates packet loss
    50. 50. Tracert (from xtra to mit) C:>tracert web.mit.edu Tracing route to web.mit.edu [18.7.22.69] over a maximum of 30 hops: 1 1 ms 1 ms 1 ms 192.168.1.1 2 2 ms 2 ms 2 ms 192.168.8.1 3 56 ms 59 ms 55 ms 219-89-32-1.dialup.xtra.co.nz [219.89.32.1] 4 * 53 ms 54 ms 222.152.127.169 5 * 66 ms * 202.50.236.105 6 * * * Request timed out. 7 482 ms * * so-0-2-0.labr3.global-gateway.net.nz [202.50.232.26] 8 * * * Request timed out. 9 * 341 ms 290 ms g11-2-107.core01.lax05.atlas.cogentco.com [154.54.11.145] 10 243 ms 213 ms * t3-4.mpd01.lax01.atlas.cogentco.com [154.54.6.189] 11 217 ms 280 ms * g9-0-0.core01.lax01.atlas.cogentco.com [154.54.2.117] 12 * 344 ms 325 ms p2-0.core01.dfw01.atlas.cogentco.com [154.54.5.93] 13 * * 282 ms p15-0.core02.dfw01.atlas.cogentco.com [66.28.4.26] 14 250 ms * * p15-0.core01.mci01.atlas.cogentco.com [66.28.4.38] 15 * * * Request timed out. 16 * 367 ms * p15-0.core01.ord01.atlas.cogentco.com [66.28.4.61] 17 * 386 ms 434 ms p14-0.core01.alb02.atlas.cogentco.com [154.54.1.57] 18 * 345 ms 448 ms p6-0.core01.bos01.atlas.cogentco.com [154.54.7.42] 19 * 282 ms 285 ms g8.ba21.b002250-1.bos01.atlas.cogentco.com [66.250.14.210] 20 * * 408 ms MIT.demarc.cogentco.com [38.112.2.214] 21 342 ms * * W92-RTR-1-BACKBONE.MIT.EDU [18.168.0.25] 22 * 344 ms * WEB.MIT.EDU [18.7.22.69] 23 * 342 ms 380 ms WEB.MIT.EDU [18.7.22.69] Trace complete. C:> Tracert (also known as traceroute) is a Windows based tool that allows you to help test your network infrastructure.
    51. 51. Tracert (from Massey to MIT) D:Massey Papers159334CodesGame Protocol v3.6>tracert web.mit.edu Tracing route to web.mit.edu [18.7.22.69] over a maximum of 30 hops: 1 <1 ms <1 ms <1 ms it023453-vlan205.massey.ac.nz [130.123.246.129] 2 <1 ms <1 ms <1 ms it028100-vlan801.massey.ac.nz [10.100.254.3] 3 1 ms <1 ms <1 ms 210.7.32.1 4 1 ms <1 ms <1 ms 210.7.36.67 5 142 ms 142 ms 142 ms 210.7.47.22 6 142 ms 142 ms 142 ms abilene-1-lo-jmb-706.sttlwa.pacificwave.net [207.231.240.8] 7 179 ms 187 ms 180 ms dnvrng-sttlng.abilene.ucaid.edu [198.32.8.50] 8 189 ms 189 ms 202 ms kscyng-dnvrng.abilene.ucaid.edu [198.32.8.14] 9 201 ms 214 ms 201 ms iplsng-kscyng.abilene.ucaid.edu [198.32.8.80] 10 202 ms 215 ms 202 ms chinng-iplsng.abilene.ucaid.edu [198.32.8.76] 11 202 ms 206 ms 207 ms ge-0-0-0.10.rtr.chic.net.internet2.edu [64.57.28.1] 12 219 ms 230 ms 220 ms so-3-0-0.0.rtr.wash.net.internet2.edu [64.57.28.13] 13 225 ms 224 ms 224 ms ge-1-0-0.418.rtr.chic.net.internet2.edu [64.57.28.10] 14 229 ms 229 ms 229 ms nox300gw1-Vl-110-NoX-ABILENE.nox.org [192.5.89.221] 15 229 ms 229 ms 229 ms nox230gw1-Vl-802-NoX.nox.org [192.5.89.254] 16 481 ms 230 ms 230 ms nox230gw1-PEER-NoX-MIT-192-5-89-90.nox.org [192.5.89.90] 17 230 ms 230 ms 230 ms W92-RTR-1-BACKBONE.MIT.EDU [18.168.0.25] 18 230 ms 230 ms 230 ms WEB.MIT.EDU [18.7.22.69] Trace complete. D:Massey Papers159334CodesGame Protocol v3.6>
    52. 52. Residential ISPs (e.g. AOL, MSN) University ISPs (e.g. Stanford University) Corporate ISPs (e.g. Ford Motor Company) ISP – Internet Service Provider End Systems access the Internet through ISPs ISPs - Network of routers and communication links 56 kbps dial-up modem access Residential broadband access (DSL, cable modem) High-speed LAN access Different types of Network Access provided by ISPs Wireless access ACCESS NETWORKS
    53. 53. Translates digital data into analog data Max. speed: 56kbps Least expensive, but slow Ties up your phone line to the Internet, making unavailable for making voice calls Standard Telephone Modem Residential Access: Point-to-Point Access
    54. 54. <ul><li>shared wireless access network connects end system to router </li></ul><ul><li>wireless LANs: </li></ul><ul><ul><li>radio spectrum replaces wire </li></ul></ul><ul><ul><li>e.g., Lucent Wavelan 11 Mbps </li></ul></ul><ul><ul><li>Serves within a radius of tens of meters </li></ul></ul>Wireless access networks base station mobile hosts router
    55. 55. Wireless Access Wireless LAN Access Also known as wireless Ethernet and Wi-Fi Based on IEEE 802.11 technology (1997, 1999, 2002, 2003) Provides a shared transmission rate of 11Mbps, 54 Mbps Each wireless network technology available today offers some advantage over the others. For those looking to build a new WLAN, 802.11g is the most promising option to consider. http://compnetworking.about.com/cs/wireless80211/a/aa80211standard.htm 802.11g 802.11a 802.11b Technology costs more than 802.11b; appliances may interfere on the unregulated signal frequency fastest maximum speed; supports more simulatenous users; signal range is best and is not easily obstructed highest cost; shorter range signal that is more easily obstructed fastest maximum speed; supports more simulatenous users; regulated frequencies prevent signal interference from other devices slowest maximum speed; supports fewer simultaneous users; appliances may interfere on the unregulated frequency band lowest cost; signal range is best and is not easily obstructed Cons Pros
    56. 56. <ul><li>CDPD (Cellular Digital Packet Data): </li></ul><ul><ul><ul><li>- wireless access to ISP router via cellular network </li></ul></ul></ul><ul><ul><ul><li>Base station is managed by telecommunications provider </li></ul></ul></ul><ul><ul><ul><li>serves users within a radius of tens of kilometers </li></ul></ul></ul><ul><ul><ul><li>works under the analog cellular system </li></ul></ul></ul><ul><ul><ul><li>CDPD usage is on the decline. </li></ul></ul></ul>Wide-Area Wireless Access Networks base station mobile hosts router
    57. 57. <ul><li>3G </li></ul><ul><ul><ul><li>- used in the context of mobile phone standards. </li></ul></ul></ul><ul><ul><ul><li>services associated with 3G provide the ability to transfer simultaneously both voice data (a telephone call) and non-voice data (such as downloading information, exchanging email, and instant messaging) </li></ul></ul></ul><ul><ul><ul><li>high-speed internet access and video telephony </li></ul></ul></ul><ul><ul><ul><li>uses 5 MHz channel carrier width </li></ul></ul></ul><ul><ul><ul><li>allows the transmission of 384kbps for mobile systems and 2Mbps for stationary systems </li></ul></ul></ul>Wide-Area Wireless Access Networks
    58. 58. Digital phone line Simultaneous use of a telephone to make voice calls while connected to the Internet Private connection: not competing for part of a shared network with other users integrated services digital network: digital telephony + data-transport services offered by regional telephone carriers. 128Kbps all-digital connect to router (ISDN) Integrated Services Digital Network Residential Access: Point-to-Point Access digital transmission bypasses the telephone company's central office equipment that handles analog signals IDSL provides always-on connections and transmits data (144 kbit/s ) via a data network rather than the carrier's voice network. ISDN Digital Subscriber Line (IDSL) :
    59. 59. http://www.azstarnet.com/service/dslfaq/idsl/2.html Comparison Chart taken from one ISP 64 Kbps 128 Kbps Max Speed (While Using Phone) 128 Kbps 128 Kbps Max Speed No Yes Equipment Included $110 $696.95 Setup Costs (Qwest) >$100-$300 $16.95 (StarNet) Monthly Dedicated Internet (24 hours/7 days) about $20-40 N/A Monthly ISP Cost (Dial-Up) $69 (replaces cost of basic line, ~$13) $69.95 (added to current phone bill) Monthly Cost (Qwest) ISDN IDSL
    60. 60. Don’t tie up your phone line Always-on connection with the Internet Private connection: not competing for part of a shared network with other users Downside: high price, service must be available for the physical location of your home (within 5.5 km) of a telephone company central switching office (CO) or local telephone exchange Broadband Residential Access DSL, ADSL (Asymmetric Digital Subscriber Line) Devices <ul><ul><li>up to 1 Mbps home-to-router ( upstream ) </li></ul></ul><ul><ul><li>up to 8 Mbps router-to-home ( downstream ) </li></ul></ul>Since DSL network provides a dedicated Internet connection via private telephone wires, you can bypass dial-up intruders or shared network hackers Uses FDM
    61. 61. Residential access: cable modems Diagram: http://www.cabledatacomnews.com/cmic/diagram.html
    62. 62. Send data over your cable-television company’s line Always connected; some stand-alone devices that can be connected to your network, others are internal or USB devices Speed up to 1 million bits/sec. (Mbps) Automatically hooked to ISP Connects to a network of other cable-modem users ( everyone is trying to use a portion of the same network bandwidth) Tied-up to local cable company (cable modem service & ISP service) Doesn’t interfere with television broadcasting Cable Modem Broadband Residential Access: Cable Modem
    63. 63. <ul><li>HFC : H ybrid F iber-optic C oaxial network </li></ul><ul><ul><li>asymmetric: up to 10Mbps upstream, 1 Mbps downstream </li></ul></ul><ul><ul><li>network of cable and fiber attaches homes to ISP router </li></ul></ul><ul><ul><ul><li>shared access to router among home </li></ul></ul></ul><ul><ul><ul><li>issues: congestion, dimensioning </li></ul></ul></ul>Residential access: cable modems
    64. 64. <ul><li>company/univ local area network (LAN) connects end system to edge router </li></ul><ul><li>Ethernet: </li></ul><ul><ul><li>shared or dedicated/switched cable connects end system and router </li></ul></ul><ul><ul><li>10 Mbs, 100Mbps, Gigabit Ethernet </li></ul></ul><ul><li>deployment: institutions, home LANs happening now </li></ul><ul><li>LANs: chapter 5 </li></ul>Institutional access: local area networks Ethernet Switch This 10/100 switch from Omnitron has 16 ports and automatically senses the transmission rate of the line and adjusts accordingly.
    65. 65. <ul><li>Typical home network components: </li></ul><ul><li>ADSL or cable modem </li></ul><ul><li>router/firewall </li></ul><ul><li>Ethernet </li></ul><ul><li>wireless access </li></ul><ul><li>point </li></ul>Home networks wireless access point wireless laptops router/ firewall cable modem to/from cable headend Ethernet (switched)
    66. 66. 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? 1024 768 Clue: Mega = 1 x 10 6 Kilo = 1 x 10 3
    67. 67. Question <ul><li>SOLUTION: </li></ul><ul><li>The image is 1024 x 768 x 3 bytes or 2,359,296 bytes. </li></ul><ul><li>This is 18,874,368 bits . </li></ul><ul><ul><li>At 56,000 bits/sec., it takes about 337.042 sec. </li></ul></ul><ul><ul><li>At 1,000,000 bits/sec, it takes about 18.874 sec. </li></ul></ul><ul><ul><li>At 10,000,000 bits/sec., it takes about 1.887 sec. </li></ul></ul><ul><ul><li>At 100,000,000 bits/sec., it takes about 0.189 sec. </li></ul></ul>Answer 1024 768 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?
    68. 68. <ul><li>Physical link: transmitted data bit propagates across link </li></ul><ul><li>guided media : </li></ul><ul><ul><li>signals propagate in solid media: copper, optic fibre </li></ul></ul><ul><li>unguided media: </li></ul><ul><ul><li>signals propagate freely, e.g., radio </li></ul></ul><ul><li>Twisted Pair (TP) </li></ul><ul><li>two insulated copper wires </li></ul><ul><ul><li>Category 3 : traditional phone wires, 10 Mbps Ethernet </li></ul></ul><ul><ul><li>Category 5 TP: 100Mbps Ethernet </li></ul></ul><ul><ul><li>Category 6 : Gigabit Ethernet </li></ul></ul>Physical Media
    69. 69. <ul><li>Coaxial cable: </li></ul><ul><li>wire (signal carrier) within a wire (shield) </li></ul><ul><ul><li>baseband: single channel on cable </li></ul></ul><ul><ul><li>broadband: multiple channel on cable </li></ul></ul><ul><li>bidirectional </li></ul><ul><li>common use in 10Mbps Ethernet </li></ul>Physical Media: coax, optic fibre <ul><li>Fibre optic cable: </li></ul><ul><li>glass fiber carrying light pulses </li></ul><ul><li>high-speed operation: </li></ul><ul><ul><li>100Mbps Ethernet </li></ul></ul><ul><ul><li>high-speed point-to-point transmission (e.g., 5 Gbps) </li></ul></ul><ul><li>low error rate </li></ul>
    70. 70. <ul><li>signal carried in electromagnetic spectrum </li></ul><ul><li>no physical “wire” </li></ul><ul><li>bidirectional </li></ul><ul><li>propagation environment effects: </li></ul><ul><ul><li>reflection </li></ul></ul><ul><ul><li>obstruction by objects </li></ul></ul><ul><ul><li>interference </li></ul></ul>Physical Media: Radio <ul><li>Radio link types: </li></ul><ul><li>microwave </li></ul><ul><ul><li>e.g. up to 45 Mbps channels </li></ul></ul><ul><li>LAN (e.g., WaveLAN) </li></ul><ul><ul><li>2Mbps, 11Mbps </li></ul></ul><ul><li>wide-area (e.g., cellular) </li></ul><ul><ul><li>e.g. CDPD, 10’s Kbps </li></ul></ul><ul><ul><li>See for example </li></ul></ul><ul><ul><li>www.woosh.co.nz </li></ul></ul>
    71. 71. Workgroup Bridge Connected to a LAN http://www.cisco.com/en/US/products/hw/wireless/ps458/products_configuration_guide_chapter09186a008007f7bf.html#18981
    72. 72. Radio Ranges Radio Ranges Because the bridge is a radio device, it is susceptible to common causes of interference that can reduce throughput and range. Follow these guidelines to ensure the best possible performance: Install the bridge in an area where large steel structures such as shelving units, bookcases, and filing cabinets will not obstruct radio signals to and from the bridge. Install the bridge away from microwave ovens . Microwave ovens operate on the same frequency as the bridge and can cause signal interference. Clear or open areas provide better radio range than closed or filled areas. Also, the less cluttered the work environment, the greater the range. The bridge operates in the 2.4-GHz license-free Industrial Scientific and Medical (ISM) band . Cell —the area of radio range or coverage in which the bridge can communicate with the access point. The size of a single cell depends upon the speed of the transmission, the type of antenna used, and the physical environment as well as other factors. A Bridge is a small, stand-alone unit that provides a wireless infrastructure connection for Ethernet-enabled devices .
    73. 73. Physical Media: Radio <ul><li>Radio link types: </li></ul><ul><li>satellite </li></ul><ul><ul><li>up to 50Mbps channel (or multiple smaller channels) </li></ul></ul><ul><ul><li>270 Msec end-end delay </li></ul></ul><ul><ul><li>Geosynchronous, i.e., seems to be stationary in relation to an earthling observer </li></ul></ul><ul><ul><li>Orbits Earth at about 35,786 km above the earth's surface </li></ul></ul><ul><ul><li>See http://liftoff.msfc.nasa.gov/academy/rocket_sci/satellites/geo-high.html </li></ul></ul>
    74. 74. Delay and Loss in Packet-Switched Networks Queue - Retransmitted by application or transport layer protocol Lost packet Queue <ul><li>Incoming packet is dropped </li></ul><ul><li>packet in queue is dropped </li></ul>- Length of Queue is finite <ul><li>Packets are lost when queue is full </li></ul>
    75. 75. <ul><li>packets experience delay on end-to-end path </li></ul><ul><li>four sources of delay at each hop </li></ul><ul><li>nodal processing: </li></ul><ul><ul><li>check bit errors </li></ul></ul><ul><ul><li>determine output link </li></ul></ul><ul><li>queueing </li></ul><ul><ul><li>time waiting at output link for transmission </li></ul></ul><ul><ul><li>depends on congestion level of router </li></ul></ul>Delay in packet-switched networks A B propagation transmission nodal processing queueing
    76. 76. Delay and Loss in Packet-Switched Networks Later, we’ll see a real measurement of END-to-END delay Assuming that: END-TO-END DELAY - there are N-1 routers, and - Queuing delays are negligible Delay END-to-END : = N(d proc + d trans + d prop ) Processing delay at router and source host Propagation delay at each link Transmission rate out of each router and out of source host
    77. 77. <ul><li>R=link bandwidth (bits/sec) </li></ul><ul><li>L=packet length (bits) </li></ul><ul><li>a=average packet arrival rate (packets/sec) </li></ul>Queueing delay (revisited) This estimates the extent of queuing delay. Design your system so that traffic intensity is no greater than 1. traffic intensity = La/R <ul><li>La/R ~ 0: average queueing delay small </li></ul><ul><li>La/R -> 1: delays become large </li></ul><ul><li>La/R > 1: more “work” arriving than can be serviced, average delay infinite! </li></ul>
    78. 78. Exercises Chapter 1 – True or False Questions
    79. 79. Exercises <ul><li>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 </li></ul><ul><li>3 seconds </li></ul><ul><li>3.05 seconds </li></ul><ul><li>50 milliseconds </li></ul><ul><li>none of the above. </li></ul>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.
    80. 80. Exercises <ul><li>2 . Referring to the above question, the end-to-end delay (transmission delay plus propagation delay) is </li></ul><ul><li>3.05 seconds </li></ul><ul><li>3 seconds </li></ul><ul><li>6 seconds </li></ul><ul><li>none of the above </li></ul>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.
    81. 81. Exercises <ul><li>3 . Referring to the above question, how many bits will the source have transmitted when the first bit arrives at the destination. </li></ul><ul><li>1 bit </li></ul><ul><li>30,000,000 bits </li></ul><ul><li>500,000 bits </li></ul><ul><li>none of the above </li></ul>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.
    82. 82. Exercises <ul><li>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 </li></ul><ul><li>3.05 seconds </li></ul><ul><li>6.1 seconds </li></ul><ul><li>6.05 seconds </li></ul><ul><li>none of the above </li></ul>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.
    83. 83. End of Session 

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