Slide 1Slide 2Slide 3Slide 4Slide 5Slide 6Slide 7Slide 8Slide 9Slide 10Slide 11Slide 12Slide 13Slide 14Slide 15Slide 16Slide 17Slide 18Slide 19Slide 20Slide 21Slide 22Slide 23Slide 24Slide 25Slide 26Slide 27Slide 28Slide 29Slide 30Slide 31Slide 32Slide 33Slide 34Slide 35Slide 36Slide 37Slide 38Slide 39Slide 40Slide 41Slide 42Slide 43Slide 44Slide 45Slide 46Slide 47Slide 48Slide 49Slide 50Slide 51Slide 52Slide 53Slide 54Slide 55Slide 56Slide 57Slide 58Slide 59Slide 60Slide 61Slide 62Slide 63Slide 64Slide 65Slide 66Slide 67Slide 68Slide 69Slide 70Slide 71Slide 72Slide 73Slide 74Slide 75Slide 76Slide 77Slide 78Slide 79Slide 80Slide 81Slide 82Slide 83Slide 84Slide 85Slide 86Slide 87Slide 88Slide 89Slide 90Slide 91Slide 92Slide 93Slide 94Slide 95Slide 961Introduction to Comer Chapter 10Protocol Layering2Figure 2.2 Ethernet Frame Format0800Figure 6.6 Encapsulation of IP datagram in frameIP Datagram3Application ApplicationApplication ApplicationL4 Transport LayerL4 Transport LayerPort ?Port 69Port 25Port ?138.26.66.64Chapter 6 – Internet Protocol: Connectionless Datagram DeliveryChapter 6 was about this levelTCPThink of the port number as an extension to the IP address:<netID> <hostID> <port>If needed, reliability can also be provided in Layer 45Fig 10.1 – Conceptual organization of protocol software in layers6Fig 10.5 – The four layers of TCP/IP software above the hardware layer1234510.7 The Protocol Layering PrincipleLayered protocols are designed so that layer n at the destination receives exactly the same object sent by layer n at the source.7Fig 10.6 – Path of a message from application to applicationSender and receiver on same network – no routers involved.8Fig 10.7 – The layering principle when a router is involvedSender and receiver on different networks9Routers don’t care what is in the DATA fieldFig 6.3 – IP datagram formatEverything a router needs is in the IP datagram header.10Fig 10.9 Two important boundaries in the TCP/IP model10.9 Two Important Boundaries in the TCP/IP Model11Fig 7.4ARP IS NOT PART OF IP !!1210.11 Multiplexing and DemultiplexingSending SideMultiple applications pass down messages, which merge into a IP single stream.This is called “multiplexing”Receiving SideDatagrams in the stream are routed to the correct destination application“Demultiplexing”Imagine several applications in one computer sending a stream of messages to the same destination computer.130800IP DatagramL2L314TCPTCPUDP UDP17615Fig. 10.10Fig. 10.11Layer 2Layer 3Layer 4Layer 3176We are only at layer 4! Need one more stage of demultiplexing0800080616Fig.11.1Fig.11.411.4 Format of UDP Messages11.6 UDP Encapsulation and Protocol Layering17The IP layer is responsible only for transferring data between a pair of hosts on an internet, while the UDP layer is responsible only for differentiating among multiple sources or destinations within one host.11.8 UDP Multiplexing, Demultiplexing, and Ports11.7 Layering and the UDP Checksum Computation Omit section18Fig.11.5Fig. 10.11How does the sending application know what port is used by the receiving application?Think of UDP port as a queue.19At request-sending time the client does need to know the port number being used by the application on the server.Until sending reply the server does not need to know the port number being used by the client -- -- the server can get the client port number from the incoming UDP header.Client initiates exchange with request, server responds with reply.20Port numbers below 1024 are permanently assigned and are well-known.These are used by “standard” servers.Port numbers above 1024 are available for dynamic use by clients.These are called “random” or “ephemeral.”11.9 Reserved and Available UDP Port Numbers21Figure 11.611.9 Reserved and Available UDP Port Numbers - continued22Figure 11.5 modified23Fig 20.1691027Chapter 20 – Client-Server Model of Interaction1027The particular client/server protocol that we explore in Lab Session #2 is the Trivial File Transfer Protocol (TFTP)24TFTP application runs on top of UDP (UNRELIABLE!)The sending side transmits a file in fixed-size blocks (512 octets) and awaits acknowledgement for each block before sending the next.The receiver acknowledges each block upon receipt.Blocks of the file are numbered consecutively, starting at 1 ACK specifies number of block being acknowledged A block of fewer than 512 octets signals the end of the file.25.12 TFTPSender uses acknowledgment, timeout and retransmission to ensure that the data arrive (RELIABLE!)25Fig 25.22627Lab Session 2UDP, TFTP, and Wi-Fi NetworksUse TFTP on a Client to Read a File from a ServerMeasuring the Speed of TFTP Use TFTP to Write a File to the Server LEFT as client, RIGHT as serverRIGHT as client, LEFT as server28Frame 3 client -> TFTP serverEthernet IIInternet Protocol Source: 192.168.1.1 Destination: 192.168.1.2User Datagram Protocol Source port: 1027 Destination port: tftp (69) Length: 26 Checksum: 0x9b11 (correct)Trivial File Transfer Protocol Opcode: Read Request (1) Source File: milton Type: netasciiFrame 4 TFTP server -> clientEthernet IIInternet ProtocolUser Datagram Protocol Source port: 1025 Destination port: 1027 Length: 466 Checksum: 0x9a36 (correct)Trivial File Transfer Protocol Opcode: Data Packet (3) Block: 1 Data (454 bytes)Frame 5 client -> TFTP serverEthernet IIInternet ProtocolUser Datagram Protocol Source port: 1027 Destination port: 1025 Length: 12 Checksum: 0x7479 (correct)Trivial File Transfer Protocol Opcode: Acknowledgement (4) Block: 129Lab Session 2 - continuedUDP, TFTP, and Wi-Fi NetworksAdvertising a Wi-Fi “Infrastructure” network Probe RequestRIGHT joining a Wi-Fi “Infrastructure” network Authentication RequestAssociation Request Pinging between RIGHT and the AP Repeat TFTP Experiment using Wireless LinkBeacon frames30tftp 192.168.1.2TFTP client invites input: get milton User keys in:tftp>User keys in:TFTP client generates messageDestination IP address?Consider user in lab wanting to get remote file using TFTP31Still considering sending side:From Comer page 162, discussing TCP:“The transport software divides the stream of data being transmitted into small pieces (sometimes called packets) and passes each packet along with a destination address to the next layer for transmission.”Same applies to UDPIP dest addr32 192.168.1.2TFTP client invites input: