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Network Standards

Network Standards. Chapter 2 Updated January 2009 Raymond Panko’s Business Data Networks and Telecommunications , 7th edition May only be used by adopters of the book. Introduction. Five components of data communication. Message Sender Receiver Medium Protocol.

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Network Standards

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  1. Network Standards Chapter 2Updated January 2009 Raymond Panko’sBusiness Data Networks and Telecommunications, 7th edition May only be used by adopters of the book

  2. Introduction Five components of data communication • Message • Sender • Receiver • Medium • Protocol

  3. Data flow (simplex, half-duplex, and full-duplex)

  4. DATA FLOW/ Transmission Modes Simplex mode: The communication is unidirectional, as on one way street. Only one of the two devices on a link can transmit. For Example, Television Half-Duplex mode:Each station can both transmit and receive, but not at the same time. When one device is sending, the other can only receive, and vice versa. Full-Duplex mode: In full-duplex mode, both stations can transmit and receive simultaneously. For Example, Telephone Network

  5. 2-1: Network Standards Message 2-5 • Network Standards (Protocols) • Network standards govern the exchange of messages between different host computers, including message order, semantics, syntax, reliability, and connection orientation • Computers are not intelligent, so standards must be very rigid

  6. 1.Message Standards (Protocols) Message syntax Message semantics Message order

  7. 2-1: Network Standards • NetworkStandards Govern • Message Syntax (organization) • Like human grammar • Header, data field, and trailer (Figure 2-2) • Message semantics (meaning) • HTTP request message: “Please give me this file” • HTTP response message: Here is the file. (Or, I could not comply for the following reason) • Message order • Turn taking, order of messages in a complex transaction, who must initiate communication, etc.

  8. 2-2: General Message Organization • General Message Syntax (Organization) • Primary parts of messages • Data Field (content to be delivered) • Header (everything before the data field) • Trailer (everything after the data field) • The header and trailer act like a delivery envelope for the data field Trailer Data Field Header

  9. 2-2: General Message Organization • General Message Syntax (Organization) • Header and trailer are further divided into fields Trailer Data Field Header Destination Address Field is Used by Switches and Routers Like the Address on an Envelope Message with all three parts

  10. 2-2: General Message Organization Data Field Header Message without a trailer Other Header Field Destination Address Field

  11. 2-2: General Message Organization Header Other Header Field Destination Address Field Message with only a header e.g. TCP supervisory messages are pure headers (there is no data field content to deliver)

  12. 2.Reliability Error Detection and Correction

  13. 2-3: Reliable Transmission Control Protocol (TCP) Session • TCP enables two hosts to establish a connection and exchange streams of data. • Provides guarantee that packets delivered • Provide two-way (full duplex) communication

  14. 2-3: Reliable Transmission Control Protocol (TCP) Session 2 • The Transmission Control Protocol (TCP) is an important standard in Internet transmission • TCP • Receiver acknowledges each correctly-received TCP message (called a TCP segment) • If an acknowledgments is not received by the sender, the sender retransmits the TCP segment • This gives reliability: error detection AND error correction

  15. TCP { Source Destination Can I talk to you? Establish connection. OK. Can I talk to you? OK. { Here’s a packet. Send packet with acknowledgment. Got it. { Here’s a packet. Resend packet if no (or delayed) acknowledgment. Here’s a resent packet. Got it.

  16. 2-3: Reliable TCP Session 1 Client PC TCP Process Webserver TCP Process 4. Data = HTTP Request 5. ACK (4) Carry HTTP Req & Resp (4) 6. Data = HTTP Response TCP Segment (Message) 4Carries an HTTP Request Segment 5 Acknowledges It There Is No Need to Resend 7. ACK (6) Request-Response Cycle for Data Transfer

  17. 2-3: Reliable TCP Session 3 Client PC TCP Process Webserver TCP Process 8. Data = HTTP Request (Error) No receipt, so so no ACK Carry HTTP Req & Resp (4) 8. Data = Retransmits HTTP Request because No ACK was received 9. ACK (8) Error Handling

  18. Unreliable Protocols Message • HTTP is an unreliable protocol • If an HTTP message is lost, there is no retransmission • Some protocols detect errors, dropping incorrect messages • There is no retransmission, so these protocols are unreliable • There must be both error detection and error correction for a protocol to be reliable

  19. 3.Connection-Oriented andConnectionless Protocols

  20. 2-4: Connection-Oriented and Connectionless Protocols In TCP Client PC TCP Process Webserver TCP Process Connection-Opening Messages Messages During the Connection Time Connection-Closing Messages Connection-oriented protocols have formal openings and closings, like human telephone calls

  21. A B Open Connection 2-4: Connection-Oriented and Connectionless Protocols 4 Connection-Oriented Protocol Connectionless Protocol A B Message (No Sequence Number) Message with Sequence Number A1 Connectionless protocols, like HTTP simply send messages without prior connection openings and without subsequent connection closings Connection-oriented protocols give each message a unique sequence number Message with Sequence Number B1 Message with Sequence Number A2 Close Connection

  22. 4.The Hybrid TCP/IP-OSI Standards Architecture

  23. Standards Architecture The dominant architecture today is the hybrid TCP/IP-OSI standards architecture shown in the next slide

  24. Figure 2-8: Hybrid TCP/IP-OSI Architecture

  25. 2-7: Physical and Data Link Layer Standards in a Switched or Wireless Network 1 A data link is a frame’s path though a single switched or wireless network: A-R1 (host-router) A physical link is a connection between two devices: A-X1 (host-switch), X1-X2 (switch-switch), X2-R1 (switch-router)

  26. 2-7: Physical and Data Link Layer Standards in a Switched or Wireless Network • Physical Layer • Physical layer standards govern transmission between adjacent devices connected by a transmission medium Host A Physical Link A-X1 Switch X1

  27. 2-7: Physical and Data Link Layer Standards in a Switched or Wireless Network • Data Link Layer • Data link layer standards govern the transmission of frames across a single network—typically by sending them through several switches along the data link Frame Data Link A-B Host B Switch X1 Host A Switch X2

  28. 2-8: Internet and Data Link Layers in a Routed Network • Internet Layer • Internet layer standards govern the transmission of packets across an internet—typically by sending them through several routers along the route

  29. 2-8: Internet and Data Link Layers in a Routed Network 3 Host A Data Link A-R1 R1 Network X 3 Data Links: One per Network Network Y Data Link R1-R2 1 Route through the internet Route A-B Network Z R2 Host B Data Link R3-B

  30. 2-8: Internet and Data Link Layers in a Routed Network Frame X Packet In Network X: Two destination addresses: Packet: Host B (destination host) Frame: Router R1 Data Link A-R1 Switch Host A Switch Server Station Switch X1 Mobile Client Station Switch X2 Route A-B Router R1 Network X

  31. 2-8: Internet and Data Link Layers in a Routed Network To Network X Route A-B Router R1 Frame Y Data Link R1-R2 In Network Y: Two destination addresses: Packet: Host B (destination host) Frame: Router R2 Packet Router R2 Network Y To Network Z

  32. 2-8: Internet and Data Link Layers in a Routed Network Frame Z Packet Data Link R2-B Switch Z1 Host B Router R2 Switch Z2 Mobile Client Stations Switch X2 Router Network Z

  33. 2-9: Internet and Transport Layers Standards • Transport Layer • Transport layer standards govern aspects of end-to-end communication between two end hosts that are not handled by the data link layer • These standards also allow hosts to work together even if the two computers are from different vendors and have different internal designs

  34. 2-9: Internet and Transport Layers Standards 1 The transport layer adds functionality for the two hosts to talk with each other to fix errors and do other things The internet layer carries packets on the route between the two hosts, across a series of routers. There will be many hops across pairs of routers, so internet layer protocols are kept very simple to reduce cost

  35. 2-9: Internet and Transport Layers Standards 1 The transport layer adds functionality for the two hosts to talk with each other to fix errors and do other things Transport Layer End-to-End (Host-to-Host) TCP is reliable and connection-oriented UDP is unreliable and connectionless Internet Layer Hop-by-Hop (Router to Router) IP is connectionless and unreliable The internet layer carries packets on the route between the two hosts, across a series of routers. There will be many hops across pairs of routers, so internet layer protocols are kept very simple to reduce cost

  36. 2-10: Application Layer Standards • Application Layer Standards • Govern how two applications work with each other, even if they are from different vendors • There are many application layer standards because there are many applications • World Wide Web (HTTP) • E-Mail (SMTP, POP, etc.) • FTP (FTP) • Database (ODBC) • etc.

  37. Standards Layers: Recap • Application (5) • Transport (4) • Internet (3) • Data Link (2) • Physical (1)

  38. 6.Reliability Options at the Transport Layer TCP versus UDP

  39. 2-14: TCP and UDP at the Transport Layer • Reliability Is Expensive • Not all applications need reliability • Voice over IP cannot wait for lost or damaged packets to be retransmitted • Network management protocols need to place as low a burden on the network as possible • Both types of applications use the simpler User Datagram Protocol (UDP) instead of TCP

  40. 2-14: TCP and UDP at the Transport Layer *Note: TCP and UDP are the only transport-layer protocols

  41. 7.Vertical Communication Between Layer Processes on the Same Host

  42. 2-15: Layered Communication on the Source Host

  43. 2-15: Layered Communication on the Source Host 2 The process begins when a browser creates an HTTP request message Application Process HTTP Message Passes Message Down to Transport Process HTTP Message Fragment 3 HTTP Message Fragment 2 Transport Process HTTP Message Fragment 1 If the application message is long, the transport process will first fragment it into fragments small enough to fit into single packets

  44. 2-15: Layered Communication on the Source Host The process begins when a browser creates an HTTP request message Application Process HTTP Message Passes Message Down to Transport Process Transport Process HTTP Message TCP Hdr Encapsulation of HTTP Message in Data Field of TCP Segment by adding a TCP header

  45. 2-15: Layered Communication on the Source Host • When a layer process (N) creates a message, it passes it down to the next-lower-layer process (N-1) immediately • The receiving process (N-1) will encapsulate the Layer N message, that is, place it in the data field of its own (N-1) message

  46. 2-15: Layered Communication on the Source Host 1 The transport process then passes the message down to the internet layer process Transport Process HTTP Message TCP Hdr Internet Process HTTP Message TCP Hdr IP Hdr The internet layer process encapsulates The TCP segment in the data field of an IP Packet

  47. 2-15: Layered Communication on the Source Host 1 Internet Process HTTP Message TCP Hdr IP Hdr Data Link Process Eth Trlr HTTP Message TCP Hdr IP Hdr Eth Hdr Encapsulation of IP Packet in Data Field of Ethernet Frame

  48. 2-15: Layered Communication on the Source Host 1 Data Link Process Eth Trlr HTTP Message TCP Hdr IP Hdr Eth Hdr The data link process passes the frame down to the physical layer Physical Process Physical Layer converts the bits of the frame into signals. There are no messages at the physical layer, so there is no encapsulation at the physical layer

  49. 2-15: Layered Communication on the Source Host Recap

  50. 2-15: Layered Communication on the Source Host 4 The following is the final frame for an HTTP message on an Ethernet LAN Eth Trlr HTTP Message TCP Hdr IP Hdr Eth Hdr L2 L5 L4 L3 L2 Notice the Pattern: From Right to Left: L2, L3, L4, L5, maybe L2 Start with the highest-layer message (in this case, 5) Add headers for each lower layer (L4, L3, and L2, in this case) Don’t forget the possible trailing L2 trailer

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