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Chapter Four

Chapter Four. Making Connections Data Communications and Computer Networks: A Business User’s Approach, Fourth Edition. After reading this chapter, you should be able to:. List the four components of all interface standards

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Chapter Four

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  1. Chapter Four Making Connections Data Communications and Computer Networks: A Business User’s Approach, Fourth Edition

  2. After reading this chapter, you should be able to: • List the four components of all interface standards • Discuss the basic operations of the USB and EIA-232F interface standards • Cite the advantages of FireWire, SCSI, iSCSI, InfiniBand, and Fibre Channel interface standards • Outline the characteristics of asynchronous, synchronous, and isochronous data link interfaces Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  3. After reading this chapter, you should be able to (continued): • Recognize the difference between half-duplex and full-duplex connections • Identify the operating characteristics of terminal-to-mainframe connections and why they are unique compared to other types of computer connections Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  4. Introduction • Connecting peripheral devices to a computer has, in the past, been a fairly challenging task • Newer interfaces have made this task much easier • Let’s examine the interface between a computer and a device • This interface occurs primarily at the physical layer Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  5. Interfacing a Computer to Peripheral Devices • The connection to a peripheral is often called the interface • The process of providing all the proper interconnections between a computer and a peripheral is called interfacing Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  6. Characteristics of Interface Standards • There are essentially two types of standards • Official standards • Created by standards-making organizations such as ITU (International Telecommunications Union), IEEE (Institute for Electrical and Electronics Engineers), EIA (Electronic Industries Association), ISO (International Organization for Standardization), and ANSI (American National Standards Institute) • De facto standards • Created by other groups that are not official standards but because of their widespread use, become “almost” standards Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  7. Characteristics of Interface Standards (continued) • There are four possible components to an interface standard: • Electrical component • Mechanical component • Functional component • Procedural component Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  8. Characteristics of Interface Standards (continued) • Four components • Electrical component – deals with voltages, line capacitance, and other electrical characteristics • Mechanical component – deals with items such as the connector or plug description • Functional component – describes the function of each pin or circuit that is used in a particular interface • Procedural component – describes how the particular circuits are used to perform an operation Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  9. Important Interface Standards • EIA-232F – an older standard originally designed to connect a modem to a computer • USB-2 (Universal Serial Bus-2) – a newer standard that is more powerful than EIA-232F • I-1394 (Firewire) – another newer standard that is much more powerful than EIA 232F but has different focus in functionality than USB • (Ulra)-IDE, (Ultra)SCSI, FC-AL – internal PC buses Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  10. EIA-232F • Originally named RS-232 but has gone through many revisions • The electrical component is defined by another standard: V.28 • The mechanical component is often defined by ISO 2110, the DB-25 connector. The DB-9 connector is now more common than the DB-25. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  11. EIA-232F (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  12. EIA-232F (continued) • The functional and procedural components are defined by the V.24 standard • For example, V.24 defines the function of each of the pins on the DB-9 connector, as shown on the next slide Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  13. EIA-232F (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  14. EIA-232F (continued) • The next slide shows an example of the procedural dialog that can be used to create a connection between two endpoints • Note the level of complexity needed to establish a full-duplex connection Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  15. EIA-232F (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  16. EIA-232F (continued) • A half-duplex connection transmits data in both directions but in only one direction at a time • A full-duplex connection transmits data in both directions and at the same time • A simplex connection can transmit data in only one direction Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  17. Universal Serial Bus (USB) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  18. Universal Serial Bus (USB) (continued) • The USB interface is a modern standard for interconnecting a wide range of peripheral devices to computers • Supports plug and play • Can daisy-chain multiple devices • USB 2.0 can support 480 Mbps (USB 1.0 is only 12 Mbps) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  19. Universal Serial Bus (USB) (continued) • The USB interface defines all four components • The electrical component defines two wires VBUS and Ground to carry a 5-volt signal, while the D+ and D- wires carry the data and signaling information • The mechanical component precisely defines the size of four different connectors and uses only four wires (the metal shell counts as one more connector) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  20. Universal Serial Bus (USB) (continued) • The USB standard uses the NRZI combined with 4B/5B bit stuffing scheme • USB networks use a tiered-star topology – Hubs up to 16 devices but can be chained so no limit on the number of devices. • The functional and procedural components are fairly complex but are based on the polled bus • The computer takes turns asking each peripheral if it has anything to send Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  21. Universal Serial Bus (USB): functions, endpoints, pipes • USB device can be used as a host, peripheral device, hub, or host controller. Each use has associated functions. These can be seen as USB devices which provide a capability (or function) such as a Printer, FAX, scanner, etc. • Endpoints are sources/sinks of data. As the bus is host centric, endpoints occur at the end of the communications channel at the USB function. • Client software transfers data through pipes. A pipe is a logical connection between the host and an endpoint or (endpoints). Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  22. Universal Serial Bus (USB): addressing Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  23. Universal Serial Bus (USB): transactions Each USB transaction consists of • Token Packet: header that defines what it expects to follow, • (Optional) Data Packet: contains the data (payload) • Status Packet: used to acknowledge transactions and to provide a means of error correction Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  24. Universal Serial Bus (USB): a scenario for control function Setup Stageis where the request is sent. • The setup token that contains the address and endpoint number is sent first. • The data packet is sent next. It contains a setup packet which details the type of request. • The last packet is a handshake used for acknowledging successful receipt or to indicate an error. If the function successfully receives the setup data (CRC, PID, etc. are OK) it responds with ACK, otherwise it ignores the data and doesn’t send a handshake packet. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  25. Universal Serial Bus (USB): a scenario for control function (continued) Data Stage: is where IN or OUT data transfers happen (one or multiple – determined by amount of data requested by SETUP packet). • IN:The host is ready to receive control data, it issues an IN Token. Reply can be a DATA packet containing the control data, a STALL packet indicating an error at the endpoint or a NAK packet indicating that the endpoint is OK, but temporary has no data to send. • OUT:The host needs to send a control data packet, it issues an OUT token followed by a data packet containing the control data. If the function's endpoint buffer got the data OK the endpoint issues an ACK, if endpoint is busy then NAK, if error then STALL. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  26. Universal Serial Bus (USB): a scenario for control function (continued) Status Stagereports the status of the overall request. Status reporting is always performed by the function. • IN:If the host sent IN token during the data stage, the host acknowledges the successful receipt of this data by sending an OUT token followed by a zero length data packet. An ACK indicates the function has completed the command. If an error occurred during the processing of this command, the function issues a STALL. If the function is still processing the command, it returns a NAK indicating to the host to repeat the status stage later. • OUT:If the host sent OUT token during the data stage, the function acknowledges the receipt of data by sending a zero length packet in response to an IN token issued by the host. If an error occurred during processing, the function issues a STALL. If it is still busy processing data, it issues a NAK asking the host to retry the status stage later. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  27. Universal Serial Bus (USB) (continued) Supports three types of data transfers: • Interrupt (asynchronous) transfers: • Guaranteed Latency • Stream Pipe - Unidirectional • Error detection and next period retry. • Isochronous transfers • Guaranteed access to USB bandwidth. • Bounded latency. • Stream Pipe - Unidirectional • Error detection via CRC, but no retry or guarantee of delivery. • Full & high speed modes only. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  28. Universal Serial Bus (USB) (continued) • Bulk transfers • Used to transfer large bursty data. • Error detection via CRC, with guarantee of delivery. • No guarantee of bandwidth or minimum latency. • Stream Pipe - Unidirectional • Full & high speed modes only. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  29. FireWire • Low-cost digital interface (non-polled, peer-to-peer device network) – 63 peripherials. • Capable of supporting transfer speeds of up to 400 Mbps • Hot pluggable, daisy-chainable. • Supports two types of data connections: • Asynchronous connection • Isochronous connection • Uses Serial Bus Protocol – 2 (for more see FireWire Concepts) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  30. FireWire functions Identification: When a device is plugged in, it immediately broadcasts its unique identification number to other devices on the network and becomes part of that network. • Asynchronous mode transfer: The address of both the sender and the receiver is transmitted followed by the actual packet data. Once the receiver accepts the packet, a packet acknowledgment is returned to the original sender. To improve throughput, the sender may continue transmission until 64 transactions are outstanding. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  31. FireWire functions (continued) • Isochronous mode transfer: The sender requests an isochronous channel by introducing a request token into a time slot that must not be disrupted by peers. Channel IDs are transmitted followed by the packet data. The receiver monitors the incoming data's channel ID and accepts only data with the specified ID, 64 isochronous channels may be defined. Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  32. SCSI and iSCSI • SCSI (Small Computer System Interface)- a protocol of 64 commands. Initially, parallel bus (8 bits)- uses Low Voltage Differential signaling: • A technique for interfacing a computer to high-speed devices such as hard disk drives, tape drives, CDs, and DVDs • Designed to support devices of a more permanent nature: SCSI is a systems interface (for more information see what is SCSI?) • iSCSI (Internet SCSI) • A technique for interfacing disk storage to a computer via the Internet Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  33. InfiniBand and Fibre Channel • InfiniBand – a serial connection or switched bus connection that can carry multiple channels of data at the same time • Can support data transfer speeds of 2.5 billion bits (2.5 gigabits) per second and address thousands of devices, using both copper wire and fiber-optic cables • A network of high-speed links and switches (for more see High Performance Computing- SW fabric and What is InfiniBand?) • Fibre Channel- Arbitrated Loop (FC-AL) – also a serial, high-speed network that connects a computer to multiple input/output devices. Designed for RAID at a speed 400 MBYTES/s. • Supports data transfer rates up to billions of bits per second, but can support the interconnection of up to 126 devices only (for more see Arbitrated loop and What is FC-AL?) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  34. Interface speeds • standard parallel port: 115kBYTES/s (.115MBYTES/s) • Original USB: 12Mbits/s (1.5MBYTES/s) • ECP/EPP parallel port: 3MBYTES/s • IDE: 3.3-16.7MBYTES/s • SCSI-1: 5MBYTES/s • SCSI-2 (Fast SCSI, Fast Narrow SCSI): 10MBYTES/s • Fast Wide SCSI (Wide SCSI): 20MBYTES/s • Ultra SCSI (SCSI-3, Fast-20, Ultra Narrow): 20MBYTES/s • UltraIDE: 33MBYTES/s Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  35. Interface speeds (continued) • Wide Ultra SCSI (Fast Wide 20): 40MBYTES/s • Ultra2 SCSI: 40MBYTES/s • IEEE-1394: 100-400Mbits/s (12.5--50MBYTES/s) • Hi-Speed USB: 480Mbits/s (60MBYTES/s) • Wide Ultra2 SCSI: 80MBYTES/s • Ultra3 SCSI: 80MBYTES/s • Wide Ultra3 SCSI: 160MBYTES/s • FC-AL Fiber Channel: 100-400MBYTES/s • Infini-BAND: 2.5 Gbits/s (312MBYTES/s) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  36. Asynchronous Connections • A type of connection defined at the data link layer • To transmit data from sender to receiver, an asynchronous connection creates a one-character package called a frame • Added to the front of the frame is a start bit, while a stop bit is added to the end of the frame • An optional parity bit can be added which can be used to detect errors Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  37. Asynchronous Connections (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  38. Asynchronous Connections (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  39. Asynchronous Connections (continued) • The term asynchronous is misleading here because you must always maintain synchronization between the incoming data stream and the receiver • Asynchronous connections maintain synchronization by using small frames with a leading start bit Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  40. Synchronous Connections • A second type of connection defined at the data link layer • A synchronous connection creates a large frame that consists of header and trailer flags, control information, optional address information, error detection code, and data • A synchronous connection is more elaborate but transfers data in a more efficient manner Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  41. Synchronous Connections (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  42. Isochronous Connections • A third type of connection defined at the data link layer used to support real-time applications • Data must be delivered at just the right speed (real-time) – not too fast and not too slow • Typically an isochronous connection must allocate resources on both ends to maintain real-time • USB and Firewire can both support isochronous Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  43. Terminal-to-Mainframe Computer Connections • Point-to-point connection – a direct, unshared connection between a terminal and a mainframe computer • Multipoint connection – a shared connection between multiple terminals and a mainframe computer • The mainframe is the primary and the terminals are the secondaries Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  44. Terminal-to-Mainframe Computer Connections (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  45. Terminal-to-Mainframe Computer Connections (continued) • To allow a terminal to transmit data to a mainframe, the mainframe must poll the terminal • Two basic forms of polling: roll-call polling and hub polling • In roll-call polling, the mainframe polls each terminal in a round-robin fashion • In hub polling, the mainframe polls the first terminal, and this terminal passes the poll onto the next terminal Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  46. Terminal-to-Mainframe Computer Connections (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  47. Making Computer Connections In Action • The back panel of a personal computer has many different types of connectors, or connections: • RS-232 connectors • USB connectors • Parallel printer connectors • Serial port connectors Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  48. Making Computer Connections In Action (continued) Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  49. Making Computer Connections In Action (continued) • 1 and 2 – DIN connectors for keyboard and mouse • 3 – USB connectors • 4 and 6 – DB-9 connectors • 5 – Parallel port connector (Centronics) • 7, 8, and 9 – audio connectors • Will Bluetooth replace these someday? Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

  50. Making Computer Connections In Action (continued) • A company wants to transfer files that are typically 700K chars in size • If an asynchronous connection is used, each character will have a start bit, a stop bit, and maybe a parity bit • 700,000 chars * 11 bits/char (8 bits data + start + stop + parity) = 7,700,000 bits Data Communications and Computer Networks: A Business User's Approach, Fourth Edition

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