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Chapter 4 Making Connections

Chapter 4 Making Connections. Introduction. Examine the interface between a computer and a device. This interface occurs at the physical layer. Connecting peripheral devices to a computer (called interface) has, in the past, been a fairly challenging task.

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Chapter 4 Making Connections

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  1. Chapter 4Making Connections

  2. Introduction • Examine the interface between a computer and a device. This interface occurs at the physical layer. • Connecting peripheral devices to a computer (called interface) has, in the past, been a fairly challenging task. • Newer interfaces have made this task much easier. • Interface standards define modes of transmission: • Serial/parallel • Simplex/duplex • Asynchronous/synchronous • Point-to-point/multi-point

  3. Standards Organizations • International Telecommunications Union (ITU) (formerly CCITT) • Electronics Industries Association (EIA) • Institute for Electrical and Electronics Engineers (IEEE) • International Organization for Standards (ISO) • American National Standards Institute (ANSI)

  4. DCEs and DTEs • Communication circuits can be defined in terms of the devices that are designed to transmit signals on a circuit, and the destination • DCE - Data communicating equipment: • The device that forwards the signals being sent along a particular circuit, e.g., a Modem • DTE – Data terminating equipment: • The device to which the signal is being directed, e.g., a computer

  5. Interface Standards • Electrical: • Voltages, line capacitance, and other electrical characteristics • Mechanical: • Connector or plug description • Functional: • Function of each pin or circuit that is used in a particular interface • Procedural: • How the particular circuits are used to perform an operation • For example, the functional component may describe two circuits, Request to Send and Clear to Send • The procedural component describes how those two circuits are used so that the DTE can transfer data to the DCE

  6. Two Important Standards • EIA-232F – an older standard originally designed to connect a modem to a computer. • USB (Universal Serial Bus) – a newer standard that is much more powerful than EIA-232F

  7. EIA-232F • Older interface standard designed to connect a device such as a modem to a computer or terminal. • 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. • The functional and procedural components are defined by the V.24 standard.

  8. Serial & Parallel

  9. Data flow • Circuits can be designed to permit data to flow in one or both directions: • Simplex • One-way transmission • Half-duplex • Two-way communication link, but only one system can “talk” at a time • Full duplex • Transmit in both directions simultaneously

  10. Universal Serial Bus (USB) • 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 1.0 – 12 Mbps; Use 2.0 – 480 Mbps; USB 3.0 – 4.8 Gbps. • 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). • 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.

  11. FireWire • Low-cost digital interface • Capable of supporting transfer speeds of up to 400 Mbps • Hot pluggable • Supports two types of data connections: • Asynchronous connection • Isochronous connection

  12. SCSI and iSCSI • SCSI (Small Computer System Interface) • 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. • Need SCSI adapter. • iSCSI (Internet SCSI) • A technique for interfacing disk storage to a computer via the Internet. • It looks like the disk storage is down the hall, but it could be anywhere on the Internet.

  13. InfiniBand & Fibre Channel • InfiniBand – a serial connection or bus 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 • Fibre Channel – also a serial, high-speed network that connects a computer to multiple input/output devices • Supports data transfer rates up to billions of bits per second, but can support the interconnection of up to 126 devices only

  14. Asynchronous Connections • A type of connection defined at the data link layer. • No “clocking signal” to say when a frame starts or ends, so, how does the receiver know when a frame starts or ends? • Add a Start bit, while a Stop bit is added to the end of the frame. • An optional parity bit can be added to the frame which can be used to detect errors. • Used in slower, cheaper equipment, because of start/stop overhead.

  15. Synchronous Connections • A second type of connection defined at the data link layer. • A synchronous connection creates a large package (frame) that consists of header and trailer flags, control information, optional address information, error detection code (checksum), and the data. • A synchronous connection is more elaborate but transfers data in a more efficient manner.

  16. 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

  17. Terminal-to-Mainframe (I) • A point-to-point connection is a direct, unshared connection between a terminal and a mainframe computer. • A multipoint connection is a shared connection between multiple terminals and a mainframe computer. • The mainframe is called the primary, and each terminal is called a secondary.

  18. Terminal-to-Mainframe (II) • 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

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