COTN 1220 Data Communication PDF

COTN 1220 – Data Communication Making Connections 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...

COTN 1220 – Data Communication Making Connections 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 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 Characteristics of Interface 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) ANSI (American National Standards Institute) Characteristics of Interface Standards De facto standards Created by other groups that are not official standards but because of their widespread use, become “almost” standards Like Clorox™ for bleach Characteristics of Interface Standards There are four possible components to an interface standard: 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 Two Important Interface Standards In order to better understand the components of an interface, let’s examine two interface 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 An Early Standard: EIA-232F Originally named RS-232 (1962) but has gone through many revisions EIA-232F also used the definitions DTE and DCE An example of a DTE, or data terminating equipment, is a computer An example of a DCE, or data circuit-terminating equipment, is some form of modem What is meant by duplexity? EIA-232F defines a full-duplex connection. What does this mean? A full-duplex connection transmits data in both directions and at the same time A half-duplex connection transmits data in both directions but in only one direction at a time A simplex connection can transmit data in only one direction 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 can support 12 Mbps USB 2.0 can support 480 Mbps USB 3.0 can support 20 GBs (v3.2 Gen 2x2) USB 4.0 can support 40 GBs Universal Serial Bus (USB) (continued) Universal Serial Bus (USB) (continued) Universal Serial Bus (USB) (continued) 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 FireWire Low-cost digital interface Capable of supporting transfer speeds of up to 800 Mbps Hot pluggable Supports two types of data connections: Asynchronous connection Isochronous connection 4-conductor (left) and 6-conductor (right) FireWire 400 alpha connectors Thunderbolt Digital interface currently found on Apple products Capable of supporting transfer speeds of up to 10 Gbps Uses same connector as existing Mini DisplayPort and similar protocol as PCI Express Can daisy-chain devices and may get even faster with later versions Lightning Newer digital interface currently found on Apple products Replaces the older 30-pin connector found on devices such as iPhones with a new 8-pin connector Cannot be plugged in backwards 30-pin connector Lightning 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 80-pin Single Connector Attachment (SCA) InfiniBand and 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 InfiniBand and Fibre Channel 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 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 Asynchronous Connections (continued) An ASCII character in 8-bit ASCII encoding is 8 bits (1 byte), though it can fit in 7 bits. Asynchronous Connections (cont.) Asynchronous Connections (cont.) 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 Asynchronous Connections (continued) How they maintain synchronization? Frame size—The small size means that it should not be difficult for the receiver to stay synchronized for that short of a period. Start bit—When the receiver recognizes the start bit, the synchronization begins. Because only approximately 8 or 9 bits follow, there will not be a long sequence of unchanging values. 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 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 Terminal-to-Mainframe Computer Connections Terminal-to-Mainframe Computer Connections 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 Terminal-to-Mainframe Computer Connections Making Computer Connections In Action A laptop computer has many different types of connectors, or connections While every laptop can be different, if anyone has a laptop in class, maybe someone will volunteer to use theirs for show-and-tell Making Computer Connections In Action Power cord connection (why does the power cord have a big “brick” on it?) USB connectors (one or more) RJ-11 (telephone jack) RJ-45 (LAN jack) PC Card / SmartCard DisplayPort (to connect your laptop to a video device) Media card slot (SD, SDHC, xD, etc) DB-15 (to connect to an external monitor or video projector) Making Computer Connections In Action 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 * 10 bits/char (7 bits data + start + stop + parity) = 7,000,000 bits Making Computer Connections In Action If a synchronous connection is used, assume maximum payload size – 1500 bytes (MTU) To transfer a 700K char file requires 467 frames 700,000 𝑐ℎ𝑎𝑟 (1 𝑏𝑦𝑡𝑒 𝑒𝑎𝑐ℎ) ¯ = 466. 6 𝑓𝑟𝑎𝑚𝑒𝑠 1500 𝑏𝑦𝑡𝑒𝑠 Making Computer Connections In Action Each frame will also contain 3-byte header, 2-byte checksum, and 1-byte delimiter, thus 6 bytes overhead 1500-bytes payload + 6-bytes overhead = 1506-bytes frames 1506 𝑏𝑦𝑡𝑒𝑠 467 𝑓𝑟𝑎𝑚𝑒𝑠 𝑥 = 703,302 𝑏𝑦𝑡𝑒𝑠 𝑜𝑟 5,626,416 𝑏𝑖𝑡𝑠 𝑓𝑟𝑎𝑚𝑒 Significantly less data using synchronous connection https://www.youtube.com/watch?v=SLjjgjp2bAA Summary Connection between a computer and a peripheral is often called the interface Process of providing all the proper interconnections between a computer and a peripheral is called interfacing The interface between computer and peripheral is composed of one to four components: electrical, mechanical, functional, and procedural A DTE is a data terminating device Computer A DCE is a data circuit-terminating device Modem Summary (cont.) Half-duplex systems can transmit data in both directions, but in only one direction at a time Full-duplex systems can transmit data in both directions at the same time Other peripheral interfacing standards that provide power, flexibility, and ease-of-installation include FireWire, Lightning, SCSI, iSCSI, InfiniBand, and Fibre Channel Summary (continued) While much of an interface standard resides at the physical layer, a data link connection is also required when data is transmitted between two points on a network Three common data link connections include asynchronous connections, synchronous connections, and isochronous connections Asynchronous connections use single-character frames and start and stop bits to establish the beginning and ending points of the frame Summary (cont.) Synchronous connections use multiple-character frames, sometimes consisting of thousands of characters Isochronous connections provide real-time connections between computers and peripherals and require a fairly involved dialog to support the connection A point-to-point connection is one between a computer terminal and a mainframe computer that is dedicated to one terminal A multipoint connection is a shared connection between more than one computer terminal and a mainframe computer