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Lecture 04. Making Connection. Introduction. Connection concept Interface concept and standard (Level 1) EIA-232F USB Data Link Connections (Level 2) Terminal-to-mainframe computer connections Application examples. (to p3). (to p35). (to p48). (to p52). Connection concept.

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Lecture 04

Lecture 04

Making Connection


  • Connection concept

    • Interface concept and standard (Level 1)

      • EIA-232F

      • USB

  • Data Link Connections (Level 2)

  • Terminal-to-mainframe computer connections

  • Application examples

(to p3)

(to p35)

(to p48)

(to p52)

Connection concept
Connection concept

  • How computer networks are connected?

(to p4)

Connection concept1
Connection concept

  • Recalled: OSI model – level 1

    • Physical level, which requires peripheral devices to connect two different computers or devices together

    • Termed as “interface”

  • Two types of standards

  • Modes of data flow

  • Connection to systems

(to p7)

(to p8)

(to p9)

(to p14)

(to p5)

Connection cont
Connection (cont.)

(to p18)

  • Characteristics of interface standards

  • Two important interface standards

    • EIA-232F

    • USB (Universal Serial Bus)

  • Other interfacing standards

(to p20)

(to p27)

(to p6)

Other interfacing standards
Other interfacing standards

  • Other peripheral interfacing standards that provide power, flexibility and ease-of-installation include:

    • FireWire (low cost device for digital)

    • SCSI, iSCSC(mainly for permanent storage, CD/DVD)

    • InfiniBand, Fibre Channel (high speed connection)

(to p32)

(to p33)

(to p34)

(to p2)

Lecture 04

Level 2

Level 1

Data terminating equipment

Data communicating equipment

(to p4)

Characteristics of interface standards
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)

      • CSA (Canadian standard), UL (USA for computer hardware)

    • De facto standards

      • Created by other groups that are not official standards but because of their widespread use, become “almost” standards

(to p4)

Data flow
data flow

There are 3 types of data flow:

i) simplex transmission

ii) half-duplex transmission

iii) full duplex transmission

(to p10)

(to p12)

(to p13)

(to p4)

Simplex transmission
simplex transmission

  • i) simplex transmission

    • data is transmitted in one direction only

    • ie no data transmission on opposite direction is allowed

      • see Figure 8-2

    • Application examples?

(to p11)

(to p9)

Lecture 04

(to p10)

(to p12)

(to p13)

Half duplex transmission
half-duplex transmission

  • ii) half-duplex transmission

    • transmission in either direction on a circuit but only one direction at a time

    • eg an inquiry is sent to the computer and then a response is sent back on the same circuit to the terminal

    • Application examples?

(to p11)

(to p9)

Full duplex transmission
full duplex transmission

  • iii) full duplex transmission

    • data transmission in both directions simultaneously on the circuit

    • machine needs to be intelligence at both ends (why?)

    • Application examples?

(to p11)

(to p9)

Connection to the system
connection to the system

  • two types of physical connection in the system

    • i) Parallel data transmission

    • ii) Series data transmission

(to p15)

(to p17)

(to p4)

Parallel data transmission
Parallel data transmission

  • i) Parallel data transmission

    • connected via direct cable that has one wire for each bit in a character of data code being used by the terminal

      • See Figure 8.3

  • with multiple wires, all the bits of a characters can be transmitted between the terminals and computer at once

  • Disadv: very expensive & no practice over long distance (why?)

  • (to p16)

    (to p14)

    Figure 8 3 parallel and serial transmission
    FIGURE 8-3 Parallel and serial transmission.

    (to p15)

    (to p17)

    Lecture 04

    • ii) Series data transmission

      • bits of each character are sent down to a line one after another

      • complicated process because machine needs to know how to decompose and to reconstruct of bits at each respective end

      • Adv or Disadv?

    (to p16)

    (to p14)

    Characteristics of interface standards continued
    Characteristics of Interface Standards (continued)

    • There are four possible components to an interface standard:

      • Electrical component

      • Mechanical component

      • Functional component

      • Procedural component

    (to p19)


    (to p5)

    Characteristics of interface standards continued1
    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

    (to p18)

    Eia 232f

    • EIA-232F – an older standard originally designed to connect a modem to a computer

    • 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.

    (to p21)

    (to p23)

    (to p24)

    Lecture 04

    Worked as full duplex (why?)

    Its functions

    (to p22)

    (to p20)

    Eia 232f continued
    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 Table 4.1

    • Table 4.2 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

    (to p25)

    (to p26)

    (to p5)

    Universal serial bus usb
    Universal Serial Bus (USB)

    • a newer standard that is much more powerful than EIA-232F

    • 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); USB 3.0

    (to p28)

    Universal serial bus usb continued
    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)

    (to p29)

    Universal serial bus usb continued1
    Universal Serial Bus (USB) (continued)

    • Four types of USB connectors

    • 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

    • More on polling near the end of this chapter

    (to p30)

    (to p31)

    (to p5)

    Universal serial bus usb continued3
    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

    • More on polling near the end of this chapter

    (to p29)


    • Low-cost digital interface(real time connection for PC)

    • A FireWire connection lets you send data to and from high-bandwidth digital devices such as digital camcorders, and it's faster than USB

    • Capable of supporting transfer speeds of up to 400 Mbps

    • Hot pluggable

    • Supports two types of data connections:

      • Asynchronous connection

      • Isochronous connection

    (to p6)

    Scsi and iscsi
    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

    (to p6)

    Infiniband and fibre channel
    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

    • 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

    (to p6)

    Data link connections
    Data Link Connections

    • Take place at level 2

    • technique used to transmit data on a comm line

    • two methods could be used to transmit data:

      • i) Asynchronous transmission (Asych)

      • ii) Synchronous transmission (Synch)

      • Iii) Isochronous Connections (Isoch)

    (to p36)

    (to p42)

    (to p47)

    (to p2)

    Asynchronous transmission
    Asynchronous transmission

    i) Asynchronous transmission (Asych)

    Pattern of data presentation:

    • data transmission is sent preceded by an extra bit, called a start bit, and followed by one more extra bit called stop bit (start/stop transmission)

    (to p37)

    Asynchronous transmission1
    Asynchronous transmission

    • Eg:

    • 1 1 0 0 0 0 0 1 0

      represent a A character Stop bit

      start bit or representation of or space bit

      mark bit a code system

    (to p38)

    Alternative presentation

    (to p40)

    Asynchronous connections continued1
    Asynchronous Connections (continued)

    Send the word “ H E L L O”

    (to p37)

    Asynchronous transmission2
    Asynchronous transmission

    • Penalty term is used to measure the efficiency of a code system

    • known as transmission efficiency


      Code No. of bits start/stoptotal biteEff.

      Baudot 5 2 7 5/7=71.5

      ASCII 7 2 9 7/9=77

      EBCDIC 8 2 10 8/10=80

    (to p41)

    Asynchronous transmission3
    Asynchronous transmission

    • Asyn has a function of character synchronization, which allows when a start bit is sensed, the receiver knows that the next n bits on the line make up a characters

    • Without Char Syn, receiver cannot rocog the first bit of charc, and thus character could not be interpreted.

    • Adv. Equipment cost is low

    • Disadv. Slow speed, less than 300bps

    (to p35)

    Synchronous transmission
    Synchronous transmission

    • ii) Synchronous transmission (Synch)

      • design for line speed that cannot handle by Asyn

      • its function is that bit Synch is maintained by clock circuitry in the transmitter and in the receiver

    (to p43)

    Synchronous transmission1
    Synchronous transmission

    • that is timing generated by the transmitter’s clock is sent along with data so that the receiver can keep its clock synchronized with that of the transmitter throughout a long transmission

    • data is usually sent in a block oriented, contains special synch character with a unique bit pattern

    • similar the Asych, synch char performs a function similar to that of start bit

    (to p44)

    Synchronous transmission2
    Synchronous transmission

    • It has 1 to 4 synchronizing “characters” for each “block” of data; whereas Asych has 2 bits for each character

    • Semantic view

    • efficiency

    (to p45)

    (to p46)

    Synchronous transmission3
    Synchronous transmission

    • Example: consider a character consists of


      Asynch: 250 char x (7 data + 2 start/stop) = 2250

      Synch: (250 + 4 synch char) x 7 bits) = 1778

      Thus, Synch is 21% more efficient than Aysnch

    • Note: Mostly, host computers adopt Synch transmission.

    (to p35)

    Isochronous connections
    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

    • (provide data transmission in a regular period of time)

    (to p35)

    Terminal to mainframe computer connections
    Terminal-to-Mainframe Computer Connections

    • Two main ways for 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 (how do you draw them semantically?)

    (to p49)

    (to p49)

    (to p50)

    Terminal to mainframe computer connections continued
    Terminal-to-Mainframe Computer Connections (continued)

    (to p48)

    (to p48)

    Terminal to mainframe computer connections continued1
    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 (how it works, semantically?)

    (to p51)

    (to p2)

    Terminal to mainframe computer connections continued2
    Terminal-to-Mainframe Computer Connections (continued)

    Roll-call pulling

    (to p50)

    Making computer connections in action
    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

    (to p53)


    Making computer connections in action continued
    Making Computer Connections In Action (continued)

    (to p54)

    Making computer connections in action continued1
    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?

    (to p55)


    Making computer connections in action continued2
    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

    (to p56)

    Making computer connections in action continued3
    Making Computer Connections In Action (continued)

    • If a synchronous connection is used, assume maximum payload size – 1500 bytes

    • To transfer a 700K char file requires 467 1500-character (byte) frames

    • Each frame will also contain 1-byte header, 1-byte address, 1-byte control, and 2-byte checksum, thus 5 bytes overhead

    (to p57)

    Making computer connections in action continued4
    Making Computer Connections In Action (continued)

    • 1500 bytes payload + 5 byte overhead = 1505 byte frames

    • 467 frames * 1505 bytes/frame = 716,380 bytes, or 5,731,040 bits

    • Significantly less data using synchronous connection