Making Connection

1
Lecture 04

• Making Connection

2
Introduction

• Connection concept
• Interface concept and standard (Level 1)
• EIA-232F
• USB
• Data Link Connections (Level 2)
• Terminal-to-mainframe computer connections
• Application examples

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Connection concept

• How computer networks are connected?

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4
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

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Connection (cont.)
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• Characteristics of interface standards
• Two important interface standards
• EIA-232F
• USB (Universal Serial Bus)
• Other interfacing standards

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Other interfacing standards

• Other peripheral interfacing standards that
  provide power, flexibility and ease-of-installatio
  n include
• FireWire (low cost device for digital)
• SCSI, iSCSC(mainly for permanent storage,
  CD/DVD)
• InfiniBand, Fibre Channel (high speed connection)

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Level 2
Level 1
Data terminating equipment
Data communicating equipment
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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

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data flow

• There are 3 types of data flow
• i) simplex transmission
• ii) half-duplex transmission
• iii) full duplex transmission

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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?

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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?

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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?

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connection to the system

• two types of physical connection in the system
• i) Parallel data transmission
• ii) Series data transmission

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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?)

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FIGURE 8-3 Parallel and serial transmission.
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• 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?

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Characteristics of Interface Standards
(continued)

• There are four possible components to an
  interface standard
• Electrical component
• Mechanical component
• Functional component
• Procedural component

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Explanations
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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

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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.

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Worked as full duplex (why?) Its functions
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EIA-232F (continued)
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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

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EIA-232F (continued)
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EIA-232F (continued)
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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

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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)

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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

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Universal Serial Bus (USB) (continued)
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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

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FireWire

• 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

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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

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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

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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)

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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)

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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

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Alternative presentation
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Asynchronous Connections (continued)
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More example
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Asynchronous Connections (continued)
Send the word H E L L O
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Asynchronous transmission

• Penalty term is used to measure the efficiency of
  a code system
• known as transmission efficiency
• Eg.
• Code No. of bits start/stop total bite Eff.
• Baudot 5 2 7 5/771.5
• ASCII 7 2 9 7/977
• EBCDIC 8 2 10 8/1080

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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

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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

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Synchronous transmission

• that is timing generated by the transmitters
  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

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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

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Synchronous Connections (continued)
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Synchronous transmission

• Example consider a character consists of
• 0100101
• 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.

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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)

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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?)

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Terminal-to-Mainframe Computer Connections
(continued)
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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?)

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Terminal-to-Mainframe Computer Connections
(continued)
Roll-call pulling
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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

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Layout
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Making Computer Connections In Action (continued)
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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?

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Solution!
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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

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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

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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