Chapter 4: Making Connections

Chapter 4: Making Connection

Introduction

To many people, a computer only has its use when it is connected to monitor or keyboard for viewing and entering data. Some also feel computer doesn't worth much if it can't be connected to a local network for internet access because they rely on the interconnection between their computer and local network for emails, internet, and other software applications. Connecting a peripheral device to a computer can be a challenging task. Various hardware and software have to comply with each other completely before the devices can connect to one another. And to better understand the interconnection between a computer and a peripheral device, we must understand the concept of interfacing. There are four basic components of an interface: electrical, mechanical, functional and procedural.

Interfacing a computer to peripheral device 

Interfacing is the process of providing all the proper interconnections between a computer and a peripheral. Interfacing a device to a computer is a physical activity because it deals directly with analog signals, and hardware components

1. Characteristics of interface standards

·       Official standards: they have been created and approved by an acceptable standards making organization, and they can consist of one to four components

1)    International telecommunications Unions (ITU)

2)    Institute for electrical and electronics engineers (IEEE)

3)    The now defunct Electronic Industries Association (EIA)

4)    International organization for standardization (ISO)

5)    American national standards institute (ANSI)

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

·       The second basic characteristics of an interface standard is its composition, which consists of 4 parts:

1)    Electrical component: deals with voltages, line capacitance, and other electrical characteristics

2)    Mechanical component: deals with items such as the connector or plug description

3)    Functional component: describes the function of each pin or circuit that is used in a particular interface

4)    Procedural component: describes how the particular circuits are used to perform an operation

2. An early interface standard

o   Originally named RS-232 but has gone through many revisions

o   EIA-232F is an interface standard for connecting a computer or terminal (DTE) to a voice-grade modem (DCE) for use on analog public telecommunications systems.

-       The computer end of an interface is referred to as data terminating equipment (DTE)

-       The modem is referred to as data communicating equipment (DCE)

o   A full-duplex connection transmits data in both directions and at the same time

o   A half-duplex connection transmits data in both directions but in only one direction at a time

o   A simplex connection can transmit data in only one direction

3. Universal Serial Bus (USB)

o   The USB is a modern standard for interconnecting a wide range of peripheral devices to computers

o   Hot Pluggable: the peripheral can be plugged in and turned on and that the computer should dynamically recognize the device and establish the interface.

o   Can daisy-chain multiple devices

o   USB 2.0 can support 480 Mbps (USB 1.0 is only 12 Mbps)

o   USB 3.0 can support 4.8 Gbps

o   The USB interface defines all four components

    o   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

    o   The mechanical component precisely defines the size of four different connectors and uses only four wires (the metal shell counts as one more connector)

    o   The functional and procedural components are fairly complex but are based on the polled bus

    o   The computer takes turns asking each peripheral if it has anything to send

4. Other interface standards

·       Firewire: a type of interconnection between peripheral devices and a microcomputer.

o   Easy to use, flexible and low-cost digital interface

o   Capable of supporting transfer speeds of up to 400 Mbps

o   Supports two types of data connections:

- Asynchronous connection

- Isochronous connection

·       Thunderbolt:

o   Digital interface currently found on Apple products

o   Capable of supporting transfer speeds of up to 10 Gbps

o   Uses same connector as existing Mini DisplayPort and similar protocol as PCI Express

o   Can daisy-chain devices and may get even faster with later versions

·       Lightning:

o   Newer digital interface currently found on Apple products

o   Replaces the older 30-pin connector found on devices such as iPhones with a new 8-pin connector

o   Cannot be plugged in backwards

·       SCSI and iSCSI

o   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

o   iSCSI (Internet SCSI): a technique for interfacing disk storage to a computer via the Internet

·       InfiniBand and Fibre Channel

o   InfiniBand is 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

o   Fibre Channel also a serial is a 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

Data Link Connections

1.     Asynchronous Connections

·       A single character, or byte of data, is the unit of transfer between the sender and receiver

·       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 – always a logic 0, while a stop bit – always logic 1s, is added to the end of the frame

·       An optional parity bit can be added which can be used to detect errors

·       The term asynchronous is misleading here because the protocol actually does, despite the word “asynchronous”, maintain synchronization with the incoming data stream

·       Asynchronous connections maintain synchronization by using small frames with a leading start bit

2.     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

 

 

3.     Isochronous Connections

·       Special kind of data link connection 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

Terminal-to-mainframe Computer Connections

•       To allow a terminal to transmit data to a mainframe, the mainframe must poll the terminal
•        Point to point connection: a single wire runs between the 2 devices and no other terminals or computers share this connections
• ·      Multipoint connection: a single wire with the mainframe connected on one end and multiple terminals connected on the other end. 

 

•       Two basic forms of polling: roll-call polling and hub polling

1.     Roll-call polling, the mainframe polls each terminal in a round-robin fashion

2.     Hub polling, the mainframe polls the first terminal, and this terminal passes the poll onto the next terminal