Slides for Chapter 4

Chapter Four

Making Connections

Data Communications and Computer Networks: A Business User’s Approach,

Fourth Edition

Data Communications and Computer Networks: A Business User's Approach, Fourth Edition 2

After reading this chapter, you should be able to:

• List the four components of all interface standards

• Discuss the basic operations of the USB and EIA-232F interface standards

• Cite the advantages of FireWire, SCSI, iSCSI, InfiniBand, and Fibre Channel interface standards

• Outline the characteristics of asynchronous, synchronous, and isochronous data link interfaces


After reading this chapter, you should be able to (continued):

• Recognize the difference between half-duplex and full-duplex connections

• Identify the operating characteristics of terminal-to-mainframe connections and why they are unique compared to other types of computer 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


Interfacing a Computer to Peripheral Devices

• 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

• 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)

– De facto standards • Created by other groups that are not official standards but

because of their widespread use, become “almost” standards


Characteristics of Interface Standards (continued)

• There are four possible components to an interface standard:– Electrical component

– Mechanical component

– Functional component

– Procedural component


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


Important Interface Standards

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

– USB-2 (Universal Serial Bus-2) – a newer standard that is more powerful than EIA-232F

– I-1394 (Firewire) – another newer standard that is much more powerful than EIA 232F but has different focus in functionality than USB

– (Ulra)-IDE, (Ultra)SCSI, FC-AL – internal PC buses


EIA-232F

• 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.


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 next slide



• The next slide 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



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

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

• A simplex connection can transmit data in only one direction


Universal Serial Bus (USB)


Universal Serial Bus (USB) (continued)

• 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)



• 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 USB standard uses the NRZI combined with 4B/5B bit stuffing scheme

• USB networks use a tiered-star topology – Hubs up to 16 devices but can be chained so no limit on the number of devices.

• 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


Universal Serial Bus (USB): functions, endpoints, pipes

• USB device can be used as a host, peripheral device, hub, or host controller. Each use has associated functions. These can be seen as USB devices which provide a capability (or function) such as a Printer, FAX, scanner, etc.

• Endpoints are sources/sinks of data. As the bus is host centric, endpoints occur at the end of the communications channel at the USB function.

• Client software transfers data through pipes. A pipe is a logical connection between the host and an endpoint or (endpoints).


Universal Serial Bus (USB): addressing


Universal Serial Bus (USB): transactions

Each USB transaction consists of• Token Packet: header that defines what it

expects to follow,• (Optional) Data Packet: contains the data

(payload)• Status Packet: used to acknowledge

transactions and to provide a means of error correction


Universal Serial Bus (USB): a scenario for control function

Setup Stage is where the request is sent.

• The setup token that contains the address and endpoint number is sent first.

• The data packet is sent next. It contains a setup packet which details the type of request.

• The last packet is a handshake used for acknowledging successful receipt or to indicate an error. If the function successfully receives the setup data (CRC, PID, etc. are OK) it responds with ACK, otherwise it ignores the data and doesn’t send a handshake packet.


Universal Serial Bus (USB): a scenario for control function (continued)

Data Stage: is where IN or OUT data transfers happen (one or multiple – determined by amount of data requested by SETUP packet).

• IN: The host is ready to receive control data, it issues an IN Token. Reply can be a DATA packet containing the control data, a STALL packet indicating an error at the endpoint or a NAK packet indicating that the endpoint is OK, but temporary has no data to send.

• OUT: The host needs to send a control data packet, it issues an OUT token followed by a data packet containing the control data. If the function's endpoint buffer got the data OK the endpoint issues an ACK, if endpoint is busy then NAK, if error then STALL.


Universal Serial Bus (USB): a scenario for control function (continued)

Status Stage reports the status of the overall request. Status reporting is always performed by the function.

• IN: If the host sent IN token during the data stage, the host acknowledges the successful receipt of this data by sending an OUT token followed by a zero length data packet. An ACK indicates the function has completed the command. If an error occurred during the processing of this command, the function issues a STALL. If the function is still processing the command, it returns a NAK indicating to the host to repeat the status stage later.

• OUT: If the host sent OUT token during the data stage, the function acknowledges the receipt of data by sending a zero length packet in response to an IN token issued by the host. If an error occurred during processing, the function issues a STALL. If it is still busy processing data, it issues a NAK asking the host to retry the status stage later.



Supports three types of data transfers: – Interrupt (asynchronous) transfers:

• Guaranteed Latency• Stream Pipe - Unidirectional• Error detection and next period retry.

– Isochronous transfers• Guaranteed access to USB bandwidth.• Bounded latency.• Stream Pipe - Unidirectional• Error detection via CRC, but no retry or guarantee of delivery.• Full & high speed modes only.



– Bulk transfers

• Used to transfer large bursty data.

• Error detection via CRC, with guarantee of delivery.

• No guarantee of bandwidth or minimum latency.

• Stream Pipe - Unidirectional• Full & high speed modes only.


FireWire

• Low-cost digital interface (non-polled, peer-to-peer device network) – 63 peripherials.

• Capable of supporting transfer speeds of up to 400 Mbps

• Hot pluggable, daisy-chainable.• Supports two types of data connections:

– Asynchronous connection– Isochronous connection

• Uses Serial Bus Protocol – 2 (for more see FireWire Concepts)

http://developer.apple.com/documentation/HardwareDrivers/Conceptual/HWTech_FireWire/Articles/FireW_concepts.html


FireWire functions

Identification: When a device is plugged in, it immediately broadcasts its unique identification number to other devices on the network and becomes part of that network.

• Asynchronous mode transfer: The address of both the sender and the receiver is transmitted followed by the actual packet data. Once the receiver accepts the packet, a packet acknowledgment is returned to the original sender. To improve throughput, the sender may continue transmission until 64 transactions are outstanding.


FireWire functions (continued)

• Isochronous mode transfer: The sender requests an isochronous channel by introducing a request token into a time slot that must not be disrupted by peers. Channel IDs are transmitted followed by the packet data. The receiver monitors the incoming data's channel ID and accepts only data with the specified ID, 64 isochronous channels may be defined.


SCSI and iSCSI

• SCSI (Small Computer System Interface)- a protocol of 64 commands. Initially, parallel bus (8 bits)- uses Low Voltage Differential signaling:– 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 (for more information see what is SCSI?)

• iSCSI (Internet SCSI) – A technique for interfacing disk storage to a computer

via the Internet

http://en.wikipedia.org/wiki/Low_voltage_differential_signaling

http://www.freebsd.org/doc/en_US.ISO8859-1/articles/storage-devices/scsi.html


InfiniBand and Fibre Channel• InfiniBand – a serial connection or switched bus connection 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 (for more see High Performance Computing- SW fabric and What is InfiniBand?)

• Fibre Channel- Arbitrated Loop (FC-AL) – also a serial, high-speed network that connects a computer to multiple input/output devices. Designed for RAID at a speed 400 MBYTES/s.– Supports data transfer rates up to billions of bits per second, but

can support the interconnection of up to 126 devices only (for more see Arbitrated loop and What is FC-AL?)

http://en.wikipedia.org/wiki/InfiniBand

http://www.oreillynet.com/pub/a/network/2002/02/04/windows.html



http://en.wikipedia.org/wiki/Arbitrated_loop

http://www.snseurope.com/snslink/magazine/features-full.php?id=3381&magazine=SNS%20-%20June%202005


Interface speeds

• standard parallel port: 115kBYTES/s (.115MBYTES/s)

• Original USB: 12Mbits/s (1.5MBYTES/s)• ECP/EPP parallel port: 3MBYTES/s• IDE: 3.3-16.7MBYTES/s• SCSI-1: 5MBYTES/s• SCSI-2 (Fast SCSI, Fast Narrow SCSI):

10MBYTES/s• Fast Wide SCSI (Wide SCSI): 20MBYTES/s• Ultra SCSI (SCSI-3, Fast-20, Ultra Narrow):

20MBYTES/s• UltraIDE: 33MBYTES/s


Interface speeds (continued)

• Wide Ultra SCSI (Fast Wide 20): 40MBYTES/s • Ultra2 SCSI: 40MBYTES/s• IEEE-1394: 100-400Mbits/s (12.5--50MBYTES/s)• Hi-Speed USB: 480Mbits/s (60MBYTES/s)• Wide Ultra2 SCSI: 80MBYTES/s• Ultra3 SCSI: 80MBYTES/s• Wide Ultra3 SCSI: 160MBYTES/s• FC-AL Fiber Channel: 100-400MBYTES/s• Infini-BAND: 2.5 Gbits/s (312MBYTES/s)


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)



• 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


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


Synchronous Connections (continued)


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


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 (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


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


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?



• 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



• 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



• 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


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 (continued)

• Two interface standards worthy of additional study: Universal Serial Bus, and EIA-232F– EIA-232F was one of the first highly popular standards– Universal Serial Bus is currently the most popular interface

standard

• 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, 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

• 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


Summary (continued)

• 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

Slides for Chapter 4

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