COMP 421 /CMPET 401

COMP 421 /CMPET 401COMP 421 /CMPET 401

COMMUNICATIONS and NETWORKING

CLASS 6

Physical LayerPhysical Layer

Refers to transmission of unstructured bits over physical medium

Deals with characteristics of and access to the physical medium

Data Link LayerData Link Layer

Provides for reliable transfer of information across physical link

Includes:– transmission of blocks of data (“frames”)– synchronization– error control– flow control

Asynchronous & Synchronous TransmissionAsynchronous & Synchronous Transmission

Timing problems require a mechanism to synchronize the transmitter and receiver

Two solutions exist– Asynchronous– Synchronous

Both methods are concerned with timing issues How does the receiver know when the bit period begins and

ends? Small timing difference becomes more significant over time

if no synchronization takes place between sender and receiver Synchronization occurs on the data link layer

Asynchronous TransmissionAsynchronous Transmission

Used in serial communication

Data transmitted 1 character at a time

Character format is usually 1 start & 1+ stop bits, plus data of 5-8 bits

Character may include parity bit

Timing needed only within each character

Resynchronization is accomplished with each start bit

Uses simple, cheap technology

Wastes 20-30% of bandwidth

Asynchronous CommunicationsAsynchronous CommunicationsAsynchronous communicationsThis is the method most widely used for PC or simple terminal serial communications.In asynch. serial communication, the electrical interface is held in the mark position between characters. The start of transmission of a character is signaled by a drop in signal level to the space level. At this point, the receiver starts its clock. After one bit time (the start bit) come 8 bits of true data followed by one or more stop bits at the mark level. The receiver tries to sample the signal in the middle of each bit time. The byte will be read correctly if the line is still in the intended state when the last stop bit is read . Thus the transmitter and receiver only have to have approximately the same clock rate. A little arithmetic will show that for a 10 bit sequence, the last bit will be interpreted correctly even if the sender and receiver clocks differ by as much as 5%. Asynch. is relatively simple, and therefore inexpensive. However, it has a high overhead, in that each byte carries at least two extra bits: a 25% loss of line bandwidth. A 56kbps line can only carry 5600 bytes/second asynchronously, in ideal conditions.

Asynchronous Character StreamAsynchronous Character Stream

NextIdle State

StartBit

P

Bit0

1IdleState

5 to 8 data bits

OddEvenNone

Stop Bits

1 to 2StopBits

•Parity bit is set so that the total number of 1’s will be even or odd, depending on which parity is set•The stop can be 1, 1.5 or 2 2 bits. It is a binary 1 and is the same as the idle state level.•This data stream is called a frame and if the receive and transmit clocks are off by toomuch a framing error may occur.

Synchronous TransmissionSynchronous Transmission

Used in parallel communication

Large blocks of bits transmitted without start/stop codes

Synchronized by a clock signal or clocking data

Data framed by preamble (opening)/ postamble (closing) bit patterns

More efficient than asynchronous

Overhead typically below 5%

Used at higher speeds than asynchronous

Synchronous FrameSynchronous Frame

8-bitflag

Controlfields

Data Field Controlfields

8-bitflag

•One side pulses the line regularly with one short pulse per bit time. the other uses these pulses as a clock

•Each block begins with a preamble to help synchronize the frameother bits are added to convey control information.

•The exact format of the frame depends on which data link procedure being used (such SDLC or HDLC, etc)

•Less overhead than asynchronous, but over long distances data impairmentsand timing errors can become issues

SynchronizationSynchronizationThe synchronization problemSerial communication normally consists of transmitting binary data across an electrical or optical link such as RS232 or V.35. The data, being binary, is usually represented by two physical states. For example, +5v may represent 1 and -5v represent 0. The accurate decoding of the data at the remote end is dependent on the sender and receiver maintaining synchronization during decoding. The receiver must sample the signal in phase with the sender.If the sender and receiver were both supplied by exactly the same clock source, then transmission could take place forever with the assurance that signal sampling at the receiver was always in perfect synchronization with the transmitter. This is seldom the case, so in practice the receiver is periodically brought into synch. with the transmitter. It is left to the internal clocking accuracy of the transmitter and receiver to maintain sampling integrity between synchronization pulses.

Synchronization ChoicesSynchronization Choices

Low-speed terminals and PCs commonly use asynchronous transmission– inexpensive

Large systems and networks commonly use synchronous transmission– overhead too expensive; efficiency necessary– error-checking more important

Isochronous TransmissionIsochronous Transmission

•Isochronous data is synchronous data transmitted without a clocking source

•Bits are sent continuously•Timing is recovered from transitions in the data stream•Isochronous transmission is transparent•Isochronous transmission does not recognize control characters

•Used mostly for secure military applications

•Some new LAN standards such as ISOEthernet (Isochronous Ethernet)

Pleisiochronous TransmissionPleisiochronous Transmission

•Pleisiochronous data is synchronous data that carefully clocked usually through a GPS based time source

Digital InterfacesDigital Interfaces

The point at which one device connects to another

Standards define what signals are sent, and how

Some standards also define the physical connector to be used

Generic Communications Generic Communications Interface IllustrationInterface Illustration

DTE and DCEDTE and DCE

RS-232 OverviewRS-232 Overview

RS-232 — Defines three types of connections: electrical, functional, and mechanical. The RS-232 interface is ideal for the data-transmission range of 0–20 kbps/50 ft. (15.2 m). It employs unbalanced signaling and is usually used with DB25 connectors to interconnect DTEs (computers, controllers, etc.) and DCEs (modems, converters, etc.). Serial data exits through an RS-232 port via the Transmit Data (TD) lead and arrives at the destination device’s RS-232 port through its Receive Data (RD) lead. RS-232 is compatible with these standards: ITU V.24, V.28; ISO IS2110.

RS-232C (EIA 232C)RS-232C (EIA 232C)

EIA’s “Recommended Standard” (RS)

Specifies mechanical, electrical, functional, and procedural aspects of the interface

Used for connections between DTEs and voice-grade modems, and many other applications

BAUD DISTANCE (ft)1200 10002400

5004800

2509600

150

EIA-232-DEIA-232-D

Newer version of RS-232-C adopted in 1987

Improvements in grounding shield, test and loop-back signals

The popularity of RS-232-C in use made it difficult for EIA-232-D to enter into the marketplace

V.24/EIA-232-FV.24/EIA-232-F ITU-T v.24 Only specifies functional and procedural

– References other standards for electrical and mechanical EIA-232-F (USA)

– Based on RS-232

– Mechanical aspects are defined by ISO 2110

– Electrical v.28

– Functional v.24

– Procedural v.24

ITU-International Telecommunication Union

ISO-International Standards Organization

EIA-Electronics Industries Association

LimitsLimits

The standards for RS-232 and similar interfaces usually restrict RS-232 to 20kbps or less and line lengths of 15m (50 ft) or less. These restrictions are mostly throwbacks to the days when 20kbps was considered a very high line speed, and cables were thick, with high capacitance.

However, in practice, RS-232 is far more robust than the traditional specified limits of 20kbps over a 15m line would imply. Most 56kbps DSUs are supplied with both V.35 and RS-232 ports because RS-232 is perfectly adequate at speeds up to 200kbps.

DTE / DCEDTE / DCE

If the full EIA232 standard is implemented as defined, the equipment at the far end of the connection is named the DTE device (Data Terminal Equipment, usually a computer or terminal), has a male DB25 connector, and utilizes 22 of the 25 available pins for signals or ground. Equipment at the near end of the connection (the telephone line interface) is named the DCE device (Data Circuit-terminating Equipment, usually a modem), has a female DB25 connector, and utilizes the same 22 available pins for signals and ground.

The DTE ConnectorThe DTE Connector

The DCE ConnectorThe DCE Connector

Mechanical SpecificationsMechanical Specifications

25-pin connector with a specific arrangement of leads

DTE devices usually have male DB25 connectors while DCE devices have female

In practice, fewer than 25 wires are generally used in applications

RS232 DB25 ConnectorRS232 DB25 Connector

RS-232 Serial PC Port Connector DB-25

DB-25M Function Abbreviation

Pin #1 Chassis/Frame Ground GND

Pin #2 Transmitted Data TD

Pin #3 Receive Data RD

Pin #4 Request To Send RTS

Pin #5 Clear To Send CTS

Pin #6 Data Set Ready DSR

Pin #7 Signal Ground GND

Pin #8 Data Carrier Detect DCD or CD

Pin #9 Transmit + (Current Loop) TD+

Pin #11 Transmit - (Current Loop) TD-

Pin #18 Receive + (Current Loop) RD+

Pin #20 Data Terminal Ready DTR

Pin #22 Ring Indicator RI

Pin #25 Receive - (Current Loop) RD-

V.24/EIA-232-FV.24/EIA-232-F ITU-T v.24 Only specifies functional and procedural

– References other standards for electrical and mechanical EIA-232-F (USA)

– Based on RS-232

– Mechanical aspects are defined by ISO 2110

– Electrical v.28

– Functional v.24

– Procedural v.24

ITU-International Telecommunication Union

ISO-International Standards Organization

EIA-Electronics Industries Association

DB-25 Female

DB-25 Male

RS-232 DB-25 ConnectorsRS-232 DB-25 Connectors

DB Connector-Data Bus Connector

RS-232 DB-25 PinoutsRS-232 DB-25 Pinouts

Important PinsImportant Pins

See Table 6.1, Page 184

For the older RS-232-C standard, some of the pin definitions are:

Pin Number Name (function)

2 TD (Transmitted Data)

3 RD (Received Data)

4 RS (Request to Send)

5 CS (Clear to Send)

6 DSR (Data Set Ready)

20 DTR (Data Terminal Ready)

8 CD (Carrier Detect)

21 SQ (Signal Quality detector)

Limited Distance Modem Limited Distance Modem Example (Point-to-Point)Example (Point-to-Point) Only a few circuits are

necessary:– Signal Ground (7)– Transmitted Data (2)– Received Data (3)– Request to Send (4)– Clear to Send (5)– DCE Ready (6)– Received Line Signal

Detector [Carrier Detect] (8)

Additional circuits necessary sometimes:– DTE Ready(20)

– Ring Indicator (22)

RS-232 DB-9 ConnectorsRS-232 DB-9 Connectors

Limited RS-232

Electrical SpecificationsElectrical Specifications

Specifies signaling between DTE and DCEUses NRZ-L encoding

– Voltage < -3V = binary 1– Voltage > +3V = binary 0– Voltage could be as high as 25 volts

Rated for >20Kbps and <15M– greater distances and rates are theoretically

possible, but not necessarily wise

Functional SpecificationsFunctional Specifications

Specifies the role of the individual circuits

Data circuits in both directions allow full-duplex communication

Timing signals allow for synchronous transmission (although asynchronous transmission is more common)

Procedural SpecificationsProcedural Specifications

Multiple procedures are specifiedSimple example: exchange of asynchronous

data on private line– Provides means of attachment between

computer and modem– Specifies method of transmitting asynchronous

data between devices– Specifies method of cooperation for exchange

of data between devices

Control LinesControl LinesThe essential feature of RS-232 is that the signals are carried as single voltages referred to a common earth on pin 7.Data is transmitted and received on pins 2 and 3 respectively. Data set ready (DSR) is an indication from the Dataset (i.e., the modem or DSU/CSU) that it is on. Similarly, DTR indicates to the Dataset that the DTE is on. Data Carrier Detect (DCD) indicates that carrier for the transmit data is on.

Control LinesControl Lines

Pins 4 and 5 carry the RTS and CTS signals. In most situations, RTS and CTS are constantly on throughout the communication session. However where the DTE is connected to a multipoint line, RTS is used to turn carrier on the modem on and off. On a multipoint line, it is imperative that only one station is transmitting at a time. When a station wants to transmit, it raises RTS. The modem turns on carrier, typically waits a few milliseconds for carrier to stabilize, and raises CTS. The DTE transmits when it sees CTS up. When the station has finished its transmission, it drops RTS and the modem drops CTS and carrier together.

ClocksClocksThe clock signals are only used for synchronous communications. The modem or DSU extracts the clock from the data stream and provides a steady clock signal to the DTE. Note that the transmit and receive clock signals do not have to be the same, or even at the same baud rate. The auxiliary clock signal on pin 24 is supplied on in order to allow local connections without the need for a modem eliminator. The baud rate of the auxiliary clock is programmable. By jumpering this signal to pins 15 and 17 each side, you can use a simple null-modem cable for synchronous connections. This arrangement is much less expensive that using Modem Eliminator boxes to provide the cable crossover and clocking

Signal TimingSignal Timing

4 - The slope of the rising and falling edges of a transition should not exceed 30v/µS. Rates higher than this may induce crosstalk in adjacent conductors of a cable.

An acceptable pulse (top) moves through the transition region quickly and without hesitation or reversal. Defective pulses (bottom) could cause data errors.

RS-232 Signals (Asynch)RS-232 Signals (Asynch)

Even Parity

Odd Parity

No Parity

See ASCII Table 3.1, Page 83

Connection EstablishmentConnection Establishment

Dial Up Operation (1)Dial Up Operation (1)



Voltage LevelsVoltage Levels

Signal State Voltage Assignments - Voltages of -3v to -25v with respect to signal ground (pin 7) are considered logic '1' (the marking condition), whereas voltages of +3v to +25v are considered logic '0' (the spacing condition). The range of voltages between -3v and +3v is considered a transition region for which a signal state is not assigned .

Voltage LevelsVoltage Levels

The truth table for RS232 is:Signal > +3v = 0 Signal < -3v = 1 <-3v>The output signal level usually swings between +12v and -12v. The "dead area" between +3v and -3v is designed to absorb line noise. In the various RS-232-like definitions this dead area may vary. For instance, the definition for V.10 has a dead area from +0.3v to -0.3v. Many receivers designed for RS-232 are sensitive to differentials of 1 volt or less.

Asynchronous OperationAsynchronous Operation

Signal TimingSignal Timing The EIA232 standard is applicable to data rates of up to 20,000 bits per second (the usual upper limit is 19,200 baud). Fixed baud rates are not set by the EIA232 standard. However, the commonly used values are 300, 1200, 2400, 9600, and 19,200 baud. Other accepted values that are not often used are 110 (mechanical teletype machines), 600, and 4800 baud.

Changes in signal state from logic '1' to logic '0' or vice versa must abide by several requirements, as follows: 1 - Signals that enter the transition region during a change of state must move through the transition region to the opposite signal state without reversing direction or reentering.

2 - For control signals, the transit time through the transition region should be less than 1ms.

3 - For Data and Timing signals, the transit time through the transition region should bea - less than 1ms for bit periods greater than 25ms,

b - 4% of the bit period for bit periods between 25ms and 125µs,

c - less than 5µs for bit periods less than 125µs.The rise and fall times of data and timing signals ideally should be equal, but in any case vary by no more than a factor of three.

Limited Distance Modem Limited Distance Modem Example (Point-to-Point)Example (Point-to-Point) Only a few circuits are

necessary:– Signal Ground (7)

– Transmitted Data (2)

– Received Data (3)

– Request to Send (4)

– Clear to Send (5)

– DCE Ready (6)

– Received Line Signal Detector [Carrier Detect] (8)

Additional circuits necessary sometimes:– DTE Ready(20)

– Ring Indicator (22)

Null Modem CableNull Modem Cable

SGDTR

DSR

RTS

CTSCDTDRD

SGDTR

DSR

RTS

CTSCDTDRD

Allows DTE to DTE direct communication

Balanced InterfacesBalanced Interfaces

RS-422, RS-485, V.11 and other balanced interfaces.

The limitations of RS-232 are largely eliminated by the balanced line interface. A pair of wires is used to carry each signal. The data is encoded and decoded as a differential voltage between the two lines. A typical truth table for a balanced interface is as follows:VA-VB < -0.2v =0VA-VB > +0.2v=1

As a differential voltage, in principle the interface is unaffected by differences in ground voltage between sender and receiver.

RS-232 and RS-449RS-232 and RS-449 It is a physical protocol to interface computers with

modems

– specify mechanical, electrical, functional, and procedural interface

Computeror

TerminalModem

Protective Ground (1)

Transmit (2)

Receive (3)

Request to Send (4)

Clear to Send (5)

Data Set Ready (6)

Common Return (7)

Carrier Detect (8)

Date Terminal Ready (20)

RS-449RS-449An EIA standard that improves on the capabilities

of RS-232-CProvides for a 37-pin connection, cable lengths

up to 200 feet, and data transmission rates up to 2 million bps

Equates with the functional and procedural portions of R-232-C– the electrical and mechanical specifications are

covered by RS-422 and RS-423

RS-449RS-449

RS-449 — Defines functional/mechanical interfaces for DTEs/DCEs that employ serial binary data interchange and is usually used with synchronous transmissions. It identifies signals (TD, RD, etc.) that correspond with the pin numbers for a balanced interface on DB37 and DB9 connectors. RS-449 was originally intended to replace RS-232, but RS-232 and RS-449 are completely incompatible in mechanical and electrical specifications

RS-449 PinsRS-449 PinsPin

EIACKT

DescriptionFromDCE

ToDCE

A B

12

SI

ShieldSignaling Rate Indicator *C

45

2223

SDST

Send DataSend Timing *T

*D

67

2425

RDRS

Receive DataRequest to Send

*D*C

89

2627

RTCS

Receive TimingClear to Send *T *C

1011 29

LLDM

Local LoopbackData Mode *C

*C

1213

3031

TRRR

Terminal ReadyReceiver Ready *C

*C

1415

RLIC

Remote LoopbackIncoming Call *C

*C

1617 35

SRTT

Signaling Rate SelectorIncoming Call

*C*T

1819

TMSG

Test ModeSignal Ground

*C

2028

RCIS

Receive CommonTerminal in Service

*C

3233

SSSQ

Select StandbySignal Quality *C

*C

343637

NSSBSC

New SignalStandby IndicatorSend Common

*C

*C

RS-530RS-530RS-530 — Supersedes RS-449 and complements RS-232. Based on a 25-pin connection, it works in conjunction with either electrical interface RS-422 (balanced electrical circuits) or RS-423 (unbalanced electrical circuits). RS-530 defines the mechanical/electrical interfaces between DTEs and DCEs that transmit serial binary data, sync or async, at rates from 20 kbps to 2 Mbps. (Maximum distance depends on the electrical interface.) RS-530 takes advantage of higher data rates with the same mechanical connector used for RS-232. Though RS-530 and RS-232 are not compatible, RS-530 is compatible with these standards: ITU V.10, V.11, X.26; MIL-188/114; RS-449.

RS-530 Speed and DistanceRS-530 Speed and DistanceTerminated Circuits

10 MHz 10 Meters6 MHz 17 Meters2 MHz 40 Meters

1 MHz 100 Meters100 KHz 1000 Meters10 KHz 1000 Meters

Non- Terminated Circuits

1 MHz 10 Meters100 KHz 100 Meters56 KHz 110 Meters

10 KHz 1000 Meters

RS-530RS-530

25 pin D-SUB FEMALE connector at the DCE (Modem)

25 pin D-SUB MALE connector at the DTE (Computer)

RS-530 PINSRS-530 PINSPin Name Dir Description Circuit Paired with

1 Shield 182 TxD Transmitted Data BA 143 RxD Received Data BB 164 RTS Request To Send CA 195 CTS Clear To Send CB 136 DSR Data Set Ready CC 22

7 SGND Signal Ground Ground 21

8 DCD Data Carrier Detect CF 109 Rtrn Receive Sig. Elmnt Timing DD 1710 Rtrn DCD CF 8

11 Rtrn Transmit Sig. Elmnt Timing DA 24

12 Rtrn Transmit Sig. Elmnt Timing DB 15

13 Rtrn CTS CB 514 Rtrn TxD BA 2

15 Transmit Signal Element Timing DB 12

16 Rtrn RxD BB 317 Receive Signal Element Timing DD 918 LL Local Loopback LL 119 Rtrn RTS CA 420 DTR Data Terminal Ready CD 2321 RL Remote Loopback RL 722 Rtrn DSR CC 623 Rtrn DTR CD 2024 Transmit Signal Element timing DA 1125 Test Mode TM

RS-422RS-422RS-422 — Defines a balanced interface with no accompanying physical connector. Manufacturers who adhere to this standard use many different connectors, including screw terminals, DB9, DB25 with nonstandard pinning, DB25 following RS-530, and DB37 following RS-449. RS-422 is commonly used in point-to-point communications conducted with a dual-state driver

This is accomplished by splitting each signal across two separate wires in opposite states, one inverted and one not inverted. The difference in voltage between the two lines is compared by the receiver to determine the logical state of the signal. This wire configuration, called differential data transmission or balanced transmission

RS-485RS-485

RS-485 — Resembles RS-422. It may be used in multipoint applications where one computer controls many different devices. Up to 64 devices may be interconnected with RS-485.

A ComparisonA ComparisonRS-232 RS-422 RS-485

Mode of Operation single ended differential differential

Drivers per Line 1 1 32

Receivers per Line 1 10 32

Maximum Cable Length 50 feet 4000 feet 4000 feet

Maximum Data Rate 20 kbps 10 Mbps 10 Mbps

Driver Output Maximum Voltage ±25V -0.25 to +6V -7 to +12V

Driver Output Signal Level (loaded) ±5V ±2V ±1.5V

Driver Output Signal Level (unloaded) ±15V ±5V ±5V

Driver Load Impedance 3k to 7k 100k 54k

Max. Driver Output Current (Power on) n/a n/a ±100A

Max. Driver Output Current (Power off) VMAX/300 ±100A ±100A

Slew Rate 30V/s max. n/a n/a

Receiver Input Voltage Range ±15V -7V to +7V -7V to +12V

Receiver Input Sensitivity ±3V ±200mV ±200mV

Receiver Input Resistance 3k to 7k 4k 12k

V.35V.35V.35 —

V.35 has been around for quite some time and was originally designed for a 48K bps modem, that's right officially it's top speed is 48Kbps. However, it has been shown if implemented correctly 2.048Mhz and faster is possible. In 1989 CCITT BLUE BOOK (UIT) recommended the interface to become obsolete, however it hasn't, but most vendors are using the specifications from V.11 for the differential part of the V.35 interface as recommended by the CCITT

V.35 Connector / PinsV.35 Connector / Pins

Pin Signal Pin Signal

A Chassis Ground B Signal Ground

C Request to Send D Clear to Send

E Data Set Ready F Receive Line Signal Detect

H Data Terminal Ready J Ring Indicator

P Transmitted Data (Signal A) R Recieved Data (Signal A)

S Transmitted Data (Signal B) T Received Data (Signal B)

U Terminal Timing V Receive Timing A

W Terminal Timing X Receive Timing

Y Transmit Timing AA Transmit Timing

V.35 Cable RecommendationsV.35 Cable Recommendations

V.35/RS449 Data Rate:

Max cable length recommended: (feet)

Max cable length recommended: ( meters)

2 Mb/sec 50 ft. 15.24 m1 Mb/sec 100 ft. 30.48 m512 Kb/sec 200 ft. 60.96 m

256 Kb/sec 400 ft. 121.92 m

128 Kb/sec 800 ft. 243.84 m

56 K 1600 ft. 487.68 m1.2 Kb/sec 3000 ft. 914.40 m

HSSI CharacteristicsHSSI Characteristics

Characteristic Value

Maximum signaling rate 52 Mbps

Maximum cable length 50 feet

Number of connector points 50

Interface DTE-DCE

Electrical technology Differential ECL

Typical power consumption 610 mW

Topology Point-to-point

Cable type Shielded twisted-pair wire

The High-Speed Serial Interface (HSSI) is a DTE/DCE interface that was developed by Cisco Systems and T3plus Networking to address the need for high-speed communication over WAN links HSSI defines both electrical and physical interfaces on DTE and DCE devices. It operates at the physical layer of the OSI reference model

HSSI CABLE SPECIFICATION

•Cable type: multi-conductor cable, consisting of 25 twisted pairs cabled

together with an overall double shield and PVC jacket

•Gauge: 28 AWG, 7 strands of 36 AWG, tinned annealed copper, nominal 0.015 in. diameter

•Insulation: polyethylene or polypropylene; 0.24 mm, .0095 in. nominal wall

•Thickness;0.86 mm +/- 0.025 mm, .034 in. +/- 0.001 in. out-side diameter

•Foil shield: 0.051 mm, 0.002 in. nominal aluminum/polyester/aluminum

laminated tape spiral wrapped around the cable core with a 25% minimum overlap

•Braid shield: braided 36 AWG, tinned plated copper in accordance with 80% minimum coverage

•Jacket: 75 degrees C flexible polyvinylchloride

•Jacket wall: 0.51 mm, 0.020 in. minimum thickness

•Dielectic strength: 1000 VAC for 1 minute

•Outside diameter: 10.41 mm +/- 0.18 mm, 0.405 in. +/- 0.015 in.

•Plug type:2 row, 50 pin, shielded tab connectors AMP plug part number

•Receptacle type:2 row, 50 pin, receptical header with rails and latch blocks.

USBUSBThe standard defines three different devices: hosts, hubs and functions. Hosts are the initiating devices, like PCs, and only 1 host may exist in a network. Functions are dumb devices, like keyboards, mice, printers. And hubs are multi-port repeaters which act like distributing devices in the serial network.

12

Mbps1.5

Mbps

Cable STP UTP

Max. Cable length 5 meter 3 meter

Connector A-Series or B-Series

Max. amount of HUBs 5

Max. amount of units 127

USB CableUSB Cable

Signal Color Pin

+Data Green 3

-data White 2

VCC Red 1

GND Black 4

There are two types of cables. The standard USB cable which is used for 12 Mbps and has an A-series connector consists of one pair 20-28 AWG wire for power and one 28 AWG twisted pair for data. The cable has a shield and an overall jacket which makes it a STP-cable. The alternative cable is used for the 1.5 Mbps version and has a B-type connector. This cable has one pair of 28 AWG wire stranded copper for data and one pair 20-28 AWG for power. This cable is only used in sub-channel applications.

Electrical SpecificationsElectrical Specifications

Electrical SpecificationsA differential "1" is defined as (D+) - (D-) > 200 mV and a "0" is defined as (D+) - (D-) < -200 mV.

The line encoding used is always NRZI. This is independent of the low or high speed version.

The maximum end-to-end signal delay is 70 ns, which gives us a maximum configuration of 5 hubs per link between function and host. If all cables are high-speed cables, the max. distance between a function and a host is 30 meters.

IEEE 1394IEEE 1394 A very fast external bus standard that supports data transfer rates of up to 400Mbps(in 1394a) and 800Mbps (in 1394b). Products supporting the 1394 standard go under different names, depending on the company. Apple, which originally developed the technology, uses the trademarked name FireWire. Other companies use other names, such as i.link and Lynx, to describe their 1394 products.

A single 1394port can be used to connect up 63 external devices. In addition to its high speed, 1394 also supports isochroous data -- delivering data at a guaranteed rate. This makes it ideal for devices that need to transfer high levels of data in real-time, such as video devices.

Although extremely fast and flexible, 1394 is also expensive. Like USB, 1394 also provides power to peripheral devices.

SCSISCSIAcronym for small computer system interface. Pronounced "scuzzy," SCSI is a parallel interface standard used by for attaching peripheral devices to computers. SCSI ports are used for attaching devices such as disk drives and printers.

SCSI interfaces provide for faster data transmission rates (up to 80 Mbps) than standard serial and parallel ports. In addition, you can attach many devices to a single SCSI port, so that SCSI is really an I/O bus rather than simply an interface.

Although SCSI is an ANSI standard, there are many variations of it, so two SCSI interfaces may be incompatible. For example, SCSI supports

several types of connectors.

SCSI SpecsSCSI Specs

The following varieties of SCSI are currently implemented: •SCSI-1: Uses an 8-bit bus, and supports data rates of 4 Mbps•SCSI-2: Same as SCSI-1, but uses a 50-pin connector instead of a 25-pin connector, and supports multiple devices. This is what most people mean when they refer to plain SCSI. •Wide SCSI: Uses a wider cable (168 cable lines to 68 pins) to support 16-bit transfers. •Fast SCSI: Uses an 8-bit bus, but doubles the clock rate to support data rates of 10 MBps. •Fast Wide SCSI: Uses a 16-bit bus and supports data rates of 20 MBps. •Ultra SCSI: Uses an 8-bit bus, and supports data rates of 20 MBps. •SCSI-3: Uses a 16-bit bus and supports data rates of 40 MBps. Also called Ultra Wide SCSI. •Ultra2 SCSI: Uses an 8-bit bus and supports data rates of 40 MBps. •Wide Ultra2 SCSI: Uses a 16-bit bus and supports data rates of 80 MBps

END Class 6END Class 6

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COMP 421 /CMPET 401