Computer Network Systems Part 2 Flashcards
serial interface
bits transmitted one at a time along a single line in a cable
parallel interface
- all bits representing a character (typically seven, eight, or nine) transmitted at once
- a separate line in the cable for each bit
- additional line used as a strobe signal to carry a timing signal
universal serial bus (USB)
External bus standard that supports serial data transfer
- can connect up to 127 devices
- supports plug and play
- allows hot plugging (also called hot swapping)
buffer
- small amount of memory within a peripheral device
- peripheral sends status of buffer to computer by means of flow control (handshaking)
software flow control (handshaking)
technique for the computer to monitor the peripheral and begin sending more data as soon as the device is ready
peripheral signals
XOFF–> transmission off; buffer full, do not send data
XON –> transmission on; buffer is ready for more data
hardware handshaking
One or more lines between the computer and peripheral can be used for this.
- serial printers require only two or three lines: data in, data out, and ground
- further lines can be used for data terminal ready (DTR) or clear to send (CTS) handshaking
composite link
- several peripherals along a single cable
- data can be carried via multiplexers
- achieved using frequency division or time division multiplexing
frequency division multiplexing (FDM)
available transmission band is divided into narrower bands, each used for a separate channel
time division multiplexing (TDM)
- connection channel is operated at a much higher clock rate, and each peripheral shares equally in the available cycles
multiplexer (MUX)
Device that combines two or more signals for transmission over a single channel or line
demultiplexer (DMUX or DEMUX)
device used to separate two or more signals previously combined and transmitted over a single channel or line
random access (direct access) storage device (mass storage devices)
permit access to individual records without having to read through entire file types include: - magnetic disk drives - hard drives - optical disk drives
hard drives
- composed of several platters, each with one or more read/write heads
- platters spin at high speeds (thousands of rpms)
- organized into tracks, sectors, and cylinders
track
concentric storage areas
sector
pie-shaped subdivisions of each track
cylinder
consists of the same numbered track on all drive platters
optical disk drives
- drive that uses laser light as part of the process of reading or writing data
- -> read only (R/0)
- -> read/write (R/W)
- -> WORM (write once, read many)
- -> CDR
- -> DVD-R
- -> CD-ROM
solid state drives (SSD)
Store data in arrays of interconnected, nonvolatile flash memory chips
- faster data transfers than traditional disk drives
- also more expensive
performance measures of a disk drive
- memory size in MB (megabytes)
- area density
- -> a measure of the number of data bits stored per square inch of disk surface
- -> the number of bits per track multiplied by the number of tracks per radial inch
- average seek time
- -> average time it takes to move from one location to a new location
- track-to-track seek time
- -> time required to move from one track to an adjacent track
latency (rotational delay)
- time it takes to for a disk to spin a particular sector under the head for reading
- latency is one-half the time to spin a full revolution
average access time
- time required to move to a new sector and read the data
access time
- the sum of average latency and average seek time
sequential access drives
- computer has to read all information stored up to the point where data is located (for example, tape drives)
indexed sequential format
- format uses directory of files placed at start of tape
- tape can be quickly wound to location of information without having to read everything in between
formats
- nine track format
- quarter inch cartridge (QIC)
- digital audio tape (DAT)
nine track format
- tape divide into nine tracks running the length of the tape
- width divided into frames (characters)
- eight tracks used to record in ASCII or EBCDIC formats
- ninth track used to record the parity bit
- 1600 bpi (bits per inch) up to 9600 bpi typically used
sequential access drives (continued)
- frames are grouped into fixed length blocks separated by interblock gaps (IBG)
- reflective spots for photoelectric detection can be used to indicate the beginning and end of magnetic tapes, called load point and end-of-file (EOF) markers.
- Magnetic tape is sometimes used to back up hard disks
- Streaming tape is continuously running while data is written or read
batch processing
- all jobs of a particular type held and batched together for subsequent processing
real-time processing
a program runs when submitted, often with user interaction during processing
virtual machine
has computer memory allocated for partitioned among several users running applications simultaneously
- CPU and main memory must be large enought
- Each user appears to have his or her own machine
multitasking, multiprogramming, time sharing (swapping)
user take turns using the entire computer main memory for a certain length of time (less than a second)
- under the control of operating system
- at end of time period, all active memory is written to private area
- memory for the next user is loaded
- swapping is so quick that all users are able to accomplish useful work in real time
network
connected arrangement of physically separated computers and components
networking
the use of communication links to connect these computer transmission line may be - standard metal conductor - fiber optic cable - infrared connection - microwave connection - some other communication path
wide are network (WAN)
centrally located main computer interacts with, and is fed by, smaller computers located elsewhere
- larger geographic area, used for the internet, government facilities, large corporations
- slower than LAN, about 150 Mbps
local area network (LAN)
many computers linked together in order to share storage and printing resources
- smaller are than WAN, used for homes, offices, schools
- up to 100 Gbps
download, upload
referenced from user’s perspective
- download a file: user receives a file
- upload a file: user sends a file
Downstream and upstream are also referenced from the user’s perspective
- user sends data upstream to the host
- user receives data downstream from the host
asymmetrical digital subscriber line (ADSL)
refers to direction-driven transmission speeds, typically lower for uploading than for downloading
circuit switching
- uses a dedicated path between sending and receiving units
packet switching
transmits a message in separate pieces (packets) over multiple paths through control computers (nodes)
- packets of data treated independently
- can be routed through different nodes
- can arrive at the end in any order
- encoding allows data to be assembled into proper sequence
simplex communication
data transmission in one direction only
half-duplex communication
data transmission in both directions but only one direction at a time
duplex or full-duplex communication
data transmission in both direction simultaneously
asynchronous transmission
each character preceded and followed by special signals
- start and stop bits
- every 8-bit character is transmitted as 10 bits
- character transmission rate is 1/10 of transmission speed in bps
- possible to distinguish the beginning and end of each character within the bit stream
synchronous transmission
transmits blocks of data continuously without pause requiring a built-in clock to maintain synchronization
- synchronous transmission preceded by and interwoven with special clock-synchronizing characters
- separation of a bit stream into individual characters performed by counting bits from the start of the previous character
- about 20% faster than asynchronous communication
communication lines
narrow band
- supports a single channel
voice grade
- supports frequencies between 300 Hz and 3300 Hz
wideband
- supports highest transfer rates
errors in transmission
- can occur at the rate of 1 in 10,000 over voice-grade lines
- communication protocols and transmission standards are methods to ensure accuracy
loop or echo checking
each block of data is sent back to the sender and if the characters in the block do not match, they are re-sent
check digit or block check character
derived from the remainder after dividing all serialized bits in transmission block by a predetermined binary number
network topology
physical or logical arrangement of the components of a computer system
protocol
operational and communications rules followed by computers and other devices
- standards
- recommended standards
standards organizations
international organization for standardization (ISO)
American National Standards Institute (ANSI)
internet
consists of numerous interconnected computers, servers, nodes, and networks using common communication protocols
- transmission control protocol/ internet protocol (TCP/IP)
- file transfers protocols (FTP)
- graphical user interfaces (GUI)
- hypertext data structures and hypertext markup language (HTML)
domain names
device addresses used to allow the movement of information between networks and hosts of the internet
top level domain names; .com, .edu, .gov, .org, .net
