Tc 361 Definitions

Front 1

Local Loop

Back 1

Local network of wires, terminating at the CO, ran by LECs

Front 2

Packet

Back 2

a message at the internet layer, a chunk of data, sometimes called frames, blocks, or segments

Front 3

Frame

Back 3

1) a message at the data link layer, 2) In time division multiplexing, a brief time period, which is further subdivided into slots

Front 4

Encapsulation

Back 4

packets at one layer become payload for the next layer, the placing of a message in the data field of another message

Front 5

Circuit switching

Back 5

Switching in which capacity for a voice conversation is reserved on every switch and trunk line end-to-end between the two subscribers

Front 6

Packet switching

Back 6

the breaking of conversations into short messages (typically a few hundred bits long); allows multiplexing on trunk lines to reduce trunk line costs

Front 7

Serial

Back 7

Ethernet transmission over a single pair in each direction

Front 8

Parallel

Back 8

a form of transmission that uses multiple wire pairs or other transmission media simultaneously to send a signal; increases transmission speed

Front 9

Synchronous

Back 9

synchronization bits are sent at fixed intervals whether you are transmitting or not, 99% efficient using 7-bit ASCII

Front 10

Asynchronous

Back 10

start and stop bits are sent for each byte, time between bytes can vary, 77% efficient using 7-bit ASCII

Front 11

Modulation

Back 11

converting a digital to an analog signal

Front 12

Amplitude

Back 12

The height or power of a wave

Front 13

Frequency

Back 13

the number of cycles of a wave within a period of time, measured in Hz, or Hertz, or cycles per second

Front 14

Multiplexing

Back 14

sending multiple messages over the same channel

Front 15

I-picture

Back 15

Intra-coding frames in video compression, similar to JPEG, offer moderate compression

Front 16

P-picture

Back 16

Forward Prediction frames in video compression, start with an I-picture and estimate which pixels change; introduces error, but has good compression

Front 17

B-picture

Back 17

Bidirectional Prediction, the average between I- and P-pictures, though B-pictures are not used to predict P-pictures, offers excellent compression, but is computationally expensive

Front 18

Physical Topology

Back 18

how devices on a network are physically linked, not necessarily the same as the logical topography, normally using the following three approaches

Front 19

Bus

Back 19

Linear arrangement, requiring terminators at each end of the line

Front 20

Ring

Back 20

similar to bus, though forms a ring instead of a line, requiring no terminators

Front 21

Star

Back 21

Hub-and-spoke, each device is connected to a central unit, most common topography today, easy to centrally manage, but with a single point of failure

Front 22

Flow control

Back 22

one device sends faster than another, causing a backlog, fixed by queuing packets, sending a pause request, or a sliding window technique

Front 23

Token Passing

Back 23

a centralized MAC scheme, transmit if have permission by the token, some systems you ask for the token and others it is passed at regular intervals

Front 24

Logical Topology

Back 24

Determine how messages are passed, two options, sequential and broadcast

Front 25

Sequential

Back 25

Ring, aka Bucket-brigade, packet sent to neighbor, they read the address, if addressed to them they read it, if not they pass it to the next machine

Front 26

Broadcast

Back 26

message sent to all, everyone reads the address, if addressed to them, they read it, if not they ignore it

Front 27

Ethernet

Back 27

standard datalink protocol, IEEE 802.3, Error Checking using CRC, Flow control of pause or sliding window, CSMA/CD access control, logical topology is broadcast, physical topology is usually a Star

Front 28

Token Ring

Back 28

datalink architecture IEEE 802.5, Checksum error checking, sliding window flow control, Token MAC, Sequential logic, physical star

Front 29

T1

Back 29

a standard for digital transmission circuits over twisted pair, 1.544Mbps, synchronous needing framing bits, 24 channels at 64 Kbps each, 8 bits per channel, TDM- like

Front 30

Channel

Back 30

small frequency range that is a subdivision of a service band

Front 31

Virtual Tributaries

Back 31

packing multiple data types into SONET

Front 32

Virtual Circuit

Back 32

a tool to create pseudo circuits on a packet switched network. Send call set-up packets to find best route, then send data packets along that route. Requires cooperation from other protocols to work properly

Front 33

X.25

Back 33

defines how data get on and off a packet switched network, not how packets move across the network, performs hop by hop error checking

Front 34

Frame Relay

Back 34

lets end nodes worry about errors, ignores bad packets, minimal flow control, still supports virtual circuits

Front 35

Class A

Back 35

Small number of big networks have Class A IPv4 address, first bit 0, 7 bits to ID segment, 24 bits to ID hosts

Front 36

Class B

Back 36

Midway between A&C

Front 37

Class C

Back 37

first 3 address bits are 110, 21 bits to ID segment, 8 bits to ID host, large number of small networks

Front 38

Class D

Back 38

IP addresses used in multicasting

Front 39

Port

Back 39

In TCP and UDP messages, a header field that designates the application layer process on the server side and a specific connection on the client side

Front 40

Steganography

Back 40

The practice of hiding messages, often in plain sight

Front 41

Cryptography

Back 41

Encrypting messages, the practice/study of hiding information

Front 42

Transposition

Back 42

rearrange the letters in a message, ex. A=C, B=D, C=E, etc

Front 43

Substitution

Back 43

Replace letters with other letters, usually with random mapping, but requires key

Front 44

Key Exchange

Back 44

problem of securely sharing a decryption key with the communication partner alone.

Front 45

Symmetric Key

Back 45

the same key is used to encrypt as is used to decrypt the message

Front 46

Asymmetric Key

Back 46

a different key is used to decrypt than is to encrypt the message. A public key is used to encrypt, and a private key is used to decrypt

Front 47

Digital Signature

Back 47

a private key is used to encrypt the message, and a public key is used to decrypt the message. Only your public key can decrypt a message from you, so the receiver knows the message was encrypted by you alone

Front 48

Rectilinear Orientation

Back 48

Photon transmission scheme where 1s and 0s can only be read if the correct detector is used, in this case, a vertical or horizontal reader. If the wrong reader is used, the message is lost. Eavesdropping is prevented as a key is needed to know when to change orientations when reading the message

Front 49

Diagonal orientation

Back 49

same as Rectilinear, in this case, a diagonal reader

Front 50

Virus

Back 50

a piece of executable code that attaches itself to programs or data files. When the program is executed or the data file opened, the virus spreads to other programs or data files

Front 51

Worm

Back 51

an attack program that propagates on its own by seeking out other computers, jumping to them and installing itself

Front 52

Trojan Horse

Back 52

a program that looks like an ordinary system file, but continues to exploit the user indefinitely