midterm 1 - networks

Question 1

define network protocols

Answer 1

instructions for how computers will comm over networks

Question 2

how does communicaiton move through layers

Answer 2

high level –> low level –> high level

eg thought –> mouth moves –> sound waves –> ear drum –> signal interpretation –> thought

Question 3

cs100 model for communication layering

Answer 3

high = end user application
med = network protocol
low = data transmission mechanism

Question 4

low level layers of comms - 4 examples

Answer 4

C-WED-C
cable modem
wifi
ethernet
DSL
cellular

Question 5

cable modem comms

Answer 5

protocol
signals transmitted over cable at designated “slots” to avoid signal collision
devices wait for free slot to send

receiving devices monitor cable transmissions to pick up on the specific signal of interest

Question 6

wifi comms - mechanism

Answer 6

fancy radio waves
diff freq = diff speeds –> 2.4 ghz slower than 5 ghz

wifi transmission by centralized towers

Question 7

wifi protocols

Answer 7

polite ethernet protocols
devices have MAC addresses

devices constantly attempting to transmit
BUT with extra step –> must request perms from router before transmitting

therefore prevents signal collision

router does not provide perms –> device resends request

Question 8

ethernet comms

Answer 8

uses fiber optics + copper cables
every device has unique media access control (MAC) address

devices are constantly attempting to transmit signals –> will check network for opportunity to send signals

if devices transmit simultaneously –> signal collision detected –> devices reattempt transmission to send 1 at a time (transmit at random time to avoid collision with eachother again)

Question 9

DSL comms

Answer 9

phone line transmission
pt to pt protocols = direct user-ISP comms
ADSL = asym DSL –> downloads faster than uploads

Question 10

cellular comms

Answer 10

network uses regulated lanes (diff freq)

several devices assigned per lane/freq
devices are assigned specific intervals for comms –> prevents signal interference

recipients monitor same freq for signal

Question 11

how do postcards explain network traffic

Answer 11

signals are sent in packets (1500 bytes each) which are then reassembled together to form the full/original signal/message

packets are tagged with origin IP address + target recipient IP address –> like a postcard

Question 12

TCP explained

Answer 12

• transmission control protocol
• protocol for establishing device-device connections
• protocol for breaking signals down into packets
• ensures packets are sent/received
• failure to receive –> resend packets

Question 13

IP explained

Answer 13

• internet protocols
• IP address = unique device identifier over the internet –> is assigned by internet protocol
• MAC addresses = device identifier over a local network tied to hardware

Question 14

how are packets transmitted

Answer 14

packets transmitted between intermediate network devices

therefore packets are relayed between other servers, routers, etc –> allows long range transmission

Question 15

IPv4

Answer 15

IP addresses are based on 4 digits 0-255 each

0-255 each = 8 bits –> 4 digit IP = 32 bit address

Question 16

IPv6

Answer 16

32 bit IPs –> limited to 4 billion unique addresses

IPv6 –> 128 bit IPs –> 32 bit length addresses split into 8x 4bit digits

not limited to decimal –> can use hex digits

therefore significantly larger range of unique IP addresses

Question 17

IPv4 vs v6

Answer 17

v4 –> 32 bit addresses –> 4 bn addresses

v6 –> 128 bit addresses + can use hex digits –> WAYYY more possible addresses

Question 18

DNS

Answer 18

domain name system –> ties web address with corresponding IP address

user inputs website –> PC requests corresponding IP address

ISP servers have database of X IP = Y website

Question 19

DHCP

Answer 19

dynamic host config protocol

devices connect to network –> router assigns temporary IP address

IP addresses are assigned on time limits –> expire –> device will request new IP address from router

Question 20

NAT

Answer 20

net address translation
“apt building” analogy

devices will share IPs but router knows how to distinguish between devices

packets transmitted to router –> relayed as normal
incoming packets are received by router –> router translates shared IP to target device IP

Question 21

HTTP

Answer 21

hyper text transfer protocol
high level human intractable protocol

responsible for establishing TCP connections to specific paths within a website

device sends header info + data related to device-handling (eg language, cookies, OS, browser, etc)