midterm 1 - networks Flashcards
lect 10 - 11
define network protocols
instructions for how computers will comm over networks
how does communicaiton move through layers
high level –> low level –> high level
eg thought –> mouth moves –> sound waves –> ear drum –> signal interpretation –> thought
cs100 model for communication layering
high = end user application
med = network protocol
low = data transmission mechanism
low level layers of comms - 4 examples
C-WED-C
cable modem
wifi
ethernet
DSL
cellular
cable modem comms
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
wifi comms - mechanism
fancy radio waves
diff freq = diff speeds –> 2.4 ghz slower than 5 ghz
wifi transmission by centralized towers
wifi protocols
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
ethernet comms
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)
DSL comms
phone line transmission
pt to pt protocols = direct user-ISP comms
ADSL = asym DSL –> downloads faster than uploads
cellular comms
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
how do postcards explain network traffic
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
TCP explained
- 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
IP explained
- 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
how are packets transmitted
packets transmitted between intermediate network devices
therefore packets are relayed between other servers, routers, etc –> allows long range transmission
IPv4
IP addresses are based on 4 digits 0-255 each
0-255 each = 8 bits –> 4 digit IP = 32 bit address
IPv6
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
IPv4 vs v6
v4 –> 32 bit addresses –> 4 bn addresses
v6 –> 128 bit addresses + can use hex digits –> WAYYY more possible addresses
DNS
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
DHCP
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
NAT
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
HTTP
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)
