module 3 Flashcards
Network
All of the stuff that connects computers, devices and allows them to comunicate with eachother
Synchronous vs Asynchronous
Synchrnous communication:
-happens in real time
ie: convo u have with your friend or talking thru walkie talkie or radio
Asynchronous:
Think postcards: you both could be writing eachother a postcard at the same time, but by the time they reach eachother its on a different day, (not on the same schedule)
ie the internet works like this (messaging ur friend on imessages, it may seem as though it is in real time, but the timing of the text is bundled in with the text)
-a way to know asynchronous communication is that as soon as there is a time on it, you know that it is asynchronous: ie with imessage, the time is the tie that bob actually recieved the mesage
All of the internet communication is what type of communication
Asynchronous
Communication Layers
when communication comes IN:
goes from low levels of communication to high
When commmunication goes OUT (send a message):
goes from high levels to low
think example:
when u talk, u vibrate air molecules in the air adn that is what os carruing info to ur friend, and then it travels thru ear adn then begins to vibrate the hair stuff in ear which stimulates nerves, which displays the sounds as frequencies then processes the sounds as PHONIES (phonetic things) so going from lower to higher
but talking to someone u go from high to low cuz u go from brain (think what to say), then brain impules send to nose mouth and teeth and finally the mouth says it and back into air (low layer)
BASICALLY:
order is from high to low
Semantic meaning of words
words
phonemes
soundwaves
when in goes soundwaves up when out it goes semantic meaning and down
same idea with postcards:
Semantic meaning of words
words
letters
mail delivery system (instead of air)
Protocols
-handshake, when someone puts out their hand, u know the protocol is to shake it
-in verbal communication: u know not to speak too loud, dont stand to close
for postcards:
-need a specific address, stamp, etc
-essentially, every lauyer has a protocol, and it allows for communication because of how strict it is
computer protocol is similar to a form: like doctors office form
Layers of Communication over the internet
High to low
HTTP
Transmission COntrol Protocol (TCP)
Internet Protocol (IP)
Physical layer
Physical Layer
-lowest communication layer
4 different physical layers:
- Ethernet
-communicate over a physical wire/cable
-need a device that can transmit info through wire
-each device that connects to ethernet needs an identifier (MAC: Media Access Control) ie computer if has ethernet port, it has a mac address
-works like if multiple devices talking at same time, it backs off and tries again after(like dinner party) this happens on wire
-different speeds, if one device is slower or one cable is slower it will slow the whole chain (like traffic on highway)
2.Phone, ADSL or Cable Modems
-old way, to connect internet, u connect computer to modem and call a phone line, so must keep on phone line to have connection to internet
-tones on this call are the protocols
-only one computer at a time
ADSL is modern modem, stands for Asymmetric digital subscriber line
-assymetric because download speed much faster than upload speed
Cable modem:
similar to phone modem but it works with frequencey that transmits television signals instead of voice
- WIFI
-electromagnetic radiation: only a small area on this spectrum is visible to us
-the different types of waves can pass thru different things ie, light is easily blocked but radio waves can pass thru walls
-wifi is a fancy radio wave
-length is 20-100 m
for it to work…
a) need access point (router)
b) name for wifi
c)password
-works like ethernet where it backs off when multiple people are asking for requests at once - Cellular (3G/LTE)
-electromagnetic radiation
3G( third generation)
lte (long term evolution
range: kilometers, communicating with cell tower
-unique identifier: IMEI (international Mobile Station Equiment Identity)
TCP/IP
-doesnt matter what the lower layer is (doesnt matter if the physical layer is wifi, ethernet, lte
TCP: Transmission Control Protocol
IP: Internet Protocol
IP(Internet Protocol)
-when communicating, we need a sending address and a receiving address (like a postcard)
IP Address:
-4 numbers, each within the range of 0-255 (256 possible numbers), seperated by .
-so have 256^4 possible combinations so (4 billion devices)
-this is not enough so we have two solutions to the fact that we are running out of IP address
1)IPv6
-a much longer IP address
-can server 340 trillion trillion trillion
2) NAT
-100s of devices just share an ip address
-works becaues there is a middle man that intercepts ur request, changes the sending address to the common address u guys all share, and sends it to the person u want.
-that person will send it back to thecommon ddress, and the middle man will change it back to ur own address and give it to u
Two types of IP addresses:
1)Fixed IP Address:
-big companies, organizations all hve these fixed ip addresses
-so every ip address for that org will start with certain similar numers
2)DHCP
-protocol
-temporary ip addresses for devices sent outthis way
-they have a bank of ip addresses that it can give out and these will expire after a certain amount of time
Domain Name System
-protocol
-when we type in a website, it sends it to the local DNS server, and it sends back the IP address
-if local DNS doesnt know where it is, then it will send to the .ca DNS server
IP ROuting
-when we send out a message, it sends it to a router, which sends it to another router, eventually it reaches the comupiter it wants to reach, this is how message gets to someone across the world
-all routers are connected ot each other
-usually to get from one destination to another it takes less than 50 hops
Transmission Control Protocol (TCP)
Another middle layer
-quality control
-3 messages go back and forther before twp people talk
1) hey can we talk
2) yes this is how we can galk
3) ok we will talk according to these rules
How it works:
-breaks large message into smaller numbered PACKETS
-Acknowledge received packets
-request missing packets
-reassemble large message from packets
think a book is sent as ltitle postcards, u acknlwodege u receive it, u assemble it back into novel again and bam
High Layer Protocols
HTTP
-hypertext transfer protocol
-basically a protocol for requesting and sending information
requests include:
a) ip address
b)doc requested(ie html)
c) browser and lang info
d) cookies
http:// is the protocol
uwaterloo.ca is the host
/about is the path
protocol, domain and path
protocol: requests info and sends it
domain: gets translated into an Ip address that is sent back tot he user to take it to main page
path: the specific page whih the user is reuqesting
