exam review module 5 Flashcards
the network
internet (biggest network in the world
the web
the biggest piece of the internet puzzle
synchronous
happens in real time. Ex: conversation you have with your friend. television, walkie talkie
asynchronous
post cards (could be days, weeks_ -> write what day you sent it
all of the internet works over asynchronous communication
text messages -> timestamp
involves a timestamp
communication layers
sending and receiving messages
when a message come sin, it goes from low layers of communication to high layers of communication
when you send it - goes from high to low layers
verbal communication example
There is a semantic meaning on top of the words (different ways of saying hello!)
IN semantic meaning of words words OUT phonemes sound waves
Example 2: Postcard
IN semantic meaning of words OUT
words
letters (on postcard)
mail delivery system
protocols
ex: Handshake protocol (stick out your hand, grasp, etc.)
ex: Verbal protocol (don’t stand too close, dont talk too loud, etc.
For a postcard, there is a specific protocol
Stamp
Address
Postal Code
Name
(Every layer of communication has a protocol.)
(A computer protocol is communicated as a FORM.) -> filling of fields.
physical layer
IN
High Layer Protocols
OUT
Middle: TCP/IP
Low: Physical Layer
Different Physical Layers
¥ Ethernet
¥ Phone, ADSL and Cable Modems
¥ WiFi
¥ Cellular (3G/LTE)
Phone, ADSL, Cable Modems
¥ Phone Modems : 2 device communication -> your modem to another computer.
¥ 2-Device communication
¥ ADSL (Asymmetric Digital Subscriber Line) (more modern) -> asymmetric means your downloads speeds are much higher than upload speeds. The technology and ideas are very similar to phone modems.
¥ Cable Modems uses the same ideas as a phone cable -> communicates over frequencies designed to transmit telephone signals (higher bandwidth through a cable modem).
WiFi includes:
¥ Access point (wireless router) which
¥ Broadcasts a name
¥ Has Additional Security (user? password) -> wifi protocol
¥ Eduroam
¥ Multiple standars for example (802.11g)
¥ Very similar to ethernet (wifi decides can all be shouting at the same time, but allow time for others to speak.
Cellular (3G/LTE)
¥ Electromagnet Radiation (very similar to wifi, but very different protocols)
¥ 3G : (3rd Generation)
¥ LTE : Long-Term Evolution (not quite 4G, 3.5G.) -> marketing sales
¥ Range: Kilometers
¥ Noisier environment -> more devices, more error correction.
¥ More power -> the power required to get the signal from your phone and to your phone will use more battery power.
¥ Unique Identifiers: All devices need unique IMEI (International Mobile Station Equipment Identity) -> devices can be locked into certain cellular companies using IMEI.
¥ “Locked” Devices
TCP
transmission control protocol
IP
internet protocol
ip adress
4 numbers, each in the range of 0-255
129.97.208.23
IPv6
longer, more complex
2620:101:f000:701:f87:e00b:4ea8:e0b3
DNS
Domain name system
Your device will communicate with your local DNS server to find uwaterloo.ca
If it can’t find this, it will try to communicate with a .ca DNS server, and might come back with a name.
DHCP
dynamic host configuration protocol
A device will communicate to the DHCP server and the DHCP server will give that device an IP from a bank of IPs. and it will last x amount of time. ex: 1 hour at a Starbucks.
NAT
Network Adress Translation
When you connect to a network, this system is used so that we don’t run out of IPs.
If you (think) you live at 100 Imaginary lane, and send a postcard out to 123 destination st., your “postman” (NAT) will change-> (translate) your return address to 555 real st (your real address).
192.168 (you live in imaginary lane)
Ip Routing
the way that messages get delivered.
ex: Physical delivery: Mail from your house to England.
Mail -> cambridge post office -> ontario dispatch -> canada dispatch -> international dispatch -> england dispatch -> london, england dispatch -> customer.
The same applies with any internet communication, but it works with multiple different routers who are all talking to one another.
Most messages can be transferred around the world with less than 50 hops (hops referring to different router paths.
TCP
Transmission control protocol
TCP (Quality Control)
Establishing a “session” -> handshake protocol between 2 devices (“can we talk”)
3 messages between you and a destination PC before anything happens.
¥ Break Large Message into smaller packets (numbered)
¥ Acknowledge received packets
¥ Request missing packets
¥ Reassemble large message from packets
ex: Sending a whole book to someone via postal -> send them individually by page. Some pages will get lost, and some pages will arrive at different times. This same analogy applies to sending a message over the internet. The individual pages can be referred to as “packets”.
The TCP takes these big messages, and breaks them up into small packets, and numbers them
The TCP protocol realizes which packets have not been sent (or received) properly, and will make an attempt to re-send
re-receive them. The destination computer then reorganizes these packets into whatever you’re downloading. (could be a movie download, etc.)
High layer protocol
HTTP
hypertext transfer protocol
http:// = protocol (highest layer)
uwaterloo.ca = host (middle layer)
/about = path
HTTP requests include:
¥ Your IP address
¥ Document requested (e.g : HTML)
¥ Browser & Language Information
¥ Cookies
what is HTTP for
sending and receiving information
