Mod 2 - Network Organization Flashcards
What is a network?
it is all the “stuff” & devices that connect and allow computers to communicate with each other (infrastructure)
ex. the internet is the largest network
What is synchronous communication?
It is real time communication.
ex. talking on the phone, radio broadcast
What is asynchronous communication?
It uses a time stamp to keep track (like a postcard) and is not done on a particular schedule, meaning there is a time lag.
ex. internet, text messages
(if there is a time stamp on it, it is likely asynchronous)
What are communication layers?
When a message comes in, it goes from low layers to high layers. When a message is sent out, it goes from high layers to low layers.
Ex. postcard coming in:
mail delivery system>letters on postcard>words>semantic meaning of words
(vice versa for sent out)
What are protocols?
They are found in every layer of communication. Some protocols will be strict or basic, etc. Think about computer protocols like a form - it must be filled out to work.
Ex. postcard: needs a stamp, address, postal code, etc.
What are examples that fall under the physical layer (lowest)?
It provides physical interactions & components
- ethernet
- phone, ADSL & cable modems (all used to communicate from one computer to another)
- wifi
- 3G/LTE
- IMEI
What is required to use ethernet?
It needs a device that can transmit info over a wire & each connection requires a unique identifier known as a Media Access Control (MAC) address (every device with an ethernet port has one).
How does communication through ethernet work?
It uses sophisticated protocols to allow conversation. So, if one device is “talking”, others back off until there is a gap for them to “talk” - like a dinner party. There are different speed ratings for cables & devices, so a slower device/cable may slow down the entire communication chain.
How do phone modems (dial-up) work?
It connects a computer to a modem and is also connected to the phone line. There are many different protocols that occur because two devices must communicate to work.
How does ADSL work?
Asymmetric Digital Subscriber Line (ADSL) evolved from a modem and uses the same idea, but is slightly more sophisticated. The asymmetric means the download speed is faster than the upload speed.
How do cable modems work?
It uses the the same idea as other modems but communicates over frequencies designed to transmit TV signals & has a higher bandwidth.
How does wifi work?
It is just a radio wave on the electromagnetic radiation spectrum (can go through walls). Wifi ranges are typically 20-100m & use less power than radio signals. To work, an access point that broadcasts & receives from devices is required. Broadcasting name & security is part of protocol.
How does cellular 3G/LTE work?
It uses electromagnetic radiation similar to wifi, but has different protocols, frequencies & energies. Cellular range is much farther than wifi (several km) & often communicates with cell towers which is a much noisier environment. This means better error correction & signal change detection is required, so more power is needed (uses lots of battery).
What does 3G stand for? What does LTE stand for?
3G: 3rd generation (marketing scheme)
LTE: Long-Term Evolution (basically a 3 1/2 G)
What is IMEI?
an International Mobile Equipment Identity (IMEI) is required by all devices that communicate with cell towers. It is a unique identifier and explains why phones are locked to carriers.
What are examples that fall in the middle layer?
Middle layer provides interpretations as patterns & symbols. It does matter how lower layer is working (can be using wifi, ethernet, 3G - doesn’t matter)
- IP
- DNS
- DHCP
- IP Routing - TCP (this is actually a higher layer than IP)
What is IP?
Internet Protocol (IP) is used to communicate on the internet & just like postcards, it needs a sending address and a destination address (IP address).
What is an IP address? What is the issue with IP addresses?
It is an identifier that uses four numbers ranging from 0-255. Usually large corporations/organizations (like UW & Google) have a fixed IP address.
ex. UWaterloo is: 129.97.208.23
The problem is, there is a maximum of 4 billion IP addresses possible, but we are past that point by now.
What are some solutions to the IP address problem?
- IPv6 (IP version 6): uses a much longer IP address and can handle 340 trillion trillion trillion
- NAT (Network Address Translation): is many different computers sharing the same physical address - may not be real IP address, but solves the issue of potentially running out.
What is DNS?
Domain Naming System (DNS) is a server that receives a request when you type in a website name (the protocol) and the DNS server returns back an IP address. A local DNS server may not know a website name so it can go to the “.ca” server to narrow it down to find the appropriate result.
Give some examples of domain names
- .ca
- .edu
- .org
What is DHCP?
A Dynamic Host Configuration Protocol (DHCP) server provides temporary IP addresses. When an individual device tries to connect to a network, it asks for an IP address from the DHCP server (the server has a bank of IP addresses). It gives you one to use that later expires so others can use the same IP address.
What is IP routing?
Core component for communication. When a computer sends a message, it has a destination IP address which is sent to the local router, then another, etc. until the message reaches the destination computer.
What is TCP?
Transmission Control Protocol (TCP) is like quality control. If you want to visit something on the internet, first a TCP session is created that messages back & forth b/w computers to establish rules before talking.
How are big files/images sent?
Through TCP! The big files and images are broken down into smaller pieces called packets, then they “hop” b/w computers and the destination computer reassembles them. Packets can get out of order or go missing so the TCP can request it be resent.
What is TCP responsible for?
- breaking down large messages in ordered packets
- acknowledging received packets
- requesting missing packets be resent
- reassembling packets
What falls under higher layer protocols?
It provides the context & meaning
- HTTP
- HTTPS*
- DHCP & DNS
- FTP
- SFTP*
- POP, SMTP, IMAP
*S is used for encryption
What is HTTP?
HyperText Transfer Protocol (HTTP) is the most common protocol used for requesting & sending info. Uses URLs which have 3 components for requesting:
- http:// } protocol
- uwaterloo.ca } host
- /about } path
What does an HTTP request include?
- your IP address
- document requested (most in HTML)
- browser/language info
- cookies
What is (S)FTP? What is POP, SMTP, IMAP?
(S)FTP: used for transferring files between computers outside of web browswers
POP, SMTP, IMAP: used for sending emails between computers
