Ch. 2 - Application Layer Flashcards
HTTP
HyperText Transfer Protocol - the protocol used for transmitting web pages over the Internet
TLS
Transport Layer Security provides encrypted TCP connections, data integrity, and end-point authentication.
Stateless HTTP
Server maintains no information about past client requests.
Web client
Browser that requests, receives (using HTTP protocol), and “displays” Web objects
Web server
Sends objects (using HTTP protocol) in response to requests.
Web page objects
e.g. HTML files, JPEG images, Java applets, audio files, etc.
Why are protocols that maintain “state” complex?
- Past history must be maintained
- If server/client crashes, their views of “state” may be inconsistent and must be reconciled
What are the two types of HTTP connections?
Non-persistent HTTP:
- At most one object is sent over a TCP connection
- Downloading multiple objects requires multiple connections
Persistent HTTP:
- Multiple objects can be sent over a single TCP connection between client and server.
Socket
Process that connects an application with a network protocol.
P2P Architecture
No always-on server; arbitrary end-systems directly communicate; peers request service from other peers, provide service in return; peers are intermittently connected and change IP addresses
Client-Server Architecture
Client computers use a centrally administered, always-on server to share data, data storage space, and devices.
Process
A program that is running within an end system
FTP
File Transfer Protocol: uses a TCP-based network to pass files from host to host.
Web Cache
A file that stores copies of Web pages to make frequently accessed pages load faster. (a.k.a. Proxy Server)
Define CDN
Content Delivery Network: a network of servers that deliver web content to users from locations closest to them, improving performance and reliability.
CBR
Constant Bit Rate: video encoding rate fixed
VBR
Variable Bit Rate: video encoding rate changes as amount of spatial, temporal coding changes
DASH
Dynamic, Adaptive Streaming over HTTP
DNS
Domain Name System - Maps domain names to IP addresses.
Cookies
Small text files stored on a user’s computer by a web server.
Application Layer Protocols (4)
HTTP, FTP, SMTP, POP3/IMAP
TLD
Top Level Domain. The last section of the domain name (e.g. “.com” or “.org”)
Root name server
13 servers around the world that contain all IP address mappings for all domain names in existence. It is essentially the master “phone book” of the internet to look everything up.
DNS spoofing
the DNS server is given information about a name server that it thinks is legit when it isn’t
HTTP Status Codes
1xx : informational / 2xx : success / 3xx : redirection / 4xx : client error / 5xx : server error
Data integrity for applications
some apps (e.g., file transfer, web transactions) require 100% reliable data transfer, while other apps (e.g., audio) can tolerate some loss
Timing for applications
some apps (e.g., Internet telephony, interactive games) require low delay to be “effective”
POST method
- web page often includes form input
- user input sent from client to server in entity body of HTTP POST request message
GET method
- Used to retrieve data from a server.
- include user data in URL field of HTTP GET request message (following a ‘?’):
www.site.com/search?monkeys&banana
HEAD method
requests headers (only) that would be returned if specified URL were requested with an HTTP GET method.
PUT method
- uploads new file (object) to server
- completely replaces file that exists at specified URL with content in entity body of POST HTTP request message
HTTP 1.0 vs 2
HTTP 1.0: One request per connection, slow page loads.
HTTP 2: Multiple requests per connection, faster page loads, header compression.
Email components (3)
User agents, mail servers, SMTP
DNS name resolution queries (2)
Iterative query: “I don’t know this name, but ask this server”
Recursive query: Client asks server, server queries other servers until it finds the answer, then returns it to the client.
Headers
- info added to data packets at each layer of the network protocol stack.
- Contains metadata like source and destination addresses, port numbers, and protocol information.
SMTP
Simple Mail Transfer Protocol - The main protocol used to send electronic mail from server to server on the Internet.
TTL
Time to Live
RTT
Round Trip Time: time for a small packet to travel from client to server and back.
