Week 5 Flashcards
What are objects of a web page?
a file, like an HTML file, image, CCS file, addressable by a single URL.
What is a webpage?
a document that consists of one or more objects
What transport protocol does HTTP use? Port Number?
TCP
Port number 80
What does it mean that HTTP is “stateless”?
the server keeps no information about the past clients and its reqiuests
What are the main components of a URL?
- the host name of the server
- the object’s path name
What are the 2 types of HTTP connections?
- Non Persistent HTTP
- Persistent HTTP
What is Non Persistent HTTP?
at most one object is sent over the TCP connection.
TCP connection closes after server sends the object
What is Persistent HTTP?
A persistent TCP connection that allows to send multiple objects over a single TCP connection.
What is RTT?
Round-Trip Time for Non Persistent HTTP.
The time for a packet for client -> server -> client.Ho
How much RTT for non persistent HTTP?
2 RTT
1 RTT to establish connection
1 RTT to send/receive
What are the 2 types of HTTP messages?
- Request
- Response
Format of an HTTP Request message?
- Request Line
- Header Lines
- Blank Line
- Body
- IN ASCII: human readable format
What is in the request line of a HTTP Request message?
Method, URL, HTTP version
What is the entity body used for in a HTTP Request message?
Other methods such as POST or PUT
What are the methods?
GET, POST, HEAD, PUT, DELETE
What is “user-agent”
the browser type making the request to the server
Format of an HTTP Response message?
- Status Line
- Header Lines
- Blank Line
- Entity Body
What is “Server” in an HTTP response message?
Like similar agent, the browser type
What is “Date” in an HTTP response
time when the server retrieves the object.
What is a web cache / proxy server?
An entity that does HTTP request on behalf of an original web server.
How does a web cache work?
- web cache has its own storage
- keep copies of recently requested objects
- if it doesn’t have the object it requests a TCP connection to the origin server
Is a cache a server or client?
Both.
Pros of web caching?
keeps copies of recently requested objects, so it saves response time and reduce costs
What is a stale object?
an object that has been modified after it’s been cached.
How to solve a stale object in web caching?
Use the conditional GET
2 characteristics of a conditional get?
- request uses the GET method
- request has an “if-modified-since” header line
