Cookies

Question 1

Four components of cookies

Answer 1

• Cookie header line of HTTP
  response message
• Cookie header line in next
  HTTP request message
• Cookie file kept on user’s
  host, managed by user’s
  browser
• Back-end database at Web
  site

Question 2

What cookies can be used for:

Answer 2

• Authorization
• Shopping carts
• Recommendations

Question 3

Cookies and privacy:

Answer 3

• Cookies permit sites to learn a lot about you
  -> e.g., your name, address, e-mail, etc

Question 4

What is the goal of web caches (proxy server)

Answer 4

Satisfy client request without involving origin server.

Question 5

How does Web Cache work?

Answer 5

• User sets browser: Web
  accesses via cache
• browser sends all HTTP
  requests to cache
• if object in cache: cache
  returns object
• else cache requests object
  from origin server, then
  returns object to client

Question 6

What else can be said about Web caching

Answer 6

Cache acts as both client and
server:
* Server for original requesting
client
* Client to origin server
Typically cache is installed by ISP
(university, company, residential
ISP)

Question 7

Why Web caching?

Answer 7

▪ Reduce response time for client
request
▪ Reduce traffic on an institution’s
access link
▪ Internet dense with caches:
enables “poor” content providers
to effectively deliver content

Question 8

Conditional GET

Answer 8

Goal: don’t send object if cache
has up-to-date cached version
* No object transmission delay
* Lower link utilization
▪ Cache: specify date of cached
copy in HTTP request
If-modified-since: <date>
▪ Server: response contains no
object if cached copy is up-todate:
HTTP/1.0 304 Not Modified</date>