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Introduction

Summary

keywords

TODO

HW performance calculation on installing web cache

Exercise*

Next time HOL blocking

Recap

What kind of Application need which transport protocol?

TCP & UDP have no encryptions, throughput guarantee, timing,,

Web and HTTP

HTTP uses TCP TCP is closed after a certain amount of time, or certain amount of transmissions HTTP is stateless. headers do not store any stateful meanings.

Non-persistent TCP no longer used. High RTT One single connection on one transmssion

request and response

all human readable. Written in ASCII codes)

HTTP request message​

composed of

  • request line (method, url, version)
  • header lines (header values)
  • body (data)

in the request message,

  • GET, POST, HEAD, PUT request types
  • lines are broken down by \r\n

For normal GET request, there's no body

GET​

  • send data to server by URL query (after question mark).

POST​

  • form input
  • request headers only.
  • only used when checking server up status.
  • will only send essential info

PUT​

  • upload a file; alternative for FTP.
  • completely replaces file that exist at specified URL

Response message​

composed of

  • status line (HTTP/1.1 200 OK)
  • header lines
  • body

in the header

  • Date, Server, Last-Modified,
  • Etag,
  • Accept-Ranges,
  • (Content-Length, Content-Type..)
  • and more..

Etag is used for caching page purposes. version controlling for page. ex . ( Etag : "abb-43kfnnldocmmdkvndls")

#todo : what is Accept-Ranges

Response status codes​

codenamedescription
200OKsuccess
301Moved Permanentlyrequest object moved, new location specified
400Bad requestnot understood by server
404Not foundnot found
505HTTP Version Not supported-

and more..

Cookies​

client-side tool to make WEB stateful.

  • in HTTP, all request are independent of each other
  • browser stores the cookie
  • widely used in server identifying a client browser&machine
    • Authorization, shopping carts, recommendations, user session state(e-mail..)
  • when written in browser, it transcends time and can be used in the long apart future and show the seamless cookie-specific action.

four components of data storages

  • cookie header line ( of response message)
  • cookie header in next HTTP request message)
  • cookie file kept on user's host, managed by user's
  • back-end database at web site

#todo : check the python example on the slides.

import requests

response = requests.get("https://www.google.com")

if response.status_code == 200:
	cookies = response.cookies
	for cookie in cookies:
		print(f"Cookie Name: {cookie.name}")
		print(f"Cookie value: {cookie.value}")

else :
	print("HTTP Error:",response.status_code,response.reason)
Cookie Name: 1P_JAR
Cookie value: 2023-09-14-04
Cookie Name: AEC
Cookie value: Ad49MVFXS3NX5m3l8PO4X5FUaFZvQI8b1Czl9-Ym1cAxZn7fTXSC5fXdAw
Cookie Name: NID
Cookie value: 511=m0D8Dti7MEGMgrBAZI_1a3ZfZ8xr9ydTVeHn60MicQtJztyPIo5Qj7U73zEnhAm8i1KeRJfAjsANOwpxvqaKfemnBYIWKnfl_OZOjFbDw6rMPjH_aEG9PFVAp20YMu8ZOpIaj7b7NBSauxhKPq3-ceyC3o-pyKj-X-5_T1G0ou4

  • Cookie has trade-offs on privacy
    • it is a info a lot about you.
  • How to keep state? (other than cookies?)*
    • cookies inside the HTTP message
    • protocol endpoint ?
    • #todo what is protocol endpoint

Web Caches

Intermediate servers that saves a server and sending pages instead of the origin server

  • satisfy client request without involving origin server
  • Act as a client against origin server, act as a server for end-users
  • server tells cache about whether the object can be cached or not
    • Cache-Control: max-age=<seconds>

advantage​

  • makes less load on the origin server
  • reduce response time
  • reduces traffic on the backbone network

following is a small server

from flask import Flask, make_response

app = Flask(__name__)

@app.route('/')
def hello():
	response = make_response("hello, world")
	respon.headers["Cache-Control"]= 'public, amx-age=3600'
	return response

if __name__ == '__main__':
	app.run()

Caching Scenario​

![[../images/20230914140127.png]] $$ L = 100K;bits; a = 15/sec; R = 1.54 MBps;

access link utilization = La/R = .97 LAN utilization = 0.0015 delay : 2sec + access link delay(minutes) + LAN delay $$

So slow. How will it be 해결?

  1. buy a faster link high R cost-ineffective
  2. install a web cache #todo : make performance calculations

Conditional GET

Don't send object if cache has up-to-date cached version

  • no object transmission delay

Client sends a If-modified-since header message of cache that they have 304 Not modified status code tells us "you don't need a newer one"

![[../images/20230914140912.png]]