3600 quiz 2 WIP

Application Architectures

client-server
peer-to-peer (P2P)

server

always-on host
permanent IP address
data centers for scaling

clients

communicate with server
may be intermittently connected
may have dynamic IP addresses
do not communicate with each other

P2P Architecture

NO always-on server
arbitrary end systems directly communicate
peers request service from other peers, provide service in return to other peers
peers are intermittently connected and change IP addresses

self scalability (P2P)

new peers bring new service capacity, as well as new service demands

process

program running within a host

inter-process communication

how two processes communicate within the same host

processes in different hosts communicate by exchanging ____

messages

client process

process that initiates communication

server process

process that waits to be contacted

process sends/receives messages to/from its ______

socket

socket is analogous to a

door

sending process

shoves message out the door (socket)

sending process relies on _____ to deliver message socket at receiving process

transport infrastructure

to receive messages, processes must have

identifier

host device has unique ____ IP address

32-bit

Does IP address of a host on which process runs suffice for identifying the process?

No, many processes can be running on the same host

Identifier includes:

IP address and port numbers associated with the process of a host

App-layer protocal defines:

types of messages exchanged
message syntax
message semantics
open protocols
proprietary protocols

message syntax

what fields in messages & how fields are delineated

message semantics

meaning of information in fields

rules

how processes send and respond to messages

open protocols

defined in RFCs (HTTP, SMTP)

data integrity

Some apps (file transfer, web transactions) require 100% reliable data transfer

timing

some apps (Internet telephony, interactive games) require low delay to be effective

throughput

some apps (multimedia) require minimum amount of throughput to be effective

TCP Service provides:

reliable transport
flow control
congestion control
connection-oriented

UDP service provides

Unreliable data transfer

HTTP stands for

Hypertext transfer protocol

HTTP follows ___ model

client/server

HTTP client

browser that requests, receives and displays web objects

HTTP server

web server sends (HTTP protocol) objects in response to requests

HTTP uses ___

TCP

HTTP is

stateless, server maintains no information about past client requests

Types of HTTP connection

Non-persistent & persistent HTTP

non-persistent HTTP

at most one object sent over TCP connection

persistent HTTP

multiple objects can be sent over single TCP connection between client, server

RTT

time for a small packet to travel from client to server and back

HTTP response time:

One RTT to initiate TCP connection, one RTT for HTTP request and first few bytes of HTTP response to return, file transmission time

non-persistent HTTP response time

2RTT + file transmission time

non-persistent HTTP issues

requires 2RTT per object
OS overhead for EACH tcp connection
browsers often open parallel TCP connections to fetch referenced objects

persistent HTTP:

server leaves connection open after sending response
as little as one RTT for all objects

types of HTTP messages

request, response

HTTP request message

ASCII - Human readable

POST

web page often includes form input
input is uploaded to server in entity body
input does not appear as part of URL field

GET

used to request a resource
input is loaded in URL field of request line

HEAD

Similar to GET, but only header is returned and body is empty

PUT and DELETE

Upload or delete files from server (not always allowed)

HTTP/1.0

GET, POST, HEAD

HTTP/1.1

GET, POST, HEAD, PUT, DELETE

HTTPS response status code: 200

OK, request succeeded

HTTP Codes: 301

Moved Permanently, request object moved

HTTP Code: 400

Bad request, request msg not understood by server

HTTP code: 505

HTTP version not supported

User-side state: cookies components

1. Cookie header line of HTTP response message

   2. Cookie header line in next HTTP request message
      3. cookie file kept on user’s host
      4. Back-end db at website

What are cookies used for?

Authorization, shopping carts, recommendations, user session state

web caches proxy server

Satisfy client request without involving origin server

cache acts as both

client and server

E-Mail major components

user agents, mail servers, simple mail transfer protocol (SMTP)

User Agent

outgoing, incoming messages stored on server (outlook)

three phases of SMTP

handshaking, transfer of messages, closure