202401200817
Status: #idea
Tags: CN

Application Layer

P2P Architecture

• Does not have an always-on server
• Arbitrary end systems directly communicate
• Self scalability
  • New peers bring new service capacity, as well as service demands
• Peers are intermittently connected and change IP addresses
  • Complex to manage

Sockets

• Process sends/recieves messages to/from its socket
• TODO: Slides chp2 from beg to 15

TCP & UDP

• Streaming multimedia and internet telephony maybe use either TCP or UDP
• If latency is not important, most protocols use TCP

Securing TCP

• TCP and UDP do not have any encryption
• SSL/TLS
  • At app layer
  • Apps use SSL or TLS libraries which talk to TCP

Web and HTTP

• Web pages consist of objects (HTML file, image, audio file, etc.)
• Each object is addressed by a URL
• Client-server model
  • Client: Requests, receives and displays web objects
  • Server: Sends objects in response to requests
• Uses TCP
  1. Client initiates TCP connection to port 80
  2. Server accepts TCP connection from client
  3. HTTP messages are exchanged
  4. TCP connection is closed
• HTTP is stateless
  • Server maintains no information about client's past requests

Non-Persistent HTTP & Persistent HTTP

• Non-persistent HTTP
  • At most one object sent over the TCP connection
  • Downloading multiple objects requires multiple connections
  • Image from slide 2-23 and 2-24
  • 1 RTT to initiate TCP connection
  • 1 RTT for HTTP request and first few bytes of HTTP response to return
  • $$\text{Non-persistent HTTP response time}=2\text{RTT}+\text{file transmission}$$
  • TODO: Slide 2-26 till 2-32
• Persistent HTTP
  • Multiple objects can be sent over a single TCP connection

HTTP Messages

• ASCII (human-reabable) format

Status Code Response Groups

References