Computer Network

用户8279

2025年12月10日修改

P2P distribution: t((M-1)+logN) M chunks N peers

Application Layer

Client-server paradigm

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Server: permanent IP address​

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Client:  may be intermittently connected, may have dynamic IP addresses​

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Examples: HTTP, IMAP, FTP​

Peer-peer paradigm

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Peers request service from other peers, provide service in return to other peers​

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Peers are intermittently connected and change IP addresses​

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Example: P2P file sharing​

Network app

Socket: process sends/receives messages to/from its socket 类似一个门 一次连接需要两个socket (one on each side)​

Identifier: includes both IP address and port numbers associated with process on host.​

Web and HTTP

HTTP

hypertext transfer protocol

Client:  browser that requests, receives, (using HTTP protocol) and displays Web objects​

Server: Web server sends (using HTTP protocol) objects in response to requests

HTTP uses TCP

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client initiates TCP connection (creates socket) to server, port 80​

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server accepts TCP connection from client​

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HTTP exchanged between browser (HTTP client) and Web server (HTTP server)​

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TCP connection closed​

HTTP is stateless, server maintains no information about past client requests

Non-persistent HTTP

1.
TCP connection opened​

2.
at most one object sent over TCP connection​

3.
TCP connection closed​

Downloading multiple objects requires multiple connections

Persistent HTTP

1.
TCP connection opened to a server​

2.
Multiple objects can be sent over single TCP connection​

3.
TCP connection closed​

Non-persistent HTTP

Non-persistent HTTP response time=2RTT+file transmission time

Persistent HTTP (HTTP 1.1)

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Server leaves connection open after sending response​

Computer Network​