MindMap Gallery Computer Network Fundamentals_Computer Network Applications
Basics of Computer Network (Top-down) HIT Harbin Institute of Technology course notes, detailed introduction, allowing you to understand and learn more quickly and conveniently. If you need it, collect it quickly!
Edited at 2024-03-31 23:21:06This Valentine's Day brand marketing handbook provides businesses with five practical models, covering everything from creating offline experiences to driving online engagement. Whether you're a shopping mall, restaurant, or online brand, you'll find a suitable strategy: each model includes clear objectives and industry-specific guidelines, helping brands transform traffic into real sales and lasting emotional connections during this romantic season.
This Valentine's Day map illustrates love through 30 romantic possibilities, from the vintage charm of "handwritten love letters" to the urban landscape of "rooftop sunsets," from the tactile experience of a "pottery workshop" to the leisurely moments of "wine tasting at a vineyard"—offering a unique sense of occasion for every couple. Whether it's cozy, experiential, or luxurious, love always finds the most fitting expression. May you all find the perfect atmosphere for your love story.
The ice hockey schedule for the Milano Cortina 2026 Winter Olympics, featuring preliminary rounds, quarterfinals, and medal matches for both men's and women's tournaments from February 5–22. All game times are listed in Eastern Standard Time (EST).
This Valentine's Day brand marketing handbook provides businesses with five practical models, covering everything from creating offline experiences to driving online engagement. Whether you're a shopping mall, restaurant, or online brand, you'll find a suitable strategy: each model includes clear objectives and industry-specific guidelines, helping brands transform traffic into real sales and lasting emotional connections during this romantic season.
This Valentine's Day map illustrates love through 30 romantic possibilities, from the vintage charm of "handwritten love letters" to the urban landscape of "rooftop sunsets," from the tactile experience of a "pottery workshop" to the leisurely moments of "wine tasting at a vineyard"—offering a unique sense of occasion for every couple. Whether it's cozy, experiential, or luxurious, love always finds the most fitting expression. May you all find the perfect atmosphere for your love story.
The ice hockey schedule for the Milano Cortina 2026 Winter Olympics, featuring preliminary rounds, quarterfinals, and medal matches for both men's and women's tournaments from February 5–22. All game times are listed in Eastern Standard Time (EST).
computer network applications
Difficulties and key points
1. What is a socket?
2. Problem with non-persistent connections
3. SMTP vs. HTTP
4. POP3 stateless?
5. IMAP and POP3
6. Not scalable
7. DNS load balancing?
Network applications and protocols
Web application
Overview
WEB composition
Web pages link to each other
Web page
multiple objects
Basic HTML file
Addressing of objects
URL: Uniform Resource Locator
basic format
All resources on the WEB have unique identifiers
HTTP protocol
C/S structure
Client—Browser
Request, receive, and display WEB objects
Server—Web Server
Respond to the client's request and send the object
Version
1.0RFC1945
non-persistent connection
method type
1.1 RFC 2068
Default persistent connection
method type
TCP transport service
Specific steps
no status
Why not use stateful protocols
The server does not maintain any information about past requests made by the client
HTTP connection type
non-persistent connection
Features
A maximum of one object is allowed to be transferred per TCP connection
step
Response time analysis and modeling
RTT
Response time
1 RTT each
Send, establish TCP connection
The client sends requests and receives response messages
File sending time
File/object transfer time contained in response message
non-persistent connection
Features
Allows multiple objects to be transferred per TCP connection
After sending the response, the server keeps the TCP connection open
Classification
No running water
The client only sends a new request after receiving the previous response.
Each referenced object takes 1 RTT
With water flow mechanism
The client makes a request as soon as it encounters a reference object
Ideally, it only takes about 1 RTT to receive all reference objects.
3 RTT (TCP established text reference object) file sending time
HTTP message format
request message
request line
Request method URL HTTP version
heaner lines (extensible)
host: server domain name
user-agent browser
CR LF
Entity Body
response message
status line
HTTP version status code status phrase
heaner lines (extensible)
Date: The event in which the web server generates a response message
Last—Modified: The time when the web page was last modified
CR LF
requested HTML file
How to upload input
POST method (large amount of information)
Web pages often require filling out forms
Upload client input in the entity body of the request message
GET method (less information)
Input information is uploaded through the URL field of the request line
Cookie technology
Definition RFC6265
components
HTTP request/response messages
Browser managed cookie files
WEB server database file
principle
PPT notes
Web caching/proxy server technology
Function
Satisfy the client's HTTP request without accessing the server
reason
Reduce response time for customer requests (offloading)
Reduce the traffic of institutions/organizations (caching example in PPT)
Enable effective content distribution at large scale
organizational form
The proxy server acts as both a client and a server
Conditional GET method
Purpose
Used to synchronize the WEB object version between the cache server and the remote server
Email application
Components
Mail client
Mail Server
SMTP protocol
client
The server sending the message
server
The server that receives the message
SMTP protocol: RFC2821
port
25
Transport Protocol TCP (Reliable Transport)
shake hands
Transmission of messages (persistent connections)
closure
command/response interaction mode
Command: ASCII text
Response: status code and statement
SMTP interaction example
220
Indicates successful connection establishment
250
Confirmation code that the information is correct
RCPT TO
Receiver name
DATA
Official command to start sending data
MAIL FROM
Sender name
SMTA server determines end of message
CRLF.CRLF
Message format
Header row
TO
from
Subject
message body
The message itself (can only be ASCII characters)
MIME
Purpose
To send multimedia files
Format
Multimedia files still need to be ASCII encoded
Mail Access Protocol
POP
Certification process
client command
Server response
transaction phase
model
Download and delete
download and keep
no status
IMAP
HTTP
163, QQmail, etc.
DNS application
Distributed hierarchical database
Hierarchy
root server
top-level domain name server
Institutional Server
Local domain name resolution server
Generally, the mapping of the top-level domain name server is cached.
application
DNS query example
Iterative query
The queried server returns the name of the domain name resolution server (kicking the ball)
recursive query
The task of domain name resolution is handed over to the contacted server (results are returned after completing subsequent query work)
DNS records (resource records)
Record caching and updating
The domain name resolution server obtains the domain name-IP mapping, that is, caches this mapping
Type
A
Name: host domain name; Value: IP address
NS
Name: domain name; Value: host domain name of the authoritative domain name resolution server in this domain (non-IP)
CNAME
Name: an alias of a real domain name; Value: the real domain name
MX
Value is the mail server corresponding to name
DNS protocol
Inquiries and replies
The message format is the same
Message header
Identification
flags
think
DNS service
Use UDP or TCP?
Why is DNS not centralized?
Not scalable
P2P applications
Features
file distribution
C/S structure
The server needs a copy of the node for each request
Customer service machine i takes time to download
P2P structure
The server must send a copy
Customer service machine i takes time to download
subtopic
Protocol: BitTorrent
Indexing technology
centralized index
process
Nodes join, notifying the central server of their IP address and content
The node queries the central server for a file
Client—The client transfers files
question
Single point of failure problem
Performance bottleneck
Flood query
Features
Fully distributed architecture
Each node only indexes the files it shares
How to query files
overlay network
process
Query messages are sent over an existing TCP connection
Node forwarding query information
If the query hits, use the reverse path to return to the query node.
question
Messages are flooding the web. Consuming a lot of network bandwidth, causing network congestion
hierarchical overlay network
Between centralized and flooded queries
composition
super node
Responsible for tracking the content of child nodes
Ordinary node
Connection between nodes and super nodes (centralized) Super node and super node connection (flooding)
case
skype
Socket programming
TCP
UDP
Fundamental
The foundation of network applications: inter-process communication
process
Programs running on the host
Communication between processes on the same host
Inter-process communication mechanism
Operating system provides
Communication of processes on different hosts (key points)
Message exchange (message exchange)
client process
server process
Applications of P2P architecture are also divided into client process/server process.
Socket
Inter-process communication uses sockets to send/receive information.
How to address a process
Addressing the host
IP address
addressing process
Port number/Port number
Some processes use specific port numbers, and these port numbers cannot be used.
Application layer protocol
meaning
Network applications need to follow application layer protocols
Classification
Disclosure agreement
RFC definition
Purpose: Allow interoperability
private protocol
Most P2P file sharing applications
content
Message type (type)
request message
response message
Message syntax/format
What fields are in the message
How each field is described
Semantics of fields
The meaning of the information in the fields
rules
When does a process send/respond to information?
How processes send/respond to information
Application (layer) content overview
Features (essentially different from stand-alone applications)
physical medium
Certain software and hardware on the remote Internet
Architecture
Client/server structure
server
7*24h service available
Permanent access address/domain name
Leverage large numbers of servers for scalability
Client computer
Communicate with the server and use the services provided by the server
Intermittent access to the network
May use dynamic IP address
Does not communicate directly with other clients
Functional role division
application
Web access (client request - server response)
point-to-point structure
Features
No always-on server
Direct communication between any end system/node
Nodes intermittently intervene in the network
Node may change IP address
Advantages and Disadvantages
Pros: Highly scalable
Disadvantages: Difficult to manage
hybrid structure
P2P structure
file transfer
C/S structure
File search
advantage
Avoid the server becoming a performance bottleneck (the client does not need to obtain files from the server)
service requirements
Network application requirements for transmission services
data loss/reliability
time/delay
Bandwidth
Transmission services provided by the Internet
TCP service
connection oriented
transmit reliably
flow control
congestion control
No time/delay guarantee
No minimum bandwidth guarantee is provided
UDP service
Only provide basic services of the transport layer to the application layer