Computer Network Reading Notes (1)

Main features of the TCP Transport Control Protocol:

1. connection-oriented transport layer protocol, similar to calling

2. Point-to-point (one-to-one), each TCP can have only two endpoints

3. provide reliable delivery services

4. full-duplex communication

5. byte stream oriented (so-called stream: byte sequence of inbound to or from process)

TCP determines the number of bytes of a packet segment based on the window value given by the peer party and the current degree of network congestion. this parameter is equivalent to UDP (the length of the packet sent by UDP is determined by the application process).

TCPConnection

TCP uses the connection as the most basic abstraction. Each TCP connection is uniquely identified by two endpoints (that is, two sockets) at both ends of the communication.

So-called endpoint: also teach socket or socket = (IP Address: port number)

The transport layer of TCP/IP identifies a port with a 16-bit port number. The port number is only meaningful locally.Current computerProcesses in the application layer and Transport LayerInteraction.

The IP address and port uniquely identify the network application in a network. This combination is called "IP EndPoint", which is the access point of a network service.

How TCP reliable transmission works:

1. Stop the waiting protocol. Confirm each group sent.

2. Continuous ARQ protocol, cumulative confirmation, that is, after receiving several groups, send confirmation to the last group that arrives in order.

TCP transport connection management

TCP connection establishment: three-way handshake

Release of TCP connection: Four handshakes

 

Application Layer

The specific content of the application layer is the protocol that the application process follows during communication.

Domain Name System DNS

The naming system used by the Internet is used to convert the names of machines that are easy to use into IP addresses.

Domain Name

The logical concept does not represent the physical location of the computer.

◆ The reason why the machine uses an IP address instead of a domain name when processing IP Packets: the IP address is fixed (Ipv6 is 128 bits, IPV4 is 32 bits), and the length of the domain name is not fixed, it is difficult to process machines.

Domain name resolution process:

First,
GenerallyRecursive query

Second,
The yin Local Domain Name Server usually usesIterative Query

The Root Domain Name Server adopts the anycast Technology: The End Of The anycast IP datagram is a group of hosts in different locations, but with the same IP address, IP datagram is delivered to a host closest to the source point.

FTP Overview

The file transfer protocol FTP only provides some basic services for file transfer. It uses TCP reliable transmission services. The main function of FTP is to reduce or eliminate the incompatibility of File Processing in different operating systems.

World Wide Web

Distributed hypermedia system

Hypertext

Text that contains links to other documents. Hypertext is linked by multiple information sources. Hypertext is the foundation of the world wide web.

Hypertext Transfer Protocol (HTTP)

The HTTP protocol defines how the web browser (the Web Client process) requests the Web documents from the Web server, and how the server sends the documents to the browser.

HTTP is a transaction-oriented application protocol. (Transaction-oriented refers to a series of information exchanges, which are an inseparable whole, that is, either all information exchanges are completed, or one exchange is not performed ).

HTTP packets are usually transmitted over TCP connections.

The browser requests 10 thousand documents to the process of receiving the entire document.

Differences between HTTP/1.0 and HTTP/1.1:

HTTP/1.0 disadvantages: every request to a document requires two times the RTT overhead

The HTTP/1.1 persistent connection method can solve the above shortcomings. There are two methods: the non-pipeline mode is characteristic that the customer can send the next request only after receiving the previous response; the pipeline mode is characterized by the ability of the customer to send new request packets before receiving the HTTP Response Message.

March 9