"Computer network" Application Layer 1

I read no order, like where to see where, so, first look at my usual use of the network the most relevant application layer ~

Domain and URL

Domain name is an alias of IP, such as www.baidu.com, which the more the more the more the higher the domain name, COM is the top-level domain name, Baidu is a two-level domain name, but www is not a three-level domain name I do not understand . Also, a domain name corresponds to an IP, So much information is put on an IP ah, is that there are a lot of cattle broken server use this one IP? in order to match the domain name and IP, the DNS server is going to work, the DNS is the IP when we query the domain name of the server, but so much information will not exist on a DNS, this DNS will help us to ask other servers.

URL is the alias of the file on the network, commonly known as the URL such as http://i.cnblogs.com//HTTP Indicates that reading this file content needs to follow the HTTP Hypertext Transfer Protocol i.cnblogs.com represents the host IP of the file, indicating where to find this file, in the back of which is the host's sub-folder

Proxy Server:

Also known as the World Wide Web cache, if the use of Proxy server, user a request URL c.com information, the proxy server first cache the information to their own here, return to a, User B again request this URL information, proxy server directly from their own here to return the information to B, do not go to the source site to find information.

?? This I do not understand, such as Youku has a click, a, B, C, D, E are all using the same proxy point to see, that the number of clicks only counted 1 times? There are some information changes in the moment, such as micro-blog someone to reply to my message, then ask the agent to get the previous saved page?? Not getting update information??

Cookies

HTTP is stateless, but the site sometimes want to know the user information, then the site to the user set a cookie, return to the user's browser, the browser to save the cookie, the next time to visit the same website with their own cookie information, then the site can identify this person, If you don't like it, just clear the cookie.

"Computer network" Application Layer 1