Web Develop > Comm Layer

The Comm Layer exchanges HTTP packages on the client and server and manages the protocol used for communications between two or more machines. At this level, the protocol consists of TCP/IP, DECNet, or any protocol that allows communications over any network.

The primary purpose of this layer is to provide an efficient, error-free communications medium for the higher-level applications. For example, if the URL http://it-check.blogspot.comis entered into a Web browser, the browser will first locate the host (i.e., http://it-check.blogspot.com) by resolving the address with a Domain Name Server (DNS). The browser resolves the address by sending the host name to the DNS server, provided by the user's ISP.

The DNS server will attempt to locate the numeric address of the host and return the address to the Web Client. If the address is found, the browser connects to the Web Server using an HTTP connection. This connection is a network request by the browser to initiate communications with the server on port 80, 81, or any specified port number.

The port is a unique service point that identifies an entry-point on a server that is using a specific protocol. This is similar to having three doorways into a room, with each one leading to a person that translates a discussion in that room using a different language. If an English speaking person enters the Japanese doorway, then of course, the English person would not be able to understand the discussion.

For ports, if a client makes a request to a port number that does not use the same protocol (i.e., speak the same language), there can be no communication. In this case, port 80 is the standard port through which Web-based communications occurs. Each individual port corresponds to a particular protocol handler. The client applications know the port numbers as part of their design and configuration.

For instance, when an e-mail client checks for new messages, it connects to port 110 of a mail server. The POP3 protocol handler processes the requests and sends the mail client the e-mail in the respective user's mailbox. This same type of processing occurs for all protocols used on the Internet.