Network Protocols

We have already noted that the network must have a set of rules, called protocols, to transmit data in an orderly manner that is understood by other computers. Recall that the protocol is built into the network software. There are four layers of protocols that are commonly used in the ISO:
Data Link Layer - Data Link Layer defines how digital data is on the pulse of public transport such as how many bits at a time when the pulse of how often the pulse, etc. There are two most prevalent protocols Ethernet Data Link Layer and Point-To-Point Protocol (PPP). Ethernet is used in local area networks and cable modems, and PPP is used for connecting a DSL modem and a telephone.
Ethernet uses a bus topology and is an inexpensive and relatively simple. Since all nodes (computers) on the LAN use the same cable to transmit and receive data, the nodes must follow guidelines about how to communicate, otherwise two or more nodes may transmit at the same time, which results in damaged or lost messages . Operating as the party line before transmitting the data node "listens" to find out if the cable is in use. If the cable is used, the node must wait. When the cable is free from other transmissions, the node can begin transmission immediately. This method of transmission is called by the fancy name for a carrier sense multiple access with collision detection, or CSMVCD.
If by chance, two nodes transmit data at the same time, the messages collide. After the collision a special message, which lasted a split second, it is sent across the network to indicate that it is locked. Each node stops transmitting, waits a random period of time, and then forward again. Since the waiting time for each node is random, it is unlikely that the transmission will start at the same time re-
Unlike Ethernet, PPP is a direct connection from one modem to another modem on a telephone line. There is no collision when the data is transmitted. Most Internet service providers (ISPs), such as America On-line or Edgenet (Rhode Island) are expected to interact with clients via PPP. 95/98/ME/2000 Windows are built into the PPP dial-up adapter software that most people use to call your ISP.

Internet Layer - Layer Internet allows computers from different networks to talk to each other - in fact, form a large multi-faceted network that we know as the Internet. The key to the Internet Layer is that each computer that participates is assigned a unique 32-bit address called an IP address (Internet Protocol address). IP addresses are usually displayed in the four digit numbers. For example, a web server for this text, homepage.cs.uri.edu has an IP address 131.128.81.37. Every computer that does not do anything on the Internet (send and receive e-mail, serve Web pages, Web browsing, page, etc.) must have an IP address. If your computer is on the LAN, the IP address is probably fixed. For example, students in the dorm room URI computers connected to the campus network IP address is specified, the address to your room. They had to go to this address to the computer via the network control panel in Windows 95, 98 or Macintosh. If your ISP chooses to access, then the IP address is assigned to your computer by your ISP for the duration of the modem to your ISP. ISPs have a large pool of IP addresses that temporarily assigned to customers who are linked. You can have a different IP address every time you use America Online, for example. With 32 bits, not 4 billion possible IP addresses - and the world ends! The new format of an IP address is designed to allow many more IP addresses.
The software adds bits of the IP for all messages, stating that the computers sends the IP address of destination of the message.

Transport Layer - Transport Layer protocol control messages are sent and received, to make sure that they are free from errors and received in the correct order. If the Transport Layer obtain software from your computer detects errors, it sends a message to the sending computer's original request to re-pass. Transport Layer used on the Internet is called TCP (Transmission Control Protocol). On the Internet, IP and TCP are used together so often you can see the protocol, TCP / IP. The software TCP / IP is usually part of the operating system. Other than from time to time set the IP address for the Network Control Panel, you probably will not comment directly, or interact with the TCP / IP software.
In the application layer. The application layer includes the protocols for specific tasks such as sending e-mails or retrieve a Web page. For example, Simple Mail Transfer Protocol (SMTP) is used on the Internet to e-mail format. This is the SMTP, which requires the fields we know: the subject, etc, as well as the date of the message, and any other information, see the email headers. Here are some common application layer protocols on the Internet:
SMTP - protocol relay e-mail;
POP - the protocol to retrieve e-mail from the server to your local disk (Eudora uses this protocol).
IMAP - the protocol to view email through a web browser, where email is stored on the server (URI WebMail uses this protocol).
HTTP - the protocol for the client (eg Netscape) requests a Web page from a web server (eg einstein.cs.uri.edu).
FTP - protocol remote computer, ask for the file will be transferred to or from him.
Telnet - A protocol to allow one computer to act as a terminal to a remote login on another computer. In this way, you can access the URI or Brown library catalog from a remote computer.
SSL - the protocol that allows secure transmission of data. This protocol encrypts the message at the end of sending and de-mixing them at your destination.
There are other protocols. Application layer protocols are usually hidden in applications, such as Netscape or Eudora. In fact, the most important programs like Netscape, something about not being able to "speak" these protocols to other computers on the Internet.
Each layer of the protocol, the following bits of news. Suppose you want to send a "HI" in the e-mail to a friend. "H" and "I" everyone takes eight bits for their representation of ASCII, so you want to transfer 16 bits. However, when the message leaves your email program, the SMTP protocol requires that, subject to the following fields, etc. - all of which add several hundred more bits. IP protocol software in the operating system and then adds 32 bits to the target computer's IP address and 32 bits for the IP address of the computer, sending (and a few other bits) - for the next 100 bits, and so he adds. Software TCP adds bits to enable error checking and sequencing. Software Ethernet or PPP also add a bit to control the pulsing of the communication link. Thus, a simple 16-bit "HI" message will be transmitted as several hundred bits! This seems wasteful, but is necessary for computers from all over the world to understand each other.