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Network protocols.

First off, a protocol is a set of rules and prescriptions which are necessarily for communication between computers and other devices in a network environment.

There are several protocols (some of them explained bellow) all with the same goal : they have to progress the communication within a network. Some protocols have a more specific task. Other protocols can't work with additional ones.

Some important keywords :

• A device : A side-device of a computer which processes data, e.g. a printer, modem or a scanner. Each device in located in a network needs to understand the rules and they have to "support" it to be able to function within the network.
  
• A segment : a part of a complete network, existing out of a few computers and devices.
  
• A node : a workstation linked to a segment.
  
• A backbone : A series of very fast computer connections through which the traffic of data runs. (the network data)
  

One of the main network protocols is TCP/IP. Due to it's important I'll tell you guys about it later.

Communication Protocol
To connect one node with another, you need have a wide range of choices of protocols.

PPP
The PPP or Point-to-point protocol is one of the TCP/IP protocols. It can be used to establish a TCP/IP connection between several computers and a network or between 2 routers. Synchronous as well as a-synchronous connections. The PPP protocol is mostly known to connect a computer through a modem to the internet.



PPTP
The PPTP or Point to point tunneling protocol is an extended version of the PPP-protocol. It gets used to extend a safe connection with the internet. The details of the external client can be transmitted throughout a VPN (Virtual Private Network) to the server of a private network.

First off there needs to be created a connection with network acces. We can use the Dial-up networking and the protocol for external acces (PPP) for this. When the connection is established users can send and receive data packages through the internet. The network server uses the TCP/IP-protocol for all the traffic towards the internet.
Then a second logical connection gets created through the existing PPP-connection. The data going through this connection gets the form of IP-datagrams containing the PPP-packages. With this connection the VPN-connection becomes a PPTP-server on the LAN. This connection is also known as "Tunneling"



PPTP exists out of the following parts :

• Authentication of the users (Username/Password)
  
• Adjusting Layer3 protocols. (TCP/IP, Netbios, ..)
  

The PPTP-connection uses TCP-port 1723 for authentication and the exchange of data. The tunnel itself uses Protocol 47.

CSMA/CD

This protocol works on base of line scanning.

Each computer constantly listens whether the line is free to send their packages. A package can only be sent when there is no other package on the line. If the line is free the first package can be sent. If the line isn't available the computer has to wait till the transmission of the current package has been completed.

You can prevent 2 computers sending files simultaneously concluding that the line is free. This is where CSMA/CD comes in.

CSM/CD falls out in 3 parts :

• CS / Carrier Sense : Each PC listens whether the line is available for transmission or not.
  
• MA / Multiple Access : Each pc listens : The line is free, simultaneous sending is possible..
  
• CD / Collision Detect : The stations track or report a collision and wait a random time interval before they try again.
  

Network protocols cooperating with TCP/IP

UDP
User Datagram protocol is one of the basic protocols of the internet and works on the same level as TCP. UDP doesn't work based on connections. It's a connectionless protocol creating connectionless packages.

When does the UDP protocol gets used?

• When data has to be send quickly.
  
• When the reaction speed is important
  
• When the order of arrival isn't important
  
• When it's not that big of a problem when data gets destroyed.
  

Think of videoconferencing, online gaming or DNS.

HTTP / Hypter Text Transport Protocol
This protocol is used to send/receive webpages through the internet. A browser uses the HTTP-protocol.



FTP / File Transfer Protocol
This protocol makes sure that the transmission of binary / numeric data over a TCP/IP connection is secured and is constantly available for data-traffic.



Telnet / Terminal Emulation Protocol
This protocol can be used over a TCP-connection. By doing this the users can decide to log-on on certain sources to use their services. A lot of switches, routers and services can be used through this "telnet" protocol.

POP / Post Office Protocol
POP3 is worldwide the most used version of the standard protocol to send/receive e-mails. This is a client/server protocol with which e-mails can be requested. An internet server maintains these

SMTP / Simple Mail Transfer Protocol
This protocol was designed to send e-mail mesages from a computer through a TCP/IP-connection to a server somewhere on the internet.

SNMP / Simple Network Management Protocol
This is a simple protocol deciding how the messages get send over the network. This protocol can configure nodes within a network. SNMP allows to question devices on a network which are located about their state and to change their configuration.

DNS / Domain Name System
This is a protocol laying connection between an IP-number and a name of a domain. This protocol gets used when you look-up a website on the internet/intranet.

DHCP / Dynamic Host Configuration Protocol
This is a protocol which allows network administrators to chose the divide of IP-numbers. Without the use of DHCP each IP-adress has to be added by hand on each client-computer. This also means that if they get replaced within the network, it has to be adjusted manually.

This is it, for now. I hope that you enjoyed reading. mile:

This is a very HQ tutorial. I hate it to see some very nice tutorials just have 0 replies while I think the tutorial contains information many people do not know about. Thanks a lot for this HQ tutorial!

I agree with the above comment. Very HQ and detailed tutorial. Anyways, you are awesome on HF.

CSMA also comes with a Collision Avoidance protocol for wireless networks known as CSMA/CA.
Basically it allocates channels or better known as frequencies using wireless recievers and transmitters to stop two devices transmitting on the the same frequency.

Very nice guide, I hated having to memorise the OSI reference model.

Great guide.

EDIT: Include the ports for the specific protocols

FTP: 20/21
SMTP: 25
POP3: 110
Telnet: 23

Think they're correct.