Computer network

A computer network is a data communications system that interconnects computer systems at various different sites. Today we are going to learn about the pieces that make a network , some of which you are familar with:

• PC - Computer like the one your on now
• NIC - Network Interface card - This is both an electrical interface to the router/modem , and a logical board that communicates to the rest of the pc , usually registered jack forty five or registered jack eleven standard the cable to provide a carrier for the signals either shielded or unsheilded. When you connect to the Internet for example the nic should send out fast link pulses that try to establish the acceptable speed of connection between the computer and the modem/router on the global side. These pulses are of a fixed length - if one side can respond within x number of miliseconds it will communicate at y speed, assuming both sides are set to autonegociate. NIC has a Media access control or a Burned in address inside one of its microchips - this will NEVER change (though it can be falsified) unless you get a new nic.
• hub - seldom used, this splits the connection betwen multiple PCs. It may regenerate the signal - or may just send it on
• switch - used to split multiple PCs into different groupings based on logical needs or security needs , within the same subnet or lan
• router - used to send data between phyisical networks.

These are the basic parts of a network. These parts speak different languages called protocols, which are didived into routing and routed protocols. In the next lesson we will learn about different kinds of cabling and different languages such as RIP.

OSI Seven Layer Model

• Layer 7, the Application layer, privides service riderctly related to the applications. THose services vay on applications.
• Layer 6, the Presentation layer, format the data to look like common for all applications
• Layer 5, the Session Layer, establishes a connection between two nodes. Deal with, whether the conneciton is full duplex, half duplex etc.
• Layer 4, Transport layer, handles and delivers data, whenever it is conneciton-oriented or connecitonless. It includes some flow control issues.
• Layer 3, Network Layer, establishes the connection between two nodes, suing the IP addressing.
• Layer 2, the Data Link Layer, frames data and privodes low-level flow control
• layer 1, Physical layer, transmits low bitstreats (data), deals with electrical singalling, cabling and hardware interface.