Week 1: Day 003 & Weekend 1: Days 001-002 - MAC Address and NIC + 2nd and 3rd Layer of OSI Model and Some TCP/IP

    So, today I applied/enrolled to NOVA. Funny enough, I don't have to take the Math entry test, due to my Math SOLs. In addition, I might also be exempt from the English entry test if my PSAT score was 50 on Reading and Writing. Anyways, onto what I have learned today.

     Today, I learned a little more about the NIC (Network Interface Card) not all there is though. However, I learned more about the importance and the mechanics of a MAC Address. So, the mac address is built in the NIC as a way to identify the sender/recipients' computer. The first 6 digits represent the manufacturer, and the rest are uniquely given as a serial number. Continuing, the NICs send information known as "frames" to the switches. Each frame has a set amount of data it can carry, and when there is more data than it can carry, then more frames are sent. The way that the data travels to the switch is through binary code which is representative of the electric pulses sent through from A to B. Each of these frames have an FCS (Frame Check Sequence) implemented and that uses CRC (Cyclic Redundancy Check) to make sure the data arrived to its destination intact. So with that said, each NIC connected to the network reads all data in the network. Since only one system can speak at a time in this model, networks use frames to restrict the data an NIC can send at once. But how is an NIC able to identify the NIC to which it is sending data to? Well it usually knows from an earlier communication, but if not it sends a broadcast asking for the name of the other NIC. To summarize the process, the NIC creates the frame, adds the FCS, and of course the data into the said frame, it then inputs the destination MAC Address and its own Mac Address into the frame, then ships the frame (once no other NIC is using the cable) to the switch. The frame then proceeds to transport itself to the switch through the wire. If the receiving NIC sees that the frame is addressed to itself, then it will read it, but if it's not then it erases the frame. So to complete its task, the receiving NIC scans the data with its FCS then sends the data to the software (Network Operating System) to be processed. However the tasks I've just written about are broken down into two jobs. The first is LLC (Logical Link Control). This job require talking to the Network Operating System, placing data into frames (plus the CRCs). In addition, it deals with processing of the incoming frames, discarding the ones addressed to other machines/NICs in the network. The second job is MAC (Media Access Control) and all it does is remember the NICs own MAC Address and attaches MAC Addresses to frames which include sender and recipient. And the MAC job's final task is to send the frame to its destination. The NICs are placed in the Data Link Layer (2nd Layer) of the OSI model (although many students think it should be Physical due to its task of putting binary code into the network cable).

     Now layer 3 is where you get to the real Network nitty gritty. First off, when you have so many MAC Addresses being broadcast how is it organised in a way that wouldn't flood the internet? Well when networks get so large they can't look at the MAC Address anymore, instead another system is used to identify computers/networks known as the "logical addressing method". This gives the ability for networks to be broken up into subnets when they become to large. To use this system a special software must be used, known as the "network protocol". This software gives unique identifiers to each system, and also handles chopped up packets to make sure packets get from one subnet to another. At layer 3 you have Internet Protocol used as the logical addressing protocol for TCP/IP and gives each device a unique identifier known as an IP Address. This differs from the MAC Address because it is a "logical address" rather than a physical one. An IP address is made up of four 8-bit numbers with numbers ranging from 0 to 255. No two devices or systems on a network share the same IP addresses. The router is what connects each of the subnets. Routers use the IP not MAC address to forward data. In a TCP/IP networks to send data successfully, they need to be put in two containers. A frame lets you move data from one device to another and inside is an IP specified container which tells the frame where to go. Now the inner container is the "packet". The IP packets are shipped in an NIC frame and sent to its destination. The data is then received by the router which opens the frame takes the packet and sends it to its destination (possibly a subnet router), in a new frame which is made for whatever type of connection the user has (DSL or Cable). When the packet reaches a subnet router, then that router once again opens the frame then adds another frame with the MAC address of the device with the meant IP address destination. Once it reaches the NIC of the meant destination, it opens the frame and sends the packet to software that knows what to do with it. And that pretty much ends my reading on the first three layers of the OSI model plus my first look at TCP/IP. Took me three days with all the work I'm doing for other classes. Now it's onto the next four which seems to be 20 more pages of reading. Thanks for reading this entry, more to come!