*this is a guide that was created from lecture videos and is used to help you gain an understanding of what is a network model.
Network Interface Card/NIC- plugged into computers and connects into a hub.
Hub- acts as an interface to computers to interconnect to share resources such as webpage to a word document.
Data is somehwta like morse code with flashing lights. Data is not sent in continuous streams but discrete chunks of (1’s and 0’s) called frames or packets.
Packetized data- cornerstone of networking. A single frame can be up to 1500 bytes long, or 10,000 1’0s and 0’s. A frame is generated in the NIC. Data goes from the system into the NIC, the NIC then creates the frame and then puts out into the network. They have a discrete beginning and end. Frames are destroyed inside the NIC once the receiving system gets the data.
The MAC Address
Hub/Repeater- data comes in through white cable and creates multiple copies and then sends out. A hub sends out a frame to every computer or system on the network, even when it is only for a specific computer. This is controlled by using a MAC address/Physical address which are 48 bits, broken up by groups of 2. The first part of a MAC address is used to the manufacturer/OEM and the second part is the unique identifier. MAC addresses are used for NIC’s if they should process data from a certain system that is meant for them or to ignore . Ipconfig /all command will show you a computer’s MAC address.
A CRC is used to identify that the data is good in a frame sent out from the NIC.
Broadcast vs. Unicast
A unicast is when the exact MAC address from the NIC matches the computer it is being sent to. A broadcast is when a computer does not know who it will be sending the frame to. Every computer that receives a destination MAC address of all F’s will be a broadcast. It is used when a computer is unsure the MAC address of the computer it intends to send a frame to.
Broadcast domain- any time a group of computers can hear each other’s broadcast.
Hubs and Switches
A switch is different than a hub as it is smarter and keeps track of all the MAC addresses that have connected with it based on ports. The switch stores the port number and associated MAC number. A switch only sends a frame to the appropriate device.
Mac Addresses don’t identify that computers are all part of a single LAN. If you want big networks to work then you need logical addressing.
Logical addressing is IP addressing. IP addresses can identify a particular network. The first three numbers in an IP address will identify all the computers on the network, which is the Network ID. The fourth value will be different for each computer.
A router will have 2 connections or more. A router can also physically be a switch as well. A router connects 2 networks together and then can act like a switch to determine which computer receives the frame.
A frame is made of a Mac address destination, Mac address source code data and a CRC, as well as a destination IP and then a source IP address. A destination IP address and source IP address in a frame, is called an IP packet.
A default gateway is the connection to your router itself. Your computer will place a frame that also has the destination Mac address of the router, and goes around the IP packet.
The router will then strip the frame to leave just the IP address. A routing table is used to tell where to send the data. Your tutor will get the MAC address of the destination computer, will put the frame together and then will be sent. Packets do not travel within themselves, they have to be surrounded by the frame. The IP packets never change. Routers look at IP addresses to send to the proper network.
Packets and ports
How do i get this to the right application?
-Add more to the IP packet, which is port numbers.
Port numbers- unique to individual applications that are used all over the internet. Port 80 defines a web page or WWW. The port number defines where it is going, such as a web server. The second number is how the packet gets back once the web server, for example, responds. Well known ports are the first 1024 are reserved. Ports are used once the data gets into the computer, that they get into the right application.
How do I ensure that the data that I’m trying to get gets to my computer?
-TCP is transmission control protocol and is a connection oriented conversation between two computers to ensure that the data gets to you. TCP is made of sequencing number, which allows you to resemble the number, and acknowledgment.
We also use UDP, user datagram protocol, the only difference is that UDP is not connection oriented. IT is the application’s responsibility to verify the data.
A model by nature is representational and used to simplify a process which can represent form and function. That is the basic of networking models; they are used to represent how networks function. The two main networking models are OSI and TCP/IP model.
OSI Seven-layer model has 7 distinct functions that a network must do, and currently it is being replaced by the TCP/IP model.
Physical is what type of cables
Data link is whatever works with the MAC address such as the network cards, switches,
Network has to do with logical addressing such as IP addressing and routers
Transport disassembles packets and ensure they get delivered to the other system
Session is about the connection between two systems such as a TCP/IP connection
Presentation was used to convert data into a format your applications can read
Applications uses smarts that make the network aware
The term API, which is application programming interface is the definition of the smarts that are built into the application that allow us to make the application network-aware.
Network Interface/Link covers all hardware except routers: physical cabling, MAC, NIC
Internet is for anything to do with IP addresses and routing
Transport does all the assembly and TCP or UDP to get data from 1 app to the next
Application is the application, presentation and session layer of OSI
TCP/IP looks at applications as applications such as web server, FTP or email.
OSI or TCP/IP model example-
Physical or Network Interface/Link
network card awaiting data -> receives ethernet frame ->
Data Link (OSI) or Network Interface/Link (TCP/IP)
looks at MAC address -> looks at frame, and strips off the MAC address but stores information to later send a frame back out -> the stripped frame is now an IP packet ->
Network or Internet
Looks at IP address and ensures if it for them -> pulls IP address information and keeps the destination where it came from to resend an Ip packet back -> TCP segment is what is left and is designed for the computer it is being sent to ->
Transport for Both Models
Acts as assembler/disassembler for data -> takes data and breaks it into bite size chunks OR reassembles data with the use of the sequencing number ->
Application, Presentation and Session or Application
(OSI) Session layer connects server to a client on a remote system
(OSI) Presentation layer was designed to translate data into a readable file for applications
Applications is built in smarts that allow them to interface with a network, such as port numbers