One such model is called the OSI model and have 7 levels. When studying the IP-communication you will find that it doesn't comply fully with the OSI model but in general it works the same way. The OSI model will not be explained here. You will find plenty of information on the Internet about the OSI model.
Ethernet Frame Format
On an Ethernet network you do not have to use IP-communication to communicate. Many companies already have working local networks when Internet and IP-communication become popular. However there is no problem running several different protocols at the same time on an Ethernet network as long as all "physical" low level communication uses the fundamental Ethernet rules using Ethernet frames with source and destination MAC-addresses.
Today the majority of Ethernet networks only runs the IP-protocol. Network packets are like Russian dolls. An IP-packet resides within an Ethernet-packet. The data part of an Ethernet packet can hold up to bytes. That gives the maximum size of an Ethernet frame to be bytes. By using a number that is greater than the maximum length an Ethernet frame can hold indicates that the Ethernet frame holds another protocol frame in the data part.
The Ethernet standard says that if the Number Of Bytes field is greater than 0x the Ethernet frame holds another protocol. No, that would be inefficient. How this is done efficiently is there is one specific bit in a Ethernet MAC address that signifies if the frame is unicast or multicast. The switch need only look at this one bit to make the distinction.
Tutorial: Ethernet Frames and MAC Addresses
The IEEE has specified that the most significant bit of the most significant byte be used for this purpose. If its a 1, that means multicast, 0 means unicast. The most significant byte is the left most byte in the address, and the most significant bit is the right most bit of the byte this is counter intuitive to most binary implementations where the left most bit usually labeled most significant.
Each of the bolded numbers represents a 1 or 0 present in the most significant bit of the most significant byte. From the perspective of an Ethernet hub device, none of this matters, as all frames are flooded out all ports regardless of their address being unicast, broadcast, or multicast. An inter-office envelope cannot be sent outside of the company because the envelope does not have a mailing address.
To send the contents to an office outside of the local area, the inter-office envelope will need to be placed inside a postal envelope and labeled with a proper postal address. An Ethernet frame works in a similar way. It is a container for data with a source and destination address to deliver information, called the payload, between two locations on the same network.
This is an ID number that is unique to every Ethernet device in the entire world. The frame is sent onto the network where an Ethernet switch checks the destination address of the frame against a MAC lookup table in its memory. The lookup table tells the switch which physical port, i. The switch will forward the frame to the physical port determined by the lookup table.
If the cable is connected directly to the destination device the transmission is complete. If the cable is connected to another switch, the next switch will repeat the lookup and forward process until the frame reaches the intended destination. Remember - all of this is happening on Layer 2 switches in the LAN. To send data to a device on a different network or to an internet server, a frame must be built into a packet.